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Sample records for bayesian quasar selection

  1. A SIMPLE LIKELIHOOD METHOD FOR QUASAR TARGET SELECTION

    SciTech Connect

    Kirkpatrick, Jessica A.; Schlegel, David J.; Ross, Nicholas P.; Myers, Adam D.; Hennawi, Joseph F.; Sheldon, Erin S.; Schneider, Donald P.; Weaver, Benjamin A.

    2011-12-20

    We present a new method for quasar target selection using photometric fluxes and a Bayesian probabilistic approach. For our purposes, we target quasars using Sloan Digital Sky Survey (SDSS) photometry to a magnitude limit of g = 22. The efficiency and completeness of this technique are measured using the Baryon Oscillation Spectroscopic Survey (BOSS) data taken in 2010. This technique was used for the uniformly selected (CORE) sample of targets in BOSS year-one spectroscopy to be realized in the ninth SDSS data release. When targeting at a density of 40 objects deg{sup -2} (the BOSS quasar targeting density), the efficiency of this technique in recovering z > 2.2 quasars is 40%. The completeness compared to all quasars identified in BOSS data is 65%. This paper also describes possible extensions and improvements for this technique.

  2. Bayesian High-redshift Quasar Classification from Optical and Mid-IR Photometry

    NASA Astrophysics Data System (ADS)

    Richards, Gordon T.; Myers, Adam D.; Peters, Christina M.; Krawczyk, Coleman M.; Chase, Greg; Ross, Nicholas P.; Fan, Xiaohui; Jiang, Linhua; Lacy, Mark; McGreer, Ian D.; Trump, Jonathan R.; Riegel, Ryan N.

    2015-08-01

    We identify 885,503 type 1 quasar candidates to i≲ 22 using the combination of optical and mid-IR photometry. Optical photometry is taken from the Sloan Digital Sky Survey-III: Baryon Oscillation Spectroscopic Survey (SDSS-III/BOSS), while mid-IR photometry comes from a combination of data from the Wide-field Infrared Survey Explorer (WISE) “AllWISE” data release and several large-area Spitzer Space Telescope fields. Selection is based on a Bayesian kernel density algorithm with a training sample of 157,701 spectroscopically confirmed type 1 quasars with both optical and mid-IR data. Of the quasar candidates, 733,713 lack spectroscopic confirmation (and 305,623 are objects that we have not previously classified as photometric quasar candidates). These candidates include 7874 objects targeted as high-probability potential quasars with 3.5\\lt z\\lt 5 (of which 6779 are new photometric candidates). Our algorithm is more complete to z\\gt 3.5 than the traditional mid-IR selection “wedges” and to 2.2\\lt z\\lt 3.5 quasars than the SDSS-III/BOSS project. Number counts and luminosity function analysis suggest that the resulting catalog is relatively complete to known quasars and is identifying new high-z quasars at z\\gt 3. This catalog paves the way for luminosity-dependent clustering investigations of large numbers of faint, high-redshift quasars and for further machine-learning quasar selection using Spitzer and WISE data combined with other large-area optical imaging surveys.

  3. Quasar target selection fiber efficiency

    SciTech Connect

    Newberg, H.; Yanny, B.

    1996-05-01

    We present estimates of the efficiency for finding QSOs as a function of limiting magnitude and galactic latitude. From these estimates, we have formulated a target selection strategy that should net 80,000 QSOs in the north galactic cap with an average of 70 fibers per plate, not including fibers reserved for high-redshift quasars. With this plan, we expect 54% of the targets to be QSOs. The North Galactic Cap is divided into two zones of high and low stellar density. We use about five times as many fibers for QSO candidates in the half of the survey with the lower stellar density as we use in the half with higher stellar density. The current plan assigns 15% of the fibers to FIRST radio sources; if these are not available, those fibers would be allocated to lower probability QSO sources, dropping the total number of QSOs by a small factor (5%). We will find about 17,000 additional quasars in the southern strips, and maybe a few more at very high redshift. Use was made of two data sets: the star and quasar simulated test data generated by Don Schneider, and the data from UJFN plate surveys by Koo (1986) and Kron (1980). This data was compared to results from the Palomar-Green Survey and a recent survey by Pat Osmer and collaborators.

  4. OPTIMAL TIME-SERIES SELECTION OF QUASARS

    SciTech Connect

    Butler, Nathaniel R.; Bloom, Joshua S.

    2011-03-15

    We present a novel method for the optimal selection of quasars using time-series observations in a single photometric bandpass. Utilizing the damped random walk model of Kelly et al., we parameterize the ensemble quasar structure function in Sloan Stripe 82 as a function of observed brightness. The ensemble model fit can then be evaluated rigorously for and calibrated with individual light curves with no parameter fitting. This yields a classification in two statistics-one describing the fit confidence and the other describing the probability of a false alarm-which can be tuned, a priori, to achieve high quasar detection fractions (99% completeness with default cuts), given an acceptable rate of false alarms. We establish the typical rate of false alarms due to known variable stars as {approx}<3% (high purity). Applying the classification, we increase the sample of potential quasars relative to those known in Stripe 82 by as much as 29%, and by nearly a factor of two in the redshift range 2.5 < z < 3, where selection by color is extremely inefficient. This represents 1875 new quasars in a 290 deg{sup 2} field. The observed rates of both quasars and stars agree well with the model predictions, with >99% of quasars exhibiting the expected variability profile. We discuss the utility of the method at high redshift and in the regime of noisy and sparse data. Our time-series selection complements well-independent selection based on quasar colors and has strong potential for identifying high-redshift quasars for Baryon Acoustic Oscillations and other cosmology studies in the LSST era.

  5. Quasar Selection in the Optical + MIR

    NASA Astrophysics Data System (ADS)

    Richards, Gordon T.; Myers, Adam D.; Peters, Christina M.

    2015-01-01

    We identify 885,503 type 1 quasar candidates to i<22 using the combination of optical and mid-IR photometry. Optical photometry is taken from SDSS-III, while mid-IR photometry comes from a combination of data from ALLWISE and several large-area Spitzer-IRAC fields. Selection was based on a training sample of 157,701 spectroscopically-confirmed type 1 quasars with both optical and mid-IR data. Of these candidates, 306,686 lack spectroscopic confirmation, including 8665 quasar candidates with 3.53.5 than the traditional mid-IR selection ``wedges'' and to 2.2quasars than the SDSS-III/BOSS project. This catalog paves the way for luminosity-dependent clustering investigations of large numbers of faint, high-redshift quasars. This work was supported in part by NASA-ADAP grant NNX12AI49G.

  6. Probabilistic Selection of High-redshift Quasars with Subaru/Hyper Suprime-Cam Survey

    NASA Astrophysics Data System (ADS)

    Onoue, Masafusa

    High-redshift quasars are an important probe of the distant Universe. They enable observational studies of the early growth of supermassive blackholes, cosmic reionization, chemical enrichment of host galaxies, and so on. Through pioneering optical and near-infrared wide-area surveys such as the SDSS and the VIKING Survey, about one hundred quasars have been found at z > 6 (e.g., Fan et al. (2006b), Venemans et al. (2013)). However, its current small sample size and the fact that most of them are the most luminous (M 1450 <~ -24) population in this epoch prevents one from constraining statistics on high-redshift quasars, namely quasar luminosity function (QLF), and redshift evolution of IGM neutral fraction. Thus, discovery of large number of z > 6 quasars, especially low-luminous or z > 7 quasars, is highly desired for further understanding of the early universe. We are now starting a new ground-breaking survey of high-redshift (z > 6) quasars using the exquisite imaging data provided by the Hyper Suprime-Cam (HSC) Subaru Strategic Program (SSP) Survey. Thanks to its extremely wide coverage and its high sensitivity thorough five optical bands (1,400 deg2 to the depth of r ~ 26 in HSC-Wide layer), it is one of the most powerful contemporary surveys that makes it possible for us to increase the number of z > 6 quasars by almost an order of magnitude, i.e., 300 at z ~ 6 and 50 at z ~ 7, based on the current estimate of the QLF at z > 6 by Willott et al. (2010b). One of the biggest challenges in z > 6 quasar candidate selection is contamination of Galactic brown dwarfs, which have the same point-like appearance as and similarly red colors to the quasars. To overcome this issue and maximize the selection efficiency, we apply a double-layered approach to the HSC survey products, namely combination of two probabilistic selections: SED-fitting and Bayesian selection. In particular, we have developed a template SED fitting method optimized to high-redshift quasars

  7. The luminosity function of quasars and its evolution: A comparison of optically selected quasars and quasars found in radio catalogs

    NASA Technical Reports Server (NTRS)

    Petrosian, V.

    1973-01-01

    The luminosity function of quasars and its evolution are discussed, based on comparison of available data on optically selected quasars and quasars found in radio catalogs. It is assumed that the red shift of quasars is cosmological and the results are expressed in the framework of the Lambda = 0, Q sub Q = 1 cosmological model. The predictions of various density evolution laws are compared with observations of an optically selected sample of quasars and quasar samples from radio catalogs. The differences between the optical luminosity functions, the red shift distributions and the radio to optical luminosity ratios of optically selected quasars and radio quasars rule out luminosity functions where there is complete absence of correlation between radio and optical luminosities. These differences also imply that Schmidt's (1970) luminosity function, where there exists a statistical correlation between radio and optical luminosities, although may be correct for high red shift objects, disagrees with observation at low red shifts. These differences can be accounted for by postulating existence of two classes (1 and 2) of objects.

  8. SPECTROPOLARIMETRY OF RADIO-SELECTED BROAD ABSORPTION LINE QUASARS

    SciTech Connect

    DiPompeo, M. A.; Brotherton, M. S.; Becker, R. H.; Gregg, M. D.; Tran, H. D.; White, R. L.; Laurent-Muehleisen, S. A.

    2010-07-15

    We report spectropolarimetry of 30 radio-selected broad absorption line (BAL) quasars with the Keck Observatory, 25 from the sample of Becker et al. Both high- and low-ionization BAL quasars are represented, with redshifts ranging from 0.5 to 2.5. The spectropolarimetric properties of radio-selected BAL quasars are very similar to those of radio-quiet BAL quasars: a sizeable fraction (20%) shows large continuum polarization (2%-10%) usually rising toward short wavelengths; emission lines are typically less polarized than the continuum; and absorption line troughs often show large polarization jumps. There are no significant correlations between polarization properties and radio properties, including those indicative of system orientation, suggesting that BAL quasars are not simply normal quasars seen from an edge-on perspective.

  9. The quasar luminosity function from a variability-selected sample

    NASA Astrophysics Data System (ADS)

    Hawkins, M. R. S.; Veron, P.

    1993-01-01

    A sample of quasars is selected from a 10-yr sequence of 30 UK Schmidt plates. Luminosity functions are derived in several redshift intervals, which in each case show a featureless power-law rise towards low luminosities. There is no sign of the 'break' found in the recent UVX sample of Boyle et al. It is suggested that reasons for the disagreement are connected with biases in the selection of the UVX sample. The question of the nature of quasar evolution appears to be still unresolved.

  10. DISCOVERY OF A RADIO-SELECTED z {approx} 6 QUASAR

    SciTech Connect

    Zeimann, Gregory R.; Becker, Robert H.; Hodge, Jacqueline A.; Stanford, Spencer A.; White, Richard L.; Richards, Gordon T.

    2011-07-20

    We present the discovery of only the second radio-selected z {approx} 6 quasar. We identified SDSS J222843.54+011032.2 (z = 5.95) by matching the optical detections of the deep Sloan Digital Sky Survey Stripe 82 with their radio counterparts in the Stripe 82 Very Large Array Survey. We also matched the Canadian-France-Hawaiian Telescope Legacy Survey Wide with the Faint Images of the Radio Sky at Twenty cm survey but have yet to find any z {approx} 6 quasars in this survey area. The discovered quasar is optically faint, z = 22.3 and M{sub 1450} {approx} -24.5, but radio bright, with a flux density of f{sub 1.4GHz,peak} = 0.31 mJy and a radio loudness of R {approx} 1100 (where R {identical_to} f{sub 5GHz}/f{sub 2500}). The i - z color of the discovered quasar places it outside the color selection criteria for existing optical surveys. We conclude by discussing the need for deeper wide-area radio surveys in the context of high-redshift quasars.

  11. Quasars.

    PubMed

    Smith, H J

    1966-11-01

    A short historical outline of the discovery and a description of observed properties of quasars introduces questions as to their nature. Some of the principal arguments concerning their reality, distance, intrinsic properties and age lead to the conclusion that, while there is room for other points of view; a strong case can be made for the interpretation, on which quasars are the most distant observable objects in the known universe. To produce such luminosities over times of thousands to millions of years requires the presence of millions of solar masses. For each quasar this enormous mass may be concentrated into a single object, in which case novel physics comes into play. Whatever the final interpretation, quasars seem certain to illuminate such questions as the origin and evolution of galaxies, perhaps also the structure and origin of the universe.

  12. SDSS QUASARS IN THE WISE PRELIMINARY DATA RELEASE AND QUASAR CANDIDATE SELECTION WITH OPTICAL/INFRARED COLORS

    SciTech Connect

    Wu Xuebing; Hao Guoqiang; Jia Zhendong; Zhang Yanxia; Peng Nanbo

    2012-08-15

    We present a catalog of 37,842 quasars in the Sloan Digital Sky Survey (SDSS) Data Release 7, which have counterparts within 6'' in the Wide-field Infrared Survey Explorer (WISE) Preliminary Data Release. The overall WISE detection rate of the SDSS quasars is 86.7%, and it decreases to less than 50.0% when the quasar magnitude is fainter than i = 20.5. We derive the median color-redshift relations based on this SDSS-WISE quasar sample and apply them to estimate the photometric redshifts of the SDSS-WISE quasars. We find that by adding the WISE W1- and W2-band data to the SDSS photometry we can increase the photometric redshift reliability, defined as the percentage of sources with photometric and spectroscopic redshift difference less than 0.2, from 70.3% to 77.2%. We also obtain the samples of WISE-detected normal and late-type stars with SDSS spectroscopy, and present a criterion in the z - W1 versus g - z color-color diagram, z - W1 > 0.66(g - z) + 2.01, to separate quasars from stars. With this criterion we can recover 98.6% of 3089 radio-detected SDSS-WISE quasars with redshifts less than four and overcome the difficulty in selecting quasars with redshifts between 2.2 and 3 from SDSS photometric data alone. We also suggest another criterion involving the WISE color only, W1 - W2 > 0.57, to efficiently separate quasars with redshifts less than 3.2 from stars. In addition, we compile a catalog of 5614 SDSS quasars detected by both WISE and UKIDSS surveys and present their color-redshift relations in the optical and infrared bands. By using the SDSS ugriz, UKIDSS, YJHK, and WISE W1- and W2-band photometric data, we can efficiently select quasar candidates and increase the photometric redshift reliability up to 87.0%. We discuss the implications of our results on the future quasar surveys. An updated SDSS-WISE quasar catalog consisting of 101,853 quasars with the recently released WISE all-sky data is also provided.

  13. Posterior Predictive Bayesian Phylogenetic Model Selection

    PubMed Central

    Lewis, Paul O.; Xie, Wangang; Chen, Ming-Hui; Fan, Yu; Kuo, Lynn

    2014-01-01

    We present two distinctly different posterior predictive approaches to Bayesian phylogenetic model selection and illustrate these methods using examples from green algal protein-coding cpDNA sequences and flowering plant rDNA sequences. The Gelfand–Ghosh (GG) approach allows dissection of an overall measure of model fit into components due to posterior predictive variance (GGp) and goodness-of-fit (GGg), which distinguishes this method from the posterior predictive P-value approach. The conditional predictive ordinate (CPO) method provides a site-specific measure of model fit useful for exploratory analyses and can be combined over sites yielding the log pseudomarginal likelihood (LPML) which is useful as an overall measure of model fit. CPO provides a useful cross-validation approach that is computationally efficient, requiring only a sample from the posterior distribution (no additional simulation is required). Both GG and CPO add new perspectives to Bayesian phylogenetic model selection based on the predictive abilities of models and complement the perspective provided by the marginal likelihood (including Bayes Factor comparisons) based solely on the fit of competing models to observed data. [Bayesian; conditional predictive ordinate; CPO; L-measure; LPML; model selection; phylogenetics; posterior predictive.] PMID:24193892

  14. Rest-frame optical properties of luminous, radio-selected broad absorption line quasars

    NASA Astrophysics Data System (ADS)

    Runnoe, Jessie C.; Ganguly, R.; Brotherton, M. S.; DiPompeo, M. A.

    2013-08-01

    We have obtained Infrared Telescope Facility/SpeX spectra of eight moderate-redshift (z = 0.7-2.4), radio-selected (log R* ≈ 0.4-1.9) broad absorption line (BAL) quasars. The spectra cover the rest-frame optical band. We compare the optical properties of these quasars to those of canonically radio-quiet (log R* ≲ 1) BAL quasars at similar redshifts and to low-redshift quasars from the Palomar-Green catalogue. As with previous studies of BAL quasars, we find that [O III] λ5007 is weak, and optical Fe II emission is strong, a rare combination in canonically radio-loud (log R* ≳ 1) quasars. With our measurements of the optical properties, particularly the Balmer emission-line widths and the continuum luminosity, we have used empirical scaling relations to estimate black hole masses and Eddington ratios. These lie in the range (0.4-2.6) × 109 M⊙ and 0.1-0.9, respectively. Despite their comparatively extreme radio properties relative to most BAL quasars, their optical properties are quite consistent with those of radio-quiet BAL quasars and dissimilar to those of radio-loud non-BAL quasars. While BAL quasars generally appear to have low values of [O III] λ5007/Fe II an extreme of `Eigenvector 1', the Balmer line widths and Eddington ratios do not appear to significantly differ from those of unabsorbed quasars at similar redshifts and luminosities.

  15. X-ray to infrared continua of optically selected quasars

    NASA Technical Reports Server (NTRS)

    Elvis, Martin

    1986-01-01

    X-ray-to-IR continuum data for nine optically selected (PG) quasars show a form which can be simply described in terms of two components - a power law of slope about 1 joining smoothly the 1-10-micron IR with the 0.1-10-keV X-ray points and (superimposed on this) a 'big bump' of optical-UV emission. The 'big bump' can be interpreted as thermal emission from an accretion disk. In a unique case where this 'big bump' extends to soft X-rays, the accretion disk parameters can be constrained interestingly.

  16. Bayesian model selection analysis of WMAP3

    SciTech Connect

    Parkinson, David; Mukherjee, Pia; Liddle, Andrew R.

    2006-06-15

    We present a Bayesian model selection analysis of WMAP3 data using our code CosmoNest. We focus on the density perturbation spectral index n{sub S} and the tensor-to-scalar ratio r, which define the plane of slow-roll inflationary models. We find that while the Bayesian evidence supports the conclusion that n{sub S}{ne}1, the data are not yet powerful enough to do so at a strong or decisive level. If tensors are assumed absent, the current odds are approximately 8 to 1 in favor of n{sub S}{ne}1 under our assumptions, when WMAP3 data is used together with external data sets. WMAP3 data on its own is unable to distinguish between the two models. Further, inclusion of r as a parameter weakens the conclusion against the Harrison-Zel'dovich case (n{sub S}=1, r=0), albeit in a prior-dependent way. In appendices we describe the CosmoNest code in detail, noting its ability to supply posterior samples as well as to accurately compute the Bayesian evidence. We make a first public release of CosmoNest, now available at www.cosmonest.org.

  17. Posterior predictive Bayesian phylogenetic model selection.

    PubMed

    Lewis, Paul O; Xie, Wangang; Chen, Ming-Hui; Fan, Yu; Kuo, Lynn

    2014-05-01

    We present two distinctly different posterior predictive approaches to Bayesian phylogenetic model selection and illustrate these methods using examples from green algal protein-coding cpDNA sequences and flowering plant rDNA sequences. The Gelfand-Ghosh (GG) approach allows dissection of an overall measure of model fit into components due to posterior predictive variance (GGp) and goodness-of-fit (GGg), which distinguishes this method from the posterior predictive P-value approach. The conditional predictive ordinate (CPO) method provides a site-specific measure of model fit useful for exploratory analyses and can be combined over sites yielding the log pseudomarginal likelihood (LPML) which is useful as an overall measure of model fit. CPO provides a useful cross-validation approach that is computationally efficient, requiring only a sample from the posterior distribution (no additional simulation is required). Both GG and CPO add new perspectives to Bayesian phylogenetic model selection based on the predictive abilities of models and complement the perspective provided by the marginal likelihood (including Bayes Factor comparisons) based solely on the fit of competing models to observed data. PMID:24193892

  18. Mid-infrared-selected quasars. I. Virial black hole mass and eddington ratios

    SciTech Connect

    Dai, Y. Sophia; Elvis, Martin; Fazio, Giovanni G.; Huang, Jia-Sheng; Wilkes, Belinda J.; Bergeron, Jacqueline; Omont, Alain; Willmer, Christopher N. A.; Papovich, Casey

    2014-08-20

    We provide a catalog of 391 mid-infrared-selected (MIR; 24 μm) broad-emission-line (BEL; type 1) quasars in the 22 deg{sup 2} SWIRE Lockman Hole field. This quasar sample is selected in the MIR from Spitzer MIPS with S {sub 24} > 400 μJy, jointly with an optical magnitude limit of r (AB) < 22.5 for broad line identification. The catalog is based on MMT and Sloan Digital Sky Survey (SDSS) spectroscopy to select BEL quasars, extending the SDSS coverage to fainter magnitudes and lower redshifts, and recovers a more complete quasar population. The MIR-selected quasar sample peaks at z ∼ 1.4 and recovers a significant and constant (20%) fraction of extended objects with SDSS photometry across magnitudes, which were not included in the SDSS quasar survey dominated by point sources. This sample also recovers a significant population of z < 3 quasars at i > 19.1. We then investigate the continuum luminosity and line profiles of these MIR quasars, and estimate their virial black hole masses and the Eddington ratios. The supermassive black hole mass shows evidence of downsizing, although the Eddington ratios remain constant at 1 < z < 4. Compared to point sources in the same redshift range, extended sources at z < 1 show systematically lower Eddington ratios. The catalog and spectra are publicly available online.

  19. X-ray Properties of Deep Radio-Selected Quasars

    NASA Technical Reports Server (NTRS)

    Becker, Robert

    2002-01-01

    This report summarizes the research supported by the ADP grant entitled 'X-ray Properties of Deep Radio-Selected Quasars'. The primary effort consisted of correlating the ROSAT All-Sky Survey catalog with the April 1997 release of the FIRST (Faint Images of the Radio Sky at Twenty centimeters) radio catalog. We found that a matching radius of 60 sec excluded most false matches while retaining most of the true radio-X-ray sources. The correlation of the approx. 80,000 source RASS and approx. 268,000 FIRST catalogs matched 2,588 FIRST sources with 1,649 RASS sources out of a possible 5,520 RASS sources residing in the FIRST survey area. This number is much higher than expected from our previous experience of correlating the RASS with radio surveys and indicates we detected new classes of objects not seen in the correlations with less sensitive radio surveys.

  20. Newton, Einstein, Jeffreys and Bayesian model selection

    NASA Astrophysics Data System (ADS)

    Chettri, Samir; Batchelor, David; Campbell, William; Balakrishnan, Karthik

    2005-11-01

    In Jefferys and Berger apply Bayesian model selection to the problem of choosing between rival theories, in particular between Einstein's theory of general relativity (GR) and Newtonian gravity (NG). [1] presents a debate between Harold Jeffreys and Charles Poor regarding the observed 43''/century anomalous perhelion precession of Mercury. GR made a precise prediction of 42.98''/century while proponents of NG suggested several physical mechanisms that were eventually refuted, with the exception of a modified inverse square law. Using Bayes Factors (BF) and data available in 1921, shows that GR is preferable to NG by a factor of about 25 to 1. A scale for BF used by Jeffreys, suggests that this is positive to strong evidence for GR over modified NG but it is not very strong or even overwhelming. In this work we calculate the BF from the period 1921 till 1993. By 1960 we see that the BF, due to better data gathering techniques and advances in technology, had reached a factor of greater than 100 to 1, making GR strongly preferable to NG and by 1990 the BF reached 1000:1. Ironically while BF had reached a state of near certainty even in 1960 rival theories of gravitation were on the rise - notably the Brans-Dicke (BD) scalar-tensor theory of gravity. The BD theory is postulated in such a way that for small positive values of a scalar parameter ω, the BF would favor GR while the BF would approach unity with certainty as ω grows larger, at which point either theory would be prefered, i.e., it is a theory that cannot lose. Does this mean Bayesian model selection needs to be overthrown? This points to the need for cogent prior information guided by physics and physical experiment.

  1. Bayesian Item Selection in Constrained Adaptive Testing Using Shadow Tests

    ERIC Educational Resources Information Center

    Veldkamp, Bernard P.

    2010-01-01

    Application of Bayesian item selection criteria in computerized adaptive testing might result in improvement of bias and MSE of the ability estimates. The question remains how to apply Bayesian item selection criteria in the context of constrained adaptive testing, where large numbers of specifications have to be taken into account in the item…

  2. A sensorimotor paradigm for Bayesian model selection.

    PubMed

    Genewein, Tim; Braun, Daniel A

    2012-01-01

    Sensorimotor control is thought to rely on predictive internal models in order to cope efficiently with uncertain environments. Recently, it has been shown that humans not only learn different internal models for different tasks, but that they also extract common structure between tasks. This raises the question of how the motor system selects between different structures or models, when each model can be associated with a range of different task-specific parameters. Here we design a sensorimotor task that requires subjects to compensate visuomotor shifts in a three-dimensional virtual reality setup, where one of the dimensions can be mapped to a model variable and the other dimension to the parameter variable. By introducing probe trials that are neutral in the parameter dimension, we can directly test for model selection. We found that model selection procedures based on Bayesian statistics provided a better explanation for subjects' choice behavior than simple non-probabilistic heuristics. Our experimental design lends itself to the general study of model selection in a sensorimotor context as it allows to separately query model and parameter variables from subjects. PMID:23125827

  3. Bayesian analysis of X-ray jet features of the high redshift quasar jets observed with Chandra

    NASA Astrophysics Data System (ADS)

    McKeough, Kathryn; Siemiginowska, Aneta; Kashyap, Vinay; Stein, Nathan; Cheung, Chi C.

    2015-01-01

    X-ray emission of powerful quasar jets may be a result of the inverse Compton (IC) process in which the Cosmic Microwave Background (CMB) photons gain energy by interactions with the jet's relativistic electrons. However, there is no definite evidence that IC/CMB process is responsible for the observed X-ray emission of large scale jets. A step toward understanding the X-ray emission process is to study the Radio and X-ray morphologies of the jet. Results from Chandra X-ray and multi-frequency VLA imaging observations of a sample of 11 high- redshift (z > 2) quasars with kilo-parsec scale radio jets are reported. The sample consists of a set of four z ≥ 3.6 flat-spectrum radio quasars, and seven intermediate redshift (z = 2.1 - 2.9) quasars comprised of four sources with integrated steep radio spectra and three with flat radio spectra.We implement a Bayesian image analysis program, Low-count Image Reconstruction and Analysis (LIRA) , to analyze jet features in the X-ray images of the high redshift quasars. Out of the 36 regions where knots are visible in the radio jets, nine showed detectable X-ray emission. Significant detections are based on the upper bound p-value test based on LIRA simulations. The X-ray and radio properties of this sample combined are examined and compared to lower-redshift samples.This work is supported in part by the National Science Foundation REU and the Department of Defense ASSURE programs under NSF Grant no.1262851 and by the Smithsonian Institution, and by NASA Contract NAS8-39073 to the Chandra X-ray Center (CXC). This research has made use of data obtained from the Chandra Data Archive and Chandra Source Catalog, and software provided by the CXC in the application packages CIAO, ChIPS, and Sherpa. Work is also supported by the Chandra grant GO4-15099X.

  4. A VERY LARGE ARRAY SURVEY OF RADIO-SELECTED SDSS BROAD ABSORPTION LINE QUASARS

    SciTech Connect

    DiPompeo, M. A.; Brotherton, M. S.; De Breuck, C.; Laurent-Muehleisen, Sally

    2011-12-10

    We have built a sample of 74 radio-selected broad absorption line (BAL) quasars from the Sloan Digital Sky Survey Data Release 5 and Faint Images of the Radio Sky at Twenty Centimeters, along with a well-matched sample of 74 unabsorbed 'normal' quasars. The sources have been observed with the NRAO Very Large Array/Expanded Very Large Array at 8.4 GHz (3.5 cm) and 4.9 GHz (6 cm). All sources have additional archival 1.4 GHz (21 cm) data. Here we present the measured radio fluxes, spectral indices, and our initial findings. The percentage of BAL quasars with extended structure (on the order of 10%) in our sample is similar to previous studies at similar resolutions, suggesting that BAL quasars are indeed generally compact, at least at arsecond resolutions. The majority of sources do not appear to be significantly variable at 1.4 GHz, but we find two previously unidentified BAL quasars that may fit into the 'polar' BAL category. We also identify a significant favoring of steeper radio spectral index for BAL compared to non-BAL quasars. This difference is apparent for several different measures of the spectral index and persists even when restricting the samples to only include compact objects. Because radio spectral index is a statistical indicator of viewing angle for large samples, these results suggest that BAL quasars do have a range of orientations but are more often observed farther from the jet axis compared to normal quasars.

  5. New quasars behind the Magellanic Clouds. Spectroscopic confirmation of near-infrared selected candidates

    NASA Astrophysics Data System (ADS)

    Ivanov, Valentin D.; Cioni, Maria-Rosa L.; Bekki, Kenji; de Grijs, Richard; Emerson, Jim; Gibson, Brad K.; Kamath, Devika; van Loon, Jacco Th.; Piatti, Andrés E.; For, Bi-Qing

    2016-04-01

    Context. Quasi-stellar objects (quasars) located behind nearby galaxies provide an excellent absolute reference system for astrometric studies, but they are difficult to identify because of fore- and background contamination. Deep wide-field, high angular resolution surveys spanning the entire area of nearby galaxies are needed to obtain a complete census of such quasars. Aims: We embarked on a program to expand the quasar reference system behind the Large and the Small Magellanic Clouds, the Magellanic Bridge, and the Magellanic Stream that connects the Clouds with the Milky Way. Methods: Hundreds of quasar candidates were selected based on their near-infrared colors and variability properties from the ongoing public ESO VISTA Magellanic Clouds survey. A subset of 49 objects was followed up with optical spectroscopy. Results: We confirmed the quasar nature of 37 objects (34 new identifications): four are low redshift objects, three are probably stars, and the remaining three lack prominent spectral features for a secure classification. The bona fide quasars, identified from their broad emisison lines, are located as follows: 10 behind the LMC, 13 behind the SMC, and 14 behind the Bridge. The quasars span a redshift range from z ~ 0.5 to z ~ 4.1. Conclusions: Upon completion the VMC survey is expected to yield a total of ~1500 quasars with Y< 19.32 mag, J< 19.09 mag, and Ks< 18.04 mag.

  6. Entropic Priors and Bayesian Model Selection

    NASA Astrophysics Data System (ADS)

    Brewer, Brendon J.; Francis, Matthew J.

    2009-12-01

    We demonstrate that the principle of maximum relative entropy (ME), used judiciously, can ease the specification of priors in model selection problems. The resulting effect is that models that make sharp predictions are disfavoured, weakening the usual Bayesian ``Occam's Razor.'' This is illustrated with a simple example involving what Jaynes called a ``sure thing'' hypothesis. Jaynes' resolution of the situation involved introducing a large number of alternative ``sure thing'' hypotheses that were possible before we observed the data. However, in more complex situations, it may not be possible to explicitly enumerate large numbers of alternatives. The entropic priors formalism produces the desired result without modifying the hypothesis space or requiring explicit enumeration of alternatives; all that is required is a good model for the prior predictive distribution for the data. This idea is illustrated with a simple rigged-lottery example, and we outline how this idea may help to resolve a recent debate amongst cosmologists: is dark energy a cosmological constant, or has it evolved with time in some way? And how shall we decide, when the data are in?

  7. HOT-DUST-POOR QUASARS IN MID-INFRARED AND OPTICALLY SELECTED SAMPLES

    SciTech Connect

    Hao Heng; Elvis, Martin; Civano, Francesca; Lawrence, Andy E-mail: elvis@cfa.harvard.edu

    2011-06-01

    We show that the hot-dust-poor (HDP) quasars, originally found in the X-ray-selected XMM-COSMOS type 1 active galactic nucleus (AGN) sample, are just as common in two samples selected at optical/infrared wavelengths: the Richards et al. Spitzer/SDSS sample (8.7% {+-} 2.2%) and the Palomar-Green-quasar-dominated sample of Elvis et al. (9.5% {+-} 5.0%). The properties of the HDP quasars in these two samples are consistent with the XMM-COSMOS sample, except that, at the 99% ({approx} 2.5{sigma}) significance, a larger proportion of the HDP quasars in the Spitzer/SDSS sample have weak host galaxy contributions, probably due to the selection criteria used. Either the host dust is destroyed (dynamically or by radiation) or is offset from the central black hole due to recoiling. Alternatively, the universality of HDP quasars in samples with different selection methods and the continuous distribution of dust covering factor in type 1 AGNs suggest that the range of spectral energy distributions could be related to the range of tilts in warped fueling disks, as in the model of Lawrence and Elvis, with HDP quasars having relatively small warps.

  8. A guide to Bayesian model selection for ecologists

    USGS Publications Warehouse

    Hooten, Mevin B.; Hobbs, N.T.

    2015-01-01

    The steady upward trend in the use of model selection and Bayesian methods in ecological research has made it clear that both approaches to inference are important for modern analysis of models and data. However, in teaching Bayesian methods and in working with our research colleagues, we have noticed a general dissatisfaction with the available literature on Bayesian model selection and multimodel inference. Students and researchers new to Bayesian methods quickly find that the published advice on model selection is often preferential in its treatment of options for analysis, frequently advocating one particular method above others. The recent appearance of many articles and textbooks on Bayesian modeling has provided welcome background on relevant approaches to model selection in the Bayesian framework, but most of these are either very narrowly focused in scope or inaccessible to ecologists. Moreover, the methodological details of Bayesian model selection approaches are spread thinly throughout the literature, appearing in journals from many different fields. Our aim with this guide is to condense the large body of literature on Bayesian approaches to model selection and multimodel inference and present it specifically for quantitative ecologists as neutrally as possible. We also bring to light a few important and fundamental concepts relating directly to model selection that seem to have gone unnoticed in the ecological literature. Throughout, we provide only a minimal discussion of philosophy, preferring instead to examine the breadth of approaches as well as their practical advantages and disadvantages. This guide serves as a reference for ecologists using Bayesian methods, so that they can better understand their options and can make an informed choice that is best aligned with their goals for inference.

  9. The Color Selection of Quasars from Redshifts 5 to 10: Cloning and Discovery

    NASA Astrophysics Data System (ADS)

    Chiu, Kuenley; Zheng, Wei; Schneider, Donald P.; Glazebrook, Karl; Iye, Masanori; Kashikawa, Nobunari; Tsvetanov, Zlatan; Yoshida, Michitoshi; Brinkmann, Jon

    2005-07-01

    We present simulations of quasar colors, magnitudes, and numbers at redshifts 5quasars and the cloning of lower redshift Sloan Digital Sky Survey (SDSS) quasars. The 10 quasars have redshifts ranging from z=4.7 to 5.3 and i magnitudes of 20.21-20.94. The natural diversity of spectral features in the cloned sample allows more realistic simulation of the quasar locus width than was previously possible with synthetic template spectra. Colors are generated for the z>6 epoch, taking advantage of the new UKIRT Infrared Deep Sky Survey near-infrared filter set, and we examine the redshift intervals of maximum productivity, discussing color selection and survey depth issues. On the basis of the SDSS sample, we find that the surface density of z>4.7 quasars increases by a factor of 3 times by extending 0.7 i magnitudes deeper than the SDSS spectroscopic survey limit of i=20.2; correspondingly, we predict a total of ~400 faint quasars in the SDSS main area that have redshift z>4.7 and magnitudes i<20.9.

  10. Discovery of low-redshift X-ray selected quasars - New clues to the QSO phenomenon

    NASA Technical Reports Server (NTRS)

    Grindlay, J. E.; Forman, W. R.; Steiner, J. E.; Canizares, C. R.; Mcclintock, J. E.

    1980-01-01

    The identification of six X-ray sources discovered by the Einstein Observatory with X-ray quasars is reported, and the properties of these X-ray selected quasars are discussed. The four high-latitude fields of 1 sq deg each in which the Einstein imaging proportional counter detected serendipitous X-ray sources at intermediate exposures of 10,000 sec were observed by 4-m and 1.5-m telescopes, and optical sources with uv excesses and emission line spectra typical of many low-redshift quasars and Seyfert 1 galaxies were found within the 1-arcsec error boxes of the X-ray sources. All six quasars identified were found to be radio quiet, with low redshift and relatively faint optical magnitudes, and to be similar in space density, colors and magnitude versus redshift relation to an optically selected sample at the same mean magnitude. X-ray luminosity was found to be well correlated with both continuum and broad-line emission luminosities for the known radio-quiet quasars and Seyfert 1 galaxies, and it was observed that the five objects with the lowest redshifts have very similar X-ray/optical luminosity ratios despite tenfold variations in X-ray luminosity. It is concluded that photoionization by a continuum extending to X-ray energies is the dominant excitation mechanism in radio-quiet quasars.

  11. The Quasar Fraction in Low-Frequency Selected Complete Samples and Implications for Unified Schemes

    NASA Technical Reports Server (NTRS)

    Willott, Chris J.; Rawlings, Steve; Blundell, Katherine M.; Lacy, Mark

    2000-01-01

    Low-frequency radio surveys are ideal for selecting orientation-independent samples of extragalactic sources because the sample members are selected by virtue of their isotropic steep-spectrum extended emission. We use the new 7C Redshift Survey along with the brighter 3CRR and 6C samples to investigate the fraction of objects with observed broad emission lines - the 'quasar fraction' - as a function of redshift and of radio and narrow emission line luminosity. We find that the quasar fraction is more strongly dependent upon luminosity (both narrow line and radio) than it is on redshift. Above a narrow [OII] emission line luminosity of log(base 10) (L(sub [OII])/W) approximately > 35 [or radio luminosity log(base 10) (L(sub 151)/ W/Hz.sr) approximately > 26.5], the quasar fraction is virtually independent of redshift and luminosity; this is consistent with a simple unified scheme with an obscuring torus with a half-opening angle theta(sub trans) approximately equal 53 deg. For objects with less luminous narrow lines, the quasar fraction is lower. We show that this is not due to the difficulty of detecting lower-luminosity broad emission lines in a less luminous, but otherwise similar, quasar population. We discuss evidence which supports at least two probable physical causes for the drop in quasar fraction at low luminosity: (i) a gradual decrease in theta(sub trans) and/or a gradual increase in the fraction of lightly-reddened (0 approximately < A(sub V) approximately < 5) lines-of-sight with decreasing quasar luminosity; and (ii) the emergence of a distinct second population of low luminosity radio sources which, like M8T, lack a well-fed quasar nucleus and may well lack a thick obscuring torus.

  12. Ca II AND Na I QUASAR ABSORPTION-LINE SYSTEMS IN AN EMISSION-SELECTED SAMPLE OF SDSS DR7 GALAXY/QUASAR PROJECTIONS. I. SAMPLE SELECTION

    SciTech Connect

    Cherinka, B.; Schulte-Ladbeck, R. E.

    2011-10-15

    The aim of this project is to identify low-redshift host galaxies of quasar absorption-line systems by selecting galaxies that are seen in projection onto quasar sightlines. To this end, we use the Seventh Data Release of the Sloan Digital Sky Survey to construct a parent sample of 97,489 galaxy/quasar projections at impact parameters of up to 100 kpc to the foreground galaxy. We then search the quasar spectra for absorption-line systems of Ca II and Na I within {+-}500 km s{sup -1} of the galaxy's velocity. This yields 92 Ca II and 16 Na I absorption systems. We find that most of the Ca II and Na I systems are sightlines through the Galactic disk, through high-velocity cloud complexes in our halo, or Virgo Cluster sightlines. Placing constraints on the absorption line rest equivalent width significance ({>=}3.0{sigma}), the local standard of rest velocity along the sightline ({>=}345 km s{sup -1}), and the ratio of the impact parameter to the galaxy optical radius ({<=}5.0), we identify four absorption-line systems that are associated with low-redshift galaxies at high confidence, consisting of two Ca II systems (one of which also shows Na I) and two Na I systems. These four systems arise in blue, {approx}L*{sub r} galaxies. Tables of the 108 absorption systems are provided to facilitate future follow-up.

  13. Probabilistic Selection of High-redshfit Quasars with Subaru / Hyper Suprime-Cam Survey

    NASA Astrophysics Data System (ADS)

    Onoue, Masafusa

    2015-08-01

    High-redshift quasrs are an important probe of the distant Universe. They enable observational studies of the early growth of supermassive blackholes, cosmic reionization, chemical enrichment of host galaxies, and so on. We are now starting a new ground-breaking survey of high-redsfhit quasars (z>6) using the exquisite imaging data provided by the Hyper Suprime-Cam (HSC) Subaru Strategic Program (SSP) Survey. With the extremely wide-area coverage and high sensitivity thorugh five optical bands (1,400 deg2 to the depth of r~26 in Wide layer), it is one of the most powerful contemporary surveys that makes it possible for the HSC-AGN collaboration to increase the number of z>6 quasars by almost an order of magnitude, i.e., 300 at z~6 and 50 at z~7 based on the current estimate of the QLF at z>6 (Willott et al. 2010).One of the biggest challenges in the candidate selection is the significant contamination of Galactic brown dwarfs, which have the same point-like appearance as and similarly red colors to z>6 quasars. To overcome this issue, we have developed template SED fitting method optimized to high-redshift quasars selection for constructing the largest z>6 quasar sample with the HSC survey. Since 500 deg2 of the footprints of the HSC survey overlaps with the VISTA/VIKING survey, it is expected that z>6 quasars, with characteristic large Lyman break and flat red-continuum in its SED, can be separated out from contaminating sources by applying SED fitting with multi-wavelength photometric data. In practice, its application with 27 photometric bands to the COSMOS quasars at 3quasars are correctly classified with small dispersion σΔz/(1+z)=0.01 and as low as η=2.5% outlier rate.In our poster, we present the detailed evaluation of the efficiency of our strategy, and also the progress of our z>6 quasar search with the first-year data products of the HSC survey, which results in extracting several promising candidates

  14. A Survey of Luminous High-redshift Quasars with SDSS and WISE. I. Target Selection and Optical Spectroscopy

    NASA Astrophysics Data System (ADS)

    Wang, Feige; Wu, Xue-Bing; Fan, Xiaohui; Yang, Jinyi; Yi, Weimin; Bian, Fuyan; McGreer, Ian D.; Yang, Qian; Ai, Yanli; Dong, Xiaoyi; Zuo, Wenwen; Jiang, Linhua; Green, Richard; Wang, Shu; Cai, Zheng; Wang, Ran; Yue, Minghao

    2016-03-01

    High-redshift quasars are important tracers of structure and evolution in the early universe. However, they are very rare and difficult to find when using color selection because of contamination from late-type dwarfs. High-redshift quasar surveys based on only optical colors suffer from incompleteness and low identification efficiency, especially at z≳ 4.5. We have developed a new method to select 4.7≲ z≲ 5.4 quasars with both high efficiency and completeness by combining optical and mid-IR Wide-field Infrared Survey Explorer (WISE) photometric data, and are conducting a luminous z˜ 5 quasar survey in the whole Sloan Digital Sky Survey (SDSS) footprint. We have spectroscopically observed 99 out of 110 candidates with z-band magnitudes brighter than 19.5, and 64 (64.6%) of them are quasars with redshifts of 4.4≲ z≲ 5.5 and absolute magnitudes of -29≲ {M}1450≲ -26.4. In addition, we also observed 14 fainter candidates selected with the same criteria and identified 8 (57.1%) of them as quasars with 4.7\\lt z\\lt 5.4. Among 72 newly identified quasars, 12 of them are at 5.2\\lt z\\lt 5.7, which leads to an increase of ˜36% of the number of known quasars at this redshift range. More importantly, our identifications doubled the number of quasars with {M}1450\\lt -27.5 at z\\gt 4.5, which will set strong constraints on the bright end of the quasar luminosity function. We also expand our method to select quasars at z ≳ 5.7. In this paper we report the discovery of four new luminous z ≳ 5.7 quasars based on SDSS-WISE selection.

  15. Bayesian natural selection and the evolution of perceptual systems.

    PubMed Central

    Geisler, Wilson S; Diehl, Randy L

    2002-01-01

    In recent years, there has been much interest in characterizing statistical properties of natural stimuli in order to better understand the design of perceptual systems. A fruitful approach has been to compare the processing of natural stimuli in real perceptual systems with that of ideal observers derived within the framework of Bayesian statistical decision theory. While this form of optimization theory has provided a deeper understanding of the information contained in natural stimuli as well as of the computational principles employed in perceptual systems, it does not directly consider the process of natural selection, which is ultimately responsible for design. Here we propose a formal framework for analysing how the statistics of natural stimuli and the process of natural selection interact to determine the design of perceptual systems. The framework consists of two complementary components. The first is a maximum fitness ideal observer, a standard Bayesian ideal observer with a utility function appropriate for natural selection. The second component is a formal version of natural selection based upon Bayesian statistical decision theory. Maximum fitness ideal observers and Bayesian natural selection are demonstrated in several examples. We suggest that the Bayesian approach is appropriate not only for the study of perceptual systems but also for the study of many other systems in biology. PMID:12028784

  16. The Composite Spectrum of BOSS Quasars Selected for Studies of the Lyα Forest

    NASA Astrophysics Data System (ADS)

    Harris, David W.; Jensen, Trey W.; Suzuki, Nao; Bautista, Julian E.; Dawson, Kyle S.; Vivek, M.; Brownstein, Joel R.; Ge, Jian; Hamann, Fred; Herbst, H.; Jiang, Linhua; Moran, Sarah E.; Myers, Adam D.; Olmstead, Matthew D.; Schneider, Donald P.

    2016-06-01

    The Baryon Oscillation Spectroscopic Survey (BOSS) has collected more than 150,000 2.1 ≤ z ≤ 3.5 quasar spectra since 2009. Using this unprecedented sample, we create a composite spectrum in the rest-frame of 102,150 quasar spectra from 800-3300 Å at a signal-to-noise ratio close to 1000 per pixel (Δv of 69 km s-1). Included in this analysis is a correction to account for flux calibration residuals in the BOSS spectrophotometry. We determine the spectral index as a function of redshift of the full sample, warp the composite spectrum to match the median spectral index, and compare the resulting spectrum to Sloan Digital Sky Survey (SDSS) photometry used in target selection. The quasar composite matches the color of the quasar population to 0.02 mag in g - r, 0.03 mag in r - i, and 0.01 mag in i - z over the redshift range 2.2 < z < 2.6. The composite spectrum deviates from the imaging photometry by 0.05 mag around z = 2.7, likely due to differences in target selection as the quasar colors become similar to the stellar locus at this redshift. Finally, we characterize the line features in the high signal-to-noise composite and identify nine faint lines not found in the previous composite spectrum from SDSS.

  17. A Bayesian variable selection procedure to rank overlapping gene sets

    PubMed Central

    2012-01-01

    Background Genome-wide expression profiling using microarrays or sequence-based technologies allows us to identify genes and genetic pathways whose expression patterns influence complex traits. Different methods to prioritize gene sets, such as the genes in a given molecular pathway, have been described. In many cases, these methods test one gene set at a time, and therefore do not consider overlaps among the pathways. Here, we present a Bayesian variable selection method to prioritize gene sets that overcomes this limitation by considering all gene sets simultaneously. We applied Bayesian variable selection to differential expression to prioritize the molecular and genetic pathways involved in the responses to Escherichia coli infection in Danish Holstein cows. Results We used a Bayesian variable selection method to prioritize Kyoto Encyclopedia of Genes and Genomes pathways. We used our data to study how the variable selection method was affected by overlaps among the pathways. In addition, we compared our approach to another that ignores the overlaps, and studied the differences in the prioritization. The variable selection method was robust to a change in prior probability and stable given a limited number of observations. Conclusions Bayesian variable selection is a useful way to prioritize gene sets while considering their overlaps. Ignoring the overlaps gives different and possibly misleading results. Additional procedures may be needed in cases of highly overlapping pathways that are hard to prioritize. PMID:22554182

  18. THE SDSS-III BARYON OSCILLATION SPECTROSCOPIC SURVEY: QUASAR TARGET SELECTION FOR DATA RELEASE NINE

    SciTech Connect

    Ross, Nicholas P.; Kirkpatrick, Jessica A.; Carithers, William C.; Ho, Shirley; Myers, Adam D.; Sheldon, Erin S.; Yeche, Christophe; Aubourg, Eric; Strauss, Michael A.; Lee, Khee-Gan; Bovy, Jo; Blanton, Michael R.; Hogg, David W.; Richards, Gordon T.; Brandt, W. N.; Croft, Rupert A. C.; Da Silva, Robert; Dawson, Kyle; Eisenstein, Daniel J.; Hennawi, Joseph F.; and others

    2012-03-01

    The SDSS-III Baryon Oscillation Spectroscopic Survey (BOSS), a five-year spectroscopic survey of 10,000 deg{sup 2}, achieved first light in late 2009. One of the key goals of BOSS is to measure the signature of baryon acoustic oscillations (BAOs) in the distribution of Ly{alpha} absorption from the spectra of a sample of {approx}150,000 z > 2.2 quasars. Along with measuring the angular diameter distance at z Almost-Equal-To 2.5, BOSS will provide the first direct measurement of the expansion rate of the universe at z > 2. One of the biggest challenges in achieving this goal is an efficient target selection algorithm for quasars in the redshift range 2.2 < z < 3.5, where their colors tend to overlap those of the far more numerous stars. During the first year of the BOSS survey, quasar target selection (QTS) methods were developed and tested to meet the requirement of delivering at least 15 quasars deg{sup -2} in this redshift range, with a goal of 20 out of 40 targets deg{sup -2} allocated to the quasar survey. To achieve these surface densities, the magnitude limit of the quasar targets was set at g {<=} 22.0 or r {<=} 21.85. While detection of the BAO signature in the distribution of Ly{alpha} absorption in quasar spectra does not require a uniform target selection algorithm, many other astrophysical studies do. We have therefore defined a uniformly selected subsample of 20 targets deg{sup -2}, for which the selection efficiency is just over 50% ({approx}10 z > 2.20 quasars deg{sup -2}). This 'CORE' subsample will be fixed for Years Two through Five of the survey. For the remaining 20 targets deg{sup -2}, we will continue to develop improved selection techniques, including the use of additional data sets beyond the Sloan Digital Sky Survey (SDSS) imaging data. In this paper, we describe the evolution and implementation of the BOSS QTS algorithms during the first two years of BOSS operations (through 2011 July), in support of the science investigations based on

  19. Quasar Classification Using Color and Variability

    NASA Astrophysics Data System (ADS)

    Peters, Christina M.; Richards, Gordon

    2015-08-01

    We use the Non-parametric Bayesian Classification Kernel Density Estimation (NBC KDE) quasar selection algorithm (Richards et al. 2004) to identify 36,569 type 1 quasar candidates in the Sloan Digital Sky Survey (SDSS) Stripe 82 field using the combination of optical photometry and variability. 5-band coadded optical photometry is taken from the SDSS-I/II to a depth of r ~ 22.4; from these data variability parameters are calculated by fitting the structure function of each object in each band with a power law using 10 to >100 observations for timescales from ~1 day to ~8 years. Selection was based on a training sample of 13,221 spectroscopically-confirmed type 1 quasars from SDSS-I/II and the Baryon Oscillation Spectroscopic Survey (BOSS). Using variability alone, colors alone, and combining variability and colors we achieve 91%, 93%, and 97% quasar completeness and 98%, 98%, and 97% efficiency respectively, with particular improvement in the selection of quasars at 2.7 < z < 3.5 where quasars and stars have similar optical colors. The 23,043 quasar candidates that are not spectroscopically confirmed reach a depth of coadd i ~ 22: 0 and 21,380 (92.8%) are dimmer than coadded i -band magnitude of 20.2, the cut off for spectroscopic follow-up for SDSSDR7.

  20. The Einstein database of IPC x-ray observations of optically selected and radio-selected quasars, 1.

    NASA Technical Reports Server (NTRS)

    Wilkes, Belinda J.; Tananbaum, Harvey; Worrall, D. M.; Avni, Yoram; Oey, M. S.; Flanagan, Joan

    1994-01-01

    We present the first volume of the Einstein quasar database. The database includes estimates of the X-ray count rates, fluxes, and luminosities for 514 quasars and Seyfert 1 galaxies observed with the Imaging Proportional Counter (IPC) aboard the Einstein Observatory. All were previously known optically selected or radio-selected objects, and most were the targets of the X-ray observations. The X-ray properties of the Active Galactic Nuclei (AGNs) have been derived by reanalyzing the IPC data in a systematic manner to provide a uniform database for general use by the astronomical community. We use the database to extend earlier quasar luminosity studies which were made using only a subset of the currently available data. The database can be accessed on internet via the SAO Einstein on-line system ('Einline') and is available in ASCII format on magnetic tape and DOS diskette.

  1. Bayesian model selection for LISA pathfinder

    NASA Astrophysics Data System (ADS)

    Karnesis, Nikolaos; Nofrarias, Miquel; Sopuerta, Carlos F.; Gibert, Ferran; Armano, Michele; Audley, Heather; Congedo, Giuseppe; Diepholz, Ingo; Ferraioli, Luigi; Hewitson, Martin; Hueller, Mauro; Korsakova, Natalia; McNamara, Paul W.; Plagnol, Eric; Vitale, Stefano

    2014-03-01

    The main goal of the LISA Pathfinder (LPF) mission is to fully characterize the acceleration noise models and to test key technologies for future space-based gravitational-wave observatories similar to the eLISA concept. The data analysis team has developed complex three-dimensional models of the LISA Technology Package (LTP) experiment onboard the LPF. These models are used for simulations, but, more importantly, they will be used for parameter estimation purposes during flight operations. One of the tasks of the data analysis team is to identify the physical effects that contribute significantly to the properties of the instrument noise. A way of approaching this problem is to recover the essential parameters of a LTP model fitting the data. Thus, we want to define the simplest model that efficiently explains the observations. To do so, adopting a Bayesian framework, one has to estimate the so-called Bayes factor between two competing models. In our analysis, we use three main different methods to estimate it: the reversible jump Markov chain Monte Carlo method, the Schwarz criterion, and the Laplace approximation. They are applied to simulated LPF experiments in which the most probable LTP model that explains the observations is recovered. The same type of analysis presented in this paper is expected to be followed during flight operations. Moreover, the correlation of the output of the aforementioned methods with the design of the experiment is explored.

  2. Determining the fraction of reddened quasars in COSMOS with multiple selection techniques from X-ray to radio wavelengths

    NASA Astrophysics Data System (ADS)

    Heintz, K. E.; Fynbo, J. P. U.; Møller, P.; Milvang-Jensen, B.; Zabl, J.; Maddox, N.; Krogager, J.-K.; Geier, S.; Vestergaard, M.; Noterdaeme, P.; Ledoux, C.

    2016-10-01

    The sub-population of quasars reddened by intrinsic or intervening clouds of dust are known to be underrepresented in optical quasar surveys. By defining a complete parent sample of the brightest and spatially unresolved quasars in the COSMOS field, we quantify to which extent this sub-population is fundamental to our understanding of the true population of quasars. By using the available multiwavelength data of various surveys in the COSMOS field, we built a parent sample of 33 quasars brighter than J = 20 mag, identified by reliable X-ray to radio wavelength selection techniques. Spectroscopic follow-up with the NOT/ALFOSC was carried out for four candidate quasars that had not been targeted previously to obtain a 100% redshift completeness of the sample. The population of high AV quasars (HAQs), a specific sub-population of quasars selected from optical/near-infrared photometry, some of which were shown to be missed in large optical surveys such as SDSS, is found to contribute 21%+9-5 of the parent sample. The full population of bright spatially unresolved quasars represented by our parent sample consists of 39%+9-8 reddened quasars defined by having AV > 0.1, and 21%+9-5 of the sample having E(B-V) > 0.1 assuming the extinction curve of the Small Magellanic Cloud. We show that the HAQ selection works well for selecting reddened quasars, but some are missed because their optical spectra are too blue to pass the g-r color cut in the HAQ selection. This is either due to a low degree of dust reddening or anomalous spectra. We find that the fraction of quasars with contributing light from the host galaxy, causing observed extended spatial morphology, is most dominant at z ≲ 1. At higher redshifts the population of spatially unresolved quasars selected by our parent sample is found to be representative of the full population of bright active galactic nuclei at J< 20 mag. This work quantifies the bias against reddened quasars in studies that are based solely on

  3. The extended Baryon Oscillation Spectroscopic Survey: Variability selection and quasar luminosity function

    NASA Astrophysics Data System (ADS)

    Palanque-Delabrouille, N.; Magneville, Ch.; Yèche, Ch.; Pâris, I.; Petitjean, P.; Burtin, E.; Dawson, K.; McGreer, I.; Myers, A. D.; Rossi, G.; Schlegel, D.; Schneider, D.; Streblyanska, A.; Tinker, J.

    2016-03-01

    The extended Baryon Oscillation Spectroscopic Survey of the Sloan Digital Sky Survey (SDSS-IV/eBOSS) has an extensive quasar program that combines several selection methods. Among these, the photometric variability technique provides highly uniform samples, which are unaffected by the redshift bias of traditional optical-color selections, when z = 2.7-3.5 quasars cross the stellar locus or when host galaxy light affects quasar colors at z< 0.9. We present the variability selection of quasars in eBOSS, focusing on a specific program that led to a sample of 13 876 quasars to gdered = 22.5 over a 94.5 deg2 region in Stripe 82, which has an areal density 1.5 times higher than over the rest of the eBOSS footprint. We use these variability-selected data to provide a new measurement of the quasar luminosity function (QLF) in the redshift range of 0.68 2.2. Both models are constrained to be continuous at z = 2.2. They present a flattening of the bright-end slope at high redshift. The LEDE model indicates a reduction of the break density with increasing redshift, but the evolution of the break magnitude depends on the parameterization. The models are in excellent accord, predicting quasar counts that agree within 0.3% (resp., 1.1%) to g< 22.5 (resp., g< 23). The models are also in good agreement over the entire redshift range with models from previous studies.

  4. Unusual quasars from the Sloan Digital Sky Survey selected by means of Kohonen self-organising maps

    NASA Astrophysics Data System (ADS)

    Meusinger, H.; Schalldach, P.; Scholz, R.-D.; in der Au, A.; Newholm, M.; de Hoon, A.; Kaminsky, B.

    2012-05-01

    Context. Large spectroscopic surveys have discovered very peculiar and hitherto unknown types of active galactic nuclei (AGN). Such rare objects may hold clues to the accretion history of the supermassive black holes at the centres of galaxies. Aims: We aim to create a sizeable sample of unusual quasars from the unprecedented spectroscopic database of the Sloan Digital Sky Survey (SDSS). Methods: We exploit the spectral archive of the SDSS Data Release 7 to select unusual quasar spectra. The selection method is based on a combination of the power of self-organising maps and the visual inspection of a huge number of spectra. Self-organising maps were applied to nearly 105 spectra classified as quasars at redshifts from z = 0.6 to 4.3 by the SDSS pipeline. Particular attention was paid to minimise possible contamination by rare peculiar stellar spectral types. All selected quasar spectra were individually studied to determine the object type and the redshift. Results: We present a catalogue of 1005 quasars with unusual spectra. These spectra are dominated by either broad absorption lines (BALs; 42%), unusual red continua (27%), weak emission lines (18%), or conspicuously strong optical and/or UV iron emission (11%). This large sample provides a useful resource for both studying properties and relations of/between different types of unusual quasars and selecting particularly interesting objects, even though the compilation is not aimed at completeness in a quantifiable sense. The spectra are grouped into six types for which composite spectra are constructed and mean properties are computed. Remarkably, all these types turn out to be on average more luminous than comparison samples of normal quasars after a statistical correction is made for intrinsic reddening (E(B - V) ≈ 0 to 0.4 for SMC-like extinction). Both the unusual BAL quasars and the strong iron emitters have significantly lower radio luminosities than normal quasars. We also confirm that strong BALs avoid

  5. GB 1508+5714, The First Z Greater than 4 Radio-Selected Quasar In X Rays

    NASA Technical Reports Server (NTRS)

    Mathur, Smita; Elvis, Martin

    1997-01-01

    We report the detection in X ray of a high redshift (z=4.30) radio-loud quasar, GB 1508+5714, the first radio-selected z greater than 4 quasar seen in X rays. The quasar was observed serendipitously with the Einstein observatory lPC at 0.02 +/- 0.003 counts/s. It is ten times brighter than the other two z greater than 4 X-ray detected quasars. The X-ray source is unusually hard, implying either alpha(sub E) less than 0.2, or N(sub H) greater than 10(exp 22) atoms/sq cm (1(sigma) limits) for a simple power-law plus intrinsic (z=4.3) absorption. Intrinsic absorption would make GB 1508+5714 similar to a large fraction of z approx. 3 radio-loud quasars.

  6. SDSS J131339.98+515128.3: A new GravitationallyLensed Quasar Selected Based on Near-infrared Excess

    SciTech Connect

    Ofek, E.O.; Oguri, M.; Jackson, N.; Inada, N.; Kayo, I.

    2007-09-28

    We report the discovery of a new gravitationally lensed quasar, SDSS J131339.98+515128.3, at a redshift of 1:875 with an image separation of 1: 0024. The lensing galaxy is clearly detected in visible-light follow-up observations. We also identify three absorption-line doublets in the spectra of the lensed quasar images, from which we measure the lens redshift to be 0:194. Like several other known lenses, the lensed quasar images have different continuum slopes. This difference is probably the result of reddening and microlensing in the lensing galaxy. The lensed quasar was selected by correlating Sloan Digital Sky Survey (SDSS) spectroscopic quasars with Two Micron All Sky Survey (2MASS) sources and choosing quasars that show near-infrared (IR) excess. The near-IR excess can originate, for example, from the contribution of the lensing galaxy at near-IR wavelengths. We show that the near-IR excess technique is indeed an efficient method to identify lensed systems from a large sample of quasars.

  7. FUBAR: a fast, unconstrained bayesian approximation for inferring selection.

    PubMed

    Murrell, Ben; Moola, Sasha; Mabona, Amandla; Weighill, Thomas; Sheward, Daniel; Kosakovsky Pond, Sergei L; Scheffler, Konrad

    2013-05-01

    Model-based analyses of natural selection often categorize sites into a relatively small number of site classes. Forcing each site to belong to one of these classes places unrealistic constraints on the distribution of selection parameters, which can result in misleading inference due to model misspecification. We present an approximate hierarchical Bayesian method using a Markov chain Monte Carlo (MCMC) routine that ensures robustness against model misspecification by averaging over a large number of predefined site classes. This leaves the distribution of selection parameters essentially unconstrained, and also allows sites experiencing positive and purifying selection to be identified orders of magnitude faster than by existing methods. We demonstrate that popular random effects likelihood methods can produce misleading results when sites assigned to the same site class experience different levels of positive or purifying selection--an unavoidable scenario when using a small number of site classes. Our Fast Unconstrained Bayesian AppRoximation (FUBAR) is unaffected by this problem, while achieving higher power than existing unconstrained (fixed effects likelihood) methods. The speed advantage of FUBAR allows us to analyze larger data sets than other methods: We illustrate this on a large influenza hemagglutinin data set (3,142 sequences). FUBAR is available as a batch file within the latest HyPhy distribution (http://www.hyphy.org), as well as on the Datamonkey web server (http://www.datamonkey.org/).

  8. An efficient sampling algorithm with adaptations for Bayesian variable selection.

    PubMed

    Araki, Takamitsu; Ikeda, Kazushi; Akaho, Shotaro

    2015-01-01

    In Bayesian variable selection, indicator model selection (IMS) is a class of well-known sampling algorithms, which has been used in various models. The IMS is a class of methods that uses pseudo-priors and it contains specific methods such as Gibbs variable selection (GVS) and Kuo and Mallick's (KM) method. However, the efficiency of the IMS strongly depends on the parameters of a proposal distribution and the pseudo-priors. Specifically, the GVS determines their parameters based on a pilot run for a full model and the KM method sets their parameters as those of priors, which often leads to slow mixings of them. In this paper, we propose an algorithm that adapts the parameters of the IMS during running. The parameters obtained on the fly provide an appropriate proposal distribution and pseudo-priors, which improve the mixing of the algorithm. We also prove the convergence theorem of the proposed algorithm, and confirm that the algorithm is more efficient than the conventional algorithms by experiments of the Bayesian variable selection.

  9. Bayesian Variable Selection for Detecting Adaptive Genomic Differences Among Populations

    PubMed Central

    Riebler, Andrea; Held, Leonhard; Stephan, Wolfgang

    2008-01-01

    We extend an Fst-based Bayesian hierarchical model, implemented via Markov chain Monte Carlo, for the detection of loci that might be subject to positive selection. This model divides the Fst-influencing factors into locus-specific effects, population-specific effects, and effects that are specific for the locus in combination with the population. We introduce a Bayesian auxiliary variable for each locus effect to automatically select nonneutral locus effects. As a by-product, the efficiency of the original approach is improved by using a reparameterization of the model. The statistical power of the extended algorithm is assessed with simulated data sets from a Wright–Fisher model with migration. We find that the inclusion of model selection suggests a clear improvement in discrimination as measured by the area under the receiver operating characteristic (ROC) curve. Additionally, we illustrate and discuss the quality of the newly developed method on the basis of an allozyme data set of the fruit fly Drosophila melanogaster and a sequence data set of the wild tomato Solanum chilense. For data sets with small sample sizes, high mutation rates, and/or long sequences, however, methods based on nucleotide statistics should be preferred. PMID:18245358

  10. Photometric selection of quasars in large astronomical data sets with a fast and accurate machine learning algorithm

    NASA Astrophysics Data System (ADS)

    Gupta, Pramod; Connolly, Andrew J.; Gardner, Jeffrey P.

    2014-03-01

    Future astronomical surveys will produce data on ˜108 objects per night. In order to characterize and classify these sources, we will require algorithms that scale linearly with the size of the data, that can be easily parallelized and where the speedup of the parallel algorithm will be linear in the number of processing cores. In this paper, we present such an algorithm and apply it to the question of colour selection of quasars. We use non-parametric Bayesian classification and a binning algorithm implemented with hash tables (BASH tables). We show that this algorithm's run time scales linearly with the number of test set objects and is independent of the number of training set objects. We also show that it has the same classification accuracy as other algorithms. For current data set sizes, it is up to three orders of magnitude faster than commonly used naive kernel-density-estimation techniques and it is estimated to be about eight times faster than the current fastest algorithm using dual kd-trees for kernel density estimation. The BASH table algorithm scales linearly with the size of the test set data only, and so for future larger data sets, it will be even faster compared to other algorithms which all depend on the size of the test set and the size of the training set. Since it uses linear data structures, it is easier to parallelize compared to tree-based algorithms and its speedup is linear in the number of cores unlike tree-based algorithms whose speedup plateaus after a certain number of cores. Moreover, due to the use of hash tables to implement the binning, the memory usage is very small. While our analysis is for the specific problem of selection of quasars, the ideas are general and the BASH table algorithm can be applied to any density-estimation problem involving sparse high-dimensional data sets. Since sparse high-dimensional data sets are a common type of scientific data set, this method has the potential to be useful in a broad range of

  11. Accurate Model Selection of Relaxed Molecular Clocks in Bayesian Phylogenetics

    PubMed Central

    Baele, Guy; Li, Wai Lok Sibon; Drummond, Alexei J.; Suchard, Marc A.; Lemey, Philippe

    2013-01-01

    Recent implementations of path sampling (PS) and stepping-stone sampling (SS) have been shown to outperform the harmonic mean estimator (HME) and a posterior simulation-based analog of Akaike’s information criterion through Markov chain Monte Carlo (AICM), in Bayesian model selection of demographic and molecular clock models. Almost simultaneously, a Bayesian model averaging approach was developed that avoids conditioning on a single model but averages over a set of relaxed clock models. This approach returns estimates of the posterior probability of each clock model through which one can estimate the Bayes factor in favor of the maximum a posteriori (MAP) clock model; however, this Bayes factor estimate may suffer when the posterior probability of the MAP model approaches 1. Here, we compare these two recent developments with the HME, stabilized/smoothed HME (sHME), and AICM, using both synthetic and empirical data. Our comparison shows reassuringly that MAP identification and its Bayes factor provide similar performance to PS and SS and that these approaches considerably outperform HME, sHME, and AICM in selecting the correct underlying clock model. We also illustrate the importance of using proper priors on a large set of empirical data sets. PMID:23090976

  12. Model Selection in Historical Research Using Approximate Bayesian Computation

    PubMed Central

    Rubio-Campillo, Xavier

    2016-01-01

    Formal Models and History Computational models are increasingly being used to study historical dynamics. This new trend, which could be named Model-Based History, makes use of recently published datasets and innovative quantitative methods to improve our understanding of past societies based on their written sources. The extensive use of formal models allows historians to re-evaluate hypotheses formulated decades ago and still subject to debate due to the lack of an adequate quantitative framework. The initiative has the potential to transform the discipline if it solves the challenges posed by the study of historical dynamics. These difficulties are based on the complexities of modelling social interaction, and the methodological issues raised by the evaluation of formal models against data with low sample size, high variance and strong fragmentation. Case Study This work examines an alternate approach to this evaluation based on a Bayesian-inspired model selection method. The validity of the classical Lanchester’s laws of combat is examined against a dataset comprising over a thousand battles spanning 300 years. Four variations of the basic equations are discussed, including the three most common formulations (linear, squared, and logarithmic) and a new variant introducing fatigue. Approximate Bayesian Computation is then used to infer both parameter values and model selection via Bayes Factors. Impact Results indicate decisive evidence favouring the new fatigue model. The interpretation of both parameter estimations and model selection provides new insights into the factors guiding the evolution of warfare. At a methodological level, the case study shows how model selection methods can be used to guide historical research through the comparison between existing hypotheses and empirical evidence. PMID:26730953

  13. The Infrared Medium-Deep Survey. V. A New Selection Strategy for Quasars at z > 5 Based on Medium-Band Observations with SQUEAN

    NASA Astrophysics Data System (ADS)

    Jeon, Yiseul; Im, Myungshin; Pak, Soojong; Hyun, Minhee; Kim, Sanghyuk; Kim, Yongjung; Lee, Hye-In; Park, Woojin

    2016-02-01

    Multiple color selection techniques are successful in identifying quasars from wide-field broad-band imaging survey data. Among the quasars that have been discovered so far, however, there is a redshift gap at 5 ≲ z ≲ 5.7 due to the limitations of filter sets in previous studies. In this work, we present a new selection technique of high redshift quasars using a sequence of medium-band filters: nine filters with central wavelengths from 625 to 1025 nm and bandwidths of 50 nm. Photometry with these medium-bands traces the spectral energy distribution (SED) of a source, similar to spectroscopy with resolution R ˜ 15. By conducting medium-band observations of high redshift quasars at 4.7 ≤ z ≤ 6.0 and brown dwarfs (the main contaminants in high redshift quasar selection) using the SED camera for QUasars in EArly uNiverse (SQUEAN) on the 2.1-m telescope at the McDonald Observatory, we show that these medium-band filters are superior to multi-color broad-band color section in separating high redshift quasars from brown dwarfs. In addition, we show that redshifts of high redshift quasars can be determined to an accuracy of Δ{z}/(1+{z}) = 0.002 - 0.026. The selection technique can be extended to z ˜ 7, suggesting that the medium-band observation can be powerful in identifying quasars even at the re-ionization epoch.

  14. Quantitative structure-activity relationships of selective antagonists of glucagon receptor using QuaSAR descriptors.

    PubMed

    Manoj Kumar, Palanivelu; Karthikeyan, Chandrabose; Hari Narayana Moorthy, Narayana Subbiah; Trivedi, Piyush

    2006-11-01

    In the present paper, quantitative structure activity relationship (QSAR) approach was applied to understand the affinity and selectivity of a novel series of triaryl imidazole derivatives towards glucagon receptor. Statistically significant and highly predictive QSARs were derived for glucagon receptor inhibition by triaryl imidazoles using QuaSAR descriptors of molecular operating environment (MOE) employing computer-assisted multiple regression procedure. The generated QSAR models revealed that factors related to hydrophobicity, molecular shape and geometry predominantly influences glucagon receptor binding affinity of the triaryl imidazoles indicating the relevance of shape specific steric interactions between the molecule and the receptor. Further, QSAR models formulated for selective inhibition of glucagon receptor over p38 mitogen activated protein (MAP) kinase of the compounds in the series highlights that the same structural features, which influence the glucagon receptor affinity, also contribute to their selective inhibition.

  15. Dynamic sensor action selection with Bayesian decision analysis

    NASA Astrophysics Data System (ADS)

    Kristensen, Steen; Hansen, Volker; Kondak, Konstantin

    1998-10-01

    The aim of this work is to create a framework for the dynamic planning of sensor actions for an autonomous mobile robot. The framework uses Bayesian decision analysis, i.e., a decision-theoretic method, to evaluate possible sensor actions and selecting the most appropriate ones given the available sensors and what is currently known about the state of the world. Since sensing changes the knowledge of the system and since the current state of the robot (task, position, etc.) determines what knowledge is relevant, the evaluation and selection of sensing actions is an on-going process that effectively determines the behavior of the robot. The framework has been implemented on a real mobile robot and has been proven to be able to control in real-time the sensor actions of the system. In current work we are investigating methods to reduce or automatically generate the necessary model information needed by the decision- theoretic method to select the appropriate sensor actions.

  16. A Bayesian random effects discrete-choice model for resource selection: Population-level selection inference

    USGS Publications Warehouse

    Thomas, D.L.; Johnson, D.; Griffith, B.

    2006-01-01

    Modeling the probability of use of land units characterized by discrete and continuous measures, we present a Bayesian random-effects model to assess resource selection. This model provides simultaneous estimation of both individual- and population-level selection. Deviance information criterion (DIC), a Bayesian alternative to AIC that is sample-size specific, is used for model selection. Aerial radiolocation data from 76 adult female caribou (Rangifer tarandus) and calf pairs during 1 year on an Arctic coastal plain calving ground were used to illustrate models and assess population-level selection of landscape attributes, as well as individual heterogeneity of selection. Landscape attributes included elevation, NDVI (a measure of forage greenness), and land cover-type classification. Results from the first of a 2-stage model-selection procedure indicated that there is substantial heterogeneity among cow-calf pairs with respect to selection of the landscape attributes. In the second stage, selection of models with heterogeneity included indicated that at the population-level, NDVI and land cover class were significant attributes for selection of different landscapes by pairs on the calving ground. Population-level selection coefficients indicate that the pairs generally select landscapes with higher levels of NDVI, but the relationship is quadratic. The highest rate of selection occurs at values of NDVI less than the maximum observed. Results for land cover-class selections coefficients indicate that wet sedge, moist sedge, herbaceous tussock tundra, and shrub tussock tundra are selected at approximately the same rate, while alpine and sparsely vegetated landscapes are selected at a lower rate. Furthermore, the variability in selection by individual caribou for moist sedge and sparsely vegetated landscapes is large relative to the variability in selection of other land cover types. The example analysis illustrates that, while sometimes computationally intense, a

  17. Black Hole Models for Quasar-Like Objects: Some Selected Topics

    NASA Astrophysics Data System (ADS)

    Tsuruta, Sachiko

    The following sections are included: * INTRODUCTION * QUASAR-LIKE OBJECTS (AGNs) * Seyfert Galaxies * Quasars * BL Lac Objects * Radio Galaxies * Other AGNs * SUPERMASSIVE BLACK HOLE MODELS * Rapid Large Amplitude Variabilities * Beams and Jets * Composite Models (Tentative) * SPECTRA OF RADIATION FROM ACTIVE GALACTIC NUCLEI * X-Ray Spectra * Infrared-Optical-Ultraviolet Spectra * SOME MODELS FOR EMISSION MECHANISMS * DISCUSSION AND CONCLUDING REMARKS * FOOTNOTES * ACKNOWLEDGEMENTS * REFERENCES

  18. Using Bayesian variable selection to analyze regular resolution IV two-level fractional factorial designs

    DOE PAGES

    Chipman, Hugh A.; Hamada, Michael S.

    2016-06-02

    Regular two-level fractional factorial designs have complete aliasing in which the associated columns of multiple effects are identical. Here, we show how Bayesian variable selection can be used to analyze experiments that use such designs. In addition to sparsity and hierarchy, Bayesian variable selection naturally incorporates heredity . This prior information is used to identify the most likely combinations of active terms. We also demonstrate the method on simulated and real experiments.

  19. Bayesian Variable Selection for Multivariate Spatially-Varying Coefficient Regression

    PubMed Central

    Reich, Brian J.; Fuentes, Montserrat; Herring, Amy H.; Evenson, Kelly R.

    2009-01-01

    Summary Physical activity has many well-documented health benefits for cardiovascular fitness and weight control. For pregnant women, the American College of Obstetricians and Gynecologists currently recommends 30 minutes of moderate exercise on most, if not all, days; however, very few pregnant women achieve this level of activity. Traditionally, studies have focused on examining individual or interpersonal factors to identify predictors of physical activity. There is a renewed interest in whether characteristics of the physical environment in which we live and work may also influence physical activity levels. We consider one of the first studies of pregnant women that examines the impact of characteristics of the built environment on physical activity levels. Using a socioecologic framework, we study the associations between physical activity and several factors including personal characteristics, meteorological/air quality variables, and neighborhood characteristics for pregnant women in four counties of North Carolina. We simultaneously analyze six types of physical activity and investigate cross-dependencies between these activity types. Exploratory analysis suggests that the associations are different in different regions. Therefore we use a multivariate regression model with spatially-varying regression coefficients. This model includes a regression parameter for each covariate at each spatial location. For our data with many predictors, some form of dimension reduction is clearly needed. We introduce a Bayesian variable selection procedure to identify subsets of important variables. Our stochastic search algorithm determines the probabilities that each covariate’s effect is null, non-null but constant across space, and spatially-varying. We found that individual level covariates had a greater influence on women’s activity levels than neighborhood environmental characteristics, and some individual level covariates had spatially-varying associations with

  20. Hybrid nested sampling algorithm for Bayesian model selection applied to inverse subsurface flow problems

    SciTech Connect

    Elsheikh, Ahmed H.; Wheeler, Mary F.; Hoteit, Ibrahim

    2014-02-01

    A Hybrid Nested Sampling (HNS) algorithm is proposed for efficient Bayesian model calibration and prior model selection. The proposed algorithm combines, Nested Sampling (NS) algorithm, Hybrid Monte Carlo (HMC) sampling and gradient estimation using Stochastic Ensemble Method (SEM). NS is an efficient sampling algorithm that can be used for Bayesian calibration and estimating the Bayesian evidence for prior model selection. Nested sampling has the advantage of computational feasibility. Within the nested sampling algorithm, a constrained sampling step is performed. For this step, we utilize HMC to reduce the correlation between successive sampled states. HMC relies on the gradient of the logarithm of the posterior distribution, which we estimate using a stochastic ensemble method based on an ensemble of directional derivatives. SEM only requires forward model runs and the simulator is then used as a black box and no adjoint code is needed. The developed HNS algorithm is successfully applied for Bayesian calibration and prior model selection of several nonlinear subsurface flow problems.

  1. A spectroscopic survey of WISE-selected obscured quasars with the southern african large telescope

    SciTech Connect

    Hainline, Kevin N.; Hickox, Ryan C.; Carroll, Christopher M.; Myers, Adam D.; DiPompeo, Michael A.; Trouille, Laura

    2014-11-10

    We present the results of an optical spectroscopic survey of a sample of 40 candidate obscured quasars identified on the basis of their mid-infrared emission detected by the Wide-Field Infrared Survey Explorer (WISE). Optical spectra for this survey were obtained using the Robert Stobie Spectrograph on the Southern African Large Telescope. Our sample was selected with WISE colors characteristic of active galactic nuclei (AGNs), as well as red optical to mid-IR colors indicating that the optical/UV AGN continuum is obscured by dust. We obtain secure redshifts for the majority of the objects that comprise our sample (35/40), and find that sources that are bright in the WISE W4 (22 μm) band are typically at moderate redshift ((z) = 0.35) while sources fainter in W4 are at higher redshifts ((z) = 0.73). The majority of the sources have narrow emission lines with optical colors and emission line ratios of our WISE-selected sources that are consistent with the locus of AGN on the rest-frame g – z color versus [Ne III] λ3869/[O II] λλ3726+3729 line ratio diagnostic diagram. We also use empirical AGN and galaxy templates to model the spectral energy distributions (SEDs) for the objects in our sample, and find that while there is significant variation in the observed SEDs for these objects, the majority require a strong AGN component. Finally, we use the results from our analysis of the optical spectra and the SEDs to compare our selection criteria to alternate criteria presented in the literature. These results verify the efficacy of selecting luminous obscured AGNs based on their WISE colors.

  2. Bayesian parameter inference and model selection by population annealing in systems biology.

    PubMed

    Murakami, Yohei

    2014-01-01

    Parameter inference and model selection are very important for mathematical modeling in systems biology. Bayesian statistics can be used to conduct both parameter inference and model selection. Especially, the framework named approximate Bayesian computation is often used for parameter inference and model selection in systems biology. However, Monte Carlo methods needs to be used to compute Bayesian posterior distributions. In addition, the posterior distributions of parameters are sometimes almost uniform or very similar to their prior distributions. In such cases, it is difficult to choose one specific value of parameter with high credibility as the representative value of the distribution. To overcome the problems, we introduced one of the population Monte Carlo algorithms, population annealing. Although population annealing is usually used in statistical mechanics, we showed that population annealing can be used to compute Bayesian posterior distributions in the approximate Bayesian computation framework. To deal with un-identifiability of the representative values of parameters, we proposed to run the simulations with the parameter ensemble sampled from the posterior distribution, named "posterior parameter ensemble". We showed that population annealing is an efficient and convenient algorithm to generate posterior parameter ensemble. We also showed that the simulations with the posterior parameter ensemble can, not only reproduce the data used for parameter inference, but also capture and predict the data which was not used for parameter inference. Lastly, we introduced the marginal likelihood in the approximate Bayesian computation framework for Bayesian model selection. We showed that population annealing enables us to compute the marginal likelihood in the approximate Bayesian computation framework and conduct model selection depending on the Bayes factor.

