The Sloan Digital Sky Survey Quasar Catalog: Twelfth data release

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pâris, Isabelle; Petitjean, Patrick; Ross, Nicholas P.

In this paper, we present the Data Release 12 Quasar catalog (DR12Q) from the Baryon Oscillation Spectroscopic Survey (BOSS) of the Sloan Digital Sky Survey III. This catalog includes all SDSS-III/BOSS objects that were spectroscopically targeted as quasar candidates during the full survey and that are confirmed as quasars via visual inspection of the spectra, have luminosities M i [z = 2] < -20.5 (in a ΛCDM cosmology with H 0 = 70 km s -1 Mpc -1, Ω M = 0.3, and Ω Λ = 0.7), and either display at least one emission line with a full width atmore » half maximum (FWHM) larger than 500 km s -1 or, if not, have interesting/complex absorption features. The catalog also includes previously known quasars (mostly from SDSS-I and II) that were reobserved by BOSS. The catalog contains 297 301 quasars (272 026 are new discoveries since the beginning of SDSS-III) detected over 9376 deg 2 with robust identification and redshift measured by a combination of principal component eigenspectra. The number of quasars with z > 2.15 (184 101, of which 167 742 are new discoveries) is about an order of magnitude greater than the number of z > 2.15 quasars known prior to BOSS. Redshifts and FWHMs are provided for the strongest emission lines (C iv, C iii], Mg ii). The catalog identifies 29 580 broad absorption line quasars and lists their characteristics. For each object, the catalog presents five-band (u, g, r, i, z) CCD-based photometry with typical accuracy of 0.03 mag together with some information on the optical morphology and the selection criteria. When available, the catalog also provides information on the optical variability of quasars using SDSS and Palomar Transient Factory multi-epoch photometry. The catalog also contains X-ray, ultraviolet, near-infrared, and radio emission properties of the quasars, when available, from other large-area surveys. The calibrated digital spectra, covering the wavelength region 3600–10 500 Å at a spectral resolution in the range 1300 < R

The Sloan Digital Sky Survey Quasar Catalog: Twelfth data release

DOE PAGES

Pâris, Isabelle; Petitjean, Patrick; Ross, Nicholas P.; ...

2017-01-05

In this paper, we present the Data Release 12 Quasar catalog (DR12Q) from the Baryon Oscillation Spectroscopic Survey (BOSS) of the Sloan Digital Sky Survey III. This catalog includes all SDSS-III/BOSS objects that were spectroscopically targeted as quasar candidates during the full survey and that are confirmed as quasars via visual inspection of the spectra, have luminosities M i [z = 2] < -20.5 (in a ΛCDM cosmology with H 0 = 70 km s -1 Mpc -1, Ω M = 0.3, and Ω Λ = 0.7), and either display at least one emission line with a full width atmore » half maximum (FWHM) larger than 500 km s -1 or, if not, have interesting/complex absorption features. The catalog also includes previously known quasars (mostly from SDSS-I and II) that were reobserved by BOSS. The catalog contains 297 301 quasars (272 026 are new discoveries since the beginning of SDSS-III) detected over 9376 deg 2 with robust identification and redshift measured by a combination of principal component eigenspectra. The number of quasars with z > 2.15 (184 101, of which 167 742 are new discoveries) is about an order of magnitude greater than the number of z > 2.15 quasars known prior to BOSS. Redshifts and FWHMs are provided for the strongest emission lines (C iv, C iii], Mg ii). The catalog identifies 29 580 broad absorption line quasars and lists their characteristics. For each object, the catalog presents five-band (u, g, r, i, z) CCD-based photometry with typical accuracy of 0.03 mag together with some information on the optical morphology and the selection criteria. When available, the catalog also provides information on the optical variability of quasars using SDSS and Palomar Transient Factory multi-epoch photometry. The catalog also contains X-ray, ultraviolet, near-infrared, and radio emission properties of the quasars, when available, from other large-area surveys. The calibrated digital spectra, covering the wavelength region 3600–10 500 Å at a spectral resolution in the range 1300 < R

THE CANADA-FRANCE HIGH-z QUASAR SURVEY: NINE NEW QUASARS AND THE LUMINOSITY FUNCTION AT REDSHIFT 6

DOE Office of Scientific and Technical Information (OSTI.GOV)

Willott, Chris J.; Crampton, David; Hutchings, John B.

2010-03-15

We present discovery imaging and spectroscopy for nine new z {approx} 6 quasars found in the Canada-France High-z Quasar Survey (CFHQS) bringing the total number of CFHQS quasars to 19. By combining the CFHQS with the more luminous Sloan Digital Sky Survey sample, we are able to derive the quasar luminosity function from a sample of 40 quasars at redshifts 5.74 < z < 6.42. Our binned luminosity function shows a slightly lower normalization and flatter slope than found in previous work. The binned data also suggest a break in the luminosity function at M {sub 1450} {approx} -25. Amore » double power-law maximum likelihood fit to the data is consistent with the binned results. The luminosity function is strongly constrained (1{sigma} uncertainty <0.1 dex) over the range -27.5 < M {sub 1450} < -24.7. The best-fit parameters are {phi}(M*{sub 1450}) = 1.14 x 10{sup -8} Mpc{sup -3} mag{sup -1}, break magnitude M*{sub 1450} = -25.13, and bright end slope {beta} = -2.81. However, the covariance between {beta} and M*{sub 1450} prevents strong constraints being placed on either parameter. For a break magnitude in the range -26 < M*{sub 1450} < -24, we find -3.8 < {beta} < -2.3 at 95% confidence. We calculate the z = 6 quasar intergalactic ionizing flux and show it is between 20 and 100 times lower than that necessary for reionization. Finally, we use the luminosity function to predict how many higher redshift quasars may be discovered in future near-IR imaging surveys.« less

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

New quasar survey with WIRO: The light curves of quasars over ~15 year timescales

NASA Astrophysics Data System (ADS)

Griffith, Emily; Bassett, Neil; Deam, Sophie; Dixon, Don; Harvey, William; Lee, Daniel; Lyke, Bradley; Haze Nunez, Evan; Parziale, Ryan; Witherspoon, Catherine; Myers, Adam D.; Findlay, Joseph; Kobulnicky, Henry A.; Dale, Daniel A.

2017-01-01

Quasars, a type of active galactic nuclei (AGN), are known to vary in brightness on 10 day to 7 year timescales. While it has been proposed that this variability is caused by instability in the accretion disk, Poisson processes, or microlensing, the exact cause remains mysterious. Understanding the physical mechanisms that drive quasar variability will require imaging of quasars over a wide range of timescales. In particular, the observations required to constrain longer timescales can be difficult to conduct. This summer ~1000 quasars in Stripe 82 were observed in ugriz wavelength bands using WIRO, the University of Wyoming’s 2.3-meter telescope. Using these images, earlier data from the Sloan Digital Sky Survey's observations of Stripe 82, as well as various data reduction methods, the quasars’ magnitude can be studied on our extended 3 day to 15 year timescale. Here, we present the light curves of ~1000 quasars in ugriz bands as observed over the last 15 years. Thiswork is supported by the National Science Foundation under REU grant AST 1560461.

GNIRS-DQS: A Gemini Near Infrared Spectrograph Distant Quasar Survey

NASA Astrophysics Data System (ADS)

Matthews, Brandon; Shemmer, Ohad; Brotherton, Michael S.; Andruchow, Ileana; Boroson, Todd A.; Brandt, W. Niel; Cellone, Sergio; Ferrero, Gabriel; Gallagher, Sarah; Green, Richard F.; Hennawi, Joseph F.; Lira, Paulina; Myers, Adam D.; Plotkin, Richard; Richards, Gordon T.; Runnoe, Jessie; Schneider, Donald P.; Shen, Yue; Strauss, Michael A.; Willott, Chris J.; Wills, Beverley J.