  3. ALMA DETECTED OVERDENSITY OF SUB-MILLIMETER SOURCES AROUND WISE/NVSS-SELECTED z ∼ 2 DUSTY QUASARS

    SciTech Connect

    Silva, Andrea; Sajina, Anna; Lonsdale, Carol; Lacy, Mark

    2015-06-20

    We study the environments of 49 WISE/NVSS-selected dusty, hyper-luminous, z ∼ 2 quasars using the Atacama Large Millimeter/Sub-millimeter Array (ALMA) 345 GHz images. We find that 17 of the 49 WISE/NVSS sources show additional sub-millimeter galaxies within the ALMA primary beam, probing scales within ∼150 kpc. We find a total of 23 additional sub-millimeter sources, four of which are in the field of a single WISE/NVSS source. The measured 870 μm source counts are ∼10× what is expected for unbiased regions, suggesting such hyper-luminous dusty quasars are excellent at probing high-density peaks.

  4. H I-SELECTED GALAXIES AS A PROBE OF QUASAR ABSORPTION SYSTEMS

    SciTech Connect

    Okoshi, Katsuya; Nagashima, Masahiro; Gouda, Naoteru; Minowa, Yousuke

    2010-02-20

    We investigate the properties of H I-rich galaxies detected in blind radio surveys within the hierarchical structure formation scenario using a semianalytic model of galaxy formation. By drawing a detailed comparison between the properties of H I-selected galaxies and H I absorption systems, we argue a link between the local galaxy population and quasar absorption systems, particularly for damped Lyalpha absorption (DLA) systems and sub-DLA systems. First, we evaluate how many H I-selected galaxies exhibit H I column densities as high as those of DLA systems. We find that H I-selected galaxies with H I masses M{sub H{sub I}} {approx}> 10{sup 8} M{sub sun} have gaseous disks that produce H I column densities comparable to those of DLA systems. We conclude that DLA galaxies where the H I column densities are as high as those of DLA systems, contribute significantly to the population of H I-selected galaxies at M{sub H{sub I}} {approx}> 10{sup 8} M{sub sun}. Second, we find that star formation rates (SFRs) correlate tightly with H I masses (M{sub H{sub I}}) rather than B- (and J-) band luminosities: SFR {proportional_to} M {sup alpha}{sub H{sub I}}, alpha = 1.25-1.40 for 10{sup 6} <= M{sub H{sub I}}/M{sub sun} <= 10{sup 11}. In the low-mass range M{sub H{sub I}} {approx}< 10{sup 8} M{sub sun}, sub-DLA galaxies replace DLA galaxies as the dominant population. The number fraction of sub-DLA galaxies relative to galaxies reaches 40%-60% for M{sub H{sub I}} {approx} 10{sup 8} M{sub sun} and 30%-80% for M{sub H{sub I}} {approx} 10{sup 7} M{sub sun}. The H I-selected galaxies at M{sub H{sub I}} {approx} 10{sup 7} M{sub sun} are a strong probe of sub-DLA systems that place stringent constraints on galaxy formation and evolution.

  5. On Numerical Aspects of Bayesian Model Selection in High and Ultrahigh-dimensional Settings

    PubMed Central

    Johnson, Valen E.

    2014-01-01

    This article examines the convergence properties of a Bayesian model selection procedure based on a non-local prior density in ultrahigh-dimensional settings. The performance of the model selection procedure is also compared to popular penalized likelihood methods. Coupling diagnostics are used to bound the total variation distance between iterates in an Markov chain Monte Carlo (MCMC) algorithm and the posterior distribution on the model space. In several simulation scenarios in which the number of observations exceeds 100, rapid convergence and high accuracy of the Bayesian procedure is demonstrated. Conversely, the coupling diagnostics are successful in diagnosing lack of convergence in several scenarios for which the number of observations is less than 100. The accuracy of the Bayesian model selection procedure in identifying high probability models is shown to be comparable to commonly used penalized likelihood methods, including extensions of smoothly clipped absolute deviations (SCAD) and least absolute shrinkage and selection operator (LASSO) procedures. PMID:24683431

  6. Bayesian methods for quantitative trait loci mapping based on model selection: approximate analysis using the Bayesian information criterion.

    PubMed Central

    Ball, R D

    2001-01-01

    We describe an approximate method for the analysis of quantitative trait loci (QTL) based on model selection from multiple regression models with trait values regressed on marker genotypes, using a modification of the easily calculated Bayesian information criterion to estimate the posterior probability of models with various subsets of markers as variables. The BIC-delta criterion, with the parameter delta increasing the penalty for additional variables in a model, is further modified to incorporate prior information, and missing values are handled by multiple imputation. Marginal probabilities for model sizes are calculated, and the posterior probability of nonzero model size is interpreted as the posterior probability of existence of a QTL linked to one or more markers. The method is demonstrated on analysis of associations between wood density and markers on two linkage groups in Pinus radiata. Selection bias, which is the bias that results from using the same data to both select the variables in a model and estimate the coefficients, is shown to be a problem for commonly used non-Bayesian methods for QTL mapping, which do not average over alternative possible models that are consistent with the data. PMID:11729175

  7. Discovery of a Color-selected Quasar at z = 5.50.

    PubMed

    Stern; Spinrad; Eisenhardt; Bunker; Dawson; Stanford; Elston

    2000-04-20

    We present observations of RD J030117+002025, a quasar at z=5.50 discovered from deep, multicolor, ground-based observations covering 74 arcmin2. This is the most distant quasar or active galaxy currently known. The object was targeted as an R-band dropout, with RAB>26.3 (3 sigma limit in a 3&arcsec; diameter region), IAB=23.8, and zAB=23.4. The Keck/Low-Resolution Imaging Spectrometer spectrum shows broad Lyalpha/N v lambda1240 emission and sharp absorption decrements from the highly redshifted hydrogen forests. The fractional continuum depression due to the Lyalpha forest is DA=0.90. RD J030117+002025 is the least luminous high-redshift quasar known (MB approximately -22.7).

  8. Towards a Fundamental Astrometric Reference System behind the Magellanic Clouds: Spectroscopic Confirmation of New Quasar Candidates Selected in the Near-infrared

    NASA Astrophysics Data System (ADS)

    Ivanov, V. D.; Cioni, M.-R. L.; Bekki, K.; de Grijs, R.; Emerson, J.; Gibson, B. K.; Kamath, D.; van Loon, J. Th.; Piatti, A. E.; For, B.-Q.

    2016-03-01

    Quasi-stellar objects (quasars) located behind nearby galaxies provide an excellent absolute reference system for astrometric studies, but they are difficult to identify because of fore- and background contamination. We have embarked on a programme to expand the quasar reference system behind the Large and Small Magellanic Clouds, the Magellanic Bridge and Magellanic Stream. Hundreds of quasar candidates were selected, based on their near-infrared colours and variability properties from the ESO VISTA Magellanic Clouds (VMC) Public Survey. A subset of 49 objects was followed up with optical spectroscopy with FORS2. We confirmed the quasar nature of 37 objects (34 new identifications) that span a redshift range from z ~ 0.5 to 4.1.

  9. Subaru High-z Exploration of Low-luminosity Quasars (SHELLQs). I. Discovery of 15 Quasars and Bright Galaxies at 5.7 z > 6.9

    NASA Astrophysics Data System (ADS)

    Matsuoka, Yoshiki; Onoue, Masafusa; Kashikawa, Nobunari; Iwasawa, Kazushi; Strauss, Michael A.; Nagao, Tohru; Imanishi, Masatoshi; Niida, Mana; Toba, Yoshiki; Akiyama, Masayuki; Asami, Naoko; Bosch, James; Foucaud, Sébastien; Furusawa, Hisanori; Goto, Tomotsugu; Gunn, James E.; Harikane, Yuichi; Ikeda, Hiroyuki; Kawaguchi, Toshihiro; Kikuta, Satoshi; Komiyama, Yutaka; Lupton, Robert H.; Minezaki, Takeo; Miyazaki, Satoshi; Morokuma, Tomoki; Murayama, Hitoshi; Nishizawa, Atsushi J.; Ono, Yoshiaki; Ouchi, Masami; Price, Paul A.; Sameshima, Hiroaki; Silverman, John D.; Sugiyama, Naoshi; Tait, Philip J.; Takada, Masahiro; Takata, Tadafumi; Tanaka, Masayuki; Tang, Ji-Jia; Utsumi, Yousuke

    2016-09-01

    We report the discovery of 15 quasars and bright galaxies at 5.7 < z < 6.9. This is the initial result from the Subaru High-z Exploration of Low-Luminosity Quasars project, which exploits the exquisite multiband imaging data produced by the Subaru Hyper Suprime-Cam (HSC) Strategic Program survey. The candidate selection is performed by combining several photometric approaches including a Bayesian probabilistic algorithm to reject stars and dwarfs. The spectroscopic identification was carried out with the Gran Telescopio Canarias and the Subaru Telescope for the first 80 deg2 of the survey footprint. The success rate of our photometric selection is quite high, approaching 100% at the brighter magnitudes (z AB < 23.5 mag). Our selection also recovered all the known high-z quasars on the HSC images. Among the 15 discovered objects, six are likely quasars, while the other six with interstellar absorption lines and in some cases narrow emission lines are likely bright Lyman-break galaxies. The remaining three objects have weak continua and very strong and narrow Lyα lines, which may be excited by ultraviolet light from both young stars and quasars. These results indicate that we are starting to see the steep rise of the luminosity function of z ≥ 6 galaxies, compared with that of quasars, at magnitudes fainter than M 1450 ˜ ‑22 mag or z AB ˜ 24 mag. Follow-up studies of the discovered objects as well as further survey observations are ongoing.

  10. Subaru High-z Exploration of Low-luminosity Quasars (SHELLQs). I. Discovery of 15 Quasars and Bright Galaxies at 5.7 < z < 6.9

    NASA Astrophysics Data System (ADS)

    Matsuoka, Yoshiki; Onoue, Masafusa; Kashikawa, Nobunari; Iwasawa, Kazushi; Strauss, Michael A.; Nagao, Tohru; Imanishi, Masatoshi; Niida, Mana; Toba, Yoshiki; Akiyama, Masayuki; Asami, Naoko; Bosch, James; Foucaud, Sébastien; Furusawa, Hisanori; Goto, Tomotsugu; Gunn, James E.; Harikane, Yuichi; Ikeda, Hiroyuki; Kawaguchi, Toshihiro; Kikuta, Satoshi; Komiyama, Yutaka; Lupton, Robert H.; Minezaki, Takeo; Miyazaki, Satoshi; Morokuma, Tomoki; Murayama, Hitoshi; Nishizawa, Atsushi J.; Ono, Yoshiaki; Ouchi, Masami; Price, Paul A.; Sameshima, Hiroaki; Silverman, John D.; Sugiyama, Naoshi; Tait, Philip J.; Takada, Masahiro; Takata, Tadafumi; Tanaka, Masayuki; Tang, Ji-Jia; Utsumi, Yousuke

    2016-09-01

    We report the discovery of 15 quasars and bright galaxies at 5.7 < z < 6.9. This is the initial result from the Subaru High-z Exploration of Low-Luminosity Quasars project, which exploits the exquisite multiband imaging data produced by the Subaru Hyper Suprime-Cam (HSC) Strategic Program survey. The candidate selection is performed by combining several photometric approaches including a Bayesian probabilistic algorithm to reject stars and dwarfs. The spectroscopic identification was carried out with the Gran Telescopio Canarias and the Subaru Telescope for the first 80 deg2 of the survey footprint. The success rate of our photometric selection is quite high, approaching 100% at the brighter magnitudes (z AB < 23.5 mag). Our selection also recovered all the known high-z quasars on the HSC images. Among the 15 discovered objects, six are likely quasars, while the other six with interstellar absorption lines and in some cases narrow emission lines are likely bright Lyman-break galaxies. The remaining three objects have weak continua and very strong and narrow Lyα lines, which may be excited by ultraviolet light from both young stars and quasars. These results indicate that we are starting to see the steep rise of the luminosity function of z ≥ 6 galaxies, compared with that of quasars, at magnitudes fainter than M 1450 ˜ -22 mag or z AB ˜ 24 mag. Follow-up studies of the discovered objects as well as further survey observations are ongoing.

  11. Using Bayesian Model Selection to Characterize Neonatal Eeg Recordings

    NASA Astrophysics Data System (ADS)

    Mitchell, Timothy J.

    2009-12-01

    The brains of premature infants must undergo significant maturation outside of the womb and are thus particularly susceptible to injury. Electroencephalographic (EEG) recordings are an important diagnostic tool in determining if a newborn's brain is functioning normally or if injury has occurred. However, interpreting the recordings is difficult and requires the skills of a trained electroencephelographer. Because these EEG specialists are rare, an automated interpretation of newborn EEG recordings would increase access to an important diagnostic tool for physicians. To automate this procedure, we employ Bayesian probability theory to compute the posterior probability for the EEG features of interest and use the results in a program designed to mimic EEG specialists. Specifically, we will be identifying waveforms of varying frequency and amplitude, as well as periods of flat recordings where brain activity is minimal.

  12. Quasar microlensing

    NASA Astrophysics Data System (ADS)

    Schmidt, R. W.; Wambsganss, J.

    2010-09-01

    Quasar microlensing deals with the effect of compact objects along the line of sight on the apparent brightness of the background quasars. Due to the relative motion between quasar, lenses and observer, the microlensing magnification changes with time which results in uncorrelated brightness variations in the various images of multiple quasar systems. The amplitudes of the signal can be more than a magnitude with time scales of weeks to months to years. The effect is due to the “granular” nature of the gravitational microlenses—stars or other compact objects in the stellar mass range. Quasar microlensing allows to study the quasar accretion disk with a resolution of tens of microarcseconds, hence quasar microlensing can be used to explore an astrophysical field that is hardly accessible by any other means. Quasar microlensing can also be used to study the lensing objects in a statistical sense, their nature (compact or smoothly distributed, normal stars or dark matter) as well as transverse velocities. Quasar microlensing light curves are now being obtained from monitoring programs across the electromagnetic spectrum from the radio through the infrared and optical range to the X-ray regime. Recently, spectroscopic microlensing was successfully applied, it provides quantitative comparisons with quasar/accretion disk models. There are now more than a handful of systems with several-year long light curves and significant microlensing signal, lending to detailed analysis. This review summarizes the current state of the art of quasar microlensing and shows that at this point in time, observational monitoring programs and complementary intense simulations provide a scenario where some of the early promises of quasar microlensing can be quantitatively applied. It has been shown, e.g., that smaller sources display more violent microlensing variability, first quantitative comparison with accretion disk models has been achieved, and quasar microlensing has been used to

  13. Increasing selection response by Bayesian modeling of heterogeneous environmental variances

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Heterogeneity of environmental variance among genotypes reduces selection response because genotypes with higher variance are more likely to be selected than low-variance genotypes. Modeling heterogeneous variances to obtain weighted means corrected for heterogeneous variances is difficult in likel...

  14. THE JET POWER AND EMISSION-LINE CORRELATIONS OF RADIO-LOUD OPTICALLY SELECTED QUASARS

    SciTech Connect

    Punsly, Brian; Zhang Shaohua E-mail: brian.punsly@comdev-usa.com

    2011-07-01

    In this Letter, the properties of the extended radio emission form Sloan Digital Sky Survey Data Release 7 quasars with 0.4 < z < 0.8 is studied. This low-redshift sample is useful since any corresponding FIRST radio observations are sensitive enough to detect extended flux in even the weakest Fanaroff-Riley II (FR II) radio sources. In the sample, 2.7% of the sources have detectable extended emission on larger than galactic scales (>20-30 kpc). The frequency of quasars with FR II level extended radio emission is {approx}2.3% and >0.4% of quasars have FR I level extended radio emission. The lower limit simply reflects the flux density limit of the survey. The distribution of the long-term time-averaged jet powers of these quasars, Q-bar , has a broad peak {approx}3 x 10{sup 44} erg s{sup -1} that turns over below 10{sup 44} erg s{sup -1} and sources above 10{sup 45} erg s{sup -1} are extremely rare. It is found that the correlation between the bolometric (total thermal) luminosity of the accretion flow, L{sub bol}, and Q-bar is not strong. The correlation of Q-bar with narrow line luminosity is stronger than the correlation with broad line luminosity and the continuum luminosity. It is therefore concluded that previous interpretations of correlations of Q-bar with narrow line strengths in radio galaxies as a direct correlation of jet power and accretion power have been overstated. It is explained why this interpretation mistakenly overlooks the sizeable fraction of sources with weak accretion luminosity and powerful jets discovered by Ogle et al.

  15. Diagnosing Hybrid Systems: a Bayesian Model Selection Approach

    NASA Technical Reports Server (NTRS)

    McIlraith, Sheila A.

    2005-01-01

    In this paper we examine the problem of monitoring and diagnosing noisy complex dynamical systems that are modeled as hybrid systems-models of continuous behavior, interleaved by discrete transitions. In particular, we examine continuous systems with embedded supervisory controllers that experience abrupt, partial or full failure of component devices. Building on our previous work in this area (MBCG99;MBCG00), our specific focus in this paper ins on the mathematical formulation of the hybrid monitoring and diagnosis task as a Bayesian model tracking algorithm. The nonlinear dynamics of many hybrid systems present challenges to probabilistic tracking. Further, probabilistic tracking of a system for the purposes of diagnosis is problematic because the models of the system corresponding to failure modes are numerous and generally very unlikely. To focus tracking on these unlikely models and to reduce the number of potential models under consideration, we exploit logic-based techniques for qualitative model-based diagnosis to conjecture a limited initial set of consistent candidate models. In this paper we discuss alternative tracking techniques that are relevant to different classes of hybrid systems, focusing specifically on a method for tracking multiple models of nonlinear behavior simultaneously using factored sampling and conditional density propagation. To illustrate and motivate the approach described in this paper we examine the problem of monitoring and diganosing NASA's Sprint AERCam, a small spherical robotic camera unit with 12 thrusters that enable both linear and rotational motion.

  16. EXONEST: Bayesian model selection applied to the detection and characterization of exoplanets via photometric variations

    SciTech Connect

    Placek, Ben; Knuth, Kevin H.; Angerhausen, Daniel E-mail: kknuth@albany.edu

    2014-11-10

    EXONEST is an algorithm dedicated to detecting and characterizing the photometric signatures of exoplanets, which include reflection and thermal emission, Doppler boosting, and ellipsoidal variations. Using Bayesian inference, we can test between competing models that describe the data as well as estimate model parameters. We demonstrate this approach by testing circular versus eccentric planetary orbital models, as well as testing for the presence or absence of four photometric effects. In addition to using Bayesian model selection, a unique aspect of EXONEST is the potential capability to distinguish between reflective and thermal contributions to the light curve. A case study is presented using Kepler data recorded from the transiting planet KOI-13b. By considering only the nontransiting portions of the light curve, we demonstrate that it is possible to estimate the photometrically relevant model parameters of KOI-13b. Furthermore, Bayesian model testing confirms that the orbit of KOI-13b has a detectable eccentricity.

  17. Mining for Dust in Type 1 Quasars

    NASA Astrophysics Data System (ADS)

    Krawczyk, Coleman M.; Richards, Gordon T.; Gallagher, S. C.; Leighly, Karen M.; Hewett, Paul C.; Ross, Nicholas P.; Hall, P. B.

    2015-06-01

    We explore the extinction/reddening of ˜35,000 uniformly selected quasars with 0\\lt z≤slant 5.3 in order to better understand their intrinsic optical/ultraviolet (UV) spectral energy distributions. Using rest-frame optical-UV photometry taken from the Sloan Digital Sky Survey’s (SDSS) 7th data release, cross-matched to WISE in the mid-infrared, 2MASS and UKIDSS in the near-infrared, and GALEX in the UV, we isolate outliers in the color distribution and find them well described by an SMC-like reddening law. A hierarchical Bayesian model with a Markov Chain Monte Carlo sampling method was used to find distributions of power law indices and E(B-V) consistent with both the broad absorption line (BAL) and non-BAL samples. We find that, of the ugriz color-selected type 1 quasars in SDSS, 2.5% (13%) of the non-BAL (BAL) sample are consistent with E(B-V)\\gt 0.1 and 0.1% (1.3%) with E(B-V)\\gt 0.2. Simulations show both populations of quasars are intrinsically bluer than the mean composite, with a mean spectral index ({{α }λ }) of -1.79 (-1.83). The emission and absorption-line properties of both samples reveal that quasars with intrinsically red continua have narrower Balmer lines and stronger high-ionization emission lines, the latter indicating a harder continuum in the extreme-UV and the former pointing to differences in black hole mass and/or orientation.

  18. A biological mechanism for Bayesian feature selection: Weight decay and raising the LASSO.

    PubMed

    Connor, Patrick; Hollensen, Paul; Krigolson, Olav; Trappenberg, Thomas

    2015-07-01

    Biological systems are capable of learning that certain stimuli are valuable while ignoring the many that are not, and thus perform feature selection. In machine learning, one effective feature selection approach is the least absolute shrinkage and selection operator (LASSO) form of regularization, which is equivalent to assuming a Laplacian prior distribution on the parameters. We review how such Bayesian priors can be implemented in gradient descent as a form of weight decay, which is a biologically plausible mechanism for Bayesian feature selection. In particular, we describe a new prior that offsets or "raises" the Laplacian prior distribution. We evaluate this alongside the Gaussian and Cauchy priors in gradient descent using a generic regression task where there are few relevant and many irrelevant features. We find that raising the Laplacian leads to less prediction error because it is a better model of the underlying distribution. We also consider two biologically relevant online learning tasks, one synthetic and one modeled after the perceptual expertise task of Krigolson et al. (2009). Here, raising the Laplacian prior avoids the fast erosion of relevant parameters over the period following training because it only allows small weights to decay. This better matches the limited loss of association seen between days in the human data of the perceptual expertise task. Raising the Laplacian prior thus results in a biologically plausible form of Bayesian feature selection that is effective in biologically relevant contexts. PMID:25897512

  19. Bayesian Nonlinear Model Selection for Gene Regulatory Networks

    PubMed Central

    Ni, Yang; Stingo, Francesco C.; Baladandayuthapani, Veerabhadran

    2015-01-01

    Summary Gene regulatory networks represent the regulatory relationships between genes and their products and are important for exploring and defining the underlying biological processes of cellular systems. We develop a novel framework to recover the structure of nonlinear gene regulatory networks using semiparametric spline-based directed acyclic graphical models. Our use of splines allows the model to have both flexibility in capturing nonlinear dependencies as well as control of overfitting via shrinkage, using mixed model representations of penalized splines. We propose a novel discrete mixture prior on the smoothing parameter of the splines that allows for simultaneous selection of both linear and nonlinear functional relationships as well as inducing sparsity in the edge selection. Using simulation studies, we demonstrate the superior performance of our methods in comparison with several existing approaches in terms of network reconstruction and functional selection. We apply our methods to a gene expression dataset in glioblastoma multiforme, which reveals several interesting and biologically relevant nonlinear relationships. PMID:25854759

  20. A DIRECT MEASUREMENT OF THE LINEAR BIAS OF MID-INFRARED-SELECTED QUASARS AT z ≈ 1 USING COSMIC MICROWAVE BACKGROUND LENSING

    SciTech Connect

    Geach, J. E.; Hickox, R. C.; Hainline, K. N.; Bleem, L. E.; Benson, B. A.; Bhattacharya, S.; Carlstrom, J. E.; Chang, C. L.; Crawford, T. M.; Crites, A. T.; Brodwin, M.; Holder, G. P.; De Haan, T.; Dobbs, M. A.; Dudley, J.; Aird, K. A.; Cho, H.-M.; George, E. M.; Holzapfel, W. L.; Halverson, N. W.; and others

    2013-10-20

    We measure the cross-power spectrum of the projected mass density as traced by the convergence of the cosmic microwave background lensing field from the South Pole Telescope (SPT) and a sample of Type 1 and 2 (unobscured and obscured) quasars at (z) ∼ 1 selected with the Wide-field Infrared Survey Explorer, over 2500 deg{sup 2}. The cross-power spectrum is detected at ≈7σ, and we measure a linear bias b = 1.61 ± 0.22, consistent with clustering analyses. Using an independent lensing map, derived from Planck observations, to measure the cross-spectrum, we find excellent agreement with the SPT analysis. The bias of the combined sample of Type 1 and 2 quasars determined in this work is similar to that previously determined for Type 1 quasars alone; we conclude that obscured and unobscured quasars trace the matter field in a similar way. This result has implications for our understanding of quasar unification and evolution schemes.

  1. NuSTAR and XMM-Newton Observations of Luminous, Heavily Obscured, WISE-selected Quasars at z ~ 2

    NASA Astrophysics Data System (ADS)

    Stern, D.; Lansbury, G. B.; Assef, R. J.; Brandt, W. N.; Alexander, D. M.; Ballantyne, D. R.; Baloković, M.; Bauer, F. E.; Benford, D.; Blain, A.; Boggs, S. E.; Bridge, C.; Brightman, M.; Christensen, F. E.; Comastri, A.; Craig, W. W.; Del Moro, A.; Eisenhardt, P. R. M.; Gandhi, P.; Griffith, R. L.; Hailey, C. J.; Harrison, F. A.; Hickox, R. C.; Jarrett, T. H.; Koss, M.; Lake, S.; LaMassa, S. M.; Luo, B.; Tsai, C.-W.; Urry, C. M.; Walton, D. J.; Wright, E. L.; Wu, J.; Yan, L.; Zhang, W. W.

    2014-10-01

    We report on a NuSTAR and XMM-Newton program that has observed a sample of three extremely luminous, heavily obscured WISE-selected active galactic nuclei (AGNs) at z ~ 2 across a broad X-ray band (0.1 - 79 keV). The parent sample, selected to be faint or undetected in the WISE 3.4 μm (W1) and 4.6 μm (W2) bands but bright at 12 μm (W3) and 22 μm (W4), are extremely rare, with only ~1000 so-called "W1W2-dropouts" across the extragalactic sky. Optical spectroscopy reveals typical redshifts of z ~ 2 for this population, implying rest-frame mid-IR luminosities of νL ν(6 μm) ~ 6 × 1046 erg s-1 and bolometric luminosities that can exceed L bol ~ 1014 L ⊙. The corresponding intrinsic, unobscured hard X-ray luminosities are L(2-10 keV) ~ 4 × 1045 erg s-1 for typical quasar templates. These are among the most AGNs known, though the optical spectra rarely show evidence of a broad-line region and the selection criteria imply heavy obscuration even at rest-frame 1.5 μm. We designed our X-ray observations to obtain robust detections for gas column densities N H <= 1024 cm-2. In fact, the sources prove to be fainter than these predictions. Two of the sources were observed by both NuSTAR and XMM-Newton, with neither being detected by NuSTAR (f 3-24 keV <~ 10-13 erg cm-2 s-1), and one being faintly detected by XMM-Newton (f 0.5-10 keV ~ 5 × 10-15 erg cm-2 s-1). A third source was observed only with XMM-Newton, yielding a faint detection (f 0.5-10 keV ~ 7 × 10-15 erg cm-2 s-1). The X-ray data imply these sources are either X-ray weak, or are heavily obscured by column densities N H >~ 1024 cm-2. The combined X-ray and mid-IR analysis seems to favor this second possibility, implying the sources are extremely obscured, consistent with Compton-thick, luminous quasars. The discovery of a significant population of heavily obscured, extremely luminous AGNs would not conform to the standard paradigm of a receding torus, in which more luminous quasars are less likely to be

  2. Bayesian Factor Analysis as a Variable-Selection Problem: Alternative Priors and Consequences.

    PubMed

    Lu, Zhao-Hua; Chow, Sy-Miin; Loken, Eric

    2016-01-01

    Factor analysis is a popular statistical technique for multivariate data analysis. Developments in the structural equation modeling framework have enabled the use of hybrid confirmatory/exploratory approaches in which factor-loading structures can be explored relatively flexibly within a confirmatory factor analysis (CFA) framework. Recently, Muthén & Asparouhov proposed a Bayesian structural equation modeling (BSEM) approach to explore the presence of cross loadings in CFA models. We show that the issue of determining factor-loading patterns may be formulated as a Bayesian variable selection problem in which Muthén and Asparouhov's approach can be regarded as a BSEM approach with ridge regression prior (BSEM-RP). We propose another Bayesian approach, denoted herein as the Bayesian structural equation modeling with spike-and-slab prior (BSEM-SSP), which serves as a one-stage alternative to the BSEM-RP. We review the theoretical advantages and disadvantages of both approaches and compare their empirical performance relative to two modification indices-based approaches and exploratory factor analysis with target rotation. A teacher stress scale data set is used to demonstrate our approach.

  3. Bayesian Factor Analysis as a Variable-Selection Problem: Alternative Priors and Consequences.

    PubMed

    Lu, Zhao-Hua; Chow, Sy-Miin; Loken, Eric

    2016-01-01

    Factor analysis is a popular statistical technique for multivariate data analysis. Developments in the structural equation modeling framework have enabled the use of hybrid confirmatory/exploratory approaches in which factor-loading structures can be explored relatively flexibly within a confirmatory factor analysis (CFA) framework. Recently, Muthén & Asparouhov proposed a Bayesian structural equation modeling (BSEM) approach to explore the presence of cross loadings in CFA models. We show that the issue of determining factor-loading patterns may be formulated as a Bayesian variable selection problem in which Muthén and Asparouhov's approach can be regarded as a BSEM approach with ridge regression prior (BSEM-RP). We propose another Bayesian approach, denoted herein as the Bayesian structural equation modeling with spike-and-slab prior (BSEM-SSP), which serves as a one-stage alternative to the BSEM-RP. We review the theoretical advantages and disadvantages of both approaches and compare their empirical performance relative to two modification indices-based approaches and exploratory factor analysis with target rotation. A teacher stress scale data set is used to demonstrate our approach. PMID:27314566

  4. Bayesian approach increases accuracy when selecting cowpea genotypes with high adaptability and phenotypic stability.

    PubMed

    Barroso, L M A; Teodoro, P E; Nascimento, M; Torres, F E; Dos Santos, A; Corrêa, A M; Sagrilo, E; Corrêa, C C G; Silva, F A; Ceccon, G

    2016-01-01

    This study aimed to verify that a Bayesian approach could be used for the selection of upright cowpea genotypes with high adaptability and phenotypic stability, and the study also evaluated the efficiency of using informative and minimally informative a priori distributions. Six trials were conducted in randomized blocks, and the grain yield of 17 upright cowpea genotypes was assessed. To represent the minimally informative a priori distributions, a probability distribution with high variance was used, and a meta-analysis concept was adopted to represent the informative a priori distributions. Bayes factors were used to conduct comparisons between the a priori distributions. The Bayesian approach was effective for selection of upright cowpea genotypes with high adaptability and phenotypic stability using the Eberhart and Russell method. Bayes factors indicated that the use of informative a priori distributions provided more accurate results than minimally informative a priori distributions. PMID:26985961

  5. Approximate Bayesian computation scheme for parameter inference and model selection in dynamical systems

    PubMed Central

    Toni, Tina; Welch, David; Strelkowa, Natalja; Ipsen, Andreas; Stumpf, Michael P.H.

    2008-01-01

    Approximate Bayesian computation (ABC) methods can be used to evaluate posterior distributions without having to calculate likelihoods. In this paper, we discuss and apply an ABC method based on sequential Monte Carlo (SMC) to estimate parameters of dynamical models. We show that ABC SMC provides information about the inferability of parameters and model sensitivity to changes in parameters, and tends to perform better than other ABC approaches. The algorithm is applied to several well-known biological systems, for which parameters and their credible intervals are inferred. Moreover, we develop ABC SMC as a tool for model selection; given a range of different mathematical descriptions, ABC SMC is able to choose the best model using the standard Bayesian model selection apparatus. PMID:19205079

  6. Bayesian approach increases accuracy when selecting cowpea genotypes with high adaptability and phenotypic stability.

    PubMed

    Barroso, L M A; Teodoro, P E; Nascimento, M; Torres, F E; Dos Santos, A; Corrêa, A M; Sagrilo, E; Corrêa, C C G; Silva, F A; Ceccon, G

    2016-03-11

    This study aimed to verify that a Bayesian approach could be used for the selection of upright cowpea genotypes with high adaptability and phenotypic stability, and the study also evaluated the efficiency of using informative and minimally informative a priori distributions. Six trials were conducted in randomized blocks, and the grain yield of 17 upright cowpea genotypes was assessed. To represent the minimally informative a priori distributions, a probability distribution with high variance was used, and a meta-analysis concept was adopted to represent the informative a priori distributions. Bayes factors were used to conduct comparisons between the a priori distributions. The Bayesian approach was effective for selection of upright cowpea genotypes with high adaptability and phenotypic stability using the Eberhart and Russell method. Bayes factors indicated that the use of informative a priori distributions provided more accurate results than minimally informative a priori distributions.

  7. Bayesian model selection applied to artificial neural networks used for water resources modeling

    NASA Astrophysics Data System (ADS)

    Kingston, Greer B.; Maier, Holger R.; Lambert, Martin F.

    2008-04-01

    Artificial neural networks (ANNs) have proven to be extremely valuable tools in the field of water resources engineering. However, one of the most difficult tasks in developing an ANN is determining the optimum level of complexity required to model a given problem, as there is no formal systematic model selection method. This paper presents a Bayesian model selection (BMS) method for ANNs that provides an objective approach for comparing models of varying complexity in order to select the most appropriate ANN structure. The approach uses Markov Chain Monte Carlo posterior simulations to estimate the evidence in favor of competing models and, in this study, three known methods for doing this are compared in terms of their suitability for being incorporated into the proposed BMS framework for ANNs. However, it is acknowledged that it can be particularly difficult to accurately estimate the evidence of ANN models. Therefore, the proposed BMS approach for ANNs incorporates a further check of the evidence results by inspecting the marginal posterior distributions of the hidden-to-output layer weights, which unambiguously indicate any redundancies in the hidden layer nodes. The fact that this check is available is one of the greatest advantages of the proposed approach over conventional model selection methods, which do not provide such a test and instead rely on the modeler's subjective choice of selection criterion. The advantages of a total Bayesian approach to ANN development, including training and model selection, are demonstrated on two synthetic and one real world water resources case study.

  8. The SDSS-III BOSS quasar lens survey: discovery of 13 gravitationally lensed quasars

    NASA Astrophysics Data System (ADS)

    More, Anupreeta; Oguri, Masamune; Kayo, Issha; Zinn, Joel; Strauss, Michael A.; Santiago, Basilio X.; Mosquera, Ana M.; Inada, Naohisa; Kochanek, Christopher S.; Rusu, Cristian E.; Brownstein, Joel R.; da Costa, Luiz N.; Kneib, Jean-Paul; Maia, Marcio A. G.; Quimby, Robert M.; Schneider, Donald P.; Streblyanska, Alina; York, Donald G.

    2016-02-01

    We report the discovery of 13 confirmed two-image quasar lenses from a systematic search for gravitationally lensed quasars in the SDSS-III Baryon Oscillation Spectroscopic Survey (BOSS). We adopted a methodology similar to that used in the SDSS Quasar Lens Search (SQLS). In addition to the confirmed lenses, we report 11 quasar pairs with small angular separations ( ≲ 2 arcsec) confirmed from our spectroscopy, which are either projected pairs, physical binaries, or possibly quasar lens systems whose lens galaxies have not yet been detected. The newly discovered quasar lens system, SDSS J1452+4224 at zs ≈ 4.8 is one of the highest redshift multiply imaged quasars found to date. Furthermore, we have over 50 good lens candidates yet to be followed up. Owing to the heterogeneous selection of BOSS quasars, the lens sample presented here does not have a well-defined selection function.

  9. Bayesian analysis of response to selection: a case study using litter size in Danish Yorkshire pigs.

    PubMed Central

    Sorensen, D; Vernersen, A; Andersen, S

    2000-01-01

    Implementation of a Bayesian analysis of a selection experiment is illustrated using litter size [total number of piglets born (TNB)] in Danish Yorkshire pigs. Other traits studied include average litter weight at birth (WTAB) and proportion of piglets born dead (PRBD). Response to selection for TNB was analyzed with a number of models, which differed in their level of hierarchy, in their prior distributions, and in the parametric form of the likelihoods. A model assessment study favored a particular form of an additive genetic model. With this model, the Monte Carlo estimate of the 95% probability interval of response to selection was (0.23; 0.60), with a posterior mean of 0.43 piglets. WTAB showed a correlated response of -7.2 g, with a 95% probability interval equal to (-33.1; 18.9). The posterior mean of the genetic correlation between TNB and WTAB was -0.23 with a 95% probability interval equal to (-0.46; -0.01). PRBD was studied informally; it increases with larger litters, when litter size is >7 piglets born. A number of methodological issues related to the Bayesian model assessment study are discussed, as well as the genetic consequences of inferring response to selection using additive genetic models. PMID:10978292

  10. NuSTAR and XMM-Newton observations of luminous, heavily obscured, WISE-selected quasars at z ∼ 2

    SciTech Connect

    Stern, D.; Eisenhardt, P. R. M.; Lansbury, G. B.; Alexander, D. M.; Del Moro, A.; Gandhi, P.; Assef, R. J.; Brandt, W. N.; Griffith, R. L.; Ballantyne, D. R.; Baloković, M.; Bridge, C.; Bauer, F. E.; Benford, D.; Blain, A.; Boggs, S. E.; Craig, W. W.; Brightman, M.; Christensen, F. E.; Comastri, A.; and others

    2014-10-20

    We report on a NuSTAR and XMM-Newton program that has observed a sample of three extremely luminous, heavily obscured WISE-selected active galactic nuclei (AGNs) at z ∼ 2 across a broad X-ray band (0.1 – 79 keV). The parent sample, selected to be faint or undetected in the WISE 3.4 μm (W1) and 4.6 μm (W2) bands but bright at 12 μm (W3) and 22 μm (W4), are extremely rare, with only ∼1000 so-called 'W1W2-dropouts' across the extragalactic sky. Optical spectroscopy reveals typical redshifts of z ∼ 2 for this population, implying rest-frame mid-IR luminosities of νL {sub ν}(6 μm) ∼ 6 × 10{sup 46} erg s{sup –1} and bolometric luminosities that can exceed L {sub bol} ∼ 10{sup 14} L {sub ☉}. The corresponding intrinsic, unobscured hard X-ray luminosities are L(2-10 keV) ∼ 4 × 10{sup 45} erg s{sup –1} for typical quasar templates. These are among the most AGNs known, though the optical spectra rarely show evidence of a broad-line region and the selection criteria imply heavy obscuration even at rest-frame 1.5 μm. We designed our X-ray observations to obtain robust detections for gas column densities N {sub H} ≤ 10{sup 24} cm{sup –2}. In fact, the sources prove to be fainter than these predictions. Two of the sources were observed by both NuSTAR and XMM-Newton, with neither being detected by NuSTAR (f {sub 3-24} {sub keV} ≲ 10{sup –13} erg cm{sup –2} s{sup –1}), and one being faintly detected by XMM-Newton (f {sub 0.5-10} {sub keV} ∼ 5 × 10{sup –15} erg cm{sup –2} s{sup –1}). A third source was observed only with XMM-Newton, yielding a faint detection (f {sub 0.5-10} {sub keV} ∼ 7 × 10{sup –15} erg cm{sup –2} s{sup –1}). The X-ray data imply these sources are either X-ray weak, or are heavily obscured by column densities N {sub H} ≳ 10{sup 24} cm{sup –2}. The combined X-ray and mid-IR analysis seems to favor this second possibility, implying the sources are extremely obscured, consistent with Compton

  11. Model selection on solid ground: Rigorous comparison of nine ways to evaluate Bayesian model evidence

    PubMed Central

    Schöniger, Anneli; Wöhling, Thomas; Samaniego, Luis; Nowak, Wolfgang

    2014-01-01

    Bayesian model selection or averaging objectively ranks a number of plausible, competing conceptual models based on Bayes' theorem. It implicitly performs an optimal trade-off between performance in fitting available data and minimum model complexity. The procedure requires determining Bayesian model evidence (BME), which is the likelihood of the observed data integrated over each model's parameter space. The computation of this integral is highly challenging because it is as high-dimensional as the number of model parameters. Three classes of techniques to compute BME are available, each with its own challenges and limitations: (1) Exact and fast analytical solutions are limited by strong assumptions. (2) Numerical evaluation quickly becomes unfeasible for expensive models. (3) Approximations known as information criteria (ICs) such as the AIC, BIC, or KIC (Akaike, Bayesian, or Kashyap information criterion, respectively) yield contradicting results with regard to model ranking. Our study features a theory-based intercomparison of these techniques. We further assess their accuracy in a simplistic synthetic example where for some scenarios an exact analytical solution exists. In more challenging scenarios, we use a brute-force Monte Carlo integration method as reference. We continue this analysis with a real-world application of hydrological model selection. This is a first-time benchmarking of the various methods for BME evaluation against true solutions. Results show that BME values from ICs are often heavily biased and that the choice of approximation method substantially influences the accuracy of model ranking. For reliable model selection, bias-free numerical methods should be preferred over ICs whenever computationally feasible. PMID:25745272

  12. Model selection on solid ground: Rigorous comparison of nine ways to evaluate Bayesian model evidence

    NASA Astrophysics Data System (ADS)

    Schöniger, Anneli; Wöhling, Thomas; Samaniego, Luis; Nowak, Wolfgang

    2014-12-01

    Bayesian model selection or averaging objectively ranks a number of plausible, competing conceptual models based on Bayes' theorem. It implicitly performs an optimal trade-off between performance in fitting available data and minimum model complexity. The procedure requires determining Bayesian model evidence (BME), which is the likelihood of the observed data integrated over each model's parameter space. The computation of this integral is highly challenging because it is as high-dimensional as the number of model parameters. Three classes of techniques to compute BME are available, each with its own challenges and limitations: (1) Exact and fast analytical solutions are limited by strong assumptions. (2) Numerical evaluation quickly becomes unfeasible for expensive models. (3) Approximations known as information criteria (ICs) such as the AIC, BIC, or KIC (Akaike, Bayesian, or Kashyap information criterion, respectively) yield contradicting results with regard to model ranking. Our study features a theory-based intercomparison of these techniques. We further assess their accuracy in a simplistic synthetic example where for some scenarios an exact analytical solution exists. In more challenging scenarios, we use a brute-force Monte Carlo integration method as reference. We continue this analysis with a real-world application of hydrological model selection. This is a first-time benchmarking of the various methods for BME evaluation against true solutions. Results show that BME values from ICs are often heavily biased and that the choice of approximation method substantially influences the accuracy of model ranking. For reliable model selection, bias-free numerical methods should be preferred over ICs whenever computationally feasible.

  13. Bayesian model selection for a finite element model of a large civil aircraft

    SciTech Connect

    Hemez, F. M.; Rutherford, A. C.

    2004-01-01

    Nine aircraft stiffness parameters have been varied and used as inputs to a finite element model of an aircraft to generate natural frequency and deflection features (Goge, 2003). This data set (147 input parameter configurations and associated outputs) is now used to generate a metamodel, or a fast running surrogate model, using Bayesian model selection methods. Once a forward relationship is defined, the metamodel may be used in an inverse sense. That is, knowing the measured output frequencies and deflections, what were the input stiffness parameters that caused them?

  14. Evaluation of candidate gene effects for beef backfat via Bayesian model selection.

    PubMed

    Wu, Xiao-Lin; Macneil, Michael D; De, Sachinadan; Xiao, Qian-Jun; Michal, Jennifer J; Gaskins, Charles T; Reeves, Jerry J; Busboom, Jan R; Wright, Raymond W; Jiang, Zhihua

    2005-09-01

    Candidate gene approaches provide tools for exploring and localizing causative genes affecting quantitative traits and the underlying variation may be better understood by determining the relative magnitudes of effects of their polymorphisms. Diacyglycerol O-acyltransferase 1 (DGAT1), fatty acid binding protein (heart) 3 (FABP3), growth hormone 1 (GH1), leptin (LEP) and thyroglobulin (TG) have been previously identified as genes contributing to genetic control of subcutaneous fat thickness (SFT) in beef cattle. In the present research, Bayesian model selection was used to evaluate effects of these five candidate genes by comparing competing non-nested models and treating candidate gene effects as either random or fixed. The analyses were implemented in SAS to simplify the programming and computation. Phenotypic data were gathered from a F(2) population of Wagyu x Limousin cattle. The five candidate genes had significant but varied effects on SFT in this population. Bayesian model selection identified the DGAT1 model as the one with the greatest model probability, whether candidate gene effects were considered random or fixed, and DGAT1 had the greatest additive effect on SFT. The SAS codes developed in the study are freely available and can be downloaded at: http://www.ansci.wsu.edu/programs/.

  15. Bayesian cross-validation for model evaluation and selection with application to the North American breeding survey

    USGS Publications Warehouse

    Link, William; Sauer, John

    2016-01-01

    The analysis of ecological data has changed in two important ways over the last fifteen years. The development and easy availability of Bayesian computational methods has allowed and encouraged the fitting of complex hierarchical models. At the same time, there has been increasing emphasis on acknowledging and accounting for model uncertainty. Unfortunately, the ability to fit complex models has outstripped the development of tools for model selection and model evaluation: familiar model selection tools such as Akaike's information criterion and the deviance information criterion are widely known to be inadequate for hierarchical models. In addition, little attention has been paid to the evaluation of model adequacy in context of hierarchical modeling, i.e., to the evaluation of fit for a single model. In this paper we describe Bayesian cross-validation, which provides tools for model selection and evaluation. We describe the Bayesian predictive information criterion (BPIC) and a Bayesian approximation to the BPIC known as the Watanabe-Akaike information criterion (WAIC). We illustrate the use of these tools for model selection, and the use of Bayesian cross-validation as a tool for model evaluation, using 3 large data sets from the North American Breeding Bird Survey.

  16. Bayesian cross-validation for model evaluation and selection, with application to the North American Breeding Bird Survey

    USGS Publications Warehouse

    Link, William; Sauer, John R.

    2016-01-01

    The analysis of ecological data has changed in two important ways over the last 15 years. The development and easy availability of Bayesian computational methods has allowed and encouraged the fitting of complex hierarchical models. At the same time, there has been increasing emphasis on acknowledging and accounting for model uncertainty. Unfortunately, the ability to fit complex models has outstripped the development of tools for model selection and model evaluation: familiar model selection tools such as Akaike's information criterion and the deviance information criterion are widely known to be inadequate for hierarchical models. In addition, little attention has been paid to the evaluation of model adequacy in context of hierarchical modeling, i.e., to the evaluation of fit for a single model. In this paper, we describe Bayesian cross-validation, which provides tools for model selection and evaluation. We describe the Bayesian predictive information criterion and a Bayesian approximation to the BPIC known as the Watanabe-Akaike information criterion. We illustrate the use of these tools for model selection, and the use of Bayesian cross-validation as a tool for model evaluation, using three large data sets from the North American Breeding Bird Survey.

  17. Bayesian model selection without evidences: application to the dark energy equation-of-state

    NASA Astrophysics Data System (ADS)

    Hee, S.; Handley, W. J.; Hobson, M. P.; Lasenby, A. N.

    2016-01-01

    A method is presented for Bayesian model selection without explicitly computing evidences, by using a combined likelihood and introducing an integer model selection parameter n so that Bayes factors, or more generally posterior odds ratios, may be read off directly from the posterior of n. If the total number of models under consideration is specified a priori, the full joint parameter space (θ, n) of the models is of fixed dimensionality and can be explored using standard Markov chain Monte Carlo (MCMC) or nested sampling methods, without the need for reversible jump MCMC techniques. The posterior on n is then obtained by straightforward marginalization. We demonstrate the efficacy of our approach by application to several toy models. We then apply it to constraining the dark energy equation of state using a free-form reconstruction technique. We show that Λ cold dark matter is significantly favoured over all extensions, including the simple w(z) = constant model.

  18. A Bayesian Framework for Landing Site Selection During Autonomous Spacecraft Descent

    NASA Technical Reports Server (NTRS)

    Serrano, Navid

    2006-01-01

    The success of a landed space exploration mission depends largely on the final landing site. Factors influencing site selection include safety, fuel-consumption, and scientific return. This paper addresses the problem of selecting the best available landing site based on these factors in real-time during autonomous spacecraft descent onto a planetary surface. The problem is modeled probabilistically using Bayesian Networks (BNs). BNs provide a means of representing the causal relationships between variables that impact the quality of a landing site. The final landing site is determined via probabilistic reasoning based on terrain safety derived from on-board sensors, available fuel based on spacecraft descent dynamics, and regions of interest defined by mission scientists.

  19. Bayesian inference of selection in a heterogeneous environment from genetic time-series data.

    PubMed

    Gompert, Zachariah

    2016-01-01

    Evolutionary geneticists have sought to characterize the causes and molecular targets of selection in natural populations for many years. Although this research programme has been somewhat successful, most statistical methods employed were designed to detect consistent, weak to moderate selection. In contrast, phenotypic studies in nature show that selection varies in time and that individual bouts of selection can be strong. Measurements of the genomic consequences of such fluctuating selection could help test and refine hypotheses concerning the causes of ecological specialization and the maintenance of genetic variation in populations. Herein, I proposed a Bayesian nonhomogeneous hidden Markov model to estimate effective population sizes and quantify variable selection in heterogeneous environments from genetic time-series data. The model is described and then evaluated using a series of simulated data, including cases where selection occurs on a trait with a simple or polygenic molecular basis. The proposed method accurately distinguished neutral loci from non-neutral loci under strong selection, but not from those under weak selection. Selection coefficients were accurately estimated when selection was constant or when the fitness values of genotypes varied linearly with the environment, but these estimates were less accurate when fitness was polygenic or the relationship between the environment and the fitness of genotypes was nonlinear. Past studies of temporal evolutionary dynamics in laboratory populations have been remarkably successful. The proposed method makes similar analyses of genetic time-series data from natural populations more feasible and thereby could help answer fundamental questions about the causes and consequences of evolution in the wild.

  20. A new sample of quasars to B = 22.0

    NASA Technical Reports Server (NTRS)

    Marano, B.; Zamorani, G.; Zitelli, V.

    1988-01-01

    A new sample of quasars with complete spectroscopic information down to about 22 mag is presented. The candidate selection and preliminary spectroscopic results are reported. Results are reported from the application of color-color diagrams, grism plates, and variability analysis in the quasar selection. The results on quasar counts, redshift distribution, and luminosity function at high redshift are discussed.

  1. Informative Bayesian Model Selection: a method for identifying interactions in genome-wide data.

    PubMed

    Aflakparast, Mehran; Masoudi-Nejad, Ali; Bozorgmehr, Joseph H; Visweswaran, Shyam

    2014-10-01

    In high-dimensional genome-wide (GWA) data, a key challenge is to detect genomic variants that interact in a nonlinear fashion in their association with disease. Identifying such genomic interactions is important for elucidating the inheritance of complex phenotypes and diseases. In this paper, we introduce a new computational method called Informative Bayesian Model Selection (IBMS) that leverages correlation among variants in GWA data due to the linkage disequilibrium to identify interactions accurately in a computationally efficient manner. IBMS combines several statistical methods including canonical correlation analysis, logistic regression analysis, and a Bayesians statistical measure of evaluating interactions. Compared to BOOST and BEAM that are two widely used methods for detecting genomic interactions, IBMS had significantly higher power when evaluated on synthetic data. Furthermore, when applied to Alzheimer's disease GWA data, IBMS identified previously reported interactions. IBMS is a useful method for identifying variants in GWA data, and software that implements IBMS is freely available online from http://lbb.ut.ac.ir/Download/LBBsoft/IBMS.

  2. A Framework for Parameter Estimation and Model Selection from Experimental Data in Systems Biology Using Approximate Bayesian Computation

    PubMed Central

    Liepe, Juliane; Kirk, Paul; Filippi, Sarah; Toni, Tina; Barnes, Chris P.; Stumpf, Michael P.H.

    2016-01-01

    As modeling becomes a more widespread practice in the life- and biomedical sciences, we require reliable tools to calibrate models against ever more complex and detailed data. Here we present an approximate Bayesian computation framework and software environment, ABC-SysBio, which enables parameter estimation and model selection in the Bayesian formalism using Sequential Monte-Carlo approaches. We outline the underlying rationale, discuss the computational and practical issues, and provide detailed guidance as to how the important tasks of parameter inference and model selection can be carried out in practice. Unlike other available packages, ABC-SysBio is highly suited for investigating in particular the challenging problem of fitting stochastic models to data. Although computationally expensive, the additional insights gained in the Bayesian formalism more than make up for this cost, especially in complex problems. PMID:24457334

  3. Crossing statistic: Bayesian interpretation, model selection and resolving dark energy parametrization problem

    SciTech Connect

    Shafieloo, Arman

    2012-05-01

    By introducing Crossing functions and hyper-parameters I show that the Bayesian interpretation of the Crossing Statistics [1] can be used trivially for the purpose of model selection among cosmological models. In this approach to falsify a cosmological model there is no need to compare it with other models or assume any particular form of parametrization for the cosmological quantities like luminosity distance, Hubble parameter or equation of state of dark energy. Instead, hyper-parameters of Crossing functions perform as discriminators between correct and wrong models. Using this approach one can falsify any assumed cosmological model without putting priors on the underlying actual model of the universe and its parameters, hence the issue of dark energy parametrization is resolved. It will be also shown that the sensitivity of the method to the intrinsic dispersion of the data is small that is another important characteristic of the method in testing cosmological models dealing with data with high uncertainties.

  4. Bayesian model selection for multiple QTLs mapping combining linkage disequilibrium and linkage.

    PubMed

    Jiang, Dan; Ma, Guoda; Yang, Runqing; Li, Keshen; Fang, Ming

    2014-01-01

    Linkage disequilibrium (LD) mapping is able to localize quantitative trait loci (QTL) within a rather small region (e.g. 2 cM), which is much narrower than linkage analysis (LA, usually 20 cM). The multilocus LD method utilizes haplotype information around putative mutation and takes historical recombination events into account, and thus provides a powerful method for further fine mapping. However, sometimes there are more than one QTLs in the region being studied. In this study, the Bayesian model selection implemented via the Markov chain Monte Carlo (MCMC) method is developed for fine mapping of multiple QTLs using haplotype information in a small region. The method combines LD as well as linkage information. A series of simulation experiments were conducted to investigate the behavior of the method. The results showed that this new multiple QTLs method was more efficient in separating closely linked QTLs than single-marker association studies. PMID:25579473

  5. Bayesian model selection for multiple QTLs mapping combining linkage disequilibrium and linkage.

    PubMed

    Jiang, Dan; Ma, Guoda; Yang, Runqing; Li, Keshen; Fang, Ming

    2014-09-19

    Linkage disequilibrium (LD) mapping is able to localize quantitative trait loci (QTL) within a rather small region (e.g. 2 cM), which is much narrower than linkage analysis (LA, usually 20 cM). The multilocus LD method utilizes haplotype information around putative mutation and takes historical recombination events into account, and thus provides a powerful method for further fine mapping. However, sometimes there are more than one QTLs in the region being studied. In this study, the Bayesian model selection implemented via the Markov chain Monte Carlo (MCMC) method is developed for fine mapping of multiple QTLs using haplotype information in a small region. The method combines LD as well as linkage information. A series of simulation experiments were conducted to investigate the behavior of the method. The results showed that this new multiple QTLs method was more efficient in separating closely linked QTLs than single-marker association studies.

  6. A Bayesian hierarchical model with spatial variable selection: the effect of weather on insurance claims

    PubMed Central

    Scheel, Ida; Ferkingstad, Egil; Frigessi, Arnoldo; Haug, Ola; Hinnerichsen, Mikkel; Meze-Hausken, Elisabeth

    2013-01-01

    Climate change will affect the insurance industry. We develop a Bayesian hierarchical statistical approach to explain and predict insurance losses due to weather events at a local geographic scale. The number of weather-related insurance claims is modelled by combining generalized linear models with spatially smoothed variable selection. Using Gibbs sampling and reversible jump Markov chain Monte Carlo methods, this model is fitted on daily weather and insurance data from each of the 319 municipalities which constitute southern and central Norway for the period 1997–2006. Precise out-of-sample predictions validate the model. Our results show interesting regional patterns in the effect of different weather covariates. In addition to being useful for insurance pricing, our model can be used for short-term predictions based on weather forecasts and for long-term predictions based on downscaled climate models. PMID:23396890

  7. QTL mapping in outbred half-sib families using Bayesian model selection.

    PubMed

    Fang, M; Liu, J; Sun, D; Zhang, Y; Zhang, Q; Zhang, Y; Zhang, S

    2011-09-01

    In this article, we propose a model selection method, the Bayesian composite model space approach, to map quantitative trait loci (QTL) in a half-sib population for continuous and binary traits. In our method, the identity-by-descent-based variance component model is used. To demonstrate the performance of this model, the method was applied to map QTL underlying production traits on BTA6 in a Chinese half-sib dairy cattle population. A total of four QTLs were detected, whereas only one QTL was identified using the traditional least square (LS) method. We also conducted two simulation experiments to validate the efficiency of our method. The results suggest that the proposed method based on a multiple-QTL model is efficient in mapping multiple QTL for an outbred half-sib population and is more powerful than the LS method based on a single-QTL model.

  8. The Hubble Space Telescope quasar absorption line key project. II - Data calibration and absorption-line selection

    NASA Technical Reports Server (NTRS)

    Schneider, Donald P.; Hartig, George F.; Jannuzi, Buell T.; Kirhakos, Sofia; Saxe, David H.; Weymann, Ray J.; Bahcall, John N.; Bergeron, Jacqueline; Boksenberg, Alec; Sargent, W. L. W.

    1993-01-01

    We present the observational and data processing aspects of the Hubble Space Telescope Quasar Absorption Line Key Project. Topics discussed include the observational technique, calibration of the data, software that simulates the data, the automated procedure used to identify and characterize the absorption features, and the determination of the sensitivity limits of the survey.

  9. Bayesian model selection of template forward models for EEG source reconstruction.

    PubMed

    Strobbe, Gregor; van Mierlo, Pieter; De Vos, Maarten; Mijović, Bogdan; Hallez, Hans; Van Huffel, Sabine; López, José David; Vandenberghe, Stefaan

    2014-06-01

    Several EEG source reconstruction techniques have been proposed to identify the generating neuronal sources of electrical activity measured on the scalp. The solution of these techniques depends directly on the accuracy of the forward model that is inverted. Recently, a parametric empirical Bayesian (PEB) framework for distributed source reconstruction in EEG/MEG was introduced and implemented in the Statistical Parametric Mapping (SPM) software. The framework allows us to compare different forward modeling approaches, using real data, instead of using more traditional simulated data from an assumed true forward model. In the absence of a subject specific MR image, a 3-layered boundary element method (BEM) template head model is currently used including a scalp, skull and brain compartment. In this study, we introduced volumetric template head models based on the finite difference method (FDM). We constructed a FDM head model equivalent to the BEM model and an extended FDM model including CSF. These models were compared within the context of three different types of source priors related to the type of inversion used in the PEB framework: independent and identically distributed (IID) sources, equivalent to classical minimum norm approaches, coherence (COH) priors similar to methods such as LORETA, and multiple sparse priors (MSP). The resulting models were compared based on ERP data of 20 subjects using Bayesian model selection for group studies. The reconstructed activity was also compared with the findings of previous studies using functional magnetic resonance imaging. We found very strong evidence in favor of the extended FDM head model with CSF and assuming MSP. These results suggest that the use of realistic volumetric forward models can improve PEB EEG source reconstruction.

  10. Multiple SNP Set Analysis for Genome-Wide Association Studies Through Bayesian Latent Variable Selection.

    PubMed

    Lu, Zhao-Hua; Zhu, Hongtu; Knickmeyer, Rebecca C; Sullivan, Patrick F; Williams, Stephanie N; Zou, Fei

    2015-12-01

    The power of genome-wide association studies (GWAS) for mapping complex traits with single-SNP analysis (where SNP is single-nucleotide polymorphism) may be undermined by modest SNP effect sizes, unobserved causal SNPs, correlation among adjacent SNPs, and SNP-SNP interactions. Alternative approaches for testing the association between a single SNP set and individual phenotypes have been shown to be promising for improving the power of GWAS. We propose a Bayesian latent variable selection (BLVS) method to simultaneously model the joint association mapping between a large number of SNP sets and complex traits. Compared with single SNP set analysis, such joint association mapping not only accounts for the correlation among SNP sets but also is capable of detecting causal SNP sets that are marginally uncorrelated with traits. The spike-and-slab prior assigned to the effects of SNP sets can greatly reduce the dimension of effective SNP sets, while speeding up computation. An efficient Markov chain Monte Carlo algorithm is developed. Simulations demonstrate that BLVS outperforms several competing variable selection methods in some important scenarios. PMID:26515609

  11. Adverse and Advantageous Selection in the Medicare Supplemental Market: A Bayesian Analysis of Prescription drug Expenditure.

    PubMed

    Li, Qian; Trivedi, Pravin K

    2016-02-01

    This paper develops an extended specification of the two-part model, which controls for unobservable self-selection and heterogeneity of health insurance, and analyzes the impact of Medicare supplemental plans on the prescription drug expenditure of the elderly, using a linked data set based on the Medicare Current Beneficiary Survey data for 2003-2004. The econometric analysis is conducted using a Bayesian econometric framework. We estimate the treatment effects for different counterfactuals and find significant evidence of endogeneity in plan choice and the presence of both adverse and advantageous selections in the supplemental insurance market. The average incentive effect is estimated to be $757 (2004 value) or 41% increase per person per year for the elderly enrolled in supplemental plans with drug coverage against the Medicare fee-for-service counterfactual and is $350 or 21% against the supplemental plans without drug coverage counterfactual. The incentive effect varies by different sources of drug coverage: highest for employer-sponsored insurance plans, followed by Medigap and managed medicare plans. PMID:25504934

  12. Comparison of Two Gas Selection Methodologies: An Application of Bayesian Model Averaging

    SciTech Connect

    Renholds, Andrea S.; Thompson, Sandra E.; Anderson, Kevin K.; Chilton, Lawrence K.

    2006-03-31

    One goal of hyperspectral imagery analysis is the detection and characterization of plumes. Characterization includes identifying the gases in the plumes, which is a model selection problem. Two gas selection methods compared in this report are Bayesian model averaging (BMA) and minimum Akaike information criterion (AIC) stepwise regression (SR). Simulated spectral data from a three-layer radiance transfer model were used to compare the two methods. Test gases were chosen to span the types of spectra observed, which exhibit peaks ranging from broad to sharp. The size and complexity of the search libraries were varied. Background materials were chosen to either replicate a remote area of eastern Washington or feature many common background materials. For many cases, BMA and SR performed the detection task comparably in terms of the receiver operating characteristic curves. For some gases, BMA performed better than SR when the size and complexity of the search library increased. This is encouraging because we expect improved BMA performance upon incorporation of prior information on background materials and gases.

  13. Adverse and Advantageous Selection in the Medicare Supplemental Market: A Bayesian Analysis of Prescription drug Expenditure.

    PubMed

    Li, Qian; Trivedi, Pravin K

    2016-02-01

    This paper develops an extended specification of the two-part model, which controls for unobservable self-selection and heterogeneity of health insurance, and analyzes the impact of Medicare supplemental plans on the prescription drug expenditure of the elderly, using a linked data set based on the Medicare Current Beneficiary Survey data for 2003-2004. The econometric analysis is conducted using a Bayesian econometric framework. We estimate the treatment effects for different counterfactuals and find significant evidence of endogeneity in plan choice and the presence of both adverse and advantageous selections in the supplemental insurance market. The average incentive effect is estimated to be $757 (2004 value) or 41% increase per person per year for the elderly enrolled in supplemental plans with drug coverage against the Medicare fee-for-service counterfactual and is $350 or 21% against the supplemental plans without drug coverage counterfactual. The incentive effect varies by different sources of drug coverage: highest for employer-sponsored insurance plans, followed by Medigap and managed medicare plans.

  14. Exploration of quasars with the Gaia mission

    NASA Astrophysics Data System (ADS)

    Proft, Svea; Wambsganss, Joachim

    2015-01-01

    We analyze the opportunities in and limits to investigating quasars with the Gaia satellite by studying Gaia's low- and high-resolution quasar spectra, with consideration of their signal-to-noise ratios. Furthermore, we explore bright quasars from the Sloan Digital Sky Survey with broad emission lines (BELs) redshifted into the spectral range of Gaia's Radial Velocity Spectrograph (RVS). We find that Gaia low-resolution spectra of quasars enable a determination of equivalent widths, continuum variability, and the Baldwin effect. Additionally, it will be feasible to analyze BEL reverberation mapping with Gaia data for a small sample of objects. These quasars should have a high cadence of measurements or higher time lags due to large redshifts, high quasar luminosities, or selected low-ionization lines. More than 500 known quasars will also get high-resolution spectra of individual BELs in the small wavelength range of the RVS. This allows an investigation of broad emission line shapes and their variabilities to get information on the spatial structure and kinematics of the broad line region. We identify six known variable SDSS quasars with BELs in the RVS that have interesting spectra for a potential intrinsic line variability investigation. However, the signal-to-noise ratio of the RVS is too small for studying narrow and broad absorption lines in quasar spectra.

  15. The Environments of Obscured Quasars

    NASA Astrophysics Data System (ADS)

    Jones, Kristen M.; Lacy, Mark; Nielsen, Danielle

    2016-01-01

    Supermassive Black Hole (SMBH) feedback is prescribed for driving the high-end shape of the galaxy luminosity function, clearing the circumnuclear environment during the end stages of mergers, and eventually turning off its own accretion. Yet the dominant processes and characteristics of active galactic nuclei are indistinct. Chief among this confusion is how significant the role of dust is in each galaxy. Orientation of the dusty torus is attributed to causing the differences between Sy1 and Sy2, but whether obscured quasars are found in particularly dusty host galaxies, if they exist at a different stage in the merger process (early on, before the dust is blown out), or if they are merely oriented differently than optical quasars is not yet so well distinguished. With obscured quasars now observed to make up 50% or greater of the population of quasars, the question of what causes obscuration becomes vital to address. With this in mind, I study matched samples of obscured and unobscured quasars to characterize their environments, with the intent of addressing what contribution environment has to obscuration levels. I investigate the megaparsec-scale environments of SIRTF Wide-field Infra-Red Extragalactic Survey (SWIRE) quasars at z ˜ 1-3 by cross-correlating the sample with 3.8 million galaxies from the Spitzer Extragalactic Representative Volume Survey (SERVS). Optically obscured quasars are compared to a control sample of optically-bright quasars via selection in the mid-infrared. Environments were observed at 3.6 and 4.5 μm to a depth of ≈ 2 μJy (AB = 23.1). Recent work has found diverse results in such studies, with dependence of environmental richness on both redshift and level of obscuration. I find that, within reasonable error, on average there is no distinct difference between the level of clustering for obscured and normal quasars, and that there is no dependence on redshift of this result within the range of 1.3 < z < 2.5. I compare our results

  16. Quasar evolution - Not a deficit at 'low' redshifts

    NASA Technical Reports Server (NTRS)

    Avni, Y.; Schiller, N.

    1983-01-01

    Hawkins and Stewart (1981) have argued that the conventional interpretation of complete quasar samples in terms of a cosmological evolution of quasars is not unique. It has been suggested that these data can also be interpreted as due to a deficit in the density of quasars. Hawkins and Stewart have argued that such a deficit could be either apparent, due to an observational selection which biases against the inclusion of low-z quasars, or real, due to a lower density of quasars at low redshifts. The present investigation is concerned with this new interpretation. In order to test the interpretation of Hawkins and Stewart (1981) as directly as possible, the investigation is restricted to the same type of quasar samples considered by Hawkins and Stewart. It is found that the obtained results contradict clearly Hawkins and Stewart's assertion. Quasar evolution is not just a deficit of quasars at low redshifts, neither apparent nor real.

  17. SIX MORE QUASARS AT REDSHIFT 6 DISCOVERED BY THE CANADA-FRANCE HIGH-z QUASAR SURVEY

    SciTech Connect

    Willott, Chris J.; Crampton, David; Hutchings, John B.; Schade, David; Delorme, Philippe; Delfosse, Xavier; Forveille, Thierry; Reyle, Celine; Albert, Loic; Bergeron, Jacqueline; Omont, Alain; McLure, Ross J.

    2009-03-15

    We present imaging and spectroscopic observations for six quasars at z {>=} 5.9 discovered by the Canada-France High-z Quasar Survey (CFHQS). The CFHQS contains subsurveys with a range of flux and area combinations to sample a wide range of quasar luminosities at z {approx} 6. The new quasars have luminosities 10-75 times lower than the most luminous Sloan Digital Sky Survey quasars at this redshift. The least luminous quasar, CFHQS J0216-0455 at z = 6.01, has absolute magnitude M {sub 1450} = -22.21, well below the likely break in the luminosity function. This quasar is not detected in a deep XMM-Newton survey showing that optical selection is still a very efficient tool for finding high-redshift quasars.

  18. A bayesian integrative model for genetical genomics with spatially informed variable selection.

    PubMed

    Cassese, Alberto; Guindani, Michele; Vannucci, Marina

    2014-01-01

    We consider a Bayesian hierarchical model for the integration of gene expression levels with comparative genomic hybridization (CGH) array measurements collected on the same subjects. The approach defines a measurement error model that relates the gene expression levels to latent copy number states. In turn, the latent states are related to the observed surrogate CGH measurements via a hidden Markov model. The model further incorporates variable selection with a spatial prior based on a probit link that exploits dependencies across adjacent DNA segments. Posterior inference is carried out via Markov chain Monte Carlo stochastic search techniques. We study the performance of the model in simulations and show better results than those achieved with recently proposed alternative priors. We also show an application to data from a genomic study on lung squamous cell carcinoma, where we identify potential candidates of associations between copy number variants and the transcriptional activity of target genes. Gene ontology (GO) analyses of our findings reveal enrichments in genes that code for proteins involved in cancer. Our model also identifies a number of potential candidate biomarkers for further experimental validation. PMID:25288877

  19. Hyperspectral remote sensing of plant biochemistry using Bayesian model averaging with variable and band selection

    SciTech Connect

    Zhao, Kaiguang; Valle, Denis; Popescu, Sorin; Zhang, Xuesong; Malick, Bani

    2013-05-15

    Model specification remains challenging in spectroscopy of plant biochemistry, as exemplified by the availability of various spectral indices or band combinations for estimating the same biochemical. This lack of consensus in model choice across applications argues for a paradigm shift in hyperspectral methods to address model uncertainty and misspecification. We demonstrated one such method using Bayesian model averaging (BMA), which performs variable/band selection and quantifies the relative merits of many candidate models to synthesize a weighted average model with improved predictive performances. The utility of BMA was examined using a portfolio of 27 foliage spectral–chemical datasets representing over 80 species across the globe to estimate multiple biochemical properties, including nitrogen, hydrogen, carbon, cellulose, lignin, chlorophyll (a or b), carotenoid, polar and nonpolar extractives, leaf mass per area, and equivalent water thickness. We also compared BMA with partial least squares (PLS) and stepwise multiple regression (SMR). Results showed that all the biochemicals except carotenoid were accurately estimated from hyerspectral data with R2 values > 0.80.

  20. Finding the right balance between groundwater model complexity and experimental effort via Bayesian model selection

    NASA Astrophysics Data System (ADS)

    Schöniger, Anneli; Illman, Walter A.; Wöhling, Thomas; Nowak, Wolfgang

    2015-12-01

    Groundwater modelers face the challenge of how to assign representative parameter values to the studied aquifer. Several approaches are available to parameterize spatial heterogeneity in aquifer parameters. They differ in their conceptualization and complexity, ranging from homogeneous models to heterogeneous random fields. While it is common practice to invest more effort into data collection for models with a finer resolution of heterogeneities, there is a lack of advice which amount of data is required to justify a certain level of model complexity. In this study, we propose to use concepts related to Bayesian model selection to identify this balance. We demonstrate our approach on the characterization of a heterogeneous aquifer via hydraulic tomography in a sandbox experiment (Illman et al., 2010). We consider four increasingly complex parameterizations of hydraulic conductivity: (1) Effective homogeneous medium, (2) geology-based zonation, (3) interpolation by pilot points, and (4) geostatistical random fields. First, we investigate the shift in justified complexity with increasing amount of available data by constructing a model confusion matrix. This matrix indicates the maximum level of complexity that can be justified given a specific experimental setup. Second, we determine which parameterization is most adequate given the observed drawdown data. Third, we test how the different parameterizations perform in a validation setup. The results of our test case indicate that aquifer characterization via hydraulic tomography does not necessarily require (or justify) a geostatistical description. Instead, a zonation-based model might be a more robust choice, but only if the zonation is geologically adequate.

  1. Elucidation of Genetic Interactions in the Yeast GATA-Factor Network Using Bayesian Model Selection

    PubMed Central

    Milias-Argeitis, Andreas; Oliveira, Ana Paula; Gerosa, Luca; Falter, Laura; Sauer, Uwe; Lygeros, John

    2016-01-01

    Understanding the structure and function of complex gene regulatory networks using classical genetic assays is an error-prone procedure that frequently generates ambiguous outcomes. Even some of the best-characterized gene networks contain interactions whose validity is not conclusively proven. Founded on dynamic experimental data, mechanistic mathematical models are able to offer detailed insights that would otherwise require prohibitively large numbers of genetic experiments. Here we attempt mechanistic modeling of the transcriptional network formed by the four GATA-factor proteins, a well-studied system of central importance for nitrogen-source regulation of transcription in the yeast Saccharomyces cerevisiae. To resolve ambiguities in the network organization, we encoded a set of five interactions hypothesized in the literature into a set of 32 mathematical models, and employed Bayesian model selection to identify the most plausible set of interactions based on dynamic gene expression data. The top-ranking model was validated on newly generated GFP reporter dynamic data and was subsequently used to gain a better understanding of how yeast cells organize their transcriptional response to dynamic changes of nitrogen sources. Our work constitutes a necessary and important step towards obtaining a holistic view of the yeast nitrogen regulation mechanisms; on the computational side, it provides a demonstration of how powerful Monte Carlo techniques can be creatively combined and used to address the great challenges of large-scale dynamical system inference. PMID:26967983

  2. Dynamics of attentional selection under conflict: toward a rational Bayesian account.

    PubMed

    Yu, Angela J; Dayan, Peter; Cohen, Jonathan D

    2009-06-01

    The brain exhibits remarkable facility in exerting attentional control in most circumstances, but it also suffers apparent limitations in others. The authors' goal is to construct a rational account for why attentional control appears suboptimal under conditions of conflict and what this implies about the underlying computational principles. The formal framework used is based on Bayesian probability theory, which provides a convenient language for delineating the rationale and dynamics of attentional selection. The authors illustrate these issues with the Eriksen flanker task, a classical paradigm that explores the effects of competing sensory inputs on response tendencies. The authors show how 2 distinctly formulated models, based on compatibility bias and spatial uncertainty principles, can account for the behavioral data. They also suggest novel experiments that may differentiate these models. In addition, they elaborate a simplified model that approximates optimal computation and may map more directly onto the underlying neural machinery. This approximate model uses conflict monitoring, putatively mediated by the anterior cingulate cortex, as a proxy for compatibility representation. The authors also consider how this conflict information might be disseminated and used to control processing.

  3. HST Imaging of Quasar Host Galaxies

    NASA Astrophysics Data System (ADS)

    Hooper, E. J.; Impey, C. D.; Foltz, C. B.

    1996-12-01

    A sample of 16 quasars from the Large Bright Quasar Survey (LBQS) has been imaged with WFPC2 on the Hubble Space Telescope. The sample was selected to cover a range of radio luminosity typical of optically selected quasars in narrow intervals of redshift (0.4 <= z >= 0.5) and absolute magnitude (-25 < MB < -23). Two-dimensional cross-correlation techniques were used to determine the magnitudes of the host galaxies and quasar nuclear components, as well as the axial ratios of the hosts. The derived host galaxy magnitudes are near or below L(*) and are correlated with the quasar nuclear magnitude, similar to the trend in near-infrared host galaxy luminosity found by McLeod & Rieke (1995, ApJ, 454, L77). There is no discernable difference in host galaxy luminosity between radio-loud and radio-quiet quasars in the sample. Preliminary analysis of the host galaxy morphologies indicates that many, including several of the radio-quiet quasars, are probably in early type galaxies, consistent with other high-resolution imaging studies of quasar hosts. However, the distribution of axial ratios is not consistent with a population of early type galaxies. The hosts in the LBQS sample are rather flattened, with half having axial ratios <= 0.5. It is possible that these are inclined disk systems or galaxies with substantial bar components.

  4. Verification Techniques for Parameter Selection and Bayesian Model Calibration Presented for an HIV Model

    NASA Astrophysics Data System (ADS)

    Wentworth, Mami Tonoe

    Uncertainty quantification plays an important role when making predictive estimates of model responses. In this context, uncertainty quantification is defined as quantifying and reducing uncertainties, and the objective is to quantify uncertainties in parameter, model and measurements, and propagate the uncertainties through the model, so that one can make a predictive estimate with quantified uncertainties. Two of the aspects of uncertainty quantification that must be performed prior to propagating uncertainties are model calibration and parameter selection. There are several efficient techniques for these processes; however, the accuracy of these methods are often not verified. This is the motivation for our work, and in this dissertation, we present and illustrate verification frameworks for model calibration and parameter selection in the context of biological and physical models. First, HIV models, developed and improved by [2, 3, 8], describe the viral infection dynamics of an HIV disease. These are also used to make predictive estimates of viral loads and T-cell counts and to construct an optimal control for drug therapy. Estimating input parameters is an essential step prior to uncertainty quantification. However, not all the parameters are identifiable, implying that they cannot be uniquely determined by the observations. These unidentifiable parameters can be partially removed by performing parameter selection, a process in which parameters that have minimal impacts on the model response are determined. We provide verification techniques for Bayesian model calibration and parameter selection for an HIV model. As an example of a physical model, we employ a heat model with experimental measurements presented in [10]. A steady-state heat model represents a prototypical behavior for heat conduction and diffusion process involved in a thermal-hydraulic model, which is a part of nuclear reactor models. We employ this simple heat model to illustrate verification

  5. Evaluating experimental design for soil-plant model selection with Bayesian model averaging

    NASA Astrophysics Data System (ADS)

    Wöhling, Thomas; Geiges, Andreas; Nowak, Wolfgang; Gayler, Sebastian

    2013-04-01

    The objective selection of appropriate models for realistic simulations of coupled soil-plant processes is a challenging task since the processes are complex, not fully understood at larger scales, and highly non-linear. Also, comprehensive data sets are scarce, and measurements are uncertain. In the past decades, a variety of different models have been developed that exhibit a wide range of complexity regarding their approximation of processes in the coupled model compartments. We present a method for evaluating experimental design for maximum confidence in the model selection task. The method considers uncertainty in parameters, measurements and model structures. Advancing the ideas behind Bayesian Model Averaging (BMA), the model weights in BMA are perceived as uncertain quantities with assigned probability distributions that narrow down as more data are made available. This allows assessing the power of different data types, data densities and data locations in identifying the best model structure from among a suite of plausible models. The models considered in this study are the crop models CERES, SUCROS, GECROS and SPASS, which are coupled to identical routines for simulating soil processes within the modelling framework Expert-N. The four models considerably differ in the degree of detail at which crop growth and root water uptake are represented. Monte-Carlo simulations were conducted for each of these models considering their uncertainty in soil hydraulic properties and selected crop model parameters. The models were then conditioned on field measurements of soil moisture, leaf-area index (LAI), and evapotranspiration rates (from eddy-covariance measurements) during a vegetation period of winter wheat at the Nellingen site in Southwestern Germany. Following our new method, we derived the BMA model weights (and their distributions) when using all data or different subsets thereof. We discuss to which degree the posterior BMA mean outperformed the prior BMA

  6. The FIRST-2MASS Red Quasar Survey

    SciTech Connect

    Glikman, E; Helfand, D J; White, R L; Becker, R H; Gregg, M D; Lacy, M

    2007-06-28

    Combining radio observations with optical and infrared color selection--demonstrated in our pilot study to be an efficient selection algorithm for finding red quasars--we have obtained optical and infrared spectroscopy for 120 objects in a complete sample of 156 candidates from a sky area of 2716 square degrees. Consistent with our initial results, we find our selection criteria--J-K > 1.7,R-K > 4.0--yield a {approx} 50% success rate for discovering quasars substantially redder than those found in optical surveys. Comparison with UVX- and optical color-selected samples shows that {approx}> 10% of the quasars are missed in a magnitude-limited survey. Simultaneous two-frequency radio observations for part of the sample indicate that a synchrotron continuum component is ruled out as a significant contributor to reddening the quasars spectra. We go on to estimate extinctions for our objects assuming their red colors are caused by dust. Continuum fits and Balmer decrements suggest E(B-V) values ranging from near zero to 2.5 magnitudes. Correcting the K-band magnitudes for these extinctions, we find that for K {le} 14.0, red quasars make up between 25% and 60% of the underlying quasar population; owing to the incompleteness of the 2MASS survey at fainter K-band magnitudes, we can only set a lower limit to the radio-detected red quasar population of > 20-30%.

  7. The hidden quasar nucleus of a WISE-selected, hyperluminous, dust-obscured galaxy at z ~ 2.3

    NASA Astrophysics Data System (ADS)

    Piconcelli, E.; Vignali, C.; Bianchi, S.; Zappacosta, L.; Fritz, J.; Lanzuisi, G.; Miniutti, G.; Bongiorno, A.; Feruglio, C.; Fiore, F.; Maiolino, R.