2018-06-01

We describe an ongoing three-year Gemini survey, launched in 2017, that will obtain near-infrared spectroscopy of 416 Sloan Digital Sky Survey (SDSS) quasars between redshifts of 1.5 and 3.5 in the ~1.0-2.5 μm band. These spectra will cover critical diagnostic emission lines, such as Mg II, Hβ, and [O III], in each source. This project will more than double the existing inventory of near-infrared spectra of luminous quasars at these redshifts, including the era of fast quasar growth. Additional rest frame ultraviolet coverage of at least the C IV emission line is provided by the SDSS spectrum of each source. We will utilize the spectroscopic inventory to determine the most accurate and precise quasar black hole masses, accretion rates, and redshifts, and use the results to derive improved prescriptions for UV-based proxies for these parameters. The improved redshifts will establish velocities of quasar outflows that interact with the host galaxies, and will help constrain how imprecise distance estimates bias quasar clustering measurements. Furthermore, our measurements will facilitate a more complete understanding of how the rest-frame UV-optical spectral properties depend on redshift and luminosity, and test whether the physical properties of the quasar central engine evolve over cosmic time. We will make our data immediately available to the public, provide reduced spectra via a dedicated website, and produce a catalog of measurements and fundamental quasar properties.

Extreme Variability Quasars from the Sloan Digital Sky Survey and the Dark Energy Survey

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rumbaugh, N.; Shen, Yue; Morganson, Eric

2018-02-20

We perform a systematic search for long-term extreme variability quasars (EVQs) in the overlapping Sloan Digital Sky Survey (SDSS) and 3-Year Dark Energy Survey (DES) imaging, which provide light curves spanning more than 15 years. We identified ~1000 EVQs with a maximum g band magnitude change of more than 1 mag over this period, about 10% of all quasars searched. The EVQs have L_bol~10^45-10^47 erg/s and L/L_Edd~0.01-1. Accounting for selection effects, we estimate an intrinsic EVQ fraction of ~30-50% among all g<~22 quasars over a baseline of ~15 years. These EVQs are good candidates for so-called "changing-look quasars", where amore » spectral transition between the two types of quasars (broad-line and narrow-line) is observed between the dim and bright states. We performed detailed multi-wavelength, spectral and variability analyses for the EVQs and compared to their parent quasar sample. We found that EVQs are distinct from a control sample of quasars matched in redshift and optical luminosity: (1) their UV broad emission lines have larger equivalent widths; (2) their Eddington ratios are systematically lower; and (3) they are more variable on all timescales. The intrinsic difference in quasar properties for EVQs suggest that internal processes associated with accretion are the main driver for the observed extreme long-term variability. However, despite their different properties, EVQs seem to be in the tail of a continuous distribution of quasar properties, rather than standing out as a distinct population. We speculate that EVQs are normal quasars accreting at relatively low accretion rates, where the accretion flow is more likely to experience instabilities that drive the factor of few changes in flux on multi-year timescales.« less

The Sloan Digital Sky Survey Quasar Catalog: Fourteenth data release

NASA Astrophysics Data System (ADS)

Pâris, Isabelle; Petitjean, Patrick; Aubourg, Éric; Myers, Adam D.; Streblyanska, Alina; Lyke, Brad W.; Anderson, Scott F.; Armengaud, Éric; Bautista, Julian; Blanton, Michael R.; Blomqvist, Michael; Brinkmann, Jonathan; Brownstein, Joel R.; Brandt, William Nielsen; Burtin, Étienne; Dawson, Kyle; de la Torre, Sylvain; Georgakakis, Antonis; Gil-Marín, Héctor; Green, Paul J.; Hall, Patrick B.; Kneib, Jean-Paul; LaMassa, Stephanie M.; Le Goff, Jean-Marc; MacLeod, Chelsea; Mariappan, Vivek; McGreer, Ian D.; Merloni, Andrea; Noterdaeme, Pasquier; Palanque-Delabrouille, Nathalie; Percival, Will J.; Ross, Ashley J.; Rossi, Graziano; Schneider, Donald P.; Seo, Hee-Jong; Tojeiro, Rita; Weaver, Benjamin A.; Weijmans, Anne-Marie; Yèche, Christophe; Zarrouk, Pauline; Zhao, Gong-Bo

2018-05-01

We present the data release 14 Quasar catalog (DR14Q) from the extended Baryon Oscillation Spectroscopic Survey (eBOSS) of the Sloan Digital Sky Survey IV (SDSS-IV). This catalog includes all SDSS-IV/eBOSS objects that were spectroscopically targeted as quasar candidates and that are confirmed as quasars via a new automated procedure combined with a partial visual inspection of spectra, have luminosities Mi [z = 2] < -20.5 (in a Λ CDM cosmology with H0 = 70 km s-1 Mpc-1, Ω M =0.3, and Ω Λ = 0.7), and either display at least one emission line with a full width at half maximum larger than 500 km s-1 or, if not, have interesting/complex absorption features. The catalog also includes previously spectroscopically-confirmed quasars from SDSS-I, II, and III. The catalog contains 526 356 quasars (144 046 are new discoveries since the beginning of SDSS-IV) detected over 9376 deg2 (2044 deg2 having new spectroscopic data available) with robust identification and redshift measured by a combination of principal component eigenspectra. The catalog is estimated to have about 0.5% contamination. Redshifts are provided for the Mg II emission line. The catalog identifies 21 877 broad absorption line quasars and lists their characteristics. For each object, the catalog presents five-band (u, g, r, i, z) CCD-based photometry with typical accuracy of 0.03 mag. The catalog also contains X-ray, ultraviolet, near-infrared, and radio emission properties of the quasars, when available, from other large-area surveys. The calibrated digital spectra, covering the wavelength region 3610-10 140 Å at a spectral resolution in the range 1300 < R < 2500, can be retrieved from the SDSS Science Archiver Server. http://www.sdss.org/dr14/algorithms/qso_catalog

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

Extreme Variability Quasars from the Sloan Digital Sky Survey and the Dark Energy Survey

DOE PAGES

Rumbaugh, N.

2018-02-21

Here, we perform a systematic search for long-term extreme variability quasars (EVQs) in the overlapping Sloan Digital Sky Survey (SDSS) and 3-Year Dark Energy Survey (DES) imaging, which provide light curves spanning more than 15 years. We also identified 1000 EVQs with a maximum g band magnitude change of more than 1 mag over this period, about 10% of all quasars searched. The EVQs have L bol 10 45 - 10 47 erg s -1 and L=L Edd 0:01-1. Accounting for selection effects, we estimate an intrinsic EVQ fraction of 30-50% among all g.22 quasars over a baseline of 15more » years. These EVQs are good candidates for so-called “changing-look quasars”, where a spectral transition between the two types of quasars (broad-line and narrow-line) is observed between the dim and bright states. We performed detailed multi-wavelength, spectral and variability analyses for the EVQs and compared to their parent quasar sample. We found that EVQs are distinct from a control sample of quasars matched in redshift and optical luminosity: (1) their UV broad emission lines have larger equivalent widths; (2) their Eddington ratios are systematically lower; and (3) they are more variable on all timescales. The intrinsic difference in quasar properties for EVQs suggest that internal processes associated with accretion are the main driver for the observed extreme long-term variability. In spit of their different properties, EVQs seem to be in the tail of a continuous distribution of quasar properties, rather than standing out as a distinct population. We speculate that EVQs are normal quasars accreting at relatively low accretion rates, where the accretion flow is more likely to experience instabilities that drive the factor of few changes in flux on multi-year timescales.« less

Extreme Variability Quasars from the Sloan Digital Sky Survey and the Dark Energy Survey

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rumbaugh, N.