    2015-02-01

    We present the first X-ray spectrum of a hot dust-obscured galaxy (DOG), namely W1835+4355 at z ~ 2.3. Hot DOGs represent a very rare population of hyperluminous (≥1047 erg s-1), dust-enshrouded objects at z ≥ 2 recently discovered in the WISE All Sky Survey. The 40 ks XMM-Newton spectrum reveals a continuum as flat (Γ ~ 0.8) as typically seen in heavily obscured AGN. This, along with the presence of strong Fe Kα emission, clearly suggests a reflection-dominated spectrum due to Compton-thick absorption. In this scenario, the observed luminosity of L2-10~ 2 × 1044 erg s-1 is a fraction (<10%) of the intrinsic one, which is estimated to be ≳ 5 × 1045 erg s-1 by using several proxies. The Herschel data allow us to constrain the SED up to the sub-mm band, providing a reliable estimate of the quasar contribution (~75%) to the IR luminosity as well as the amount of star formation (~2100 M⊙ yr-1). Our results thus provide additional pieces of evidence that associate Hot DOGs with an exceptionally dusty phase during which luminous quasars and massive galaxies co-evolve and a very efficient and powerful AGN-driven feedback mechanism is predicted by models.

  8. Accurate characterization of delay discounting: a multiple model approach using approximate Bayesian model selection and a unified discounting measure.

    PubMed

    Franck, Christopher T; Koffarnus, Mikhail N; House, Leanna L; Bickel, Warren K

    2015-01-01

    The study of delay discounting, or valuation of future rewards as a function of delay, has contributed to understanding the behavioral economics of addiction. Accurate characterization of discounting can be furthered by statistical model selection given that many functions have been proposed to measure future valuation of rewards. The present study provides a convenient Bayesian model selection algorithm that selects the most probable discounting model among a set of candidate models chosen by the researcher. The approach assigns the most probable model for each individual subject. Importantly, effective delay 50 (ED50) functions as a suitable unifying measure that is computable for and comparable between a number of popular functions, including both one- and two-parameter models. The combined model selection/ED50 approach is illustrated using empirical discounting data collected from a sample of 111 undergraduate students with models proposed by Laibson (1997); Mazur (1987); Myerson & Green (1995); Rachlin (2006); and Samuelson (1937). Computer simulation suggests that the proposed Bayesian model selection approach outperforms the single model approach when data truly arise from multiple models. When a single model underlies all participant data, the simulation suggests that the proposed approach fares no worse than the single model approach.

  9. ON THE LINK BETWEEN ASSOCIATED Mg II ABSORBERS AND STAR FORMATION IN QUASAR HOSTS

    SciTech Connect

    Shen Yue; Menard, Brice E-mail: menard@pha.jhu.edu

    2012-04-01

    A few percent of quasars show strong associated Mg II absorption, with velocities (v{sub off}) lying within a few thousand km s{sup -1} from the quasar systemic redshift. These associated absorption line (AAL) systems are usually interpreted as absorbers that are either intrinsic to the quasar and its host, or arising from external galaxies clustering around the quasar. Using composite spectra of {approx}1800 Mg II AAL quasars selected from SDSS DR7 at 0.4 {approx}< z {approx}< 2, we show that quasars with AALs with v{sub off} < 1500 km s{sup -1} have a prominent excess in [O II] {lambda}3727 emission (detected at >7{sigma}) at rest relative to the quasar host, compared to unabsorbed quasars. We interpret this [O II] excess as due to enhanced star formation in the quasar host. Our results suggest that a significant fraction of AALs with v{sub off} < 1500 km s{sup -1} are physically associated with the quasar and its host. AAL quasars also have dust reddening lying between normal quasars and the so-called dust-reddened quasars. We suggest that the unique properties of AAL quasars can be explained if they are the transitional population from heavily dust-reddened quasars to normal quasars in the formation process of quasars and their hosts. This scenario predicts a larger fraction of young bulges, disturbed morphologies, and interactions of AAL quasar hosts compared to normal quasars. The intrinsic link between associated absorbers and quasar hosts opens a new window to probe massive galaxy formation and galactic-scale feedback processes, and provides a crucial test of the evolutionary picture of quasars.

  10. THE DEMOGRAPHICS OF BROAD-LINE QUASARS IN THE MASS-LUMINOSITY PLANE. II. BLACK HOLE MASS AND EDDINGTON RATIO FUNCTIONS

    SciTech Connect

    Kelly, Brandon C.; Shen, Yue

    2013-02-10

    We employ a flexible Bayesian technique to estimate the black hole (BH) mass and Eddington ratio functions for Type 1 (i.e., broad line) quasars from a uniformly selected data set of {approx}58, 000 quasars from the Sloan Digital Sky Survey (SDSS) DR7. We find that the SDSS becomes significantly incomplete at M {sub BH} {approx}< 3 Multiplication-Sign 10{sup 8} M {sub Sun} or L/L {sub Edd} {approx}< 0.07, and that the number densities of Type 1 quasars continue to increase down to these limits. Both the mass and Eddington ratio functions show evidence of downsizing, with the most massive and highest Eddington ratio BHs experiencing Type 1 quasar phases first, although the Eddington ratio number densities are flat at z < 2. We estimate the maximum Eddington ratio of Type 1 quasars in the observable universe to be L/L {sub Edd} {approx} 3. Consistent with our results in Shen and Kelly, we do not find statistical evidence for a so-called sub-Eddington boundary in the mass-luminosity plane of broad-line quasars, and demonstrate that such an apparent boundary in the observed distribution can be caused by selection effect and errors in virial BH mass estimates. Based on the typical Eddington ratio in a given mass bin, we estimate growth times for the BHs in Type 1 quasars and find that they are comparable to or longer than the age of the universe, implying an earlier phase of accelerated (i.e., with higher Eddington ratios) and possibly obscured growth. The large masses probed by our sample imply that most of our BHs reside in what are locally early-type galaxies, and we interpret our results within the context of models of self-regulated BH growth.

  11. Selectivity curves of the capture of mangrove crab (Ucides cordatus) on the northern coast of Brazil using bayesian inference.

    PubMed

    Furtado-Junior, I; Abrunhosa, F A; Holanda, F C A F; Tavares, M C S

    2016-06-01

    Fishing selectivity of the mangrove crab Ucides cordatus in the north coast of Brazil can be defined as the fisherman's ability to capture and select individuals from a certain size or sex (or a combination of these factors) which suggests an empirical selectivity. Considering this hypothesis, we calculated the selectivity curves for males and females crabs using the logit function of the logistic model in the formulation. The Bayesian inference consisted of obtaining the posterior distribution by applying the Markov chain Monte Carlo (MCMC) method to software R using the OpenBUGS, BRugs, and R2WinBUGS libraries. The estimated results of width average carapace selection for males and females compared with previous studies reporting the average width of the carapace of sexual maturity allow us to confirm the hypothesis that most mature individuals do not suffer from fishing pressure; thus, ensuring their sustainability. PMID:26934154

  12. Extreme Red Quasars in SDSS-BOSS

    NASA Astrophysics Data System (ADS)

    Hamann, Fred; Zakamska, Nadia; Paris, Isabelle; Herbst, Hanna; Villforth, Carolin; Alexandroff, Rachael; Ross, Nicholas; Greene, Jenny; Strauss, Michael

    2015-08-01

    Red quasars are believed to mark a critical transition stage of massive galaxy evolution when a blowout of gas and dust truncates the initial starburst and provides our first visible views of a luminous central AGN. Red quasars could therefore have unusual properties associated with a young evolution stage, such as higher accretion rates, higher rates of mergers and interactions, and more common or more powerful outflows capable of driving a galaxy-wide blowout (e.g., compared to normal blue quasars in presumably more evolved galaxy hosts). The recently completed Baryon Oscillation Spectroscopy Survey (BOSS) of SDSS-III has discovered many more faint quasars with higher redshifts and redder colors than any previous large survey. We combine BOSS spectra with SDSS and Wide-Field Infrared Survey Explorer (WISE) photometry of nearly 100,000 quasars to identify and characterize the red quasar population at redshifts >2. We find a number of strong trends with the amount of reddening/obscuration. For example, red quasars are 5 to 8 times more likely to have broad absorption lines and other "intrinsic" absorption lines that identify quasar-driven outflows. Perhaps most interesting is that extreme red quasars (ERQs), selected via rest-frame UV to near-IR colors similar to Dust Obscured Galaxies (DOGs), have uniquely exotic emission line properties that include extreme velocity shifts between lines and the broadest and most blueshifted [OIII] lines yet discovered (with FWHMs reaching >3000 km/s). We will discuss the implications of these results for models of the structure and evolution of quasars and their host galaxy environments.

  13. Automatised selection of load paths to construct reduced-order models in computational damage micromechanics: from dissipation-driven random selection to Bayesian optimization

    NASA Astrophysics Data System (ADS)

    Goury, Olivier; Amsallem, David; Bordas, Stéphane Pierre Alain; Liu, Wing Kam; Kerfriden, Pierre

    2016-08-01

    In this paper, we present new reliable model order reduction strategies for computational micromechanics. The difficulties rely mainly upon the high dimensionality of the parameter space represented by any load path applied onto the representative volume element. We take special care of the challenge of selecting an exhaustive snapshot set. This is treated by first using a random sampling of energy dissipating load paths and then in a more advanced way using Bayesian optimization associated with an interlocked division of the parameter space. Results show that we can insure the selection of an exhaustive snapshot set from which a reliable reduced-order model can be built.

  14. Bayesian inference-based environmental decision support systems for oil spill response strategy selection.

    PubMed

    Davies, Andrew J; Hope, Max J

    2015-07-15

    Contingency plans are essential in guiding the response to marine oil spills. However, they are written before the pollution event occurs so must contain some degree of assumption and prediction and hence may be unsuitable for a real incident when it occurs. The use of Bayesian networks in ecology, environmental management, oil spill contingency planning and post-incident analysis is reviewed and analysed to establish their suitability for use as real-time environmental decision support systems during an oil spill response. It is demonstrated that Bayesian networks are appropriate for facilitating the re-assessment and re-validation of contingency plans following pollutant release, thus helping ensure that the optimum response strategy is adopted. This can minimise the possibility of sub-optimal response strategies causing additional environmental and socioeconomic damage beyond the original pollution event.

  15. Bayesian Methods in Cosmology

    NASA Astrophysics Data System (ADS)

    Hobson, Michael P.; Jaffe, Andrew H.; Liddle, Andrew R.; Mukherjee, Pia; Parkinson, David

    2014-02-01

    Preface; Part I. Methods: 1. Foundations and algorithms John Skilling; 2. Simple applications of Bayesian methods D. S. Sivia and Steve Rawlings; 3. Parameter estimation using Monte Carlo sampling Antony Lewis and Sarah Bridle; 4. Model selection and multi-model interference Andrew R. Liddle, Pia Mukherjee and David Parkinson; 5. Bayesian experimental design and model selection forecasting Roberto Trotta, Martin Kunz, Pia Mukherjee and David Parkinson; 6. Signal separation in cosmology M. P. Hobson, M. A. J. Ashdown and V. Stolyarov; Part II. Applications: 7. Bayesian source extraction M. P. Hobson, Graça Rocha and R. Savage; 8. Flux measurement Daniel Mortlock; 9. Gravitational wave astronomy Neil Cornish; 10. Bayesian analysis of cosmic microwave background data Andrew H. Jaffe; 11. Bayesian multilevel modelling of cosmological populations Thomas J. Loredo and Martin A. Hendry; 12. A Bayesian approach to galaxy evolution studies Stefano Andreon; 13. Photometric redshift estimation: methods and applications Ofer Lahav, Filipe B. Abdalla and Manda Banerji; Index.

  16. Bayesian Methods in Cosmology

    NASA Astrophysics Data System (ADS)

    Hobson, Michael P.; Jaffe, Andrew H.; Liddle, Andrew R.; Mukherjee, Pia; Parkinson, David

    2009-12-01

    Preface; Part I. Methods: 1. Foundations and algorithms John Skilling; 2. Simple applications of Bayesian methods D. S. Sivia and Steve Rawlings; 3. Parameter estimation using Monte Carlo sampling Antony Lewis and Sarah Bridle; 4. Model selection and multi-model interference Andrew R. Liddle, Pia Mukherjee and David Parkinson; 5. Bayesian experimental design and model selection forecasting Roberto Trotta, Martin Kunz, Pia Mukherjee and David Parkinson; 6. Signal separation in cosmology M. P. Hobson, M. A. J. Ashdown and V. Stolyarov; Part II. Applications: 7. Bayesian source extraction M. P. Hobson, Graça Rocha and R. Savage; 8. Flux measurement Daniel Mortlock; 9. Gravitational wave astronomy Neil Cornish; 10. Bayesian analysis of cosmic microwave background data Andrew H. Jaffe; 11. Bayesian multilevel modelling of cosmological populations Thomas J. Loredo and Martin A. Hendry; 12. A Bayesian approach to galaxy evolution studies Stefano Andreon; 13. Photometric redshift estimation: methods and applications Ofer Lahav, Filipe B. Abdalla and Manda Banerji; Index.

  17. THE SUBARU HIGH-z QUASAR SURVEY: DISCOVERY OF FAINT z ∼ 6 QUASARS

    SciTech Connect

    Kashikawa, Nobunari; Furusawa, Hisanori; Niino, Yuu; Ishizaki, Yoshifumi; Onoue, Masafusa; Toshikawa, Jun; Ishikawa, Shogo; Willott, Chris J.; Im, Myungshin; Shimasaku, Kazuhiro; Ouchi, Masami; Hibon, Pascale

    2015-01-01

    We present the discovery of one or two extremely faint z ∼ 6 quasars in 6.5 deg{sup 2} utilizing a unique capability of the wide-field imaging of the Subaru/Suprime-Cam. The quasar selection was made in (i'-z{sub B} ) and (z{sub B} -z{sub R} ) colors, where z{sub B} and z{sub R} are bandpasses with central wavelengths of 8842 Å and 9841 Å, respectively. The color selection can effectively isolate quasars at z ∼ 6 from M/L/T dwarfs without the J-band photometry down to z{sub R} < 24.0, which is 3.5 mag deeper than the Sloan Digital Sky Survey (SDSS). We have selected 17 promising quasar candidates. The follow-up spectroscopy for seven targets identified one apparent quasar at z = 6.156 with M {sub 1450} = –23.10. We also identified one possible quasar at z = 6.041 with a faint continuum of M {sub 1450} = –22.58 and a narrow Lyα emission with HWHM =427 km s{sup –1}, which cannot be distinguished from Lyman α emitters. We derive the quasar luminosity function at z ∼ 6 by combining our faint quasar sample with the bright quasar samples by SDSS and CFHQS. Including our data points invokes a higher number density in the faintest bin of the quasar luminosity function than the previous estimate employed. This suggests a steeper faint-end slope than lower z, though it is yet uncertain based on a small number of spectroscopically identified faint quasars, and several quasar candidates still remain to be diagnosed. The steepening of the quasar luminosity function at the faint end does increase the expected emission rate of the ionizing photon; however, it only changes by a factor of approximately two to six. This was found to still be insufficient for the required photon budget of reionization at z ∼ 6.

  18. An astrophysics data program investigation of a synoptic study of quasar continua

    NASA Technical Reports Server (NTRS)

    Elvis, Martin

    1991-01-01

    A summary of the program is presented. The major product of the program, an atlas of quasar energy distributions, is presented in the appendices along with papers written as a result of this research. The topics covered in the papers include: (1) accurate galactic N(sub h) values toward quasars and active galactic nuclei (AGN); (2) weak bump quasars; (3) millimeter measurements of hard x ray selected active galaxies- implications for the nature of the continuous spectrum; (3) persistence and change in the soft x ray spectrum of the quasar PG1211+143; (4) the soft x ray excess in einstein quasar spectra; and (5) EXOSAT x ray spectra of quasars.

  19. ACCRETION RATES OF RED QUASARS FROM THE HYDROGEN Pβ LINE

    SciTech Connect

    Kim, Dohyeong; Im, Myungshin; Glikman, Eilat; Woo, Jong-Hak; Urrutia, Tanya E-mail: mim@astro.snu.ac.kr

    2015-10-10

    Red quasars are thought to be an intermediate population between merger-driven star-forming galaxies in dust-enshrouded phase and normal quasars. If so, they are expected to have high accretion ratios, but their intrinsic dust extinction hampers reliable determination of Eddington ratios. Here, we compare the accretion rates of 16 red quasars at z ∼ 0.7 to those of normal type 1 quasars at the same redshift range. The red quasars are selected by their red colors in optical through near-infrared (NIR) and radio detection. The accretion rates of the red quasars are derived from the Pβ line in NIR spectra, which is obtained by the SpeX on the Infrared Telescope Facility in order to avoid the effects of dust extinction. We find that the measured Eddington ratios (L{sub bol}/L{sub Edd} ≃ 0.69) of red quasars are significantly higher than those of normal type 1 quasars, which is consistent with a scenario in which red quasars are the intermediate population and the black holes of red quasars grow very rapidly during such a stage.

  20. Similarity of ionized gas nebulae around unobscured and obscured quasars

    NASA Astrophysics Data System (ADS)

    Liu, Guilin; Zakamska, Nadia L.; Greene, Jenny E.

    2014-08-01

    Quasar feedback is suspected to play a key role in the evolution of massive galaxies, by removing or reheating gas in quasar host galaxies and thus limiting the amount of star formation. In this paper, we continue our investigation of quasar-driven winds on galaxy-wide scales. We conduct Gemini Integral Field Unit spectroscopy of a sample of luminous unobscured (type 1) quasars, to determine the morphology and kinematics of ionized gas around these objects, predominantly via observations of the [O III] λ5007 Å emission line. We find that ionized gas nebulae extend out to ˜13 kpc from the quasar, that they are smooth and round, and that their kinematics are inconsistent with gas in dynamical equilibrium with the host galaxy. The observed morphological and kinematic properties are strikingly similar to those of ionized gas around obscured (type 2) quasars with matched [O III] luminosity, with marginal evidence that nebulae around unobscured quasars are slightly more compact. Therefore, in samples of obscured and unobscured quasars carefully matched in [O III] luminosity, we find support for the standard geometry-based unification model of active galactic nuclei, in that the intrinsic properties of the quasars, of their hosts and of their ionized gas appear to be very similar. Given the apparent ubiquity of extended ionized regions, we are forced to conclude that either the quasar is at least partially illuminating pre-existing gas or that both samples of quasars are seen during advanced stages of quasar feedback. In the latter case, we may be biased by our [O III]-based selection against quasars in the early `blow-out' phase, for example due to dust obscuration.

  1. Bayesian model selection framework for identifying growth patterns in filamentous fungi.

    PubMed

    Lin, Xiao; Terejanu, Gabriel; Shrestha, Sajan; Banerjee, Sourav; Chanda, Anindya

    2016-06-01

    This paper describes a rigorous methodology for quantification of model errors in fungal growth models. This is essential to choose the model that best describes the data and guide modeling efforts. Mathematical modeling of growth of filamentous fungi is necessary in fungal biology for gaining systems level understanding on hyphal and colony behaviors in different environments. A critical challenge in the development of these mathematical models arises from the indeterminate nature of their colony architecture, which is a result of processing diverse intracellular signals induced in response to a heterogeneous set of physical and nutritional factors. There exists a practical gap in connecting fungal growth models with measurement data. Here, we address this gap by introducing the first unified computational framework based on Bayesian inference that can quantify individual model errors and rank the statistical models based on their descriptive power against data. We show that this Bayesian model comparison is just a natural formalization of Occam׳s razor. The application of this framework is discussed in comparing three models in the context of synthetic data generated from a known true fungal growth model. This framework of model comparison achieves a trade-off between data fitness and model complexity and the quantified model error not only helps in calibrating and comparing the models, but also in making better predictions and guiding model refinements. PMID:27000772

  2. How Reliable is Bayesian Model Averaging Under Noisy Data? Statistical Assessment and Implications for Robust Model Selection

    NASA Astrophysics Data System (ADS)

    Schöniger, Anneli; Wöhling, Thomas; Nowak, Wolfgang

    2014-05-01

    Bayesian model averaging ranks the predictive capabilities of alternative conceptual models based on Bayes' theorem. The individual models are weighted with their posterior probability to be the best one in the considered set of models. Finally, their predictions are combined into a robust weighted average and the predictive uncertainty can be quantified. This rigorous procedure does, however, not yet account for possible instabilities due to measurement noise in the calibration data set. This is a major drawback, since posterior model weights may suffer a lack of robustness related to the uncertainty in noisy data, which may compromise the reliability of model ranking. We present a new statistical concept to account for measurement noise as source of uncertainty for the weights in Bayesian model averaging. Our suggested upgrade reflects the limited information content of data for the purpose of model selection. It allows us to assess the significance of the determined posterior model weights, the confidence in model selection, and the accuracy of the quantified predictive uncertainty. Our approach rests on a brute-force Monte Carlo framework. We determine the robustness of model weights against measurement noise by repeatedly perturbing the observed data with random realizations of measurement error. Then, we analyze the induced variability in posterior model weights and introduce this "weighting variance" as an additional term into the overall prediction uncertainty analysis scheme. We further determine the theoretical upper limit in performance of the model set which is imposed by measurement noise. As an extension to the merely relative model ranking, this analysis provides a measure of absolute model performance. To finally decide, whether better data or longer time series are needed to ensure a robust basis for model selection, we resample the measurement time series and assess the convergence of model weights for increasing time series length. We illustrate

  3. Spectral Properties of X-ray-Emitting Quasars

    NASA Astrophysics Data System (ADS)

    Morgan, W. A., Jr.

    1996-12-01

    I present spectral indices obtained from 112 X-ray-selected and fully optically-identified quasars in four sky fields in the southern hemisphere, detected by the Rosat Position Sensitive Proportional Counters. These fields were originally studied by Boyle et al. (1990) for the ultraviolet-excess properties of objects in the fields; only 47 of the quasars in the field were listed in Boyle et al. I determine the quasars' power-law spectral index alpha_E with three different methods: spectral ``stacking'', hardness ratios, and direct fitting. Both spectral stacking and the hardness ratio methods are used because several of the quasars were too dim to reliably calculate spectral indices individually. The spectral stacking method, which involves co-adding quasar spectra energy bins, shows a definite change in quasar spectral index with redshift.

  4. Joint high-dimensional Bayesian variable and covariance selection with an application to eQTL analysis.

    PubMed

    Bhadra, Anindya; Mallick, Bani K

    2013-06-01

    We describe a Bayesian technique to (a) perform a sparse joint selection of significant predictor variables and significant inverse covariance matrix elements of the response variables in a high-dimensional linear Gaussian sparse seemingly unrelated regression (SSUR) setting and (b) perform an association analysis between the high-dimensional sets of predictors and responses in such a setting. To search the high-dimensional model space, where both the number of predictors and the number of possibly correlated responses can be larger than the sample size, we demonstrate that a marginalization-based collapsed Gibbs sampler, in combination with spike and slab type of priors, offers a computationally feasible and efficient solution. As an example, we apply our method to an expression quantitative trait loci (eQTL) analysis on publicly available single nucleotide polymorphism (SNP) and gene expression data for humans where the primary interest lies in finding the significant associations between the sets of SNPs and possibly correlated genetic transcripts. Our method also allows for inference on the sparse interaction network of the transcripts (response variables) after accounting for the effect of the SNPs (predictor variables). We exploit properties of Gaussian graphical models to make statements concerning conditional independence of the responses. Our method compares favorably to existing Bayesian approaches developed for this purpose. PMID:23607608

  5. Double Lobed Radio Quasars from the Sloan Digital Sky Survey

    SciTech Connect

    de Vries, W H; Becker, R H; White, R L

    2005-11-10

    We have combined a sample of 44 984 quasars, selected from the Sloan Digital Sky Survey (SDSS) Data Release 3, with the FIRST radio survey. Using a novel technique where the optical quasar position is matched to the complete radio environment within 450'', we are able to characterize the radio morphological make-up of what is essentially an optically selected quasar sample, regardless of whether the quasar (nucleus) itself has been detected in the radio. About 10% of the quasar population have radio cores brighter than 0.75 mJy at 1.4 GHz, and 1.7% have double lobed FR2-like radio morphologies. About 75% of the FR2 sources have a radio core (> 0.75mJy). A significant fraction ({approx}40%) of the FR2 quasars are bent by more than 10 degrees, indicating either interactions of the radio plasma with the ICM or IGM. We found no evidence for correlations with redshift among our FR2 quasars: radio lobe flux densities and radio source diameters of the quasars have similar distributions at low (mean 0.77) and high (mean 2.09) redshifts. Using a smaller high reliability FR2 sample of 422 quasars and two comparison samples of radio-quiet and non-FR2 radio-loud quasars, matched in their redshift distributions, we constructed composite optical spectra from the SDSS spectroscopic data. Based on these spectra we can conclude that the FR2 quasars have stronger high-ionization emission lines compared to both the radio quiet and non-FR2 radio loud sources. This is consistent with the notion that the emission lines are brightened by ongoing shock ionization of ambient gas in the quasar host as the radio source expands.

  6. Catalog of candidates for quasars at 3 < z < 5.5 selected among X-Ray sources from the 3XMM-DR4 survey of the XMM-Newton observatory

    NASA Astrophysics Data System (ADS)

    Khorunzhev, G. A.; Burenin, R. A.; Meshcheryakov, A. V.; Sazonov, S. Yu.

    2016-05-01

    We have compiled a catalog of 903 candidates for type 1 quasars at redshifts 3 < z < 5.5 selected among the X-ray sources of the "serendipitous" XMM-Newton survey presented in the 3XMMDR4 catalog (the median X-ray flux is ≈5 × 10-15 erg s-1 cm-2 in the 0.5-2 keV energy band) and located at high Galactic latitudes | b| > 20° in Sloan Digital Sky Survey (SDSS) fields with a total area of about 300 deg2. Photometric SDSS data as well infrared 2MASS and WISE data were used to select the objects. We selected the point sources from the photometric SDSS catalog with a magnitude error δ mz' < 0.2 and a color i' - z' < 0.6 (to first eliminate the M-type stars). For the selected sources, we have calculated the dependences χ2( z) for various spectral templates from the library that we compiled for these purposes using the EAZY software. Based on these data, we have rejected the objects whose spectral energy distributions are better described by the templates of stars at z = 0 and obtained a sample of quasars with photometric redshift estimates 2.75 < z phot < 5.5. The selection completeness of known quasars at z spec > 3 in the investigated fields is shown to be about 80%. The normalized median absolute deviation (Δ z = | z spec - z phot|) is σ Δ z /(1+ z spec) = 0.07, while the outlier fraction is η = 9% when Δ z/(1 + z cпek.) > 0.2. The number of objects per unit area in our sample exceeds the number of quasars in the spectroscopic SDSS sample at the same redshifts approximately by a factor of 1.5. The subsequent spectroscopic testing of the redshifts of our selected candidates for quasars at 3 < z < 5.5 will allow the purity of this sample to be estimated more accurately.

  7. Bayesian Selection of Markov Models for Symbol Sequences: Application to Microsaccadic Eye Movements

    PubMed Central

    Bettenbühl, Mario; Rusconi, Marco; Engbert, Ralf; Holschneider, Matthias

    2012-01-01

    Complex biological dynamics often generate sequences of discrete events which can be described as a Markov process. The order of the underlying Markovian stochastic process is fundamental for characterizing statistical dependencies within sequences. As an example for this class of biological systems, we investigate the Markov order of sequences of microsaccadic eye movements from human observers. We calculate the integrated likelihood of a given sequence for various orders of the Markov process and use this in a Bayesian framework for statistical inference on the Markov order. Our analysis shows that data from most participants are best explained by a first-order Markov process. This is compatible with recent findings of a statistical coupling of subsequent microsaccade orientations. Our method might prove to be useful for a broad class of biological systems. PMID:22970124

  8. Model Selection on Solid Ground: Comparison of Techniques to Evaluate Bayesian Evidence

    NASA Astrophysics Data System (ADS)

    Nowak, W.; Schöniger, A.; Samaniego, L. E.; Wöhling, T.

    2014-12-01

    Bayesian model averaging (BMA) ranks and averages a set of plausible, competing models, based on their fit to available data and based on their model complexity. BMA requires determining Bayesian model evidence (BME), which is the likelihood of the observed data integrated over each model parameter space. The BME integral is highly challenging, because it is as high-dimensional as the number of model parameters. Three classes of techniques are available to evaluate BME, each with its own challenges and limitations: Exact analytical solutions are fast, but restricted by strong assumptions. Brute-force numerical evaluation is accurate, but quickly becomes computationally unfeasible. Approximations known as information criteria (AIC, BIC, KIC) are known to yield contradicting results in model ranking. We conduct a systematic comparison of available techniques to evaluate BME, including a list of numerical schemes. We highlight their common features and differences, and investigate their computational effort and accuracy. For the latter, we investigate the impact of (a) data set size and (b) overlap between the prior and the likelihood. We use a synthetic example with an exact analytical solution (as a first-time validation against a true solution), and a real-world hydrological application, where we use a brute-force Monte-Carlo method as benchmark solution. Our results show that all IC differ drastically in their quality of approximation. From all IC, the KIC evaluated at the MAP performs best, but in general none of them is satisfying for non-linear model problems. Since they share the goodness-of-fit term, the observed differences imply an inaccurate penalty for model complexity. Our findings indicate that the choice of approximation method substantially influences the accuracy of the BME estimate and, consequently, the final model ranking and BMA results.

  9. An evaluation of Bayesian techniques for controlling model complexity and selecting inputs in a neural network for short-term load forecasting.

    PubMed

    Hippert, Henrique S; Taylor, James W

    2010-04-01

    Artificial neural networks have frequently been proposed for electricity load forecasting because of their capabilities for the nonlinear modelling of large multivariate data sets. Modelling with neural networks is not an easy task though; two of the main challenges are defining the appropriate level of model complexity, and choosing the input variables. This paper evaluates techniques for automatic neural network modelling within a Bayesian framework, as applied to six samples containing daily load and weather data for four different countries. We analyse input selection as carried out by the Bayesian 'automatic relevance determination', and the usefulness of the Bayesian 'evidence' for the selection of the best structure (in terms of number of neurones), as compared to methods based on cross-validation.

  10. Study of quasar variability

    NASA Astrophysics Data System (ADS)

    Jerke, Jonathan Lee

    The Palomar-QUEST Variability Survey has been completed. This thesis has analyzed the data set with the goal of determining the variability of a large sample of quasars. We construct light curves for each individual quasar. We interpret the light curves in terms of a structure function analysis. A slope is extracted from the scaling of the structure function to measure the power law of the quasar optical variability, taking the power spectral density to behave as a power law of the frequency of variation, f-alpha. Monte carlo simulations are used to estimate the errors on the model and the final data quality. With these estimates, individual quasars are assigned a chi2 value and nearly every event has a reduced chi 2 less than 10. The first 100 light curves and structure functions with errors are shown in the Appendix. We have shown that the final distribution of power law coefficients alpha of 1944 quasars is inconsistent with a model with a simple value of alpha. Several models with different alpha are required to explain the behavior of the sample. We find that quasars are less variable on all time scales for increasing luminosity. We also find that the quasars with black hole masses below 10 8 show a lower power law then the average. This means less massive quasars are less variable at long time scales.

  11. Robust Bayesian Fluorescence Lifetime Estimation, Decay Model Selection and Instrument Response Determination for Low-Intensity FLIM Imaging

    PubMed Central

    Rowley, Mark I.; Coolen, Anthonius C. C.; Vojnovic, Borivoj; Barber, Paul R.

    2016-01-01

    We present novel Bayesian methods for the analysis of exponential decay data that exploit the evidence carried by every detected decay event and enables robust extension to advanced processing. Our algorithms are presented in the context of fluorescence lifetime imaging microscopy (FLIM) and particular attention has been paid to model the time-domain system (based on time-correlated single photon counting) with unprecedented accuracy. We present estimates of decay parameters for mono- and bi-exponential systems, offering up to a factor of two improvement in accuracy compared to previous popular techniques. Results of the analysis of synthetic and experimental data are presented, and areas where the superior precision of our techniques can be exploited in Förster Resonance Energy Transfer (FRET) experiments are described. Furthermore, we demonstrate two advanced processing methods: decay model selection to choose between differing models such as mono- and bi-exponential, and the simultaneous estimation of instrument and decay parameters. PMID:27355322

  12. Action selection performance of a reconfigurable basal ganglia inspired model with Hebbian-Bayesian Go-NoGo connectivity.

    PubMed

    Berthet, Pierre; Hellgren-Kotaleski, Jeanette; Lansner, Anders

    2012-01-01

    Several studies have shown a strong involvement of the basal ganglia (BG) in action selection and dopamine dependent learning. The dopaminergic signal to striatum, the input stage of the BG, has been commonly described as coding a reward prediction error (RPE), i.e., the difference between the predicted and actual reward. The RPE has been hypothesized to be critical in the modulation of the synaptic plasticity in cortico-striatal synapses in the direct and indirect pathway. We developed an abstract computational model of the BG, with a dual pathway structure functionally corresponding to the direct and indirect pathways, and compared its behavior to biological data as well as other reinforcement learning models. The computations in our model are inspired by Bayesian inference, and the synaptic plasticity changes depend on a three factor Hebbian-Bayesian learning rule based on co-activation of pre- and post-synaptic units and on the value of the RPE. The model builds on a modified Actor-Critic architecture and implements the direct (Go) and the indirect (NoGo) pathway, as well as the reward prediction (RP) system, acting in a complementary fashion. We investigated the performance of the model system when different configurations of the Go, NoGo, and RP system were utilized, e.g., using only the Go, NoGo, or RP system, or combinations of those. Learning performance was investigated in several types of learning paradigms, such as learning-relearning, successive learning, stochastic learning, reversal learning and a two-choice task. The RPE and the activity of the model during learning were similar to monkey electrophysiological and behavioral data. Our results, however, show that there is not a unique best way to configure this BG model to handle well all the learning paradigms tested. We thus suggest that an agent might dynamically configure its action selection mode, possibly depending on task characteristics and also on how much time is available. PMID:23060764

  13. A spatio-temporal nonparametric Bayesian variable selection model of fMRI data for clustering correlated time courses.

    PubMed

    Zhang, Linlin; Guindani, Michele; Versace, Francesco; Vannucci, Marina

    2014-07-15

    In this paper we present a novel wavelet-based Bayesian nonparametric regression model for the analysis of functional magnetic resonance imaging (fMRI) data. Our goal is to provide a joint analytical framework that allows to detect regions of the brain which exhibit neuronal activity in response to a stimulus and, simultaneously, infer the association, or clustering, of spatially remote voxels that exhibit fMRI time series with similar characteristics. We start by modeling the data with a hemodynamic response function (HRF) with a voxel-dependent shape parameter. We detect regions of the brain activated in response to a given stimulus by using mixture priors with a spike at zero on the coefficients of the regression model. We account for the complex spatial correlation structure of the brain by using a Markov random field (MRF) prior on the parameters guiding the selection of the activated voxels, therefore capturing correlation among nearby voxels. In order to infer association of the voxel time courses, we assume correlated errors, in particular long memory, and exploit the whitening properties of discrete wavelet transforms. Furthermore, we achieve clustering of the voxels by imposing a Dirichlet process (DP) prior on the parameters of the long memory process. For inference, we use Markov Chain Monte Carlo (MCMC) sampling techniques that combine Metropolis-Hastings schemes employed in Bayesian variable selection with sampling algorithms for nonparametric DP models. We explore the performance of the proposed model on simulated data, with both block- and event-related design, and on real fMRI data. PMID:24650600

  14. A Spatio-Temporal Nonparametric Bayesian Variable Selection Model of fMRI Data for Clustering Correlated Time Courses

    PubMed Central

    Zhang, Linlin; Guindani, Michele; Versace, Francesco; Vannucci, Marina

    2014-01-01

    In this paper we present a novel wavelet-based Bayesian nonparametric regression model for the analysis of functional magnetic resonance imaging (fMRI) data. Our goal is to provide a joint analytical framework that allows to detect regions of the brain which exhibit neuronal activity in response to a stimulus and, simultaneously, infer the association, or clustering, of spatially remote voxels that exhibit fMRI time series with similar characteristics. We start by modeling the data with an hemodynamic response function (HRF) with a voxel-dependent shape parameter. We detect regions of the brain activated in response to a given stimulus by using mixture priors with a spike at zero on the coefficients of the regression model. We account for the complex spatial correlation structure of the brain by using a Markov Random Field (MRF) prior on the parameters guiding the selection of the activated voxels, therefore capturing correlation among nearby voxels. In order to infer association of the voxel time courses, we assume correlated errors, in particular long memory, and exploit the whitening properties of discrete wavelet transforms. Furthermore, we achieve clustering of the voxels by imposing a Dirichlet Process (DP) prior on the parameters of the long memory process. For inference, we use Markov Chain Monte Carlo (MCMC) sampling techniques that combine Metropolis- Hastings schemes employed in Bayesian variable selection with sampling algorithms for nonparametric DP models. We explore the performance of the proposed model on simulated data, with both block- and event-related design, and on real fMRI data. PMID:24650600

  15. THE z = 5 QUASAR LUMINOSITY FUNCTION FROM SDSS STRIPE 82

    SciTech Connect

    McGreer, Ian D.; Fan Xiaohui; Jiang Linhua; Richards, Gordon T.; Strauss, Michael A.; Ross, Nicholas P.; White, Martin; Shen Yue; Schneider, Donald P.; Brandt, W. Niel; Myers, Adam D.; DeGraf, Colin; Glikman, Eilat; Ge Jian; Streblyanska, Alina

    2013-05-10

    We present a measurement of the Type I quasar luminosity function at z = 5 using a large sample of spectroscopically confirmed quasars selected from optical imaging data. We measure the bright end (M{sub 1450} < -26) with Sloan Digital Sky Survey (SDSS) data covering {approx}6000 deg{sup 2}, then extend to lower luminosities (M{sub 1450} < -24) with newly discovered, faint z {approx} 5 quasars selected from 235 deg{sup 2} of deep, coadded imaging in the SDSS Stripe 82 region (the celestial equator in the Southern Galactic Cap). The faint sample includes 14 quasars with spectra obtained as ancillary science targets in the SDSS-III Baryon Oscillation Spectroscopic Survey, and 59 quasars observed at the MMT and Magellan telescopes. We construct a well-defined sample of 4.7 < z < 5.1 quasars that is highly complete, with 73 spectroscopic identifications out of 92 candidates. Our color selection method is also highly efficient: of the 73 spectra obtained, 71 are high-redshift quasars. These observations reach below the break in the luminosity function (M{sub 1450}{sup *}{approx}-27). The bright-end slope is steep ({beta} {approx}< -4), with a constraint of {beta} < -3.1 at 95% confidence. The break luminosity appears to evolve strongly at high redshift, providing an explanation for the flattening of the bright-end slope reported previously. We find a factor of {approx}2 greater decrease in the number density of luminous quasars (M{sub 1450} < -26) from z = 5 to z = 6 than from z = 4 to z = 5, suggesting a more rapid decline in quasar activity at high redshift than found in previous surveys. Our model for the quasar luminosity function predicts that quasars generate {approx}30% of the ionizing photons required to keep hydrogen in the universe ionized at z = 5.

  16. Covering factors of the dusty obscurers in radio-loud and radio-quiet quasars

    NASA Astrophysics Data System (ADS)

    Gupta, Maitrayee; Sikora, Marek; Nalewajko, Krzysztof

    2016-09-01

    We compare covering factors of circumnuclear dusty obscurers in radio-loud and radio-quiet quasars. The radio-loud quasars are represented by a sample of FR II quasars obtained by cross-matching a catalog of the FR II radio sources selected by van Velzen et al. with the SDSS DR7 catalog of quasars. Covering factors of FR II quasars are compared with covering factors of the radio-quiet quasars matched with them in redshift, black hole mass, and Eddington-ratio. We found that covering factors, proxied by the infrared-to-bolometric luminosity ratio, are on average slightly smaller in FR II quasars than in radio-quiet quasars, however, this difference is statistically significant only for the highest Eddington ratios. For both samples, no statistically significant dependence of a median covering factor on Eddington ratio, black hole mass, nor redshift can be claimed.

  17. RX J1759.4+6638: An x-ray selected quasars at a redshift of 4.320

    NASA Technical Reports Server (NTRS)

    Henry, J. P.; Gioia, I. M.; Boehringer, H.; Bower, R. G.; Briel, U. G.; Hasinger, G. H.; Aragon-Salamanca, A.; Castander, F. J.; Ellis, R. S.; Huchra, J. P.

    1994-01-01

    We report the discovery of an x-ray selected Quasi-Stellar Objects (QSO) at a redshift of 4.320 +/- 0.005. This is the most distant x-ray selected object known, and it is the eighth most distant QSO known. The properties of this QSO are very similar to other QSOs at redshifts greater than 4. The x-ray discovery of this object, and that of high redshift clusters of galaxies, shows that present x-ray surveys are reaching depths competitive with other methods.

  18. Quasar Dust Factories.

    NASA Astrophysics Data System (ADS)

    Marengo, Massimo; Elvis, Martin; Karovska, Margarita

    We show that quasars are naturally copious producers of dust, assuming only that the quasar broad emission lines (BELs) are produced by gas clouds that are part of an outflowing wind. These BEL clouds have large initial densities (ne ˜109 - 1011 cm-3) so that as they expand quasi-adiabatically they cool from an initial T = 104 K to a dust-capable T = 103 K, and reduce their pressures from ˜0.1 dyn cm-2 to ˜ 10-3 -10-5 dyn cm-2.. This places the expanded BEL clouds in the (T,P) dust forming regime of late-type giants extended atmospheres, both static and pulsing. The result applies whether the clouds have C/O abundance ratio greater or lower than 1. Photo-destruction of the grains by the quasar UV/X-ray continuum is not important, as the BEL clouds reach these conditions several parsecs from the quasar nucleus, well below the dust evaporation temperature. This result offers a new insight for the strong link between quasars and dust, and for the heavy obscuration around many quasars. It also introduces a new means of forming dust at early cosmological times, and a direct mechanism for the injection of such dust in the intergalactic medium. Since dust at high z is found only by observing quasars, our result allows far less dust to be present at early epochs, since dust only need be present where a quasar is, rather than the quasar illuminating pre-existing dust which would then need to be present in all galaxies at high z. See astro-ph/0202002 or ApJ 576, L107 (2002).

  19. Bayesian Probability Theory

    NASA Astrophysics Data System (ADS)

    von der Linden, Wolfgang; Dose, Volker; von Toussaint, Udo

    2014-06-01

    Preface; Part I. Introduction: 1. The meaning of probability; 2. Basic definitions; 3. Bayesian inference; 4. Combinatrics; 5. Random walks; 6. Limit theorems; 7. Continuous distributions; 8. The central limit theorem; 9. Poisson processes and waiting times; Part II. Assigning Probabilities: 10. Transformation invariance; 11. Maximum entropy; 12. Qualified maximum entropy; 13. Global smoothness; Part III. Parameter Estimation: 14. Bayesian parameter estimation; 15. Frequentist parameter estimation; 16. The Cramer-Rao inequality; Part IV. Testing Hypotheses: 17. The Bayesian way; 18. The frequentist way; 19. Sampling distributions; 20. Bayesian vs frequentist hypothesis tests; Part V. Real World Applications: 21. Regression; 22. Inconsistent data; 23. Unrecognized signal contributions; 24. Change point problems; 25. Function estimation; 26. Integral equations; 27. Model selection; 28. Bayesian experimental design; Part VI. Probabilistic Numerical Techniques: 29. Numerical integration; 30. Monte Carlo methods; 31. Nested sampling; Appendixes; References; Index.

  20. Selecton 2007: advanced models for detecting positive and purifying selection using a Bayesian inference approach.

    PubMed

    Stern, Adi; Doron-Faigenboim, Adi; Erez, Elana; Martz, Eric; Bacharach, Eran; Pupko, Tal

    2007-07-01

    Biologically significant sites in a protein may be identified by contrasting the rates of synonymous (K(s)) and non-synonymous (K(a)) substitutions. This enables the inference of site-specific positive Darwinian selection and purifying selection. We present here Selecton version 2.2 (http://selecton.bioinfo.tau.ac.il), a web server which automatically calculates the ratio between K(a) and K(s) (omega) at each site of the protein. This ratio is graphically displayed on each site using a color-coding scheme, indicating either positive selection, purifying selection or lack of selection. Selecton implements an assembly of different evolutionary models, which allow for statistical testing of the hypothesis that a protein has undergone positive selection. Specifically, the recently developed mechanistic-empirical model is introduced, which takes into account the physicochemical properties of amino acids. Advanced options were introduced to allow maximal fine tuning of the server to the user's specific needs, including calculation of statistical support of the omega values, an advanced graphic display of the protein's 3-dimensional structure, use of different genetic codes and inputting of a pre-built phylogenetic tree. Selecton version 2.2 is an effective, user-friendly and freely available web server which implements up-to-date methods for computing site-specific selection forces, and the visualization of these forces on the protein's sequence and structure.

  1. Disentangling the formation of contrasting tree-line physiognomies combining model selection and Bayesian parameterization for simulation models.

    PubMed

    Martínez, Isabel; Wiegand, Thorsten; Camarero, J Julio; Batllori, Enric; Gutiérrez, Emilia

    2011-05-01

    Alpine tree-line ecotones are characterized by marked changes at small spatial scales that may result in a variety of physiognomies. A set of alternative individual-based models was tested with data from four contrasting Pinus uncinata ecotones in the central Spanish Pyrenees to reveal the minimal subset of processes required for tree-line formation. A Bayesian approach combined with Markov chain Monte Carlo methods was employed to obtain the posterior distribution of model parameters, allowing the use of model selection procedures. The main features of real tree lines emerged only in models considering nonlinear responses in individual rates of growth or mortality with respect to the altitudinal gradient. Variation in tree-line physiognomy reflected mainly changes in the relative importance of these nonlinear responses, while other processes, such as dispersal limitation and facilitation, played a secondary role. Different nonlinear responses also determined the presence or absence of krummholz, in agreement with recent findings highlighting a different response of diffuse and abrupt or krummholz tree lines to climate change. The method presented here can be widely applied in individual-based simulation models and will turn model selection and evaluation in this type of models into a more transparent, effective, and efficient exercise.

  2. How to avoid mismodelling in GLM-based fMRI data analysis: cross-validated Bayesian model selection.

    PubMed

    Soch, Joram; Haynes, John-Dylan; Allefeld, Carsten

    2016-11-01

    Voxel-wise general linear models (GLMs) are a standard approach for analyzing functional magnetic resonance imaging (fMRI) data. An advantage of GLMs is that they are flexible and can be adapted to the requirements of many different data sets. However, the specification of first-level GLMs leaves the researcher with many degrees of freedom which is problematic given recent efforts to ensure robust and reproducible fMRI data analysis. Formal model comparisons that allow a systematic assessment of GLMs are only rarely performed. On the one hand, too simple models may underfit data and leave real effects undiscovered. On the other hand, too complex models might overfit data and also reduce statistical power. Here we present a systematic approach termed cross-validated Bayesian model selection (cvBMS) that allows to decide which GLM best describes a given fMRI data set. Importantly, our approach allows for non-nested model comparison, i.e. comparing more than two models that do not just differ by adding one or more regressors. It also allows for spatially heterogeneous modelling, i.e. using different models for different parts of the brain. We validate our method using simulated data and demonstrate potential applications to empirical data. The increased use of model comparison and model selection should increase the reliability of GLM results and reproducibility of fMRI studies.

  3. Quasars: A Progress Report.

    ERIC Educational Resources Information Center

    Weedman, Daniel

    1988-01-01

    Reports on some of the discoveries over the last quarter century regarding quasars including spectra and energy sources, formation and evolution, and cosmological probes. Describes some of the fundamental mysteries that remain. (CW)

  4. High Redshift Quasars

    NASA Technical Reports Server (NTRS)

    Elvis, Martin S.

    1996-01-01

    The report for this period includes three papers: 'Associated Absorption at Low and High Redshift'; 'Strong X-ray Absorption in a Broad Absorption Line Quasar: PHL5200'; and 'ASCA and ROSAT X-ray Spectra of High-Redshift Radio-Loud Quasars'. The first gives examples from both low and high redshift for combining information on absorbing material in active galactic nuclei from both x-ray and the UV. The second presents ASCA observations of the z = 1.98 prototype broad absorption line quasar (BALQSO): PHL 5200, detected with both the solid-state imaging spectrometers and the gas imaging spectometers. The third paper presents results on the x-ray properties of 9 high-redshift radio-loud quasars observed by ASCA and ROSAT, including ASCA observations of S5 0014+81 (z = 3.38) and S5 0836+71 (z = 2.17) and ROSAT observations of PKS 2126-158.

  5. OBSCURATION BY GAS AND DUST IN LUMINOUS QUASARS

    SciTech Connect

    Usman, S. M.; Murray, S. S.; Hickox, R. C.; Brodwin, M.

    2014-06-10

    We explore the connection between absorption by neutral gas and extinction by dust in mid-infrared (IR) selected luminous quasars. We use a sample of 33 quasars at redshifts 0.7 < z ≲ 3 in the 9 deg{sup 2} Boötes multiwavelength survey field that are selected using Spitzer Space Telescope Infrared Array Camera colors and are well-detected as luminous X-ray sources (with >150 counts) in Chandra observations. We divide the quasars into dust-obscured and unobscured samples based on their optical to mid-IR color, and measure the neutral hydrogen column density N {sub H} through fitting of the X-ray spectra. We find that all subsets of quasars have consistent power law photon indices Γ ≈ 1.9 that are uncorrelated with N {sub H}. We classify the quasars as gas-absorbed or gas-unabsorbed if N {sub H} > 10{sup 22} cm{sup –2} or N {sub H} < 10{sup 22} cm{sup –2}, respectively. Of 24 dust-unobscured quasars in the sample, only one shows clear evidence for significant intrinsic N {sub H}, while 22 have column densities consistent with N {sub H} < 10{sup 22} cm{sup –2}. In contrast, of the nine dust-obscured quasars, six show evidence for intrinsic gas absorption, and three are consistent with N {sub H} < 10{sup 22} cm{sup –2}. We conclude that dust extinction in IR-selected quasars is strongly correlated with significant gas absorption as determined through X-ray spectral fitting. These results suggest that obscuring gas and dust in quasars are generally co-spatial, and confirm the reliability of simple mid-IR and optical photometric techniques for separating quasars based on obscuration.

  6. Quasars and gravitational lenses.

    PubMed

    Turner, E L

    1984-03-23

    Despite the expenditure of large amounts of telescope time and other resources, most of the fundamental questions concerning quasi-stellar objects (quasars) remain unanswered. A complex phenomenology of radio, infrared, optical, and x-ray properties has accumulated but has not yielded even a satisfactory classification system. The large red shifts (distances) of quasars make them very valuable tools for studying cosmology and the properties of intervening matter in the Universe through observations of absorption lines and gravitational lenses.

  7. Infrared/optical energy distributions of high redshifted quasars

    NASA Technical Reports Server (NTRS)

    Soifer, B. T.; Neugebauer, G.; Oke, J. B.; Matthews, K.; Lacy, J. H.

    1982-01-01

    Measurements at 1.2, 1.6 and 2.2 microns were combined with visual spectrophotometry of 21 quasars having redshifts z or = 2.66. The primary result is that the rest frame visual/ultraviolet continua of the high redshift quasars are well described by a sum of a power law continuum with slope of approximately -0.4 and a 3000 A bump. The rest frame visual/ultraviolet continua of these quasars are quite similar to that of 3C273, the archetype of low redshift quasars. There does not appear to be any visual/ultraviolet properties distinguishing high redshift quasars selected via visual or radio techniques.

  8. Testing the unified model of Active Galactic Nuclei in X-ray selected type 1 and type 2 quasars

    NASA Astrophysics Data System (ADS)

    Mateos, S.; Alonso-Herrero, A.; Carrera, F.

    2014-07-01

    We have investigated whether the dusty tori invoked in the standard orientation-based unified scheme of Active Galactic Nuclei (AGN) is valid for all AGN types at both low and high luminosities. We used the Bright Ultra-hard XMM-Newton Survey (BUXS), one of the largest flux-limited samples of bright AGN selected above 4.5 keV with XMM-Newton, and the Wide-field Infrared Survey Explorer (WISE). BUXS includes 255 AGN detected over 44 deg2 of which to date 161 are identified as type 1 AGN and 89 as type 2 AGN and 98% are detected with WISE. We determined the distribution of covering factors of the obscuring region in X-ray type 1 and type 2 AGN by computing the AGN power re-processed into the IR (apparent covering factors) and the torus geometrical covering factor (i.e. the relative fraction of obscured AGN) using the clumpy torus models of Nenkova et al. We have also investigated whether our results favor the so-called receding torus scenario. Finally, I will discuss the possibility of using the spectral energy distributions of the sources in the 3XMM-DR4 catalogue, produced by the "Astronomical Resource Cross-matching for High Energy Studies" (ARCHES) project, to extend such studies over a broader range of AGN parameters.

  9. UNDERSTANDING THE AGN-HOST CONNECTION IN BROAD Mg II EMISSION-SELECTED AGN-HOST HYBRID QUASARS

    SciTech Connect

    Wang, J.; Wei, J. Y.

    2009-05-01

    We study the issue of active galactic nucleus (AGN)-host connection in intermediate-z (1.2>z > 0.4) galaxies with hybrid spectra (hybrid QSOs for short). The observed spectra redward of the Balmer limit are dominated by starlight, and the spectra at the blue end by both an AGN continuum and an Mg II broad emission line. This unique property allows us to examine both an AGN and its host galaxy in an individual galaxy simultaneously. First, 15 hybrid QSOs are selected from the Sloan Digital Sky Survey (SDSS) Data Release 6. The spectra are then analyzed in detail for three objects: SDSS J162446.49+461946.7, SDSS J102633.32+103443.8, and SDSS J090036.44+381353.0. Our spectral analysis shows that the current star formation activities are strongly suppressed, and that the latest burst ages range from {approx}400 Myr to 1 Gyr. Based on the Mg II black hole masses, the three hybrid QSOs are consistent with the D{sub n} (4000) - L/L {sub Edd} sequence that was previously established in local AGNs. The three hybrid QSOs are located in the middle range of the sequence, which implies that the hybrid QSOs are at the transition stage not only from young to old AGNs, but also from a host-dominated phase to an AGN-dominated phase.

  10. SDSS J094604.90+183541.8: A GRAVITATIONALLY LENSED QUASAR AT z = 4.8

    SciTech Connect

    McGreer, Ian D.; Fan Xiaohui; Bian Fuyan; Farnsworth, Kara; Hall, Patrick B.; Inada, Naohisa; Oguri, Masamune; Strauss, Michael A.; Schneider, Donald P.

    2010-08-15

    We report the discovery of a gravitationally lensed quasar identified serendipitously in the Sloan Digital Sky Survey (SDSS). The object, SDSS J094604.90+183541.8, was initially targeted for spectroscopy as a luminous red galaxy, but the SDSS spectrum has the features of both a z = 0.388 galaxy and a z = 4.8 quasar. We have obtained additional imaging that resolves the system into two quasar images separated by 3.''06 and a bright galaxy that is strongly blended with one of the quasar images. We confirm spectroscopically that the two quasar images represent a single-lensed source at z = 4.8 with a total magnification of 3.2, and we derive a model for the lensing galaxy. This is the highest redshift lensed quasar currently known. We examine the issues surrounding the selection of such an unusual object from existing data and briefly discuss implications for lensed quasar surveys.

  11. Quasar Absorption Studies

    NASA Technical Reports Server (NTRS)

    Mushotzky, Richard (Technical Monitor); Elvis, Martin

    2004-01-01

    The aim of the proposal is to investigate the absorption properties of a sample of inter-mediate redshift quasars. The main goals of the project are: Measure the redshift and the column density of the X-ray absorbers; test the correlation between absorption and redshift suggested by ROSAT and ASCA data; constrain the absorber ionization status and metallicity; constrain the absorber dust content and composition through the comparison between the amount of X-ray absorption and optical dust extinction. Unanticipated low energy cut-offs where discovered in ROSAT spectra of quasars and confirmed by ASCA, BeppoSAX and Chandra. In most cases it was not possible to constrain adequately the redshift of the absorber from the X-ray data alone. Two possibilities remain open: a) absorption at the quasar redshift; and b) intervening absorption. The evidences in favour of intrinsic absorption are all indirect. Sensitive XMM observations can discriminate between these different scenarios. If the absorption is at the quasar redshift we can study whether the quasar environment evolves with the Cosmic time.

  12. Distributions of Quasar Hosts on the Galaxy Main Sequence Plane

    NASA Astrophysics Data System (ADS)

    Zhang, Zhoujian; Shi, Yong; Rieke, George H.; Xia, Xiaoyang; Wang, Yikang; Sun, Bingqing; Wan, Linfeng

    2016-03-01

    The relation between star formation rates (SFRs) and stellar masses, i.e., the galaxy main sequence, is a useful diagnostic of galaxy evolution. We present the distributions relative to the main sequence of 55 optically selected PG and 12 near-IR-selected Two Micron All Sky Survey (2MASS) quasars at z ≤ 0.5. We estimate the quasar host stellar masses from Hubble Space Telescope or ground-based AO photometry, and the SFRs through the mid-infrared aromatic features and far-IR photometry. We find that PG quasar hosts more or less follow the main sequence defined by normal star-forming galaxies while 2MASS quasar hosts lie systematically above the main sequence. PG and 2MASS quasars with higher nuclear luminosities seem to have higher specific SFRs (sSFRs), although there is a large scatter. No trends are seen between sSFRs and SMBH masses, Eddington ratios, or even morphology types (ellipticals, spirals, and mergers). Our results could be placed in an evolutionary scenario with quasars emerging during the transition from ULIRGs/mergers to ellipticals. However, combined with results at higher redshift, they suggest that quasars can be widely triggered in normal galaxies as long as they contain abundant gas and have ongoing star formation.

  13. VizieR Online Data Catalog: SDSS DLA and absorber quasar samples (Murphy+, 2016)

    NASA Astrophysics Data System (ADS)

    Murphy, M. T.; Bernet, M. L.

    2016-07-01

    Using spectral slope fits of the SDSS DR7 quasar spectra, and the DLA/sub-DLA identifications of Noterdaeme et al. (2009, Cat. J/A+A/505/1087), we found that the 774 selected quasars with a single foreground DLA are significantly (3.2σ) redder, on average, than carefully selected control groups drawn from a sample of ~7000 quasars without foreground DLAs. (4 data files).

  14. BINARY QUASARS AT HIGH REDSHIFT. I. 24 NEW QUASAR PAIRS AT z {approx} 3-4

    SciTech Connect

    Hennawi, Joseph F.; Myers, Adam D.; Shen, Yue; Strauss, Michael A.; Djorgovski, S. G.; Glikman, Eilat; Mahabal, Ashish; Fan Xiaohui; Martin, Crystal L.; Richards, Gordon T.; Schneider, Donald P.; Shankar, Francesco

    2010-08-20

    The clustering of quasars on small scales yields fundamental constraints on models of quasar evolution and the buildup of supermassive black holes. This paper describes the first systematic survey to discover high-redshift binary quasars. Using color-selection and photometric redshift techniques, we searched 8142 deg{sup 2} of Sloan Digital Sky Survey imaging data for binary quasar candidates, and confirmed them with follow-up spectroscopy. Our sample of 27 high-redshift binaries (24 of them new discoveries) at redshifts 2.9 < z < 4.3 with proper transverse separations 10 kpc < R{sub perpendicular} < 650 kpc increases the number of such objects known by an order of magnitude. Eight members of this sample are very close pairs with R{sub perpendicular} < 100 kpc, and of these close systems four are at z>3.5. The completeness and efficiency of our well-defined selection algorithm are quantified using simulated photometry and we find that our sample is {approx}50% complete. Our companion paper uses this knowledge to make the first measurement of the small-scale clustering (R < 1 h {sup -1} Mpc comoving) of high-redshift quasars. High-redshift binaries constitute exponentially rare coincidences of two extreme (M {approx}> 10{sup 9} M {sub sun}) supermassive black holes. At z {approx} 4, there is about one close binary per 10 Gpc{sup 3}, thus these could be the highest sigma peaks, the analogs of superclusters, in the early universe.

  15. THE DEMOGRAPHICS OF BROAD-LINE QUASARS IN THE MASS-LUMINOSITY PLANE. I. TESTING FWHM-BASED VIRIAL BLACK HOLE MASSES

    SciTech Connect

    Shen Yue; Kelly, Brandon C.

    2012-02-20

    We jointly constrain the luminosity function (LF) and black hole mass function (BHMF) of broad-line quasars with forward Bayesian modeling in the quasar mass-luminosity plane, based on a homogeneous sample of {approx}58, 000 Sloan Digital Sky Survey (SDSS) Data Release 7 quasars at z {approx} 0.3-5. We take into account the selection effect of the sample flux limit; more importantly, we deal with the statistical scatter between true BH masses and FWHM-based single-epoch virial mass estimates, as well as potential luminosity-dependent biases of these mass estimates. The LF is tightly constrained in the regime sampled by SDSS and makes reasonable predictions when extrapolated to {approx}3 mag fainter. Downsizing is seen in the model LF. On the other hand, we find it difficult to constrain the BHMF to within a factor of a few at z {approx}> 0.7 (with Mg II and C IV-based virial BH masses). This is mainly driven by the unknown luminosity-dependent bias of these mass estimators and its degeneracy with other model parameters, and secondly driven by the fact that SDSS quasars only sample the tip of the active BH population at high redshift. Nevertheless, the most likely models favor a positive luminosity-dependent bias for Mg II and possibly for C IV, such that at fixed true BH mass, objects with higher-than-average luminosities have overestimated FWHM-based virial masses. There is tentative evidence that downsizing also manifests itself in the active BHMF, and the BH mass density in broad-line quasars contributes an insignificant amount to the total BH mass density at all times. Within our model uncertainties, we do not find a strong BH mass dependence of the mean Eddington ratio, but there is evidence that the mean Eddington ratio (at fixed BH mass) increases with redshift.

  16. Towards a comprehensive picture of powerful quasars, their host galaxies and quasar winds at z ˜ 0.5

    NASA Astrophysics Data System (ADS)

    Wylezalek, Dominika; Zakamska, Nadia L.; Liu, Guilin; Obied, Georges

    2016-03-01

    Luminous type-2 quasars in which the glow from the central black hole is obscured by dust are ideal targets for studying their host galaxies and the quasars' effect on galaxy evolution. Such feedback appears ubiquitous in luminous obscured quasars where high-velocity-ionized nebulae have been found. We present rest-frame yellow-band (˜5000 Å) observations using the Hubble Space Telescope (HST) for a sample of 20 luminous quasar host galaxies at 0.2 < z < 0.6 selected from the Sloan Digital Sky Survey. For the first time, we combine host galaxy observations with geometric measurements of quasar illumination using blue-band HST observations and [O III] integral field unit observations probing the quasar winds. The HST images reveal bright merger signatures in about half the galaxies; a significantly higher fraction than in comparison inactive ellipticals. We show that the host galaxies are primarily bulge-dominated, with masses close to M*, but belong to <30 per cent of elliptical galaxies that are highly star forming at z ˜ 0.5. Ionized gas signatures are uncorrelated with faint stellar discs (if present), confirming that the ionized gas is not concentrated in a disc. Scattering cones and [O III] ionized gas velocity field are aligned with the forward scattering cones being co-spatial with the blue-shifted side of the velocity field, suggesting the high-velocity gas is indeed photo-ionized by the quasar. Based on the host galaxies' high star formation rates and bright merger signatures, we suggest that this low-redshift outbreak of luminous quasar activity is triggered by recent minor mergers. Combining these novel observations, we present new quasar unification tests, which are in agreement with expectations of the orientation-based unification model for quasars.

  17. FIRST-2MASS RED QUASARS: TRANSITIONAL OBJECTS EMERGING FROM THE DUST

    SciTech Connect

    Glikman, Eilat; Urrutia, Tanya; Lacy, Mark; Djorgovski, S. George; Mahabal, Ashish; Myers, Adam D.; Ross, Nicholas P.; Petitjean, Patrick; Ge, Jian; Schneider, Donald P.; York, Donald G.

    2012-09-20

    We present a sample of 120 dust-reddened quasars identified by matching radio sources detected at 1.4 GHz in the Faint Images of the Radio Sky at Twenty Centimeters survey with the near-infrared Two Micron All Sky Survey catalog and color-selecting red sources. Optical and/or near-infrared spectroscopy provide broad wavelength sampling of their spectral energy distributions that we use to determine their reddening, characterized by E(B - V). We demonstrate that the reddening in these quasars is best described by Small-Magellanic-Cloud-like dust. This sample spans a wide range in redshift and reddening (0.1 {approx}< z {approx}< 3, 0.1 {approx}< E(B - V) {approx}< 1.5), which we use to investigate the possible correlation of luminosity with reddening. At every redshift, dust-reddened quasars are intrinsically the most luminous quasars. We interpret this result in the context of merger-driven quasar/galaxy co-evolution where these reddened quasars are revealing an emergent phase during which the heavily obscured quasar is shedding its cocoon of dust prior to becoming a 'normal' blue quasar. When correcting for extinction, we find that, depending on how the parent population is defined, these red quasars make up {approx}< 15%-20% of the luminous quasar population. We estimate, based on the fraction of objects in this phase, that its duration is 15%-20% as long as the unobscured, blue quasar phase.

  18. How do optically-similar quasars look elsewhere?

    NASA Astrophysics Data System (ADS)

    Shang, Zhaohui; Ma, Bin; Brotherton, Michael S.

    2016-06-01

    As too many spectroscopic and physical parameters complicates the study of quasars, reducing the number of parameters can help to isolate many problems in general. Using spectral principal component analysis, we selected from SDSS a pilot sample of quasars with virtually identical spectral features in H-beta region. We found that they also show very similar spectral features outside the H-beta region in the optical band. We also explore their properties in other available wavelength bands and plan to study the accretion, ionization, and possibly geometry of quasars using this controlled sample.

  19. A survey of z > 5.7 quasars in the sloan digital sky survey. 4. discovery of seven additional quasars

    SciTech Connect

    Fan, Xiao-Hui; Strauss, Michael A.; Richards, Gordon T.; Hennawi, Joseph F.; Becker, Robert H.; White, Richard L.; Diamond-Stanic, Aleksandar M.; onley, Jennifer L.D; Jiang, Lin-Hua; Kim, J.Serena; Vestergaard, Marianne; Young, Jason E.; Gunn, James E.; Lupton, Robert H.; Knapp, Gillian R.; Schneider, Donald P.; Brandt, W.N.; Bahcall, Neta A.; Barentine, J.C.; Brinkmann, J.; Brewington, Howard J.; /Arizona U., Astron. Dept. - Steward Observ. /Princeton U. Observ. /Johns Hopkins U. /UC, Berkeley, Astron. Dept. /UC, Davis /LLNL, Livermore /Baltimore, Space Telescope Sci. /Penn State U., Astron. Astrophys. /Apache Point Observ. /Tokyo U., ICRR /Mt. Suhora Observ., Cracow /Fermilab /Garching, Max Planck Inst., MPE

    2005-12-01

    We present the discovery of seven quasars at z > 5.7, selected from {approx}2000 deg{sup 2} of multicolor imaging data of the Sloan Digital Sky Survey (SDSS). The new quasars have redshifts z from 5.79 to 6.13. Five are selected as part of a complete flux-limited sample in the SDSS Northern Galactic Cap; two have larger photometric errors and are not part of the complete sample. One of the new quasars, SDSS J1335+3533 (z = 5.93), exhibits no emission lines; the 3-{sigma} limit on the rest-frame equivalent width of Ly{alpha} + NV line is 5 {angstrom}. It is the highest redshift lineless quasar known, and could be a gravitational lensed galaxy, a BL Lac object or a new type of quasar. Two new z > 6 quasars, SDSS 1250+3130 (z = 6.13) and SDSS J1137+3549 (z = 6.01), show deep Gunn-Peterson absorption gaps in Ly{alpha}. These gaps are narrower the complete Gunn-Peterson absorption troughs observed among quasars at z > 6.2 and do not have complete Ly{beta} absorption.

  20. THE COLOR VARIABILITY OF QUASARS

    SciTech Connect

    Schmidt, Kasper B.; Rix, Hans-Walter; Knecht, Matthias; Hogg, David W.; Shields, Joseph C.; Maoz, Dan; Bovy, Jo

    2012-01-10

    We quantify quasar color variability using an unprecedented variability database-ugriz photometry of 9093 quasars from Sloan Digital Sky Survey (SDSS) Stripe 82, observed over 8 years at {approx}60 epochs each. We confirm previous reports that quasars become bluer when brightening. We find a redshift dependence of this blueing in a given set of bands (e.g., g and r), but show that it is the result of the flux contribution from less-variable or delayed emission lines in the different SDSS bands at different redshifts. After correcting for this effect, quasar color variability is remarkably uniform, and independent not only of redshift, but also of quasar luminosity and black hole mass. The color variations of individual quasars, as they vary in brightness on year timescales, are much more pronounced than the ranges in color seen in samples of quasars across many orders of magnitude in luminosity. This indicates distinct physical mechanisms behind quasar variability and the observed range of quasar luminosities at a given black hole mass-quasar variations cannot be explained by changes in the mean accretion rate. We do find some dependence of the color variability on the characteristics of the flux variations themselves, with fast, low-amplitude, brightness variations producing more color variability. The observed behavior could arise if quasar variability results from flares or ephemeral hot spots in an accretion disk.

  1. X-ray spectral modelling of the AGN obscuring region in the CDFS: Bayesian model selection and catalogue

    NASA Astrophysics Data System (ADS)

    Buchner, J.; Georgakakis, A.; Nandra, K.; Hsu, L.; Rangel, C.; Brightman, M.; Merloni, A.; Salvato, M.; Donley, J.; Kocevski, D.

    2014-04-01

    Context. Aims: Active galactic nuclei are known to have complex X-ray spectra that depend on both the properties of the accreting super-massive black hole (e.g. mass, accretion rate) and the distribution of obscuring material in its vicinity (i.e. the "torus"). Often however, simple and even unphysical models are adopted to represent the X-ray spectra of AGN, which do not capture the complexity and diversity of the observations. In the case of blank field surveys in particular, this should have an impact on e.g. the determination of the AGN luminosity function, the inferred accretion history of the Universe and also on our understanding of the relation between AGN and their host galaxies. Methods: We develop a Bayesian framework for model comparison and parameter estimation of X-ray spectra. We take into account uncertainties associated with both the Poisson nature of X-ray data and the determination of source redshift using photometric methods. We also demonstrate how Bayesian model comparison can be used to select among ten different physically motivated X-ray spectral models the one that provides a better representation of the observations. This methodology is applied to X-ray AGN in the 4 Ms Chandra Deep Field South. Results: For the ~350 AGN in that field, our analysis identifies four components needed to represent the diversity of the observed X-ray spectra: (1) an intrinsic power law; (2) a cold obscurer which reprocesses the radiation due to photo-electric absorption, Compton scattering and Fe-K fluorescence; (3) an unabsorbed power law associated with Thomson scattering off ionised clouds; and (4) Compton reflection, most noticeable from a stronger-than-expected Fe-K line. Simpler models, such as a photo-electrically absorbed power law with a Thomson scattering component, are ruled out with decisive evidence (B > 100). We also find that ignoring the Thomson scattering component results in underestimation of the inferred column density, NH, of the obscurer

  2. Ultraviolet (UV) From Quasars - Skylab Student Experiment ED-23

    NASA Technical Reports Server (NTRS)

    1973-01-01

    This chart describes the Skylab student experiment Ultraviolet (UV) from Quasars, proposed by John C. Hamilton of Aiea, Hawaii. This experiment utilized Skylab's Ultraviolet Stellar Astronomy equipment to photograph quasars in the UV spectrum and compare those images to existing radio and visible data. In March 1972 NASA and the National Science Teachers Association selected 25 experiment proposals for flight on Skylab. Science advisors from the Marshall Space Flight Center aided and assisted the students in developing the proposals for flight on Skylab.

  3. Fifty Years of Quasars

    NASA Astrophysics Data System (ADS)

    Kellermann, Kenneth I.

    2013-01-01

    Although the extragalactic nature of quasars was discussed as early as 1960, it was dismissed largely because of preconceived ideas about what appeared to be an unrealistically high luminosity. Following the 1962 occultations of the strong radio source 3C 273 at Parkes, and the subsequent identification with an apparent stellar object, Maartin Schmidt recognized that the relatively simple hydrogen line Balmer series spectrum implied a redshift of 0.16 leading to the general acceptance of the quasars as being extragalactic origin and the most luminous objects in the Universe. Subsequent radio and optical measurements quickly led to the identification of other quasars with increasingly large redshifts. However, claims for a more local population continued for at least several decades confused perhaps by the recognition of the much larger class of radio quiet quasars and active galactic nuclei (AGN), and the uncertain connection with Seyfert galaxies and Zwicky’s compact galaxies. Curiously, 3C 273, which is one of the brightest extragalactic extragalactic sources in the sky, was first catalogued in 1959 and the mag 13 optical counterpart was known at least as early as 1887. Although, since 1960, much fainter optical counterparts were being routinely identified using accurate radio interferometer positions, 3C273 eluded identification until the series of lunar occultations by Cyril Hazard and others were used to determine the position and morphology of the radio source.

  4. Metallicity and Quasar Outflows

    NASA Astrophysics Data System (ADS)

    Wang, Huiyuan; Zhou, Hongyan; Yuan, Weimin; Wang, Tinggui

    2012-06-01

    Correlations of the outflow strength of quasars, as measured by the blueshift and asymmetry index (BAI) of the C IV line, with intensities and ratios of broad emission lines, based on composite quasar spectra built from the Sloan Digital Sky Survey, are investigated. We find that most of the line ratios of other ions to C IV increase prominently with BAI. These behaviors can be well understood in the context of increasing metallicity with BAI. The strength of the dominant coolant, C IV line, decreases, and weak collisionally excited lines increase with gas metallicity as a result of the competition between different line coolants. Using Si IV+O IV]/C IV as an indicator of gas metallicity, we present, for the first time, a strong correlation between the metallicity and the outflow strength of quasars over a wide range of 1.7-6.9 times solar abundance. Our result implies that metallicity plays an important role in the formation of quasar outflows, likely by affecting outflow acceleration. This effect may have a profound impact on galaxy evolution via momentum feedback and chemical enrichment.

  5. METALLICITY AND QUASAR OUTFLOWS

    SciTech Connect

    Wang, Huiyuan; Zhou, Hongyan; Wang, Tinggui; Yuan, Weimin

    2012-06-01

    Correlations of the outflow strength of quasars, as measured by the blueshift and asymmetry index (BAI) of the C IV line, with intensities and ratios of broad emission lines, based on composite quasar spectra built from the Sloan Digital Sky Survey, are investigated. We find that most of the line ratios of other ions to C IV increase prominently with BAI. These behaviors can be well understood in the context of increasing metallicity with BAI. The strength of the dominant coolant, C IV line, decreases, and weak collisionally excited lines increase with gas metallicity as a result of the competition between different line coolants. Using Si IV+O IV]/C IV as an indicator of gas metallicity, we present, for the first time, a strong correlation between the metallicity and the outflow strength of quasars over a wide range of 1.7-6.9 times solar abundance. Our result implies that metallicity plays an important role in the formation of quasar outflows, likely by affecting outflow acceleration. This effect may have a profound impact on galaxy evolution via momentum feedback and chemical enrichment.

  6. Physical Evolution of Quasars

    NASA Astrophysics Data System (ADS)

    Kuhn, Olga Patricia

    1996-01-01

    The evolution of the quasar luminosity function is well described by pure luminosity evolution (PLE), in which the statistical luminosity, L^*(z), declines by a factor of ~100 from z = 3 to z sim 0.1 (Boyle et al. 1988a). If PLE is produced by the gradual dimming of a single generation of long-lived quasars, then the emitted continua of high redshift, younger, quasars are expected to differ from those of their low redshift, older, counterparts. This thesis aims to test this interpretation of PLE via a statistical comparison between the continua of sets of high and low redshift quasars which match in evolved luminosity, having similar L/L^ *(z).. Rest-frame ~ 1200A-5500A spectral energy distributions were constructed for 15 high redshift quasars and compared to those of 27 z sim 0.1 quasars (Elvis et al. 1994a). Optical/UV spectral indices, alpha (F_ nu ~nu^alpha), were determined by fitting single power laws through narrow (Deltalambda/lambda < 2%) continuum bands at 1285A, 1460A, 4200A, 4650A and 5100A. The mean spectral indices are -0.38 +/- 0.07 for the low and -0.32 +/- 0.07 for the high redshift samples. No significant evolution is found in the optical/UV continuum shapes. K-S tests give probabilities < 4% that the distributions of alpha for the high and low redshift samples differ. There is a significant range in continuum shapes within the low (alpha = -1.2 to +0.5) and high (alpha = { -}0.75 to +0.2) redshift samples. The spread is real, being about 20 times greater than the typical errors, sim 0.01 - 0.08. The distributions of spectral indices that result from fits using a power law plus SMC reddening model are not consistent with the hypothesis that the range is produced by intrinsic extinction. The predicted spectra from non-steady accretion disks, as would result from temperature redistribution due to irradiation or unstable mass accretion, can explain values of alpha from 1/3 down to at least - 1, and may account for the full range. The strengths of

  7. THE RADIO PROPERTIES OF TYPE 2 QUASARS

    SciTech Connect

    Lal, Dharam Vir; Ho, Luis C.

    2010-03-15

    This paper presents the first high-resolution and high-sensitivity study of the radio properties of optically selected type 2 quasars. We used the Very Large Array at 8.4 GHz to observe 59 sources drawn from the Sloan Digital Sky Survey sample of Zakamska et al.. The detection rate of our survey is 59% (35/59), comparable to the detection rate in FIRST at 1.4 GHz. Ongoing star formation, although present, contributes negligible radio emission at the current sensitivity limit. Comparing the radio powers with the [O III] {lambda}5007 luminosities, we find that roughly 15% {+-} 5% of the sample can be considered radio loud. Intriguingly, the vast majority of the detected sources in our sample fall in a region intermediate between those traditionally occupied by radio loud and radio quiet quasars. Moreover, most of these 'radio intermediate' sources tend to have flat or inverted radio spectra, which we speculate may be caused by free-free absorption by ionized gas in the narrow-line region. The incidence of flat-spectrum sources in type 2 quasars appears to be much higher than in type 1 quasars, in apparent violation of the simple orientation-based unified model for active galaxies.

  8. The discovery of quasars

    NASA Astrophysics Data System (ADS)

    Kellermann, K. I.

    2013-03-01

    Although the extragalactic nature of quasars was discussed as early as 1960, it was rejected largely because of preconceived ideas about what appeared to be an unrealistically high radio and optical luminosity. Following the 1962 occultations of the strong radio source 3C 273 at Parkes, and the subsequent identification with an apparent stellar object, Maarten Schmidt recognized that the relatively simple hydrogen line Balmer series spectrum implied a redshift of 0.16. Successive radio and optical measurements quickly led to the identification of other quasars with increasingly large redshifts and the general, although for some decades not universal, acceptance of quasars as being by far the most distant and the most luminous objects in the Universe. Arguments for a more local population continued for at least several decades, fueled in part by a greater willingness to accept the unclear new physics needed to interpret the large observed redshifts rather than the extreme luminosities and energies implied by the cosmological interpretation of the redshifts. Curiously, 3C 273, which is one of the strongest extragalactic sources in the sky, was first catalogued in 1959 and the magnitude 13 optical counterpart was observed at least as early as 1887. Since 1960, much fainter optical counterparts were being routinely identified using accurate radio interferometer positions, measured primarily at the Caltech Owens Valley Radio Observatory. However, 3C 273 eluded identification until the series of lunar occultation observations led by Cyril Hazard. Subsequent attempts to classify quasars into numerous sub-categories based on their observed optical, radio, IR and high energy properties have perhaps led to more confusion than clarity. However, quasars and the broader class of AGN are now a fundamental part of astrophysics and cosmology. They were the basis for the recognition of supermassive black holes in galactic nuclei, which are intimately tied to the formation and

  9. The luminosity function of quasars

    NASA Technical Reports Server (NTRS)

    Pei, Yichuan C.

    1995-01-01

    We propose a new evolutionary model for the optical luminosity function of quasars. Our analytical model is derived from fits to the empirical luminosity function estimated by Hartwick and Schade and Warren, Hewett, and Osmer on the basis of more than 1200 quasars over the range of redshifts 0 approximately less than z approximately less than 4.5. We find that the evolution of quasars over this entire redshift range can be well fitted by a Gaussian distribution, while the shape of the luminosity function can be well fitted by either a double power law or an exponential L(exp 1/4) law. The predicted number counts of quasars, as a function of either apparent magnitude or redshift, are fully consistent with the observed ones. Our model indicates that the evolution of quasars reaches its maximum at z approximately = 2.8 and declines at higher redshifts. An extrapolation of the evolution to z approximately greater than 4.5 implies that quasars may have started their cosmic fireworks at z(sub f) approximately = 5.2-5.5. Forthcoming surveys of quasars at these redshifts will be critical to constrain the epoch of quasar formation. All the results we derived are based on observed quasars and are therefore subject to the bias of obscuration by dust in damped Ly alpha systems. Future surveys of these absorption systems at z approximately greater than 3 will also be important if the formation epoch of quasars is to be known unambiguously.

  10. Phylogenetic systematics and biogeography of hummingbirds: Bayesian and maximum likelihood analyses of partitioned data and selection of an appropriate partitioning strategy.