Here, we perform a systematic search for long-term extreme variability quasars (EVQs) in the overlapping Sloan Digital Sky Survey (SDSS) and 3-Year Dark Energy Survey (DES) imaging, which provide light curves spanning more than 15 years. We also identified 1000 EVQs with a maximum g band magnitude change of more than 1 mag over this period, about 10% of all quasars searched. The EVQs have L bol 10 45 - 10 47 erg s -1 and L=L Edd 0:01-1. Accounting for selection effects, we estimate an intrinsic EVQ fraction of 30-50% among all g.22 quasars over a baseline of 15more » years. These EVQs are good candidates for so-called “changing-look quasars”, where a spectral transition between the two types of quasars (broad-line and narrow-line) is observed between the dim and bright states. We performed detailed multi-wavelength, spectral and variability analyses for the EVQs and compared to their parent quasar sample. We found that EVQs are distinct from a control sample of quasars matched in redshift and optical luminosity: (1) their UV broad emission lines have larger equivalent widths; (2) their Eddington ratios are systematically lower; and (3) they are more variable on all timescales. The intrinsic difference in quasar properties for EVQs suggest that internal processes associated with accretion are the main driver for the observed extreme long-term variability. In spit of their different properties, EVQs seem to be in the tail of a continuous distribution of quasar properties, rather than standing out as a distinct population. We speculate that EVQs are normal quasars accreting at relatively low accretion rates, where the accretion flow is more likely to experience instabilities that drive the factor of few changes in flux on multi-year timescales.« less

Extreme Variability Quasars from the Sloan Digital Sky Survey and the Dark Energy Survey

NASA Astrophysics Data System (ADS)

Rumbaugh, N.; Shen, Yue; Morganson, Eric; Liu, Xin; Banerji, M.; McMahon, R. G.; Abdalla, F. B.; Benoit-Lévy, A.; Bertin, E.; Brooks, D.; Buckley-Geer, E.; Capozzi, D.; Carnero Rosell, A.; Carrasco Kind, M.; Carretero, J.; Cunha, C. E.; D’Andrea, C. B.; da Costa, L. N.; DePoy, D. L.; Desai, S.; Doel, P.; Frieman, J.; García-Bellido, J.; Gruen, D.; Gruendl, R. A.; Gschwend, J.; Gutierrez, G.; Honscheid, K.; James, D. J.; Kuehn, K.; Kuhlmann, S.; Kuropatkin, N.; Lima, M.; Maia, M. A. G.; Marshall, J. L.; Martini, P.; Menanteau, F.; Plazas, A. A.; Reil, K.; Roodman, A.; Sanchez, E.; Scarpine, V.; Schindler, R.; Schubnell, M.; Sheldon, E.; Smith, M.; Soares-Santos, M.; Sobreira, F.; Suchyta, E.; Swanson, M. E. C.; Walker, A. R.; Wester, W.; (DES Collaboration

2018-02-01

We perform a systematic search for long-term extreme variability quasars (EVQs) in the overlapping Sloan Digital Sky Survey and 3 Year Dark Energy Survey imaging, which provide light curves spanning more than 15 years. We identified ∼1000 EVQs with a maximum change in g-band magnitude of more than 1 mag over this period, about 10% of all quasars searched. The EVQs have L bol ∼ 1045–1047 erg s‑1 and L/L Edd ∼ 0.01–1. Accounting for selection effects, we estimate an intrinsic EVQ fraction of ∼30%–50% among all g≲ 22 quasars over a baseline of ∼15 yr. We performed detailed multi-wavelength, spectral, and variability analyses for the EVQs and compared them to their parent quasar sample. We found that EVQs are distinct from a control sample of quasars matched in redshift and optical luminosity: (1) their UV broad emission lines have larger equivalent widths; (2) their Eddington ratios are systematically lower; and (3) they are more variable on all timescales. The intrinsic difference in quasar properties for EVQs suggests that internal processes associated with accretion are the main driver for the observed extreme long-term variability. However, despite their different properties, EVQs seem to be in the tail of a continuous distribution of quasar properties, rather than standing out as a distinct population. We speculate that EVQs are normal quasars accreting at relatively low rates, where the accretion flow is more likely to experience instabilities that drive the changes in flux by a factor of a few on multi-year timescales.

VizieR Online Data Catalog: LAMOST quasar survey: quasar properties from the DR1 (Ai+, 2016)

NASA Astrophysics Data System (ADS)

Ai, Y. L.; Wu, X.-B.; Yang, J.; Yang, Q.; Wang, F.; Guo, R.; Zuo, W.; Dong, X.; Zhang, Y.-X.; Yuan, H.-L.; Song, Y.-H.; Wang, J.; Dong, X.; Yang, M.; Wu, H.; Shen, S.-Y.; Shi, J.-R.; He, B.-L.; Lei, Y.-J.; Li, Y.-B.; Luo, A.-L.; Zhao, Y.-H.; Zhang, H.-T.

2018-03-01

LAMOST began a pilot survey in 2011 October and a regular survey in 2012 September. The regular survey, carried out over five to six years, has two major components: the LAMOST Experiment for Galactic Understanding and Exploration (LEGUE) and the LAMOST Extragalactic Survey (LEGAS; Zhao et al. 2012RAA....12..723Z). LEGAS only uses a small part of the available observing time due to the limitations of the LAMOST site, especially the bright sky background and poor seeing. The first data release (DR1) contains spectra taken before 2013 June (Luo et al. 2015, Cat. V/146). In this paper we present the results of the quasar survey from LEGAS. LAMOST LEGAS spectroscopic observations are taken in a series of at least three 30 minute exposures. There are 70290 quasar candidates observed, with 82625 spectra in DR1. (2 data files).

Population mixtures and searches of lensed and extended quasars across photometric surveys

NASA Astrophysics Data System (ADS)

Williams, Peter; Agnello, Adriano; Treu, Tommaso

2017-04-01

Wide-field photometric surveys enable searches of rare yet interesting objects, such as strongly lensed quasars or quasars with a bright host galaxy. Past searches for lensed quasars based on their optical and near-infrared properties have relied on photometric cuts and spectroscopic preselection (as in the Sloan Quasar Lens Search), or neural networks applied to photometric samples. These methods rely on cuts in morphology and colours, with the risk of losing many interesting objects due to scatter in their population properties, restrictive training sets, systematic uncertainties in catalogue-based magnitudes and survey-to-survey photometric variations. Here, we explore the performance of a Gaussian mixture model to separate point-like quasars, quasars with an extended host and strongly lensed quasars using griz psf and model magnitudes and WISE W1, W2. The choice of optical magnitudes is due to their presence in all current and upcoming releases of wide-field surveys, whereas UV information is not always available. We then assess the contamination from blue galaxies and the role of additional features such as W3 magnitudes or psf-model terms as morphological information. As a demonstration, we conduct a search in a random 10 per cent of the SDSS footprint, and provide the catalogue of the 43 SDSS object with the highest 'lens' score in our selection that survive visual inspection, and are spectroscopically confirmed to host active nuclei. We inspect archival data and find images of 5/43 objects in the Hubble Legacy Archive, including two known lenses. The code and materials are available to facilitate follow-up.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ross, Nicholas P.; Kirkpatrick, Jessica A.; Carithers, William C.