    PubMed

    McGuire, Jimmy A; Witt, Christopher C; Altshuler, Douglas L; Remsen, J V

    2007-10-01

    Hummingbirds are an important model system in avian biology, but to date the group has been the subject of remarkably few phylogenetic investigations. Here we present partitioned Bayesian and maximum likelihood phylogenetic analyses for 151 of approximately 330 species of hummingbirds and 12 outgroup taxa based on two protein-coding mitochondrial genes (ND2 and ND4), flanking tRNAs, and two nuclear introns (AK1 and BFib). We analyzed these data under several partitioning strategies ranging between unpartitioned and a maximum of nine partitions. In order to select a statistically justified partitioning strategy following partitioned Bayesian analysis, we considered four alternative criteria including Bayes factors, modified versions of the Akaike information criterion for small sample sizes (AIC(c)), Bayesian information criterion (BIC), and a decision-theoretic methodology (DT). Following partitioned maximum likelihood analyses, we selected a best-fitting strategy using hierarchical likelihood ratio tests (hLRTS), the conventional AICc, BIC, and DT, concluding that the most stringent criterion, the performance-based DT, was the most appropriate methodology for selecting amongst partitioning strategies. In the context of our well-resolved and well-supported phylogenetic estimate, we consider the historical biogeography of hummingbirds using ancestral state reconstructions of (1) primary geographic region of occurrence (i.e., South America, Central America, North America, Greater Antilles, Lesser Antilles), (2) Andean or non-Andean geographic distribution, and (3) minimum elevational occurrence. These analyses indicate that the basal hummingbird assemblages originated in the lowlands of South America, that most of the principle clades of hummingbirds (all but Mountain Gems and possibly Bees) originated on this continent, and that there have been many (at least 30) independent invasions of other primary landmasses, especially Central America.

  11. Dusty Quasars at High Redshifts

    NASA Astrophysics Data System (ADS)

    Weedman, Daniel; Sargsyan, Lusine

    2016-09-01

    A population of quasars at z ˜ 2 is determined based on dust luminosities νL ν (7.8 μm) that includes unobscured, partially obscured, and obscured quasars. Quasars are classified by the ratio νL ν (0.25 μm)/νL ν (7.8 μm) = UV/IR, assumed to measure obscuration of UV luminosity by the dust that produces IR luminosity. Quasar counts at rest-frame 7.8 μm are determined for quasars in the Boötes field of the NOAO Deep Wide Field Survey using 24 μm sources with optical redshifts from the AGN and Galaxy Evolution Survey (AGES) or infrared redshifts from the Spitzer Infrared Spectrograph. Spectral energy distributions are extended to far-infrared wavelengths using observations from the Herschel Space Observatory Spectral and Photometric Imaging Receiver (SPIRE), and new SPIRE photometry is presented for 77 high-redshift quasars from the Sloan Digital Sky Survey. It is found that unobscured and obscured quasars have similar space densities at rest-frame 7.8 μm, but the ratio L ν (100 μm)/L ν (7.8 μm) is about three times higher for obscured quasars than for unobscured, so that far-infrared or submillimeter quasar detections are dominated by obscured quasars. We find that only ˜5% of high-redshift submillimeter sources are quasars and that existing 850 μm surveys or 2 mm surveys should already have detected sources at z ˜ 10 if quasar and starburst luminosity functions remain the same from z = 2 until z = 10.

  12. DISCOVERING THE MISSING 2.2 < z < 3 QUASARS BY COMBINING OPTICAL VARIABILITY AND OPTICAL/NEAR-INFRARED COLORS

    SciTech Connect

    Wu Xuebing; Wang Ran; Bian Fuyan; Jiang Linhua; Fan Xiaohui; Schmidt, Kasper B.

    2011-09-15

    The identification of quasars in the redshift range 2.2 < z < 3 is known to be very inefficient because the optical colors of such quasars are indistinguishable from those of stars. Recent studies have proposed using optical variability or near-infrared (near-IR) colors to improve the identification of the missing quasars in this redshift range. Here we present a case study combining both methods. We select a sample of 70 quasar candidates from variables in Sloan Digital Sky Survey (SDSS) Stripe 82, which are non-ultraviolet excess sources and have UKIDSS near-IR public data. They are clearly separated into two parts on the Y - K/g - z color-color diagram, and 59 of them meet or lie close to a newly proposed Y - K/g - z selection criterion for z < 4 quasars. Of these 59 sources, 44 were previously identified as quasars in SDSS DR7, and 35 of them are quasars at 2.2 < z < 3. We present spectroscopic observations of 14 of 15 remaining quasar candidates using the Bok 2.3 m telescope and the MMT 6.5 m telescope, and successfully identify all of them as new quasars at z = 2.36-2.88. We also apply this method to a sample of 643 variable quasar candidates with SDSS-UKIDSS nine-band photometric data selected from 1875 new quasar candidates in SDSS Stripe 82 given by Butler and Bloom based on the time-series selections, and find that 188 of them are probably new quasars with photometric redshifts at 2.2 < z < 3. Our results indicate that the combination of optical variability and optical/near-IR colors is probably the most efficient way to find 2.2 < z < 3 quasars and is very helpful for constructing a complete quasar sample. We discuss its implications for ongoing and upcoming large optical and near-IR sky surveys.

  13. False periodicities in quasar time-domain surveys

    NASA Astrophysics Data System (ADS)

    Vaughan, S.; Uttley, P.; Markowitz, A. G.; Huppenkothen, D.; Middleton, M. J.; Alston, W. N.; Scargle, J. D.; Farr, W. M.

    2016-09-01

    There have recently been several reports of apparently periodic variations in the light curves of quasars, e.g. PG 1302-102 by Graham et al. Any quasar showing periodic oscillations in brightness would be a strong candidate to be a close binary supermassive black hole and, in turn, a candidate for gravitational wave studies. However, normal quasars - powered by accretion on to a single, supermassive black hole - usually show stochastic variability over a wide range of time-scales. It is therefore important to carefully assess the methods for identifying periodic candidates from among a population dominated by stochastic variability. Using a Bayesian analysis of the light curve of PG 1302-102, we find that a simple stochastic process is preferred over a sinusoidal variation. We then discuss some of the problems one encounters when searching for rare, strictly periodic signals among a large number of irregularly sampled, stochastic time series, and use simulations of quasar light curves to illustrate these points. From a few thousand simulations of steep spectrum (`red noise') stochastic processes, we find many simulations that display few-cycle periodicity like that seen in PG 1302-102. We emphasize the importance of calibrating the false positive rate when the number of targets in a search is very large.

  14. Bayesian Analysis for Risk Assessment of Selected Medical Events in Support of the Integrated Medical Model Effort

    NASA Technical Reports Server (NTRS)

    Gilkey, Kelly M.; Myers, Jerry G.; McRae, Michael P.; Griffin, Elise A.; Kallrui, Aditya S.

    2012-01-01

    The Exploration Medical Capability project is creating a catalog of risk assessments using the Integrated Medical Model (IMM). The IMM is a software-based system intended to assist mission planners in preparing for spaceflight missions by helping them to make informed decisions about medical preparations and supplies needed for combating and treating various medical events using Probabilistic Risk Assessment. The objective is to use statistical analyses to inform the IMM decision tool with estimated probabilities of medical events occurring during an exploration mission. Because data regarding astronaut health are limited, Bayesian statistical analysis is used. Bayesian inference combines prior knowledge, such as data from the general U.S. population, the U.S. Submarine Force, or the analog astronaut population located at the NASA Johnson Space Center, with observed data for the medical condition of interest. The posterior results reflect the best evidence for specific medical events occurring in flight. Bayes theorem provides a formal mechanism for combining available observed data with data from similar studies to support the quantification process. The IMM team performed Bayesian updates on the following medical events: angina, appendicitis, atrial fibrillation, atrial flutter, dental abscess, dental caries, dental periodontal disease, gallstone disease, herpes zoster, renal stones, seizure, and stroke.

  15. Quasars at 25.

    PubMed

    Trimble, V; Woltjer, L

    1986-10-10

    In the quarter century since the first optical identification of a "radio star" (3C 48), astronomers have come to general agreement that the underlying quasar energy source is accretion onto a massive black hole. There is much less agreement on the detailed physics of the processes by which this energy is converted to the forms observed, but this has not prevented the objects from serving as valuable probes of the universe at distant times and places.

  16. The road to quasars

    NASA Astrophysics Data System (ADS)

    Kellermann, K. I.

    2015-03-01

    Although the extragalactic nature of 3C 48 and other quasi stellar radio sources was discussed as early as 1960 by John Bolton and others, it was rejected largely because of preconceived ideas about what appeared to be unrealistically high radio and optical luminosities. Not until the 1962 occultations of the strong radio source 3C 273 at Parkes, which led Maarten Schmidt to identify 3C 273 with an apparent stellar object at a redshift of 0.16, was the true nature understood. Successive radio and optical measurements quickly led to the identification of other quasars with increasingly large redshifts and the general, although for some decades not universal, acceptance of quasars as the very luminous nuclei of galaxies. Curiously, 3C 273, which is one of the strongest extragalactic sources in the sky, was first cataloged in 1959 and the magnitude 13 optical counterpart was observed at least as early as 1887. Since 1960, much fainter optical counterparts were being routinely identified using accurate radio interferometer positions which were measured primarily at the Caltech Owens Valley Radio Observatory. However, 3C 273 eluded identification until the series of lunar occultation observations led by Cyril Hazard. Although an accurate radio position had been obtained earlier with the OVRO interferometer, inexplicably 3C 273 was initially misidentified with a faint galaxy located about an arc minute away from the true quasar position.

  17. A Bayesian mixed shrinkage prior procedure for spatial-stochastic basis selection and evaluation of gPC expansions: Applications to elliptic SPDEs

    NASA Astrophysics Data System (ADS)

    Karagiannis, Georgios; Konomi, Bledar A.; Lin, Guang

    2015-03-01

    We propose a new fully Bayesian method to efficiently obtain the spectral representation of a spatial random field, which can conduct spatial-stochastic basis selection and evaluation of generalized Polynomial Chaos (gPC) expansions when the number of the available basis functions is significantly larger than the size of the training data-set. We develop a fully Bayesian stochastic procedure, called mixed shrinkage prior (MSP), which performs both basis selection and coefficient evaluation simultaneously. MSP involves assigning a prior probability to the gPC structure and assigning conjugate priors to the expansion coefficients that can be thought of as mixtures of Ridge-LASSO shrinkage priors, in augmented form. The method offers a number of advantages over existing compressive sensing methods in gPC literature, such that it recovers possible sparse structures in both stochastic and spatial domains while the resulting expansion can be re-used directly to economically obtain results at any spatial input values. Yet, it inherits all the advantages of Bayesian model uncertainty methods, e.g. accounts for uncertainty about basis significance and provides interval estimation through posterior distributions. A unique highlight of the MSP procedure is that it can address heterogeneous sparsity in the spatial domain for different random dimensions. Furthermore, it yields a compromise between Ridge and LASSO regressions, and hence combines a weak (l2-norm) and strong (l1-norm) shrinkage, in an adaptive, data-driven manner. We demonstrate the good performance of the proposed method, and compare it against other existing compressive sensing ones on elliptic stochastic partial differential equations.

  18. Thermal Emission from Warm Dust in the Most Distant Quasars

    NASA Astrophysics Data System (ADS)

    Wang, Ran; Carilli, Chris L.; Wagg, Jeff; Bertoldi, Frank; Walter, Fabian; Menten, Karl M.; Omont, Alain; Cox, Pierre; Strauss, Michael A.; Fan, Xiaohui; Jiang, Linhua; Schneider, Donald P.

    2008-11-01

    We report new continuum observations of 14 z ~ 6 quasars at 250 GHz and 14 quasars at 1.4 GHz. We summarize all recent millimeter and radio observations of the sample of the 33 quasars known with 5.71 <= z<= 6.43 and present a study of the rest-frame far-infrared (FIR) properties of this sample. These quasars were observed with the Max Planck Millimeter Bolometer Array (MAMBO) at 250 GHz with mJy sensitivity, and 30% of them were detected. We also recover the average 250 GHz flux density of the MAMBO undetected sources at 4 σ by stacking the on-source measurements. The derived mean radio-to-UV spectral energy distributions (SEDs) of the full sample and the 250 GHz nondetections show no significant differences from lower redshift optical quasars. Obvious FIR excesses are seen in the individual SEDs of the strong 250 GHz detections, with FIR-to-radio emission ratios consistent with those of typical star-forming galaxies. Most 250 GHz-detected sources follow the LFIR-Lbol relationship derived from a sample of local IR-luminous quasars (LIR > 1012 L⊙), while the average LFIR/Lbol ratio of the nondetections is consistent with that of the optically selected PG quasars. The MAMBO detections also tend to have weaker Lyα emission than the nondetected sources. We discuss possible FIR dust-heating sources and critically assess the possibility of active star formation in the host galaxies of the z ~ 6 quasars. The average star formation rate of the MAMBO nondetections is likely to be less than a few hundred M⊙ yr-1, but in the strong detections, the host galaxy star formation is probably at a rate of gtrsim103 M⊙ yr-1, which dominates the FIR dust heating.

  19. Quasar probabilities and redshifts from WISE mid-IR through GALEX UV photometry

    NASA Astrophysics Data System (ADS)

    DiPompeo, M. A.; Bovy, J.; Myers, A. D.; Lang, D.

    2015-09-01

    Extreme deconvolution (XD) of broad-band photometric data can both separate stars from quasars and generate probability density functions for quasar redshifts, while incorporating flux uncertainties and missing data. Mid-infrared photometric colours are now widely used to identify hot dust intrinsic to quasars, and the release of all-sky WISE data has led to a dramatic increase in the number of IR-selected quasars. Using forced photometry on public WISE data at the locations of Sloan Digital Sky Survey (SDSS) point sources, we incorporate this all-sky data into the training of the XDQSOz models originally developed to select quasars from optical photometry. The combination of WISE and SDSS information is far more powerful than SDSS alone, particularly at z > 2. The use of SDSS+WISE photometry is comparable to the use of SDSS+ultraviolet+near-IR data. We release a new public catalogue of 5537 436 (total; 3874 639 weighted by probability) potential quasars with probability PQSO > 0.2. The catalogue includes redshift probabilities for all objects. We also release an updated version of the publicly available set of codes to calculate quasar and redshift probabilities for various combinations of data. Finally, we demonstrate that this method of selecting quasars using WISE data is both more complete and efficient than simple WISE colour-cuts, especially at high redshift. Our fits verify that above z ˜ 3 WISE colours become bluer than the standard cuts applied to select quasars. Currently, the analysis is limited to quasars with optical counterparts, and thus cannot be used to find highly obscured quasars that WISE colour-cuts identify in significant numbers.

  20. Neutral atomic-carbon quasar absorption-line systems at z> 1.5. Sample selection, H i content, reddening, and 2175 Å extinction feature

    NASA Astrophysics Data System (ADS)

    Ledoux, C.; Noterdaeme, P.; Petitjean, P.; Srianand, R.

    2015-08-01

    We present the results of a search for cold gas at high redshift along quasar lines of sight carried out without any a priori assumption on the neutral atomic-hydrogen content of the absorption-line systems. To do this, we systematically looked for neutral-carbon (C i) λλ1560, 1656 transition lines in 41 696 low-resolution quasar spectra (1.5 < zem < 4.46) from the SDSS-II - Data Release 7 - database. C i absorption lines should indeed probe the shielded gas in the neutral interstellar medium of galaxies more efficiently than traditional tracers such as neutral atomic-hydrogen (H i) damped Lyman-α (DLA) and/or Mg ii systems. We built up a sample of 66 C i absorbers with redshifts in the range 1.5 < z < 3.1 and rest-frame equivalent widths 0.1 quasars and their reddened spectral energy distributions, with E(B-V) values up to ~0.3. The overall N(H i) distribution of C i systems is, however, relatively flat. As a consequence, among the C i systems classifying as DLAs, there is a probable excess of strong DLAs with log N(H i) > 21 (atoms cm-2) compared to systematic DLA surveys. Whilst the dust content

  1. The Circumgalactic Medium of Quasars

    NASA Astrophysics Data System (ADS)

    Hennawi, Joe

    2014-07-01

    I will argue that observations of the diffuse gas in the outskirts of quasar host galaxies, or the so called circumgalactic medium, are essential for understanding how luminous quasars evolve in a cosmological context. Such observations also provide a fruitful comparison to theory, because hydrodynamics at moderate overdensities is much easier to simulate than the complicated processes which trigger quasar activity. A novel technique will be introduced, whereby a foreground quasar can be studied in absorption against a background quasar, resolving scales as small as 30 kpc. This experiment reveals a rich absorption spectrum which contains a wealth of information about the physical conditions of diffuse gas around quasars. Hydrodynamical simulations of the massive dark matter halos which host luminous quasars under predict the amount of cool gas observed in quasar environs by a large factor, challenging our understanding of how massive galaxies form. I will also discuss a very sensitive search for Ly-alpha emission from the same gas which we study in absorption.

  2. Selection of Polynomial Chaos Bases via Bayesian Model Uncertainty Methods with Applications to Sparse Approximation of PDEs with Stochastic Inputs

    SciTech Connect

    Karagiannis, Georgios; Lin, Guang

    2014-02-15

    Generalized polynomial chaos (gPC) expansions allow the representation of the solution of a stochastic system as a series of polynomial terms. The number of gPC terms increases dramatically with the dimension of the random input variables. When the number of the gPC terms is larger than that of the available samples, a scenario that often occurs if the evaluations of the system are expensive, the evaluation of the gPC expansion can be inaccurate due to over-fitting. We propose a fully Bayesian approach that allows for global recovery of the stochastic solution, both in spacial and random domains, by coupling Bayesian model uncertainty and regularization regression methods. It allows the evaluation of the PC coefficients on a grid of spacial points via (1) Bayesian model average or (2) medial probability model, and their construction as functions on the spacial domain via spline interpolation. The former accounts the model uncertainty and provides Bayes-optimal predictions; while the latter, additionally, provides a sparse representation of the solution by evaluating the expansion on a subset of dominating gPC bases when represented as a gPC expansion. Moreover, the method quantifies the importance of the gPC bases through inclusion probabilities. We design an MCMC sampler that evaluates all the unknown quantities without the need of ad-hoc techniques. The proposed method is suitable for, but not restricted to, problems whose stochastic solution is sparse at the stochastic level with respect to the gPC bases while the deterministic solver involved is expensive. We demonstrate the good performance of the proposed method and make comparisons with others on 1D, 14D and 40D in random space elliptic stochastic partial differential equations.

  3. Selection of polynomial chaos bases via Bayesian model uncertainty methods with applications to sparse approximation of PDEs with stochastic inputs

    SciTech Connect

    Karagiannis, Georgios Lin, Guang

    2014-02-15

    Generalized polynomial chaos (gPC) expansions allow us to represent the solution of a stochastic system using a series of polynomial chaos basis functions. The number of gPC terms increases dramatically as the dimension of the random input variables increases. When the number of the gPC terms is larger than that of the available samples, a scenario that often occurs when the corresponding deterministic solver is computationally expensive, evaluation of the gPC expansion can be inaccurate due to over-fitting. We propose a fully Bayesian approach that allows for global recovery of the stochastic solutions, in both spatial and random domains, by coupling Bayesian model uncertainty and regularization regression methods. It allows the evaluation of the PC coefficients on a grid of spatial points, via (1) the Bayesian model average (BMA) or (2) the median probability model, and their construction as spatial functions on the spatial domain via spline interpolation. The former accounts for the model uncertainty and provides Bayes-optimal predictions; while the latter provides a sparse representation of the stochastic solutions by evaluating the expansion on a subset of dominating gPC bases. Moreover, the proposed methods quantify the importance of the gPC bases in the probabilistic sense through inclusion probabilities. We design a Markov chain Monte Carlo (MCMC) sampler that evaluates all the unknown quantities without the need of ad-hoc techniques. The proposed methods are suitable for, but not restricted to, problems whose stochastic solutions are sparse in the stochastic space with respect to the gPC bases while the deterministic solver involved is expensive. We demonstrate the accuracy and performance of the proposed methods and make comparisons with other approaches on solving elliptic SPDEs with 1-, 14- and 40-random dimensions.

  4. The Cluster and Large Scale Environments of Quasars at z<0.9

    NASA Astrophysics Data System (ADS)

    Harris, Kathryn A.

    2012-01-01

    In this thesis, I present an investigation into the environments of quasars with respect to galaxy clusters, and environment evolution with redshift and luminosity. The orientation of the quasar with respect to the major axis of the closest cluster was calculated, introducing new information to previous work. The aim of this work was i.) to study the large scale environment over a large redshift range, ii.) to study the evolution as well as any change in environment with quasar luminosity and redshift, and iii.) to study the orientation of a quasar with respect to a galaxy cluster. There is a deficit of quasars lying close to cluster centres for 0.4quasars as a function of absolute quasar magnitude, nor preferred orientation between the quasar and the cluster major axis for bright or faint quasars. Spectra of a selection of 680 star forming galaxies, red galaxies, and AGN were taken, and used to study the environments of quasars with respect to star-forming galaxies and galaxy clusters. The objects were classified (33 classed as AGN), and star formation rates calculated. Three AGN and 10 star forming galaxies lie at the same redshift (z=0.29) as three galaxy clusters. The three galaxy clusters have the same orientation angle and may be part of a filament along with the star forming galaxies and AGN. A number of high redshift quasars showed evidence of ultra-strong UV FeII emission in their spectra in the direction of three LQGs in the redshift range 1.1Quasar Group (CCLQG). Though there has been no previous indication that the LQG environment is unique, the high level of iron emission may indicate a difference in environment.

  5. Discovery of eight z ∼ 6 quasars from Pan-STARRS1

    SciTech Connect

    Bañados, E.; Venemans, B. P.; Morganson, E.; Decarli, R.; Walter, F.; Rix, H.-W.; Farina, E. P.; Chambers, K. C.; Morgan, J. S.; Burgett, W. S.; Kaiser, N.; Kudritzki, R.-P.; Fan, X.; McGreer, I.; Jiang, L.; De Rosa, G.; Simcoe, R.; Weiß, A.; Price, P. A.; Greiner, J.; and others

    2014-07-01

    High-redshift quasars are currently the only probes of the growth of supermassive black holes and potential tracers of structure evolution at early cosmic time. Here we present our candidate selection criteria from the Panoramic Survey Telescope and Rapid Response System 1 and follow-up strategy to discover quasars in the redshift range 5.7 ≲ z ≲ 6.2. With this strategy we discovered eight new 5.7 ≤ z ≤ 6.0 quasars, increasing the number of known quasars at z > 5.7 by more than 10%. We additionally recovered 18 previously known quasars. The eight quasars presented here span a large range of luminosities (–27.3 ≤ M {sub 1450} ≤ –25.4; 19.6 ≤ z {sub P1} ≤ 21.2) and are remarkably heterogeneous in their spectral features: half of them show bright emission lines whereas the other half show a weak or no Lyα emission line (25% with rest-frame equivalent width of the Lyα +N V line lower than 15 Å). We find a larger fraction of weak-line emission quasars than in lower redshift studies. This may imply that the weak-line quasar population at the highest redshifts could be more abundant than previously thought. However, larger samples of quasars are needed to increase the statistical significance of this finding.

  6. THE SLOAN DIGITAL SKY SURVEY QUASAR LENS SEARCH. V. FINAL CATALOG FROM THE SEVENTH DATA RELEASE

    SciTech Connect

    Inada, Naohisa; Oguri, Masamune; Kayo, Issha; Fukugita, Masataka; Shin, Min-Su; Strauss, Michael A.; Bahcall, Neta A.; Morokuma, Tomoki; Rusu, Cristian E.; Kochanek, Christopher S.; Richards, Gordon T.; Schneider, Donald P.; York, Donald G.; Frieman, Joshua A.; Hall, Patrick B.; White, Richard L.

    2012-05-15

    We present the final statistical sample of lensed quasars from the Sloan Digital Sky Survey (SDSS) Quasar Lens Search (SQLS). The well-defined statistical lens sample consists of 26 lensed quasars brighter than i = 19.1 and in the redshift range of 0.6 < z < 2.2 selected from 50,826 spectroscopically confirmed quasars in the SDSS Data Release 7 (DR7), where we restrict the image separation range to 1'' < {theta} < 20'' and the i-band magnitude differences in two images to be smaller than 1.25 mag. The SDSS DR7 quasar catalog also contains 36 additional lenses identified with various techniques. In addition to these lensed quasars, we have identified 81 pairs of quasars from follow-up spectroscopy, 26 of which are physically associated binary quasars. The statistical lens sample covers a wide range of image separations, redshifts, and magnitudes, and therefore is suitable for systematic studies of cosmological parameters and surveys of the structure and evolution of galaxies and quasars.

  7. Studies of Quasar Outflows

    NASA Technical Reports Server (NTRS)

    Arav, Nahum

    2002-01-01

    The main aim of this research program is to determine the ionization equilibrium and abundances in quasar outflows. Especially in the broad absorption line QSO PG 0946+301. We find that the outflow's metalicity is consistent with being solar, while the abundance ratio of phosphorus to other metals is at least ten times solar. These findings are based on diagnostics that are not sensitive to saturation and partial covering effects in the BALs (Broad Adsorption Lines), which considerably weakened previous claims for enhanced metalicity. Ample evidence for these effects is seen in the spectrum.

  8. Measuring Quasar Variability with Pan-STARRS1 and SDSS

    NASA Astrophysics Data System (ADS)

    Morganson, E.; Burgett, W. S.; Chambers, K. C.; Green, P. J.; Kaiser, N.; Magnier, E. A.; Marshall, P. J.; Morgan, J. S.; Price, P. A.; Rix, H.-W.; Schlafly, E. F.; Tonry, J. L.; Walter, F.

    2014-04-01

    We measure quasar variability using the Panoramic Survey Telescope and Rapid Response System 1 Survey (Pan-STARRS1 or PS1) and the Sloan Digital Sky Survey (SDSS) and establish a method of selecting quasars via their variability in 104 deg2 surveys. We use 105 spectroscopically confirmed quasars that have been well measured in both PS1 and SDSS and take advantage of the decadal timescales that separate SDSS measurements and PS1 measurements. A power law model fits the data well over the entire time range tested, 0.01-10 yr. Variability in the current PS1-SDSS data set can efficiently distinguish between quasars and nonvarying objects. It improves the purity of a griz quasar color cut from 4.1% to 48% while maintaining 67% completeness. Variability will be very effective at finding quasars in data sets with no u band and in redshift ranges where exclusively photometric selection is not efficient. We show that quasars' rest-frame ensemble variability, measured as a root mean squared in Δ magnitudes, is consistent with V(z, L, t) = A 0(1 + z)0.37(L/L 0)-0.16(t/1 yr)0.246, where L 0 = 1046 erg s-1 and A 0 = 0.190, 0.162, 0.147, or 0.141 in the g P1, r P1, i P1, or z P1filter, respectively. We also fit across all four filters and obtain median variability as a function of z, L, and λ as V(z, L, λ, t) = 0.079(1 + z)0.15(L/L 0)-0.2(λ/1000 nm)-0.44(t/1 yr)0.246.

  9. Measuring quasar variability with Pan-STARRS1 and SDSS

    SciTech Connect

    Morganson, E.; Rix, H.-W.; Schlafly, E. F.; Walter, F.; Burgett, W. S.; Chambers, K. C.; Kaiser, N.; Magnier, E. A.; Morgan, J. S.; Tonry, J. L.; Green, P. J.; Marshall, P. J.; Price, P. A.

    2014-04-01

    We measure quasar variability using the Panoramic Survey Telescope and Rapid Response System 1 Survey (Pan-STARRS1 or PS1) and the Sloan Digital Sky Survey (SDSS) and establish a method of selecting quasars via their variability in 10{sup 4} deg{sup 2} surveys. We use 10{sup 5} spectroscopically confirmed quasars that have been well measured in both PS1 and SDSS and take advantage of the decadal timescales that separate SDSS measurements and PS1 measurements. A power law model fits the data well over the entire time range tested, 0.01-10 yr. Variability in the current PS1-SDSS data set can efficiently distinguish between quasars and nonvarying objects. It improves the purity of a griz quasar color cut from 4.1% to 48% while maintaining 67% completeness. Variability will be very effective at finding quasars in data sets with no u band and in redshift ranges where exclusively photometric selection is not efficient. We show that quasars' rest-frame ensemble variability, measured as a root mean squared in Δ magnitudes, is consistent with V(z, L, t) = A {sub 0}(1 + z){sup 0.37}(L/L {sub 0}){sup –0.16}(t/1 yr){sup 0.246}, where L {sub 0} = 10{sup 46} erg s{sup –1} and A {sub 0} = 0.190, 0.162, 0.147, or 0.141 in the g {sub P1}, r {sub P1}, i {sub P1}, or z {sub P1}filter, respectively. We also fit across all four filters and obtain median variability as a function of z, L, and λ as V(z, L, λ, t) = 0.079(1 + z){sup 0.15}(L/L {sub 0}){sup –0.2}(λ/1000 nm){sup –0.44}(t/1 yr){sup 0.246}.

  10. Selecting Relevant Descriptors for Classification by Bayesian Estimates: A Comparison with Decision Trees and Support Vector Machines Approaches for Disparate Data Sets.

    PubMed

    Carbon-Mangels, Miriam; Hutter, Michael C

    2011-10-01

    Classification algorithms suffer from the curse of dimensionality, which leads to overfitting, particularly if the problem is over-determined. Therefore it is of particular interest to identify the most relevant descriptors to reduce the complexity. We applied Bayesian estimates to model the probability distribution of descriptors values used for binary classification using n-fold cross-validation. As a measure for the discriminative power of the classifiers, the symmetric form of the Kullback-Leibler divergence of their probability distributions was computed. We found that the most relevant descriptors possess a Gaussian-like distribution of their values, show the largest divergences, and therefore appear most often in the cross-validation scenario. The results were compared to those of the LASSO feature selection method applied to multiple decision trees and support vector machine approaches for data sets of substrates and nonsubstrates of three Cytochrome P450 isoenzymes, which comprise strongly unbalanced compound distributions. In contrast to decision trees and support vector machines, the performance of Bayesian estimates is less affected by unbalanced data sets. This strategy reveals those descriptors that allow a simple linear separation of the classes, whereas the superior accuracy of decision trees and support vector machines can be attributed to nonlinear separation, which are in turn more prone to overfitting.

  11. Data mining for gravitationally lensed quasars

    NASA Astrophysics Data System (ADS)

    Agnello, Adriano; Kelly, Brandon C.; Treu, Tommaso; Marshall, Philip J.

    2015-04-01

    Gravitationally lensed quasars are brighter than their unlensed counterparts and produce images with distinctive morphological signatures. Past searches and target-selection algorithms, in particular the Sloan Quasar Lens Search (SQLS), have relied on basic morphological criteria, which were applied to samples of bright, spectroscopically confirmed quasars. The SQLS techniques are not sufficient for searching into new surveys (e.g. DES, PS1, LSST), because spectroscopic information is not readily available and the large data volume requires higher purity in target/candidate selection. We carry out a systematic exploration of machine-learning techniques and demonstrate that a two-step strategy can be highly effective. In the first step, we use catalogue-level information (griz+WISE magnitudes, second moments) to pre-select targets, using artificial neural networks. The accepted targets are then inspected with pixel-by-pixel pattern recognition algorithms (gradient-boosted trees), to form a final set of candidates. The results from this procedure can be used to further refine the simpler SQLS algorithms, with a twofold (or threefold) gain in purity and the same (or 80 per cent) completeness at target-selection stage, or a purity of 70 per cent and a completeness of 60 per cent after the candidate-selection step. Simpler photometric searches in griz+WISE based on colour cuts would provide samples with 7 per cent purity or less. Our technique is extremely fast, as a list of candidates can be obtained from a Stage III experiment (e.g. DES catalogue/data base) in a few CPU hours. The techniques are easily extendable to Stage IV experiments like LSST with the addition of time domain information.

  12. Long-term variability of a complete sample of quasars

    SciTech Connect

    Cristiani, S.; Vio, R.; Andreani, P. )

    1990-07-01

    The long-term variability of a complete sample of quasars selected in the field of the SA 94 has been investigated. Using Schmidt plates covering a time baseline of seven years, about one-third of the quasars are found to be variable. It is suggested that all the quasi-stellar objects are variable with amplitudes of a few tenths of a magnitude on timescales of the order of some years in their restframes. The application of the variability technique to the selection of complete samples of quasars is discussed. The timescales estimated can be easily accounted for in the accreting black hole with thermal and viscous timescales. The variability is found to be correlated with the absolute magnitude and/or the redshift. 21 refs.

  13. Canada-France Redshift Survey - X. The quasar sample

    NASA Astrophysics Data System (ADS)

    Schade, David; Crampton, David; Hammer, F.; Le Fevre, O.; Lilly, S. J.

    1996-01-01

    Six objects with broad emission lines and redshifts from 0.48 to 2.07 were discovered among 736 extragalactic objects in the Canada-France Redshift Survey (CFRS). Although the luminosities of half of the objects are such that they are in the Seyfert regime (M_B<~-23), all would be designated as quasars in traditional surveys. Since the only selection criterion was that 17.5<=I_AB<=22.5, or approximately B<23 (assuming a continuum power-law slope alpha=-0.5), these quasars represent an unbiased, flux-limited sample. Although uncertain, the implied surface density, 200^-120-80 deg^-2, is the highest yet measured, and is in good agreement with extrapolations from other faint surveys and the evolving luminosity function models of Boyle. The distributions of the continuum properties, emission-line strengths, etc. of the quasars do not differ significantly from those of quasars selected by other means, and therefore they would have been detected in most traditional surveys. Three of the quasars may be associated with clusters or large structures of galaxies at z<~1.

  14. X-RAY ABSORPTION OF HIGH-REDSHIFT QUASARS

    SciTech Connect

    Eitan, Assaf; Behar, Ehud E-mail: behar@physics.technion.ac.il

    2013-09-01

    The soft X-ray photoelectric absorption of high-z quasars has been known for two decades, but has no unambiguous astrophysical context. We construct the largest sample to date of 58 high-redshift quasars (z > 0.45) selected from the XMM-Newton archive based on a high photon count criterion (>1800). We measure the optical depth {tau} at 0.5 keV and find that 43% of the quasars show significant absorption. We aim to find which physical parameters of the quasars, e.g., redshift, radio luminosity, radio loudness, or X-ray luminosity, drive their observed absorption. We compare the absorption behavior with redshift with the pattern expected if the diffuse intergalactic medium (IGM) is responsible for the observed absorption. We also compare the absorption with a comparison sample of gamma-ray burst (GRB) X-ray afterglows. Although the z > 2 quasar opacity is consistent with diffuse IGM absorption, many intermediate-z (0.45 < z < 2) quasars are not sufficiently absorbed for this scenario, and are appreciably less absorbed than GRBs. Only 10/37 quasars at z < 2 are absorbed, and only 5/30 radio-quiet quasars are absorbed. We find a weak correlation between {tau} and z, and an even weaker correlation between {tau} and radio luminosity. These findings lead to the conclusion that although a diffuse IGM origin for the quasar absorption is unlikely, the optical depth does seem to increase with redshift, roughly as (1 + z){sup 2.2{+-}0.6}, tending to {tau} Almost-Equal-To 0.4 at high redshifts, similar to the high-z GRBs. This result can be explained by an ionized and clumpy IGM at z < 2, and a cold, diffuse IGM at higher redshift. If, conversely, the absorption occurs at the quasar, and owing to the steep L{sub x} {proportional_to}(1 + z){sup 7.1{+-}0.5} correlation in the present sample, the host column density scales as N{sub H}{proportional_to}L{sub x}{sup 0.7{+-}0.1}.

  15. The ISO View of Palomar-Green Quasars

    NASA Technical Reports Server (NTRS)

    Haas, M.; Klaas, U.; Mueller, S. A. H.; Bertoldi, F.; Camenzind, M.; Chini, R.; Krause, O.; Lemke, D.; Meisenheimer; Richards, P. J.

    2003-01-01

    Mining the ISO data archive we provide the complete ISO view of PG quasars containing 64 infrared spectral energy distributions between 5 and 200 mu m. About half of the sample was supplemented by MAMBO and SCUBA (sub-)millimeter data. Since the PG quasars were selected optically, the high infrared detection rate of more than 80% suggests that every quasar possesses luminous to hyper-luminous dust emission with dust masses comparable to Seyferts and ultra-luminous IR galaxies (ULIRGs). The gas to-dust mass ratio (of those sources where CO measurements are available in the literature) is consistent with the galactic value providing further evidence for the thermal nature of the IR emission of radio quiet quasars. The SEDs represent templates of unprecedented detail and sensitivity. We suggest that the diversity of the SEDs reflects largely the evolution of the dust distribution, and we propose a classification of the SED shapes as well as an evolutionary scheme in which this variety can be understood. During the evolution the surrounding dust redistributes, settling more and more into a torus/disk like configuration, while the SEDs show an initial FIR bump, then an increasing MIR emission and a steeper near- to mid-infrared slope, both of which finally also decrease. Regarding cosmic evolution, our hyper-luminous quasars in the "local" universe at z=l do not show the hyper-luminous (LFIR >? 10(exp 13) L(sub sun)) starburst activity inferred for z=4 quasars detected in several (sub-)millimeter surveys. In view of several caveats this difference should be established further, but it already suggests that in the early dense universe stronger merger events led to more powerful starbursts accompanying the quasar phenomenon, while at later cosmic epochs any coeval starbursts obviously do not reach that high power and are outshone by the AGN. Additional information is included in the original extended abstract.

  16. Through BAL Quasars Brightly

    NASA Technical Reports Server (NTRS)

    Chartas, George

    2003-01-01

    We report on an observation of the broad absorption line (BAL) quasar PG 1115+080 performed with the XMM-Newton observatory. Spectral analysis reveals the second case of a relativistic X-ray-absorbing outflow in a BAL quasar. The first case was revealed in a recent observation of APM 08279+5255 with the Chandra X-Ray Observatory. As in the case of APM 08279+5255, the observed flux of PG 1115+080 is greatly magnified by gravitational lensing. The relatively high redshift (z=1.72) of the quasar places the redshifted energies of resonant absorption features in a sensitive portion of the XMM- Newton spectral response. The spectrum indicates the presence of complex low-energy absorption in the 0.2-0.6 keV observed energy band and high-energy absorption in the 2-5 keV observed energy band. The high-energy absorption is best modeled by two Gaussian absorption lines with rest-frame energies of 7.4 and 9.5 keV. Assuming that these two lines axe produced by resonant absorption due to Fe XXV, we infer that the X-ray absorbers are outflowing with velocities of approx. 0.10c and approx. 0.34c respectively. We have detected significant variability of the energies and widths of the X-ray BALs in PG 1115+080 and APM 08279+5255 over timescales of 19 and 1.8 weeks (proper time), respectively. The BAL variability observed from APM 08279+5255 supports our earlier conclusion that these absorbers are most likely launched at relatively small radii of less than 10(exp 16)(Mbh/M8)(sup 1/2) cm. A comparison of the ionization properties and column densities of the low-energy and high-energy absorbers indicates that these absorbers are likely distinct; however, higher spectral resolution is needed to confirm this result. Finally, we comment on prospects for constraining the kinematic and ionization properties of these X-ray BALs with the next generation of X-ray observatories.

  17. Bayesian learning

    NASA Technical Reports Server (NTRS)

    Denning, Peter J.

    1989-01-01

    In 1983 and 1984, the Infrared Astronomical Satellite (IRAS) detected 5,425 stellar objects and measured their infrared spectra. In 1987 a program called AUTOCLASS used Bayesian inference methods to discover the classes present in these data and determine the most probable class of each object, revealing unknown phenomena in astronomy. AUTOCLASS has rekindled the old debate on the suitability of Bayesian methods, which are computationally intensive, interpret probabilities as plausibility measures rather than frequencies, and appear to depend on a subjective assessment of the probability of a hypothesis before the data were collected. Modern statistical methods have, however, recently been shown to also depend on subjective elements. These debates bring into question the whole tradition of scientific objectivity and offer scientists a new way to take responsibility for their findings and conclusions.

  18. Asteroids to Quasars

    NASA Astrophysics Data System (ADS)

    Lugger, Phyllis M.

    2004-12-01

    Asteroid dedication; William Liller: Biographical Sketch; William Liller: Autobiographical Meanderings; Preface; List of Participants; Conference Photo; Part I. 1. Solar System Astronomy: Asteroids Joseph Veverka; 2. Sixteen years of stellar occultations James Elliott; 3. Comets to Quasars: Surface photometry from standard stars and the morphology of the galaxy-quasar interface Peter Usher; 4. Observing Solar Eclipses Jay Pasachoff; Part II. 5. Planetary Nebulae: new insights and opportunities Lawrence Aller; 6. Studies of planetary nebulae at radio wavelengths Yervant Terzian; 7. Optical identifications of compact galactic X-ray sources: Liller Lore Jonathan Grindlay; 8. Ages of globular clusters derived from BVRI CCD photometry Gonzalo Alcaino; 9. Stellar spectrum synthesis Jun Jugaku; 10. Mass exchange and stellar abundance anomalies Benjamin Peery; Part III. Extragalactic Astronomy: 11. The M31 globular cluster system John Huchra; 12. Spiral structure and star formation in galaxies Debra Elmegreen; 13. The discovery of hot coronae around early type galaxies William Forman and Christine Jones; 14. The morphology of clusters of galaxies, the formation efficiency of galaxies and the origin of the intracluster medium Christine Jones and William Forman; 15. Testing models for the dynamical evolution of clusters of galaxies Phyllis Lugger; 16. What is in the X-ray sky? Rudolph Schild; 17. Einstein deep surveys Stephen Murray, Christine Jones and William Forman; Part IV. History, Lore and Archaeoastronomy: 18. Robert Wheeler Willson: His Life and Legacy Barbara Welther; 19. The great mnemonics contest Owen Gingerich; 20. Hetu'u Rapanui: The archaeoastronomy of Easter Island William Liller; Indexes; Names; Objects; Subjects.

  19. HST/COS OBSERVATIONS OF THIRTEEN NEW He II QUASARS

    SciTech Connect

    Syphers, David; Anderson, Scott F.; Zheng Wei; Meiksin, Avery; Schneider, Donald P.; York, Donald G.

    2012-04-15

    The full reionization of intergalactic helium was a major event in the history of the intergalactic medium (IGM), and UV observations of the He II Gunn-Peterson trough allow us to characterize the end of this process at z {approx} 3. Due to intervening hydrogen absorption, quasars allowing such study are rare, with only 33 known in the literature, and most of those are very recent discoveries. We expand on our previous discovery work, and present 13 new He II quasars with redshifts 2.82 < z < 3.77, here selected with {approx}80% efficiency, and including several that are much brighter than the vast majority of those previously known. This is the largest sample of uniformly observed He II quasars covering such a broad redshift range, and they show evidence of IGM opacity increasing with redshift, as expected for the helium reionization epoch. No evidence of He II Ly{alpha} quasar emission is seen in individual or averaged spectra, posing a problem for standard models of the broad-line region. The current rapid advance in the study of He II quasars has been greatly facilitated by the Cosmic Origins Spectrograph on the Hubble Space Telescope, and we discuss the instrumental and other subtleties that must be taken into account in IGM He II observations.

  20. FAR-INFRARED PROPERTIES OF TYPE 1 QUASARS

    SciTech Connect

    Hanish, D. J.; Teplitz, H. I.; Capak, P.; Desai, V.; Armus, L.; Brinkworth, C.; Brooke, T.; Colbert, J.; Fadda, D.; Noriega-Crespo, A.; Paladini, R.; Frayer, D.; Huynh, M.; Lacy, M.; Murphy, E.; Scarlata, C.; Shenoy, S.

    2013-05-01

    We use the Spitzer Space Telescope Enhanced Imaging Products and the Spitzer Archival Far-InfraRed Extragalactic Survey to study the spectral energy distributions (SEDs) of spectroscopically confirmed type 1 quasars selected from the Sloan Digital Sky Survey (SDSS). By combining the Spitzer and SDSS data with the Two Micron All Sky Survey, we are able to construct a statistically robust rest-frame 0.1-100 {mu}m type 1 quasar template. We find that the quasar population is well-described by a single power-law SED at wavelengths less than 20 {mu}m, in good agreement with previous work. However, at longer wavelengths, we find a significant excess in infrared luminosity above an extrapolated power-law, along with significant object-to-object dispersion in the SED. The mean excess reaches a maximum of 0.8 dex at rest-frame wavelengths near 100 {mu}m.

  1. Comparison of Approaches to Photometric Redshift Estimation of Quasars

    NASA Astrophysics Data System (ADS)

    Tu, Yang; Zhang, Yan-Xia; Zhao, Yong-Heng; Tian, Hai-Jun

    We probe many kinds of approaches used for photometric redshift estimation of quasars, including KNN (K-nearest neighbor algorithm), Lasso (Least Absolute Shrinkage and Selection Operator), PLS (Partial Least Square regression), ridge regression, SGD (Stochastic Gradient Descent) and Extra-Trees.

  2. BINARY QUASARS IN THE SLOAN DIGITAL SKY SURVEY: EVIDENCE FOR EXCESS CLUSTERING ON SMALL SCALES

    SciTech Connect

    Hennawi, J F; Strauss, M A; Oguri, M; Inada, N; Richards, G T; Pindor, B; Schneider, D P; Becker, R H; Gregg, M D; Hall, P B; Johnston, D E; Fan, X; Burles, S; Schlegel, D J; Gunn, J E; Lupton, R; Bahcall, N A; Brunner, R J; Brinkman, J

    2005-11-10

    We present a sample of 218 new quasar pairs with proper transverse separations R{sub prop} < 1 h{sup -1} Mpc over the redshift range 0.5 < z < 3.0, discovered from an extensive follow up campaign to find companions around the Sloan Digital Sky Survey and 2dF Quasar Redshift Survey quasars. This sample includes 26 new binary quasars with separations R{sub prop} < 50 h{sup -1} kpc ({theta} < 10''), more than doubling the number of such systems known. We define a statistical sample of binaries selected with homogeneous criteria and compute its selection function, taking into account sources of incompleteness. The first measurement of the quasar correlation function on scales 10 h{sup -1} kpc < R{sub prop} < 400 h{sup -1} kpc is presented. For R{sub prop} {approx}< 40 h{sup -1} kpc, we detect an order of magnitude excess clustering over the expectation from the large scale (R{sub prop} {approx}> 3 h{sup -1} Mpc) quasar correlation function, extrapolated down as a power law to the separations probed by our binaries. The excess grows to {approx}30 at R{sub prop} {approx} 10 h{sup -1} kpc, and provides compelling evidence that the quasar autocorrelation function gets progressively steeper on sub-Mpc scales. This small scale excess can likely be attributed to dissipative interaction events which trigger quasar activity in rich environments. Recent small scale measurements of galaxy clustering and quasar-galaxy clustering are reviewed and discussed in relation to our measurement of small scale quasar clustering.

  3. Counts of low-Redshift SDSS quasar candidates

    SciTech Connect

    Zeljko Ivezic et al.

    2004-03-12

    We analyze the counts of low-redshift quasar candidates selected using nine-epoch SDSS imaging data. The co-added catalogs are more than 1 mag deeper than single-epoch SDSS data, and allow the selection of low-redshift quasar candidates using UV-excess and also variability techniques. The counts of selected candidates are robustly determined down to g = 21.5. This is about 2 magnitudes deeper than the position of a change in the slope of the counts reported by Boyle et al. (1990, 2000) for a sample selected by UV-excess, and questioned by Hawkins & Veron (1995), who utilized a variability-selected sample. Using SDSS data, we confirm a change in the slope of the counts for both UV-excess and variability selected samples, providing strong support for the Boyle et al. results.

  4. Volume-limited SDSS/First quasars and the radio dichotomy

    SciTech Connect

    Sebastian Jester; R.G. Kron

    2004-03-12

    Much evidence has been presented in favor of and against the existence of two distinct populations of quasars, radio-loud and radio-quiet. The SDSS differs from earlier optically selected quasar surveys in the large number of quasars and the targeting of FIRST radio source counterparts as quasar candidates. This allows a qualitatively different approach of constructing a series of samples at different redshifts which are volume-limited with respect to both radio and optical luminosity. This technique avoids any biases from the strong evolution of quasar counts with redshift and potential redshift-dependent selection effects. We find that optical and radio luminosities of quasars detected in both SDSS and FIRST are not well correlated within each redshift shell, although the fraction of radio detections among optically selected quasars remains roughly constant at 10% for z {le} 3.2. The distribution in the luminosity-luminosity plane does not appear to be strongly bimodal. The optical luminosity function is marginally flatter at higher radio luminosities.

  5. Dust reddened quasars in first and UKIDSS: Beyond the tip of the iceberg

    SciTech Connect

    Glikman, Eilat; Urrutia, Tanya; Lacy, Mark; Djorgovski, S. G.; Mahabal, Ashish; Graham, Matthew; Urry, Meg; Croom, Scott; Schneider, Donald P.; Ge, Jian

    2013-12-01

    We present the results of a pilot survey to find dust-reddened quasars by matching the Faint Images of the Radio Sky at Twenty-Centimeters (FIRST) radio catalog to the UKIDSS near-infrared survey and using optical data from Sloan Digital Sky Survey to select objects with very red colors. The deep K-band limit provided by UKIDSS allows for finding more heavily reddened quasars at higher redshifts as compared with previous work using FIRST and Two Micron All Sky Survey (2MASS). We selected 87 candidates with K ≤ 17.0 from the UKIDSS Large Area Survey (LAS) First Data Release (DR1), which covers 190 deg{sup 2}. These candidates reach up to ∼1.5 mag below the 2MASS limit and obey the color criteria developed to identify dust-reddened quasars. We have obtained 61 spectroscopic observations in the optical and/or near-infrared, as well as classifications in the literature, and have identified 14 reddened quasars with E(B – V) > 0.1, including 3 at z > 2. We study the infrared properties of the sample using photometry from the Wide-Field Infrared Survey Explorer and find that infrared colors improve the efficiency of red quasar selection, removing many contaminants in an infrared-to-optical color-selected sample alone. The highest-redshift quasars (z ≳ 2) are only moderately reddened, with E(B – V) ∼ 0.2-0.3. We find that the surface density of red quasars rises sharply with faintness, comprising up to 17% of blue quasars at the same apparent K-band flux limit. We estimate that to reach more heavily reddened quasars (i.e., E(B – V) ≳ 0.5) at z > 2 and a depth of K = 17, we would need to survey at least ∼2.5 times more area.

  6. Dust Reddened Quasars in FIRST and UKIDSS: Beyond the Tip of the Iceberg

    NASA Astrophysics Data System (ADS)

    Glikman, Eilat; Urrutia, Tanya; Lacy, Mark; Djorgovski, S. G.; Urry, Meg; Croom, Scott; Schneider, Donald P.; Mahabal, Ashish; Graham, Matthew; Ge, Jian

    2013-12-01

    We present the results of a pilot survey to find dust-reddened quasars by matching the Faint Images of the Radio Sky at Twenty-Centimeters (FIRST) radio catalog to the UKIDSS near-infrared survey and using optical data from Sloan Digital Sky Survey to select objects with very red colors. The deep K-band limit provided by UKIDSS allows for finding more heavily reddened quasars at higher redshifts as compared with previous work using FIRST and Two Micron All Sky Survey (2MASS). We selected 87 candidates with K <= 17.0 from the UKIDSS Large Area Survey (LAS) First Data Release (DR1), which covers 190 deg2. These candidates reach up to ~1.5 mag below the 2MASS limit and obey the color criteria developed to identify dust-reddened quasars. We have obtained 61 spectroscopic observations in the optical and/or near-infrared, as well as classifications in the literature, and have identified 14 reddened quasars with E(B - V) > 0.1, including 3 at z > 2. We study the infrared properties of the sample using photometry from the Wide-Field Infrared Survey Explorer and find that infrared colors improve the efficiency of red quasar selection, removing many contaminants in an infrared-to-optical color-selected sample alone. The highest-redshift quasars (z >~ 2) are only moderately reddened, with E(B - V) ~ 0.2-0.3. We find that the surface density of red quasars rises sharply with faintness, comprising up to 17% of blue quasars at the same apparent K-band flux limit. We estimate that to reach more heavily reddened quasars (i.e., E(B - V) >~ 0.5) at z > 2 and a depth of K = 17, we would need to survey at least ~2.5 times more area.

  7. Variable selection in Bayesian generalized linear-mixed models: an illustration using candidate gene case-control association studies.

    PubMed

    Tsai, Miao-Yu

    2015-03-01

    The problem of variable selection in the generalized linear-mixed models (GLMMs) is pervasive in statistical practice. For the purpose of variable selection, many methodologies for determining the best subset of explanatory variables currently exist according to the model complexity and differences between applications. In this paper, we develop a "higher posterior probability model with bootstrap" (HPMB) approach to select explanatory variables without fitting all possible GLMMs involving a small or moderate number of explanatory variables. Furthermore, to save computational load, we propose an efficient approximation approach with Laplace's method and Taylor's expansion to approximate intractable integrals in GLMMs. Simulation studies and an application of HapMap data provide evidence that this selection approach is computationally feasible and reliable for exploring true candidate genes and gene-gene associations, after adjusting for complex structures among clusters.

  8. LOW-z Mg II BROAD ABSORPTION-LINE QUASARS FROM THE SLOAN DIGITAL SKY SURVEY

    SciTech Connect

    Zhang Shaohua; Wang Tingi; Wang Huiyuan; Zhou Hongyan; Dong Xiaobo; Wang Jianguo E-mail: whywang@mail.ustc.edu.c

    2010-05-01

    We present a sample of 68 low-z Mg II low-ionization broad absorption-line (loBAL) quasars. The sample is uniformly selected from the Sloan Digital Sky Survey Data Release 5 according to the following criteria: (1) redshift 0.4 < z {<=} 0.8, (2) median spectral S/N>7 pixel{sup -1}, and (3) Mg II absorption-line width {Delta}v{sub c} {>=} 1600 km s{sup -1}. The last criterion is a trade-off between the completeness and consistency with respect to the canonical definition of BAL quasars that have the 'balnicity index' BI>0 in C IV BAL. We adopted such a criterion to ensure that {approx}90% of our sample are classical BAL quasars and the completeness is {approx}80%, based on extensive tests using high-z quasar samples with measurements of both C IV and Mg II BALs. We found (1) Mg II BAL is more frequently detected in quasars with narrower H{beta} emission line, weaker [O III] emission line, stronger optical Fe II multiplets, and higher luminosity. In term of fundamental physical parameters of a black hole accretion system, loBAL fraction is significantly higher in quasars with a higher Eddington ratio than those with a lower Eddington ratio. The fraction is not dependent on the black hole mass in the range concerned. The overall fraction distribution is broad, suggesting a large range of covering factor of the absorption material. (2) [O III]-weak loBAL quasars averagely show undetected [Ne V] emission line and a very small line ratio of [Ne V] to [O III]. However, the line ratio in non-BAL quasars, which is much larger than that in [O III]-weak loBAL quasars, is independent of the strength of the [O III] line. (3) loBAL and non-loBAL quasars have similar colors in near-infrared to optical band but different colors in ultraviolet. (4) Quasars with Mg II absorption lines of intermediate width are indistinguishable from the non-loBAL quasars in optical emission line properties but their colors are similar to loBAL quasars, redder than non-BAL quasars. We also discuss

  9. Joint feature selection and classification using a Bayesian neural network with automatic relevance determination priors: potential use in CAD of medical imaging

    NASA Astrophysics Data System (ADS)

    Chen, Weijie; Zur, Richard M.; Giger, Maryellen L.

    2007-03-01

    Bayesian neural network (BNN) with automatic relevance determination (ARD) priors has the ability to assess the relevance of each input feature during network training. Our purpose is to investigate the potential use of BNN-with-ARD-priors for joint feature selection and classification in computer-aided diagnosis (CAD) of medical imaging. With ARD priors, each group of weights that connect an input feature to the hidden units is associated with a hyperparameter controlling the magnitudes of the weights. The hyperparameters and the weights are updated simultaneously during neural network training. A smaller hyperparameter will likely result in larger weight values and the corresponding feature will likely be more relevant to the output, and thus, to the classification task. For our study, a multivariate normal feature space is designed to include one feature with high classification performance in terms of both ideal observer and linear observer, two features with high ideal observer performance but low linear observer performance and 7 useless features. An exclusive-OR (XOR) feature space is designed to include 2 XOR features and 8 useless features. Our simulation results show that the ARD-BNN approach has the ability to select the optimal subset of features on the designed nonlinear feature spaces on which the linear approach fails. ARD-BNN has the ability to recognize features that have high ideal observer performance. Stepwise linear discriminant analysis (SWLDA) has the ability to select features that have high linear observer performance but fails to select features that have high ideal observer performance and low linear observer performance. The cross-validation results on clinical breast MRI data show that ARD-BNN yields statistically significant better performance than does the SWLDA-LDA approach. We believe that ARD-BNN is a promising method for pattern recognition in computer-aided diagnosis of medical imaging.

  10. DISCLOSING THE RADIO LOUDNESS DISTRIBUTION DICHOTOMY IN QUASARS: AN UNBIASED MONTE CARLO APPROACH APPLIED TO THE SDSS-FIRST QUASAR SAMPLE

    SciTech Connect

    Balokovic, M.; Smolcic, V.; Ivezic, Z.; Zamorani, G.; Schinnerer, E.; Kelly, B. C.

    2012-11-01

    We investigate the dichotomy in the radio loudness distribution of quasars by modeling their radio emission and various selection effects using a Monte Carlo approach. The existence of two physically distinct quasar populations, the radio-loud and radio-quiet quasars, is controversial and over the last decade a bimodal distribution of radio loudness of quasars has been both affirmed and disputed. We model the quasar radio luminosity distribution with simple unimodal and bimodal distribution functions. The resulting simulated samples are compared to a fiducial sample of 8300 quasars drawn from the SDSS DR7 Quasar Catalog and combined with radio observations from the FIRST survey. Our results indicate that the SDSS-FIRST sample is best described by a radio loudness distribution which consists of two components, with (12 {+-} 1)% of sources in the radio-loud component. On the other hand, the evidence for a local minimum in the loudness distribution (bimodality) is not strong and we find that previous claims for its existence were probably affected by the incompleteness of the FIRST survey close to its faint limit. We also investigate the redshift and luminosity dependence of the radio loudness distribution and find tentative evidence that at high redshift radio-loud quasars were rarer, on average louder, and exhibited a smaller range in radio loudness. In agreement with other recent work, we conclude that the SDSS-FIRST sample strongly suggests that the radio loudness distribution of quasars is not a universal function, and that more complex models than presented here are needed to fully explain available observations.

  11. Disclosing the Radio Loudness Distribution Dichotomy in Quasars: An Unbiased Monte Carlo Approach Applied to the SDSS-FIRST Quasar Sample

    NASA Astrophysics Data System (ADS)

    Baloković, M.; Smolčić, V.; Ivezić, Ž.; Zamorani, G.; Schinnerer, E.; Kelly, B. C.

    2012-11-01

    We investigate the dichotomy in the radio loudness distribution of quasars by modeling their radio emission and various selection effects using a Monte Carlo approach. The existence of two physically distinct quasar populations, the radio-loud and radio-quiet quasars, is controversial and over the last decade a bimodal distribution of radio loudness of quasars has been both affirmed and disputed. We model the quasar radio luminosity distribution with simple unimodal and bimodal distribution functions. The resulting simulated samples are compared to a fiducial sample of 8300 quasars drawn from the SDSS DR7 Quasar Catalog and combined with radio observations from the FIRST survey. Our results indicate that the SDSS-FIRST sample is best described by a radio loudness distribution which consists of two components, with (12 ± 1)% of sources in the radio-loud component. On the other hand, the evidence for a local minimum in the loudness distribution (bimodality) is not strong and we find that previous claims for its existence were probably affected by the incompleteness of the FIRST survey close to its faint limit. We also investigate the redshift and luminosity dependence of the radio loudness distribution and find tentative evidence that at high redshift radio-loud quasars were rarer, on average louder, and exhibited a smaller range in radio loudness. In agreement with other recent work, we conclude that the SDSS-FIRST sample strongly suggests that the radio loudness distribution of quasars is not a universal function, and that more complex models than presented here are needed to fully explain available observations.

  12. Quasar Structure from Microlensing in Gravitationally Lensed Quasars

    NASA Astrophysics Data System (ADS)

    Morgan, Christopher W.

    2007-12-01

    I investigate microlensing in gravitationally lensed quasars and discuss the use of its signal to probe quasar structure on small angular scales. I describe our lensed quasar optical monitoring program and RETROCAM, the optical camera I built for the 2.4m Hiltner telescope to monitor lensed quasars. I use the microlensing variability observed in 11 gravitationally lensed quasars to show that the accretion disk size at 2500Å is related to the black hole mass by log(R2500/cm) = (15.70±0.16) + (0.64±0.18)log(MBH/109M⊙). This scaling is consistent with the expectation from thin disk theory (R ∝ MBH2/3), but it implies that black holes radiate with relatively low efficiency, log(η) = -1.54±0.36 + log(L/LE) where η=L/(Mdotc2). With one exception, these sizes are larger by a factor of 4 than the size needed to produce the observed 0.8µm quasar flux by thermal radiation from a thin disk with the same T ∝ R-3/4 temperature profile. More sophisticated disk models are clearly required, particularly as our continuing observations improve the precision of the measurements and yield estimates of the scaling with wavelength and accretion rate. This research made extensive use of a Beowulf computer cluster obtained through the Cluster Ohio program of the Ohio Supercomputer Center. Support for program HST-GO-9744 was provided by NASA through a grant from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS-5-26666.

  13. VizieR Online Data Catalog: UV-bright quasars (Syphers+, 2009)

    NASA Astrophysics Data System (ADS)

    Syphers, D.; Anderson, S. F.; Zheng, W.; Haggard, D.; Meiksin, A.; Schneider, D. P.; York, D. G.

    2010-03-01

    Absorption along quasar sightlines remains among the most sensitive direct measures of HeII reionization in much of the intergalactic medium (IGM). Until recently, fewer than a half-dozen unobscured quasar sightlines suitable for the HeII Gunn-Peterson test were known; although these handful demonstrated great promise, the small sample size limited confidence in cosmological inferences. We have recently added nine more such clean HeII quasars, exploiting Sloan Digital Sky Survey (SDSS) quasar samples, broadband ultraviolet (UV) imaging from Galaxy Evolution Explorer (GALEX), and high-yield UV spectroscopic confirmations from Hubble Space Telescope (HST). Here we markedly expand this approach by cross-correlating SDSS DR7 and GALEX GR4+5 to catalog 428 SDSS and 165 other quasars with z>2.78 having likely (~70%) GALEX detections, suggesting they are bright into the far-UV. Reconnaissance HST Cycle 16 Supplemental prism data for 29 of these new quasar-GALEX matches spectroscopically confirm 17 as indeed far-UV bright. At least 10 of these confirmations have clean sightlines all the way down to HeII Lyα, substantially expanding the number of known clean HeII quasars, and reaffirming the order of magnitude enhanced efficiency of our selection technique. Combined confirmations from this and our past programs yield more than 20 HeII quasars, quintupling the sample. These provide substantial progress toward a sample of HeII quasar sightlines large enough, and spanning a sufficient redshift range, to enable statistical IGM studies that may avoid individual object peculiarity and sightline variance. Our expanded catalog of hundreds of high-likelihood far-UV-bright QSOs additionally will be useful for understanding the extreme-UV properties of the quasars themselves. (2 data files).

  14. The SDSS view of the Palomar-Green bright quasar survey

    SciTech Connect

    Jester, Sebastian; Schneider, Donald P.; Richards, Gordon T.; Green, Richard F.; Schmidt, Maarten; Hall, Patrick B.; Strauss, Michael A.; Vanden Berk, Daniel E.; Stoughton, Chris; Gunn, James E.; Brinkmann, Jon; Kent, Stephen M.; Smith, J.Allyn; Tucker, Douglas, L.; Yanny, Brian; /Fermilab /Penn State U., Astron. Astrophys. /Princeton U. Observ. /Kitt Peak Observ. /Caltech /Chicago U., Astron. Astrophys. Ctr. /York U., Canada /Apache Point Observ. /Wyoming U. /Los Alamos

    2005-02-01

    The author investigates the extent to which the Palomar-Green (PG) Bright Quasar Survey (BQS) is complete and representative of the general quasar population by comparing with imaging and spectroscopy from the Sloan Digital Sky Survey. A comparison of SDSS and PG photometry of both stars and quasars reveals the need to apply a color and magnitude recalibration to the PG data. Using the SDSS photometric catalog, they define the PG's parent sample of objects that are not main-sequence stars and simulate the selection of objects from this parent sample using the PG photometric criteria and errors. This simulation shows that the effective U-B cut in the PG survey is U-B < -0.71, implying a color-related incompleteness. As the color distribution of bright quasars peaks near U-B = -0.7 and the 2-{sigma} error in U-B is comparable to the full width of the color distribution of quasars, the color incompleteness of the BQS is approximately 50% and essentially random with respect to U-B color for z < 0.5. There is however, a bias against bright quasars at 0.5 < z < 1, which is induced by the color-redshift relation of quasars (although quasars at z > 0.5 are inherently rare in bright surveys in any case). They find no evidence for any other systematic incompleteness when comparing the distributions in color, redshift, and FIRST radio properties of the BQS and a BQS-like subsample of the SDSS quasar sample. However, the application of a bright magnitude limit biases the BQS toward the inclusion of objects which are blue in g-i, in particular compared to the full range of g-i colors found among the i-band limited SDSS quasars, and even at i-band magnitudes comparable to those of the BQS objects.

  15. The 2QDES Pilot: the luminosity and redshift dependence of quasar clustering

    NASA Astrophysics Data System (ADS)

    Chehade, Ben; Shanks, T.; Findlay, J.; Metcalfe, N.; Sawangwit, U.; Irwin, M.; González-Solares, E.; Fine, S.; Drinkwater, M. J.; Croom, S.; Jurek, R. J.; Parkinson, D.; Bielby, R.

    2016-06-01

    We present a new redshift survey, the 2dF Quasar Dark Energy Survey pilot (2QDESp), which consists of ≈10 000 quasars from ≈150 deg2 of the southern sky, based on VST-ATLAS imaging and 2dF/AAOmega spectroscopy. Combining our optical photometry with the WISE (W1,W2) bands we can select essentially contamination free quasar samples with 0.8 < z < 2.5 and g < 20.5. At fainter magnitudes, optical UVX selection is still required to reach our g ≈ 22.5 limit. Using both these techniques we observed quasar redshifts at sky densities up to 90 deg-2. By comparing 2QDESp with other surveys (SDSS, 2QZ and 2SLAQ) we find that quasar clustering is approximately luminosity independent, with results for all four surveys consistent with a correlation scale of r0 = 6.1 ± 0.1 h-1 Mpc, despite their decade range in luminosity. We find a significant redshift dependence of clustering, particularly when BOSS data with r0 = 7.3 ± 0.1 h-1 Mpc are included at z ≈ 2.4. All quasars remain consistent with having a single host halo mass of ≈2 ± 1 × 1012 h-1 M⊙. This result implies that either quasars do not radiate at a fixed fraction of the Eddington luminosity or AGN black hole and dark matter halo masses are weakly correlated. No significant evidence is found to support fainter, X-ray selected quasars at low redshift having larger halo masses as predicted by the `hot halo' mode AGN model of Fanidakis et al. (2013). Finally, although the combined quasar sample reaches an effective volume as large as that of the original SDSS LRG sample, we do not detect the BAO feature in these data.

  16. Discovery of Eight z ∼ 6 Quasars in the Sloan Digital Sky Survey Overlap Regions

    NASA Astrophysics Data System (ADS)

    Jiang, Linhua; McGreer, Ian D.; Fan, Xiaohui; Bian, Fuyan; Cai, Zheng; Clément, Benjamin; Wang, Ran; Fan, Zhou

    2015-06-01

    We present the discovery of eight quasars at z∼ 6 identified in the Sloan Digital Sky Survey (SDSS) overlap regions. Individual SDSS imaging runs have some overlap with each other, leading to repeat observations over an area spanning >4000 deg2 (more than one-fourth of the total footprint). These overlap regions provide a unique data set that allows us to select high-redshift quasars more than 0.5 mag fainter in the z band than those found with the SDSS single-epoch data. Our quasar candidates were first selected as i-band dropout objects in the SDSS imaging database. We then carried out a series of follow-up observations in the optical and near-IR to improve photometry, remove contaminants, and identify quasars. The eight quasars reported here were discovered in a pilot study utilizing the overlap regions at high galactic latitude (|b|\\gt 30{}^\\circ ). These quasars span a redshift range of 5.86\\lt z\\lt 6.06 and a flux range of 19.3\\lt {{z}AB}\\lt 20.6 mag. Five of them are fainter than {{z}AB}=20 mag, the typical magnitude limit of z∼ 6 quasars used for the SDSS single-epoch images. In addition, we recover eight previously known quasars at z∼ 6 that are located in the overlap regions. These results validate our procedure for selecting quasar candidates from the overlap regions and confirming them with follow-up observations, and they provide guidance to a future systematic survey over all SDSS imaging regions with repeat observations.

  17. HOST GALAXIES OF z = 4 QUASARS

    SciTech Connect

    McLeod, K. K.; Bechtold, Jill E-mail: jbechtold@as.arizona.ed

    2009-10-10

    We have undertaken a project to investigate the host galaxies and environments of a sample of quasars at z approx 4. In this paper, we describe deep near-infrared imaging of 34 targets using the Magellan I and Gemini North telescopes. We discuss in detail special challenges of distortion and nonlinearity that must be addressed when performing point-spread function (PSF) subtraction with data from these telescopes and their IR cameras, especially in very good seeing. We derive black hole masses from emission-line spectroscopy, and we calculate accretion rates from our K{sub s} -band photometry, which directly samples the rest frame B for these objects. We introduce a new isophotal diameter technique for estimating host galaxy luminosities. We report the detection of four host galaxies on our deepest, sharpest images, and present upper limits for the others. We find that if host galaxies passively evolve such that they brighten by 2 mag or more in the rest-frame B band between the present and z = 4, then high-z hosts are less massive at a given black hole mass than are their low-z counterparts. We argue that the most massive hosts plateau at approx<10 L*. We estimate the importance of selection effects on this survey and the subsequent limitations of our conclusions. These results are in broad agreement with recent semianalytical models for the formation of luminous quasars and their host spheroids by mergers of gas-rich galaxies, with significant dissipation, and self-regulation of black hole growth and star formation by the burst of merger-induced quasar activity.

  18. A DISTANT QUASAR'S BRILLIANT LIGHT

    NASA Technical Reports Server (NTRS)

    2002-01-01

    The arrow in this image, taken by a ground-based telescope, points to a distant quasar, the brilliant core of an active galaxy residing billions of light-years from Earth. As light from this faraway object travels across space, it picks up information on galaxies and the vast clouds of material between galaxies as it moves through them. The Space Telescope Imaging Spectrograph aboard NASA's Hubble Space Telescope decoded the quasar's light to find the spectral 'fingerprints' of highly ionized (energized) oxygen, which had mixed with invisible clouds of hydrogen in intergalactic space. The quasar's brilliant beam pierced at least four separate filaments of the invisible hydrogen laced with the telltale oxygen. The presence of oxygen between the galaxies implies there are huge quantities of hydrogen in the universe. Credits: WIYN Telescope at Kitt Peak National Observatory in Arizona. The telescope is owned and operated by the University of Wisconsin, Indiana University, Yale University, and the National Optical Astronomy Observatories.

  19. CONSTRAINTS ON THE FAINT END OF THE QUASAR LUMINOSITY FUNCTION AT z {approx} 5 IN THE COSMOS FIELD

    SciTech Connect

    Ikeda, H.; Matsuoka, K.; Kajisawa, M.; Nagao, T.; Taniguchi, Y.; Shioya, Y.; Enoki, M.; Capak, P.; Masters, D.; Scoville, N. Z.; Civano, F.; Koekemoer, A. M.; Morokuma, T.; Salvato, M.; Schinnerer, E.

    2012-09-10

    We present the result of our low-luminosity quasar survey in the redshift range of 4.5 {approx}< z {approx}< 5.5 in the COSMOS field. Using the COSMOS photometric catalog, we selected 15 quasar candidates with 22 < i' < 24 at z {approx} 5 that are {approx}3 mag fainter than the Sloan Digital Sky Survey quasars in the same redshift range. We obtained optical spectra for 14 of the 15 candidates using FOCAS on the Subaru Telescope and did not identify any low-luminosity type-1 quasars at z {approx} 5, while a low-luminosity type-2 quasar at z {approx} 5.07 was discovered. In order to constrain the faint end of the quasar luminosity function at z {approx} 5, we calculated the 1{sigma} confidence upper limits of the space density of type-1 quasars. As a result, the 1{sigma} confidence upper limits on the quasar space density are {Phi} < 1.33 Multiplication-Sign 10{sup -7} Mpc{sup -3} mag{sup -1} for -24.52 < M{sub 1450} < -23.52 and {Phi} < 2.88 Multiplication-Sign 10{sup -7} Mpc{sup -3} mag{sup -1} for -23.52 < M{sub 1450} < -22.52. The inferred 1{sigma} confidence upper limits of the space density are then used to provide constraints on the faint-end slope and the break absolute magnitude of the quasar luminosity function at z {approx} 5. We find that the quasar space density decreases gradually as a function of redshift at low luminosity (M{sub 1450} {approx} -23), being similar to the trend found for quasars with high luminosity (M{sub 1450} < -26). This result is consistent with the so-called downsizing evolution of quasars seen at lower redshifts.

  20. The Geometry of Quasar Outflows

    NASA Astrophysics Data System (ADS)

    Ganguly, Rajib

    2012-10-01

    Quasar outflows are important for understanding the accretion and growth processes of the central black hole, but also potentially play a role in feedback to the galaxy, halting star formation and infall of gas. A big uncertainty lies in the geometry and density of these outflows, especially as a function of ionization and velocity. We aim to tackle this using the archival COS M grating spectra of 266 quasars. We separate the geometry of outflows into two parts: the solid angle subtended around the black hole, and the distance of the outflow from the central engine. Large numbers of quasars with high resolution spectra are required for each aspect of this statistical investigation. First, we will determine which/how many absorption-line systems are intrinsic through both partial covering methods and statistical assessments. Second, we will consider the incidence of intrinsic absorbers as a function of quasar property {e.g., radio-loudness, SED shape, black hole mass, bolometric luminosity}. This will reveal what determines the solid angle. This can only be done at moderate redshifts where quasars with a larger range of properties are observable, and hence requires HST/COS. Third, we will use the wide range of diagnostic lines to constrain the physical conditions of the absorbers. We will target the CIII*1175 complex and apply photoionization models to constrain the densities and ionization parameters. This will provide the largest set yet of intrinsic absorbers with systematic distance constraints. In tandem with the solid angles, this work will inform models regarding the geometry of quasar outflows.

  1. A Spectral Study of a New Class of Radio Quasars

    NASA Technical Reports Server (NTRS)

    Perlman, Eric S.

    2003-01-01

    This document serves as a final technical report for NASA grants NAG5-9995 and NAG5-9533, entitled 'A Spectral Study of a New Class of Radio Quasars.' The purpose of these grants were to support observations made using the BeppoSAX satellite. The observations took place over two years and covered two SAX observing cycles, respectively AO-3 and AO-4. During this time, I was employed both at Johns Hopkins University (NAG5-9995) and the University of Maryland, Baltimore County (NAG5-9533). As the research on these grants was on the same subject and my employment at JHU and UMBC has been consecutive, this document therefore covers both grants. The targets for these observations were four radio-loud quasars chosen from the first two X-ray selected samples of such objects. These were the brightest examples of the newly found class of X-ray loud flat-spectrum radio quasars, which prior to 1997, had never been seen before. However, my previous work with collaborators Paolo Padovani and Paolo Giommi on the DXRBS survey showed that they make up about 25% of the population of flat-spectrum radio quasars, but had not been seen before because of selection biases (all previous samples of these objects had been compiled in the radio). The purpose of the SAX observations was to investigate the shape of their X-ray spectrum, which would tell us where the peak of their synchrotron emission was located.

  2. "Dead quasars" in nearby galaxies?

    PubMed

    Rees, M J

    1990-02-16

    The nuclei of some galaxies undergo violent activity, quasars being the most extreme instances of this phenomenon. Such activity is probably short-lived compared to galactic lifetimes, and was most prevalent when the universe was only about one-fifth of its present age. A massive black hole seems the inevitable end point of such activity, and dead quasars should greatly outnumber active ones. In recent years, studies of stellar motions in the cores of several nearby galaxies indicate the presence of central dark masses which could be black holes. This article discusses how such evidence might be corroborated, and the potential implications for our understanding of active galaxies and black holes.

  3. BMDS: A Collection of R Functions for Bayesian Multidimensional Scaling

    ERIC Educational Resources Information Center

    Okada, Kensuke; Shigemasu, Kazuo

    2009-01-01

    Bayesian multidimensional scaling (MDS) has attracted a great deal of attention because: (1) it provides a better fit than do classical MDS and ALSCAL; (2) it provides estimation errors of the distances; and (3) the Bayesian dimension selection criterion, MDSIC, provides a direct indication of optimal dimensionality. However, Bayesian MDS is not…

  4. The Origins and Maintenance of Female Genital Modification across Africa : Bayesian Phylogenetic Modeling of Cultural Evolution under the Influence of Selection.

    PubMed

    Ross, Cody T; Strimling, Pontus; Ericksen, Karen Paige; Lindenfors, Patrik; Mulder, Monique Borgerhoff

    2016-06-01

    We present formal evolutionary models for the origins and persistence of the practice of Female Genital Modification (FGMo). We then test the implications of these models using normative cross-cultural data on FGMo in Africa and Bayesian phylogenetic methods that explicitly model adaptive evolution. Empirical evidence provides some support for the findings of our evolutionary models that the de novo origins of the FGMo practice should be associated with social stratification, and that social stratification should place selective pressures on the adoption of FGMo; these results, however, are tempered by the finding that FGMo has arisen in many cultures that have no social stratification, and that forces operating orthogonally to stratification appear to play a more important role in the cross-cultural distribution of FGMo. To explain these cases, one must consider cultural evolutionary explanations in conjunction with behavioral ecological ones. We conclude with a discussion of the implications of our study for policies designed to end the practice of FGMo. PMID:26846688

  5. Post hoc Analysis for Detecting Individual Rare Variant Risk Associations Using Probit Regression Bayesian Variable Selection Methods in Case-Control Sequencing Studies.

    PubMed

    Larson, Nicholas B; McDonnell, Shannon; Albright, Lisa Cannon; Teerlink, Craig; Stanford, Janet; Ostrander, Elaine A; Isaacs, William B; Xu, Jianfeng; Cooney, Kathleen A; Lange, Ethan; Schleutker, Johanna; Carpten, John D; Powell, Isaac; Bailey-Wilson, Joan; Cussenot, Olivier; Cancel-Tassin, Geraldine; Giles, Graham; MacInnis, Robert; Maier, Christiane; Whittemore, Alice S; Hsieh, Chih-Lin; Wiklund, Fredrik; Catolona, William J; Foulkes, William; Mandal, Diptasri; Eeles, Rosalind; Kote-Jarai, Zsofia; Ackerman, Michael J; Olson, Timothy M; Klein, Christopher J; Thibodeau, Stephen N; Schaid, Daniel J

    2016-09-01

    Rare variants (RVs) have been shown to be significant contributors to complex disease risk. By definition, these variants have very low minor allele frequencies and traditional single-marker methods for statistical analysis are underpowered for typical sequencing study sample sizes. Multimarker burden-type approaches attempt to identify aggregation of RVs across case-control status by analyzing relatively small partitions of the genome, such as genes. However, it is generally the case that the aggregative measure would be a mixture of causal and neutral variants, and these omnibus tests do not directly provide any indication of which RVs may be driving a given association. Recently, Bayesian variable selection approaches have been proposed to identify RV associations from a large set of RVs under consideration. Although these approaches have been shown to be powerful at detecting associations at the RV level, there are often computational limitations on the total quantity of RVs under consideration and compromises are necessary for large-scale application. Here, we propose a computationally efficient alternative formulation of this method using a probit regression approach specifically capable of simultaneously analyzing hundreds to thousands of RVs. We evaluate our approach to detect causal variation on simulated data and examine sensitivity and specificity in instances of high RV dimensionality as well as apply it to pathway-level RV analysis results from a prostate cancer (PC) risk case-control sequencing study. Finally, we discuss potential extensions and future directions of this work.

  6. Post hoc Analysis for Detecting Individual Rare Variant Risk Associations Using Probit Regression Bayesian Variable Selection Methods in Case-Control Sequencing Studies.

    PubMed

    Larson, Nicholas B; McDonnell, Shannon; Albright, Lisa Cannon; Teerlink, Craig; Stanford, Janet; Ostrander, Elaine A; Isaacs, William B; Xu, Jianfeng; Cooney, Kathleen A; Lange, Ethan; Schleutker, Johanna; Carpten, John D; Powell, Isaac; Bailey-Wilson, Joan; Cussenot, Olivier; Cancel-Tassin, Geraldine; Giles, Graham; MacInnis, Robert; Maier, Christiane; Whittemore, Alice S; Hsieh, Chih-Lin; Wiklund, Fredrik; Catolona, William J; Foulkes, William; Mandal, Diptasri; Eeles, Rosalind; Kote-Jarai, Zsofia; Ackerman, Michael J; Olson, Timothy M; Klein, Christopher J; Thibodeau, Stephen N; Schaid, Daniel J

    2016-09-01

    Rare variants (RVs) have been shown to be significant contributors to complex disease risk. By definition, these variants have very low minor allele frequencies and traditional single-marker methods for statistical analysis are underpowered for typical sequencing study sample sizes. Multimarker burden-type approaches attempt to identify aggregation of RVs across case-control status by analyzing relatively small partitions of the genome, such as genes. However, it is generally the case that the aggregative measure would be a mixture of causal and neutral variants, and these omnibus tests do not directly provide any indication of which RVs may be driving a given association. Recently, Bayesian variable selection approaches have been proposed to identify RV associations from a large set of RVs under consideration. Although these approaches have been shown to be powerful at detecting associations at the RV level, there are often computational limitations on the total quantity of RVs under consideration and compromises are necessary for large-scale application. Here, we propose a computationally efficient alternative formulation of this method using a probit regression approach specifically capable of simultaneously analyzing hundreds to thousands of RVs. We evaluate our approach to detect causal variation on simulated data and examine sensitivity and specificity in instances of high RV dimensionality as well as apply it to pathway-level RV analysis results from a prostate cancer (PC) risk case-control sequencing study. Finally, we discuss potential extensions and future directions of this work. PMID:27312771

  7. A systematic search for changing-look quasars in SDSS

    NASA Astrophysics Data System (ADS)

    MacLeod, Chelsea L.; Ross, Nicholas P.; Lawrence, Andy; Goad, Mike; Horne, Keith; Burgett, William; Chambers, Ken C.; Flewelling, Heather; Hodapp, Klaus; Kaiser, Nick; Magnier, Eugene; Wainscoat, Richard; Waters, Christopher

    2016-03-01

    We present a systematic search for changing-look quasars based on repeat photometry from Sloan Digital Sky Survey (SDSS) and Pan-STARRS1, along with repeat spectra from SDSS and SDSS-III Baryon Oscillation Spectroscopic Survey. Objects with large, |Δg| > 1 mag photometric variations in their light curves are selected as candidates to look for changes in broad emission line (BEL) features. Out of a sample of 1011 objects that satisfy our selection criteria and have more than one epoch of spectroscopy, we find 10 examples of quasars that have variable and/or `changing-look' BEL features. Four of our objects have emerging BELs, five have disappearing BELs, and one object shows tentative evidence for having both emerging and disappearing BELs. With redshifts in the range 0.20 < z < 0.63, this sample includes the highest redshift changing-look quasars discovered to date. We highlight the quasar J102152.34+464515.6 at z = 0.204. Here, not only have the Balmer emission lines strongly diminished in prominence, including Hβ all but disappearing, but the blue continuum fν∝ν1/3 typical of an active galactic nuclei is also significantly diminished in the second epoch of spectroscopy. Using our selection criteria, we estimate that >15 per cent of strongly variable luminous quasars display changing-look BEL features on rest-frame time-scales of 8 to 10 yr. Plausible time-scales for variable dust extinction are factors of 2-10 too long to explain the dimming and brightening in these sources, and simple dust reddening models cannot reproduce the BEL changes. On the other hand, an advancement such as disc reprocessing is needed if the observed variations are due to accretion rate changes.

  8. Flamingos 2 Spectroscopy of Obscured and Unobscured Quasars

    NASA Astrophysics Data System (ADS)

    Ridgway, Susan; Lacy, Mark; Urrutia, Tanya; Petric, Andreea

    2013-08-01

    We will use Flamingos-2 to obtain spectra of luminous AGN and quasars selected in the mid-infrared. Mid-infrared selection is much less biased with respect to obscuration than optical and X-ray techniques, and hence allows for finding obscured (Type-2) quasars as well as Type-1 quasars. Our survey so far has been very successful and has provided an unique opportunity to construct luminosity functions for both Type-1 and Type-2 quasars selected in the same way and covering similar redshifts and luminosities. We have quantifed the change in the obscured fraction with luminosity and redshift for the first time, and find interesting indications that at high redshift the obscured fraction rises, consistent with models for the joint formation of the galaxy and black hole populations. Our samples are, however, still quite incomplete at low fluxes (and therefore lower luminosities at a given redshift), particularly in the southern hemisphere. Near-infrared spectroscopy, such as that we have previously obtained with NIRI at Gemini N, offers us the best possibility of bringing these southern samples to a reasonable completeness level, and will greatly increase the number of high z quasars in our sample. This will allow us to better judge our tantalizing initial results on the redshift evolution of the obscured fraction. In addition, these southern targets can be followed up with ALMA and GEMS/GSAOI to study the morphologies and star-formation properties of the hosts, allowing further exploration of the relationship between the formation of massive bulges and supermassive blackholes in the early universe.

  9. THE HIGH A{sub V} Quasar Survey: Reddened Quasi-Stellar Objects selected from optical/near-infrared photometry. II

    SciTech Connect

    Krogager, J.-K.; Fynbo, J. P. U.; Vestergaard, M.; Geier, S.; Venemans, B. P.; Ledoux, C.; Møller, P.; Noterdaeme, P.; Kangas, T.; Pursimo, T.; Smirnova, O.; Saturni, F. G.

    2015-03-15

    Quasi-stellar objects (QSOs) whose spectral energy distributions (SEDs) are reddened by dust either in their host galaxies or in intervening absorber galaxies are to a large degree missed by optical color selection criteria like the ones used by the Sloan Digital Sky Survey (SDSS). To overcome this bias against red QSOs, we employ a combined optical and near-infrared (near-IR) color selection. In this paper, we present a spectroscopic follow-up campaign of a sample of red candidate QSOs which were selected from the SDSS and the UKIRT Infrared Deep Sky Survey (UKIDSS). The spectroscopic data and SDSS/UKIDSS photometry are supplemented by mid-infrared photometry from the Wide-field Infrared Survey Explorer. In our sample of 159 candidates, 154 (97%) are confirmed to be QSOs. We use a statistical algorithm to identify sightlines with plausible intervening absorption systems and identify nine such cases assuming dust in the absorber similar to Large Magellanic Cloud sightlines. We find absorption systems toward 30 QSOs, 2 of which are consistent with the best-fit absorber redshift from the statistical modeling. Furthermore, we observe a broad range in SED properties of the QSOs as probed by the rest-frame 2 μm flux. We find QSOs with a strong excess as well as QSOs with a large deficit at rest-frame 2 μm relative to a QSO template. Potential solutions to these discrepancies are discussed. Overall, our study demonstrates the high efficiency of the optical/near-IR selection of red QSOs.

  10. QUANTIFYING QUASAR VARIABILITY AS PART OF A GENERAL APPROACH TO CLASSIFYING CONTINUOUSLY VARYING SOURCES

    SciTech Connect

    Kozlowski, Szymon; Kochanek, Christopher S.; Udalski, A.; Wyrzykowski, L.; Soszynski, I.; Szymanski, M. K.; Kubiak, M.; Pietrzynski, G.; Szewczyk, O.; Ulaczyk, K.; Poleski, R. E-mail: ckochanek@astronomy.ohio-state.ed

    2010-01-10

    Robust fast methods to classify variable light curves in large sky surveys are becoming increasingly important. While it is relatively straightforward to identify common periodic stars and particular transient events (supernovae, novae, microlensing events), there is no equivalent for non-periodic continuously varying sources (quasars, aperiodic stellar variability). In this paper, we present a fast method for modeling and classifying such sources. We demonstrate the method using approx86, 000 variable sources from the OGLE-II survey of the LMC and approx2700 mid-IR-selected quasar candidates from the OGLE-III survey of the LMC and SMC. We discuss the location of common variability classes in the parameter space of the model. In particular, we show that quasars occupy a distinct region of variability space, providing a simple quantitative approach to the variability selection of quasars.

  11. Bayesian Methods for High Dimensional Linear Models

    PubMed Central

    Mallick, Himel; Yi, Nengjun

    2013-01-01

    In this article, we present a selective overview of some recent developments in Bayesian model and variable selection methods for high dimensional linear models. While most of the reviews in literature are based on conventional methods, we focus on recently developed methods, which have proven to be successful in dealing with high dimensional variable selection. First, we give a brief overview of the traditional model selection methods (viz. Mallow’s Cp, AIC, BIC, DIC), followed by a discussion on some recently developed methods (viz. EBIC, regularization), which have occupied the minds of many statisticians. Then, we review high dimensional Bayesian methods with a particular emphasis on Bayesian regularization methods, which have been used extensively in recent years. We conclude by briefly addressing the asymptotic behaviors of Bayesian variable selection methods for high dimensional linear models under different regularity conditions. PMID:24511433

  12. Bayesian Methods for High Dimensional Linear Models.

    PubMed

    Mallick, Himel; Yi, Nengjun

    2013-06-01

    In this article, we present a selective overview of some recent developments in Bayesian model and variable selection methods for high dimensional linear models. While most of the reviews in literature are based on conventional methods, we focus on recently developed methods, which have proven to be successful in dealing with high dimensional variable selection. First, we give a brief overview of the traditional model selection methods (viz. Mallow's Cp, AIC, BIC, DIC), followed by a discussion on some recently developed methods (viz. EBIC, regularization), which have occupied the minds of many statisticians. Then, we review high dimensional Bayesian methods with a particular emphasis on Bayesian regularization methods, which have been used extensively in recent years. We conclude by briefly addressing the asymptotic behaviors of Bayesian variable selection methods for high dimensional linear models under different regularity conditions.

  13. THE MAGELLANIC QUASARS SURVEY. III. SPECTROSCOPIC CONFIRMATION OF 758 ACTIVE GALACTIC NUCLEI BEHIND THE MAGELLANIC CLOUDS

    SciTech Connect

    Kozłowski, Szymon; Udalski, Andrzej; Szymański, M. K.; Kubiak, M.; Pietrzyński, G.; Soszyński, I.; Wyrzykowski, Ł.; Ulaczyk, K.; Poleski, R.; Pietrukowicz, P.; Skowron, J.; Onken, Christopher A.; Kochanek, Christopher S.; Meixner, M.; Bonanos, A. Z. E-mail: onken@mso.anu.edu.au; Collaboration: OGLE Collaboration

    2013-10-01

    The Magellanic Quasars Survey (MQS) has now increased the number of quasars known behind the Magellanic Clouds by almost an order of magnitude. All survey fields in the Large Magellanic Cloud (LMC) and 70% of those in the Small Magellanic Cloud (SMC) have been observed. The targets were selected from the third phase of the Optical Gravitational Lensing Experiment (OGLE-III) based on their optical variability, mid-IR, and/or X-ray properties. We spectroscopically confirmed 758 quasars (565 in the LMC and 193 in the SMC) behind the clouds, of which 94% (527 in the LMC and 186 in the SMC) are newly identified. The MQS quasars have long-term (12 yr and growing for OGLE), high-cadence light curves, enabling unprecedented variability studies of quasars. The MQS quasars also provide a dense reference grid for measuring both the internal and bulk proper motions of the clouds, and 50 quasars are bright enough (I ∼< 18 mag) for absorption studies of the interstellar/intergalactic medium of the clouds.

  14. SDSS J0246-0825: A New Gravitationally Lensed Quasar from the Sloan Digital Sky Survey

    SciTech Connect

    Inada, N; Burles, S; Gregg, M D; Becker, R H; Schechter, P L; Eisenstein, D J; Oguri, M; Castander, F J; Hall, P B; Johnston, D E; Pindor, B; Richards, G T; Schneider, D P; White, R L; Brinkmann, J; Szalay, A; York, D G

    2005-11-10

    We report the discovery of a new two-image gravitationally lensed quasar, SDSS J024634.11-082536.2 (SDSS J0246-0825). This object was selected as a lensed quasar candidate from the Sloan Digital Sky Survey (SDSS) by the same algorithm that was used to discover other SDSS lensed quasars (e.g., SDSS J0924+0219). Multicolor imaging with the Magellan Consortium's Walter Baade 6.5-m telescope and the spectroscopic observations using the W. M. Keck Observatory's Keck II telescope confirm that SDSS J0246-0825 consists of two lensed images ({Delta}{theta} = 1''.04) of a source quasar at z = 1.68. Imaging observations with the Keck telescope and the Hubble Space Telescope reveal an extended object between the two quasar components, which is likely to be a lensing galaxy of this system. From the absorption lines in the spectra of quasar components and the apparent magnitude of the galaxy, combined with the expected absolute magnitude from the Faber-Jackson relation, we estimate the redshift of the lensing galaxy to be z = 0.724. A highly distorted ring is visible in the Hubble Space Telescope images, which is likely to be the lensed host galaxy of the source quasar. Simple mass modeling predicts the possibility that there is a small (faint) lensing object near the primary lensing galaxy.

  15. The Most Luminous Heavily Obscured Quasars Have a High Merger Fraction: Morphological Study of WISE-selected Hot Dust-obscured Galaxies

    NASA Astrophysics Data System (ADS)

    Fan, Lulu; Han, Yunkun; Fang, Guanwen; Gao, Ying; Zhang, Dandan; Jiang, Xiaoming; Wu, Qiaoqian; Yang, Jun; Li, Zhao

    2016-05-01

    Previous studies have shown that Wide-field Infrared Survey Explorer-selected hyperluminous, hot dust-obscured galaxies (Hot DOGs) are powered by highly dust-obscured, possibly Compton-thick active galactic nuclei (AGNs). High obscuration provides us a good chance to study the host morphology of the most luminous AGNs directly. We analyze the host morphology of 18 Hot DOGs at z ˜ 3 using Hubble Space Telescope/WFC3 imaging. We find that Hot DOGs have a high merger fraction (62 ± 14%). By fitting the surface brightness profiles, we find that the distribution of Sérsic indices in our Hot DOG sample peaks around 2, which suggests that most Hot DOGs have transforming morphologies. We also derive the AGN bolometric luminosity (˜1014 L ⊙) of our Hot DOG sample by using IR spectral energy distributions decomposition. The derived merger fraction and AGN bolometric luminosity relation is well consistent with the variability-based model prediction. Both the high merger fraction in an IR-luminous AGN sample and relatively low merger fraction in a UV/optical-selected, unobscured AGN sample can be expected in the merger-driven evolutionary model. Finally, we conclude that Hot DOGs are merger-driven and may represent a transit phase during the evolution of massive galaxies, transforming from the dusty starburst-dominated phase to the unobscured QSO phase.

  16. A Survey of z>5.7 Quasars in the Sloan Digital Sky Survey. III. Discovery of Five Additional Quasars

    NASA Astrophysics Data System (ADS)

    Fan, Xiaohui; Hennawi, Joseph F.; Richards, Gordon T.; Strauss, Michael A.; Schneider, Donald P.; Donley, Jennifer L.; Young, Jason E.; Annis, James; Lin, Huan; Lampeitl, Hubert; Lupton, Robert H.; Gunn, James E.; Knapp, Gillan R.; Brandt, W. N.; Anderson, Scott; Bahcall, Neta A.; Brinkmann, Jon; Brunner, Robert J.; Fukugita, Masataka; Szalay, Alexander S.; Szokoly, Gyula P.; York, Donald G.

    2004-08-01

    We present the discovery of five new quasars at z>5.7, selected from the multicolor imaging data of the Sloan Digital Sky Survey (SDSS). Three of them, at redshifts 5.93, 6.07, and 6.22, were selected from ~1700 deg2 of new SDSS Main Survey imaging in the northern Galactic cap. An additional quasar, at redshift 5.85, was discovered by co-adding the data obtained in the Fall Equatorial Stripe in the SDSS Southern Survey Region. The fifth object, at redshift 5.80, is selected from a nonstandard SDSS scan in the southern Galactic cap outside the Main Survey area. The spectrum of SDSS J162331.81+311200.5 (z=6.22) shows a complete Gunn-Peterson trough at zabs>5.95, similar to the troughs detected in the other three z>~6.2 quasars known. We present a composite spectrum of the z>5.7 quasars discovered in the SDSS to date. The average emission-line and continuum properties of z~6 quasars exhibit no significant evolution compared with those at low redshift. Using a complete sample of nine z>5.7 quasars, we find that the density of quasars with M1450<-26.7 at z~6 is (6+/-2)×10-10 Mpc-3 (H0=65 km s-1 Mpc-1, Ω=0.35, and Λ=0.65), consistent with our previous estimates. The luminosity distribution of the sample is fitted with a power-law luminosity function Ψ(L)~L-3.2+/-0.7, somewhat steeper than but consistent with our previous estimates. Based on observations obtained with the Sloan Digital Sky Survey, and with the Apache Point Observatory 3.5 m telescope, which is owned and operated by the Astrophysical Research Consortium; and with the MMT Observatory, a joint facility of the University of Arizona and the Smithsonian Institution, with the University of Arizona 2.3 m Bok Telescope, with the Kitt Peak National Observatory 4 m Mayall Telescope, with the 6.5 m Landon Clay Telescope at the Las Campanas Observatory, a collaboration between the Observatories of the Carnegie Institution of Washington, University of Arizona, Harvard University, the University of Michigan, and

  17. On the Radio and Optical Luminosity Evolution of Quasars

    SciTech Connect

    Singal, J.; Petrosian, V.; Lawrence, A.; Stawarz, L.; /JAXA, Sagamihara /Jagiellonian U., Astron. Observ.

    2011-05-20

    We calculate simultaneously the radio and optical luminosity evolutions of quasars, and the distribution in radio loudness R defined as the ratio of radio and optical luminosities, using a flux limited data set containing 636 quasars with radio and optical fluxes from White et al. We first note that when dealing with multivariate data it is imperative to first determine the true correlations among the variables, not those introduced by the observational selection effects, before obtaining the individual distributions of the variables. We use the methods developed by Efron and Petrosian which are designed to obtain unbiased correlations, distributions, and evolution with redshift from a data set truncated due to observational biases. It is found that as expected the population of quasars exhibits strong positive correlation between the radio and optical luminosities and that this correlation deviates from a simple linear relation in a way indicating that more luminous quasars are more radio loud. We also find that there is a strong luminosity evolution with redshift in both wavebands, with significantly higher radio than optical evolution. We conclude that the luminosity evolution obtained by arbitrarily separating the sources into radio loud (R > 10) and radio quiet (R < 10) populations introduces significant biases that skew the result considerably. We also construct the local radio and optical luminosity functions and the density evolution. Finally, we consider the distribution of the radio loudness parameter R obtained from careful treatment of the selection effects and luminosity evolutions with that obtained from the raw data without such considerations. We find a significant difference between the two distributions and no clear sign of bi-modality in the true distribution. Our results indicate therefore, somewhat surprisingly, that there is no critical switch in the efficiency of the production of disk outflows/jets between very radio quiet and very radio

  18. Bayesian inference in geomagnetism

    NASA Technical Reports Server (NTRS)

    Backus, George E.

    1988-01-01

    The inverse problem in empirical geomagnetic modeling is investigated, with critical examination of recently published studies. Particular attention is given to the use of Bayesian inference (BI) to select the damping parameter lambda in the uniqueness portion of the inverse problem. The mathematical bases of BI and stochastic inversion are explored, with consideration of bound-softening problems and resolution in linear Gaussian BI. The problem of estimating the radial magnetic field B(r) at the earth core-mantle boundary from surface and satellite measurements is then analyzed in detail, with specific attention to the selection of lambda in the studies of Gubbins (1983) and Gubbins and Bloxham (1985). It is argued that the selection method is inappropriate and leads to lambda values much larger than those that would result if a reasonable bound on the heat flow at the CMB were assumed.

  19. Bayesian superresolution

    NASA Astrophysics Data System (ADS)

    Isakson, Steve Wesley

    2001-12-01

    Well-known principles of physics explain why resolution restrictions occur in images produced by optical diffraction-limited systems. The limitations involved are present in all diffraction-limited imaging systems, including acoustical and microwave. In most circumstances, however, prior knowledge about the object and the imaging system can lead to resolution improvements. In this dissertation I outline a method to incorporate prior information into the process of reconstructing images to superresolve the object beyond the above limitations. This dissertation research develops the details of this methodology. The approach can provide the most-probable global solution employing a finite number of steps in both far-field and near-field images. In addition, in order to overcome the effects of noise present in any imaging system, this technique provides a weighted image that quantifies the likelihood of various imaging solutions. By utilizing Bayesian probability, the procedure is capable of incorporating prior information about both the object and the noise to overcome the resolution limitation present in many imaging systems. Finally I will present an imaging system capable of detecting the evanescent waves missing from far-field systems, thus improving the resolution further.

  20. On the Triggering of Quasars During First Passage

    NASA Astrophysics Data System (ADS)

    da Silva, Robert

    2011-10-01

    Merger induced quasar {QSO} activity is commonly invoked as a principal mechanism responsible for the growth of central super-massive black holes {SMBHs} and concurrent evolution of their host galaxies. Despite the apparent successes of such models in reproducing global populations and distributions, fundamental questions surrounding the fueling of SMBHs remain untested. In particular, theoretical treatments predict that the the evolution of the BHs during a merger is determined by their host galaxy's bulge component. We will test this observationally by imaging 10 early-stage merging pairs of galaxies where one galaxy is in a quasar phase and the other is not. By selecting a sample of merging galaxies after first close passage but before final coalescence, we may study the early stages of the merger and precisely determine the properties of the progenitors. This allows a unique 1-to-1 comparison of the QSO-host and companion galaxy that cannot be attained with any other sample. In this manner, we will establish whether quasar triggering is sensitive to the host galaxy morphology. Analysis of the morphologies and stellar masses will also equip us to tackle other key questions related to quasar evolution and triggering. The proposed imaging will constrain the stellar masses of each galaxy to characterize the merger mass ratios that trigger QSO activity. Lastly, comparisons of the SMBH to the host bulge mass, at this intermediate stage, will offer new insights into the path SMBHs take on their way to the Magorrian relation.

  1. DISCOVERING BRIGHT QUASARS AT INTERMEDIATE REDSHIFTS BASED ON OPTICAL/NEAR-INFRARED COLORS

    SciTech Connect

    Wu, Xue-Bing; Zuo, Wenwen; Yang, Jinyi; Yang, Qian; Wang, Feige

    2013-10-01

    The identification of quasars at intermediate redshifts (2.2 < z < 3.5) has been inefficient in most previous quasar surveys since the optical colors of quasars are similar to those of stars. The near-IR K-band excess technique has been suggested to overcome this difficulty. Our recent study also proposed to use optical/near-IR colors for selecting z < 4 quasars. To verify the effectiveness of this method, we selected a list of 105 unidentified bright targets with i ≤ 18.5 from the quasar candidates of SDSS DR6 with both SDSS ugriz optical and UKIDSS YJHK near-IR photometric data, which satisfy our proposed Y – K/g – z criterion and have photometric redshifts between 2.2 and 3.5 estimated from the nine-band SDSS-UKIDSS data. We observed 43 targets with the BFOSC instrument on the 2.16 m optical telescope at Xinglong station of the National Astronomical Observatory of China in the spring of 2012. We spectroscopically identified 36 targets as quasars with redshifts between 2.1 and 3.4. The high success rate of discovering these quasars in the SDSS spectroscopic surveyed area further demonstrates the robustness of both the Y – K/g – z selection criterion and the photometric redshift estimation technique. We also used the above criterion to investigate the possible stellar contamination rate among the quasar candidates of SDSS DR6, and found that the rate is much higher when selecting 3 < z < 3.5 quasar candidates than when selecting lower redshift candidates (z < 2.2). The significant improvement in the photometric redshift estimation when using the nine-band SDSS-UKIDSS data over the five-band SDSS data is demonstrated and a catalog of 7727 unidentified quasar candidates in SDSS DR6 selected with optical/near-IR colors and having photometric redshifts between 2.2 and 3.5 is provided. We also tested the Y – K/g – z selection criterion with the recently released SDSS-III/DR9 quasar catalog and found that 96.2% of 17,999 DR9 quasars with UKIDSS Y- and K

  2. A SIMPLE MODEL FOR QUASAR DEMOGRAPHICS

    SciTech Connect

    Conroy, Charlie; White, Martin

    2013-01-10

    We present a simple model for the relationship between quasars, galaxies, and dark matter halos from 0.5 < z < 6. In the model, black hole (BH) mass is linearly related to galaxy mass, and galaxies are connected to dark matter halos via empirically constrained relations. A simple 'scattered' light bulb model for quasars is adopted, wherein BHs shine at a fixed fraction of the Eddington luminosity during accretion episodes, and Eddington ratios are drawn from a lognormal distribution that is redshift independent. This model has two free, physically meaningful parameters at each redshift: the normalization of the M {sub BH}-M {sub gal} relation and the quasar duty cycle; these parameters are fit to the observed quasar luminosity function (LF) over the interval 0.5 < z < 6. This simple model provides an excellent fit to the LF at all epochs and also successfully predicts the observed projected two-point correlation of quasars from 0.5 < z < 2.5. It is significant that a single quasar duty cycle at each redshift is capable of reproducing the extant observations. The data are therefore consistent with a scenario wherein quasars are equally likely to exist in galaxies, and therefore dark matter halos, over a wide range in masses. The knee in the quasar LF is a reflection of the knee in the stellar-mass-halo-mass relation. Future constraints on the quasar LF and quasar clustering at high redshift will provide strong constraints on the model. In the model, the autocorrelation function of quasars becomes a strong function of luminosity only at the very highest luminosities and will be difficult to observe because such quasars are so rare. Cross-correlation techniques may provide useful constraints on the bias of such rare objects. The simplicity of the model allows for rapid generation of quasar mock catalogs from N-body simulations that match the observed LF and clustering to high redshift.

  3. Heavily reddened type 1 quasars at z > 2 - I. Evidence for significant obscured black hole growth at the highest quasar luminosities

    NASA Astrophysics Data System (ADS)

    Banerji, Manda; Alaghband-Zadeh, S.; Hewett, Paul C.; McMahon, Richard G.

    2015-03-01

    We present a new population of z > 2 dust-reddened, type 1 quasars with 0.5 ≲ E(B - V) ≲ 1.5, selected using near-infrared (NIR) imaging data from the UKIDSS-LAS (Large Area Survey), ESO-VHS (European Southern Obseratory-VISTA Hemisphere Survey) and WISE surveys. NIR spectra obtained using the Very Large Telescope for 24 new objects bring our total sample of spectroscopically confirmed hyperluminous (>1013 L⊙), high-redshift dusty quasars to 38. There is no evidence for reddened quasars having significantly different Hα equivalent widths relative to unobscured quasars. The average black hole masses (˜109-1010 M⊙) and bolometric luminosities (˜1047 erg s-1) are comparable to the most luminous unobscured quasars at the same redshift, but with a tail extending to very high luminosities of ˜1048 erg s-1. 66 per cent of the reddened quasars are detected at >3σ at 22 μm by WISE. The average 6-μm rest-frame luminosity is log10(L6 μm/ erg s-1) = 47.1 ± 0.4, making the objects among the mid-infrared brightest active galactic nuclei (AGN) currently known. The extinction-corrected space density estimate now extends over three magnitudes (-30 < Mi < -27) and demonstrates that the reddened quasar luminosity function is significantly flatter than that of the unobscured quasar population at z = 2-3. At the brightest magnitudes, Mi ≲ -29, the space density of our dust-reddened population exceeds that of unobscured quasars. A model where the probability that a quasar becomes dust reddened increases at high luminosity is consistent with the observations and such a dependence could be explained by an increase in luminosity and extinction during AGN-fuelling phases. The properties of our obscured type 1 quasars are distinct from the heavily obscured, Compton-thick AGN that have been identified at much fainter luminosities and we conclude that they likely correspond to a brief evolutionary phase in massive galaxy formation.

  4. Half of the Most Luminous Quasars May Be Obscured: Investigating the Nature of WISE-Selected Hot Dust-Obscured Galaxies

    NASA Astrophysics Data System (ADS)

    Assef, R. J.; Eisenhardt, P. R. M.; Stern, D.; Tsai, C.-W.; Wu, J.; Wylezalek, D.; Blain, A. W.; Bridge, C. R.; Donoso, E.; Gonzales, A.; Griffith, R. L.; Jarrett, T. H.

    2015-05-01

    The Wide-field Infrared Survey Explorer mission has unveiled a rare population of high-redshift (z = 1-4.6), dusty, hyper-luminous galaxies, with infrared luminosities {{L}IR}\\gt {{10}13} {{L}⊙ }, and sometimes exceeding {{10}14} {{L}⊙ }. Previous work has shown that their dust temperatures and overall far-infrared spectral energy distributions (SEDs) are significantly hotter than expected to be powered by star formation. We present here an analysis of the rest-frame optical through mid-infrared SEDs for a large sample of these so-called “hot, dust-obscured galaxies” (Hot DOGs). We find that the SEDs of Hot DOGs are generally well modeled by the combination of a luminous, yet obscured active galactic nuclei (AGNs) that dominates the rest-frame emission at λ \\gt 1 μ m and the bolometric luminosity output, and a less luminous host galaxy that is responsible for the bulk of the rest optical/UV emission. Even though the stellar mass of the host galaxies may be as large as 1011-1012 M⊙, the AGN emission, with a range of luminosities comparable to those of the most luminous QSOs known, require that either Hot DOGs have black hole masses significantly in excess of the local relations, or that they radiate significantly above the Eddington limit, at a level at least 10 times more efficiently than z ˜ 2 QSOs. We show that, while rare, the number density of Hot DOGs is comparable to that of equally luminous but unobscured (i.e., Type 1) QSOs. This may be at odds with the trend suggested at lower luminosities for the fraction of obscured AGNs to decrease with increasing luminosity. That trend may, instead, reverse at higher luminosities. Alternatively, Hot DOGs may not be the torus-obscured counterparts of the known optically selected, largely unobscured, hyper-luminous QSOs, and may represent a new component of the galaxy evolution paradigm. Finally, we discuss the environments of Hot DOGs and statistically show that these objects are in regions as dense as

  5. Four Quasars above Redshift 6 Discovered by the Canada-France High-z Quasar Survey

    NASA Astrophysics Data System (ADS)

    Willott, Chris J.; Delorme, Philippe; Omont, Alain; Bergeron, Jacqueline; Delfosse, Xavier; Forveille, Thierry; Albert, Loic; Reylé, Céline; Hill, Gary J.; Gully-Santiago, Michael; Vinten, Phillip; Crampton, David; Hutchings, John B.; Schade, David; Simard, Luc; Sawicki, Marcin; Beelen, Alexandre; Cox, Pierre

    2007-12-01

    The Canada-France High-z Quasar Survey (CFHQS) is an optical survey designed to locate quasars during the epoch of reionization. In this paper we present the discovery of the first four CFHQS quasars at redshifts greater than 6, including the most distant known quasar, CFHQS J2329-0301 at z = 6.43. We describe the observational method used to identify the quasars and present optical, infrared, and millimeter photometry and optical and near-infrared spectroscopy. We investigate the dust properties of these quasars, finding an unusual dust extinction curve for one quasar and a high far-infrared luminosity due to dust emission for another. The mean millimeter continuum flux for CFHQS quasars is substantially lower than that for SDSS quasars at the same redshift, likely due to a correlation with quasar UV luminosity. For two quasars with sufficiently high signal-to-noise ratio optical spectra, we use the spectra to investigate the ionization state of hydrogen at z > 5. For CFHQS J1509-1749 at z = 6.12 we find significant evolution (beyond a simple extrapolation of lower redshift data) in the Gunn-Peterson optical depth at z > 5.4. The line of sight to this quasar has one of the highest known optical depths at z approx 5.8. An analysis of the sizes of the highly ionized near-zones in the spectra of two quasars at z = 6.12 and 6.43 suggest that the intergalactic medium surrounding these quasars was substantially ionized before these quasars turned on. Together, these observations point toward an extended reionization process, but we caution that cosmic variance is still a major limitation in z > 6 quasar observations.

  6. Discovery of a narrow line quasar

    NASA Technical Reports Server (NTRS)

    Stocke, J.; Liebert, J.; Maccacaro, T.; Griffiths, R. E.; Steiner, J. E.

    1982-01-01

    A stellar object is reported which, while having X-ray and optical luminosities typical of quasars, has narrow permitted and forbidden emission lines over the observed spectral range. The narrow-line spectrum is high-excitation, the Balmer lines seem to be recombinational, and a redder optical spectrum than that of most quasars is exhibited, despite detection as a weak radio source. The object does not conform to the relationships between H-beta parameters and X-ray flux previously claimed for a large sample of the active galactic nuclei. Because reddish quasars with narrow lines, such as the object identified, may not be found by the standard techniques for the discovery of quasars, the object may be a prototype of a new class of quasars analogous to high-luminosity Seyfert type 2 galaxies. It is suggested that these objects cannot comprise more than 10% of all quasars.

  7. A Hubble Diagram for Quasars

    NASA Astrophysics Data System (ADS)

    Risaliti, G.; Lusso, E.

    2015-12-01

    We present a new method to test the ΛCDM cosmological model and to estimate cosmological parameters based on the nonlinear relation between the ultraviolet and X-ray luminosities of quasars. We built a data set of 1138 quasars by merging several samples from the literature with X-ray measurements at 2 keV and SDSS photometry, which was used to estimate the extinction-corrected 2500 Å flux. We obtained three main results: (1) we checked the nonlinear relation between X-ray and UV luminosities in small redshift bins up to z˜ 6, confirming that the relation holds at all redshifts with the same slope; (2) we built a Hubble diagram for quasars up to z˜ 6, which is well matched to that of supernovae in the common z = 0-1.4 redshift interval and extends the test of the cosmological model up to z˜ 6; and (3) we showed that this nonlinear relation is a powerful tool for estimating cosmological parameters. Using the present data and assuming a ΛCDM model, we obtain {{{Ω }}}M = 0.22{}-0.08+0.10 and {{{Ω }}}{{Λ }} = 0.92{}-0.30+0.18 ({{{Ω }}}M = 0.28 ± 0.04 and {{{Ω }}}{{Λ }} = 0.73 +/- 0.08 from a joint quasar-SNe fit). Much more precise measurements will be achieved with future surveys. A few thousand SDSS quasars already have serendipitous X-ray observations from Chandra or XMM-Newton, and at least 100,000 quasars with UV and X-ray data will be made available by the extended ROentgen Survey with an Imaging Telescope Array all-sky survey in a few years. The Euclid, Large Synoptic Survey Telescope, and Advanced Telescope for High ENergy Astrophysics surveys will further increase the sample size to at least several hundred thousand. Our simulations show that these samples will provide tight constraints on the cosmological parameters and will allow us to test for possible deviations from the standard model with higher precision than is possible today.

  8. Physical properties of luminous dust-poor quasars

    SciTech Connect

    Jun, Hyunsung David; Im, Myungshin E-mail: mim@astro.snu.ac.kr

    2013-12-20

    We identify and characterize a population of luminous, dust-poor quasars at 0 < z < 5 that is photometrically similar to objects previously found at z > 6. This class of active galactic nuclei is known to show little IR emission from dusty structure, but it is poorly understood in terms of number evolution and dependence on physical quantities. To better understand the properties of these quasars, we compile a rest-frame UV to IR library of 41,000 optically selected type 1 quasars with L {sub bol} > 10{sup 45.7} erg s{sup –1}. After fitting the broadband spectral energy distributions (SEDs) with accretion disk and dust components, we find 0.6% of our sample to be hot dust-poor, with rest-frame 2.3 μm to 0.51 μm flux density ratios of –0.5 dex or less. The dust-poor SEDs are blue in the UV-optical and weak in the mid-IR, such that their accretion disks are less obscured and the hot dust emission traces that of warm dust down to the dust-poor regime. At a given bolometric luminosity, dust-poor quasars are lower in black hole mass and higher in Eddington ratio than general luminous quasars, suggesting that they are in a rapidly growing evolutionary state in which the dust-poor phase appears as a short or rare phenomenon. The dust-poor fraction increases with redshift, and possible implications for their evolution are discussed.

  9. Sensitive radio survey of obscured quasar candidates

    NASA Astrophysics Data System (ADS)

    Alexandroff, Rachael M.; Zakamska, Nadia L.; van Velzen, Sjoert; Greene, Jenny E.; Strauss, Michael A.

    2016-08-01

    We study the radio properties of moderately obscured quasars in samples at both low (z ˜ 0.5) and high (z ˜ 2.5) redshift to understand the role of radio activity in accretion, using the Karl G. Jansky Very Large Array (VLA) at 6.0GHz and 1.4GHz. Our z ˜ 2.5 sample consists of optically-selected obscured quasar candidates, all of which are radio-quiet, with typical radio luminosities of νLν[1.4 GHz]⪉ 10^{40} erg s-1. Only a single source is individually detected in our deep (rms˜10 μJy) exposures. This population would not be identified by radio-based selection methods used for distinguishing dusty star-forming galaxies and obscured active nuclei. In our pilot A-array study of z ˜ 0.5 radio-quiet quasars, we spatially resolve four of five objects on scales ˜5 kpc and find they have steep spectral indices with an average value of α = -0.75. Therefore, radio emission in these sources could be due to jet-driven or radiatively driven bubbles interacting with interstellar material on the scale of the host galaxy. Finally, we also study the additional population of ˜200 faint (˜40μJy - 40mJy) field radio sources observed over ˜120 arcmin2 of our data. 60% of these detections (excluding our original targets) are matched in the Sloan Digital Sky Survey (SDSS) and/or Wide-Field Infrared Survey Explorer (WISE) and are, in roughly equal shares, active galactic nuclei (AGN) at a broad range of redshifts, passive galaxies with no other signs of nuclear activity and infrared-bright but optically faint sources. Spectroscopically or photometrically confirmed star-forming galaxies constitute only a small minority of the matches. Such sensitive radio surveys allow us to address important questions of AGN evolution and evaluate the AGN contribution to the radio-quiet sky.

  10. The average size and temperature profile of quasar accretion disks

    SciTech Connect

    Jiménez-Vicente, J.; Mediavilla, E.; Muñoz, J. A.; Motta, V.; Falco, E.

    2014-03-01

    We use multi-wavelength microlensing measurements of a sample of 10 image pairs from 8 lensed quasars to study the structure of their accretion disks. By using spectroscopy or narrowband photometry, we have been able to remove contamination from the weakly microlensed broad emission lines, extinction, and any uncertainties in the large-scale macro magnification of the lens model. We determine a maximum likelihood estimate for the exponent of the size versus wavelength scaling (r{sub s} ∝λ {sup p}, corresponding to a disk temperature profile of T∝r {sup –1/p}) of p=0.75{sub −0.2}{sup +0.2} and a Bayesian estimate of p = 0.8 ± 0.2, which are significantly smaller than the prediction of the thin disk theory (p = 4/3). We have also obtained a maximum likelihood estimate for the average quasar accretion disk size of r{sub s}=4.5{sub −1.2}{sup +1.5} lt-day at a rest frame wavelength of λ = 1026 Å for microlenses with a mean mass of M = 1 M {sub ☉}, in agreement with previous results, and larger than expected from thin disk theory.

  11. THE SDSS-III BARYON OSCILLATION SPECTROSCOPIC SURVEY: THE QUASAR LUMINOSITY FUNCTION FROM DATA RELEASE NINE

    SciTech Connect

    Ross, Nicholas P.; White, Martin; Bailey, Stephen; McGreer, Ian D.; Richards, Gordon T.; Myers, Adam D.; Palanque-Delabrouille, Nathalie; Yeche, Christophe; Strauss, Michael A.; Anderson, Scott F.; Shen, Yue; Swanson, Molly E. C.; Brandt, W. N.; Aubourg, Eric; Bovy, Jo; DeGraf, Colin; Di Matteo, Tiziana; and others

    2013-08-10

    We present a new measurement of the optical quasar luminosity function (QLF), using data from the Sloan Digital Sky Survey-III: Baryon Oscillation Spectroscopic Survey (SDSS-III: BOSS). From the SDSS-III Data Release Nine, a uniform sample of 22,301 i {approx}< 21.8 quasars are selected over an area of 2236 deg{sup 2}, with confirmed spectroscopic redshifts between 2.2 < z < 3.5, filling in a key part of the luminosity-redshift plane for optical quasar studies. The completeness of the survey is derived through simulated quasar photometry, and this completeness estimate is checked using a sample of quasars selected by their photometric variability within the BOSS footprint. We investigate the level of systematics associated with our quasar sample using the simulations, in the process generating color-redshift relations and a new quasar K-correction. We probe the faint end of the QLF to M{sub i} (z = 2.2) Almost-Equal-To -24.5 and see a clear break in the QLF at all redshifts up to z = 3.5. A log-linear relation (in log {Phi}* - M*) for a luminosity evolution and density evolution model is found to adequately describe our data within the range 2.2 < z < 3.5; across this interval the break luminosity increases by a factor of {approx}2.6 while {Phi}* declines by a factor of {approx}8. At z {approx}< 2.2 our data are reasonably well fit by a pure luminosity evolution model, and only a weak signature of ''AGN downsizing'' is seen, in line with recent studies of the hard X-ray luminosity function. We compare our measured QLF to a number of theoretical models and find that models making a variety of assumptions about quasar triggering and halo occupation can fit our data over a wide range of redshifts and luminosities.

  12. Quasars and Active Galaxies: A Reading List.

    ERIC Educational Resources Information Center

    Fraknoi, Andrew

    1988-01-01

    Contains the annotated bibliographies of introductory books and sections of books, recent introductory articles, more advanced articles, and more advanced books dealing with quasars and active galaxies. (CW)

  13. "Dead quasars" in nearby galaxies?

    PubMed

    Rees, M J

    1990-02-16

    The nuclei of some galaxies undergo violent activity, quasars being the most extreme instances of this phenomenon. Such activity is probably short-lived compared to galactic lifetimes, and was most prevalent when the universe was only about one-fifth of its present age. A massive black hole seems the inevitable end point of such activity, and dead quasars should greatly outnumber active ones. In recent years, studies of stellar motions in the cores of several nearby galaxies indicate the presence of central dark masses which could be black holes. This article discusses how such evidence might be corroborated, and the potential implications for our understanding of active galaxies and black holes. PMID:17746076

  14. OPTOPUS observations of quasar candidates.

    NASA Astrophysics Data System (ADS)

    Cristiani, S.

    1987-06-01

    OPTOPUS is a fiber-optic instrument for multiple-object spectroscopy with the Boiler & Chivens spectrograph and a CCD detector at the 3.6-m telescope. The system has been described in detail by the Optical Instrumentation Group (1985, The Messenger 41,25). Its application for observing Halley's comet has been reported by Lund and Surdej (1986, The Messenger 43, 1). Here another "classical" use of multiple-object spectroscopy is presented: followup observations of quasar candidates.

  15. Quasar redshifts: the intrinsic component

    NASA Astrophysics Data System (ADS)

    Hansen, Peter M.

    2016-09-01

    The large observed redshift of quasars has suggested large cosmological distances and a corresponding enormous energy output to explain the brightness or luminosity as seen at earth. Alternative or complementary sources of redshift have not been identified by the astronomical community. This study examines one possible source of additional redshift: an intrinsic component based on the plasma characteristics of high temperature and high electron density which are believed to be present.

  16. A medium-bright quasar sample - New quasar surface densities in the magnitude range from 16.4 to 17.65 for B

    NASA Technical Reports Server (NTRS)

    Mitchell, K. J.; Warnock, A., III; Usher, P. D.

    1984-01-01

    A new medium-bright quasar sample (MBQS) is constructed from spectroscopic observations of 140 bright objects selected for varying degrees of blue and ultraviolet excess (B-UVX) in five Palomar 1.2 m Schmidt fields. The MBQS contains 32 quasars with B less than 17.65 mag. The new integral surface densities in the B range from 16.45 to 17.65 mag are approximately 40 percent (or more) higher than expected. The MBQS and its redshift distribution increase the area of the Hubble diagram covered by complete samples of quasars. The general spectroscopic results indicate that the three-color classification process used to catalog the spectroscopic candidates (1) has efficiently separated the intrinsically B-UVX stellar objects from the Population II subdwarfs and (2) has produced samples of B-UVX objects which are more complete than samples selected by (U - B) color alone.

  17. The ISO view of Palomar-Green quasars

    NASA Astrophysics Data System (ADS)

    Haas, M.; Klaas, U.; Müller, S. A. H.; Bertoldi, F.; Camenzind, M.; Chini, R.; Krause, O.; Lemke, D.; Meisenheimer, K.; Richards, P. J.; Wilkes, B. J.

    2003-04-01

    Mining the ISO data archive we provide the complete ISO view of PG quasars containing 64 infrared spectral energy distributions between 5 and 200 mu m. About half of the sample was supplemented by MAMBO and SCUBA (sub-)millimetre data. Since the PG quasars were selected optically, the high infrared detection rate of more than 80% suggests that every quasar possesses luminous to hyperluminous dust emission with dust masses comparable to Seyferts and ultraluminous IR galaxies (ULIRGs). The gas-to-dust mass ratio (of those sources where CO measurements are available in the literature) is consistent with the galactic value providing further evidence for the thermal nature of the IR emission of radio quiet quasars. The SEDs represent templates of unprecedented detail and sensitivity. The power-law like near- to mid-IR SEDs (Fnu ~ nu alpha) are smooth up to far-infrared wavelengths, favouring dust heating by the central AGN, and we conclude that, in particular for our hyperluminous quasars at z=1, starbursts play only a minor role for powering the dust emission, even in the FIR. The IR spectral slopes alpha1-10 μm range from -0.9 to -2.2 with a mean of -1.3 +/- 0.3. They neither correlate with the optical spectral slope alpha0.3-1 μm, nor with the IR luminosity, nor with the FIR/MIR luminosity ratio, nor with inclination-dependent extinction effects in the picture of a dusty torus. We suggest that the diversity of the SEDs reflects largely the evolution of the dust distribution, and we propose a classification of the SED shapes as well as an evolutionary scheme in which this variety can be understood. During the evolution the surrounding dust redistributes, settling more and more into a torus/disk like configuration, while the SEDs show an initial FIR bump, then an increasing MIR emission and a steeper near- to mid-infrared slope, both of which finally also decrease. Strikingly, based on the sensitive ISO data now we do not only see the coarse IR differences between

  18. BROAD ABSORPTION LINE DISAPPEARANCE ON MULTI-YEAR TIMESCALES IN A LARGE QUASAR SAMPLE

    SciTech Connect

    Filiz Ak, N.; Brandt, W. N.; Schneider, D. P.; Hall, P. B.; Anderson, S. F.; Gibson, R. R.; Lundgren, B. F.; Myers, A. D.; Petitjean, P.; Ross, Nicholas P.; Shen Yue; York, D. G.; Bizyaev, D.; Brinkmann, J.; Malanushenko, E.; Oravetz, D. J.; Pan, K.; Simmons, A. E.; Weaver, B. A.

    2012-10-01

    We present 21 examples of C IV broad absorption line (BAL) trough disappearance in 19 quasars selected from systematic multi-epoch observations of 582 bright BAL quasars (1.9 < z < 4.5) by the Sloan Digital Sky Survey-I/II (SDSS-I/II) and SDSS-III. The observations span 1.1-3.9 yr rest-frame timescales, longer than have been sampled in many previous BAL variability studies. On these timescales, Almost-Equal-To 2.3% of C IV BAL troughs disappear and Almost-Equal-To 3.3% of BAL quasars show a disappearing trough. These observed frequencies suggest that many C IV BAL absorbers spend on average at most a century along our line of sight to their quasar. Ten of the 19 BAL quasars showing C IV BAL disappearance have apparently transformed from BAL to non-BAL quasars; these are the first reported examples of such transformations. The BAL troughs that disappear tend to be those with small-to-moderate equivalent widths, relatively shallow depths, and high outflow velocities. Other non-disappearing C IV BALs in those nine objects having multiple troughs tend to weaken when one of them disappears, indicating a connection between the disappearing and non-disappearing troughs, even for velocity separations as large as 10,000-15,000 km s{sup -1}. We discuss possible origins of this connection including disk-wind rotation and changes in shielding gas.

  19. Clustering on very small scales from a large, complete sample of confirmed quasar pairs

    NASA Astrophysics Data System (ADS)

    Eftekharzadeh, Sarah; Myers, Adam D.; Djorgovski, Stanislav G.; Graham, Matthew J.; Hennawi, Joseph F.; Mahabal, Ashish A.; Richards, Gordon T.

    2016-06-01

    We present by far the largest sample of spectroscopically confirmed binaryquasars with proper transverse separations of 17.0 ≤ Rprop ≤ 36.6 h-1 kpc. Our sample, whichis an order-of-magnitude larger than previous samples, is selected from Sloan Digital Sky Survey (SDSS) imaging over an area corresponding to the SDSS 6th data release (DR6). Our quasars are targeted using a Kernel Density Estimation technique (KDE), and confirmed using long-slit spectroscopy on a range of facilities.Our most complete sub-sample of 44 binary quasars with g<20.85, extends across angular scales of 2.9" < Δθ < 6.3", and is targeted from a parent sample that would be equivalent to a full spectroscopic survey of nearly 300,000 quasars.We determine the projected correlation function of quasars (\\bar Wp) over proper transverse scales of 17.0 ≤ Rprop ≤ 36.6 h-1 kpc, and also in 4 bins of scale within this complete range.To investigate the redshift evolution of quasar clustering on small scales, we make the first self-consistent measurement of the projected quasar correlation function in 4 bins of redshift over 0.4 ≤ z ≤ 2.3.

  20. GBT Detection of Polarization-Dependent HI Absorption and HI Outflows in Local ULIRGs and Quasars

    NASA Technical Reports Server (NTRS)

    Teng, Stacy H.; Veilleux, Sylvain; Baker, Andrew J.

    2013-01-01

    We present the results of a 21-cm HI survey of 27 local massive gas-rich late-stage mergers and merger remnants with the Green Bank Telescope (GBT). These remnants were selected from the Quasar/ULIRG Evolution Study (QUEST) sample of ultraluminous infrared galaxies (ULIRGs; L(sub 8 - 1000 micron) > 10(exp 12) solar L) and quasars; our targets are all bolometrically dominated by active galactic nuclei (AGN) and sample the later phases of the proposed ULIRG-to-quasar evolutionary sequence. We find the prevalence of HI absorption (emission) to be 100% (29%) in ULIRGs with HI detections, 100% (88%) in FIR-strong quasars, and 63% (100%) in FIR-weak quasars. The absorption features are associated with powerful neutral outflows that change from being mainly driven by star formation in ULIRGs to being driven by the AGN in the quasars. These outflows have velocities that exceed 1500 km/s in some cases. Unexpectedly, we find polarization-dependent HI absorption in 57% of our spectra (88% and 63% of the FIR-strong and FIR-weak quasars, respectively). We attribute this result to absorption of polarized continuum emission from these sources by foreground HI clouds. About 60% of the quasars displaying polarized spectra are radio-loud, far higher than the approx 10% observed in the general AGN population. This discrepancy suggests that radio jets play an important role in shaping the environments in these galaxies. These systems may represent a transition phase in the evolution of gas-rich mergers into "mature" radio galaxies.

  1. Heavily obscured quasar host galaxies at z ∼ 2 are discs, not major mergers

    NASA Astrophysics Data System (ADS)

    Schawinski, Kevin; Simmons, Brooke D.; Urry, C. Megan; Treister, Ezequiel; Glikman, Eilat

    2012-09-01

    We explore the nature of heavily obscured quasar host galaxies at z˜ 2 using deep Hubble Space Telescope Wide Field Camera 3/infrared imaging of 28 dust-obscured galaxies (DOGs) to investigate the role of major mergers in driving black hole growth. The high levels of obscuration of the quasars selected for this study act as a natural coronagraph, blocking the quasar light and allowing a clear view of the underlying host galaxy. The sample of heavily obscured quasars represents a significant fraction of the cosmic mass accretion on supermassive black holes as the quasars have inferred bolometric luminosities around the break of the quasar luminosity function. We find that only a small fraction (4 per cent, at most 11-25 per cent) of the quasar host galaxies are major mergers. Fits to their surface brightness profiles indicate that 90 per cent of the host galaxies are either disc dominated, or have a significant disc. This disc-like host morphology, and the corresponding weakness of bulges, is evidence against major mergers and suggests that secular processes are the predominant driver of massive black hole growth. Finally, we suggest that the coincidence of mergers and active galactic nucleus activity is luminosity dependent, with only the most luminous quasars being triggered mostly by major mergers. a MUSYC catalogue ID, see Cardamone et al. (2010). Objects with X-ray detections are marked with *. b See images shown in Fig. 1. c The ratio of the host luminosity to the point source luminosity, reported only when GALFIT requires an unresolved object to yield a physical fit. This may be due to an AGN point source (in the case of the X-ray-detected DOGs) or an unresolved bulge or central concentration, i.e. a central bulge. d See Fig. 2.

  2. A Population of X-ray Weak Quasars: PHL 1811 Analogs at High Redshift

    NASA Astrophysics Data System (ADS)

    Wu, Jianfeng; Brandt, W. N.; Hall, P. B.; Gibson, R. R.; Richards, G. T.; Schneider, D. P.; Shemmer, O.; Just, D. W.; Schmidt, S. J.

    2011-09-01

    Luminous X-ray emission is considered to be a universal property of efficiently accreting supermassive black holes. However, there are a few notable examples of quasars emitting X-rays much more weakly by a factor of 10-100. We report X-ray observations of a sample of 10 high-redshift (z 2.2) type 1 quasars selected to have unusual UV emission-line properties (weak and blueshifted high-ionization lines; strong UV Fe emission) similar to those of PHL 1811, a confirmed intrinsically X-ray weak quasar. All of the eight radio-quiet PHL 1811 analogs, without exception, are notably X-ray weak by a mean factor of 13. These sources lack broad absorption lines and have blue UV/optical continua, suggesting they are intrinsically X-ray weak. However, their average X-ray spectrum appears to be harder than those of typical quasars, which may indicate the presence of heavy intrinsic X-ray absorption. Our radio-quiet PHL 1811 analogs support a connection between an X-ray weak spectral energy distribution and PHL 1811-like UV emission lines; this connection provides an economical way to identify X-ray weak type 1 quasars. The fraction of radio-quiet PHL 1811 analogs in the radio-quiet quasar population is estimated to be < 1.2%. Correlations between relative X-ray brightness and UV emission-line properties suggest that PHL 1811 analogs may have extreme wind-dominated broad emission-line regions. Observationally, radio-quiet PHL 1811 analogs appear to be a subset ( 30%) of radio-quiet weak-line quasars (WLQs). The existence of a subset of quasars in which high-ionization "shielding gas" covers most of the BELR, but little more than the BELR, could potentially unify the PHL 1811 analogs and WLQs.

  3. Clustering of intermediate redshift quasars using the final SDSS III-BOSS sample

    NASA Astrophysics Data System (ADS)

    Eftekharzadeh, Sarah; Myers, Adam D.; White, Martin; Weinberg, David H.; Schneider, Donald P.; Shen, Yue; Font-Ribera, Andreu; Ross, Nicholas P.; Paris, Isabelle; Streblyanska, Alina

    2015-11-01

    We measure the two-point clustering of spectroscopically confirmed quasars from the final sample of the Baryon Oscillation Spectroscopic Survey (BOSS) on comoving scales of 4 ≲ s ≲ 22 h-1 Mpc. The sample covers 6950 deg2 [ ˜ 19 (h- 1Gpc)3] and, over the redshift range 2.2 ≤ z ≤ 2.8, contains 55 826 homogeneously selected quasars, which is twice as many as in any similar work. We deduce bQ = 3.54 ± 0.10; the most precise measurement of quasar bias to date at these redshifts. This corresponds to a host halo mass of ˜2 × 1012 h-1 M⊙ with an implied quasar duty cycle of ˜1 per cent. The real-space projected correlation function is well fitted by a power law of index 2 and correlation length r0 = (8.12 ± 0.22) h- 1 Mpc over scales of 4 ≲ rp ≲ 25 h-1 Mpc. To better study the evolution of quasar clustering at moderate redshift, we extend the redshift range of our study to z ˜ 3.4 and measure the bias and correlation length of three subsamples over 2.2 ≤ z ≤ 3.4. We find no significant evolution of r0 or bias over this range, implying that the host halo mass of quasars decreases somewhat with increasing redshift. We find quasar clustering remains similar over a decade in luminosity, contradicting a scenario in which quasar luminosity is monotonically related to halo mass at z ≈ 2.5. Our results are broadly consistent with previous BOSS measurements, but they yield more precise constraints based upon a larger and more uniform data set.

  4. A Survey of Luminous High-redshift Quasars with SDSS and WISE. II. the Bright End of the Quasar Luminosity Function at z ≈ 5

    NASA Astrophysics Data System (ADS)

    Yang, Jinyi; Wang, Feige; Wu, Xue-Bing; Fan, Xiaohui; McGreer, Ian D.; Bian, Fuyan; Yi, Weimin; Yang, Qian; Ai, Yanli; Dong, Xiaoyi; Zuo, Wenwen; Green, Richard; Jiang, Linhua; Wang, Shu; Wang, Ran; Yue, Minghao

    2016-09-01

    This is the second paper in a series on a new luminous z ˜ 5 quasar survey using optical and near-infrared colors. Here we present a new determination of the bright end of the quasar luminosity function (QLF) at z ˜ 5. Combining our 45 new quasars with previously known quasars that satisfy our selections, we construct the largest uniform luminous z ˜ 5 quasar sample to date, with 99 quasars in the range of 4.7 ≤ z < 5.4 and -29 < M 1450 ≤ -26.8, within the Sloan Digital Sky Survey (SDSS) footprint. We use a modified 1/V a method including flux limit correction to derive a binned QLF, and we model the parametric QLF using maximum likelihood estimation. With the faint-end slope of the QLF fixed as α = -2.03 from previous deeper samples, the best fit of our QLF gives a flatter bright end slope β = -3.58 ± 0.24 and a fainter break magnitude {M}1450* = -26.98 ± 0.23 than previous studies at similar redshift. Combined with previous work at lower and higher redshifts, our result is consistent with a luminosity evolution and density evolution model. Using the best-fit QLF, the contribution of quasars to the ionizing background at z ˜ 5 is found to be 18%-45% with a clumping factor C of 2-5. Our sample suggests an evolution of radio loud fraction with optical luminosity but no obvious evolution with redshift.

  5. In the Dusty Recesses: Characterizing the Dark Matter Halos of Obscured Quasars via Clustering and CMB Lensing

    NASA Astrophysics Data System (ADS)

    Myers, Adam D.; DiPompeo, Michael A.; Hickox, Ryan C.; Runnoe, Jessie C.

    2016-06-01

    The spatial clustering of obscured and unobscured quasars provides an interesting constraint on the connection between the growth of supermassive black holes and the evolution of galaxies and large-scale structure. In pursuit of these constraints, we update our recent measurements of quasar clustering using WISE and Planck data. We carefully assess how alterations in these missions' data reduction pipelines result in different systematics on a range of angular scales, and define samples of WISE-selected quasars that appear to be least-influenced by differences in data calibration. With these samples we analyze quasar clustering via two complementary methods; the angular autocorrelation function and cosmic microwave background lensing cross-correlations. We measure a higher bias and halo mass for obscured quasars (b ~ 2.1) as compared to unobscured quasars (b ~ 1.8). This is at odds with simple orientation models but at a reduced significance (1.5σ) as compared to our work with previous survey data. Assuming that some fraction (as high as 75%) of obscured quasars are intrinsically similar to unobscured quasars but viewed through a "dusty torus," we infer that the remaining non-torus obscured quasar population must have a large clustering bias of ~3, and inhabit typical halo masses of ~3 × 1013 h-1M⊙ at a redshift of z ~ 1. These massive halos are likely the descendants of high-mass unobscured quasars at high redshift, and will evolve into members of galaxy groups by z ~ 0. This work was supported in part by NSF grants 1211112, 1515404 and 1515364.

  6. Quasars: Active nuclei of young galaxies

    NASA Technical Reports Server (NTRS)

    Komberg, B. V.

    1980-01-01

    The hypothetical properties of 'young' galaxies and possible methods of observing them are discussed. It is proposed that star formation first takes place in the central regions of protogalaxies which may appear as quasar-like objects. An evolutionary scheme is outlined in which the radio quasars are transformed in time into the nuclei of radio galaxies.

  7. Quasars - powerhouses at the edge of time

    NASA Astrophysics Data System (ADS)

    Gavin, M.

    2000-06-01

    1999 was the 70th anniversary of Edwin Hubble's seminal publication1 showing a cosmological redshift in galaxies. More recent discoveries of quasars have extended the universe's boundaries back in time nearer to the Big Bang. Some amateur spectrograms of quasars are presented showing a cosmological redshift.

  8. Quasars as very-accurate clock synchronizers

    NASA Technical Reports Server (NTRS)

    Hurd, W. J.; Goldstein, R. M.

    1975-01-01

    Quasars can be employed to synchronize global data communications, geophysical measurements, and atomic clocks. It is potentially two to three orders of magnitude better than presently-used Moon-bounce system. Comparisons between quasar and clock pulses are used to develop correction or synchronization factors for station clocks.

  9. Bayesian classification theory

    NASA Technical Reports Server (NTRS)

    Hanson, Robin; Stutz, John; Cheeseman, Peter

    1991-01-01

    The task of inferring a set of classes and class descriptions most likely to explain a given data set can be placed on a firm theoretical foundation using Bayesian statistics. Within this framework and using various mathematical and algorithmic approximations, the AutoClass system searches for the most probable classifications, automatically choosing the number of classes and complexity of class descriptions. A simpler version of AutoClass has been applied to many large real data sets, has discovered new independently-verified phenomena, and has been released as a robust software package. Recent extensions allow attributes to be selectively correlated within particular classes, and allow classes to inherit or share model parameters though a class hierarchy. We summarize the mathematical foundations of AutoClass.

  10. The SDSS view of the Palomar-Green Bright Quasar Survey

    NASA Astrophysics Data System (ADS)

    Jester, S.; Richards, G. T.; Schneider, D. P.; Stoughton, C.; Green, R. F.; Gunn, J. E.; Hall, P. B.; Kron, R. G.; Schmidt, M.; Vanden Berk, D. E.

    2004-12-01

    We compare the properties of UV excess-selected PG quasars to the ``PG-like'' subset of SDSS multicolor-selected quasars. We find no statistically significant differences in the distributions of optical colors, redshift, or radio properties taken from the FIRST survey (radio flux, power, and radio-optical flux ratio). Comparing the PG quasars to the entire SDSS quasar sample, we find that the PG UV excess selection criterion does not remove any objects from the PG that are not already removed by the B-band brightness limit. Thus, PG quasars constitute a representative sample of quasars which are bright in the B-band. However, the i-band limited SDSS sample includes objects with a much wider range of colors at i-band magnitudes similar to those of the PG objects. Thus, the PG sample is not fully representative of today's fainter quasar samples and may be biased in important ways (e.g., its X-ray properties). Funding for the Sloan Digital Sky Survey (SDSS) has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Aeronautics and Space Administration, the National Science Foundation, the U.S. Department of Energy, the Japanese Monbukagakusho, and the Max Planck Society. The SDSS is managed by the Astrophysical Research Consortium (ARC) for the Participating Institutions. The Participating Institutions are The University of Chicago, Fermilab, the Institute for Advanced Study, the Japan Participation Group, The Johns Hopkins University, the Korean Scientist Group, Los Alamos National Laboratory, the Max-Planck-Institute for Astronomy (MPIA), the Max-Planck-Institute for Astrophysics (MPA), New Mexico State University, University of Pittsburgh, Princeton University, the United States Naval Observatory, and the University of Washington.

  11. Spectroscopic identification of type 2 quasars at z < 1 in SDSS-III/BOSS

    NASA Astrophysics Data System (ADS)

    Yuan, Sihan; Strauss, Michael A.; Zakamska, Nadia L.

    2016-10-01

    The physics and demographics of type 2 quasars remain poorly understood, and new samples of such objects selected in a variety of ways can give insight into their physical properties, evolution, and relationship to their host galaxies. We present a sample of 2758 type 2 quasars at z ≲ 1 from the Sloan Digital Sky Survey-III (SDSS-III)/Baryon Oscillation Spectroscopic Survey (BOSS) spectroscopic data base, selected on the basis of their emission-line properties. We probe the luminous end of the population by requiring the rest-frame equivalent width of [O III] to be >100 Å. We distinguish our objects from star-forming galaxies and type 1 quasars using line widths, standard emission line ratio diagnostic diagrams at z < 0.52 and detection of [Ne V]λ3426 Å at z > 0.52. The majority of our objects have [O III] luminosities in the range 1.2 × 1042-3.8 × 1043 erg s-1 and redshifts between 0.4 and 0.65. Our sample includes over 400 type 2 quasars with incorrectly measured redshifts in the BOSS data base; such objects often show kinematic substructure or outflows in the [O III] line. The majority of the sample has counterparts in the Wide-field Infrared Survey Explorer survey, with median infrared luminosity νLν[12 μm] = 4.2 × 1044 erg s- 1. Only 34 per cent of the newly identified type 2 quasars would be selected by infrared colour cuts designed to identify obscured active nuclei, highlighting the difficulty of identifying complete samples of type 2 quasars. We make public the multi-Gaussian decompositions of all [O III] profiles for the new sample and for 568 type 2 quasars from SDSS I/II, together with non-parametric measures of the [O III] line profile shapes. We also identify over 600 candidate double-peaked [O III] profiles.

  12. Bayesian Modeling of a Human MMORPG Player

    NASA Astrophysics Data System (ADS)

    Synnaeve, Gabriel; Bessière, Pierre

    2011-03-01

    This paper describes an application of Bayesian programming to the control of an autonomous avatar in a multiplayer role-playing game (the example is based on World of Warcraft). We model a particular task, which consists of choosing what to do and to select which target in a situation where allies and foes are present. We explain the model in Bayesian programming and show how we could learn the conditional probabilities from data gathered during human-played sessions.

  13. The 2dF-SDSS LRG and QSO (2SLAQ) Survey: the z < 2.1 quasar luminosity function from 5645 quasars to g= 21.85

    NASA Astrophysics Data System (ADS)

    Richards, Gordon T.; Croom, Scott M.; Anderson, Scott F.; Bland-Hawthorn, Joss; Boyle, Brian J.; De Propris, Roberto; Drinkwater, Michael J.; Fan, Xiaohui; Gunn, James E.; Ivezić, Željko; Jester, Sebastian; Loveday, Jon; Meiksin, Avery; Miller, Lance; Myers, Adam; Nichol, Robert C.; Outram, Phil J.; Pimbblet, Kevin A.; Roseboom, Isaac G.; Ross, Nic; Schneider, Donald P.; Shanks, Tom; Sharp, Robert G.; Stoughton, Chris; Strauss, Michael A.; Szalay, Alexander S.; Vanden Berk, Daniel E.; York, Donald G.

    2005-07-01

    We have used the Two-Degree Field (2dF) instrument on the Anglo-Australian Telescope (AAT) to obtain redshifts of a sample of z < 3 and 18.0 < g < 21.85 quasars selected from Sloan Digital Sky Survey (SDSS) imaging. These data are part of a larger joint programme between the SDSS and 2dF communities to obtain spectra of faint quasars and luminous red galaxies, namely the 2dF-SDSS LRG and QSO (2SLAQ) Survey. We describe the quasar selection algorithm and present the resulting number counts and luminosity function of 5645 quasars in 105.7 deg2. The bright-end number counts and luminosity functions agree well with determinations from the 2dF QSO Redshift Survey (2QZ) data to g~ 20.2. However, at the faint end, the 2SLAQ number counts and luminosity functions are steeper (i.e. require more faint quasars) than the final 2QZ results from Croom et al., but are consistent with the preliminary 2QZ results from Boyle et al. Using the functional form adopted for the 2QZ analysis (a double power law with pure luminosity evolution characterized by a second-order polynomial in redshift), we find a faint-end slope of β=-1.78 +/- 0.03 if we allow all of the parameters to vary, and β=-1.45 +/- 0.03 if we allow only the faint-end slope and normalization to vary (holding all other parameters equal to the final 2QZ values). Over the magnitude range covered by the 2SLAQ survey, our maximum-likelihood fit to the data yields 32 per cent more quasars than the final 2QZ parametrization, but is not inconsistent with other g > 21 deep surveys for quasars. The 2SLAQ data exhibit no well-defined `break' in the number counts or luminosity function, but do clearly flatten with increasing magnitude. Finally, we find that the shape of the quasar luminosity function derived from 2SLAQ is in good agreement with that derived from Type I quasars found in hard X-ray surveys.

  14. A MULTIWAVELENGTH STUDY OF BINARY QUASARS AND THEIR ENVIRONMENTS

    SciTech Connect

    Green, Paul J.; Aldcroft, Thomas L.; Trichas, Markos; Myers, Adam D.; Barkhouse, Wayne A.; Richards, Gordon T.; Ruiz, Angel; Hopkins, Philip F.

    2011-12-10

    We present Chandra X-ray imaging and spectroscopy for 14 quasars in spatially resolved pairs targeted as part of a complete sample of binary quasars with small transverse separations drawn from Sloan Digital Sky Survey (SDSSDR6) photometry. We measure the X-ray properties of all 14 QSOs, and study the distribution of X-ray and optical-to-X-ray power-law indices in these binary quasars. We find no significant difference when compared with large control samples of isolated quasars, true even for SDSS J1254+0846, discussed in detail in a companion paper, which clearly inhabits an ongoing, pre-coalescence galaxy merger showing obvious tidal tails. We present infrared photometry from our observations with SAO Wide-field InfraRed Camera at the MMT, and from the Wide-field Infrared Survey Explorer Preliminary Data Release, and fit simple spectral energy distributions to all 14 QSOs. We find preliminary evidence that substantial contributions from star formation are required, but possibly no more so than for isolated X-ray-detected QSOs. Sensitive searches of the X-ray images for extended emission and the optical images for optical galaxy excess show that these binary QSOs-expected to occur in strong peaks of the dark matter distribution-are not preferentially found in rich cluster environments. While larger binary QSO samples with richer far-IR and submillimeter multiwavelength data might better reveal signatures of merging and triggering, optical color selection of QSO pairs may be biased against such signatures. X-ray and/or variability selection of QSO pairs, while challenging, should be attempted. We present in an Appendix a primer on X-ray flux and luminosity calculations.

  15. Recent Star-formation in Post-Starburst Quasars

    NASA Astrophysics Data System (ADS)

    Townsend, Shonda; Ganguly, R.; Strom, A.; Cales, S.; Brotherton, M. S.

    2011-01-01

    Post-Starburst Quasars (PSQ, alternatively Q+As) show simultaneously the spectrum of a massive A-type stellar population and a quasar. The prototype PSQ, UNJ1025-0040, shows a UV excess over the quasar spectrum, indicating more recent star-formation (Brotherton et al 2002). To gauge the frequency and distribution of these younger stellar populations in PSQs, we have collected GALEX (GR45) and 2MASS photometry for 409 objects. The objects are catalog 609 spectroscopically-selected PSQs from Brotherton et al. (2010) that uses similar criteria as Zabludoff et al. (1996) for post-starburst galaxies (PSG, E+A). For comparison, we have compiled two samples: (1) 16,000 quasars that is matched in redshift (0.01-0.7) and Sloan-u magnitude (16.1-21.2), which is blueward of the Balmer edge and provides the least contamination from the massive stellar population; and (2) 500 PSGs from Goto et al. (2007). 389 (55) PSQs show an NUV (FUV) excess over the expected UV flux if the underlying quasar were ``normal.'’ 126 (460) objects show an NUV (FUV) decrement. The observed NUV to u-band flux ratio of the median PSQ rises from 1 at z=0.01 to 2.5 at z=0.4, while the same for the median QSO remains at 1. The observed FUV to u-band flux ratio of the median QSO rises slightly from 0.6 to 0.8 over the redshift range 0.05-0.2, whereas the median PSQ is nearly a factor of three lower. The disparity between the median PSQ and QSO suggests the presence of young stars that add in NUV light, but not FUV light. To quantify the youth and mass of this putative population, we will present preliminary efforts to model PSQs using two simple stellar populations, an underlying quasar, and dust reddening. We acknowledge funding from GALEX through grant NNX10AC63G.

  16. Space Shuttle RTOS Bayesian Network

    NASA Technical Reports Server (NTRS)

    Morris, A. Terry; Beling, Peter A.

    2001-01-01

    With shrinking budgets and the requirements to increase reliability and operational life of the existing orbiter fleet, NASA has proposed various upgrades for the Space Shuttle that are consistent with national space policy. The cockpit avionics upgrade (CAU), a high priority item, has been selected as the next major upgrade. The primary functions of cockpit avionics include flight control, guidance and navigation, communication, and orbiter landing support. Secondary functions include the provision of operational services for non-avionics systems such as data handling for the payloads and caution and warning alerts to the crew. Recently, a process to selection the optimal commercial-off-the-shelf (COTS) real-time operating system (RTOS) for the CAU was conducted by United Space Alliance (USA) Corporation, which is a joint venture between Boeing and Lockheed Martin, the prime contractor for space shuttle operations. In order to independently assess the RTOS selection, NASA has used the Bayesian network-based scoring methodology described in this paper. Our two-stage methodology addresses the issue of RTOS acceptability by incorporating functional, performance and non-functional software measures related to reliability, interoperability, certifiability, efficiency, correctness, business, legal, product history, cost and life cycle. The first stage of the methodology involves obtaining scores for the various measures using a Bayesian network. The Bayesian network incorporates the causal relationships between the various and often competing measures of interest while also assisting the inherently complex decision analysis process with its ability to reason under uncertainty. The structure and selection of prior probabilities for the network is extracted from experts in the field of real-time operating systems. Scores for the various measures are computed using Bayesian probability. In the second stage, multi-criteria trade-off analyses are performed between the scores

  17. Evidence for the alignment of quasar radio polarizations with large quasar group axes

    NASA Astrophysics Data System (ADS)

    Pelgrims, V.; Hutsemékers, D.

    2016-05-01

    Recently, evidence has been presented for the polarization vectors from quasars to preferentially align with the axes of the large quasar groups (LQG) to which they belong. This report was based on observations made at optical wavelengths for two LQGs at redshift ~1.3. The correlation suggests that the spin axes of quasars preferentially align with their surrounding large-scale structure that is assumed to be traced by the LQGs. Here, we consider a large sample of LQGs built from the Sloan Digital Sky Survey DR7 quasar catalogue in the redshift range 1.0-1.8. For quasars embedded in this sample, we collected radio polarization measurements with the goal to study possible correlations between quasar polarization vectors and the major axis of their host LQGs. Assuming the radio polarization vector is perpendicular to the quasar spin axis, we found that the quasar spin axis is preferentially parallel to the LQG major axis inside LQGs that have at least 20 members. This result independently supports the observations at optical wavelengths. We additionally found that when the richness of an LQG decreases, the quasar spin axis becomes preferentially perpendicular to the LQG major axis and that no correlation is detected for quasar groups with fewer than 10 members.

  18. VizieR Online Data Catalog: Quasar luminosity function (Hawkins+, 1993)

    NASA Astrophysics Data System (ADS)

    Hawkins, M. R. S.; Veron, P.

    1994-11-01

    A sample of quasars is selected from a 10-yr sequence of 30 UK Schmidt plates. Luminosity functions are derived in several redshift intervals, which in each case show a featureless power-law rise towards low luminosities. There is no sigh of the 'break' found in the recent UVX sample of Boyle, Shanks & Peterson. It is suggested that reasons for the disagreement are connected with biases in the selection of the UVX sample. The question of the nature of quasar evolution appears to be still unresolved. (1 data file).

  19. HST images of FeLoBAL quasars: Testing quasar-galaxy evolution models

    NASA Astrophysics Data System (ADS)

    Herbst, Hanna; Hamann, Fred; Villforth, Carolin; Caselli, Paola; Koekemoer, Anton M.; Veilleux, Sylvain

    2016-01-01

    We present preliminary results from an HST imaging study of FeLoBAL quasars, which have extremely low-ionization Broad Absorption Line (BAL) outflows and might be a young quasar population based on their red colors, large far-IR luminosities (suggesting high star formation rates), and powerful outflows. Some models of quasar - host galaxy evolution propose a triggering event, such as a merger, to fuel both a burst of star formation and the quasar/AGN activity. These models suggest young quasars are initially obscured inside the dusty starburst until a "blowout" phase, driven by the starburst or quasar outflows like FeLoBALs, ends the star formation and reveals the visibly luminous quasar. Despite the popularity of this evolution scheme, there is little observational evidence to support the role of mergers in triggering AGN or the youth of dust-reddened quasars (such as FeLoBALs) compared to normal blue quasars.Our Cycle 22 HST program is designed to test the youth of FeLoBAL quasars and the connection of FeLoBALs to mergers. We obtain WFC3/IR F160W images of 10 FeLoBAL quasars at redshift z~0.9 (covering ~8500A in the quasar rest frame). We will compare the host galaxy morphologies and merger signatures of FeLoBALs with normal blue quasars (which are older according to the evolution model) and non-AGN galaxies matched in redshift and stellar mass. If FeLoBAL quasars are indeed in a young evolutionary state, close in time to the initial merging event, they should have stronger merger features compared to blue quasars and non-AGN galaxies. Preliminary results suggest that this is not the case - FeLoBAL quasars appear to reside in faint, compact hosts with weak or absent merger signatures. We discuss the implications of these results for galaxy evolution models and other studies of dust-reddened quasar populations.

  20. Orientation effects on spectral emission features of quasars

    NASA Astrophysics Data System (ADS)

    Bisogni, Susanna; Marconi, Alessandro; Risaliti, Guido

    2016-09-01

    We present an analysis of the orientation effects in SDSS quasar composite spectra. In a previous work we have shown that the equivalent width EW of the [OIII] λ5008Å line is a reliable indicator of the inclination of the accretion disk. Here, we have selected a sample of ˜15,000 quasars from the SDSS 7th Data Release and divided it in sub-samples with different values of EW[OIII]. We find inclination effects both on broad and narrow quasars emission lines, among which an increasing broadening from low to high EW for the broad lines and a decreasing importance of the blue component for the narrow lines. These effects are naturally explained with a variation of source inclination from nearly face-on to edge-on, confirming the goodness of EW[OIII]as an orientation indicator. Moreover, we suggest that orientation effects could explain, at least partially, the origin of the anticorrelation between [OIII] and FeII intensities, i.e. the well known Eigenvector 1.

  1. The Birth of Quasars

    NASA Astrophysics Data System (ADS)

    Thorp, Rachel; Lonsdale, Colin J.; Lonsdale, Carol J.

    2015-01-01

    Active galactic nuclei (AGNs) play an important role in the evolution of structure in the universe. Through the accretion process, they convert gravitational potential energy into radiative and mechanical energy and inject it into surrounding media, influencing star formation and gravitational condensation processes. The sequence of black hole formation, fueling, AGN birth, and associated suppression of star formation in galaxies is poorly understood, and difficult to observe due to the relative brevity of this phase, compounded by the high dust opacities at optical and infrared wavelengths. By selecting a sample of rare, luminous transition objects from the all-sky WISE survey and studying members of the sample with high resolution radio imaging, it is possible to gain insight into the role of AGN jets in this evolutionary sequence. We present VLBA data for 90 distant, highly obscured AGNs, hypothesized to be very young, and image their radio structures on scales of 10- 100pc. We provide image analysis results, including flux densities, fitted sizes, energy densities and pressures of the structures. The structures we observe can be interpreted in terms of interactions between a powerful jet and a dense, clumpy interstellar medium. Plans for future observations with greater sensitivity and covering a wider range of size scales are described.

  2. PROBING THE FAINT END OF THE QUASAR LUMINOSITY FUNCTION AT z{approx} 4 IN THE COSMOS FIELD

    SciTech Connect

    Ikeda, H.; Nagao, T.; Matsuoka, K.; Ideue, Y.; Taniguchi, Y.; Shioya, Y.; Trump, J. R.; Comastri, A.; Enoki, M.; Koekemoer, A. M.; Morokuma, T.; Murayama, T.; Saito, T.; Silverman, J. D.; Salvato, M.; Schinnerer, E.

    2011-02-20

    We searched for quasars that are {approx}3 mag fainter than the SDSS quasars in the redshift range 3.7 {approx}< z {approx}< 4.7 in the COSMOS field to constrain the faint end of the quasar luminosity function (QLF). Using optical photometric data, we selected 31 quasar candidates with 22 < i' < 24 at z {approx} 4. We obtained optical spectra for most of these candidates using FOCAS on the Subaru telescope and identified eight low-luminosity quasars at z {approx} 4. In order to derive the QLF based on our spectroscopic follow-up campaign, we estimated the photometric completeness of our quasar survey through detailed Monte Carlo simulations. Our QLF at z {approx} 4 has a much shallower faint-end slope ({beta} = -1.67{sup +0.11}{sub -0.17}) than that obtained by other recent surveys in the same redshift. Our result is consistent with the scenario of downsizing evolution of active galactic nuclei inferred by recent optical and X-ray quasar surveys at lower redshifts.

  3. HUBBLE CAPTURES MERGER BETWEEN QUASAR AND GALAXY

    NASA Technical Reports Server (NTRS)

    2002-01-01

    This NASA Hubble Space Telescope image shows evidence fo r a merger between a quasar and a companion galaxy. This surprising result might require theorists to rethink their explanations for the nature of quasars, the most energetic objects in the universe. The bright central object is the quasar itself, located several billion light-years away. The two wisps on the (left) of the bright central object are remnants of a bright galaxy that have been disrupted by the mutual gravitational attraction between the quasar and the companion galaxy. This provides clear evidence for a merger between the two objects. Since their discovery in 1963, quasars (quasi-stellar objects) have been enigmatic because they emit prodigious amounts of energy from a very compact source. The most widely accepted model is that a quasar is powered by a supermassive black hole in the core of a galaxy. These new observations proved a challenge for theorists as no current models predict the complex quasar interactions unveiled by Hubble. The image was taken with the Wide Field Planetary Camera-2. Credit: John Bahcall, Institute for Advanced Study, NASA.

  4. Quasars, blazars, and gamma rays.

    PubMed

    Dermer, C D; Schlickeiser, R

    1992-09-18

    Before the launch of the Compton Gamma Ray Observatory (CGRO), the only source of >100-megaelectron volt (MeV) gamma radiation known outside our galaxy was the quasar 3C 273. After less than a year of observing, 13 other extragalactic sources have been discovered with the Energetic Gamma Ray Experiment Telescope (EGRET) on CGRO, and it is expected that many more will be found before the full sky survey is complete. All 14 sources show evidence of blazar properties at other wavelengths; these properties include high optical polarization, extreme optical variability, flat-spectrum radio emission associated with a compact core, and apparent superluminal motion. Such properties are thought to be produced by those few, rare extragalactic radio galaxies and quasars that are favorably aligned to permit us to look almost directly down a relativistically outflowing jet of matter expelled from a supermassive black hole. Although the origin of the gamma rays from radio jets is a subject of much controversy, the gamma-ray window probed by CGRO is providing a wealth of knowledge about the central engines of active galactic nuclei and the most energetic processes occurring in nature.