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 algorithmmore » 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

A Very Large Array Survey of Polar BAL Quasar Candidates

NASA Astrophysics Data System (ADS)

Olson, Kianna Alexandra; Brotherton, Michael S.; DiPompeo, Michael; Maithil, Jaya

2018-06-01

Polar broad absorption line quasars posses flat radio spectra and jets seen at small angles to the line of sight. Using the VLA we observed twelve polar broad absorption line quasar candidates at L (1.5GHz), C (4.5-5.5GHz), and X (8.5-9.5GHz) bands, and found that their cores display flat spectra. Compared to previous observations in the NVSS and First surveys, the peak flux densities all show significant variation σvar > 3, and brightness temperatures TB ≥ 1012K. Based on these findings, our quasars have the properties expected for objects that posses jets seen nearly pole on.

MALS–NOT: Identifying Radio-bright Quasars for the MeerKAT Absorption Line Survey

NASA Astrophysics Data System (ADS)

Krogager, J.-K.; Gupta, N.; Noterdaeme, P.; Ranjan, A.; Fynbo, J. P. U.; Srianand, R.; Petitjean, P.; Combes, F.; Mahabal, A.

2018-03-01

We present a preparatory spectroscopic survey to identify radio-bright, high-redshift quasars for the MeerKAT Absorption Line Survey. The candidates have been selected on the basis of a single flux density limit at 1.4 GHz (>200 mJy), together with mid-infrared color criteria from the Wide-field Infrared Survey Explorer. Through spectroscopic observations using the Nordic Optical Telescope, we identify 72 quasars out of 99 candidates targeted. We measure the spectroscopic redshifts based on characteristic, broad emission lines present in the spectra. Of these 72 quasars, 64 and 48 objects are at sufficiently high redshift (z > 0.6 and z > 1.4) to be used for the L-band and UHF-band spectroscopic follow-up with the Square Kilometre Array precursor in South Africa: the MeerKAT.

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.

UV-luminous, star-forming hosts of z ˜ 2 reddened quasars in the Dark Energy Survey

NASA Astrophysics Data System (ADS)

Wethers, C. F.; Banerji, M.; Hewett, P. C.; Lemon, C. A.; McMahon, R. G.; Reed, S. L.; Shen, Y.; Abdalla, F. B.; Benoit-Lévy, A.; Brooks, D.; Buckley-Geer, E.; Capozzi, D.; Carnero Rosell, A.; CarrascoKind, M.; Carretero, J.; Cunha, C. E.; D'Andrea, C. B.; da Costa, L. N.; DePoy, D. L.; Desai, S.; Doel, P.; Flaugher, B.; Fosalba, P.; Frieman, J.; García-Bellido, J.; Gerdes, D. W.; Gruen, D.; Gruendl, R. A.; Gschwend, J.; Gutierrez, G.; Honscheid, K.; James, D. J.; Jeltema, T.; Kuehn, K.; Kuhlmann, S.; Kuropatkin, N.; Lima, M.; Maia, M. A. G.; Marshall, J. L.; Martini, P.; Menanteau, F.; Miquel, R.; Nichol, R. C.; Nord, B.; Plazas, A. A.; Romer, A. K.; Sanchez, E.; Scarpine, V.; Schindler, R.; Schubnell, M.; Sevilla-Noarbe, I.; Smith, M.; Smith, R. C.; Soares-Santos, M.; Sobreira, F.; Suchyta, E.; Tarle, G.; Walker, A. R.

2018-04-01

We present the first rest-frame UV population study of 17 heavily reddened, high-luminosity [E(B - V)QSO ≳ 0.5; Lbol > 1046 erg s-1] broad-line quasars at 1.5 < z < 2.7. We combine the first year of deep, optical, ground-based observations from the Dark Energy Survey (DES) with the near-infrared VISTA Hemisphere Survey and UKIDSS Large Area Survey data, from which the reddened quasars were initially identified. We demonstrate that the significant dust reddening towards the quasar in our sample allows host galaxy emission to be detected at the rest-frame UV wavelengths probed by the DES photometry. By exploiting this reddening effect, we disentangle the quasar emission from that of the host galaxy via spectral energy distribution fitting. We find evidence for a relatively unobscured, star-forming host galaxy in at least 10 quasars, with a further three quasars exhibiting emission consistent with either star formation or scattered light. From the rest-frame UV emission, we derive instantaneous, dust-corrected star formation rates (SFRs) in the range 25 < SFRUV < 365 M⊙ yr-1, with an average SFRUV = 130 ± 95 M⊙ yr-1. We find a broad correlation between SFRUV and the bolometric quasar luminosity. Overall, our results show evidence for coeval star formation and black hole accretion occurring in luminous, reddened quasars at the peak epoch of galaxy formation.

New Quasar Surveys with WIRO: Data and Calibration for Studies of Variability

NASA Astrophysics Data System (ADS)

Lyke, Bradley; Bassett, Neil; Deam, Sophie; Dixon, Don; Griffith, Emily; Harvey, William; Lee, Daniel; Haze Nunez, Evan; Parziale, Ryan; Witherspoon, Catherine; Myers, Adam D.; Findlay, Joseph; Kobulnicky, Henry A.; Dale, Daniel A.

2017-01-01

Measurements of quasar variability offer the potential for understanding the physics of accretion processes around supermassive black holes. However, generating structure functions in order to characterize quasar variability can be observationally taxing as it requires imaging of quasars over a large variety of date ranges. To begin to address this problem, we have conducted an imaging survey of sections of Sloan Digital Sky Survey (SDSS) Stripe 82 at the Wyoming Infrared Observatory (WIRO). We used standard stars to calculate zero-point offsets between WIRO and SDSS observations in the urgiz magnitude system. After finding the zero-point offset, we accounted for further offsets by comparing standard star magnitudes in each WIRO frame to coadded magnitudes from Stripe 82 and applying a linear correction. Known (i.e. spectroscopically confirmed) quasars at the epoch we conducted WIRO observations (Summer, 2016) and at every epoch in SDSS Stripe 82 (~80 total dates) were hence calibrated to a similar magnitude system. The algorithm for this calibration compared 1500 randomly selected standard stars with an MJD within 0.07 of the MJD of each quasar of interest, for each of the five ugriz filters. Ultimately ~1000 known quasars in Stripe 82 were identified by WIRO and their SDSS-WIRO magnitudes were calibrated to a similar scale in order to generate ensemble structure functions.This work is supported by the National Science Foundation under REU grant AST 1560461.

UV-luminous, star-forming hosts of z ~ 2 reddened quasars in the Dark Energy Survey

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wethers, C. F.; Banerji, M.; Hewett, P. C.

We present the first rest-frame UV population study of 17 heavily reddened, high-luminosity (E(B-V)more » $$_{\\rm{QSO}}\\gtrsim$$ 0.5; L$$_{\\rm{bol}}>$$ 10$$^{46}$$ergs$$^{-1}$$) broad-line quasars at $1.5 < z < 2.7$. We combine the first year of deep, optical, ground-based observations from the Dark Energy Survey (DES) with the near infrared VISTA Hemisphere Survey (VHS) and UKIDSS Large Area Survey (ULAS) data, from which the reddened quasars were initially identified. We demonstrate that the significant dust reddening towards the quasar in our sample allows host galaxy emission to be detected at the rest-frame UV wavelengths probed by the DES photometry. By exploiting this reddening effect, we disentangle the quasar emission from that of the host galaxy via spectral energy distribution (SED) fitting. We find evidence for a relatively unobscured, star-forming host galaxy in at least ten quasars, with a further three quasars exhibiting emission consistent with either star formation or scattered light. From the rest-frame UV emission, we derive instantaneous, dust-corrected star formation rates (SFRs) in the range 25 < SFR$$_{\\rm{UV}}$$ < 365 M$$_{\\odot}$$yr$$^{-1}$$, with an average SFR$$_{\\rm{UV}}$$ = 130 $$\\pm$$ 95 M$$_{\\odot}$$yr$$^{-1}$$. In conclusion, we find a broad correlation between SFR$$_{\\rm{UV}}$$ and the bolometric quasar luminosity. Overall, our results show evidence for coeval star formation and black hole accretion occurring in luminous, reddened quasars at the peak epoch of galaxy formation.« less

UV-luminous, star-forming hosts of z ~ 2 reddened quasars in the Dark Energy Survey

DOE PAGES

Wethers, C. F.; Banerji, M.; Hewett, P. C.; ...

2018-01-05

We present the first rest-frame UV population study of 17 heavily reddened, high-luminosity (E(B-V)more » $$_{\\rm{QSO}}\\gtrsim$$ 0.5; L$$_{\\rm{bol}}>$$ 10$$^{46}$$ergs$$^{-1}$$) broad-line quasars at $1.5 < z < 2.7$. We combine the first year of deep, optical, ground-based observations from the Dark Energy Survey (DES) with the near infrared VISTA Hemisphere Survey (VHS) and UKIDSS Large Area Survey (ULAS) data, from which the reddened quasars were initially identified. We demonstrate that the significant dust reddening towards the quasar in our sample allows host galaxy emission to be detected at the rest-frame UV wavelengths probed by the DES photometry. By exploiting this reddening effect, we disentangle the quasar emission from that of the host galaxy via spectral energy distribution (SED) fitting. We find evidence for a relatively unobscured, star-forming host galaxy in at least ten quasars, with a further three quasars exhibiting emission consistent with either star formation or scattered light. From the rest-frame UV emission, we derive instantaneous, dust-corrected star formation rates (SFRs) in the range 25 < SFR$$_{\\rm{UV}}$$ < 365 M$$_{\\odot}$$yr$$^{-1}$$, with an average SFR$$_{\\rm{UV}}$$ = 130 $$\\pm$$ 95 M$$_{\\odot}$$yr$$^{-1}$$. In conclusion, we find a broad correlation between SFR$$_{\\rm{UV}}$$ and the bolometric quasar luminosity. Overall, our results show evidence for coeval star formation and black hole accretion occurring in luminous, reddened quasars at the peak epoch of galaxy formation.« less

A Survey of z ~ 6 Quasars in the Sloan Digital Sky Survey Deep Stripe. I. A Flux-Limited Sample at zAB < 21

NASA Astrophysics Data System (ADS)

Jiang, Linhua; Fan, Xiaohui; Annis, James; Becker, Robert H.; White, Richard L.; Chiu, Kuenley; Lin, Huan; Lupton, Robert H.; Richards, Gordon T.; Strauss, Michael A.; Jester, Sebastian; Schneider, Donald P.

2008-03-01

We present the discovery of five quasars at z ~ 6 selected from 260 deg2 of the Sloan Digital Sky Survey (SDSS) southern survey, a deep imaging survey obtained by repeatedly scanning a stripe along the celestial equator. The five quasars with 20 < zAB < 21 are 1-2 magnitudes fainter than the luminous z ~ 6 quasars discovered in the SDSS main survey. One of them was independently discovered by the UKIRT Infrared Deep Sky Survey. These quasars, combined with another z ~ 6 quasar known in this region, make a complete flux-limited quasar sample at zAB < 21. The sample spans the redshift range 5.85 <= z <= 6.12 and the luminosity range -26.5 <= M 1450 <= -25.4 (H 0 = 70 km s-1 Mpc-1, Ω m = 0.3, and ΩΛ = 0.7). We use the 1/Va method to determine that the comoving quasar spatial density at langzrang = 6.0 and langM 1450rang = -25.8 is (5.0 ± 2.1) × 10-9 Mpc-3 mag-1. We model the bright-end quasar luminosity function (QLF) at z ~ 6 as a power law Φ(L 1450) vprop L β 1450. The slope β calculated from a combination of our sample and the luminous SDSS quasar sample is -3.1 ± 0.4, significantly steeper than the slope of the QLF at z ~ 4. Based on the derived QLF, we find that the quasar/active galactic nucleus (AGN) population cannot provide enough photons to ionize the intergalactic medium (IGM) at z ~ 6 unless the IGM is very homogeneous and the luminosity (L*1450) at which the QLF power law breaks is very low. Based on observations obtained with the Sloan Digital Sky Survey, which is owned and operated by the Astrophysical Research Consortium; the MMT Observatory, a joint facility of the University of Arizona and the Smithsonian Institution; the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile; the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration, and was made possible by the generous financial

Quasars Probing Quasars: the Circumgalactic Medium Surrounding z ~ 2 Quasars

NASA Astrophysics Data System (ADS)

Lau, Marie; Quasars Probing Quasars survey

2018-01-01

Understanding the circumgalactic medium--the gaseous halo surrounding a galaxy, is an integral part to understanding galaxy evolution. The z ~ 2-3 universe is interesting as this is when the star formation rate and AGN activity peak. My thesis concludes the decade-long Quasars Probing Quasars survey designed for studying massive galaxy formation and quasar feedback. I use background quasar sightlines that pass close to foreground quasars to study the circumgalactic medium of quasar-host galaxies in absorption. My sample of 149 quasar pairs involve spectra taken with 17 different optical and near IR instruments. I present results on the statistical and physical properties of the circumgalactic medium. The circumgalactic medium is enriched even beyond the virial radius. The alpha/Fe abundance ratio is enhanced, suggesting enrichment from core-collapse supernovae. The cool gas mass within the virial radius is enough to fuel star formation for another Gyr, and may account for 1/3 of the baryonic budget of the galaxy halo. The ionization state increases with projected distance from the quasar, which implies the quasar does not dominate the ionizing radiation flux. However, detection of fluorescent Lyman-alpha emission and NV absorption imply these transverse absorbers are partially illuminated by the quasar. In one peculiar case, the absorbing clump has density >100 cm^-3 and sub-parsec size. The average absorption in the circumgalactic medium exhibits large velocity widths, and is asymmetric about the systemic redshift of the galaxies. The widths are consistent with gravitational motions and Hubble flow, and outflows are not required to explain them. The asymmetry can be explained if the ionizing radiation from the quasar is anisotropic or intermittent and the gas is not in inflow. My results pose challenges for cosmological hydrodynamic simulations to produce a substantial cool gas reservoir surrounding quasars, that is also enriched and shows extreme kinematics.

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.

2016-12-01

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 6.0 GHz and 1.4 GHz. 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] ≲ 1040 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 ( ˜ 40 μJy-40 mJy) field radio sources observed over ˜120 arcmin2 of our data. 60 per cent 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.

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 z s = 1.64. The Einstein Radius estimated from the DES images is 0.51''. DES J2146-0047 is in the area of overlap between DESmore » 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 z s = 2.38 and absorption compatible with Mg II and Fe II at z l = 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 × 10 11 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

Discovery of two gravitationally lensed quasars in the Dark Energy Survey

DOE Office of Scientific and Technical Information (OSTI.GOV)

Agnello, A.