  5. Quasars, blazars, and gamma rays.

    PubMed

    Dermer, C D; Schlickeiser, R

    1992-09-18

    Before the launch of the Compton Gamma Ray Observatory (CGRO), the only source of >100-megaelectron volt (MeV) gamma radiation known outside our galaxy was the quasar 3C 273. After less than a year of observing, 13 other extragalactic sources have been discovered with the Energetic Gamma Ray Experiment Telescope (EGRET) on CGRO, and it is expected that many more will be found before the full sky survey is complete. All 14 sources show evidence of blazar properties at other wavelengths; these properties include high optical polarization, extreme optical variability, flat-spectrum radio emission associated with a compact core, and apparent superluminal motion. Such properties are thought to be produced by those few, rare extragalactic radio galaxies and quasars that are favorably aligned to permit us to look almost directly down a relativistically outflowing jet of matter expelled from a supermassive black hole. Although the origin of the gamma rays from radio jets is a subject of much controversy, the gamma-ray window probed by CGRO is providing a wealth of knowledge about the central engines of active galactic nuclei and the most energetic processes occurring in nature. PMID:17841159

  6. Understanding post-starburst quasars

    NASA Astrophysics Data System (ADS)

    Cales, Sabrina L.

    Post-starburst quasars (PSQs) are an interesting type of hybrid galaxy that harbor both a post-starburst stellar population and luminous AGN. The starburst is hundreds of millions of years old with a mass on the order of 10 billion solar masses. This type of hybrid galaxy provides a natural breading ground for studying the role active galactic nuclei (AGN) play in galaxy evolution (i.e., the black hole mass-galaxy bulge mass relation). My thesis work has centered on testing the idea that, at z ˜ 0.3, PSQs are a phase in the life of galaxies triggered by external events (e.g., mergers, tidal interactions) or whether they are a more heterogeneous population in which multiple mechanisms can contribute to the class (i.e., external events and internal processes). This project is devoted to understanding the properties of PSQs and is comprised of three sub-projects: (i) two-dimensional image analysis with HST imaging and characterization of PSQ morphologies, (ii) determination of stellar population ages and masses and quasar black hole masses and accretion rates via spectral modeling of Keck and KPNO spectroscopy, (iii) comparisons of PSQ properties with other galaxy types and models. Finally, I briefly outline my conclusions in the context of AGN/galaxy evolution.

  7. [Bayesian methods for genomic breeding value estimation].

    PubMed

    Wang, Chonglong; Ding, Xiangdong; Liu, Jianfeng; Yin, Zongjun; Zhang, Qin

    2014-02-01

    Estimation of genomic breeding values is the key step in genomic selection. The successful application of genomic selection depends on the accuracy of genomic estimated breeding values, which is mostly determined by the estimation method. Bayes-type and BLUP-type methods are the two main methods which have been widely studied and used. Here, we systematically introduce the currently proposed Bayesian methods, and summarize their effectiveness and improvements. Results from both simulated and real data showed that the accuracies of Bayesian methods are higher than those of BLUP methods, especially for the traits which are influenced by QTL with large effect. Because the theories and computation of Bayesian methods are relatively complicated, their use in practical breeding is less common than BLUP methods. However, with the development of fast algorithms and the improvement of computer hardware, the computational problem of Bayesian methods is expected to be solved. In addition, further studies on the genetic architecture of traits will provide Bayesian methods more accurate prior information, which will make their advantage in accuracy of genomic estimated breeding values more prominent. Therefore, the application of Bayesian methods will be more extensive.

  8. Constraining the Radio-loud Fraction of Quasars at z > 5.5

    NASA Astrophysics Data System (ADS)

    Bañados, E.; Venemans, B. P.; Morganson, E.; Hodge, J.; Decarli, R.; Walter, F.; Stern, D.; Schlafly, E.; Farina, E. P.; Greiner, J.; Chambers, K. C.; Fan, X.; Rix, H.-W.; Burgett, W. S.; Draper, P. W.; Flewelling, J.; Kaiser, N.; Metcalfe, N.; Morgan, J. S.; Tonry, J. L.; Wainscoat, R. J.

    2015-05-01

    Radio-loud active galactic nuclei at z˜ 2-4 are typically located in dense environments and their host galaxies are among the most massive systems at those redshifts, providing key insights for galaxy evolution. Finding radio-loud quasars at the highest accessible redshifts (z˜ 6) is important to the study of their properties and environments at even earlier cosmic time. They could also serve as background sources for radio surveys intended to study the intergalactic medium beyond the epoch of reionization in HI 21 cm absorption. Currently, only five radio-loud (R={{f}ν ,5 GHz}/{{f}ν ,4400 \\overset{\\circA }}\\gt 10) quasars are known at z˜ 6. In this paper we search for 5.5≲ z≲ 7.2 quasars by cross-matching the optical Panoramic Survey Telescope & Rapid Response System 1 and radio Faint Images of the Radio Sky at Twenty cm surveys. The radio information allows identification of quasars missed by typical color-based selections. While we find no good 6.4≲ z≲ 7.2 quasar candidates at the sensitivities of these surveys, we discover two new radio-loud quasars at z˜ 6. Furthermore, we identify two additional z˜ 6 radio-loud quasars that were not previously known to be radio-loud, nearly doubling the current z˜ 6 sample. We show the importance of having infrared photometry for z\\gt 5.5 quasars to robustly classify them as radio-quiet or radio-loud. Based on this, we reclassify the quasar J0203+0012 (z = 5.72), previously considered radio-loud, to be radio-quiet. Using the available data in the literature, we constrain the radio-loud fraction of quasars at z˜ 6, using the Kaplan-Meier estimator, to be 8.1-3.2+5.0%. This result is consistent with there being no evolution of the radio-loud fraction with redshift, in contrast to what has been suggested by some studies at lower redshifts.

  9. Moderate resolution spectrophotometry of high redshift quasars

    NASA Technical Reports Server (NTRS)

    Schneider, Donald P.; Schmidt, Maarten; Gunn, James E.

    1991-01-01

    A uniform set of photometry and high signal-to-noise moderate resolution spectroscopy of 33 quasars with redshifts larger than 3.1 is presented. The sample consists of 17 newly discovered quasars (two with redshifts in excess of 4.4) and 16 sources drawn from the literature. The objects in this sample have r magnitudes between 17.4 and 21.4; their luminosities range from -28.8 to -24.9. Three of the 33 objects are broad absorption line quasars. A number of possible high redshift damped Ly-alpha systems were found.

  10. Merging Galaxies Create a Binary Quasar

    NASA Astrophysics Data System (ADS)

    2010-02-01

    Astronomers have found the first clear evidence of a binary quasar within a pair of actively merging galaxies. Quasars are the extremely bright centers of galaxies surrounding super-massive black holes, and binary quasars are pairs of quasars bound together by gravity. Binary quasars, like other quasars, are thought to be the product of galaxy mergers. Until now, however, binary quasars have not been seen in galaxies that are unambiguously in the act of merging. But images of a new binary quasar from the Carnegie Institution's Magellan telescope in Chile show two distinct galaxies with "tails" produced by tidal forces from their mutual gravitational attraction. "This is really the first case in which you see two separate galaxies, both with quasars, that are clearly interacting," says Carnegie astronomer John Mulchaey who made observations crucial to understanding the galaxy merger. Most, if not all, large galaxies, such as our galaxy the Milky Way, host super-massive black holes at their centers. Because galaxies regularly interact and merge, astronomers have assumed that binary super-massive black holes have been common in the Universe, especially during its early history. Black holes can only be detected as quasars when they are actively accreting matter, a process that releases vast amounts of energy. A leading theory is that galaxy mergers trigger accretion, creating quasars in both galaxies. Because most such mergers would have happened in the distant past, binary quasars and their associated galaxies are very far away and therefore difficult for most telescopes to resolve. The binary quasar, labeled SDSS J1254+0846, was initially detected by the Sloan Digital Sky Survey, a large scale astronomical survey of galaxies and over 120,000 quasars. Further observations by Paul Green of the Harvard-Smithsonian Center for Astrophysics and colleagues* using NASA's Chandra's X-ray Observatory and telescopes at Kitt Peak National Observatory in Arizona and Palomar

  11. Selection of the treatment effect for sample size determination in a superiority clinical trial using a hybrid classical and Bayesian procedure.

    PubMed

    Ciarleglio, Maria M; Arendt, Christopher D; Makuch, Robert W; Peduzzi, Peter N

    2015-03-01

    Specification of the treatment effect that a clinical trial is designed to detect (θA) plays a critical role in sample size and power calculations. However, no formal method exists for using prior information to guide the choice of θA. This paper presents a hybrid classical and Bayesian procedure for choosing an estimate of the treatment effect to be detected in a clinical trial that formally integrates prior information into this aspect of trial design. The value of θA is found that equates the pre-specified frequentist power and the conditional expected power of the trial. The conditional expected power averages the traditional frequentist power curve using the conditional prior distribution of the true unknown treatment effect θ as the averaging weight. The Bayesian prior distribution summarizes current knowledge of both the magnitude of the treatment effect and the strength of the prior information through the assumed spread of the distribution. By using a hybrid classical and Bayesian approach, we are able to formally integrate prior information on the uncertainty and variability of the treatment effect into the design of the study, mitigating the risk that the power calculation will be overly optimistic while maintaining a frequentist framework for the final analysis. The value of θA found using this method may be written as a function of the prior mean μ0 and standard deviation τ0, with a unique relationship for a given ratio of μ0/τ0. Results are presented for Normal, Uniform, and Gamma priors for θ. PMID:25583273

  12. Bayesian model selection techniques as decision support for shaping a statistical analysis plan of a clinical trial: An example from a vertigo phase III study with longitudinal count data as primary endpoint

    PubMed Central

    2012-01-01

    tools for preparing decisions within the SAP in a transparent way when structuring the primary analysis, sensitivity or ancillary analyses, and specific analyses for secondary endpoints. The mean logarithmic score and DIC discriminate well between different model scenarios. It becomes obvious that the naive choice of a conventional random effects Poisson model is often inappropriate for real-life count data. The findings are used to specify an appropriate mixed model employed in the sensitivity analyses of an ongoing phase III trial. Conclusions The proposed Bayesian methods are not only appealing for inference but notably provide a sophisticated insight into different aspects of model performance, such as forecast verification or calibration checks, and can be applied within the model selection process. The mean of the logarithmic score is a robust tool for model ranking and is not sensitive to sample size. Therefore, these Bayesian model selection techniques offer helpful decision support for shaping sensitivity and ancillary analyses in a statistical analysis plan of a clinical trial with longitudinal count data as the primary endpoint. PMID:22962944

  13. A glimpse at quasar host galaxy far-UV emission using damped Lyα's as natural coronagraphs

    SciTech Connect

    Cai, Zheng; Fan, Xiaohui; Wang, Ran; McGreer, Ian; Noterdaeme, Pasquier; Finley, Hayley; Petitjean, Patrick; Carithers, Bill; Bian, Fuyan; Miralda-Escudé, Jordi; Pâris, Isabelle; Schneider, Donald P.; Zakamska, Nadia L.; Ge, Jian; Slosar, Anze

    2014-10-01

    In merger-driven models of massive galaxy evolution, the luminous quasar phase is expected to be accompanied by vigorous star formation in quasar host galaxies. In this paper, we use high column density damped Lyα (DLA) systems along quasar sight lines as natural coronagraphs to directly study the far-UV (FUV) radiation from the host galaxies of luminous background quasars. We have stacked the spectra of ∼2000 DLA systems (N {sub H} {sub I} > 10{sup 20.6} cm{sup –2}) with a median absorption redshift (z) = 2.6 selected from quasars observed in the SDSS-III Baryon Oscillation Spectroscopic Survey. We detect residual flux in the dark troughs of the composite DLA spectra. The level of this residual flux significantly exceeds systematic errors in the Sloan Digital Sky Survey fiber sky subtraction; furthermore, the residual flux is strongly correlated with the continuum luminosity of the background quasar, while uncorrelated with DLA column density or metallicity. We conclude that the flux could be associated with the average FUV radiation from the background quasar host galaxies (with medium redshift (z) = 3.1) that is not blocked by the intervening DLA. Assuming that all of the detected flux originates from quasar hosts, for the highest quasar luminosity bin ((L) = 2.5 × 10{sup 13} L {sub ☉}), the host galaxy has an FUV intensity of 1.5 ± 0.2 × 10{sup 40} erg s{sup –1} Å{sup –1}; this corresponds to an unobscured UV star formation rate of 9 M {sub ☉} yr{sup –1}.

  14. Extreme star formation events in quasar hosts over 0.5 < z < 4

    NASA Astrophysics Data System (ADS)

    Pitchford, L. K.; Hatziminaoglou, E.; Feltre, A.; Farrah, D.; Clarke, C.; Harris, K. A.; Hurley, P.; Oliver, S.; Page, M.; Wang, L.

    2016-11-01

    We explore the relationship between active galactic nuclei (AGN) and star formation in a sample of 513 optically luminous type 1 quasars up to redshifts of ˜4 hosting extremely high star formation rates (SFRs). The quasars are selected to be individually detected by the Herschel SPIRE instrument at >3σ at 250 μm, leading to typical SFRs of order of 1000 M⊙ yr-1. We find the average SFRs to increase by almost a factor 10 from z ˜ 0.5 to z ˜ 3, mirroring the rise in the comoving SFR density over the same epoch. However, we find that the SFRs remain approximately constant with increasing accretion luminosity for accretion luminosities above 1012 L⊙. We also find that the SFRs do not correlate with black hole mass. Both of these results are most plausibly explained by the existence of a self-regulation process by the starburst at high SFRs, which controls SFRs on time-scales comparable to or shorter than the AGN or starburst duty cycles. We additionally find that SFRs do not depend on Eddington ratio at any redshift, consistent with no relation between SFR and black hole growth rate per unit black hole mass. Finally, we find that high-ionization broad absorption line (HiBAL) quasars have indistinguishable far-infrared properties to those of classical quasars, consistent with HiBAL quasars being normal quasars observed along a particular line of sight, with the outflows in HiBAL quasars not having any measurable effect on the star formation in their hosts.

  15. Bayesian Mediation Analysis

    ERIC Educational Resources Information Center

    Yuan, Ying; MacKinnon, David P.

    2009-01-01

    In this article, we propose Bayesian analysis of mediation effects. Compared with conventional frequentist mediation analysis, the Bayesian approach has several advantages. First, it allows researchers to incorporate prior information into the mediation analysis, thus potentially improving the efficiency of estimates. Second, under the Bayesian…

  16. Universal Darwinism As a Process of Bayesian Inference.

    PubMed

    Campbell, John O

    2016-01-01

    Many of the mathematical frameworks describing natural selection are equivalent to Bayes' Theorem, also known as Bayesian updating. By definition, a process of Bayesian Inference is one which involves a Bayesian update, so we may conclude that these frameworks describe natural selection as a process of Bayesian inference. Thus, natural selection serves as a counter example to a widely-held interpretation that restricts Bayesian Inference to human mental processes (including the endeavors of statisticians). As Bayesian inference can always be cast in terms of (variational) free energy minimization, natural selection can be viewed as comprising two components: a generative model of an "experiment" in the external world environment, and the results of that "experiment" or the "surprise" entailed by predicted and actual outcomes of the "experiment." Minimization of free energy implies that the implicit measure of "surprise" experienced serves to update the generative model in a Bayesian manner. This description closely accords with the mechanisms of generalized Darwinian process proposed both by Dawkins, in terms of replicators and vehicles, and Campbell, in terms of inferential systems. Bayesian inference is an algorithm for the accumulation of evidence-based knowledge. This algorithm is now seen to operate over a wide range of evolutionary processes, including natural selection, the evolution of mental models and cultural evolutionary processes, notably including science itself. The variational principle of free energy minimization may thus serve as a unifying mathematical framework for universal Darwinism, the study of evolutionary processes operating throughout nature.

  17. Universal Darwinism As a Process of Bayesian Inference.

    PubMed

    Campbell, John O

    2016-01-01

    Many of the mathematical frameworks describing natural selection are equivalent to Bayes' Theorem, also known as Bayesian updating. By definition, a process of Bayesian Inference is one which involves a Bayesian update, so we may conclude that these frameworks describe natural selection as a process of Bayesian inference. Thus, natural selection serves as a counter example to a widely-held interpretation that restricts Bayesian Inference to human mental processes (including the endeavors of statisticians). As Bayesian inference can always be cast in terms of (variational) free energy minimization, natural selection can be viewed as comprising two components: a generative model of an "experiment" in the external world environment, and the results of that "experiment" or the "surprise" entailed by predicted and actual outcomes of the "experiment." Minimization of free energy implies that the implicit measure of "surprise" experienced serves to update the generative model in a Bayesian manner. This description closely accords with the mechanisms of generalized Darwinian process proposed both by Dawkins, in terms of replicators and vehicles, and Campbell, in terms of inferential systems. Bayesian inference is an algorithm for the accumulation of evidence-based knowledge. This algorithm is now seen to operate over a wide range of evolutionary processes, including natural selection, the evolution of mental models and cultural evolutionary processes, notably including science itself. The variational principle of free energy minimization may thus serve as a unifying mathematical framework for universal Darwinism, the study of evolutionary processes operating throughout nature. PMID:27375438

  18. Unveiling hidden black holes in the cosmic web: Dark matter halos of WISE quasars from Planck CMB lensing

    NASA Astrophysics Data System (ADS)

    Hickox, Ryan

    The WISE and Planck surveys have now produced groundbreaking data sets which, in concert, can be exploited to obtain revolutionary constraints on the evolution of structure in the Universe. One particularly powerful application of WISE has been to uncover millions of the previously "hidden" obscured quasars, rapidly growing supermassive black holes that are shrouded in gas and dust and so are not detectable using traditional ground-based optical and near-IR techniques. Recently, Planck has produced the most precise all-sky map to date of dark matter structures via the lensing of the cosmic microwave background (CMB). We propose to combine these data sets to obtain a uniquely powerful measurement of the link between rapidly growing black holes and their host dark matter structures, by cross-correlating the density field of WISE-selected quasars with the CMB lensing convergence maps obtained from Planck. This proposal will build on our current ADAP program (NNX12AE38G), which studies the host dark matter halos of WISE-selected quasars via spatial clustering. NNX12AE38G involves a detailed characterization of the redshifts, luminosities, and spectral energy distributions of WISE-selected quasars and uses new techniques to measure how quasars cluster around themselves. NNX12AE38G has contributed to more than 10 journal articles and 5 conference proceedings. Building on our current work, an even more complete understanding of the link between black holes and their host dark matter structures is possible if we employ an independent method for measuring the clustering bias (and thus characteristic halo mass) of the quasar population. This has recently become possible using CMB lensing maps. In the past two years, our team has conducted an initial analysis covering 2500 square degrees using WISE-selected quasars and lensing maps from the South Pole Telescope (Geach, Hickox, Myers et al., 2013), and have implemented this technique with Planck over part of the SDSS region

  19. Black-Hole Feedback in Quasars

    NASA Video Gallery

    This animation illustrates how black-hole feedback works in quasars. Dense gas and dust in the center simultaneously fuels the black hole and shrouds it from view. The black-hole wind propels large...

  20. Quasars, pulsars, black holes and HEAO's

    NASA Technical Reports Server (NTRS)

    Doolitte, R. F.; Moritz, K.; Whilden, R. D. C.

    1974-01-01

    Astronomical surveys are discussed by large X-ray, gamma ray, and cosmic ray instruments carried onboard high-energy astronomy observatories. Quasars, pulsars, black holes, and the ultimate benefits of the new astronomy are briefly discussed.

  1. Spectrophotometry of Michigan-Tololo quasars

    NASA Technical Reports Server (NTRS)

    Lewis, D. W.; Macalpine, G. M.; Weedman, D. W.

    1979-01-01

    Emission-line quasar characteristics are confirmed for 80% of the objects observed, including at least four new quasars with spectral features indicative of supernova-like outflow. Approximately 73% of the redshifts predicted from the discovery plates are found accurate with a mean error in z of 0.03, and a large range of z (from about 0.1 to 3.16) is represented in the sample. The observed redshift distribution for quasars is marginally consistent with a constant co-moving quasar density above z approximately 2.0. The shape of the redshift distribution may be used as an isotropy probe with a cosmic time resolution of a few times one-hundred million years in the early universe; therefore, continued surveys of this sort are important even if accurate magnitudes are not determined.

  2. Quasars as tracers of cosmic flows

    NASA Astrophysics Data System (ADS)

    Modzelewska, J.; Czerny, B.; Bilicki, M.; Hryniewicz, K.; Krupa, M.; Petrogalli, F.; Pych, W.; Kurcz, A.; Udalski, A.

    2016-10-01

    Quasars, as the most luminous persistent sources in the Universe, have broad applications for cosmological studies. In particular, they can be employed to directly measure the expansion history of the Universe, similarly to SNe Ia. The advantage of quasars is that they are numerous, cover a broad range of redshifts, up to z = 7, and do not show significant evolution of metallicity with redshift. The idea is based on the relation between the time delay of an emission line and the continuum, and the absolute monochromatic luminosity of a quasar. For intermediate redshift quasars, the suitable line is Mg II. Between December 2012 and March 2014, we performed five spectroscopic observations of the QSO CTS C30.10 (z = 0.900) using the South African Large Telesope (SALT), supplemented with photometric monitoring, with the aim of determining the variability of the line shape, changes in the total line intensity and in the continuum. We show that the method is very promising.

  3. First discoveries of z ˜ 6 quasars with the Kilo-Degree Survey and VISTA Kilo-Degree Infrared Galaxy survey

    NASA Astrophysics Data System (ADS)

    Venemans, B. P.; Verdoes Kleijn, G. A.; Mwebaze, J.; Valentijn, E. A.; Bañados, E.; Decarli, R.; de Jong, J. T. A.; Findlay, J. R.; Kuijken, K. H.; Barbera, F. La; McFarland, J. P.; McMahon, R. G.; Napolitano, N.; Sikkema, G.; Sutherland, W. J.

    2015-11-01

    We present the results of our first year of quasar search in the ongoing ESO public Kilo-Degree Survey (KiDS) and VISTA Kilo-Degree Infrared Galaxy (VIKING) surveys. These surveys are among the deeper wide-field surveys that can be used to uncover large numbers of z ˜ 6 quasars. This allows us to probe a more common population of z ˜ 6 quasars that is fainter than the well-studied quasars from the main Sloan Digital Sky Survey. From this first set of combined survey catalogues covering ˜250 deg2 we selected point sources down to ZAB = 22 that had a very red i - Z (i - Z > 2.2) colour. After follow-up imaging and spectroscopy, we discovered four new quasars in the redshift range 5.8 < z < 6.0. The absolute magnitudes at a rest-frame wavelength of 1450 Å are between -26.6 < M1450 < -24.4, confirming that we can find quasars fainter than M*, which at z = 6 has been estimated to be between M* = -25.1 and M* = -27.6. The discovery of four quasars in 250 deg2 of survey data is consistent with predictions based on the z ˜ 6 quasar luminosity function. We discuss various ways to push the candidate selection to fainter magnitudes and we expect to find about 30 new quasars down to an absolute magnitude of M1450 = -24. Studying this homogeneously selected faint quasar population will be important to gain insight into the onset of the co-evolution of the black holes and their stellar hosts.

  4. QUASARS PROBING QUASARS. IV. JOINT CONSTRAINTS ON THE CIRCUMGALACTIC MEDIUM FROM ABSORPTION AND EMISSION

    SciTech Connect

    Hennawi, Joseph F.; Prochaska, J. Xavier

    2013-03-20

    We have constructed a sample of 29 close projected quasar pairs where the background quasar spectrum reveals absorption from optically thick H I gas associated with the foreground quasar. These unique sightlines allow us to study the quasar circumgalactic medium (CGM) in absorption and emission simultaneously, because the background quasar pinpoints large concentrations of gas where Ly{alpha} emission, resulting from quasar-powered fluorescence, resonant Ly{alpha} scattering, and/or cooling radiation, is expected. A sensitive search (1{sigma} surface-brightness limits of SB{sub Ly{alpha}}{approx_equal}3 Multiplication-Sign 10{sup -18} erg s{sup -1} cm{sup -2} arcsec{sup -2}) for diffuse Ly{alpha} emission in the environments of the foreground (predominantly radio-quiet) quasars is conducted using Gemini/GMOS and Keck/LRIS slit spectroscopy. We fail to detect large-scale {approx}100 kpc Ly{alpha} emission, either at the location of the optically thick absorbers or in the foreground quasar halos, in all cases except a single system. We interpret these non-detections as evidence that the gas detected in absorption is shadowed from the quasar UV radiation due to obscuration effects, which are frequently invoked in unified models of active galactic nuclei. Small-scale R {approx}< 50 kpc extended Ly{alpha} nebulosities are detected in 34% of our sample, which are likely the high-redshift analogs of the extended emission-line regions (EELRs) commonly observed around low-redshift (z < 0.5) quasars. This may be fluorescent recombination radiation from a population of very dense clouds with a low covering fraction illuminated by the quasar. We also detect a compact high rest-frame equivalent width (W{sub Ly{alpha}} > 50 A) Ly{alpha}-emitter with luminosity L{sub Ly{alpha}} = 2.1 {+-} 0.32 Multiplication-Sign 10{sup 41} erg s{sup -1} at small impact parameter R = 134 kpc from one foreground quasar, and argue that it is more likely to result from quasar-powered fluorescence

  5. Dust in the Quasar Wind (Artist Concept)

    NASA Technical Reports Server (NTRS)

    2007-01-01

    Dusty grains -- including tiny specks of the minerals found in the gemstones peridot, sapphires and rubies -- can be seen blowing in the winds of a quasar, or active black hole, in this artist's concept. The quasar is at the center of a distant galaxy.

    Astronomers using NASA's Spitzer Space Telescope found evidence that such quasar winds might have forged these dusty particles in the very early universe. The findings are another clue in an ongoing cosmic mystery: where did all the dust in our young universe come from?

    Dust is crucial for efficient star formation as it allows the giant clouds where stars are born to cool quickly and collapse into new stars. Once a star has formed, dust is also needed to make planets and living creatures. Dust has been seen as far back as when the universe was less than a tenth of its current age, but how did it get there? Most dust in our current epoch forms in the winds of evolved stars that did not exist when the universe was young.

    Theorists had predicted that winds from quasars growing in the centers of distant galaxies might be a source of this dust. While the environment close to a quasar is too hot for large molecules like dust grains to survive, dust has been found in the cooler, outer regions. Astronomers now have evidence that dust is created in these outer winds.

    Using Spitzer's infrared spectrograph instrument, scientists found a wealth of dust grains in a quasar called PG2112+059 located at the center of a galaxy 8 billion light-years away. The grains - including corundum (sapphires and rubies); forsterite (peridot); and periclase (naturally occurring in marble) - are not typically found in galaxies without quasars, suggesting they might have been freshly formed in the quasar's winds.

  6. Characterizing Quasar Outflows I: Sample, Spectral Measurements

    NASA Astrophysics Data System (ADS)

    Ganguly, Rajib; Christenson, D. H.; Richmond, J. M.; Derseweh, J. A.; Robbins, J. M.; Townsend, S. L.; Stark, M. A.

    2012-05-01

    Galaxy evolution models have shown that quasars are a crucial ingredient in the evolution of massive galaxies. Outflows play a key role in the story of quasars and their host galaxies, by helping regulate the accretion process, the star-formation rate and mass of the host galaxy (i.e., feedback). The prescription for modeling outflows as a contributor to feedback requires knowledge of the outflow velocity, geometry, and column density. In particular, we need to understand how these depend on physical parameters and how much is determined stochastically (and with what distribution). For this purpose, we are examining a sample of 11000 z=1.7-2.0 quasars from the Sloan Digital Sky Survey. This redshift range permits the following from the SDSS spectra: (1) separation of objects that do and do not exhibit outflows; (2) classification/measurement of outflow properties (ionization, velocity, velocity width); and (3) measurements of UV emission line and continuum parameters. In this poster, we subjectively divide these quasars into four categories: broad absorption-line quasars (2700 objects), associated absorption-line quasars (1700 objects), reddened quasars (160 objects), and unabsorbed/unreddened quasars (6300 objects). We present measurements of the absorption (velocities, velocity widths, equivalent widths), composite spectral profiles of outflows as a function of velocity, as well as measurements of the continuum and CIV, MgII, and FeII emission-line properties. In accompanying posters, we add photometry from the rest-frame X-ray (ROSAT and Chandra), EUV (GALEX), optical (2MASS), and infrared (WISE) bands to complete the SED. The continuum and emission-line measurements from the SDSS spectra and accompanying photometry provides estimates on the black hole masses, bolometric luminsosities, and SED. We consider empirically how these affect the outflow properties. This material is based upon work supported by the National Aeronautics and Space Administration under

  7. Quasar x-ray spectra revisited

    NASA Technical Reports Server (NTRS)

    Shastri, P.; Wilkes, B. J.; Elvis, M.; Mcdowell, J.

    1992-01-01

    A sample of 45 quasars observed by the Imaging Proportional Counter (IPC) on the Einstein satellite is used to re-examine the relationship between the soft (0.2-3.5 keV) X-ray energy index and radio-loudness. We found the following: (1) the tendency for radio-loud quasars to have systematically flatter X-ray slopes than radio-quiet quasars (RQQ's) is confirmed with the soft X-ray excess having negligible effect; (2) there is a tendency for the flatness of the X-ray slope to correlate with radio core-dominance for radio-loud quasars, suggesting that a component of the X-ray emission is relativistically beamed; (3) for the RQQ's the soft X-ray slopes, with a mean of approximately 1.0, are consistent with the slopes found at higher energies (2-10 keV) although steeper than those observed for Seyfert 1 galaxies (also 2-10 keV) where the reflection model gives a good fit to the data; (4) the correlation of FeII emission line strength with X-ray energy index is confirmed for radio-quiet quasars using a subset of 18 quasars. The radio-loud quasars show no evidence for a correlation. This relation suggests a connection between the ionizing continuum and the line emission from the broad emission line region (BELR) of radio-quiet quasars, but in the opposite sense to that predicted by current photoionization models; and (5) the correlations of X-ray slope with radio core dominance and FeII equivalent width within the radio-loud and radio-quiet sub-classes respectively imply that the observed wide range of X-ray spectral slopes is real rather than due to the large measuring uncertainties for individual objects.

  8. Luminosity calibration of low redshift quasars

    NASA Technical Reports Server (NTRS)

    Wampler, E. J.

    1983-01-01

    European (SERC) were combined with U.S. shifts on the IUE in order to obtain the long integration times required to record spectra of faint quasars. LWR spectra of the nearby giant radio galaxy Centarus A(NGC 5548) was attempted in an effort to determine the chemical composition and stellar populations in this unusual galaxy. The IUE results from the low redshift quasar study, combined with the data from an extensive ground based survey, are described.

  9. Understanding Quasar Variability through Kepler

    NASA Astrophysics Data System (ADS)

    Silano, Daniel; Wiita, P. J.; Wehrle, A. E.; Unwin, S. C.

    2012-01-01

    We are monitoring four flat spectrum radio quasars (blazars) and one powerful radio galaxy, Cygnus A, to search for variability on timescales comparable to the light crossing time of the accretion disk around the central supermassive black hole and the base of the relativistic jet. Kepler's essentially continuous monitoring at 1 min and 30 min cadences allows us to obtain high quality light curves extending for months, something not possible from even semi-dedicated collections of ground based optical telescopes. We can characterize the variability on timescales ranging from several minutes through many days to see if some optical variability in quasars might be due to a bright feature in the accretion disk as it approaches the last stable orbit, or, more likely for blazars, nearly coherent inhomogeneities in the jet, possibly in a helical structure or temporarily dominant turbulent cell. We have analyzed both the raw and "corrected” Kepler data to determine the power spectral densities of the four blazars as well as their structure functions. The principal challenge to our Kepler data analysis is that the automatic pipeline removal of day-to-week-scale drifts also removes real astrophysical brightness variations and so we have concentrated so far on the raw data while we work on better removal of only the instrumental drifts. Our preliminary results on short timescale variations indicate that three of the four blazars showed modest ( 15%) variations and relatively slow variability during three months of monitoring, but the fourth also shows many flares ( 3%) on several-day timescales, particularly during one quarter. While a visual inspection of this light curve gives a hint of a quasi-period, this is not borne out by the structure function and PDS analyses. This work is supported by NASA/Kepler grant GO20018.

  10. Quasar clustering in a galaxy and quasar formation model based on ultra high-resolution N-body simulations

    NASA Astrophysics Data System (ADS)

    Oogi, Taira; Enoki, Motohiro; Ishiyama, Tomoaki; Kobayashi, Masakazu A. R.; Makiya, Ryu; Nagashima, Masahiro

    2016-02-01

    We investigate clustering properties of quasars using a new version of our semi-analytic model of galaxy and quasar formation with state-of-the-art cosmological N-body simulations. In this study, we assume that a major merger of galaxies triggers cold gas accretion on to a supermassive black hole and quasar activity. Our model can reproduce the downsizing trend of the evolution of quasars. We find that the median mass of quasar host dark matter haloes increases with cosmic time by an order of magnitude from z = 4 (a few 1011 M⊙) to z = 1 (a few 1012 M⊙), and depends only weakly on the quasar luminosity. Deriving the quasar bias through the quasar-galaxy cross-correlation function in the model, we find that the quasar bias does not depend on the quasar luminosity, similar to observed trends. This result reflects the fact that quasars with a fixed luminosity have various Eddington ratios and thus have various host halo masses that primarily determine the quasar bias. We also show that the quasar bias increases with redshift, which is in qualitative agreement with observations. Our bias value is lower than the observed values at high redshifts, implying that we need some mechanisms that make quasars inactive in low-mass haloes and/or that make them more active in high-mass haloes.

  11. X-ray absorption and high redshift quasars

    NASA Technical Reports Server (NTRS)

    Elvis, Martin

    1996-01-01

    The low energy cut-offs toward radio-loud quasars with z greater than 2, red quasars, and broad absorption line quasars are discussed. The X-ray absorption seems to be common among different types of red shift quasar. The Rosat position sensitive proportional counter (PSPC) spectra of z = 3 quasars and of a red quasar are presented. Broad absorption lines show outflow velocities of up to 0.1 c to 0.2 c. The advantages and the disadvantages of high red shift observations are underlined.

  12. QUASARS PROBING QUASARS. VI. EXCESS H I ABSORPTION WITHIN ONE PROPER Mpc OF z ∼ 2 QUASARS

    SciTech Connect

    Prochaska, J. Xavier; Cantalupo, Sebastiano; Lau, Marie Wingyee; Bovy, Jo; Djorgovski, S. G.; Ellison, Sara L.; Martin, Crystal L.; Simcoe, Robert A.

    2013-10-20

    With close pairs of quasars at different redshifts, a background quasar sightline can be used to study a foreground quasar's environment in absorption. We use a sample of 650 projected quasar pairs to study the H I Lyα absorption transverse to luminous, z ∼ 2 quasars at proper separations of 30 kpc < R < 1 Mpc. In contrast to measurements along the line-of-sight, regions transverse to quasars exhibit enhanced H I Lyα absorption and a larger variance than the ambient intergalactic medium, with increasing absorption and variance toward smaller scales. Analysis of composite spectra reveals excess absorption characterized by a Lyα equivalent width profile W = 2.3 Å (R /100 kpc){sup –0.46}. We also observe a high (≅ 60%) covering factor of strong, optically thick H I absorbers (H I column N{sub H{sub I}}>10{sup 17.3} cm{sup -2}) at separations R < 200 kpc, which decreases to ∼20% at R ≅ 1 Mpc, but still represents a significant excess over the cosmic average. This excess of optically thick absorption can be described by a quasar-absorber cross-correlation function ξ{sub QA}(r) = (r/r{sub 0}){sup γ} with a large correlation length r{sub 0} = 12.5{sup +2.7}{sub -1.4} h{sup -1} Mpc (comoving) and γ=1.68{sup +0.14}{sub -0.30}. The H I absorption measured around quasars exceeds that of any previously studied population, consistent with quasars being hosted by massive dark matter halos M{sub halo} ≈ 10{sup 12.5} M{sub ☉} at z ∼ 2.5. The environments of these massive halos are highly biased toward producing optically thick gas, and may even dominate the cosmic abundance of Lyman limit systems and hence the intergalactic opacity to ionizing photons at z ∼ 2.5. The anisotropic absorption around quasars implies the transverse direction is much less likely to be illuminated by ionizing radiation than the line-of-sight.

  13. Extended Lyα emission around quasars with eclipsing damped Lyα systems

    NASA Astrophysics Data System (ADS)

    Fathivavsari, H.; Petitjean, P.; Noterdaeme, P.; Pâris, I.; Finley, H.; López, S.; Srianand, R.

    2016-09-01

    We present spectroscopic observations of six high redshift (zem > 2) quasars, which have been selected for their Lyman α (Lyα) emission region being only partially covered by a strong proximate (zabs ˜ zem) coronagraphic damped Lyα system (DLA). We detected spatially extended Lyα emission envelopes surrounding these six quasars, with projected spatial extent in the range 26 ≤ dLyα ≤ 51 kpc. No correlation is found between the quasar ionizing luminosity and the Lyα luminosity of their extended envelopes. This could be related to the limited covering factor of the extended gas and/or due to the AGN being obscured in other directions than towards the observer. Indeed, we find a strong correlation between the luminosity of the envelope and its spatial extent, which suggests that the envelopes are probably ionized by the AGN. The metallicity of the coronagraphic DLAs is low and varies in the range -1.75 < [Si/H] < -0.63. Highly ionized gas is observed to be associated with most of these DLAs, probably indicating ionization by the central AGN. One of these DLAs has the highest Al III/Si II ratio ever reported for any intervening and/or proximate DLA. Most of these DLAs are redshifted with respect to the quasar, implying that they might represent infalling gas probably accreted on to the quasar host galaxies through filaments.

  14. Five New High-Redshift Quasar Lenses from the Sloan Digital Sky Survey

    SciTech Connect

    Inada, Naohisa; Oguri, Masamune; Shin, Min-Su; Kayo, Issha; Strauss, Michael A.; Morokuma, Tomoki; Schneider, Donald P.; Becker, Robert H.; Bahcall, Neta A.; York, Donald G.

    2008-09-08

    We report the discovery of five gravitationally lensed quasars from the Sloan Digital Sky Survey (SDSS). All five systems are selected as two-image lensed quasar candidates from a sample of high-redshift (z > 2.2) SDSS quasars. We confirmed their lensing nature with additional imaging and spectroscopic observations. The new systems are SDSS J0819+5356 (source redshift z{sub s} = 2.237, lens redshift z{sub l} = 0.294, and image separation {theta} = 4.04 inch), SDSS J1254+2235 (z{sub s} = 3.626, {theta} = 1.56 inch), SDSS J1258+1657 (z{sub s} = 2.702, {theta} = 1.28 inch), SDSS J1339+1310 (z{sub s} = 2.243, {theta} = 1.69 cin), and SDSS J1400+3134 (z{sub s} = 3.317, {theta} = 1.74 inch). We estimate the lens redshifts of the latter four systems to be z{sub l} = 0.4-0.6 from the colors and magnitudes of the lensing galaxies. We find that the image configurations of all systems are well reproduced by standard mass models. Although these lenses will not be included in our statistical sample of z{sub s} < 2.2 lenses, they expand the number of lensed quasars which can be used for high-redshift galaxy and quasar studies.

  15. Discovery of two gravitationally lensed quasars in the Dark Energy Survey

    NASA Astrophysics Data System (ADS)

    Agnello, A.; Treu, T.; Ostrovski, F.; Schechter, P. L.; Buckley-Geer, E. J.; Lin, H.; Auger, M. W.; Courbin, F.; Fassnacht, C. D.; Frieman, J.; Kuropatkin, N.; Marshall, P. J.; McMahon, R. G.; Meylan, G.; More, A.; Suyu, S. H.; Rusu, C. E.; Finley, D.; Abbott, T.; Abdalla, F. B.; Allam, S.; Annis, J.; Banerji, M.; Benoit-Lévy, A.; Bertin, E.; Brooks, D.; Burke, D. L.; Rosell, A. Carnero; Kind, M. Carrasco; Carretero, J.; Cunha, C. E.; D'Andrea, C. B.; da Costa, L. N.; Desai, S.; Diehl, H. T.; Dietrich, J. P.; Doel, P.; Eifler, T. F.; Estrada, J.; Neto, A. Fausti; Flaugher, B.; Fosalba, P.; Gerdes, D. W.; Gruen, D.; Gutierrez, G.; Honscheid, K.; James, D. J.; Kuehn, K.; Lahav, O.; Lima, M.; Maia, M. A. G.; March, M.; Marshall, J. L.; Martini, P.; Melchior, P.; Miller, C. J.; Miquel, R.; Nichol, R. C.; Ogando, R.; Plazas, A. A.; Reil, K.; Romer, A. K.; Roodman, A.; Sako, M.; Sanchez, E.; Santiago, B.; Scarpine, V.; Schubnell, M.; Sevilla-Noarbe, I.; Smith, R. C.; Soares-Santos, M.; Sobreira, F.; Suchyta, E.; Swanson, M. E. C.; Tarle, G.; Thaler, J.; Tucker, D.; Walker, A. R.; Wechsler, R. H.; Zhang, Y.

    2015-12-01

    We present spectroscopic confirmation of two new gravitationally lensed quasars, discovered in the Dark Energy Survey (DES) and Wide-field Infrared Survey Explorer (WISE) based on their multiband photometry and extended morphology in DES images. Images of DES J0115-5244 show a red galaxy with two blue point sources at either side, which are images of the same quasar at zs = 1.64 as obtained by our long-slit spectroscopic data. The Einstein radius estimated from the DES images is 0.51 arcsec. DES J2146-0047 is in the area of overlap between DES and the Sloan Digital Sky Survey (SDSS). Two blue components are visible in the DES and SDSS images. The SDSS fibre spectrum shows a quasar component at zs = 2.38 and absorption by Mg II and Fe II at zl = 0.799, which we tentatively associate with the foreground lens galaxy. Our long-slit spectra show that the blue components are resolved images of the same quasar. The Einstein radius is 0.68 arcsec, corresponding to an enclosed mass of 1.6 × 1011 M⊙. Three other candidates were observed and rejected, two being low-redshift pairs of starburst galaxies, and one being a quasar behind a blue star. These first confirmation results provide an important empirical validation of the data mining and model-based selection that is being applied to the entire DES data set.

  16. Cloudy 94 and Applications to Quasar Emission Line Regions

    NASA Technical Reports Server (NTRS)

    Ferland, Gary J.

    2000-01-01

    This review discusses the most recent developments of the plasma simulation code Cloudy and its application to the, emission-line regions of quasars. The longterm goal is to develop the tools needed to determine the chemical composition of the emitting gas and the luminosity of the central engine for any emission line source. Emission lines and the underlying thermal continuum are formed in plasmas that are far from thermodynamic equilibrium. Their thermal and ionization states are the result of a balance of a vast set of microphysical processes. Once produced, radiation must, propagate out of the (usually) optically thick source. No analytic solutions are possible, and recourse to numerical simulations is necessary. I am developing the large-scale plasma simulation code Cloudy as an investigative tool for this work, much as an observer might build a spectrometer. This review describes the current version of Cloudy, version 94. It describes improvements made since the, release of the previous version, C90. The major recent, application has been the development of the "Locally Optimally-Emitting Cloud" (LOC) model of AGN emission line regions. Powerful selection effects, introduced by the atomic physics and line formation process, permit individual lines to form most efficiently only near certain selected parameters. These selection effects, together with the presence of gas with a wide range of conditions, are enough to reproduce the spectrum of a typical quasar with little dependence on details. The spectrum actually carries little information to the identity of the emitters. I view this as a major step forward since it provides a method to handle accidental details at the source, so that we can concentrate on essential information such as the luminosity or chemical composition of the quasar.

  17. Building classifiers using Bayesian networks

    SciTech Connect

    Friedman, N.; Goldszmidt, M.

    1996-12-31

    Recent work in supervised learning has shown that a surprisingly simple Bayesian classifier with strong assumptions of independence among features, called naive Bayes, is competitive with state of the art classifiers such as C4.5. This fact raises the question of whether a classifier with less restrictive assumptions can perform even better. In this paper we examine and evaluate approaches for inducing classifiers from data, based on recent results in the theory of learning Bayesian networks. Bayesian networks are factored representations of probability distributions that generalize the naive Bayes classifier and explicitly represent statements about independence. Among these approaches we single out a method we call Tree Augmented Naive Bayes (TAN), which outperforms naive Bayes, yet at the same time maintains the computational simplicity (no search involved) and robustness which are characteristic of naive Bayes. We experimentally tested these approaches using benchmark problems from the U. C. Irvine repository, and compared them against C4.5, naive Bayes, and wrapper-based feature selection methods.

  18. THE HALO OCCUPATION DISTRIBUTION OF SDSS QUASARS

    SciTech Connect

    Richardson, Jonathan; Chatterjee, Suchetana; Nagai, Daisuke; Zheng Zheng; Shen Yue

    2012-08-10

    We present an estimate of the projected two-point correlation function (2PCF) of quasars in the Sloan Digital Sky Survey (SDSS) over the full range of one- and two-halo scales, 0.02 h{sup -1} Mpc < r{sub p} < 120 h{sup -1} Mpc. This was achieved by combining data from SDSS DR7 on large scales and Hennawi et al. (with appropriate statistical corrections) on small scales. Our combined clustering sample is the largest spectroscopic quasar clustering sample to date, containing {approx}48, 000 quasars in the redshift range 0.4 {approx}< z {approx}< 2.5 with median redshift 1.4. We interpret these precise 2PCF measurements within the halo occupation distribution (HOD) framework and constrain the occupation functions of central and satellite quasars in dark matter halos. In order to explain the small-scale clustering, the HOD modeling requires that a small fraction of z {approx} 1.4 quasars, f{sub sat} = (7.4 {+-} 1.4) Multiplication-Sign 10{sup -4}, be satellites in dark matter halos. At z {approx} 1.4, the median masses of the host halos of central and satellite quasars are constrained to be M{sub cen} = 4.1{sup +0.3}{sub -0.4} Multiplication-Sign 10{sup 12} h{sup -1} M{sub Sun} and M{sub sat} = 3.6{sup +0.8}{sub -1.0} Multiplication-Sign 10{sup 14} h{sup -1} M{sub Sun }, respectively. To investigate the redshift evolution of the quasar-halo relationship, we also perform HOD modeling of the projected 2PCF measured by Shen et al. for SDSS quasars with median redshift 3.2. We find tentative evidence for an increase in the mass scale of quasar host halos-the inferred median mass of halos hosting central quasars at z {approx} 3.2 is M{sub cen} = 14.1{sup +5.8}{sub -6.9} Multiplication-Sign 10{sup 12} h{sup -1} M{sub Sun }. The cutoff profiles of the mean occupation functions of central quasars reveal that quasar luminosity is more tightly correlated with halo mass at higher redshifts. The average quasar duty cycle around the median host halo mass is inferred to be f{sub q

  19. FR-II Broad Absorption Line Quasars and the Life Cycle of Quasars

    SciTech Connect

    Gregg, M D; Becker, R H; de Vries, W

    2006-01-05

    By combining the Sloan Digitized Sky Survey Third Data Release quasar list with the VLA FIRST survey, we have identified five objects having both broad absorption lines in their optical spectra and FR-II radio morphologies. We identify an additional example of this class from the FIRST Bright Quasar Survey, J1408+3054. Including the original FR-II-BAL object, J1016+5209, brings the number of such objects to eight. These quasars are relatively rare; finding this small handful has required the 45,000-large quasar sample of SDSS. The FR-II-BAL quasars exhibit a significant anti-correlation between radio-loudness and the strength of the BAL features. This is easily accounted for by the evolutionary picture in which quasars emerge from cocoons of BAL-producing material which stifle the development of radio jets and lobes. There is no such simple explanation for the observed properties of FR-II-BALs in the unification-by-orientation model of quasars. The rarity of the FR-II-BAL class implies that the two phases do not coexist for very long in a single quasar, perhaps less than 10{sup 5} years, with the combined FR-II, high ionization broad absorption phase being even shorter by another factor of 10 or more.

  20. THE PROPERTIES OF QUASAR HOSTS AT THE PEAK OF THE QUASAR ACTIVITY

    SciTech Connect

    Kotilainen, Jari K.; Falomo, Renato; Decarli, Roberto; Treves, Aldo; Uslenghi, Michela; Scarpa, Riccardo E-mail: renato.falomo@oapd.inaf.i E-mail: aldo.treves@uninsubria.i E-mail: riccardo.scarpa@gtc.iac.e

    2009-10-01

    We present near-infrared imaging obtained with ESO VLT/ISAAC of a sample of 16 low luminosity radio-quiet quasars (RQQs) at the epoch around the peak of the quasar activity (2 < z < 3), aimed at investigating their host galaxies. For 11 quasars, we are able to detect the host galaxies and derive their properties, while for the other 5 quasars, upper limits to the host luminosity are estimated. The luminosities of the host galaxies of RQQs at high redshift are in the range of those of massive inactive elliptical galaxies. This work complements our previous systematic study of quasar hosts aimed to trace the cosmological luminosity evolution of the host galaxies up to z approx 2 and extends our pilot study of a few luminous quasars at z > 2. The luminosity trend with a cosmic epoch resembles that observed for massive inactive galaxies, suggesting a similar star formation history. In particular, both quasar host galaxies and massive inactive galaxies appear mostly assembled already at the peak age of the quasar activity. This result is of key importance for testing the models of joint formation and evolution of galaxies and their active nuclei.

  1. INFRARED SPECTRA AND PHOTOMETRY OF COMPLETE SAMPLES OF PALOMAR-GREEN AND TWO MICRON ALL SKY SURVEY QUASARS

    SciTech Connect

    Shi, Yong; Rieke, G. H.; Su, K. Y. L.; Ogle, P. M.; Balog, Z.

    2014-10-01

    As a step toward a comprehensive overview of the infrared (IR) diagnostics of the central engines and host galaxies of quasars at low redshift, we present Spitzer Space Telescope spectroscopic (5-40 μm) and photometric (24, 70, and 160 μm) measurements of all Palomar-Green (PG) quasars at z < 0.5 and Two Micron All Sky Survey (2MASS) quasars at z < 0.3. We supplement these data with Herschel measurements at 160 μm. The sample is composed of 87 optically selected PG quasars and 52 near-IR-selected 2MASS quasars. Here we present the data, measure the prominent spectral features, and separate emission due to star formation from that emitted by the dusty circumnuclear torus. We find that the mid-IR (5-30 μm) spectral shape for the torus is largely independent of quasar IR luminosity with scatter in the spectral energy distribution (SED) shape of ≲0.2 dex. Except for the silicate features, no large difference is observed between PG (unobscured—silicate emission) and 2MASS (obscured—silicate absorption) quasars. Only mild silicate features are observed in both cases. When in emission, the peak wavelength of the silicate feature tends to be longer than 9.7 μm, possibly indicating effects on grain properties near the active galactic nucleus. The IR color is shown to correlate with the equivalent width of the aromatic features, indicating that the slope of the quasar mid- to far-IR SED is to first order driven by the fraction of radiation from star formation in the IR bands.

  2. Herschel Observed Stripe 82 Quasars and Their Host Galaxies: Connections between AGN Activity and host Galaxy Star Formation

    NASA Astrophysics Data System (ADS)

    Dong, X. Y.; Wu, Xue-Bing

    2016-06-01

    In this work, we present a study of 207 quasars selected from the Sloan Digital Sky Survey quasar catalogs and the Herschel Stripe 82 survey. Quasars within this sample are high-luminosity quasars with a mean bolometric luminosity of 1046.4 erg s-1. The redshift range of this sample is within z < 4, with a mean value of 1.5 ± 0.78. Because we only selected quasars that have been detected in all three Herschel-SPIRE bands, the quasar sample is complete yet highly biased. Based on the multi-wavelength photometric observation data, we conducted a spectral energy distribution (SED) fitting through UV to FIR. Parameters such as active galactic nucleus (AGN) luminosity, far-IR (FIR) luminosity, stellar mass, as well as many other AGN and galaxy properties are deduced from the SED fitting results. The mean star formation rate (SFR) of the sample is 419 M ⊙ yr-1 and the mean gas mass is ˜1011.3 M ⊙. All of these results point to an IR luminous quasar system. Compared with star formation main sequence (MS) galaxies, at least 80 out of 207 quasars are hosted by starburst galaxies. This supports the statement that luminous AGNs are more likely to be associated with major mergers. The SFR increases with the redshift up to z = 2. It is correlated with the AGN bolometric luminosity, where {L}{{FIR}}\\propto {L}{{Bol}}0.46+/- 0.03. The AGN bolometric luminosity is also correlated with the host galaxy mass and gas mass. Yet the correlation between L FIR and L Bol has higher significant level, implies that the link between AGN accretion and the SFR is more primal. The M BH/M * ratio of our sample is 0.02, higher than the value 0.005 in the local universe. It might indicate an evolutionary trend of the M BH-M * scaling relation.

  3. Obscured quasars at high redshift in the Sloan Digital Sky Survey

    NASA Astrophysics Data System (ADS)

    Strauss, Michael

    2016-08-01

    The SDSS has uncovered a substantial number of luminous quasars with weak continuum, strong narrow lines, and strong evidence for obscuration, at redshifts from 0.4 to 4. I will discuss the selection of such objects and their properties in the optical and infrared. Some of these objects show evidence for significant outflows, with substantial wings in their [OIII] profiles.

  4. Dust and Molecular Gas from the Optically Faint Quasars at z 6

    NASA Astrophysics Data System (ADS)

    Wang, Ran; Carilli, C.; Neri, R.; Riechers, D.; Wagg, J.; Walter, F.; Bertoldi, F.; Omont, A.; Cox, P.; Menten, K.; Fan, X.; Strauss, M.

    2011-01-01

    We present millimeter observations of the twelve z 6 quasars discovered from the SDSS southern survey. These objects are typically one or two magnitudes fainter in the optical (i.e., 20.6 quasar sample selected from the SDSS main survey. We observed the 250 GHz dust continuum emission from these objects using the Max Plank Millimeter Bolometer Array (MAMBO) on the IRAM-30m telescope and three of them have been detected. We also searched for Molecular CO (6-5) line emission in the three MAMBO detections with the IRAM Plateau de Bure Interferometer and two of them have been detected. The millimeter continuum and CO detections in the optically faint quasars at z 6 reveal strong FIR emission from 40 to 60 K warm dust and highly excited molecular gas in the quasar host galaxies. The molecular gas masses of the two CO detections are all about 10^10 Msun, which are comparable to that of the CO-detected optically bright quasars at z 6. Their FIR-to-CO luminosity ratios are also consistent with that of the previous CO-detected quasars at z 2 to 6 and the dusty starbusrt systems, e.g., the submillimeter galaxies. However, their FIR-to-UV luminosity ratios are higher than that of the millimeter-detected optically bright quasars at z 6. This confirms the shallow nonlinear FIR-to-AGN luminosity relationship found with other AGN-starburst systems at local and high-z universe. All these results suggest massive star formation coeval with rapid black hole accretion in the host galaxies of the millimeter-detected optically faint quasars at z 6. Further high-resolution imaging of the Molecular CO emission (e.g., with ALMA) will be important to measure the dynamical masses of the spheroidal hosts and understand the black hole-bulge relationship of the optically faint quasars at the earliest epoch.

  5. An Optical-Infrared Study of Radio-Loud Quasar Environments

    NASA Astrophysics Data System (ADS)

    Hall, Patrick Brian

    1998-06-01

    I present the data for an optical/near-infrared study of radio-loud quasar environments from z = 0.6-2.0, and the analysis of the data from z = 1.0-2.0. I thoroughly discuss the sample selection, observing, data reduction, and object cataloging. Even accounting for possible systematic offsets, I find a significant excess of K/ ~ 19 galaxies in the fields of z = 1-2 RLQs, on two spatial scales. One component is at θ <40&prime‧ from the quasars and is significant compared to the galaxy surface density at θ >40'' in the same fields. The other component appears roughly uniform across the fields (to θ~100'') and is significant compared to the galaxy surface density seen in random-field surveys in the literature. The r-K color distributions of the excess galaxy populations are indistinguishable, and are significantly redder than the color distribution of the field population. The excess galaxy population is thus consistent with being predominantly early-type galaxies at the quasar redshifts. The average excess within 0.5h 75-1 Mpc (~ 65'') of the quasars corresponds to Abell richness class ~0 compared to the galaxy surface density at >0.5h75-1 Mpc from the quasars, and to Abell richness class ~1 compared to that from the literature. I estimate -0.65-0.55+0.41 magnitudes of evolution in MK* to \\bar z = 1.67 by assuming the excess galaxies are at the quasar redshifts. I discuss the spectral energy distributions (SEDs) of galaxies in fields with data in several passbands. Most candidate quasar-associated galaxies are consistent with being 2-3 Gyr old early-types at the quasar redshifts of z~ 1.5. However, some objects have SEDs similar to extremely late-type stars; others have SEDs consistent with being 4-5 Gyr old at z~ 1.5 and others are consistent with old but dust-reddened galaxies at the quasar redshifts. These potentially different galaxy types suggest there may be considerable dispersion in the properties of early-type cluster galaxies at z~ 1.5. There is also

  6. A POPULATION OF X-RAY WEAK QUASARS: PHL 1811 ANALOGS AT HIGH REDSHIFT

    SciTech Connect

    Wu Jianfeng; Brandt, W. N.; Schneider, Donald P.; Hall, Patrick B.; Gibson, Robert R.; Schmidt, Sarah J.; Richards, Gordon T.; Shemmer, Ohad; Just, Dennis W.

    2011-07-20

    We report the results from Chandra and XMM-Newton observations of a sample of 10 type 1 quasars selected to have unusual UV emission-line properties (weak and blueshifted high-ionization lines; strong UV Fe emission) similar to those of PHL 1811, a confirmed intrinsically X-ray weak quasar. These quasars were identified by the Sloan Digital Sky Survey at high redshift (z {approx} 2.2); eight are radio quiet while two are radio intermediate. All of the radio-quiet PHL 1811 analogs, without exception, are notably X-ray weak by a mean factor of {approx}13. These sources lack broad absorption lines and have blue UV/optical continua, supporting the hypothesis that they are intrinsically X-ray weak like PHL 1811 itself. However, their average X-ray spectrum appears to be harder than those of typical quasars, which may indicate the presence of heavy intrinsic X-ray absorption. Our sample of radio-quiet PHL 1811 analogs supports a connection between an X-ray weak spectral energy distribution and PHL 1811-like UV emission lines; this connection provides an economical way to identify X-ray weak type 1 quasars. The fraction of radio-quiet PHL 1811 analogs in the radio-quiet quasar population is estimated to be {approx}< 1.2%. We have investigated correlations between relative X-ray brightness and UV emission-line properties (e.g., C IV equivalent width and blueshift) for a sample combining our radio-quiet PHL 1811 analogs, PHL 1811 itself, and typical type 1 quasars. These correlation analyses suggest that PHL 1811 analogs may have extreme wind-dominated broad emission-line regions. Observationally, the radio-quiet PHL 1811 analogs appear to be a subset ({approx}30%) of radio-quiet weak-line quasars (WLQs). The existence of a subset of quasars in which high-ionization 'shielding gas' covers most of the broad emission-line region (BELR), but little more than the BELR, could potentially unify the PHL 1811 analogs and WLQs. The two radio-intermediate PHL 1811 analogs are X

  7. A Population of X-Ray Weak Quasars: PHL 1811 Analogs at High Redshift

    NASA Astrophysics Data System (ADS)

    Wu, Jianfeng; Brandt, W. N.; Hall, Patrick B.; Gibson, Robert R.; Richards, Gordon T.; Schneider, Donald P.; Shemmer, Ohad; Just, Dennis W.; Schmidt, Sarah J.

    2011-07-01

    We report the results from Chandra and XMM-Newton observations of a sample of 10 type 1 quasars selected to have unusual UV emission-line properties (weak and blueshifted high-ionization lines; strong UV Fe emission) similar to those of PHL 1811, a confirmed intrinsically X-ray weak quasar. These quasars were identified by the Sloan Digital Sky Survey at high redshift (z ≈ 2.2); eight are radio quiet while two are radio intermediate. All of the radio-quiet PHL 1811 analogs, without exception, are notably X-ray weak by a mean factor of ≈13. These sources lack broad absorption lines and have blue UV/optical continua, supporting the hypothesis that they are intrinsically X-ray weak like PHL 1811 itself. However, their average X-ray spectrum appears to be harder than those of typical quasars, which may indicate the presence of heavy intrinsic X-ray absorption. Our sample of radio-quiet PHL 1811 analogs supports a connection between an X-ray weak spectral energy distribution and PHL 1811-like UV emission lines; this connection provides an economical way to identify X-ray weak type 1 quasars. The fraction of radio-quiet PHL 1811 analogs in the radio-quiet quasar population is estimated to be <~ 1.2%. We have investigated correlations between relative X-ray brightness and UV emission-line properties (e.g., C IV equivalent width and blueshift) for a sample combining our radio-quiet PHL 1811 analogs, PHL 1811 itself, and typical type 1 quasars. These correlation analyses suggest that PHL 1811 analogs may have extreme wind-dominated broad emission-line regions. Observationally, the radio-quiet PHL 1811 analogs appear to be a subset (≈30%) of radio-quiet weak-line quasars (WLQs). The existence of a subset of quasars in which high-ionization "shielding gas" covers most of the broad emission-line region (BELR), but little more than the BELR, could potentially unify the PHL 1811 analogs and WLQs. The two radio-intermediate PHL 1811 analogs are X-ray bright. X-ray spectral

  8. The pattern of extreme star formation events in SDSS quasar hosts in Herschel fields

    NASA Astrophysics Data System (ADS)

    Pitchford, Lura Katherine; Hatziminaoglou, Evanthia; Feltre, Anna; Clarke, Charlotte; Farrah, Duncan; Harris, Kathryn Amy; Hurley, Peter; Oliver, Sebastian; Page, Mat; Wang, Lingyu

    2016-01-01

    Using a sample of ~500 quasars up to redshifts of ~4 detected by the Sloan Digital Sky Survey (SDSS) and the Spectral and Photometric Imaging Receiver (SPIRE) instrument of Herschel, we describe the behavior of intense starbursts in luminous quasars and how it correlates with the properties of the active galactic nuclei (AGN). We select our objects in the Herschel Stripe 82 Survey (HerS) and in the largest fields of the Herschel Multi-tiered Extragalactic Survey (HerMES), including the HerMES Large Mode Survey (HeLMS).The far-infrared (FIR) emission of our objects is quantified using a spectral energy distribution (SED) fitting technique. As our sources are individually detected in the SPIRE bands, they are bright in the FIR, exhibiting typical star formation rates (SFRs) of order of 1000 M⊙yr-1. We find the SFR to increase by a factor of nearly ten from z~0.5 to z~3, in line with the increasing comoving SFR density over a similar redshift range. The SFR, however, is shown to remain constant with increasing quasar luminosity for quasars with IR luminosities above 1012L⊙, indicating a self-regulating star formation process rather than a suppression effect due to the presence of powerful AGN. We find no further proof of a causal relation between star formation and accretion onto the central black hole, as the SFR and the Eddington ratio, λEdd, are found to be uncorrelated.We then compare the broad absorption line (BAL) quasars to the rest of the quasar population, as they are candidates for outflows in action from which shorter-term feedback effects could be sought. We find the accretion luminosities and λEdd values of BAL quasars to be drawn from the same population as those of the non-BAL quasars; further, the host SFRs are statistically similar among the two populations, all of which argue against feedback effects. These similarities also oppose an evolutionary scenario, as a different evolutionary stage would imply differences in either the accretion state

  9. Quasars with Anomalous Hβ Profiles. I. Demographics

    NASA Astrophysics Data System (ADS)

    Steinhardt, Charles L.; Silverman, John D.

    2013-08-01

    The Hβ emission line in a typical Type I quasar is composed of a broad base and a narrow core, with the core velocity characteristic of narrow-line region emission, and line-fitting routines typically assume this picture. We test the effects of removing this constraint, and find a substantial group of Type I quasars in the Sloan Digital Sky Survey catalog with Hβ emission line cores broader than 1200 km s-1 , above the velocity believed possible for gas in the quasar narrow-line region. We identify this group of ``anomalous Hβ quasars'' (AHQs) as a distinct population because of a variety of spectral and photometric signatures common to these AHQs but atypical of other quasars. These features are similar to some aspects of narrow-line Seyfert 1s and correlations identified by Eigenvector 1, but also contain distinct features that make it difficult to classify AHQs. We demonstrate that AHQs comprise at least 11% and most likely approximately one quarter of the SDSS Type I quasar population at 0.2 < z < 0.8. For AHQs, the [O III]λ 4959, 5007 profile is often better fit by de-linking it from the Hβ core, while a more standard linked fit produces a tight correlation between narrow- and broad-line velocities. We find that [O III] in AHQs sometimes has a standard narrow-line profile and other times matches the Hβ core, but is rarely in between the two, implying that the broadened core emission arises from a distinct physical region. Another feature of AHQs is a diminished [O II] line, which might indicate a connection between AHQs and the interstellar mediums of their host galaxies, through reduced photoionization or star formation. We find that it is difficult to produce AHQs using the current quasar standard model.

  10. Beacons in Time: Maarten Schmidt and the Discovery of Quasars.

    ERIC Educational Resources Information Center

    Preston, Richard

    1988-01-01

    Tells the story of Maarten Schmidt and the discovery of quasars. Discusses the decomposition of light, crucial observations and solving astronomical mysteries. Describes spectroscopic analysis used in astronomy and its application to quasars. (CW)

  11. Discovery of a bright quasar without a massive host galaxy.

    PubMed

    Magain, Pierre; Letawe, Géraldine; Courbin, Frédéric; Jablonka, Pascale; Jahnke, Knud; Meylan, Georges; Wisotzki, Lutz

    2005-09-15

    A quasar is thought to be powered by the infall of matter onto a supermassive black hole at the centre of a massive galaxy. Because the optical luminosity of quasars exceeds that of their host galaxy, disentangling the two components can be difficult. This led in the 1990s to the controversial claim of the discovery of 'naked' quasars. Since then, the connection between quasars and galaxies has been well established. Here we report the discovery of a quasar lying at the edge of a gas cloud, whose size is comparable to that of a small galaxy, but whose spectrum shows no evidence for stars. The gas in the cloud is excited by the quasar itself. If a host galaxy is present, it is at least six times fainter than would normally be expected for such a bright quasar. The quasar is interacting dynamically with a neighbouring galaxy, whose gas might be feeding the black hole.

  12. CLUSTERING OF OBSCURED AND UNOBSCURED QUASARS IN THE BOOeTES FIELD: PLACING RAPIDLY GROWING BLACK HOLES IN THE COSMIC WEB

    SciTech Connect

    Hickox, Ryan C.; Alexander, David M.; Goulding, Andrew D.; Myers, Adam D.; Brodwin, Mark; Forman, William R.; Jones, Christine; Murray, Stephen S.; Eisenstein, Daniel; Caldwell, Nelson; Brown, Michael J. I.; Cool, Richard J.; Kochanek, Christopher S.; Dey, Arjun; Jannuzi, Buell T.; Assef, Roberto J.; Eisenhardt, Peter R.; Gorjian, Varoujan; Stern, Daniel; Le Floc'h, Emeric

    2011-04-20

    We present the first measurement of the spatial clustering of mid-infrared-selected obscured and unobscured quasars, using a sample in the redshift range 0.7 < z < 1.8 selected from the 9 deg{sup 2} Booetes multiwavelength survey. Recently, the Spitzer Space Telescope and X-ray observations have revealed large populations of obscured quasars that have been inferred from models of the X-ray background and supermassive black hole evolution. To date, little is known about obscured quasar clustering, which allows us to measure the masses of their host dark matter halos and explore their role in the cosmic evolution of black holes and galaxies. In this study, we use a sample of 806 mid-infrared-selected quasars and {approx}250,000 galaxies to calculate the projected quasar-galaxy cross-correlation function w{sub p} (R). The observed clustering yields characteristic dark matter halo masses of log(M{sub halo} [h {sup -1} M{sub sun}]) = 12.7{sup +0.4}{sub -0.6} and 13.3{sup +0.3}{sub -0.4} for unobscured quasars (QSO-1s) and obscured quasars (Obs-QSOs), respectively. The results for QSO-1s are in excellent agreement with previous measurements for optically selected quasars, while we conclude that the Obs-QSOs are at least as strongly clustered as the QSO-1s. We test for the effects of photometric redshift errors on the optically faint Obs-QSOs, and find that our method yields a robust lower limit on the clustering; photo-z errors may cause us to underestimate the clustering amplitude of the Obs-QSOs by at most {approx}20%. We compare our results to previous studies, and speculate on physical implications of stronger clustering for obscured quasars.

  13. Practical Bayesian tomography

    NASA Astrophysics Data System (ADS)

    Granade, Christopher; Combes, Joshua; Cory, D. G.

    2016-03-01

    In recent years, Bayesian methods have been proposed as a solution to a wide range of issues in quantum state and process tomography. State-of-the-art Bayesian tomography solutions suffer from three problems: numerical intractability, a lack of informative prior distributions, and an inability to track time-dependent processes. Here, we address all three problems. First, we use modern statistical methods, as pioneered by Huszár and Houlsby (2012 Phys. Rev. A 85 052120) and by Ferrie (2014 New J. Phys. 16 093035), to make Bayesian tomography numerically tractable. Our approach allows for practical computation of Bayesian point and region estimators for quantum states and channels. Second, we propose the first priors on quantum states and channels that allow for including useful experimental insight. Finally, we develop a method that allows tracking of time-dependent states and estimates the drift and diffusion processes affecting a state. We provide source code and animated visual examples for our methods.

  14. GREEN BANK TELESCOPE DETECTION OF POLARIZATION-DEPENDENT H I ABSORPTION AND H I OUTFLOWS IN LOCAL ULIRGs AND QUASARS

    SciTech Connect

    Teng, Stacy H.; Veilleux, Sylvain; Baker, Andrew J.

    2013-03-10

    We present the results of a 21 cm H I survey of 27 local massive gas-rich late-stage mergers and merger remnants with the Robert C. Byrd Green Bank Telescope. These remnants were selected from the Quasar/ULIRG Evolution Study sample of ultraluminous infrared galaxies (ULIRGs; L{sub 8{sub -{sub 1000{sub {mu}m}}}} > 10{sup 12} L{sub Sun }) and quasars; our targets are all bolometrically dominated by active galactic nuclei (AGNs) and sample the later phases of the proposed ULIRG-to-quasar evolutionary sequence. We find the prevalence of H I absorption (emission) to be 100% (29%) in ULIRGs with H I detections, 100% (88%) in FIR-strong quasars, and 63% (100%) in FIR-weak quasars. The absorption features are associated with powerful neutral outflows that change from being mainly driven by star formation in ULIRGs to being driven by the AGN in the quasars. These outflows have velocities that exceed 1500 km s{sup -1} in some cases. Unexpectedly, we find polarization-dependent H I absorption in 57% of our spectra (88% and 63% of the FIR-strong and FIR-weak quasars, respectively). We attribute this result to absorption of polarized continuum emission from these sources by foreground H I clouds. About 60% of the quasars displaying polarized spectra are radio-loud, far higher than the {approx}10% observed in the general AGN population. This discrepancy suggests that radio jets play an important role in shaping the environments in these galaxies. These systems may represent a transition phase in the evolution of gas-rich mergers into ''mature'' radio galaxies.

  15. Updated measurements of the dark matter halo masses of obscured quasars with improved WISE and Planck data

    NASA Astrophysics Data System (ADS)

    DiPompeo, M. A.; Hickox, R. C.; Myers, A. D.

    2016-02-01

    Using the most recent releases of WISE and Planck data, we perform updated measurements of the bias and typical dark matter halo mass of infrared (IR)-selected obscured and unobscured quasars, using the angular autocorrelation function and cosmic microwave background lensing cross-correlations. Since our recent work of this kind, the WISE ALLWISE catalogue was released with improved photometry, and the Planck mission was completed and released improved products. These new data provide a more reliable measurement of the quasar bias and provide an opportunity to explore the role of changing survey pipelines in results downstream. We present a comparison of IR colour-selected quasars, split into obscured and unobscured populations based on optical-IR colours, selected from two versions of the WISE data. Which combination of data is used impacts the final results, particularly for obscured quasars, both because of mitigation of some systematics and because the newer catalogue provides a slightly different sample. We show that ALLWISE data is superior in several ways, though there may be some systematic trends with Moon contamination that were not present in the previous catalogue. We opt currently for the most conservative sample that meet our selection criteria in both the previous and new WISE catalogues. We measure a higher bias and halo mass for obscured quasars (bobsc ˜ 2.1, bunob ˜ 1.8) - at odds with simple orientation models - but at a reduced significance (˜1.5σ) as compared to our work with previous survey data.

  16. A Survey of z>5.8 Quasars in the Sloan Digital Sky Survey. I. Discovery of Three New Quasars and the Spatial Density of Luminous Quasars at z~6

    NASA Astrophysics Data System (ADS)

    Fan, Xiaohui; Narayanan, Vijay K.; Lupton, Robert H.; Strauss, Michael A.; Knapp, Gillian R.; Becker, Robert H.; White, Richard L.; Pentericci, Laura; Leggett, S. K.; Haiman, Zoltán; Gunn, James E.; Ivezić, Željko; Schneider, Donald P.; Anderson, Scott F.; Brinkmann, J.; Bahcall, Neta A.; Connolly, Andrew J.; Csabai, István; Doi, Mamoru; Fukugita, Masataka; Geballe, Tom; Grebel, Eva K.; Harbeck, Daniel; Hennessy, Gregory; Lamb, Don Q.; Miknaitis, Gajus; Munn, Jeffrey A.; Nichol, Robert; Okamura, Sadanori; Pier, Jeffrey R.; Prada, Francisco; Richards, Gordon T.; Szalay, Alex; York, Donald G.

    2001-12-01

    We present the results from a survey of i-dropout objects selected from ~1550 deg2 of multicolor imaging data from the Sloan Digital Sky Survey to search for luminous quasars at z>~5.8. Objects with i*-z*>2.2 and z*<20.2 are selected, and follow-up J-band photometry is used to separate L- and T-type cool dwarfs from high-redshift quasars. We describe the discovery of three new quasars, SDSSp J083643.85+005453.3 (z=5.82), J130608.26+035626.3 (z=5.99), and J103027.10+052455.0 (z=6.28). The quasar SDSSp J083643.85+005453.3 is a radio source with flux of 1.1 mJy at 20 cm. The spectra of all three quasars show strong and broad Lyα+N V emission lines and very strong Lyα forest absorption, with a mean continuum decrement DA>0.90. The ARC 3.5 m spectrum of SDSSp J103027.10+052455.0 shows that over a range of ~300 Å immediately blueward of the Lyα emission, the average transmitted flux is only 0.003+/-0.020 times that of the continuum level, consistent with zero flux over a ~300 Å range of the Lyα forest region and suggesting a tentative detection of the complete Gunn-Peterson trough. The existence of strong metal lines in the quasar spectra suggests early metal enrichment in the quasar environment. The three new objects, together with the previously published z=5.8 quasar SDSSp J104433.04-012502.2, form a complete color-selected flux-limited sample at z>~5.8. We estimate the selection function of this sample, taking into account the estimated variations in the quasar spectral energy distribution, as well as observational photometric errors. We find that at z=6, the comoving density of luminous quasars at M1450<-26.8 (H0=50 km s-1 Mpc-1, Ω=1) is 1.1×10-9 Mpc-3. This is a factor of ~2 lower than that at z~5 and is consistent with an extrapolation of the observed quasar evolution at z<5. Using the current sample, we discuss the constraint on the shape of the quasar luminosity function and the implications for the contribution of quasars to the ionizing background at z

  17. The SCUBA Bright Quasar Survey (SBQS): 850-μm observations of the z >~ 4 sample

    NASA Astrophysics Data System (ADS)

    Isaak, Kate G.; Priddey, Robert S.; McMahon, Richard G.; Omont, Alain; Peroux, Celine; Sharp, Robert G.; Withington, Stafford

    2002-01-01

    We present initial results of a new, systematic search for massive star formation in the host galaxies of the most luminous and probably most massive z>~4 radio-quiet quasars (MB<=-27.5 νLν(1450Å)>1013Lsolar). The survey, undertaken at 850μm using SCUBA at the James Clerk Maxwell Telescope (JCMT), has a target sensitivity limit of 3σ~10mJy, set to identify sources suitable for detailed follow-up, e.g. continuum mapping and molecular line diagnostics. A total of 38 z>~4 radio-quiet quasars have been observed at 850μm, of which eight were detected (>3σ) with S850μm>~10mJy (submillimetre-loud). The new detections almost triple the number of optically selected, submillimetre-loud z>~4 radio-quiet quasars known to date. We include a detailed description of how our quasar sample is defined in terms of radio and optical properties. As a by-product of our selection procedure, we have identified 17 radio-loud quasars with z>~4. There is no strong evidence for trends in either detectability or 850-μm flux with absolute magnitude, MB. We find that the weighted mean flux of the undetected sources is 2.0+/-0.6mJy, consistent with an earlier estimate of ~3mJy based on more sensitive observations of a sample z>~4 radio-quiet quasars. This corresponds to an inferred star formation rate of ~1000Msolaryr-1, similar to Arp220. The typical star formation time-scale for the submillimetre-bright sources is ~1Gyr, 10 times longer than the typical accretion-driven e-folding time-scale of ~ 5×107yr. Our 850-μm detection of the z=4.4 quasar PSS J1048+4407, when analysed in conjunction with 1.2-mm single-dish and interferometric observations, suggests that this source is resolved on angular scales of 1-2arcsec (6-12kpc). In addition, we present a new optical spectrum of this source, identifying it as a broad absorption line (BAL) quasar. The new redshift is outside that covered in a recent CO line search, highlighting the need for accurate redshifts for the observation and

  18. Causes and effects of the first quasars.

    PubMed

    Rees, M J

    1993-06-01

    The light we observe from the most distant known quasars set out when the Universe was about 200 times denser than it is now and less than one-tenth of its present age. The existence of these objects implies that galaxy formation had already, at that early epoch, proceeded to the stage when massive (>10(8)M[symbol, see text]) objects had accumulated in the centers of at least some young galaxies. A specific model is presented to show that the evolution and luminosity function of quasars are compatible with the cold dark matter cosmogony. Most big galaxies probably passed through a quasar phase; the remnant black holes in nearby galaxies may reveal themselves via the flares that occur whenever a star passes too close to them and gets tidally disrupted. The rich absorption spectra of quasars serve as a probe of the intervening medium. The gas responsible for the Lyman alpha absorption lines may be due to primordial gas gravitationally confined in minihalos of dark matter--shallow potential wells whose evolution and relation to dwarf galaxies are briefly discussed. The patchy heat input into the intergalactic medium from early quasars could modulate the environment in which galaxies form, leading to large-scale spatial correlations in the galaxy distribution. This review concludes with general comments on the prospects for a fully quantitative understanding of galaxy formation.

  19. Relativistic redshifts in quasar broad lines

    SciTech Connect

    Tremaine, Scott; Shen, Yue; Liu, Xin; Loeb, Abraham E-mail: yshen@obs.carnegiescience.edu E-mail: aloeb@cfa.harvard.edu

    2014-10-10

    The broad emission lines commonly seen in quasar spectra have velocity widths of a few percent of the speed of light, so special- and general-relativistic effects have a significant influence on the line profile. We have determined the redshift of the broad Hβ line in the quasar rest frame (determined from the core component of the [O III] line) for over 20,000 quasars from the Sloan Digital Sky Survey Data Release 7 quasar catalog. The mean redshift as a function of line width is approximately consistent with the relativistic redshift that is expected if the line originates in a randomly oriented Keplerian disk that is obscured when the inclination of the disk to the line of sight exceeds ∼30°-45°, consistent with simple active galactic nucleus unification schemes. This result also implies that the net line-of-sight inflow/outflow velocities in the broad-line region are much less than the Keplerian velocity when averaged over a large sample of quasars with a given line width.

  20. Causes and effects of the first quasars.

    PubMed Central

    Rees, M J

    1993-01-01

    The light we observe from the most distant known quasars set out when the Universe was about 200 times denser than it is now and less than one-tenth of its present age. The existence of these objects implies that galaxy formation had already, at that early epoch, proceeded to the stage when massive (>10(8)M[symbol, see text]) objects had accumulated in the centers of at least some young galaxies. A specific model is presented to show that the evolution and luminosity function of quasars are compatible with the cold dark matter cosmogony. Most big galaxies probably passed through a quasar phase; the remnant black holes in nearby galaxies may reveal themselves via the flares that occur whenever a star passes too close to them and gets tidally disrupted. The rich absorption spectra of quasars serve as a probe of the intervening medium. The gas responsible for the Lyman alpha absorption lines may be due to primordial gas gravitationally confined in minihalos of dark matter--shallow potential wells whose evolution and relation to dwarf galaxies are briefly discussed. The patchy heat input into the intergalactic medium from early quasars could modulate the environment in which galaxies form, leading to large-scale spatial correlations in the galaxy distribution. This review concludes with general comments on the prospects for a fully quantitative understanding of galaxy formation. PMID:11607397

  1. Giant scattering cones in obscured quasars

    NASA Astrophysics Data System (ADS)

    Obied, Georges; Zakamska, Nadia L.; Wylezalek, Dominika; Liu, Guilin

    2016-03-01

    We analyse Hubble Space Telescope observations of scattering regions in 20 luminous obscured quasars at 0.24 < z < 0.65 (11 new observations and nine archival ones) observed at rest frame ˜3000 Å. We find spectacular 5-10 kpc-scale scattering regions in almost all cases. The median scattering efficiency at this wavelength (the ratio of observed to estimated intrinsic flux) is 2.3, and 73 per cent of the observed flux at this wavelength is due to scattered light, which if unaccounted for may strongly bias estimates of quasar hosts' star formation rates. Modelling these regions as illuminated dusty cones, we estimate the radial density distributions of the interstellar medium as well as the geometric properties of circumnuclear quasar obscuration - inclinations and covering factors. Small derived opening angles (median half-angle and standard deviation 27° ± 9°) are inconsistent with a 1:1 type 1/type 2 ratio. We suggest that quasar obscuration is patchy and that the observer has an ˜40 per cent chance of seeing a type 1 source even through the obscuration. We estimate median density profile of the scattering medium to be nH = 0.04-0.5 (1 kpc/r)2 cm-3, depending on the method. Quasars in our sample likely exhibit galaxy-wide winds, but if these consist of optically thick clouds then only a small fraction of the wind mass ( ≲ 10 per cent) contributes to scattering.