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 z s = 1.64. The Einstein Radius estimated from the DES images is 0.51''. DES J2146-0047 is in the area of overlap between DESmore » 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 z s = 2.38 and absorption compatible with Mg II and Fe II at z l = 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 × 10 11 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

Quasars Probing Quasars: The Circumgalactic Medium Surrounding Z 2 Quasars

NASA Astrophysics Data System (ADS)

Lau, Marie Wingyee

Models of galaxy formation make the most direct predictions on gas related processes. Specifically, a picture on how gas flows through dark matter halos and onto galaxies to fuel star formation. A major prediction is that massive halos, including those hosting the progenitors of massive elliptical galaxies, exhibit a higher fraction of hot gas with T 107 K. Another prediction is that some mechanism must be invoked to quench the supply of cool gas in massive systems. Under the current galaxy formation paradigm, every massive galaxy has undergone a quasar phase, making high-redshift quasars the progenitors of inactive supermassive black holes found in the center of nearly all galaxies. Moreover, quasars clustering implies Mhalo = 1012.5 Msun , making quasar-host galaxies the progenitors of present day, massive, red and dead galaxies. The Quasars Probing Quasars survey is well-suited to examine gas related processes in the context of massive galaxy formation, as well as quasar feedback. To date the survey has selected 700 closely projected quasar pairs. To study the circumgalactic medium, a sub-sample of pairs with projected separation within 300 kpc at the foreground quasar's redshift are selected. From the first to seventh paper in the Quasars Probing Quasars series, the statistical results had been limited to covering fractions, equivalent widths, and without precise redshift measurements of the foreground quasars. Signatures of quasar feedback in the cool circumgalactic medium had not been identified. Hence, a sub-sample of 14 pairs with echellette spectra are selected for more detailed analysis. It is found that the low and high ions roughly trace each other in velocity structure. The HI and low ion surface densities decline with projected distance. HI absorption is strong even beyond the virial radius. Unresolved Lyalpha emission in one case and NV detection in another case together imply that a fraction of transverse sightlines are illuminated. The ionization

Deep CFHT Y-band Imaging of VVDS-F22 Field. II. Quasar Selection and Quasar Luminosity Function

NASA Astrophysics Data System (ADS)

Yang, Jinyi; Wu, Xue-Bing; Liu, Dezi; Fan, Xiaohui; Yang, Qian; Wang, Feige; McGreer, Ian D.; Fan, Zuhui; Yuan, Shuo; Shan, Huanyuan

2018-03-01

We report the results of a faint quasar survey in a one-square-degree field. The aim is to test the Y-K/g-z and J-K/i-Y color selection criteria for quasars at faint magnitudes to obtain a complete sample of quasars based on deep optical and near-infrared color–color selection and to measure the faint end of the quasar luminosity function (QLF) over a wide redshift range. We carried out a quasar survey based on the Y-K/g-z and J-K/i-Y quasar selection criteria, using the deep Y-band data obtained from our CFHT/WIRCam Y-band images in a two-degree field within the F22 field of the VIMOS VLT deep survey, optical co-added data from Sloan Digital Sky Survey Stripe 82 and deep near-infrared data from the UKIDSS Deep Extragalactic Survey in the same field. We discovered 25 new quasars at 0.5< z< 4.5 and i< 22.5 mag within one-square-degree field. The survey significantly increases the number of faint quasars in this field, especially at z∼ 2{--}3. It confirms that our color selections are highly complete in a wide redshift range (z< 4.5), especially over the quasar number density peak at z∼ 2{--}3, even for faint quasars. Combining all previous known quasars and new discoveries, we construct a sample with 109 quasars and measure the binned QLF and parametric QLF. Although the sample is small, our results agree with a pure luminosity evolution at lower redshift and luminosity evolution and density evolution model at redshift z> 2.5.

Spectroscopic CCD surveys for quasars at large redshift. 3: The Palomar Transit Grism Survey catalog

NASA Technical Reports Server (NTRS)

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

1994-01-01

This paper reports the initial results of the Palomar Transit Grism Survey (PTGS). The PTGS was designed to produce a sample of z greater than 2.7 quasars that were identified by well-defined selection criteria. The survey consists of six narrow (approximately equal to 8.5 min wide) strips of sky; the total effective area is 61.47 sq deg. Low-resolution slitless spectra, covering the wavelength range from 4400 to 7500 A, were obtained for approximately 600 000 objects. The wavelength- and flux-calibrated spectra were searched for emission lines with an automatic software algorithm. A total to 1655 emission features in the grism data satisfied our signal-to-noise ratio and equivalent width selection criteria; subsequent slit spectroscopy of the candidates confirmed the existence of 1052 lines (928 different objects). Six groups of emission lines were detected in the survey: Lyman alpha + N V, C IV, C III1, Mg II, H Beta + (O III), and H alpha + (S II). More than two-thirds of the candidates are low-redshift (z less than 0.45) emission-line galaxies; ninety objects are high-redshift quasars (z greater than 2.7) detected via their Lyman alpha + N V emission lines. The survey contains three previously unknown quasars brighter than 17th magnitude; all three have redshifts of approximately equal to 1.3. In this paper we present the observational properties of the survey, the algorithms used to select the emission-line candidates, and the catalog of emission-line objects.

Heavily reddened quasars at z ˜ 2 in the UKIDSS Large Area Survey: a transitional phase in AGN evolution

NASA Astrophysics Data System (ADS)

Banerji, Manda; McMahon, Richard G.; Hewett, Paul C.; Alaghband-Zadeh, Susannah; Gonzalez-Solares, Eduardo; Venemans, Bram P.; Hawthorn, Melanie J.

2012-12-01

We present a new sample of purely near-infrared-selected KVega < 16.5 [KAB < 18.4] extremely red [(J - K)Vega > 2.5] quasar candidates at z ˜ 2 from ≃900 deg2 of data in the UKIDSS Large Area Survey (LAS). Five of these are spectroscopically confirmed to be heavily reddened type 1 active galactic nuclei (AGN) with broad emission lines bringing our total sample of reddened quasars from the UKIDSS-LAS to 12 at z = 1.4-2.7. At these redshifts, Hα (6563 Å) is in the K band. However, the mean Hα equivalent width of the reddened quasars is only 10 per cent larger than that of the optically selected population and cannot explain the extreme colours. Instead, dust extinction of AV ˜ 2-6 mag is required to reproduce the continuum colours of our sources. This is comparable to the dust extinctions seen in submillimetre galaxies at similar redshifts. We argue that the AGN are likely being observed in a relatively short-lived breakout phase when they are expelling gas and dust following a massive starburst, subsequently turning into UV-luminous quasars. Some of our quasars show direct evidence for strong outflows (v ˜ 800-1000 km s-1) affecting the Hα line consistent with this scenario. We predict that a larger fraction of reddened quasar hosts are likely to be submillimetre bright compared to the UV-luminous quasar population. We use our sample to place new constraints on the fraction of obscured type 1 AGN likely to be missed in optical surveys. Taken at face value our findings suggest that the obscured fraction depends on quasar luminosity. The space density of obscured quasars is approximately five times that inferred for UV-bright quasars from the Sloan Digital Sky Survey (SDSS) luminosity function at Mi < -30 but seems to drop at lower luminosities even accounting for various sources of incompleteness in our sample. We find that at Mi ˜ -28 for example, this fraction is unlikely to be larger than ˜20 per cent although these fractions are highly uncertain at

Using Variability to Search for Lensed Quasars in the Dark Energy Survey

NASA Astrophysics Data System (ADS)