  2. Galaxy Clustering Around Nearby Luminous Quasars

    NASA Technical Reports Server (NTRS)

    Fisher, Karl B.; Bahcall, John N.; Kirhakos, Sofia; Schneider, Donald P.

    1996-01-01

    We examine the clustering of galaxies around a sample of 20 luminous low redshift (z approx. less than 0.30) quasars observed with the Wide Field Camera-2 on the Hubble Space Telescope (HST). The HST resolution makes possible galaxy identification brighter than V = 24.5 and as close as 1 min or 2 min to the quasar. We find a significant enhancement of galaxies within a projected separation of approx. less than 100 1/h kpc of the quasars. If we model the QSO/galaxy correlation function as a power law with a slope given by the galaxy/galaxy correlation function, we find that the ratio of the QSO/galaxy to galaxy/galaxy correlation functions is 3.8 +/- 0.8. The galaxy counts within r less than 15 1/h kpc of the quasars are too high for the density profile to have an appreciable core radius (approx. greater than 100 1/h kpc). Our results reinforce the idea that low redshift quasars are located preferentially in groups of 10-20 galaxies rather than in rich clusters. We see no significant difference in the clustering amplitudes derived from radio-loud and radio-quiet subsamples.

  3. Causes and effects of the first quasars.

    PubMed

    Rees, M J

    1993-06-01

    The light we observe from the most distant known quasars set out when the Universe was about 200 times denser than it is now and less than one-tenth of its present age. The existence of these objects implies that galaxy formation had already, at that early epoch, proceeded to the stage when massive (>10(8)M[symbol, see text]) objects had accumulated in the centers of at least some young galaxies. A specific model is presented to show that the evolution and luminosity function of quasars are compatible with the cold dark matter cosmogony. Most big galaxies probably passed through a quasar phase; the remnant black holes in nearby galaxies may reveal themselves via the flares that occur whenever a star passes too close to them and gets tidally disrupted. The rich absorption spectra of quasars serve as a probe of the intervening medium. The gas responsible for the Lyman alpha absorption lines may be due to primordial gas gravitationally confined in minihalos of dark matter--shallow potential wells whose evolution and relation to dwarf galaxies are briefly discussed. The patchy heat input into the intergalactic medium from early quasars could modulate the environment in which galaxies form, leading to large-scale spatial correlations in the galaxy distribution. This review concludes with general comments on the prospects for a fully quantitative understanding of galaxy formation. PMID:11607397

  4. Weak hard X-ray emission from broad absorption line quasars: evidence for intrinsic X-ray weakness

    SciTech Connect

    Luo, B.; Brandt, W. N.; Scott, A. E.; Alexander, D. M.; Gandhi, P.; Stern, D.; Teng, S. H.; Arévalo, P.; Bauer, F. E.; Boggs, S. E.; Craig, W. W.; Christensen, F. E.; Comastri, A.; Farrah, D.; Hailey, C. J.; Harrison, F. A.; Koss, M.; Ogle, P.; Puccetti, S.; Saez, C.; and others

    2014-10-10

    We report NuSTAR observations of a sample of six X-ray weak broad absorption line (BAL) quasars. These targets, at z = 0.148-1.223, are among the optically brightest and most luminous BAL quasars known at z < 1.3. However, their rest-frame ≈2 keV luminosities are 14 to >330 times weaker than expected for typical quasars. Our results from a pilot NuSTAR study of two low-redshift BAL quasars, a Chandra stacking analysis of a sample of high-redshift BAL quasars, and a NuSTAR spectral analysis of the local BAL quasar Mrk 231 have already suggested the existence of intrinsically X-ray weak BAL quasars, i.e., quasars not emitting X-rays at the level expected from their optical/UV emission. The aim of the current program is to extend the search for such extraordinary objects. Three of the six new targets are weakly detected by NuSTAR with ≲ 45 counts in the 3-24 keV band, and the other three are not detected. The hard X-ray (8-24 keV) weakness observed by NuSTAR requires Compton-thick absorption if these objects have nominal underlying X-ray emission. However, a soft stacked effective photon index (Γ{sub eff} ≈ 1.8) for this sample disfavors Compton-thick absorption in general. The uniform hard X-ray weakness observed by NuSTAR for this and the pilot samples selected with <10 keV weakness also suggests that the X-ray weakness is intrinsic in at least some of the targets. We conclude that the NuSTAR observations have likely discovered a significant population (≳ 33%) of intrinsically X-ray weak objects among the BAL quasars with significantly weak <10 keV emission. We suggest that intrinsically X-ray weak quasars might be preferentially observed as BAL quasars.

  5. Bayesian Methods and Universal Darwinism

    NASA Astrophysics Data System (ADS)

    Campbell, John

    2009-12-01

    Bayesian methods since the time of Laplace have been understood by their practitioners as closely aligned to the scientific method. Indeed a recent Champion of Bayesian methods, E. T. Jaynes, titled his textbook on the subject Probability Theory: the Logic of Science. Many philosophers of science including Karl Popper and Donald Campbell have interpreted the evolution of Science as a Darwinian process consisting of a `copy with selective retention' algorithm abstracted from Darwin's theory of Natural Selection. Arguments are presented for an isomorphism between Bayesian Methods and Darwinian processes. Universal Darwinism, as the term has been developed by Richard Dawkins, Daniel Dennett and Susan Blackmore, is the collection of scientific theories which explain the creation and evolution of their subject matter as due to the Operation of Darwinian processes. These subject matters span the fields of atomic physics, chemistry, biology and the social sciences. The principle of Maximum Entropy states that Systems will evolve to states of highest entropy subject to the constraints of scientific law. This principle may be inverted to provide illumination as to the nature of scientific law. Our best cosmological theories suggest the universe contained much less complexity during the period shortly after the Big Bang than it does at present. The scientific subject matter of atomic physics, chemistry, biology and the social sciences has been created since that time. An explanation is proposed for the existence of this subject matter as due to the evolution of constraints in the form of adaptations imposed on Maximum Entropy. It is argued these adaptations were discovered and instantiated through the Operations of a succession of Darwinian processes.

  6. Quasar feedback and the origin of radio emission in radio-quiet quasars

    NASA Astrophysics Data System (ADS)

    Zakamska, Nadia L.; Greene, Jenny E.

    2014-07-01

    We analyse Sloan Digital Sky Survey spectra of 568 obscured luminous quasars. The [O III] λ5007 Å emission line shows blueshifts and blue excess, indicating that some of the narrow-line gas is undergoing an organized outflow. The velocity width containing 90 per cent of line power ranges from 370 to 4780 km s-1, suggesting outflow velocities up to ˜2000 km s-1, and is strongly correlated with the radio luminosity among the radio-quiet quasars. We propose that radio emission in radio-quiet quasars is due to relativistic particles accelerated in the shocks within the quasar-driven outflows; star formation in quasar hosts is insufficient to explain the observed radio emission. The median radio luminosity of the sample of νLν[1.4 GHz] = 1040 erg s-1 suggests a median kinetic luminosity of the quasar-driven wind of Lwind = 3 × 1044 erg s-1, or about 4 per cent of the estimated median bolometric luminosity Lbol = 8 × 1045 erg s-1. Furthermore, the velocity width of [O III] is positively correlated with mid-infrared luminosity, which suggests that outflows are ultimately driven by the radiative output of the quasar. Emission lines characteristic of shocks in quasi-neutral medium increase with the velocity of the outflow, which we take as evidence of quasar-driven winds propagating into the interstellar medium of the host galaxy. Quasar feedback appears to operate above the threshold luminosity of Lbol ˜ 3 × 1045 erg s-1.

  7. Evidence for Fluorescent Fe II Emission from Extended Low Ionization Outflows in Obscured Quasars

    NASA Astrophysics Data System (ADS)

    Wang, Tinggui; Ferland, Gary J.; Yang, Chenwei; Wang, Huiyuan; Zhang, Shaohua

    2016-06-01

    Recent studies have shown that outflows in at least some broad absorption line (BAL) quasars are extended well beyond the putative dusty torus. Such outflows should be detectable in obscured quasars. We present four WISE selected infrared red quasars with very strong and peculiar ultraviolet Fe ii emission lines: strong UV Fe ii UV arising from transitions to ground/low excitation levels, and very weak Fe ii at wavelengths longer than 2800 Å. The spectra of these quasars display strong resonant emission lines, such as C iv, Al iii and Mg ii but sometimes, a lack of non-resonant lines such as C iii], S iii and He ii. We interpret the Fe ii lines as resonantly scattered light from the extended outflows that are viewed nearly edge-on, so that the accretion disk and broad line region are obscured by the dusty torus, while the extended outflows are not. We show that dust free gas exposed to strong radiation longward of 912 Å produces Fe ii emission very similar to that observed. The gas is too cool to collisionally excite Fe ii lines, accounting for the lack of optical emission. The spectral energy distribution from the UV to the mid-infrared can be modeled as emission from a clumpy dusty torus, with UV emission being reflected/scattered light either by the dusty torus or the outflow. Within this scenario, we estimate a minimum covering factor of the outflows from a few to 20% for the Fe ii scattering region, suggesting that Fe ii BAL quasars are at a special stage of quasar evolution.

  8. HOST GALAXIES OF LUMINOUS TYPE 2 QUASARS AT z {approx} 0.5

    SciTech Connect

    Liu Xin; Greene, Jenny E.; Strauss, Michael A.; Zakamska, Nadia L.; Krolik, Julian H.; Heckman, Timothy M.

    2009-09-10

    We present deep Gemini GMOS optical spectroscopy of nine luminous quasars at redshifts z {approx} 0.5, drawn from the Sloan Digital Sky Survey type 2 quasar sample. Our targets were selected to have high intrinsic luminosities (M{sub V} < -26 mag) as indicated by the [O III] {lambda}5007 A emission-line luminosity (L[{sub OIII}]). Our sample has a median black hole mass of {approx}10{sup 8.8} M{sub sun} inferred assuming the local M {sub BH}-{sigma}{sub *} relation and a median Eddington ratio of {approx}0.7, using stellar velocity dispersions {sigma}{sub *} measured from the G band. We estimate the contamination of the stellar continuum from scattered quasar light based on the strength of broad H{beta}, and provide an empirical calibration of the contamination as a function of L {sub [OIII]}; the scattered-light fraction is {approx}30% of L{sub 5100} for objects with L {sub [OIII]} = 10{sup 9.5} L{sub sun}. Population synthesis indicates that young poststarburst populations (<0.1 Gyr) are prevalent in luminous type 2 quasars, in addition to a relatively old population (>1 Gyr) which dominates the stellar mass. Broad emission complexes around He II {lambda}4686 A with luminosities up to 10{sup 8.3} L{sub sun} are unambiguously detected in three out of the nine targets, indicative of Wolf-Rayet (WR) populations. Population synthesis shows that {approx}5 Myr poststarburst populations contribute substantially to the luminosities (>50% of L{sub 5100}) of all three objects with WR detections. We find two objects with double cores and four with close companions. Our results may suggest that luminous type 2 quasars trace an early stage of galaxy interaction, perhaps responsible for both the quasar and the starburst activity.

  9. Transesophageal color Doppler evaluation of obstructive lesions using the new "Quasar" technology.

    PubMed

    Fan, P; Nanda, N C; Gatewood, R P; Cape, E G; Yoganathan, A P

    1995-01-01

    Due to the unavoidable problem of aliasing, color flow signals from high blood flow velocities cannot be measured directly by conventional color Doppler. A new technology termed Quantitative Un-Aliased Speed Algorithm Recognition (Quasar) has been developed to overcome this limitation. Employing this technology, we used transesophageal color Doppler echocardiography to investigate whether the velocities detected by the Quasar would correlate with those obtained by continuous-wave Doppler both in vitro and in vivo. In the in vitro study, a 5.0 MHz transesophageal transducer of a Kontron Sigma 44 color Doppler flow system was used. Fourteen different peak velocities calculated and recorded by color Doppler-guided continuous-wave Doppler were randomly selected. In the clinical study, intraoperative transesophageal echocardiography was performed using the same transducer 18 adults (13 aortic valve stenosis, 2 aortic and 2 mitral stenosis, 2 hypertrophic obstructive cardiomyopathy and 1 mitral valve stenosis). Following each continuous-wave Doppler measurement, the Quasar was activated, and a small Quasar marker was placed in the brightest area of the color flow jet to obtain the maximum mean velocity readout. The maximum mean velocities measured by Quasar closely correlated with maximum peak velocities obtained by color flow guided continuous-wave Doppler in both in vitro (0.53 to 1.65 m/s, r = 0.99) and in vivo studies (1.50 to 6.01 m/s, r = 0.97). We conclude that the new Quasar technology can accurately measure high blood flow velocities during transesophageal color Doppler echocardiography. This technique has the potential of obviating the need for continuous-wave Doppler.

  10. The Sloan Digital Sky Survey Quasar Catalog. 4. Fifth Data Release

    SciTech Connect

    Schneider, Donald P.; Hall, Patrick B.; Richards, Gordon T.; Strauss, Michael A.; Vanden Berk, Daniel E.; Anderson, Scott F.; Brandt, W.N.; Fan, Xiao-Hui; Jester, Sebastian; Gray, Jim; Gunn, James E.; /Penn State U., Astron. Astrophys. /York U., Canada /Johns Hopkins U. /Princeton U. Observ. /Washington U., Seattle, Astron. Dept. /Arizona U., Astron. Dept. - Steward Observ. /Southampton U. /Heidelberg, Max Planck Inst. Astron. /Microsoft, BARC /Chicago U. /Adler Planetarium, Chicago

    2007-04-01

    We present the fourth edition of the Sloan Digital Sky Survey (SDSS) Quasar Catalog. The catalog contains 77,429 objects; this is an increase of over 30,000 entries since the previous edition. The catalog consists of the objects in the SDSS Fifth Data Release that have luminosities larger than M{sub i} = -22.0 (in a cosmology with H{sub 0} = 70 km s{sup -1} Mpc{sup -1}, {Omega}{sub M} = 0.3, and {Omega}{sub {Lambda}} = 0.7), have at least one emission line with FWHM larger than 1000 km s{sup -1} or have interesting/complex absorption features, are fainter than i {approx} 15.0, and have highly reliable redshifts. The area covered by the catalog is {approx} 5740 deg{sup 2}. The quasar redshifts range from 0.08 to 5.41, with a median value of 1.48; the catalog includes 891 quasars at redshifts greater than four, of which 36 are at redshifts greater than five. Approximately half of the catalog quasars have i < 19; nearly all have i < 21. For each object the catalog presents positions accurate to better than 0.2-minutes rms per coordinate, five-band (ugriz) CCD-based photometry with typical accuracy of 0.03 mag, and information on the morphology and selection method. The catalog also contains basic radio, near-infrared, and X-ray emission properties of the quasars, when available, from other large-area surveys. The calibrated digital spectra cover the wavelength region 3800-9200 {angstrom} at a spectral resolution of {approx_equal} 2000; the spectra can be retrieved from the public database using the information provided in the catalog. The average SDSS colors of quasars as a function of redshift, derived from the catalog entries, are presented in tabular form. Approximately 96% of the objects in the catalog were discovered by the SDSS.

  11. THE SUDDEN DEATH OF THE NEAREST QUASAR

    SciTech Connect

    Schawinski, Kevin; Virani, Shanil; Megan Urry, C.; Natarajan, Priyamvada; Coppi, Paolo; Evans, Daniel A.; Keel, William C.; Manning, Anna; Lintott, Chris J.; Kaviraj, Sugata; Bamford, Steven P.; Jozsa, Gyula I. G.; Garrett, Michael; Van Arkel, Hanny; Gay, Pamela; Fortson, Lucy

    2010-11-20

    Galaxy formation is significantly modulated by energy output from supermassive black holes at the centers of galaxies which grow in highly efficient luminous quasar phases. The timescale on which black holes transition into and out of such phases is, however, unknown. We present the first measurement of the shutdown timescale for an individual quasar using X-ray observations of the nearby galaxy IC 2497, which hosted a luminous quasar no more than 70,000 years ago that is still seen as a light echo in 'Hanny's Voorwerp', but whose present-day radiative output is lower by at least two, and more likely by over four, orders of magnitude. This extremely rapid shutdown provides new insight into the physics of accretion in supermassive black holes and may signal a transition of the accretion disk to a radiatively inefficient state.

  12. Doppler interpretation of quasar red shifts.

    PubMed

    Zapolsky, H S

    1966-08-01

    The hypothesis that the quasistellar sources (quasars) are local objects moving with velocities close to the speed of light is examined. Provided there is no observational cutoff on apparent bolometric magnitude for the quasars, the transverse Doppler effect leads to the expectation of fewer blue shifts than red shifts for an isotropic distribution of velocities. Such a distribution also yields a function N(z), the number of objects with red shift less than z which is not inconsistent with the present data. On the basis of two extreme assumptions concerning the origin of such rapidly moving sources, we computed curves of red shift plotted against magnitude. In particular, the curve obtained on the assumption that the quasars originated from an explosion in or nearby our own galaxy is in as good agreement with the observations as the curve of cosmological red shift plotted against magnitude.

  13. Detecting the First Quasars with ALMA

    NASA Astrophysics Data System (ADS)

    Schleicher, Dominik R. G.; Spaans, Marco; Klessen, Ralf S.

    2010-05-01

    We show that ALMA is the first telescope that can probe the dust-obscured central region of quasars at z > 5 with a maximum resolution of ~ 30 pc employing the 18 km baseline. We explore the possibility of detecting the first quasars with ALMA (Schleicher, Spaans, & Klessen 2009). For this purpose, we adopt the Seyfert 2 galaxy NGC 1068 as a reference system and calculate the expected fluxes if this galaxy were placed at high redshift. This choice is motivated by the detailed observations available for this system and the absence of any indication for an evolution in metallicity in high-redshift quasars. It is a conservative choice due to the moderate column densities in NGC 1068, leading to moderate fluxes.

  14. Clustering of High Redshift (z>2.9) Quasars from the Sloan Digital Sky Survey

    SciTech Connect

    Shen, Yue; Strauss, Michael A.; Oguri, Masamune; Hennawi, Joseph F.; Fan, Xiaohui; Richards, Gordon T.; Hall, Patrick B.; Schneider, Donald P.; Szalay, Alexander S.; Thakar, Anirudda R.; Berk, Daniel E.Vanden; Anderson, Scott F.; Bahcall, Neta A.; /KIPAC, Menlo Park

    2006-11-30

    We study the two-point correlation function of a uniformly selected sample of 4,428 optically selected luminous quasars with redshift 2.9 {le} z {le} 5.4 selected over 4041 deg{sup 2} from the Fifth Data Release of the Sloan Digital Sky Survey. We fit a power-law to the projected correlation function w{sub p}(r{sub p}) to marginalize over redshift space distortions and redshift errors. For a real-space correlation function of the form {zeta}(r) = (r/r{sub 0}){sup -{gamma}}, the fitted parameters in comoving coordinates are r{sub 0} = 15.2 {+-} 2.7 h{sup -1} Mpc and {gamma} = 2.0 {+-} 0.3, over a scale range 4 {le} r{sub p} {le} 150 h{sup -1} Mpc. Thus high-redshift quasars are appreciably more strongly clustered than their z {approx} 1.5 counterparts, which have a comoving clustering length r{sub 0} {approx} 6.5 h{sup -1} Mpc. Dividing our sample into two redshift bins: 2.9 {le} z {le} 3.5 and z {ge} 3.5, and assuming a power-law index {gamma} = 2.0, we find a correlation length of r{sub 0} = 16.9 {+-} 1.7 h{sup -1} Mpc for the former, and r{sub 0} = 24.3 {+-} 2.4 h{sup -1} Mpc for the latter. Strong clustering at high redshift indicates that quasars are found in very massive, and therefore highly biased, halos. Following Martini & Weinberg, we relate the clustering strength and quasar number density to the quasar lifetimes and duty cycle. Using the Sheth & Tormen halo mass function, the quasar lifetime is estimated to lie in the range 4 {approx} 50 Myr for quasars with 2.9 {le} z {le} 3.5; and 30 {approx} 600 Myr for quasars with z {ge} 3.5. The corresponding duty cycles are 0.004 {approx} 0.05 for the lower redshift bin and 0.03 {approx} 0.6 for the higher redshift bin. The minimum mass of halos in which these quasars reside is 2-3 x 10{sup 12} h{sup -1} M{sub {circle_dot}} for quasars with 2.9 {le} z {le} 3.5 and 4-6 x 10{sup 12} h{sup -1} M{sub {circle_dot}} for quasars with z {ge} 3.5; the effective bias factor b{sub eff} increases with redshift, e.g., b

  15. The Extreme Ultraviolet Variability of Quasars

    NASA Astrophysics Data System (ADS)

    Punsly, Brian; Marziani, Paola; Zhang, Shaohua; Muzahid, Sowgat; O’Dea, Christopher P.

    2016-10-01

    We study the extreme ultraviolet (EUV) variability (rest frame wavelengths 500–920 Å) of high-luminosity quasars using Hubble Space Telescope (HST) (low to intermediate redshift sample) and Sloan Digital sky Survey (SDSS) (high redshift sample) archives. The combined HST and SDSS data indicates a much more pronounced variability when the sampling time between observations in the quasar rest frame is \\gt 2× {10}7 {{s}} compared to \\lt 1.5× {10}7 s. Based on an excess variance analysis, for time intervals \\lt 2× {10}7 {{s}} in the quasar rest frame, 10% of the quasars (4/40) show evidence of EUV variability. Similarly, for time intervals \\gt 2× {10}7 {{s}} in the quasar rest frame, 55% of the quasars (21/38) show evidence of EUV variability. The propensity for variability does not show any statistically significant change between 2.5× {10}7 {{s}} and 3.16× {10}7 {{s}} (1 year). The temporal behavior is one of a threshold time interval for significant variability as opposed to a gradual increase on these timescales. A threshold timescale can indicate a characteristic spatial dimension of the EUV region. We explore this concept in the context of the slim disk models of accretion. We find that for rapidly spinning black holes, the radial infall time to the plunge region of the optically thin surface layer of the slim disk that is responsible for the preponderance of the EUV flux emission (primarily within 0–7 black hole radii from the inner edge of the disk) is consistent with the empirically determined variability timescale.

  16. Understanding the near infrared spectrum of quasars

    NASA Astrophysics Data System (ADS)

    Hernán-Caballero, Antonio; Hatziminaoglou, Evanthia; Alonso-Herrero, Almudena; Mateos, Silvia

    2016-08-01

    The rest-frame near infrared (NIR) is a key spectral range for understanding the physics of AGN, but progress has been hindered by the difficulty in defining the NIR spectrum of the accretion disk and removing contamination from stellar emission in the host galaxy. In this talk I will present the analysis of a sample of 85 luminous (L3µm>10^45.5 erg/s) quasars with rest-frame NIR spectroscopy from AKARI and Spitzer/IRS. Their high luminosity allows a direct determination of the NIR shape of the quasar spectrum clean from host galaxy emission. We find that the entire UV-to-MIR SED can be accurately reproduced with a semi-empirical disk+dust model that uses a single template for the accretion disk and two blackbody components (hot and warm) for the dust. The observed diversity in individual SEDs can be accounted for by varying levels of extinction affecting the disk component and differences in the relative luminosities of the disk and dust components. We present a new quasar template [0.1-10µm] as well as separate templates for the disk and dust components, and conclude that previous templates based on less luminous quasars suffer from contamination by stellar emission in the host galaxy, which accounts for up to ~30% of the flux at 1µm. We also perform the first ever measurement of the Paschen_α emission in a large sample of luminous quasars and find that the Paschen_α to optical continuum luminosity ratio is boosted in our sample compared to less luminous quasars.

  17. SPITZER OBSERVATIONS OF YOUNG RED QUASARS

    SciTech Connect

    Urrutia, Tanya; Lacy, Mark; Spoon, Henrik; Glikman, Eilat; Petric, Andreea; Schulz, Bernhard E-mail: mlacy@nrao.edu E-mail: eilat.glikman@yale.edu E-mail: bschulz@ipac.caltech.edu

    2012-10-01

    We present mid-infrared spectra and photometry of 13 redshift 0.4 < z < 1 dust reddened quasars obtained with Spitzer IRS and MIPS. We compare properties derived from their infrared spectral energy distributions (intrinsic active galactic nucleus (AGN) luminosity and far-infrared luminosity from star formation) to the host luminosities and morphologies from Hubble Space Telescope imaging, and black hole masses estimated from optical and/or near-infrared spectroscopy. Our results are broadly consistent with models in which most dust reddened quasars are an intermediate phase between a merger-driven starburst triggering a completely obscured AGN, and a normal, unreddened quasar. We find that many of our objects have high accretion rates, close to the Eddington limit. These objects tend to fall below the black hole mass-bulge luminosity relation as defined by local galaxies, whereas most of our low accretion rate objects are slightly above the local relation, as typical for normal quasars at these redshifts. Our observations are therefore most readily interpreted in a scenario in which galaxy stellar mass growth occurs first by about a factor of three in each merger/starburst event, followed sometime later by black hole growth by a similar amount. We do not, however, see any direct evidence for quasar feedback affecting star formation in our objects, for example, in the form of a relationship between accretion rate and star formation. Five of our objects, however, do show evidence for outflows in the [O III]5007 A emission line profile, suggesting that the quasar activity is driving thermal winds in at least some members of our sample.

  18. Jansky VLA Imaging of Heavily Obscured, Luminous Quasars at Redshifts ~2

    NASA Astrophysics Data System (ADS)

    Trapp, Adam; Lonsdale, Carol J.; Patil, Palavi; Whittle, Mark; Lacy, Mark; Lonsdale, Colin J.

    2016-01-01

    We present JVLA A and B array observations in X-band (8-12 GHz) of a sample of radio powerful, bolometrically luminous, but optically obscured quasars. The quasars were selected using a cross-match between WISE mid-IR sources brighter than 7 mJ at 22 mu and NVSS and/or FIRST radio surveys, with a further constraint that the sources were optically faint. The survey aims to select young quasars with young radio sources at redshifts z ~ 1-3. Ultimately, we wish to study the role that radio jets play in quasar driven feedback. Our VLA observations provide fundamental information on radio source size, structure, power and spectral index, all of which shed light on the properties of the young radio source. We will present images and data on 155 objects from our primary sample WISE-NVSS sample of 156.The majority of sources are found to be compact, steep-spectrum, and sub-galactic in scale, with a significant minority of resolved doubles, triples, and core-jets. Using radio data at other wavelengths taken from the literature, we use SED fits to identify or constrain the turn-over frequencies. Combining size and turn-over frequency, the majority of the sources are found to be CSS, GPS or HFPs, consistent with young radio source ages.

  19. Blue outliers among intermediate redshift quasars

    NASA Astrophysics Data System (ADS)

    Marziani, P.; Sulentic, J. W.; Stirpe, G. M.; Dultzin, D.; Del Olmo, A.; Martínez-Carballo, M. A.

    2016-01-01

    [OIII]λ 5007 "blue outliers"—that are suggestive of outflows in the narrow line region of quasars—appear to be much more common at intermediate z (high luminosity) than at low z. About 40~% of quasars in a Hamburg ESO intermediate z sample of 52 sources qualify as "blue outliers" (i.e., quasars with [OIII]λλ 4959,5007 lines showing large systematic blueshifts with respect to rest frame). We discuss major findings on what has become an intriguing field in active galactic nuclei research and stress the relevance of "blue outliers" to feedback and host galaxy evolution.

  20. Einstein observations of active galaxies and quasars

    NASA Technical Reports Server (NTRS)

    Schreier, E. J.

    1979-01-01

    The radio galaxies Centaurus A and Signus B are discussed. In both these sources, a comparison of the radio and imaged X-ray flux is allowed for the measurement of the magnetic fields. Einstein observations of quasars are discussed. The number of known X-ray emitting QSO's was increased from 3 to 22 and the distances where these QSO's were seen to correspond to an age of 15 billion years. It was shown that these quasars contributed significantly to the X-ray background.

  1. The black hole spins of quasars

    NASA Astrophysics Data System (ADS)

    You, Bei; Cao, Xinwu

    2016-02-01

    We present the estimates of the black hole spins of five quasars. The peaks of the spectra of the accretion discs surrounding massive black holes in quasars are in the far-UV or soft X-ray band, which are usually not observed. However, in the disc corona model, the soft photons from the disc are Comptonized to high energy in the hot corona, and the hard X-ray spectra (luminosity and spectral shape) contain the information of the incident spectra from the disc. The values of black hole spin parameter a are inferred from the spectral fitting, which spread over a large range, ~ -0.94 to 0.998.

  2. The Sloan Digital Sky Survey Quasar Catalog V. Seventh Data Release

    SciTech Connect

    Schneider, Donald P.; Richards, Gordon T.; Hall, Patrick B.; Strauss, Michael A.; Anderson, Scott F.; Boroson, Todd A.; Ross, Nicholas P.; Shen, Yue; Brandt, W.N.; Fan, Xiaohui; Inada, Naohisa; /Wako, RIKEN /Southampton U. /Heidelberg, Max Planck Inst. Astron.

    2010-04-01

    We present the fifth edition of the Sloan Digital Sky Survey (SDSS) Quasar Catalog, which is based upon the SDSS Seventh Data Release. The catalog, which contains 105,783 spectroscopically confirmed quasars, represents the conclusion of the SDSS-I and SDSS-II quasar survey. The catalog consists of the SDSS objects that have luminosities larger than M{sub i} = -22.0 (in a cosmology with H{sub 0} = 70 km s{sup -1} Mpc{sup -1}, {Omega}{sub M} = 0.3, and {Omega}{sub {Lambda}} = 0.7), have at least one emission line with FWHM larger than 1000 km s{sup -1} or have interesting/complex absorption features, are fainter than i {approx} 15.0, and have highly reliable redshifts. The catalog covers an area of {approx} 9380 deg{sup 2}. The quasar redshifts range from 0.065 to 5.46, with a median value of 1.49; the catalog includes 1248 quasars at redshifts greater than 4, of which 56 are at redshifts greater than 5. The catalog contains 9210 quasars with i < 18; slightly over half of the entries have i < 19. For each object the catalog presents positions accurate to better than 0.1-inch rms per coordinate, five-band (ugriz) CCD-based photometry with typical accuracy of 0.03 mag, and information on the morphology and selection method. The catalog also contains radio, near-infrared, and X-ray emission properties of the quasars, when available, from other large-area surveys. The calibrated digital spectra cover the wavelength region 3800-9200 {angstrom} at a spectral resolution of {approx_equal} 2000; the spectra can be retrieved from the SDSS public database using the information provided in the catalog. Over 96% of the objects in the catalog were discovered by the SDSS. We also include a supplemental list of an additional 207 quasars with SDSS spectra whose archive photometric information is incomplete.

  3. Dust-free quasars in the early Universe.

    PubMed

    Jiang, Linhua; Fan, Xiaohui; Brandt, W N; Carilli, Chris L; Egami, Eiichi; Hines, Dean C; Kurk, Jaron D; Richards, Gordon T; Shen, Yue; Strauss, Michael A; Vestergaard, Marianne; Walter, Fabian

    2010-03-18

    The most distant quasars known, at redshifts z approximately 6, generally have properties indistinguishable from those of lower-redshift quasars in the rest-frame ultraviolet/optical and X-ray bands. This puzzling result suggests that these distant quasars are evolved objects even though the Universe was only seven per cent of its current age at these redshifts. Recently one z approximately 6 quasar was shown not to have any detectable emission from hot dust, but it was unclear whether that indicated different hot-dust properties at high redshift or if it is simply an outlier. Here we report the discovery of a second quasar without hot-dust emission in a sample of 21 z approximately 6 quasars. Such apparently hot-dust-free quasars have no counterparts at low redshift. Moreover, we demonstrate that the hot-dust abundance in the 21 quasars builds up in tandem with the growth of the central black hole, whereas at low redshift it is almost independent of the black hole mass. Thus z approximately 6 quasars are indeed at an early evolutionary stage, with rapid mass accretion and dust formation. The two hot-dust-free quasars are likely to be first-generation quasars born in dust-free environments and are too young to have formed a detectable amount of hot dust around them.

  4. Ultraviolet variability of quasars: dependence on the accretion rate

    NASA Astrophysics Data System (ADS)

    Meusinger, H.; Weiss, V.

    2013-12-01

    Aims: Although the variability in the ultraviolet and optical domain is one of the major characteristics of quasars, the dominant underlying mechanisms are still poorly understood. There is a broad consensus on the relationship between the strength of the variability and such quantities as time-lag, wavelength, luminosity, and redshift. However, evidence on a dependence on the fundamental parameters of the accretion process is still inconclusive. This paper is focused on the correlation between the ultraviolet quasar long-term variability and the accretion rate. Methods: We compiled a catalogue of about 4000 quasars including individual estimators for the variability strength derived from the multi-epoch photometry in the SDSS Stripe 82, virial black hole masses M derived from the Mg ii line, and mass accretion rates Ṁ from the Davis-Laor scaling relation. Several statistical tests were applied to evaluate the correlations of the variability with luminosity, mass, Eddington ratio, and accretion rate. Results: We confirm the existence of significant anti-correlations between the variability estimator V and the accretion rate Ṁ, the Eddington ratio ɛ, and the bolometric luminosity Lbol, respectively. The Eddington ratio is tightly correlated with Ṁ. A weak, statistically not significant positive trend is indicated for the dependence of V on M. As a side product, we find a strong correlation of the radiative efficiency η with M in our sample. We show via numerical simulations that this trend is most likely produced by selection effects in combination with the mass errors and the use of the scaling relation for Ṁ. The anti-correlations of V with Ṁ, ɛ, and Lbol cannot be explained in such a way. The strongest anti-correlation is found between V and Ṁ. However, it is difficult to decide which of the quantities L,ɛ, and Ṁ is intrinsically correlated with V and which of the observed correlations of V are produced by the L - ɛ - Ṁ relation. A V -

  5. Using quasars as standard clocks for measuring cosmological redshift.

    PubMed

    Dai, De-Chang; Starkman, Glenn D; Stojkovic, Branislav; Stojkovic, Dejan; Weltman, Amanda

    2012-06-01

    We report hitherto unnoticed patterns in quasar light curves. We characterize segments of the quasar's light curves with the slopes of the straight lines fit through them. These slopes appear to be directly related to the quasars' redshifts. Alternatively, using only global shifts in time and flux, we are able to find significant overlaps between the light curves of different pairs of quasars by fitting the ratio of their redshifts. We are then able to reliably determine the redshift of one quasar from another. This implies that one can use quasars as standard clocks, as we explicitly demonstrate by constructing two independent methods of finding the redshift of a quasar from its light curve.

  6. Bayesian methods in reliability

    NASA Astrophysics Data System (ADS)

    Sander, P.; Badoux, R.

    1991-11-01

    The present proceedings from a course on Bayesian methods in reliability encompasses Bayesian statistical methods and their computational implementation, models for analyzing censored data from nonrepairable systems, the traits of repairable systems and growth models, the use of expert judgment, and a review of the problem of forecasting software reliability. Specific issues addressed include the use of Bayesian methods to estimate the leak rate of a gas pipeline, approximate analyses under great prior uncertainty, reliability estimation techniques, and a nonhomogeneous Poisson process. Also addressed are the calibration sets and seed variables of expert judgment systems for risk assessment, experimental illustrations of the use of expert judgment for reliability testing, and analyses of the predictive quality of software-reliability growth models such as the Weibull order statistics.

  7. BIE: Bayesian Inference Engine

    NASA Astrophysics Data System (ADS)

    Weinberg, Martin D.

    2013-12-01

    The Bayesian Inference Engine (BIE) is an object-oriented library of tools written in C++ designed explicitly to enable Bayesian update and model comparison for astronomical problems. To facilitate "what if" exploration, BIE provides a command line interface (written with Bison and Flex) to run input scripts. The output of the code is a simulation of the Bayesian posterior distribution from which summary statistics e.g. by taking moments, or determine confidence intervals and so forth, can be determined. All of these quantities are fundamentally integrals and the Markov Chain approach produces variates heta distributed according to P( heta|D) so moments are trivially obtained by summing of the ensemble of variates.

  8. Bayesian least squares deconvolution

    NASA Astrophysics Data System (ADS)

    Asensio Ramos, A.; Petit, P.

    2015-11-01

    Aims: We develop a fully Bayesian least squares deconvolution (LSD) that can be applied to the reliable detection of magnetic signals in noise-limited stellar spectropolarimetric observations using multiline techniques. Methods: We consider LSD under the Bayesian framework and we introduce a flexible Gaussian process (GP) prior for the LSD profile. This prior allows the result to automatically adapt to the presence of signal. We exploit several linear algebra identities to accelerate the calculations. The final algorithm can deal with thousands of spectral lines in a few seconds. Results: We demonstrate the reliability of the method with synthetic experiments and we apply it to real spectropolarimetric observations of magnetic stars. We are able to recover the magnetic signals using a small number of spectral lines, together with the uncertainty at each velocity bin. This allows the user to consider if the detected signal is reliable. The code to compute the Bayesian LSD profile is freely available.

  9. Close companions to two high-redshift quasars

    SciTech Connect

    McGreer, Ian D.; Fan, Xiaohui; Bian, Fuyan; Strauss, Michael A.; Haiman, Zoltàn; Richards, Gordon T.; Jiang, Linhua; Schneider, Donald P.

    2014-10-01

    We report the serendipitous discoveries of companion galaxies to two high-redshift quasars. SDSS J025617.7+001904 is a z = 4.79 quasar included in our recent survey of faint quasars in the SDSS Stripe 82 region. The initial MMT slit spectroscopy shows excess Lyα emission extending well beyond the quasar's light profile. Further imaging and spectroscopy with LBT/MODS1 confirms the presence of a bright galaxy (i {sub AB} = 23.6) located 2'' (12 kpc projected) from the quasar with strong Lyα emission (EW{sub 0} ≈ 100 Å) at the redshift of the quasar, as well as faint continuum. The second quasar, CFHQS J005006.6+344522 (z = 6.25), is included in our recent HST SNAP survey of z ∼ 6 quasars searching for evidence of gravitational lensing. Deep imaging with ACS and WFC3 confirms an optical dropout ∼4.5 mag fainter than the quasar (Y {sub AB} = 25) at a separation of 0.''9. The red i {sub 775} – Y {sub 105} color of the galaxy and its proximity to the quasar (5 kpc projected if at the quasar redshift) strongly favor an association with the quasar. Although it is much fainter than the quasar, it is remarkably bright when compared to field galaxies at this redshift, while showing no evidence for lensing. Both systems may represent late-stage mergers of two massive galaxies, with the observed light for one dominated by powerful ongoing star formation and for the other by rapid black hole growth. Observations of close companions are rare; if major mergers are primarily responsible for high-redshift quasar fueling then the phase when progenitor galaxies can be observed as bright companions is relatively short.

  10. Bayesian Exploratory Factor Analysis

    PubMed Central

    Conti, Gabriella; Frühwirth-Schnatter, Sylvia; Heckman, James J.; Piatek, Rémi

    2014-01-01

    This paper develops and applies a Bayesian approach to Exploratory Factor Analysis that improves on ad hoc classical approaches. Our framework relies on dedicated factor models and simultaneously determines the number of factors, the allocation of each measurement to a unique factor, and the corresponding factor loadings. Classical identification criteria are applied and integrated into our Bayesian procedure to generate models that are stable and clearly interpretable. A Monte Carlo study confirms the validity of the approach. The method is used to produce interpretable low dimensional aggregates from a high dimensional set of psychological measurements. PMID:25431517

  11. The Einstein observatory medium sensitivity survey - The quasars sample

    NASA Technical Reports Server (NTRS)

    Gioia, I. M.; Maccacaro, T.

    1983-01-01

    A complete sample of X-ray-selected quasars and Seyfert galaxies extracted from the Einstein Observatory Medium Sensitivity Survey is described, and their physical characteristics are discussed. A Hubble constant of 50 km/s per Mpc and a Friedmann universe with a deceleration parameter of q(0)=0 are assumed throughout the survey, and the sample of X-ray sources was selected according to the following criteria: the significance of the detection exceeds a confidence level of 5 beta; the source is physically unrelated to the target of the IPC observation; and that the source is at a galactic latitude higher than 20 deg. The redshift and optical luminosity distributions of 55 Active Galactic Nuclei (AGNs) detected in the survey are discussed. A number flux relation for the different classes of extragalactic objects are analyzed in detail, using a Maximum Likelihood method and the assumption that the relation can be represented as a power law.

  12. Measuring Distances to Remote Galaxies and Quasars.

    ERIC Educational Resources Information Center

    McCarthy, Patrick J.

    1988-01-01

    Describes the use of spectroscopy and the redshift to measure how far an object is by measuring how fast it is receding from earth. Lists the most distant quasars yet found. Tables include "Redshift vs. Distance" and "Distances to Celestial Objects for Various Cosmologies." (CW)

  13. COLD FLOWS AND THE FIRST QUASARS

    SciTech Connect

    Di Matteo, T.; Khandai, N.; DeGraf, C.; Feng, Y.; Croft, R. A. C.; Lopez, J.; Springel, V.

    2012-02-15

    Observations of the most distant bright quasars imply that billion solar mass supermassive black holes (SMBHs) have to be assembled within the first 800 million years. Under our standard galaxy formation scenario such fast growth implies large gas densities providing sustained accretion at critical or supercritical rates onto an initial black hole seed. It has been a long standing question whether and how such high black hole accretion rates can be achieved and sustained at the centers of early galaxies. Here we use our new MassiveBlack cosmological hydrodynamic simulation covering a volume (0.75 Gpc){sup 3} appropriate for studying the rare first quasars to show that steady high density cold gas flows responsible for assembling the first galaxies produce the high gas densities that lead to sustained critical accretion rates and hence rapid growth commensurate with the existence of {approx}10{sup 9} M{sub Sun} black holes as early as z {approx} 7. We find that under these conditions quasar feedback is not effective at stopping the cold gas from penetrating the central regions and hence cannot quench the accretion until the host galaxy reaches M{sub halo} > or approx. 10{sup 1}2{sup M}{sub Sun }. This cold-flow-driven scenario for the formation of quasars implies that they should be ubiquitous in galaxies in the early universe and that major (proto)galaxy mergers are not a requirement for efficient fuel supply and growth, particularly for the earliest SMBHs.

  14. Quasar H II Regions During Cosmic Reionization

    SciTech Connect

    Alvarez, Marcelo A.; Abel, Tom; /KIPAC, Menlo Park

    2007-03-30

    Cosmic reionization progresses as HII regions form around sources of ionizing radiation. Their average size grows continuously until they percolate and complete reionization. We demonstrate how this typical growth can be calculated around the largest, biased sources of UV emission such as quasars by further developing an analytical model based on the excursion set formalism. This approach allows us to calculate the sizes and growth of the HII regions created by the progenitors of any dark matter halo of given mass and redshift with a minimum of free parameters. Statistical variations in the size of these pre-existing HII regions are an additional source of uncertainty in the determination of very high redshift quasar properties from their observed HII region sizes. We use this model to demonstrate that the transmission gaps seen in very high redshift quasars can be understood from the radiation of only their progenitors and associated clustered small galaxies. The fit requires the epoch of overlap to be at z = 5.8 {+-} 0.1. This interpretation makes the transmission gaps independent of the age of the quasars observed. If this interpretation were correct it would raise the prospects of using radio interferometers currently under construction to detect the epoch of reionization.

  15. Quasar Astrophysics with the Space Interferometry Mission

    NASA Technical Reports Server (NTRS)

    Unwin, Stephen; Wehrle, Ann; Meier, David; Jones, Dayton; Piner, Glenn

    2007-01-01

    Optical astrometry of quasars and active galaxies can provide key information on the spatial distribution and variability of emission in compact nuclei. The Space Interferometry Mission (SIM PlanetQuest) will have the sensitivity to measure a significant number of quasar positions at the microarcsecond level. SIM will be very sensitive to astrometric shifts for objects as faint as V = 19. A variety of AGN phenomena are expected to be visible to SIM on these scales, including time and spectral dependence in position offsets between accretion disk and jet emission. These represent unique data on the spatial distribution and time dependence of quasar emission. It will also probe the use of quasar nuclei as fundamental astrometric references. Comparisons between the time-dependent optical photocenter position and VLBI radio images will provide further insight into the jet emission mechanism. Observations will be tailored to each specific target and science question. SIM will be able to distinguish spatially between jet and accretion disk emission; and it can observe the cores of galaxies potentially harboring binary supermassive black holes resulting from mergers.

  16. A SPECTACULAR OUTFLOW IN AN OBSCURED QUASAR

    SciTech Connect

    Greene, Jenny E.; Zakamska, Nadia L.; Smith, Paul S.

    2012-02-10

    SDSS J1356+1026 is a pair of interacting galaxies at redshift z = 0.123 that hosts a luminous obscured quasar in its northern nucleus. Here we present two long-slit Magellan LDSS-3 spectra that reveal a pair of symmetric {approx}10 kpc size outflows emerging from this nucleus, with observed expansion velocities of {approx}250 km s{sup -1} in projection. We present a kinematic model of these outflows and argue that the deprojected physical velocities of expansion are likely {approx}1000 km s{sup -1} and that the kinetic energy of the expanding shells is likely 10{sup 44-45} erg s{sup -1}, with an absolute minimum of >10{sup 42} erg s{sup -1}. Although a radio counterpart is detected at 1.4 GHz, it is faint enough that the quasar is considered to be radio quiet by all standard criteria, and there is no evidence of extended emission due to radio lobes, whether aged or continuously powered by an ongoing jet. We argue that the likely level of star formation is insufficient to power the observed energetic outflow and that SDSS J1356+1026 is a good case for radio-quiet quasar feedback. In further support of this hypothesis, polarimetric observations show that the direction of quasar illumination is coincident with the direction of the outflow.

  17. Quasar feedback revealed by giant molecular outflows

    NASA Astrophysics Data System (ADS)

    Feruglio, C.; Maiolino, R.; Piconcelli, E.; Menci, N.; Aussel, H.; Lamastra, A.; Fiore, F.

    2010-07-01

    In the standard scenario for galaxy evolution young star-forming galaxies transform into red bulge-dominated spheroids, where star formation has been quenched. To explain this transformation, a strong negative feedback generated by accretion onto a central super-massive black hole is often invoked. The depletion of gas resulting from quasar-driven outflows should eventually stop star-formation across the host galaxy and lead the black hole to “suicide” by starvation. Direct observational evidence for a major quasar feedback onto the host galaxy is still missing, because outflows previously observed in quasars are generally associated with the ionized component of the gas, which only accounts for a minor fraction of the total gas content, and typically occurrs in the central regions. We used the IRAM PdB Interferometer to observe the CO(1-0) transition in Mrk 231, the closest quasar known. Thanks to the wide band we detected broad wings of the CO line, with velocities of up to 750 km s-1 and spatially resolved on the kpc scale. These broad CO wings trace a giant molecular outflow of about 700 M_⊙/year, far larger than the ongoing star-formation rate (~200 M_⊙/year) observed in the host galaxy. This wind will totally expel the cold gas reservoir in Mrk 231 in about 107 yrs, therefore halting the star-formation activity on the same timescale. The inferred kinetic energy in the molecular outflow is ~1.2 × 1044 erg/s, corresponding to a few percent of the AGN bolometric luminosity, which is very close to the fraction expected by models ascribing quasar feedback to highly supersonic shocks generated by radiatively accelerated nuclear winds. Instead, the contribution by the SNe associated with the starburst fall short by several orders of magnitude to account for the kinetic energy observed in the outflow. The direct observational evidence for quasar feedback reported here provides solid support to the scenarios ascribing the observed properties of local massive

  18. Quasars and H II regions during reionization

    NASA Astrophysics Data System (ADS)

    Kramer, Roban Hultman

    The reionization history of the intergalactic medium (IGM) at high redshift (z ≳ 6) is just beginning to be probed by observational astronomy. In this dissertation, I discuss three projects related to the epoch of reionization. The first project explores how the evolution of the IGM neutral fraction was likely shaped by feedback processes. Because the earliest ionizing sources formed at the locations of the rare density peaks, their spatial distribution was strongly clustered. By building a semi-analytical model which includes feedback and clustering simultaneously and applying this model to the suppression of star formation in minihalos due to photoionization, I demonstrate that this clustering significantly boosts the impact of feedback processes operating at high redshift. The second project exploits the fact that high-redshift quasars drive ionization fronts (I-fronts) into the IGM, with the thickness of the front generally increasing with the hardness of the ionizing spectrum. If the thickness of the front can be measured, it can provide a novel constraint on the ionizing spectral energy distribution (SED). I simulate the propagation of an I-front into a uniform IGM, and compute its thickness for a range of possible quasar spectra and ages, and IGM neutral hydrogen densities and clumping factors. With a sufficiently high intrinsic hydrogen column density obscuring the source or a sufficiently hard power-law spectrum and some obscuration, the thickness of the front exceeds ˜ 1 physical Mpc and may be measurable from the three-dimensional morphology of its redshifted 21cm signal. In the third project, I investigate one promising method for probing the tail end of reionization, through the detection and characterization of the Gunn-Peterson damping wing absorption of the IGM in bright quasar spectra. However, the use of quasar spectra to measure the IGM damping wing requires a model of the quasar's intrinsic Lyman-alpha emission line. I quantify uncertainties

  19. Discovery of two gravitationally lensed quasars in the Dark Energy Survey

    SciTech Connect

    Agnello, A.

    2015-10-01

    In this study, we present spectroscopic confirmation of two new lensed quasars via data obtained at the 6.5m Magellan/Baade Telescope. The lens candidates have been selected from the Dark Energy Survey (DES) and WISE based on their multi-band photometry and extended morphology in DES images. Images of DES J0115-5244 show two blue point sources at either side of a red galaxy. Our long-slit data confirm that both point sources are images of the same quasar at zs = 1.64. The Einstein Radius estimated from the DES images is 0.51''. DES J2146-0047 is in the area of overlap between DES and the Sloan Digital Sky Survey (SDSS). Two blue components are visible in the DES and SDSS images. The SDSS fiber spectrum shows a quasar component at zs = 2.38 and absorption compatible with Mg II and Fe II at zl = 0.799, which we tentatively associate with the foreground lens galaxy. The long-slit Magellan spectra show that the blue components are resolved images of the same quasar. Furthermore, the Einstein Radius is 0.68'' corresponding to an enclosed mass of 1.6 × 1011 M. Three other candidates were observed and rejected, two being low-redshift pairs of starburst galaxies, and one being a quasar behind a blue star. These first confirmation results provide an important empirical validation of the data-mining and model-based selection that is being applied to the entire DES dataset.

  20. Discovery of two gravitationally lensed quasars in the Dark Energy Survey

    DOE PAGES

    Agnello, A.

    2015-10-01

    In this study, we present spectroscopic confirmation of two new lensed quasars via data obtained at the 6.5m Magellan/Baade Telescope. The lens candidates have been selected from the Dark Energy Survey (DES) and WISE based on their multi-band photometry and extended morphology in DES images. Images of DES J0115-5244 show two blue point sources at either side of a red galaxy. Our long-slit data confirm that both point sources are images of the same quasar at zs = 1.64. The Einstein Radius estimated from the DES images is 0.51''. DES J2146-0047 is in the area of overlap between DES andmore » the Sloan Digital Sky Survey (SDSS). Two blue components are visible in the DES and SDSS images. The SDSS fiber spectrum shows a quasar component at zs = 2.38 and absorption compatible with Mg II and Fe II at zl = 0.799, which we tentatively associate with the foreground lens galaxy. The long-slit Magellan spectra show that the blue components are resolved images of the same quasar. Furthermore, the Einstein Radius is 0.68'' corresponding to an enclosed mass of 1.6 × 1011 M⊙. Three other candidates were observed and rejected, two being low-redshift pairs of starburst galaxies, and one being a quasar behind a blue star. These first confirmation results provide an important empirical validation of the data-mining and model-based selection that is being applied to the entire DES dataset.« less

  1. Bayesian Evidence Framework for Decision Tree Learning

    NASA Astrophysics Data System (ADS)

    Chatpatanasiri, Ratthachat; Kijsirikul, Boonserm

    2005-11-01

    This work is primary interested in the problem of, given the observed data, selecting a single decision (or classification) tree. Although a single decision tree has a high risk to be overfitted, the induced tree is easily interpreted. Researchers have invented various methods such as tree pruning or tree averaging for preventing the induced tree from overfitting (and from underfitting) the data. In this paper, instead of using those conventional approaches, we apply the Bayesian evidence framework of Gull, Skilling and Mackay to a process of selecting a decision tree. We derive a formal function to measure `the fitness' for each decision tree given a set of observed data. Our method, in fact, is analogous to a well-known Bayesian model selection method for interpolating noisy continuous-value data. As in regression problems, given reasonable assumptions, this derived score function automatically quantifies the principle of Ockham's razor, and hence reasonably deals with the issue of underfitting-overfitting tradeoff.

  2. Particle identification in ALICE: a Bayesian approach

    NASA Astrophysics Data System (ADS)

    Adam, J.; Adamová, D.; Aggarwal, M. M.; Aglieri Rinella, G.; Agnello, M.; Agrawal, N.; Ahammed, Z.; Ahmad, S.; Ahn, S. U.; Aiola, S.; Akindinov, A.; Alam, S. N.; Albuquerque, D. S. D.; Aleksandrov, D.; Alessandro, B.; Alexandre, D.; Alfaro Molina, R.; Alici, A.; Alkin, A.; Almaraz, J. R. M.; Alme, J.; Alt, T.; Altinpinar, S.; Altsybeev, I.; Alves Garcia Prado, C.; Andrei, C.; Andronic, A.; Anguelov, V.; Antičić, T.; Antinori, F.; Antonioli, P.; Aphecetche, L.; Appelshäuser, H.; Arcelli, S.; Arnaldi, R.; Arnold, O. W.; Arsene, I. C.; Arslandok, M.; Audurier, B.; Augustinus, A.; Averbeck, R.; Azmi, M. D.; Badalà, A.; Baek, Y. W.; Bagnasco, S.; Bailhache, R.; Bala, R.; Balasubramanian, S.; Baldisseri, A.; Baral, R. C.; Barbano, A. M.; Barbera, R.; Barile, F.; Barnaföldi, G. G.; Barnby, L. S.; Barret, V.; Bartalini, P.; Barth, K.; Bartke, J.; Bartsch, E.; Basile, M.; Bastid, N.; Basu, S.; Bathen, B.; Batigne, G.; Batista Camejo, A.; Batyunya, B.; Batzing, P. C.; Bearden, I. G.; Beck, H.; Bedda, C.; Behera, N. K.; Belikov, I.; Bellini, F.; Bello Martinez, H.; Bellwied, R.; Belmont, R.; Belmont-Moreno, E.; Belyaev, V.; Benacek, P.; Bencedi, G.; Beole, S.; Berceanu, I.; Bercuci, A.; Berdnikov, Y.; Berenyi, D.; Bertens, R. A.; Berzano, D.; Betev, L.; Bhasin, A.; Bhat, I. R.; Bhati, A. K.; Bhattacharjee, B.; Bhom, J.; Bianchi, L.; Bianchi, N.; Bianchin, C.; Bielčík, J.; Bielčíková, J.; Bilandzic, A.; Biro, G.; Biswas, R.; Biswas, S.; Bjelogrlic, S.; Blair, J. T.; Blau, D.; Blume, C.; Bock, F.; Bogdanov, A.; Bøggild, H.; Boldizsár, L.; Bombara, M.; Book, J.; Borel, H.; Borissov, A.; Borri, M.; Bossú, F.; Botta, E.; Bourjau, C.; Braun-Munzinger, P.; Bregant, M.; Breitner, T.; Broker, T. A.; Browning, T. A.; Broz, M.; Brucken, E. J.; Bruna, E.; Bruno, G. E.; Budnikov, D.; Buesching, H.; Bufalino, S.; Buncic, P.; Busch, O.; Buthelezi, Z.; Butt, J. B.; Buxton, J. T.; Cabala, J.; Caffarri, D.; Cai, X.; Caines, H.; Calero Diaz, L.; Caliva, A.; Calvo Villar, E.; Camerini, P.; Carena, F.; Carena, W.; Carnesecchi, F.; Castillo Castellanos, J.; Castro, A. J.; Casula, E. A. R.; Ceballos Sanchez, C.; Cepila, J.; Cerello, P.; Cerkala, J.; Chang, B.; Chapeland, S.; Chartier, M.; Charvet, J. L.; Chattopadhyay, S.; Chattopadhyay, S.; Chauvin, A.; Chelnokov, V.; Cherney, M.; Cheshkov, C.; Cheynis, B.; Chibante Barroso, V.; Chinellato, D. D.; Cho, S.; Chochula, P.; Choi, K.; Chojnacki, M.; Choudhury, S.; Christakoglou, P.; Christensen, C. H.; Christiansen, P.; Chujo, T.; Chung, S. U.; Cicalo, C.; Cifarelli, L.; Cindolo, F.; Cleymans, J.; Colamaria, F.; Colella, D.; Collu, A.; Colocci, M.; Conesa Balbastre, G.; Conesa del Valle, Z.; Connors, M. E.; Contreras, J. G.; Cormier, T. M.; Corrales Morales, Y.; Cortés Maldonado, I.; Cortese, P.; Cosentino, M. R.; Costa, F.; Crochet, P.; Cruz Albino, R.; Cuautle, E.; Cunqueiro, L.; Dahms, T.; Dainese, A.; Danisch, M. C.; Danu, A.; Das, D.; Das, I.; Das, S.; Dash, A.; Dash, S.; De, S.; De Caro, A.; de Cataldo, G.; de Conti, C.; de Cuveland, J.; De Falco, A.; De Gruttola, D.; De Marco, N.; De Pasquale, S.; Deisting, A.; Deloff, A.; Dénes, E.; Deplano, C.; Dhankher, P.; Di Bari, D.; Di Mauro, A.; Di Nezza, P.; Diaz Corchero, M. A.; Dietel, T.; Dillenseger, P.; Divià, R.; Djuvsland, Ø.; Dobrin, A.; Domenicis Gimenez, D.; Dönigus, B.; Dordic, O.; Drozhzhova, T.; Dubey, A. K.; Dubla, A.; Ducroux, L.; Dupieux, P.; Ehlers, R. J.; Elia, D.; Endress, E.; Engel, H.; Epple, E.; Erazmus, B.; Erdemir, I.; Erhardt, F.; Espagnon, B.; Estienne, M.; Esumi, S.; Eum, J.; Evans, D.; Evdokimov, S.; Eyyubova, G.; Fabbietti, L.; Fabris, D.; Faivre, J.; Fantoni, A.; Fasel, M.; Feldkamp, L.; Feliciello, A.; Feofilov, G.; Ferencei, J.; Fernández Téllez, A.; Ferreiro, E. G.; Ferretti, A.; Festanti, A.; Feuillard, V. J. G.; Figiel, J.; Figueredo, M. A. S.; Filchagin, S.; Finogeev, D.; Fionda, F. M.; Fiore, E. M.; Fleck, M. G.; Floris, M.; Foertsch, S.; Foka, P.; Fokin, S.; Fragiacomo, E.; Francescon, A.; Frankenfeld, U.; Fronze, G. G.; Fuchs, U.; Furget, C.; Furs, A.; Fusco Girard, M.; Gaardhøje, J. J.; Gagliardi, M.; Gago, A. M.; Gallio, M.; Gangadharan, D. R.; Ganoti, P.; Gao, C.; Garabatos, C.; Garcia-Solis, E.; Gargiulo, C.; Gasik, P.; Gauger, E. F.; Germain, M.; Gheata, A.; Gheata, M.; Ghosh, P.; Ghosh, S. K.; Gianotti, P.; Giubellino, P.; Giubilato, P.; Gladysz-Dziadus, E.; Glässel, P.; Goméz Coral, D. M.; Gomez Ramirez, A.; Gonzalez, A. S.; Gonzalez, V.; González-Zamora, P.; Gorbunov, S.; Görlich, L.; Gotovac, S.; Grabski, V.; Grachov, O. A.; Graczykowski, L. K.; Graham, K. L.; Grelli, A.; Grigoras, A.; Grigoras, C.; Grigoriev, V.; Grigoryan, A.; Grigoryan, S.; Grinyov, B.; Grion, N.; Gronefeld, J. M.; Grosse-Oetringhaus, J. F.; Grosso, R.; Guber, F.; Guernane, R.; Guerzoni, B.; Gulbrandsen, K.; Gunji, T.; Gupta, A.; Gupta, R.; Haake, R.; Haaland, Ø.; Hadjidakis, C.; Haiduc, M.; Hamagaki, H.; Hamar, G.; Hamon, J. C.; Harris, J. W.; Harton, A.; Hatzifotiadou, D.; Hayashi, S.; Heckel, S. T.; Hellbär, E.; Helstrup, H.; Herghelegiu, A.; Herrera Corral, G.; Hess, B. A.; Hetland, K. F.; Hillemanns, H.; Hippolyte, B.; Horak, D.; Hosokawa, R.; Hristov, P.; Humanic, T. J.; Hussain, N.; Hussain, T.; Hutter, D.; Hwang, D. S.; Ilkaev, R.; Inaba, M.; Incani, E.; Ippolitov, M.; Irfan, M.; Ivanov, M.; Ivanov, V.; Izucheev, V.; Jacazio, N.; Jacobs, P. M.; Jadhav, M. B.; Jadlovska, S.; Jadlovsky, J.; Jahnke, C.; Jakubowska, M. J.; Jang, H. J.; Janik, M. A.; Jayarathna, P. H. S. Y.; Jena, C.; Jena, S.; Jimenez Bustamante, R. T.; Jones, P. G.; Jusko, A.; Kalinak, P.; Kalweit, A.; Kamin, J.; Kang, J. H.; Kaplin, V.; Kar, S.; Karasu Uysal, A.; Karavichev, O.; Karavicheva, T.; Karayan, L.; Karpechev, E.; Kebschull, U.; Keidel, R.; Keijdener, D. L. D.; Keil, M.; Mohisin Khan, M.; Khan, P.; Khan, S. A.; Khanzadeev, A.; Kharlov, Y.; Kileng, B.; Kim, D. W.; Kim, D. J.; Kim, D.; Kim, H.; Kim, J. S.; Kim, M.; Kim, S.; Kim, T.; Kirsch, S.; Kisel, I.; Kiselev, S.; Kisiel, A.; Kiss, G.; Klay, J. L.; Klein, C.; Klein, J.; Klein-Bösing, C.; Klewin, S.; Kluge, A.; Knichel, M. L.; Knospe, A. G.; Kobdaj, C.; Kofarago, M.; Kollegger, T.; Kolojvari, A.; Kondratiev, V.; Kondratyeva, N.; Kondratyuk, E.; Konevskikh, A.; Kopcik, M.; Kostarakis, P.; Kour, M.; Kouzinopoulos, C.; Kovalenko, O.; Kovalenko, V.; Kowalski, M.; Koyithatta Meethaleveedu, G.; Králik, I.; Kravčáková, A.; Krivda, M.; Krizek, F.; Kryshen, E.; Krzewicki, M.; Kubera, A. M.; Kučera, V.; Kuhn, C.; Kuijer, P. G.; Kumar, A.; Kumar, J.; Kumar, L.; Kumar, S.; Kurashvili, P.; Kurepin, A.; Kurepin, A. B.; Kuryakin, A.; Kweon, M. J.; Kwon, Y.; La Pointe, S. L.; La Rocca, P.; Ladron de Guevara, P.; Lagana Fernandes, C.; Lakomov, I.; Langoy, R.; Lara, C.; Lardeux, A.; Lattuca, A.; Laudi, E.; Lea, R.; Leardini, L.; Lee, G. R.; Lee, S.; Lehas, F.; Lemmon, R. C.; Lenti, V.; Leogrande, E.; León Monzón, I.; León Vargas, H.; Leoncino, M.; Lévai, P.; Li, S.; Li, X.; Lien, J.; Lietava, R.; Lindal, S.; Lindenstruth, V.; Lippmann, C.; Lisa, M. A.; Ljunggren, H. M.; Lodato, D. F.; Loenne, P. I.; Loginov, V.; Loizides, C.; Lopez, X.; López Torres, E.; Lowe, A.; Luettig, P.; Lunardon, M.; Luparello, G.; Lutz, T. H.; Maevskaya, A.; Mager, M.; Mahajan, S.; Mahmood, S. M.; Maire, A.; Majka, R. D.; Malaev, M.; Maldonado Cervantes, I.; Malinina, L.; Mal'Kevich, D.; Malzacher, P.; Mamonov, A.; Manko, V.; Manso, F.; Manzari, V.; Marchisone, M.; Mareš, J.; Margagliotti, G. V.; Margotti, A.; Margutti, J.; Marín, A.; Markert, C.; Marquard, M.; Martin, N. A.; Martin Blanco, J.; Martinengo, P.; Martínez, M. I.; Martínez García, G.; Martinez Pedreira, M.; Mas, A.; Masciocchi, S.; Masera, M.; Masoni, A.; Mastroserio, A.; Matyja, A.; Mayer, C.; Mazer, J.; Mazzoni, M. A.; Mcdonald, D.; Meddi, F.; Melikyan, Y.; Menchaca-Rocha, A.; Meninno, E.; Mercado Pérez, J.; Meres, M.; Miake, Y.; Mieskolainen, M. M.; Mikhaylov, K.; Milano, L.; Milosevic, J.; Mischke, A.; Mishra, A. N.; Miśkowiec, D.; Mitra, J.; Mitu, C. M.; Mohammadi, N.; Mohanty, B.; Molnar, L.; Montaño Zetina, L.; Montes, E.; Moreira De Godoy, D. A.; Moreno, L. A. P.; Moretto, S.; Morreale, A.; Morsch, A.; Muccifora, V.; Mudnic, E.; Mühlheim, D.; Muhuri, S.; Mukherjee, M.; Mulligan, J. D.; Munhoz, M. G.; Munzer, R. H.; Murakami, H.; Murray, S.; Musa, L.; Musinsky, J.; Naik, B.; Nair, R.; Nandi, B. K.; Nania, R.; Nappi, E.; Naru, M. U.; Natal da Luz, H.; Nattrass, C.; Navarro, S. R.; Nayak, K.; Nayak, R.; Nayak, T. K.; Nazarenko, S.; Nedosekin, A.; Nellen, L.; Ng, F.; Nicassio, M.; Niculescu, M.; Niedziela, J.; Nielsen, B. S.; Nikolaev, S.; Nikulin, S.; Nikulin, V.; Noferini, F.; Nomokonov, P.; Nooren, G.; Noris, J. C. C.; Norman, J.; Nyanin, A.; Nystrand, J.; Oeschler, H.; Oh, S.; Oh, S. K.; Ohlson, A.; Okatan, A.; Okubo, T.; Olah, L.; Oleniacz, J.; Oliveira Da Silva, A. C.; Oliver, M. H.; Onderwaater, J.; Oppedisano, C.; Orava, R.; Oravec, M.; Ortiz Velasquez, A.; Oskarsson, A.; Otwinowski, J.; Oyama, K.; Ozdemir, M.; Pachmayer, Y.; Pagano, D.; Pagano, P.; Paić, G.; Pal, S. K.; Pan, J.; Pandey, A. K.; Papikyan, V.; Pappalardo, G. S.; Pareek, P.; Park, W. J.; Parmar, S.; Passfeld, A.; Paticchio, V.; Patra, R. N.; Paul, B.; Pei, H.; Peitzmann, T.; Pereira Da Costa, H.; Peresunko, D.; Pérez Lara, C. E.; Perez Lezama, E.; Peskov, V.; Pestov, Y.; Petráček, V.; Petrov, V.; Petrovici, M.; Petta, C.; Piano, S.; Pikna, M.; Pillot, P.; Pimentel, L. O. D. L.; Pinazza, O.; Pinsky, L.; Piyarathna, D. B.; Płoskoń, M.; Planinic, M.; Pluta, J.; Pochybova, S.; Podesta-Lerma, P. L. M.; Poghosyan, M. G.; Polichtchouk, B.; Poljak, N.; Poonsawat, W.; Pop, A.; Porteboeuf-Houssais, S.; Porter, J.; Pospisil, J.; Prasad, S. K.; Preghenella, R.; Prino, F.; Pruneau, C. A.; Pshenichnov, I.; Puccio, M.; Puddu, G.; Pujahari, P.; Punin, V.; Putschke, J.; Qvigstad, H.; Rachevski, A.; Raha, S.; Rajput, S.; Rak, J.; Rakotozafindrabe, A.; Ramello, L.; Rami, F.; Raniwala, R.; Raniwala, S.; Räsänen, S. S.; Rascanu, B. T.; Rathee, D.; Read, K. F.; Redlich, K.; Reed, R. J.; Rehman, A.; Reichelt, P.; Reidt, F.; Ren, X.; Renfordt, R.; Reolon, A. R.; Reshetin, A.; Reygers, K.; Riabov, V.; Ricci, R. A.; Richert, T.; Richter, M.; Riedler, P.; Riegler, W.; Riggi, F.; Ristea, C.; Rocco, E.; Rodríguez Cahuantzi, M.; Rodriguez Manso, A.; Røed, K.; Rogochaya, E.; Rohr, D.; Röhrich, D.; Ronchetti, F.; Ronflette, L.; Rosnet, P.; Rossi, A.; Roukoutakis, F.; Roy, A.; Roy, C.; Roy, P.; Rubio Montero, A. J.; Rui, R.; Russo, R.; Ryabinkin, E.; Ryabov, Y.; Rybicki, A.; Saarinen, S.; Sadhu, S.; Sadovsky, S.; Šafařík, K.; Sahlmuller, B.; Sahoo, P.; Sahoo, R.; Sahoo, S.; Sahu, P. K.; Saini, J.; Sakai, S.; Saleh, M. A.; Salzwedel, J.; Sambyal, S.; Samsonov, V.; Šándor, L.; Sandoval, A.; Sano, M.; Sarkar, D.; Sarkar, N.; Sarma, P.; Scapparone, E.; Scarlassara, F.; Schiaua, C.; Schicker, R.; Schmidt, C.; Schmidt, H. R.; Schuchmann, S.; Schukraft, J.; Schulc, M.; Schutz, Y.; Schwarz, K.; Schweda, K.; Scioli, G.; Scomparin, E.; Scott, R.; Šefčík, M.; Seger, J. E.; Sekiguchi, Y.; Sekihata, D.; Selyuzhenkov, I.; Senosi, K.; Senyukov, S.; Serradilla, E.; Sevcenco, A.; Shabanov, A.; Shabetai, A.; Shadura, O.; Shahoyan, R.; Shahzad, M. I.; Shangaraev, A.; Sharma, A.; Sharma, M.; Sharma, M.; Sharma, N.; Sheikh, A. I.; Shigaki, K.; Shou, Q.; Shtejer, K.; Sibiriak, Y.; Siddhanta, S.; Sielewicz, K. M.; Siemiarczuk, T.; Silvermyr, D.; Silvestre, C.; Simatovic, G.; Simonetti, G.; Singaraju, R.; Singh, R.; Singha, S.; Singhal, V.; Sinha, B. C.; Sinha, T.; Sitar, B.; Sitta, M.; Skaali, T. B.; Slupecki, M.; Smirnov, N.; Snellings, R. J. M.; Snellman, T. W.; Song, J.; Song, M.; Song, Z.; Soramel, F.; Sorensen, S.; Souza, R. D. de; Sozzi, F.; Spacek, M.; Spiriti, E.; Sputowska, I.; Spyropoulou-Stassinaki, M.; Stachel, J.; Stan, I.; Stankus, P.; Stenlund, E.; Steyn, G.; Stiller, J. H.; Stocco, D.; Strmen, P.; Suaide, A. A. P.; Sugitate, T.; Suire, C.; Suleymanov, M.; Suljic, M.; Sultanov, R.; Šumbera, M.; Sumowidagdo, S.; Szabo, A.; Szanto de Toledo, A.; Szarka, I.; Szczepankiewicz, A.; Szymanski, M.; Tabassam, U.; Takahashi, J.; Tambave, G. J.; Tanaka, N.; Tarhini, M.; Tariq, M.; Tarzila, M. G.; Tauro, A.; Tejeda Muñoz, G.; Telesca, A.; Terasaki, K.; Terrevoli, C.; Teyssier, B.; Thäder, J.; Thakur, D.; Thomas, D.; Tieulent, R.; Timmins, A. R.; Toia, A.; Trogolo, S.; Trombetta, G.; Trubnikov, V.; Trzaska, W. H.; Tsuji, T.; Tumkin, A.; Turrisi, R.; Tveter, T. S.; Ullaland, K.; Uras, A.; Usai, G. L.; Utrobicic, A.; Vala, M.; Valencia Palomo, L.; Vallero, S.; Van Der Maarel, J.; Van Hoorne, J. W.; van Leeuwen, M.; Vanat, T.; Vande Vyvre, P.; Varga, D.; Vargas, A.; Vargyas, M.; Varma, R.; Vasileiou, M.; Vasiliev, A.; Vauthier, A.; Vechernin, V.; Veen, A. M.; Veldhoen, M.; Velure, A.; Vercellin, E.; Vergara Limón, S.; Vernet, R.; Verweij, M.; Vickovic, L.; Viesti, G.; Viinikainen, J.; Vilakazi, Z.; Villalobos Baillie, O.; Villatoro Tello, A.; Vinogradov, A.; Vinogradov, L.; Vinogradov, Y.; Virgili, T.; Vislavicius, V.; Viyogi, Y. P.; Vodopyanov, A.; Völkl, M. A.; Voloshin, K.; Voloshin, S. A.; Volpe, G.; von Haller, B.; Vorobyev, I.; Vranic, D.; Vrláková, J.; Vulpescu, B.; Wagner, B.; Wagner, J.; Wang, H.; Wang, M.; Watanabe, D.; Watanabe, Y.; Weber, M.; Weber, S. G.; Weiser, D. F.; Wessels, J. P.; Westerhoff, U.; Whitehead, A. M.; Wiechula, J.; Wikne, J.; Wilk, G.; Wilkinson, J.; Williams, M. C. S.; Windelband, B.; Winn, M.; Yang, H.; Yang, P.; Yano, S.; Yasin, Z.; Yin, Z.; Yokoyama, H.; Yoo, I.-K.; Yoon, J. H.; Yurchenko, V.; Yushmanov, I.; Zaborowska, A.; Zaccolo, V.; Zaman, A.; Zampolli, C.; Zanoli, H. J. C.; Zaporozhets, S.; Zardoshti, N.; Zarochentsev, A.; Závada, P.; Zaviyalov, N.; Zbroszczyk, H.; Zgura, I. S.; Zhalov, M.; Zhang, H.; Zhang, X.; Zhang, Y.; Zhang, C.; Zhang, Z.; Zhao, C.; Zhigareva, N.; Zhou, D.; Zhou, Y.; Zhou, Z.; Zhu, H.; Zhu, J.; Zichichi, A.; Zimmermann, A.; Zimmermann, M. B.; Zinovjev, G.; Zyzak, M.

    2016-05-01

    We present a Bayesian approach to particle identification (PID) within the ALICE experiment. The aim is to more effectively combine the particle identification capabilities of its various detectors. After a brief explanation of the adopted methodology and formalism, the performance of the Bayesian PID approach for charged pions, kaons and protons in the central barrel of ALICE is studied. PID is performed via measurements of specific energy loss ( d E/d x) and time of flight. PID efficiencies and misidentification probabilities are extracted and compared with Monte Carlo simulations using high-purity samples of identified particles in the decay channels K0S → π-π+, φ→ K-K+, and Λ→ p π- in p-Pb collisions at √{s_{NN}}=5.02 TeV. In order to thoroughly assess the validity of the Bayesian approach, this methodology was used to obtain corrected pT spectra of pions, kaons, protons, and D0 mesons in pp collisions at √{s}=7 TeV. In all cases, the results using Bayesian PID were found to be consistent with previous measurements performed by ALICE using a standard PID approach. For the measurement of D0 → K-π+, it was found that a Bayesian PID approach gave a higher signal-to-background ratio and a similar or larger statistical significance when compared with standard PID selections, despite a reduced identification efficiency. Finally, we present an exploratory study of the measurement of Λc+ → p K-π+ in pp collisions at √{s}=7 TeV, using the Bayesian approach for the identification of its decay products.

  3. [A new automatic quasars recognition technique based on PCA and Hough transform].

    PubMed

    Huang, Ling-yun; Hu, Zhan-yi

    2003-02-01

    The main purpose of quasar recognition is to determine the observed quasar spectrum's redshift value. Previously the template of quasar rest frame in the literature was basically constructed based on astronomers' hypotheses. Due to the inaccuracy of such a template, it is hard to determine the redshift value by matching the observed quasar spectrum with the template directly. This paper's main contributions are two-fold: Firstly, the template in our paper is constructed by the principal component analysis (PCA) method from some selected spectra with known redshift values, hence the obtained template is more realistic. Secondly, a 2D standard Hough transform, rather than a 1D Hough transform, is used. This is because although only redshift needs to be determined in our system, based on our observations, the magnitude of emission peak is also changed, hence a new parameter, namely scale parameter, is also introduced to the Hough transform to enhance the reliability of the recognition. The experiments show that the proposed technique is workable and the correct recognition rate can reach about as high as 90%.

  4. [Automated recognition of quasars based on adaptive radial basis function neural networks].

    PubMed

    Zhao, Mei-Fang; Luo, A-Li; Wu, Fu-Chao; Hu, Zhan-Yi

    2006-02-01

    Recognizing and certifying quasars through the research on spectra is an important method in the field of astronomy. This paper presents a novel adaptive method for the automated recognition of quasars based on the radial basis function neural networks (RBFN). The proposed method is composed of the following three parts: (1) The feature space is reduced by the PCA (the principal component analysis) on the normalized input spectra; (2) An adaptive RBFN is constructed and trained in this reduced space. At first, the K-means clustering is used for the initialization, then based on the sum of squares errors and a gradient descent optimization technique, the number of neurons in the hidden layer is adaptively increased to improve the recognition performance; (3) The quasar spectra recognition is effectively carried out by the above trained RBFN. The author's proposed adaptive RBFN is shown to be able to not only overcome the difficulty of selecting the number of neurons in hidden layer of the traditional RBFN algorithm, but also increase the stability and accuracy of recognition of quasars. Besides, the proposed method is particularly useful for automatic voluminous spectra processing produced from a large-scale sky survey project, such as our LAMOST, due to its efficiency.

  5. Two New Gravitationally Lensed Double Quasars from theSloan Digital Sky Survey

    SciTech Connect

    Inada, Naohisa; Oguri, Masamune; Becker, Robert H.; White, Richard L.; Kayo, Issha; Kochanek, Christopher S.; Hall, Patrick B.; Schneider, Donald P.; York, Donald G.; Richards, Gordon T.; /Tokyo U., Inst. Astron. /KIPAC, Menlo Park /Princeton U. Observ. /LLNL, Livermore /UC, Davis /Baltimore, Space Telescope Sci. /Nagoya U. /Ohio State U., Dept. Astron. /York U., Canada /Penn State U., Astron. Astrophys. /Chicago U., Astron. Astrophys. Ctr. /Chicago U., EFI /Johns Hopkins U. /Drexel U.

    2006-09-28

    We report the discoveries of the two-image gravitationally lensed quasars, SDSS J0746+4403 and SDSS J1406+6126, selected from the Sloan Digital Sky Survey (SDSS). SDSS J0746+4403, which will be included in our lens sample for statistics and cosmology, has a source redshift of z{sub s} = 2.00, an estimated lens redshift of z{sub l} {approx} 0.3, and an image separation of 1.08''. SDSS J1406+6126 has a source redshift of z{sub s} = 2.13, a spectroscopically measured lens redshift of z{sub l} = 0.27, and an image separation of 1.98''. We find that the two quasar images of SDSS J1406+6126 have different intervening Mg II absorption strengths, which are suggestive of large variations of absorbers on kpc scales. The positions and fluxes of both the lensed quasar systems are easily reproduced by simple mass models with reasonable parameter values. These objects bring to 18 the number of lensed quasars that have been discovered from the SDSS data.

  6. A Study of Stellar Population Synthesis of Post-starburst Quasars

    NASA Astrophysics Data System (ADS)

    Zhang-hu, Chu; Qiu-sheng, Gu

    2016-07-01

    We present a study of stellar population synthesis of a sample of 10 post-starburst quasars (PSQs) at z ∼ 0.3. These PSGs posses the spectral signatures of massive intermediate-aged stellar populations, making them potentially useful for studying the connections between the galactic nuclear activity and the host galaxy evolution. With the help of the stellar synthesis code STARLIGHT, we have determined the stellar population ages, black hole masses, and Eddington ratios of their host galaxies. We find that the PSQs have the black hole mass MBH ∼ 108 M⊙, the bolometric luminosity of a few percent of Eddington luminosity, and the ages of host stellar populations from several hundred Myr to a few Gyr. The result may support a time delay existed between the merge-induced starburst and the quasar being triggered/becoming visible. The synthetical spectral energy distribution (SED) of the PSQs indicates that they are closely related with the Ultra Luminous Infrared Galaxies (ULIRGs), and for these PSQs, the derived infrared luminosity has attained the level of a luminous infrared galaxy, implying that very possibly, these quasars selected by their optical spectra are undergoing the evolution from ULIRGs to optical quasars.

  7. Bayesian Threshold Estimation

    ERIC Educational Resources Information Center

    Gustafson, S. C.; Costello, C. S.; Like, E. C.; Pierce, S. J.; Shenoy, K. N.