Buckley-Geer, Elizabeth J.; Dark Energy Survey Collaboration

2014-01-01

The Dark Energy Survey (DES) has just started its first season of a 5 year program using the DECam instrument on the Blanco 4m telescope at CTIO. Over the course of the 5 year survey we expect to discover about 120 lensed quasars brighter than i=21, including 20 high information-content quads (third brightest image required to be i<21). Strongly lensed quasars can be used to measure cosmological parameters. The time delays between the multiple images can be measured via dedicated monitoring campaigns, while the gravitational potential of the lensing galaxy and of structures along the line of sight can be modeled and measured using deep high resolution imaging and spectroscopy. The combination of these observables enables a distance, known as the time-delay distance (a combination of angular diameter distances) to be measured, which in turn can be converted into a measurement of cosmological parameters including those describing the Dark Energy equation of state. The first step in this measurement is to identify the lensed quasars. Traditionally, quasar candidates have been identified by their blue u-g color which allows them to be separated from the much more numerous stellar contaminants. However, the Dark Energy Survey does not take data in the u-band so other techniques must be employed. One such technique is based on the instrinsic variability of quasars (Schmidt et al, 2010, ApJ 714 1194). We have simulated what we would expect for the DES observing cadence in the first two seasons where we expect four visits to a given patch of sky spread over the two years. We will show results from the simulations as well as a first look at the data from the Science Verification phase of DES.

New Discoveries Fill the Quasar Gap

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2017-04-01

Quasars active and luminous galactic centers can be difficult to find at some high redshifts due to their camouflaging color. A team of scientists has now come up with a way to detect these distant monsters in spite of their disguise.Quasar CamouflageThe color track of quasars between 5 z 6 in the commonly used i z and r i bands. Each dot on the red line marks a 0.1 difference in redshift. The contours show the colors of M dwarfs, from early type to late type. Quasars at a redshift of 5.3 z 5.7 are clearly contaminated by M dwarfs, making them difficult to identify. [Adapted from Yang et al. 2017]One of the key ways we can study the early universe is by building a large sample of high-redshift quasars. In particular, we believe that reionization of the universe is just completing around z 6. Quasars near this redshift are crucial tools for probing the post-reionization epoch and exploring the evolution of the intergalactic medium, quasar evolution, and early supermassive black hole growth.But quasars at this redshift are difficult to detect! The problem is contamination: quasars at this distance are the same color in commonly used optical bands as cool M-dwarf stars. As a result, surveys searching for quasars have often just cut out that entire section of the color space in order to avoid this contamination.This means that theres a huge gap in our sample of quasars around z 5.5: of the more than 300,000 quasars known, only 30 have been found in the redshift range of 5.3 z 5.7.The addition of new colorcolor selection criteria using infrared bands (bottom two plots) allows the authors to differentiate quasars (blue) from M dwarfs (grey), which isnt possible when only the traditional optical colorcolor selection criteria are used (top plot). [Adapted from Yang et al. 2017]A New ApproachIn a recent publication led by Jinyi Yang (Peking University, China and Steward Observatory, University of Arizona), a team of scientists has demonstrated a new technique for finding

The Ensemble Photometric Variability of Over 105 Quasars in the Dark Energy Camera Legacy Survey and the Sloan Digital Sky Survey

NASA Astrophysics Data System (ADS)

Li, Zefeng; McGreer, Ian D.; Wu, Xue-Bing; Fan, Xiaohui; Yang, Qian

2018-07-01

We present the ensemble variability analysis results of quasars using the Dark Energy Camera Legacy Survey (DECaLS) and the Sloan Digital Sky Survey (SDSS) quasar catalogs. Our data set includes 119,305 quasars with redshifts up to 4.89. Combining the two data sets provides a 15 year baseline and permits the analysis of the long timescale variability. Adopting a power-law form for the variability structure function, V=A{(t/1{years})}γ , we use the multidimensional parametric fitting to explore the relationships between the quasar variability amplitude and a wide variety of quasar properties, including redshift (positive), bolometric luminosity (negative), rest-frame wavelength (negative), and black hole mass (uncertain). We also find that γ can be also expressed as a function of redshift (negative), bolometric luminosity (positive), rest-frame wavelength (positive), and black hole mass (positive). Tests of the fitting significance with the bootstrap method show that, even with such a large quasar sample, some correlations are marginally significant. The typical value of γ for the entire data set is ≳0.25, consistent with the results in previous studies on both the quasar ensemble variability and the structure function. A significantly negative correlation between the variability amplitude and the Eddington ratio is found, which may be explained as an effect of accretion disk instability.

A Study of Quasar Selection in the Supernova Fields of the Dark Energy Survey

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tie, S. S.; Martini, P.; Mudd, D.

In this paper, we present a study of quasar selection using the supernova fields of the Dark Energy Survey (DES). We used a quasar catalog from an overlapping portion of the SDSS Stripe 82 region to quantify the completeness and efficiency of selection methods involving color, probabilistic modeling, variability, and combinations of color/probabilistic modeling with variability. In all cases, we considered only objects that appear as point sources in the DES images. We examine color selection methods based on the Wide-field Infrared Survey Explorer (WISE) mid-IR W1-W2 color, a mixture of WISE and DES colors (g - i and i-W1),more » and a mixture of Vista Hemisphere Survey and DES colors (g - i and i - K). For probabilistic quasar selection, we used XDQSO, an algorithm that employs an empirical multi-wavelength flux model of quasars to assign quasar probabilities. Our variability selection uses the multi-band χ 2-probability that sources are constant in the DES Year 1 griz-band light curves. The completeness and efficiency are calculated relative to an underlying sample of point sources that are detected in the required selection bands and pass our data quality and photometric error cuts. We conduct our analyses at two magnitude limits, i < 19.8 mag and i < 22 mag. For the subset of sources with W1 and W2 detections, the W1-W2 color or XDQSOz method combined with variability gives the highest completenesses of >85% for both i-band magnitude limits and efficiencies of >80% to the bright limit and >60% to the faint limit; however, the giW1 and giW1+variability methods give the highest quasar surface densities. The XDQSOz method and combinations of W1W2/giW1/XDQSOz with variability are among the better selection methods when both high completeness and high efficiency are desired. We also present the OzDES Quasar Catalog of 1263 spectroscopically confirmed quasars from three years of OzDES observation in the 30 deg 2 of the DES supernova fields. Finally, the catalog

A Study of Quasar Selection in the Supernova Fields of the Dark Energy Survey

DOE PAGES

Tie, S. S.; Martini, P.; Mudd, D.; ...

2017-02-15

In this paper, we present a study of quasar selection using the supernova fields of the Dark Energy Survey (DES). We used a quasar catalog from an overlapping portion of the SDSS Stripe 82 region to quantify the completeness and efficiency of selection methods involving color, probabilistic modeling, variability, and combinations of color/probabilistic modeling with variability. In all cases, we considered only objects that appear as point sources in the DES images. We examine color selection methods based on the Wide-field Infrared Survey Explorer (WISE) mid-IR W1-W2 color, a mixture of WISE and DES colors (g - i and i-W1),more » and a mixture of Vista Hemisphere Survey and DES colors (g - i and i - K). For probabilistic quasar selection, we used XDQSO, an algorithm that employs an empirical multi-wavelength flux model of quasars to assign quasar probabilities. Our variability selection uses the multi-band χ 2-probability that sources are constant in the DES Year 1 griz-band light curves. The completeness and efficiency are calculated relative to an underlying sample of point sources that are detected in the required selection bands and pass our data quality and photometric error cuts. We conduct our analyses at two magnitude limits, i < 19.8 mag and i < 22 mag. For the subset of sources with W1 and W2 detections, the W1-W2 color or XDQSOz method combined with variability gives the highest completenesses of >85% for both i-band magnitude limits and efficiencies of >80% to the bright limit and >60% to the faint limit; however, the giW1 and giW1+variability methods give the highest quasar surface densities. The XDQSOz method and combinations of W1W2/giW1/XDQSOz with variability are among the better selection methods when both high completeness and high efficiency are desired. We also present the OzDES Quasar Catalog of 1263 spectroscopically confirmed quasars from three years of OzDES observation in the 30 deg 2 of the DES supernova fields. Finally, the catalog

Dust-reddened Quasars In First And Ukidss

NASA Astrophysics Data System (ADS)

Glikman, Eilat; Lacy, M.; Urrutia, T.