    2009-01-01

    Bayesian estimation of a threshold time (hereafter simply threshold) for the receipt of impulse signals is accomplished given the following: 1) data, consisting of the number of impulses received in a time interval from zero to one and the time of the largest time impulse; 2) a model, consisting of a uniform probability density of impulse time…

  8. Spectral Bayesian Knowledge Tracing

    ERIC Educational Resources Information Center

    Falakmasir, Mohammad; Yudelson, Michael; Ritter, Steve; Koedinger, Ken

    2015-01-01

    Bayesian Knowledge Tracing (BKT) has been in wide use for modeling student skill acquisition in Intelligent Tutoring Systems (ITS). BKT tracks and updates student's latent mastery of a skill as a probability distribution of a binary variable. BKT does so by accounting for observed student successes in applying the skill correctly, where success is…

  9. Tracing high redshift cosmic web with quasar systems

    NASA Astrophysics Data System (ADS)

    Einasto, Maret

    2016-10-01

    We study the cosmic web at redshifts 1.0 <= <= 1.8 using quasar systems based on quasar data from the SDSS DR7 QSO catalogue. Quasar systems were determined with a friend-of-friend (FoF) algorithm at a series of linking lengths. At the linking lengths l <= 30 h -1 Mpc the diameters of quasar systems are smaller than the diameters of random systems, and are comparable to the sizes of galaxy superclusters in the local Universe. The mean space density of quasar systems is close to the mean space density of local rich superclusters. At larger linking lengths the diameters of quasar systems are comparable with the sizes of supercluster complexes in our cosmic neighbourhood. The richest quasar systems have diameters exceeding 500h Mpc. Very rich systems can be found also in random distribution but the percolating system which penetrate the whole sample volume appears in quasar sample at smaller linking length than in random samples showing that the large-scale distribution of quasar systems differs from random distribution. Quasar system catalogues at our web pages (http://www.aai.ee/maret/QSOsystems.html) serve as a database to search for superclusters of galaxies and to trace the cosmic web at high redshifts.

  10. Correlaciones cruzadas quasar-galaxia y AGN-galaxia

    NASA Astrophysics Data System (ADS)

    Martínez, H. J.; Merchán, M. E.; Valotto, C. A.; García Lambas, D.

    We compute quasar-galaxy and AGN-galaxy cross-correlation functions for samples taken from the Véron-Cetty & Véron (1998) catalog of quasars and active galaxies, using tracer galaxies taken from the Edinburgh/Durham Southern Catalog. The sample of active galaxy targets shows positive correlation at projected separations rp < 6 h-1 ~Mpc consistent with the usual power-law. On the other hand, we do not find a statistically significant positive quasar-galaxy correlation signal except in the range 3 h-1 Mpc < rp < 6 h-1 Mpc where we find similar AGN-galaxy and quasar-galaxy correlation amplitudes. At separations rp<3~h-1 ~Mpc a strong decline of quasar-galaxy correlations is observed, suggesting a significant local influence of quasars in galaxy formation. In an attempt to reproduce the observed cross-correlation between quasars and galaxies, we have performed CDM cosmological hydrodynamical simulations and tested the viability of a scenario based on the model developed by Silk & Rees (1998). In this scheme a fraction of the energy released by quasars is considered to be transferred into the baryonic component of the intergalactic medium in the form of winds. The results of the simulations suggest that the shape of the observed quasar-galaxy cross-correlation function could be understood in a scenario where a substantial amount of energy is transferred to the medium at the redshift of maximum quasar activity.

  11. DES J0454–4448: Discovery of the first luminous z ≥ 6 quasar from the Dark Energy Survey

    SciTech Connect

    Reed, S. L.

    2015-10-28

    We present the first results of a survey for high-redshift, z ≥ 6, quasars using izY multicolour photometric observations from the Dark Energy Survey (DES). Here we report the discovery and spectroscopic confirmation of the zAB, YAB = 20.2, 20.2 (M1450 = –26.5) quasar DES J0454–4448 with a redshift of z = 6.09±0.02 based on the onset of the Ly α forest and an H i near zone size of 4.1+1.1–1.2 proper Mpc. The quasar was selected as an i-band drop out with i–z = 2.46 and zAB < 21.5 from an area of ~300 deg2. It is the brightest of our 43 candidates and was identified for spectroscopic follow-up solely based on the DES i–z and z–Y colours. The quasar is detected by WISE and has W1AB = 19.68. The discovery of one spectroscopically confirmed quasar with 5.7 < z < 6.5 and zAB ≤ 20.2 is consistent with recent determinations of the luminosity function at z ~ 6. DES when completed will have imaged ~5000 deg2 to YAB = 23.0 (5σ point source) and we expect to discover 50–100 new quasars with z > 6 including 3–10 with z > 7 dramatically increasing the numbers of quasars currently known that are suitable for detailed studies.

  12. DES J0454–4448: Discovery of the first luminous z ≥ 6 quasar from the Dark Energy Survey

    DOE PAGES

    Reed, S. L.

    2015-10-28

    We present the first results of a survey for high-redshift, z ≥ 6, quasars using izY multicolour photometric observations from the Dark Energy Survey (DES). Here we report the discovery and spectroscopic confirmation of the zAB, YAB = 20.2, 20.2 (M1450 = –26.5) quasar DES J0454–4448 with a redshift of z = 6.09±0.02 based on the onset of the Ly α forest and an H i near zone size of 4.1+1.1–1.2 proper Mpc. The quasar was selected as an i-band drop out with i–z = 2.46 and zAB < 21.5 from an area of ~300 deg2. It is the brightestmore » of our 43 candidates and was identified for spectroscopic follow-up solely based on the DES i–z and z–Y colours. The quasar is detected by WISE and has W1AB = 19.68. The discovery of one spectroscopically confirmed quasar with 5.7 < z < 6.5 and zAB ≤ 20.2 is consistent with recent determinations of the luminosity function at z ~ 6. DES when completed will have imaged ~5000 deg2 to YAB = 23.0 (5σ point source) and we expect to discover 50–100 new quasars with z > 6 including 3–10 with z > 7 dramatically increasing the numbers of quasars currently known that are suitable for detailed studies.« less

  13. Universal Darwinism As a Process of Bayesian Inference

    PubMed Central

    Campbell, John O.

    2016-01-01

    Many of the mathematical frameworks describing natural selection are equivalent to Bayes' Theorem, also known as Bayesian updating. By definition, a process of Bayesian Inference is one which involves a Bayesian update, so we may conclude that these frameworks describe natural selection as a process of Bayesian inference. Thus, natural selection serves as a counter example to a widely-held interpretation that restricts Bayesian Inference to human mental processes (including the endeavors of statisticians). As Bayesian inference can always be cast in terms of (variational) free energy minimization, natural selection can be viewed as comprising two components: a generative model of an “experiment” in the external world environment, and the results of that “experiment” or the “surprise” entailed by predicted and actual outcomes of the “experiment.” Minimization of free energy implies that the implicit measure of “surprise” experienced serves to update the generative model in a Bayesian manner. This description closely accords with the mechanisms of generalized Darwinian process proposed both by Dawkins, in terms of replicators and vehicles, and Campbell, in terms of inferential systems. Bayesian inference is an algorithm for the accumulation of evidence-based knowledge. This algorithm is now seen to operate over a wide range of evolutionary processes, including natural selection, the evolution of mental models and cultural evolutionary processes, notably including science itself. The variational principle of free energy minimization may thus serve as a unifying mathematical framework for universal Darwinism, the study of evolutionary processes operating throughout nature. PMID:27375438

  14. Bayesian analysis of a disability model for lung cancer survival.

    PubMed

    Armero, C; Cabras, S; Castellanos, M E; Perra, S; Quirós, A; Oruezábal, M J; Sánchez-Rubio, J

    2016-02-01

    Bayesian reasoning, survival analysis and multi-state models are used to assess survival times for Stage IV non-small-cell lung cancer patients and the evolution of the disease over time. Bayesian estimation is done using minimum informative priors for the Weibull regression survival model, leading to an automatic inferential procedure. Markov chain Monte Carlo methods have been used for approximating posterior distributions and the Bayesian information criterion has been considered for covariate selection. In particular, the posterior distribution of the transition probabilities, resulting from the multi-state model, constitutes a very interesting tool which could be useful to help oncologists and patients make efficient and effective decisions.

  15. LBQS 1429-0053: A binary quasar rather than a lensed quasar.

    NASA Astrophysics Data System (ADS)

    Faure, C.; Alloin, D.; Gras, S.; Courbin, F.; Kneib, J.-P.; Hudelot, P.

    2003-07-01

    Very deep ESO/VLT FORS1 and ISAAC images, as well as HST NICMOS2 data are used to infer the nature of the quasar pair LBQS 1429-0053 A and B, either a binary quasar or a doubly-imaged lensed quasar. Direct search of a putative lensing galaxy is unsuccessful down to R=27, J=24, Ks=22.5 and H=22.5. Moreover, no galaxy overdensity close to the quasar pair is found. A weak shear analysis of the FORS1 R-band 6.8 arcmin x 6.8 arcmin field also fails at detecting any concentration of dark matter more massive than sigma =500 km s-1 and weakens the hypothesis of a dark lens. The only sign of a possible lens consists in a group of 5 objects having colors consistent with galaxies at z ~ 1, within a radius of 5 arcsec from the quasar pair. Considering this group as the lensing potential does not allow to reproduce the image position and flux ratio of LBQS 1429-0053 A and B. Our deep R-band image shows a blue, previously unknown, extended object at the position of LBQS 1429-0053 A, which is consistent with either being the lensed quasar A host, or being an intervening galaxy at lower redshift. Unless future very deep optical images demonstrate that this object is actually the lensed host of LBQS 1429-0053, we conclude that there is very little evidence for LBQS 1429-0053 being lensed. Therefore, we are led to declare LBQS 1429-0053 A and B a genuine binary quasar. Based on observations obtained with VLT/ANTU at ESO-Paranal Observatory (program 67.A-0502) and with the Hubble Space Telescope, operated by NASA.

  16. Bayesian multimodel inference for dose-response studies

    USGS Publications Warehouse

    Link, W.A.; Albers, P.H.

    2007-01-01

    Statistical inference in dose?response studies is model-based: The analyst posits a mathematical model of the relation between exposure and response, estimates parameters of the model, and reports conclusions conditional on the model. Such analyses rarely include any accounting for the uncertainties associated with model selection. The Bayesian inferential system provides a convenient framework for model selection and multimodel inference. In this paper we briefly describe the Bayesian paradigm and Bayesian multimodel inference. We then present a family of models for multinomial dose?response data and apply Bayesian multimodel inferential methods to the analysis of data on the reproductive success of American kestrels (Falco sparveriuss) exposed to various sublethal dietary concentrations of methylmercury.

  17. THE FAINT END OF THE QUASAR LUMINOSITY FUNCTION AT z {approx} 4

    SciTech Connect

    Glikman, Eilat; Bogosavljevic, Milan; Djorgovski, S. G.; Mahabal, Ashish; Stern, Daniel; Dey, Arjun; Jannuzi, Buell T.

    2010-02-20

    The evolution of the quasar luminosity function (QLF) is one of the basic cosmological measures providing insight into structure formation and mass assembly in the universe. We have conducted a spectroscopic survey to find faint quasars (-26.0 < M{sub 1450} < -22.0) at redshifts z = 3.8-5.2 in order to measure the faint end of the QLF at these early times. Using available optical imaging data from portions of the NOAO Deep Wide-Field Survey and the Deep Lens Survey, we have color-selected quasar candidates in a total area of 3.76 deg{sup 2}. Thirty candidates have R <= 23 mag. We conducted spectroscopic follow-up for 28 of our candidates and found 23 QSOs, 21 of which are reported here for the first time, in the 3.74 < z < 5.06 redshift range. We estimate our survey completeness through detailed Monte Carlo simulations and derive the first measurement of the density of quasars in this magnitude and redshift interval. We find that the binned luminosity function (LF) is somewhat affected by the K-correction used to compute the rest-frame absolute magnitude at 1450 A. Considering only our R <= 23 sample, the best-fit single power law (PHI {proportional_to} L {sup beta}) gives a faint-end slope beta = -1.6 +- 0.2. If we consider our larger, but highly incomplete sample going 1 mag fainter, we measure a steeper faint-end slope -2 < beta < -2.5. In all cases, we consistently find faint-end slopes that are steeper than expected based on measurements at z {approx} 3. We combine our sample with bright quasars from the Sloan Digital Sky Survey to derive parameters for a double-power-law LF. Our best fit finds a bright-end slope, alpha = -2.4 +- 0.2, and faint-end slope, beta = -2.3 +- 0.2, without a well-constrained break luminosity. This is effectively a single power law, with beta = -2.7 +- 0.1. We use these results to place limits on the amount of ultraviolet radiation produced by quasars and find that quasars are able to ionize the intergalactic medium at these redshifts.

  18. The Faint End of the Quasar Luminosity Function at z ~ 4

    NASA Astrophysics Data System (ADS)

    Glikman, Eilat; Bogosavljević, Milan; Djorgovski, S. G.; Stern, Daniel; Dey, Arjun; Jannuzi, Buell T.; Mahabal, Ashish

    2010-02-01

    The evolution of the quasar luminosity function (QLF) is one of the basic cosmological measures providing insight into structure formation and mass assembly in the universe. We have conducted a spectroscopic survey to find faint quasars (-26.0 < M 1450 < -22.0) at redshifts z = 3.8-5.2 in order to measure the faint end of the QLF at these early times. Using available optical imaging data from portions of the NOAO Deep Wide-Field Survey and the Deep Lens Survey, we have color-selected quasar candidates in a total area of 3.76 deg2. Thirty candidates have R <= 23 mag. We conducted spectroscopic follow-up for 28 of our candidates and found 23 QSOs, 21 of which are reported here for the first time, in the 3.74 < z < 5.06 redshift range. We estimate our survey completeness through detailed Monte Carlo simulations and derive the first measurement of the density of quasars in this magnitude and redshift interval. We find that the binned luminosity function (LF) is somewhat affected by the K-correction used to compute the rest-frame absolute magnitude at 1450 Å. Considering only our R <= 23 sample, the best-fit single power law (Φ vprop L β) gives a faint-end slope β = -1.6 ± 0.2. If we consider our larger, but highly incomplete sample going 1 mag fainter, we measure a steeper faint-end slope -2 < β < -2.5. In all cases, we consistently find faint-end slopes that are steeper than expected based on measurements at z ~ 3. We combine our sample with bright quasars from the Sloan Digital Sky Survey to derive parameters for a double-power-law LF. Our best fit finds a bright-end slope, α = -2.4 ± 0.2, and faint-end slope, β = -2.3 ± 0.2, without a well-constrained break luminosity. This is effectively a single power law, with β = -2.7 ± 0.1. We use these results to place limits on the amount of ultraviolet radiation produced by quasars and find that quasars are able to ionize the intergalactic medium at these redshifts. The data presented herein were obtained at the

  19. Mean and extreme radio properties of quasars and the origin of radio emission

    SciTech Connect

    Kratzer, Rachael M.; Richards, Gordon T.

    2015-02-01

    We investigate the evolution of both the radio-loud fraction (RLF) and (using stacking analysis) the mean radio loudness of quasars. We consider how these properties evolve as a function of redshift and luminosity, black hole (BH) mass and accretion rate, and parameters related to the dominance of a wind in the broad emission-line region. We match the FIRST source catalog to samples of luminous quasars (both spectroscopic and photometric), primarily from the Sloan Digital Sky Survey. After accounting for catastrophic errors in BH mass estimates at high redshift, we find that both the RLF and the mean radio luminosity increase for increasing BH mass and decreasing accretion rate. Similarly, both the RLF and mean radio loudness increase for quasars that are argued to have weaker radiation line driven wind components of the broad emission-line region. In agreement with past work, we find that the RLF increases with increasing optical/UV luminosity and decreasing redshift, while the mean radio loudness evolves in the exact opposite manner. This difference in behavior between the mean radio loudness and the RLF in L−z may indicate selection effects that bias our understanding of the evolution of the RLF; deeper surveys in the optical and radio are needed to resolve this discrepancy. Finally, we argue that radio-loud (RL) and radio-quiet (RQ) quasars may be parallel sequences, but where only RQ quasars at one extreme of the distribution are likely to become RL, possibly through slight differences in spin and/or merger history.

  20. NuSTAR observations of heavily obscured quasars at z ∼ 0.5

    SciTech Connect

    Lansbury, G. B.; Alexander, D. M.; Moro, A. Del; Gandhi, P.; Aird, J.; Assef, R. J.; Stern, D.; Ballantyne, D. R.; Baloković, M.; Grefenstette, B. W.; Harrison, F. A.; Bauer, F. E.; Boggs, S. E.; Brandt, W. N.; Christensen, F. E.; Craig, W. W.; Elvis, M.; Hailey, C. J.; Hickox, R. C.; Koss, M.; and others

    2014-04-10

    We present NuSTAR hard X-ray observations of three Type 2 quasars at z ≈ 0.4-0.5, optically selected from the Sloan Digital Sky Survey. Although the quasars show evidence for being heavily obscured, Compton-thick systems on the basis of the 2-10 keV to [O III] luminosity ratio and multiwavelength diagnostics, their X-ray absorbing column densities (N {sub H}) are poorly known. In this analysis, (1) we study X-ray emission at >10 keV, where X-rays from the central black hole are relatively unabsorbed, in order to better constrain N {sub H}. (2) We further characterize the physical properties of the sources through broad-band near-UV to mid-IR spectral energy distribution analyses. One of the quasars is detected with NuSTAR at >8 keV with a no-source probability of <0.1%, and its X-ray band ratio suggests near Compton-thick absorption with N {sub H} ≳ 5 × 10{sup 23} cm{sup –2}. The other two quasars are undetected, and have low X-ray to mid-IR luminosity ratios in both the low-energy (2-10 keV) and high-energy (10-40 keV) X-ray regimes that are consistent with extreme, Compton-thick absorption (N {sub H} ≳ 10{sup 24} cm{sup –2}). We find that for quasars at z ∼ 0.5, NuSTAR provides a significant improvement compared to lower energy (<10 keV) Chandra and XMM-Newton observations alone, as higher column densities can now be directly constrained.

  1. The Sloan Digital Sky Survey Quasar Catalog. 3. Third data release

    SciTech Connect

    Schneider, Donald P.; Hall, Patrick B.; Richards, Gordon T.; Vanden Berk, Daniel E.; Anderson, Scott F.; Fan, Xiao-Hui; Jester, Sebastian; Stoughton, Chris; Strauss, Michael A.; SubbaRao, Mark; Brandt, W.N.; Gunn, James E.; Yanny, Brian; Bahcall, Neta A.; Barentine, J.C.; Blanton, Michael R.; Boroski, William N.; Brewington, Howard J.; Brinkmann, J.; Brunner, Robert; Csabai, Istvan; /Penn State U., Astron. Astrophys. /York U., Canada /Princeton U. Observ. /Washington U., Seattle, Astron. Dept. /Arizona U., Astron. Dept. - Steward Observ. /Fermilab /Chicago U., Astron. Astrophys. Ctr. /Adler Planetarium, Chicago /Apache Point Observ. /New York U. /Illinois U., Urbana, Astron. Dept. /Eotvos U. /Tokyo U., Astron. Dept. /Tokyo U., RESCEU /Tokyo U., ICRR /Princeton, Inst. Advanced Study /Microsoft, BARC /Johns Hopkins U. /Mt. Suhora Observ., Cracow /Sussex U., Astron. Ctr. /Baltimore, Space Telescope Sci.

    2005-03-01

    We present the third edition of the Sloan Digital Sky Survey (SDSS) Quasar Catalog. The catalog consists of the 46,420 objects in the SDSS Third Data Release that have luminosities larger than M{sub i} = -22 (in a cosmology with H{sub 0} = 70 km s{sup -1} Mpc{sup -1}, {Omega}{sub M} = 0.3, and {Omega}{sub {Lambda}} = 0.7), have at least one emission line with FWHM larger than 1000 km s{sup -1} or are unambiguously broad absorption line quasars, are fainter than i = 15.0, and have highly reliable redshifts. The area covered by the catalog is {approx} 4188 deg{sup 2}. The quasar redshifts range from 0.08 to 5.41, with a median value of 1.47; the high-redshift sample includes 520 quasars at redshifts greater than four, of which 17 are at redshifts greater than five. For each object the catalog presents positions accurate to better than 0.2'' rms per coordinate, five-band (ugriz) CCD-based photometry with typical accuracy of 0.03 mag, and information on the morphology and selection method. The catalog also contains radio, near-infrared, and X-ray emission properties of the quasars, when available, from other large-area surveys. The calibrated digital spectra cover the wavelength region 3800-9200 at a spectral resolution of {approx} 2000; the spectra can be retrieved from the public database using the information provided in the catalog. A total of 44,221 objects in the catalog were discovered by the SDSS; 28,400 of the SDSS discoveries are reported here for the first time.

  2. NuSTAR Observations of Heavily Obscured Quasars at z Is Approximately 0.5

    NASA Technical Reports Server (NTRS)

    Lansbury, G. B.; Alexander, D. M.; Del Moro, A.; Gandhi, P.; Assef, R. J.; Stern, D.; Aird, J.; Ballantyne, D. R.; Balokovic, M.; Bauer, F. E.; Boggs, S. E.; Brandt, W. N.; Christensen, F. E.; Craig, W. W.; Elvis, M.; Grefenstette, B. W.; Hailey, C. J.; Harrison, F. A.; Hickox, R. C.; Koss, M.; LaMassa, S. M.; Luo, B.; Mullaney, J. R.; Teng, S. H.; Urry, C. M.; Zhang, W. W.

    2014-01-01

    We present NuSTAR hard X-ray observations of three Type 2 quasars at z approx. = 0.4-0.5, optically selected from the Sloan Digital Sky Survey. Although the quasars show evidence for being heavily obscured, Compton-thick systems on the basis of the 2-10 keV to [O(sub III)] luminosity ratio and multiwavelength diagnostics, their X-ray absorbing column densities (N(sub H)) are poorly known. In this analysis, (1) we study X-ray emission at greater than 10 keV, where X-rays from the central black hole are relatively unabsorbed, in order to better constrain N(sub H). (2) We further characterize the physical properties of the sources through broad-band near-UV to mid-IR spectral energy distribution analyses. One of the quasars is detected with NuSTAR at greater than 8 keV with a no-source probability of less than 0.1%, and its X-ray band ratio suggests near Compton-thick absorption with N(sub H) is approximately greater than 5 × 10(exp 23) cm(exp -2). The other two quasars are undetected, and have low X-ray to mid-IR luminosity ratios in both the low-energy (2-10 keV) and high-energy (10-40 keV) X-ray regimes that are consistent with extreme, Compton-thick absorption (N(sub H) is approximately greater than 10(exp 24) cm(exp -2)). We find that for quasars at z is approximately 0.5, NuSTAR provides a significant improvement compared to lower energy (less than 10 keV) Chandra and XMM-Newton observations alone, as higher column densities can now be directly constrained.

  3. The optical, ultraviolet, and X-ray structure of the quasar HE 0435–1223

    SciTech Connect

    Blackburne, Jeffrey A.; Kochanek, Christopher S.; Chen, Bin; Dai, Xinyu; Chartas, George

    2014-07-10

    Microlensing has proved an effective probe of the structure of the innermost regions of quasars and an important test of accretion disk models. We present light curves of the lensed quasar HE 0435–1223 in the R band and in the ultraviolet (UV), and consider them together with X-ray light curves in two energy bands that are presented in a companion paper. Using a Bayesian Monte Carlo method, we constrain the size of the accretion disk in the rest-frame near- and far-UV, and constrain for the first time the size of the X-ray emission regions in two X-ray energy bands. The R-band scale size of the accretion disk is about 10{sup 15.23} cm (∼23r{sub g}), slightly smaller than previous estimates, but larger than would be predicted from the quasar flux. In the UV, the source size is weakly constrained, with a strong prior dependence. The UV to R-band size ratio is consistent with the thin disk model prediction, with large error bars. In soft and hard X-rays, the source size is smaller than ∼10{sup 14.8} cm (∼10r{sub g} ) at 95% confidence. We do not find evidence of structure in the X-ray emission region, as the most likely value for the ratio of the hard X-ray size to the soft X-ray size is unity. Finally, we find that the most likely value for the mean mass of stars in the lens galaxy is ∼0.3 M{sub ☉}, consistent with other studies.

  4. Hunting for Intrinsically X-ray Weak Quasars: The Case of PHL 1811 Analogs

    NASA Astrophysics Data System (ADS)

    Brandt, William

    2009-09-01

    A central dogma of X-ray astronomy is that luminous X-ray emission is a universal property of efficiently accreting supermassive black holes. One interesting challenge to this idea has come from the quasar PHL 1811 which appears to be intrinsically X-ray weak and also has distinctive emission-line properties. We propose to observe a sample of eight SDSS quasars, selected to have similar UV emission-line properties to that of PHL 1811, to test if they are also X-ray weak. Our analyses of the currently available X-ray data appear to support this hypothesis but do not provide a proper test. Our results will have implications for the nature of accretion-disk coronae, emission-line formation, and AGN selection.

  5. Bayesian network learning for natural hazard analyses

    NASA Astrophysics Data System (ADS)

    Vogel, K.; Riggelsen, C.; Korup, O.; Scherbaum, F.

    2014-09-01

    Modern natural hazards research requires dealing with several uncertainties that arise from limited process knowledge, measurement errors, censored and incomplete observations, and the intrinsic randomness of the governing processes. Nevertheless, deterministic analyses are still widely used in quantitative hazard assessments despite the pitfall of misestimating the hazard and any ensuing risks. In this paper we show that Bayesian networks offer a flexible framework for capturing and expressing a broad range of uncertainties encountered in natural hazard assessments. Although Bayesian networks are well studied in theory, their application to real-world data is far from straightforward, and requires specific tailoring and adaptation of existing algorithms. We offer suggestions as how to tackle frequently arising problems in this context and mainly concentrate on the handling of continuous variables, incomplete data sets, and the interaction of both. By way of three case studies from earthquake, flood, and landslide research, we demonstrate the method of data-driven Bayesian network learning, and showcase the flexibility, applicability, and benefits of this approach. Our results offer fresh and partly counterintuitive insights into well-studied multivariate problems of earthquake-induced ground motion prediction, accurate flood damage quantification, and spatially explicit landslide prediction at the regional scale. In particular, we highlight how Bayesian networks help to express information flow and independence assumptions between candidate predictors. Such knowledge is pivotal in providing scientists and decision makers with well-informed strategies for selecting adequate predictor variables for quantitative natural hazard assessments.

  6. Multi-wavelength Monitoring of Lensed Quasars: Deciphering Quasar Structure at Micro-arcseconds Scales

    NASA Astrophysics Data System (ADS)

    Mosquera, Ana; Morgan, Christopher W.; Kochanek, Christopher S.; Dai, Xinyu; Chen, Bin; MacLeod, Chelsea Louise; Chartas, George

    2016-01-01

    Microlensing in multiply imaged gravitationally lensed quasars provides us with a unique tool to zoom in on the structure of AGN and explore their physics in more detail. Microlensing magnification, caused primarily by stars and white dwarfs close to the line of sight towards the lensed quasar images, is seen as uncorrelated flux variations due to the relative motions of the quasar, the lens, its stars, and the observer, and it depends on the structural and dynamical properties of the source and the lens. Since the magnification depends upon the size of the source, we can use microlensing to measure the size of quasar emission regions. In essence, the amplitude of the microlensing variability encodes the source size, with smaller sources showing larger variability amplitudes. Using state of the art microlensing techniques, our team has performed pioneering research in the field based on multi-wavelength space and ground-based observations. Among the most remarkable results, using Chandra observations we have set the first quantitative constraints on the sizes of the X-ray emission regions of quasars. In this work l briefly describe the methodology, the results from our previous multi-wavelength monitoring programs, and the next frontier of exploring the dependence of the structure of the X-ray emission regions on black hole mass and X-ray energy.

  7. The UV-bright Quasar Survey (UVQS): DR1

    NASA Astrophysics Data System (ADS)

    Monroe, TalaWanda R.; Prochaska, J. Xavier; Tejos, Nicolas; Worseck, Gabor; Hennawi, Joseph F.; Schmidt, Tobias; Tumlinson, Jason; Shen, Yue

    2016-07-01

    We present the first data release (DR1) from our UV-bright Quasar Survey for new z ˜ 1 active galactic nuclei (AGNs) across the sky. Using simple GALEX UV and WISE near-IR color selection criteria, we generated a list of 1450 primary candidates with FUV < 18.5 mag. We obtained discovery spectra, primarily on 3 m-class telescopes, for 1040 of these candidates and confirmed 86% as AGNs, with redshifts generally at z > 0.5. Including a small set of observed secondary candidates, we report the discovery of 217 AGNs with FUV < 18 mag that previously had no reported spectroscopic redshift. These are excellent potential targets for UV spectroscopy before the end of the Hubble Space Telescope mission. The main data products are publicly available through the Mikulski Archive for Space Telescopes.

  8. SDSS J1029+2623: A Gravitationally Lensed Quasar with an Image Separation of 22.5 Arcseconds

    SciTech Connect

    Inada, Naohisa; Oguri, Masamune; Morokuma, Tomoki; Doi, Mamoru; Yasuda, Naoki; Becker, Robert H.; Richards, Gordon T.; Kochanek, Christopher S.; Kayo, Issha; Konishi, Kohki; Utsunomiya, Hiroyuki; Shin, Min-Su; Strauss, Michael A.; Sheldon, Erin S.; York, Donald G.; Hennawi, Joseph F.; Schneider, Donald P.; Dai, Xinyu; Fukugita, Masataka; /Tokyo U., Inst. Astron. /JSPS, Tokyo /KIPAC, Menlo Park /Princeton U. Observ. /Tokyo U., ICRR /LLNL, Livermore /UC, Davis /Drexel U. /Johns Hopkins U. /Ohio State U., Dept. Astron. /Nagoya U. /CCPP, New York /Chicago U., Astron. Astrophys. Ctr. /Chicago U., EFI /UC, Berkeley, Astron. Dept. /Penn State U., Astron. Astrophys.

    2006-11-15

    The authors report the discovery of a cluster-scale lensed quasar, SDSS J1029+2623, selected from the Sloan Digital Sky Survey. The lens system exhibits two lensed images of a quasar at z{sub s} = 2.197. The image separation of 22.5 makes it the largest separation lensed quasar discovered to date. The similarity of the optical spectra and the radio loudnesses of the two components support the lensing hypothesis. Images of the field show a cluster of galaxies at z{sub l} {approx} 0.55 that is responsible for the large image separation. The lensed images and the cluster light center are not collinear, which implies that the lensing cluster has a complex structure.

  9. Quantum Bayesian implementation

    NASA Astrophysics Data System (ADS)

    Wu, Haoyang

    2013-02-01

    Mechanism design is a reverse problem of game theory. Nash implementation and Bayesian implementation are two important parts of mechanism design theory. The former one corresponds to a setting with complete information, whereas the latter one corresponds to a setting with incomplete information. A recent work Wu (Int J Quantum Inf 9:615-623, 2011) shows that when an additional condition is satisfied, the traditional sufficient conditions for Nash implementation will fail in a quantum domain. Inspired by this work, in this paper we will propose that the traditional sufficient conditions for Bayesian implementation will also fail if agents use quantum strategies to send messages to the designer through channels (e.g., Internet, cable etc) and two additional conditions are satisfied.

  10. Hierarchical Approximate Bayesian Computation

    PubMed Central

    Turner, Brandon M.; Van Zandt, Trisha

    2013-01-01

    Approximate Bayesian computation (ABC) is a powerful technique for estimating the posterior distribution of a model’s parameters. It is especially important when the model to be fit has no explicit likelihood function, which happens for computational (or simulation-based) models such as those that are popular in cognitive neuroscience and other areas in psychology. However, ABC is usually applied only to models with few parameters. Extending ABC to hierarchical models has been difficult because high-dimensional hierarchical models add computational complexity that conventional ABC cannot accommodate. In this paper we summarize some current approaches for performing hierarchical ABC and introduce a new algorithm called Gibbs ABC. This new algorithm incorporates well-known Bayesian techniques to improve the accuracy and efficiency of the ABC approach for estimation of hierarchical models. We then use the Gibbs ABC algorithm to estimate the parameters of two models of signal detection, one with and one without a tractable likelihood function. PMID:24297436

  11. Maximum entropy and Bayesian methods. Proceedings.

    NASA Astrophysics Data System (ADS)

    Grandy, W. T., Jr.; Schick, L. H.

    This volume contains a selection of papers presented at the Tenth Annual Workshop on Maximum Entropy and Bayesian Methods. The thirty-six papers included cover a wide range of applications in areas such as economics and econometrics, astronomy and astrophysics, general physics, complex systems, image reconstruction, and probability and mathematics. Together they give an excellent state-of-the-art overview of fundamental methods of data analysis.

  12. Quasars in the MAMBO blank field survey

    NASA Astrophysics Data System (ADS)

    Voss, H.; Bertoldi, F.; Carilli, C.; Owen, F. N.; Lutz, D.; Holdaway, M.; Ledlow, M.; Menten, K. M.

    2006-03-01

    Our MAMBO 1.2 mm blank field imaging survey of ~0.75 sqd has uncovered four unusually bright sources, with flux densities between 10 and 90 mJy, all located in the Abell 2125 field. The three brightest are flat spectrum radio sources with bright optical and X-ray counterparts. Their mm and radio flux densities are variable on timescales of months. Their X-ray luminosities classify them as quasars. The faintest of the four mm bright sources appears to be a bright, radio-quiet starburst at z˜3, similar to the sources seen at lower flux densities in the MAMBO and SCUBA surveys. It may also host a mildly obscured AGN of quasar-like X-ray luminosity. The three non-thermal mm sources imply an areal density of flat spectrum radio sources higher by at least 7 compared with that expected from an extrapolation of the lower frequency radio number counts.

  13. The evolution of the quasar continuum

    NASA Technical Reports Server (NTRS)

    Elvis, M.

    1992-01-01

    We now have in hand a large data base of Roentgen Satellite (ROSAT), optical, and IR complementary data. We are in the process of obtaining a large amount of the International Ultraviolet Explorer (IUE) data for the same quasar sample. For our complementary sample at high redshifts, where the UV was redshifted into the optical, we have just had approved large amounts of observing time to cover the quasar continuum in the near-IR using the new Near-Infrared Camera and Multi-Object Spectrometer (NICMOS) array spectrographs. Ten micron, optical, and VLA radio, data also have approved time. An ISO US key program was approved to extend this work into the far-IR, and the launch of ASTRO-D (early in 1993) promises to extend it to higher energy X-rays.

  14. Microlensing of quasar ultraviolet iron emission

    SciTech Connect

    Guerras, E.; Mediavilla, E.; Kochanek, C. S.; Muñoz, J. A.; Falco, E.; Motta, V.; Rojas, K.

    2013-12-01

    We measure the differential microlensing of the UV Fe II and Fe III emission line blends between 14 quasar image pairs in 13 gravitational lenses. We find that the UV iron emission is strongly microlensed in four cases with amplitudes comparable to that of the continuum. Statistically modeling the magnifications, we infer a typical size of r{sub s}∼4√(M/M{sub ⊙}) light-days for the Fe line-emitting regions, which is comparable to the size of the region generating the UV continuum (∼3-7 light-days). This may indicate that a significant part of the UV Fe II and Fe III emission originates in the quasar accretion disk.

  15. Efficient Bayesian Phase Estimation.

    PubMed

    Wiebe, Nathan; Granade, Chris

    2016-07-01

    We introduce a new method called rejection filtering that we use to perform adaptive Bayesian phase estimation. Our approach has several advantages: it is classically efficient, easy to implement, achieves Heisenberg limited scaling, resists depolarizing noise, tracks time-dependent eigenstates, recovers from failures, and can be run on a field programmable gate array. It also outperforms existing iterative phase estimation algorithms such as Kitaev's method. PMID:27419551

  16. Experimental adaptive Bayesian tomography

    NASA Astrophysics Data System (ADS)

    Kravtsov, K. S.; Straupe, S. S.; Radchenko, I. V.; Houlsby, N. M. T.; Huszár, F.; Kulik, S. P.

    2013-06-01

    We report an experimental realization of an adaptive quantum state tomography protocol. Our method takes advantage of a Bayesian approach to statistical inference and is naturally tailored for adaptive strategies. For pure states, we observe close to N-1 scaling of infidelity with overall number of registered events, while the best nonadaptive protocols allow for N-1/2 scaling only. Experiments are performed for polarization qubits, but the approach is readily adapted to any dimension.

  17. Efficient Bayesian Phase Estimation

    NASA Astrophysics Data System (ADS)

    Wiebe, Nathan; Granade, Chris

    2016-07-01

    We introduce a new method called rejection filtering that we use to perform adaptive Bayesian phase estimation. Our approach has several advantages: it is classically efficient, easy to implement, achieves Heisenberg limited scaling, resists depolarizing noise, tracks time-dependent eigenstates, recovers from failures, and can be run on a field programmable gate array. It also outperforms existing iterative phase estimation algorithms such as Kitaev's method.

  18. Bayesian Attractor Learning

    NASA Astrophysics Data System (ADS)

    Wiegerinck, Wim; Schoenaker, Christiaan; Duane, Gregory

    2016-04-01

    Recently, methods for model fusion by dynamically combining model components in an interactive ensemble have been proposed. In these proposals, fusion parameters have to be learned from data. One can view these systems as parametrized dynamical systems. We address the question of learnability of dynamical systems with respect to both short term (vector field) and long term (attractor) behavior. In particular we are interested in learning in the imperfect model class setting, in which the ground truth has a higher complexity than the models, e.g. due to unresolved scales. We take a Bayesian point of view and we define a joint log-likelihood that consists of two terms, one is the vector field error and the other is the attractor error, for which we take the L1 distance between the stationary distributions of the model and the assumed ground truth. In the context of linear models (like so-called weighted supermodels), and assuming a Gaussian error model in the vector fields, vector field learning leads to a tractable Gaussian solution. This solution can then be used as a prior for the next step, Bayesian attractor learning, in which the attractor error is used as a log-likelihood term. Bayesian attractor learning is implemented by elliptical slice sampling, a sampling method for systems with a Gaussian prior and a non Gaussian likelihood. Simulations with a partially observed driven Lorenz 63 system illustrate the approach.

  19. Integrated Bayesian Experimental Design

    NASA Astrophysics Data System (ADS)

    Fischer, R.; Dreier, H.; Dinklage, A.; Kurzan, B.; Pasch, E.

    2005-11-01

    Any scientist planning experiments wants to optimize the design of a future experiment with respect to best performance within the scheduled experimental scenarios. Bayesian Experimental Design (BED) aims in finding optimal experimental settings based on an information theoretic utility function. Optimal design parameters are found by maximizing an expected utility function where the future data and the parameters of physical scenarios of interest are marginalized. The goal of the Integrated Bayesian Experimental Design (IBED) concept is to combine experiments as early as on the design phase to mutually exploit the benefits of the other experiments. The Bayesian Integrated Data Analysis (IDA) concept of linking interdependent measurements to provide a validated data base and to exploit synergetic effects will be used to design meta-diagnostics. An example is given by the Thomson scattering (TS) and the interferometry (IF) diagnostics individually, and a set of both. In finding the optimal experimental design for the meta-diagnostic, TS and IF, the strengths of both experiments can be combined to synergistically increase the reliability of results.

  20. Inverse compton effect: some consequences for quasars.

    PubMed

    Pfleiderer, J; Grewing, M

    1966-12-16

    The inverse Compton effect can transform enough energy of relativistic electrons into radiation so that an upper limit to the mean energy of the electrons is set. In quasars, the limit is too small to allow the production of any appreciable amount of synchrotron or inverse Compton radiation, unless either the distances are not cosmological or the lifetimes of the relativistic electrons are extremely short, of the order of hours.

  1. Photometric Monitoring of Quasars with Kepler

    NASA Astrophysics Data System (ADS)

    Unwin, Stephen C.; Wehrle, A. E.; Wiita, P. J.; Revalski, M.; Silano, D.; Sprague, D.; Di Lorenzo, P.

    2013-01-01

    We have observed the photometric variability of four flat-spectrum radio quasars, and one radio galaxy (Cyg A) with Kepler, since mid-2010. Kepler’s ability to observe uninterrupted for very extended durations provides a unique opportunity to obtain very long time sequences on active galactic nuclei, something that is hard to do even with dedicated ground-based telescope networks. It allows us to examine these light curves for variability on timescales from hours to weeks, and to probe the physical processes involved in accretion around the central black hole and the organization of some of that energy into jets that ultimately power double-lobed radio sources. Kepler was designed to detect exoplanet transits of stars, and the data analysis pipeline is highly optimized for that purpose. We cannot use the standard analysis tools for the quasi-random variability in quasars, so we re-analysed the raw data, and overcame some of the challenges in calibrating these light curves. We briefly discuss some of the issues in producing calibrated light curves for long timescales. For each quasar we computed power spectra, and found power-law slopes of around -2 for most. Although sensitive to quasi-periodic variations, we did not find any convincing evidence for periodicity in any of our targets. This research was carried out, in part, at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. Copyright 2012. California Institute of Technology. Government sponsorship acknowledged.

  2. Monitoring Emergent Absorption Troughs in Quasars

    NASA Astrophysics Data System (ADS)

    Hall, Patrick; Rodriguez Hidalgo, Paola; Brandt, W. Niel; Rogerson, Jesse; Filiz Ak, Nur; Chajet, Laura

    2014-02-01

    Outflows from luminous AGN are important ingredients in galaxy formation. These outflows manifest as broad absorption line (BAL) troughs in quasar spectra. Trough variability can be used to constrain the physical parameters of these absorbing structures through comparison to models and simulations of accretion disk winds. Monitoring appearing/disappearing BAL troughs can constrain the distribution of BAL trough lifetimes along our line of sight. By comparing spectra from the SDSS Data Release (DR) 7 and DR 9, we identified 68 quasars in whose spectra new absorption troughs have appeared over 300-1200 restframe days, including one trough outflowing at v=60,000 km/s. We propose to complete our third-epoch GMOS spectroscopy of the brightest of those quasars (48 in 2013AB and 9 proposed here) to measure the absorption strength in newly appeared troughs <=365 restframe days after their previous measurement. Preliminary 2013AB results indicate that troughs are not on average still strengthening between SDSS and Gemini epochs; we therefore propose observations of 40 targets to probe shorter rest-frame time separations. We also target 8 objects showing simultaneous absorption variations in multiple ionization states, to help develop methods to distinguish absorption variations from cloud motion vs. those from ionization changes within clouds.

  3. The optical variability of SDSS quasars from multi-epoch spectroscopy. I. Results from 60 quasars with ≥ six-epoch spectra

    SciTech Connect

    Guo, Hengxiao; Gu, Minfeng E-mail: gumf@shao.ac.cn

    2014-09-01

    In a sample of 60 quasars selected from the Sloan Digital Sky Survey with at least six-epoch spectroscopy, we investigate the variability of emission lines and continuum luminosity at various aspects. A strong anti-correlation between the variability and continuum luminosity at 2500 Å is found for the sample, which is consistent with previous works. In individual sources, we find that half of the sample objects follow the trend of being bluer when brighter, while the remaining half follow the redder-when-brighter (RWB) trend. Although the mechanism for RWB is unclear, the effects of host galaxy contribution due to seeing variations cannot be completely ruled out. As expected from the photoionization model, the positive correlations between the broad emission line and continuum luminosity are found in most individual sources, as well as for the whole sample. We confirm the Baldwin effect in most individual objects and the whole sample, while a negative Baldwin effect is also found in several quasars, which can be at least partly (if not all) due to the host galaxy contamination. We find positive correlations between the broad emission line luminosity and line width in most individual quasars, as well as the whole sample, implying a line base that is more variable than the line core.

  4. The Sloan Digital Sky Survey Quasar Lens Search. III Constraints on Dark Energy From The Third Data Release Quasar Lens Catalog

    SciTech Connect

    Oguri, M; Inada, N; Strauss, M A; Kochanek, C S; Richards, G T; Schneider, D P; Becker, R H; Fukugita, M; Gregg, M D; Hall, P B; Hennawi, J F; Johnston, D E; Kayo, I; Keeton, C R; Pindor, B; Shin, M; Turner, E; White, R L; York, D G; Anderson, S F; Bahcall, N A; Brunner, R J; Burles, S; Castander, F J; Chiu, K; Clocchiatti, A; Einsenstein, D; Frieman, J; Kawano, Y; Lupton, R; Morokuma, T; Rix, H; Scranton, R; Sheldon, E S

    2007-09-12

    We present cosmological results from the statistics of lensed quasars in the Sloan Digital Sky Survey (SDSS) Quasar Lens Search. By taking proper account of the selection function, we compute the expected number of quasars lensed by early-type galaxies and their image separation distribution assuming a flat universe, which is then compared with 7 lenses found in the SDSS Data Release 3 to derive constraints on dark energy under strictly controlled criteria. For a cosmological constant model (w = -1) we obtain {Omega}{sub {Lambda}} = 0.74{sub -0.15}{sup +0.11}(stat.){sub -0.06}{sup +0.13}(syst.). Allowing w to be a free parameter we find {Omega}{sub M} = 0.26{sub -0.06}{sup +0.07}(stat.){sub -0.05}{sup +0.03}(syst.) and w = -1.1 {+-} 0.6(stat.){sub -0.5}{sup +0.3}(syst.) when combined with the constraint from the measurement of baryon acoustic oscillations in the SDSS luminous red galaxy sample. Our results are in good agreement with earlier lensing constraints obtained using radio lenses, and provide additional confirmation of the presence of dark energy consistent with a cosmological constant, derived independently of type Ia supernovae.

  5. Computational statistics using the Bayesian Inference Engine

    NASA Astrophysics Data System (ADS)

    Weinberg, Martin D.

    2013-09-01

    This paper introduces the Bayesian Inference Engine (BIE), a general parallel, optimized software package for parameter inference and model selection. This package is motivated by the analysis needs of modern astronomical surveys and the need to organize and reuse expensive derived data. The BIE is the first platform for computational statistics designed explicitly to enable Bayesian update and model comparison for astronomical problems. Bayesian update is based on the representation of high-dimensional posterior distributions using metric-ball-tree based kernel density estimation. Among its algorithmic offerings, the BIE emphasizes hybrid tempered Markov chain Monte Carlo schemes that robustly sample multimodal posterior distributions in high-dimensional parameter spaces. Moreover, the BIE implements a full persistence or serialization system that stores the full byte-level image of the running inference and previously characterized posterior distributions for later use. Two new algorithms to compute the marginal likelihood from the posterior distribution, developed for and implemented in the BIE, enable model comparison for complex models and data sets. Finally, the BIE was designed to be a collaborative platform for applying Bayesian methodology to astronomy. It includes an extensible object-oriented and easily extended framework that implements every aspect of the Bayesian inference. By providing a variety of statistical algorithms for all phases of the inference problem, a scientist may explore a variety of approaches with a single model and data implementation. Additional technical details and download details are available from http://www.astro.umass.edu/bie. The BIE is distributed under the GNU General Public License.

  6. Helium Reionization Simulations. I. Modeling Quasars as Radiation Sources

    NASA Astrophysics Data System (ADS)

    La Plante, Paul; Trac, Hy

    2016-09-01

    We introduce a new project to understand helium reionization using fully coupled N-body, hydrodynamics, and radiative transfer simulations. This project aims to capture correctly the thermal history of the intergalactic medium as a result of reionization and make predictions about the Lyα forest and baryon temperature-density relation. The dominant sources of radiation for this transition are quasars, so modeling the source population accurately is very important for making reliable predictions. In this first paper, we present a new method for populating dark matter halos with quasars. Our set of quasar models includes two different light curves, a lightbulb (simple on/off) and symmetric exponential model, and luminosity-dependent quasar lifetimes. Our method self-consistently reproduces an input quasar luminosity function given a halo catalog from an N-body simulation, and propagates quasars through the merger history of halo hosts. After calibrating quasar clustering using measurements from the Baryon Oscillation Spectroscopic Survey, we find that the characteristic mass of quasar hosts is {M}h˜ 2.5× {10}12 {h}-1 {M}⊙ for the lightbulb model, and {M}h˜ 2.3× {10}12 {h}-1 {M}⊙ for the exponential model. In the latter model, the peak quasar luminosity for a given halo mass is larger than that in the former, typically by a factor of 1.5-2. The effective lifetime for quasars in the lightbulb model is 59 Myr, and in the exponential case, the effective time constant is about 15 Myr. We include semi-analytic calculations of helium reionization, and discuss how to include these quasars as sources of ionizing radiation for full hydrodynamics with radiative transfer simulations in order to study helium reionization.

  7. Seeking the epoch of maximum luminosity for dusty quasars

    SciTech Connect

    Vardanyan, Valeri; Weedman, Daniel; Sargsyan, Lusine E-mail: dweedman@isc.astro.cornell.edu

    2014-08-01

    Infrared luminosities νL{sub ν}(7.8 μm) arising from dust reradiation are determined for Sloan Digital Sky Survey (SDSS) quasars with 1.4 quasar Gpc{sup –3} having νL{sub ν}(7.8 μm) > 10{sup 46.6} erg s{sup –1} for all 2 quasars first reached their maximum luminosity has not yet been identified at any redshift below 5. The most ultraviolet luminous quasars, defined by rest frame νL{sub ν}(0.25 μm), have the largest values of the ratio νL{sub ν}(0.25 μm)/νL{sub ν}(7.8 μm) with a maximum ratio at z = 2.9. From these results, we conclude that the quasars most luminous in the ultraviolet have the smallest dust content and appear luminous primarily because of lessened extinction. Observed ultraviolet/infrared luminosity ratios are used to define 'obscured' quasars as those having >5 mag of ultraviolet extinction. We present a new summary of obscured quasars discovered with the Spitzer Infrared Spectrograph and determine the infrared luminosity function of these obscured quasars at z ∼ 2.1. This is compared with infrared luminosity functions of optically discovered, unobscured quasars in the SDSS and in the AGN and Galaxy Evolution Survey. The comparison indicates comparable numbers of obscured and unobscured quasars at z ∼ 2.1 with a possible excess of obscured quasars at fainter luminosities.

  8. A Study of PG Quasar-Driven Outflows with COS

    NASA Astrophysics Data System (ADS)

    Hamann, Frederick

    2013-10-01

    Quasar outflows are an important part of the quasar phenomenon, but many questions remain about their energetics, physical properties and the role they might play in providing feedback to host galaxy evolution. We searched our own COS far-UV observations from the QUEST survey and other large COS programs to find a sample of 6 bright PG quasars with broad {FWHM > 400 km/s} high velocity {v > 1000 km/s} absorption lines that clearly form in quasar-driven winds. These quasars can fill an important gap in our understanding between local Seyferts with low-speed winds and high-redshift quasars with extreme BAL outflows. They are also well-studied at other wavelengths, with some evidence for the quasars driving galaxy-scale blowouts and shutting down star formation. But almost nothing is known about the quasar outflows themselves. We propose a detailed study of these 6 outflow quasars using new COS FUV observations to 1} expand the existing wavelength coverage across critical lines that are diagnostic of the outflow physical conditions, kinetic energies, and metallicities, and 2} check for line variability as an indicator of the outflow structure and locations. This quasar sample includes unusual cases with many low-abundance {PV 1118,1128 and SIV 1063} and excited-state lines {SIV 1073*, CIII* 1175, CII* 1335} that will provide unprecedented constraints on the outflow properties, plus the first known OVI-only mini-BAL outflow {no lower ions detected} for which we will cover NeVIII 770,780 to probe the highest ionization gas. The high FUV sensitivity of COS is uniquely able to measure this wide range of outflow lines in low-redshift quasars with no Lya forest contamination.

  9. Seeking the Epoch of Maximum Luminosity for Dusty Quasars

    NASA Astrophysics Data System (ADS)

    Vardanyan, Valeri; Weedman, Daniel; Sargsyan, Lusine

    2014-08-01

    Infrared luminosities νL ν(7.8 μm) arising from dust reradiation are determined for Sloan Digital Sky Survey (SDSS) quasars with 1.4 ~ 3 with maximum luminosity νL ν(7.8 μm) >~ 1047 erg s-1 luminosity functions show one quasar Gpc-3 having νL ν(7.8 μm) > 1046.6 erg s-1 for all 2 quasars first reached their maximum luminosity has not yet been identified at any redshift below 5. The most ultraviolet luminous quasars, defined by rest frame νL ν(0.25 μm), have the largest values of the ratio νL ν(0.25 μm)/νL ν(7.8 μm) with a maximum ratio at z = 2.9. From these results, we conclude that the quasars most luminous in the ultraviolet have the smallest dust content and appear luminous primarily because of lessened extinction. Observed ultraviolet/infrared luminosity ratios are used to define "obscured" quasars as those having >5 mag of ultraviolet extinction. We present a new summary of obscured quasars discovered with the Spitzer Infrared Spectrograph and determine the infrared luminosity function of these obscured quasars at z ~ 2.1. This is compared with infrared luminosity functions of optically discovered, unobscured quasars in the SDSS and in the AGN and Galaxy Evolution Survey. The comparison indicates comparable numbers of obscured and unobscured quasars at z ~ 2.1 with a possible excess of obscured quasars at fainter luminosities.

  10. Helium Reionization Simulations. I. Modeling Quasars as Radiation Sources

    NASA Astrophysics Data System (ADS)

    La Plante, Paul; Trac, Hy

    2016-09-01

    We introduce a new project to understand helium reionization using fully coupled N-body, hydrodynamics, and radiative transfer simulations. This project aims to capture correctly the thermal history of the intergalactic medium as a result of reionization and make predictions about the Lyα forest and baryon temperature–density relation. The dominant sources of radiation for this transition are quasars, so modeling the source population accurately is very important for making reliable predictions. In this first paper, we present a new method for populating dark matter halos with quasars. Our set of quasar models includes two different light curves, a lightbulb (simple on/off) and symmetric exponential model, and luminosity-dependent quasar lifetimes. Our method self-consistently reproduces an input quasar luminosity function given a halo catalog from an N-body simulation, and propagates quasars through the merger history of halo hosts. After calibrating quasar clustering using measurements from the Baryon Oscillation Spectroscopic Survey, we find that the characteristic mass of quasar hosts is {M}h∼ 2.5× {10}12 {h}-1 {M}ȯ for the lightbulb model, and {M}h∼ 2.3× {10}12 {h}-1 {M}ȯ for the exponential model. In the latter model, the peak quasar luminosity for a given halo mass is larger than that in the former, typically by a factor of 1.5–2. The effective lifetime for quasars in the lightbulb model is 59 Myr, and in the exponential case, the effective time constant is about 15 Myr. We include semi-analytic calculations of helium reionization, and discuss how to include these quasars as sources of ionizing radiation for full hydrodynamics with radiative transfer simulations in order to study helium reionization.

  11. A QUASAR CATALOG WITH SIMULTANEOUS UV, OPTICAL, AND X-RAY OBSERVATIONS BY SWIFT

    SciTech Connect

    Wu Jian; Grupe, Dirk; Koch, Scott; Gelbord, Jonathan; Schneider, Donald P.; Gronwall, Caryl; Porterfield, Blair L.; Vanden Berk, Daniel; Wesolowski, Sarah

    2012-08-01

    We have compiled a catalog of optically selected quasars with simultaneous observations in UV/optical and X-ray bands by the Swift Gamma-ray Burst Explorer. Objects in this catalog are identified by matching the Swift pointings with the Sloan Digital Sky Survey Data Release 5 quasar catalog. The final catalog contains 843 objects, among which 637 have both Ultraviolet Optical Telescope (UVOT) and X-Ray Telescope (XRT) observations and 354 of which are detected by both instruments. The overall X-ray detection rate is {approx}60% which rises to {approx}85% among sources with at least 10 ks of XRT exposure time. We construct the time-averaged spectral energy distribution (SED) for each of the 354 quasars using UVOT photometric measurements and XRT spectra. From model fits to these SEDs, we find that the big blue bump contributes about {approx}0.3 dex to the quasar luminosity. We re-visit the {alpha}{sub ox}-L{sub 2500A} relation by selecting a clean sample with only Type 1 radio-quiet quasars; the dispersion of this relation is reduced by at least 15% compared with studies that use non-simultaneous UV/optical and X-ray data. We only found a weak correlation between L{sub bol}/L{sub Edd} and {alpha}{sub UV}. We do not find significant correlations between {alpha}{sub x} and {alpha}{sub ox}, {alpha}{sub ox} and {alpha}{sub UV}, and {alpha}{sub x} and log L(0.3-10 keV). The correlations between {alpha}{sub UV} and {alpha}{sub x}, {alpha}{sub ox} and {alpha}{sub x}, {alpha}{sub ox} and {alpha}{sub UV}, L{sub bol}/L{sub Edd} and {alpha}{sub x}, and L{sub bol}/L{sub Edd} and {alpha}{sub ox} are stronger among low-redshift quasars, indicating that these correlations are likely driven by the changes of SED shape with accretion state.

  12. Spectroscopic CCD surveys for quasars at large redshift. I - A deep PFUEI survey. [Prime Focus Universal Extragalactic Instrument

    NASA Technical Reports Server (NTRS)

    Schmidt, M.; Schneider, D. P.; Gunn, J. E.

    1986-01-01

    A survey for faint quasars has been conducted using slitless spectroscopy with the PFUEI at the 200 inch (5 m) telescope. The survey covers a total of 0.91 sq deg in 113 fields at galactic latitudes above 30 deg. Calibrated spectra in the range 4500-7200 A were obtained for more than 9000 objects. Emission-line candidates were selected on the basis of two criteria: the equivalent width must exceed 50 A, and the signal-to-noise ratio of the detection of the line versus the sky background should be larger than 7. Among 45 candidates so selected, subsequent slit spectroscopy confirmed 27 emission-line objects. Among these, 17 are emission-line galaxies with redshifts in the range 0.04-0.31, and 10 are quasars with redshifts between 0.91 and 2.66. The well-defined selection criteria for these objects, together with the distribution of rest frame equivalent widths of the emission lines, allow derivation of the area of sky covered as a function of the continuum limiting magnitude. The observed number of quasars in the redshift range 0.7-2.7 agrees well with that predicted by the luminosity function models published by Schmidt and Green in 1983. It is concluded that quasars with an absolute magnitude of M(B) = -25 suffer a redshift cutoff near or below a redshift of 3.

  13. X-RAY AND OPTICAL FLUX RATIO ANOMALIES IN QUADRUPLY LENSED QUASARS. II. MAPPING THE DARK MATTER CONTENT IN ELLIPTICAL GALAXIES

    SciTech Connect

    Pooley, David; Rappaport, Saul; Schechter, Paul L.; Blackburne, Jeffrey A.; Wambsganss, Joachim

    2012-01-10

    We present a microlensing analysis of 61 Chandra observations of 14 quadruply lensed quasars. X-ray flux measurements of the individual quasar images give a clean determination of the microlensing effects in the lensing galaxy and thus offer a direct assessment of the local fraction of stellar matter making up the total integrated mass along the lines of sight through the lensing galaxy. A Bayesian analysis of the ensemble of lensing galaxies gives a most likely local stellar fraction of 7%, with the other 93% in a smooth, dark matter component, at a mean impact parameter R{sub c} of 6.6 kpc from the center of the lensing galaxy. We divide the systems into smaller ensembles based on R{sub c} and find that the most likely local stellar fraction varies qualitatively and quantitatively as expected, decreasing as a function of R{sub c} .

  14. The LAMOST survey of background quasars in the vicinity of the Andromeda and Triangulum galaxies. II. Results from the commissioning observations and the pilot surveys

    SciTech Connect

    Huo, Zhi-Ying; Bai, Zhong-Rui; Chen, Jian-Jun; Chen, Xiao-Yan; Du, Bing; Jia, Lei; Lei, Ya-Juan; Liu, Xiao-Wei; Yuan, Hai-Bo; Xiang, Mao-Sheng; Huang, Yang; Zhang, Hui-Hua; Yan, Lin; Chu, Jia-Ru; Chu, Yao-Quan; Hu, Hong-Zhuan; Cui, Xiang-Qun; Hou, Yong-Hui; Hu, Zhong-Wen; Jiang, Fang-Hua; and others

    2013-06-01

    We present new quasars discovered in the vicinity of the Andromeda and Triangulum galaxies with the Large Sky Area Multi-Object Fiber Spectroscopic Telescope, also named the Guoshoujing Telescope, during the 2010 and 2011 observational seasons. Quasar candidates are selected based on the available Sloan Digital Sky Survey, Kitt Peak National Observatory 4 m telescope, Xuyi Schmidt Telescope Photometric Survey optical, and Wide-field Infrared Survey Explorer near-infrared photometric data. We present 509 new quasars discovered in a stripe of ∼135 deg{sup 2} from M31 to M33 along the Giant Stellar Stream in the 2011 pilot survey data sets, and also 17 new quasars discovered in an area of ∼100 deg{sup 2} that covers the central region and the southeastern halo of M31 in the 2010 commissioning data sets. These 526 new quasars have i magnitudes ranging from 15.5 to 20.0, redshifts from 0.1 to 3.2. They represent a significant increase of the number of identified quasars in the vicinity of M31 and M33. There are now 26, 62, and 139 known quasars in this region of the sky with i magnitudes brighter than 17.0, 17.5, and 18.0, respectively, of which 5, 20, and 75 are newly discovered. These bright quasars provide an invaluable collection with which to probe the kinematics and chemistry of the interstellar/intergalactic medium in the Local Group of galaxies. A total of 93 quasars are now known with locations within 2.°5 of M31, of which 73 are newly discovered. Tens of quasars are now known to be located behind the Giant Stellar Stream, and hundreds are behind the extended halo and its associated substructures of M31. The much enlarged sample of known quasars in the vicinity of M31 and M33 can potentially be utilized to construct a perfect astrometric reference frame to measure the minute proper motions (PMs) of M31 and M33, along with the PMs of substructures associated with the Local Group of galaxies. Those PMs are some of the most fundamental properties of the Local

  15. Star formation rates in luminous quasars at 2 < z < 3

    NASA Astrophysics Data System (ADS)

    Harris, Kathryn; Farrah, Duncan; Schulz, Bernhard; Hatziminaoglou, Evanthia; Viero, Marco; Anderson, Nick; Béthermin, Matthieu; Chapman, Scott; Clements, David L.; Cooray, Asantha; Efstathiou, Andreas; Feltre, Anne; Hurley, Peter; Ibar, Eduardo; Lacy, Mark; Oliver, Sebastian; Page, Mathew J.; Pérez-Fournon, Ismael; Petty, Sara M.; Pitchford, Lura K.; Rigopoulou, Dimitra; Scott, Douglas; Symeonidis, Myrto; Vieira, Joaquin; Wang, Lingyu

    2016-04-01

    We investigate the relation between star formation rates (dot{{M}}_s) and AGN properties in optically selected type 1 quasars at 2 < z < 3 using data from Herschel and the SDSS. We find that dot{{M}}_s remains approximately constant with redshift, at 300 ± 100 M⊙ yr-1. Conversely, dot{{M}}_s increases with AGN luminosity, up to a maximum of ˜ 600 M⊙ yr-1, and with C IV FWHM. In context with previous results, this is consistent with a relation between dot{{M}}_s and black hole accretion rate (dot{{M}}_{bh}) existing in only parts of the z-dot{{M}}s-dot{{M}}_{bh} plane, dependent on the free gas fraction, the trigger for activity, and the processes that may quench star formation. The relations between dot{{M}}_s and both AGN luminosity and C IV FWHM are consistent with star formation rates in quasars scaling with black hole mass, though we cannot rule out a separate relation with black hole accretion rate. Star formation rates are observed to decline with increasing C IV equivalent width. This decline can be partially explained via the Baldwin effect, but may have an additional contribution from one or more of three factors; Mi is not a linear tracer of L2500, the Baldwin effect changes form at high AGN luminosities, and high C IV EW values signpost a change in the relation between dot{{M}}_s and dot{{M}}_{bh}. Finally, there is no strong relation between dot{{M}}_s and Eddington ratio, or the asymmetry of the C IV line. The former suggests that star formation rates do not scale with how efficiently the black hole is accreting, while the latter is consistent with C IV asymmetries arising from orientation effects.

  16. Testing the Radiative-Driving Hypothesis of Quasar Outflows

    NASA Astrophysics Data System (ADS)

    Stark, Michele A.; Ganguly, R.; Gallagher, S. C.; Gibson, R.; Brotherton, M. S.

    2011-01-01

    Outflows are seen prominently in the UV spectra of Broad Absorption Line (BAL) QSOs. Models of radiatively-driven outflows predict that the velocity should scale with UV luminosity. Observations show that the UV luminosity only provides a cap to the velocity. One explanation is that the X-ray absorbing gas in an individual quasar provides a shield that improves its radiative-driving efficiency. That is, quasars with thick shields can accelerate gas to higher velocity. X-ray observations of BALQSOs support this in the sense that BALQSOs with more soft X-ray absorption tend to have higher velocity outflows. But there is much scatter in this trend, making the underlying physics difficult to extract. To combat this, we conducted an experiment using exploratory Chandra-ACIS observations of 12 carefully-selected z=1.7-2.0 BALQSOs. These BALQSOs were chosen to have very narrow ranges in (1) UV luminosity, (2) UV spectral shape, and (3) absorption velocity width. Within this otherwise uniform sample, the outflow velocities range from 4500km/s to 18000km/s, a factor of four. All objects are detected in the full band (0.5-8keV), with count rates in the range (0.5-5)e-3 cps, and have hardness ratios in the range -0.6 to 0.3. We compare the X-ray brightnesses and spectral shapes of our sample with those of more diverse samples of BALQSOs. We gratefully acknowledge support through Chandra grant GO9-0120X.

  17. Alignment of quasar polarizations with large-scale structures

    NASA Astrophysics Data System (ADS)

    Hutsemékers, D.; Braibant, L.; Pelgrims, V.; Sluse, D.

    2014-12-01

    We have measured the optical linear polarization of quasars belonging to Gpc scale quasar groups at redshift z ~ 1.3. Out of 93 quasars observed, 19 are significantly polarized. We found that quasar polarization vectors are either parallel or perpendicular to the directions of the large-scale structures to which they belong. Statistical tests indicate that the probability that this effect can be attributed to randomly oriented polarization vectors is on the order of 1%. We also found that quasars with polarization perpendicular to the host structure preferentially have large emission line widths while objects with polarization parallel to the host structure preferentially have small emission line widths. Considering that quasar polarization is usually either parallel or perpendicular to the accretion disk axis depending on the inclination with respect to the line of sight, and that broader emission lines originate from quasars seen at higher inclinations, we conclude that quasar spin axes are likely parallel to their host large-scale structures. Based on observations made with ESO Telescopes at the La Silla Paranal Observatory under program ID 092.A-0221.Table 1 is available in electronic form at http://www.aanda.org

  18. Bayesian Integrated Microbial Forensics

    SciTech Connect

    Jarman, Kristin H.; Kreuzer-Martin, Helen W.; Wunschel, David S.; Valentine, Nancy B.; Cliff, John B.; Petersen, Catherine E.; Colburn, Heather A.; Wahl, Karen L.

    2008-06-01

    In the aftermath of the 2001 anthrax letters, researchers have been exploring ways to predict the production environment of unknown source microorganisms. Different mass spectral techniques are being developed to characterize components of a microbe’s culture medium including water, carbon and nitrogen sources, metal ions added, and the presence of agar. Individually, each technique has the potential to identify one or two ingredients in a culture medium recipe. However, by integrating data from multiple mass spectral techniques, a more complete characterization is possible. We present a Bayesian statistical approach to integrated microbial forensics and illustrate its application on spores grown in different culture media.

  19. Quasar variability measurements with SDSS repeated imaging and POSS data

    NASA Astrophysics Data System (ADS)

    Ivezic, Ž.; Lupton, R. H.; Juric, M.; Anderson, S.; Hall, P. B.; Richards, G. T.; Rockosi, C. M.; vanden Berk, D. E.; Turner, E. L.; Knapp, G. R.; Gunn, J. E.; Schlegel, D.; Strauss, M. A.; Schneider, D. P.

    2004-11-01

    We analyze the properties of quasar variability using repeated SDSS imaging data in five UV-to-far red photometric bands, accurate to 0.02 mag, for ˜13,000 spectroscopically confirmed quasars. The observed time lags span the range from 3 hours to over 3 years, and constrain the quasar variability for rest-frame time lags of up to two years, and at rest-frame wavelengths from 1000Å to 6000Å. We demonstrate that ˜66,000 SDSS measurements of magnitude differences can be described within the measurement noise by a simple function of only three free parameters. The addition of POSS data constrains the long-term behavior of quasar variability and provides evidence for a turn-over in the structure function. This turn-over indicates that the characteristic time scale for optical variability of quasars is of the order 1 year.

  20. Reddening indicators for quasars and Seyfert 1 galaxies

    NASA Technical Reports Server (NTRS)

    Grandi, S. A.

    1983-01-01

    It is pointed out that a determination of the reddening caused by intervening dust is a prerequisite to understanding the astrophysics of the broad line emission in quasars and their close cousins Seyfert 1 galaxies. Previous discussions of the reddening question have tended to be incomplete. The present investigation represents an attempt to asses critically the various techniques used to measure the reddening to quasars. It is found that if certain arguments presented are correct, there are no useful reddening indicators for the broad lines of quasars and Seyfert 1 galaxies. It seems safest to assume that reddening due to dust associated with quasars is negligible. However, small amounts of reddening toward quasars are certainly possible, and large amounts of reddening, while unlikely, cannot be ruled out.

  1. X-ray studies of quasars with the Einstein Observatory

    NASA Technical Reports Server (NTRS)

    Tananbaum, H.; Branduardi, G.; Fabbiano, G.; Feigelson, E.; Giacconi, R.; Henry, J. P.; Avni, Y.; Elvis, M.; Pye, J. P.; Soltan, A.

    1979-01-01

    Results of an investigation of the X-ray properties of quasars conducted using the Einstein Observatory (HEAO 2) are reported. The positions, fluxes and luminosities of 35 known quasars were observed by the Einstein high-resolution imaging detector and the imaging proportional counter. Assuming optical redshifts as valid distance indicators, 0.5-4.5 keV X-ray luminosities ranging from 10 to the 43rd to 10 to the 47 ergs/sec are obtained, with evidence of very little cold gas absorption. Flux variability on a time scale of less than 10,000 sec is observed for the quasar OX 169, which implies a mass between 8 x 10 to the 5th and 2 x 10 to the 8th solar masses for the black hole assumed to be responsible for the emission. Preliminary results of the quasar survey also indicate that quasars contribute significantly to the diffuse X-ray background.

  2. Strong associated C 4 absorption in low redshift quasars

    NASA Technical Reports Server (NTRS)

    Tytler, David

    1990-01-01

    IUE spectra of quasars were used to determine the frequency of occurrence of strong associated C 4 absorption systems at low red shifts. Four systems are found with rest frame equivalent width (REW) greater than 5 angstroms in the spectra of 38 quasars. This rate of occurrence of 0.12 is not significantly different from the rate of 0.064 determined for high red shift quasars. The detected strong associated systems are all in low red shift quasars which have been imaged from the ground. One of the quasars is unusual, having two nuclei, a close companion and distorted isotopes. Two of the others also have close companion galaxies at projected distances of under 100 kpc. The conclusion was made that a much larger sample is needed.

  3. Searching Algorithm Using Bayesian Updates

    ERIC Educational Resources Information Center

    Caudle, Kyle

    2010-01-01

    In late October 1967, the USS Scorpion was lost at sea, somewhere between the Azores and Norfolk Virginia. Dr. Craven of the U.S. Navy's Special Projects Division is credited with using Bayesian Search Theory to locate the submarine. Bayesian Search Theory is a straightforward and interesting application of Bayes' theorem which involves searching…

  4. Bayesian inference for OPC modeling

    NASA Astrophysics Data System (ADS)

    Burbine, Andrew; Sturtevant, John; Fryer, David; Smith, Bruce W.

    2016-03-01

    The use of optical proximity correction (OPC) demands increasingly accurate models of the photolithographic process. Model building and inference techniques in the data science community have seen great strides in the past two decades which make better use of available information. This paper aims to demonstrate the predictive power of Bayesian inference as a method for parameter selection in lithographic models by quantifying the uncertainty associated with model inputs and wafer data. Specifically, the method combines the model builder's prior information about each modelling assumption with the maximization of each observation's likelihood as a Student's t-distributed random variable. Through the use of a Markov chain Monte Carlo (MCMC) algorithm, a model's parameter space is explored to find the most credible parameter values. During parameter exploration, the parameters' posterior distributions are generated by applying Bayes' rule, using a likelihood function and the a priori knowledge supplied. The MCMC algorithm used, an affine invariant ensemble sampler (AIES), is implemented by initializing many walkers which semiindependently explore the space. The convergence of these walkers to global maxima of the likelihood volume determine the parameter values' highest density intervals (HDI) to reveal champion models. We show that this method of parameter selection provides insights into the data that traditional methods do not and outline continued experiments to vet the method.

  5. A New Model for Dark Matter Halos Hosting Quasars

    NASA Astrophysics Data System (ADS)

    Cen, Renyue; Safarzadeh, Mohammadtaher

    2015-01-01

    A new model for quasar-hosting dark matter halos, meeting two physical conditions, is put forth. First, significant interactions are taken into consideration to trigger quasar activities. Second, satellites in very massive halos at low redshift are removed from consideration due to their deficiency in cold gas. We analyze the Millennium Simulation to find halos that meet these two conditions and simultaneously match two-point auto-correlation functions of quasars and cross-correlation functions between quasars and galaxies at z = 0.5-3.2. The masses of the quasar hosts found decrease with decreasing redshift, with the mass thresholds being [(2-5) × 1012, (2-5) × 1011, (1-3) × 1011] M ⊙ for median luminosities of ~[1046, 1046, 1045] erg s-1 at z = (3.2, 1.4, 0.53), respectively, an order of magnitude lower than those inferred based on halo occupation distribution modeling. In this model, quasar hosts are primarily massive central halos at z >= 2-3 but increasingly dominated by lower mass satellite halos experiencing major interactions toward lower redshift. However, below z = 1, satellite halos in groups more massive than ~2 × 1013 M ⊙ do not host quasars. Whether for central or satellite halos, imposing the condition of significant interactions substantially boosts the clustering strength compared to the total population with the same mass cut. The inferred lifetimes of quasars at z = 0.5-3.2 of 3-30 Myr are in agreement with observations. Quasars at z ~ 2 would be hosted by halos of mass ~5 × 1011 M ⊙ in this model, compared to ~3 × 1012 M ⊙ previously thought, which would help reconcile with the observed, otherwise puzzling high covering fractions for Lyman limit systems around quasars.

  6. Host Galaxies of Luminous Type 2 Quasars at z ~ 0.5

    NASA Astrophysics Data System (ADS)

    Liu, Xin; Zakamska, Nadia L.; Greene, Jenny E.; Strauss, Michael A.; Krolik, Julian H.; Heckman, Timothy M.

    2009-09-01

    We present deep Gemini GMOS optical spectroscopy of nine luminous quasars at redshifts z ~ 0.5, drawn from the Sloan Digital Sky Survey type 2 quasar sample. Our targets were selected to have high intrinsic luminosities (MV < -26 mag) as indicated by the [O III] λ5007 Å emission-line luminosity (L [O III]). Our sample has a median black hole mass of ~108.8 M sun inferred assuming the local M BH-σ* relation and a median Eddington ratio of ~0.7, using stellar velocity dispersions σ* measured from the G band. We estimate the contamination of the stellar continuum from scattered quasar light based on the strength of broad Hβ, and provide an empirical calibration of the contamination as a function of L [O III]; the scattered-light fraction is ~30% of L 5100 for objects with L [O III] = 109.5 L sun. Population synthesis indicates that young poststarburst populations (<0.1 Gyr) are prevalent in luminous type 2 quasars, in addition to a relatively old population (>1 Gyr) which dominates the stellar mass. Broad emission complexes around He II λ4686 Å with luminosities up to 108.3 L sun are unambiguously detected in three out of the nine targets, indicative of Wolf-Rayet (WR) populations. Population synthesis shows that ~5 Myr poststarburst populations contribute substantially to the luminosities (>50% of L 5100) of all three objects with WR detections. We find two objects with double cores and four with close companions. Our results may suggest that luminous type 2 quasars trace an early stage of galaxy interaction, perhaps responsible for both the quasar and the starburst activity. Based, in part, on observations obtained at the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States), the Science and Technology Facilities Council (United Kingdom), the National Research Council (Canada

  7. A census of quasar-intrinsic absorption in the Hubble Space Telescope archive: systems from high-resolution echelle spectra

    NASA Astrophysics Data System (ADS)

    Ganguly, Rajib; Lynch, Ryan S.; Charlton, Jane C.; Eracleous, Michael; Tripp, Todd M.; Palma, Christopher; Sembach, Kenneth R.; Misawa, Toru; Masiero, Joseph R.; Milutinovic, Nikola; Lackey, Benjamin D.; Jones, Therese M.

    2013-10-01

    We present a census of zabs ≲ 2 intrinsic (those showing partial coverage) and associated (zabs ˜ zem) quasar absorption-line systems detected in the Hubble Space Telescope archive of Space Telescope Imaging Spectrograph echelle spectra. This work complements the Misawa et al. survey of 2 < zem < 4 quasars that selects systems using similar techniques. We confirm the existence of so-called strong N V intrinsic systems (where the equivalent width of H I Lyα is small compared to N V λ1238) presented in that work, but find no convincing cases of `strong C IV' intrinsic systems at low redshift/luminosity. Moreover, we also report on the existence of `strong O VI' systems. From a comparison of partial coverage results as a function of ion, we conclude that systems selected by the N V ion have the highest probability of being intrinsic. By contrast, the C IV and O VI ions are poor selectors. Of the 30 O VI systems tested, only two of the systems in the spectrum on 3C 351 show convincing evidence for partial coverage. However, there is an ˜3σ excess in the number of absorbers near the quasar redshift (|Δv| ≤ 5000 km s-1) over absorbers at large redshift differences. In at least two cases, the associated O VI systems are known not to arise close to the accretion disc of the quasar.

  8. Adaptive Dynamic Bayesian Networks

    SciTech Connect

    Ng, B M

    2007-10-26

    A discrete-time Markov process can be compactly modeled as a dynamic Bayesian network (DBN)--a graphical model with nodes representing random variables and directed edges indicating causality between variables. Each node has a probability distribution, conditional on the variables represented by the parent nodes. A DBN's graphical structure encodes fixed conditional dependencies between variables. But in real-world systems, conditional dependencies between variables may be unknown a priori or may vary over time. Model errors can result if the DBN fails to capture all possible interactions between variables. Thus, we explore the representational framework of adaptive DBNs, whose structure and parameters can change from one time step to the next: a distribution's parameters and its set of conditional variables are dynamic. This work builds on recent work in nonparametric Bayesian modeling, such as hierarchical Dirichlet processes, infinite-state hidden Markov networks and structured priors for Bayes net learning. In this paper, we will explain the motivation for our interest in adaptive DBNs, show how popular nonparametric methods are combined to formulate the foundations for adaptive DBNs, and present preliminary results.

  9. The VLBI structure of radio-loud Broad Absorption Line quasars

    NASA Astrophysics Data System (ADS)

    Liu, Y.; Jiang, D. R.; Gu, M.

    2016-02-01

    The nature and origin of Broad Absorption Line (BAL) quasars and their relationship to non-BAL quasars are an open question. The BAL quasars are probably normal quasars seen along a particular line of sight. Alternatively, they are young or recently refueled. The high resolution radio morphology of BAL quasars is very important to understand the radio properties of BAL quasars. We present VLBA observations at L and C bands for a sample of BAL quasars. The observations will help us to explore the VLBI radio properties, and distinguish the present models of explaining BAL phenomena.

  10. The Overdue Discovery of Quasars and AGN

    NASA Astrophysics Data System (ADS)

    Kellermann, Ken I.

    2012-09-01

    The extragalactic nature of quasars as a major new component of the Universe was not recognized until 1963 when Maarten Schmidt somewhat accidentally measured the spectrum of 3C 273 and recognized that the relatively simple hydrogen line Balmer series spectrum implied a redshift of 0.16. Curiously, 3C 48 and other very compact radio sources had been previously identified with ``quasi-stellar'' objects several years earlier. Even though the redshift of 3C48 was measured as early as 1960 as 0.37, it was rejected due to apparent spectroscopic technicalities and preconceived ideas about what appeared to be an unrealistically high luminosity. The strong radio source known as 3C 273 was first catalogued in 1959 and the now recognized magnitude 13 optical counterpart was known at least as early as 1887. Although, since 1960, much fainter optical counterparts were being routinely identified using accurate radio interferometer positions, interestingly, 3C273 eluded identification until a series of lunar occultations by Hazard et al. in 1962 were used to determine the position and morphology of the radio source. Acceptance of the cosmological nature of quasars and the implied excessive radio and optical luminosity was not universal, and claims for a more local population continued for at least several decades, confused perhaps by the recognition of the much larger class of radio quiet quasi stellar objects and active galactic nuclei (AGN), the uncertain connection with previously known Seyfert and other compact galaxies, as well as attempts to classify quasars into numerous sub-categories based on their observed optical, radio, IR and high energy properties.

  11. The high-z quasar Hubble Diagram

    SciTech Connect

    Melia, Fulvio

    2014-01-01

    Two recent discoveries have made it possible for us to begin using high-z quasars as standard candles to construct a Hubble Diagram (HD) at z > 6. These are (1) the recognition from reverberation mapping that a relationship exists between the optical/UV luminosity and the distance of line-emitting gas from the central ionizing source. Thus, together with a measurement of the velocity of the line-emitting gas, e.g., via the width of BLR lines, such as Mg II, a single observation can therefore in principle provide a determination of the black hole's mass; and (2) the identification of quasar ULAS J1120+0641 at z = 7.085, which has significantly extended the redshift range of these sources, providing essential leverage when fitting theoretical luminosity distances to the data. In this paper, we use the observed fluxes and Mg II line-widths of these sources to show that one may reasonably test the predicted high-z distance versus redshift relationship, and we assemble a sample of 20 currently available high-z quasars for this exercise. We find a good match between theory and observations, suggesting that a more complete, high-quality survey may indeed eventually produce an HD to complement the highly-d