2012-05-01

We recently identified a large population of dust-reddened quasars by matching radio sources detected in the FIRST survey to the 2MASS near-infrared catalog (F2M) and selecting sources with red topical-to-near-infrared colors. We find that dust-reddened quasars are intrinsically the most luminous quasars in the Universe. Further analysis suggests that red quasars represent an emergent phase in merger-driven quasar/galaxy co-evolution model where the obscured quasar is shedding its dusty shroud prior to becoming a "normal" quasar. Here we use the UKIDSS Large Area Survey (LAS) First Data Release (DR1; 190 deg2) to reach fainter K-band magnitudes and expand beyond the results of the F2M survey. The deeper K-band limit provided by UKIDSS enables the discovery of more heavily reddened quasars at higher redshifts. We selected 95 candidates in the UKIDSS DR1 that had matches in the FIRST catalog with K<17.0 and obeyed color criteria similar to the F2M survey (R-K>5, J-K > 1.5). We have obtained 54 near-infrared spectra as well as 12 optical spectra from SDSS. Preliminary analysis confirm 12 new obscured quasars, including at least two with z>2 reaching lower intrinsic luminosities than were found by the F2M survey. We find that despite being a luminous quasar phenomenon, the space density of red quasars continues to rise to fainter magnitudes, representing 20% of the overall quasar population.

The large area KX quasar catalogue - I. Analysis of the photometric redshift selection and the complete quasar catalogue

NASA Astrophysics Data System (ADS)

Maddox, Natasha; Hewett, Paul C.; Péroux, Céline; Nestor, Daniel B.; Wisotzki, Lutz

2012-08-01

The results of a large area, ˜600 deg2, K-band flux-limited spectroscopic survey for luminous quasars are presented. The survey utilizes the UKIRT Infrared Deep Sky Survey (UKIDSS) Large Area Survey (LAS) in regions of sky within the Sloan Digital Sky Survey (SDSS) footprint. The K-band excess (KX) of all quasars with respect to Galactic stars is exploited in combination with a photometric redshift/classification scheme to identify quasar candidates for spectroscopic follow-up observations. The data contained within this investigation will be able to provide new constraints on the fraction of luminous quasars reddened by dust with E(B - V) ≤ 0.5 mag. The spectroscopic sample is defined using the K-band, 14.0 ≤ K ≤ 16.6, and SDSS i-band limits of i = 19.5, 19.7 and 22.0 over sky areas of 287, 150 and 196 deg2, respectively. The survey includes >3200 known quasars from the SDSS and more than 250 additional confirmed quasars from the KX selection. A well-defined subsample of quasars in the redshift interval 1.0 ≤ z ≤ 3.5 includes 1152 objects from the SDSS and 172 additional KX-selected quasars. The quasar selection is >95 per cent complete with respect to known SDSS quasars and >95 per cent efficient, largely independent of redshift and i-band magnitude. The properties of the new KX-selected quasars confirm the known redshift-dependent effectiveness of the SDSS quasar selection and provide a sample of luminous quasars experiencing intermediate levels of extinction by dust. The catalogue represents an important step towards the assembly of a well-defined sample of luminous quasars that may be used to investigate the properties of quasars experiencing intermediate levels of dust extinction within their host galaxies or due intervening absorption line systems. †Based on observations made with ESO telescopes at the La Silla Paranal Observatory under programme IDs 083.A0360 and 085.A0359.‡Based on observations collected at the Centro Astronómico Hispano

Discovery of three strongly lensed quasars in the Sloan Digital Sky Survey

NASA Astrophysics Data System (ADS)

Williams, P. R.; Agnello, A.; Treu, T.; Abramson, L. E.; Anguita, T.; Apostolovski, Y.; Chen, G. C.-F.; Fassnacht, C. D.; Hsueh, J. W.; Lemaux, B. C.; Motta, V.; Oldham, L.; Rojas, K.; Rusu, C. E.; Shajib, A. J.; Wang, X.

2018-06-01

We present the discovery of three quasar lenses in the Sloan Digital Sky Survey, selected using two novel photometry-based selection techniques. The J0941+0518 system, with two point sources separated by 5.46 arcsec on either side of a galaxy, has source and lens redshifts 1.54 and 0.343. Images of J2257+2349 show two point sources separated by 1.67 arcsec on either side of an E/S0 galaxy. The extracted spectra show two images of the same quasar at zs = 2.10. SDSS J1640+1045 has two quasar spectra at zs = 1.70 and fits to the SDSS and Pan-STARRS images confirm the presence of a galaxy between the two point sources. We observed 56 photometrically selected lens candidates in this follow-up campaign, confirming three new lenses, re-discovering one known lens, and ruling out 36 candidates, with 16 still inconclusive. This initial campaign demonstrates the power of purely photometric selection techniques in finding lensed quasars.

The fraction and mid-infrared properties of broad absorption line quasars from the Sloan Digital Sky Survey

NASA Astrophysics Data System (ADS)

Pu, Xingting

2014-02-01

We present the results of a study which uses a sample of 1822 Sloan Digital Sky Survey (SDSS) quasars with reliable Wide-field Infrared Survey Explorer (WISE) detections in the redshift range 1.7≤ z≤4.38 to investigate the mid-infrared fraction of broad absorption line (BAL) quasars. The BAL quasars in the sample include both high-ionization BAL (HiBAL) quasars that show broad absorption from C iv and low-ionization BAL (LoBAL) quasars that show additional broad absorption from Mg ii. The fraction of C iv BAL quasars with nonzero absorption index (AI) is found to be 38.7±1.2 %, in good agreement with that derived for the Two Micron All Sky Survey (2MASS) sample. The C iv BAL quasar fractions remain constant with magnitude in the WISE 3.4 μm (W1) and 4.6 μm (W2) bands, and increase rapidly with decreasing magnitude in the WISE 12 μm (W3) and 22 μm (W4) bands. The nonzero AI fraction of 44.5±2.1 % determined in the WISE W4 band is more likely to represent the intrinsic BAL quasar fraction. No evidence that the fraction is a strong function of redshift is found. At 1.7≤ z≤2.15, the overall mid-infrared LoBAL fraction is and the fractions increase significantly with decreasing magnitude in all four of WISE bands. Moreover, it is found that the mean optical-to-WISE colors of BAL quasars are ≃0.2 mag redder than that of non-BAL quasars, while the traditional (nonzero balnicity) BAL quasars are redder than the nontraditional BAL quasars by ≃0.15 mag, which suggest a continuum of more reddening from non-BAL to nontraditional BAL to traditional BAL. No evidence that nontraditional BALs are a distinct class from traditional BALs is found. Finally, it is shown that the mean optical-to-WISE colors of LoBALs are ≃0.4 mag redder than that of HiBALs at 1.7≤ z≤2.15.

Gravitational lensing of quasars as seen by the Hubble Space Telescope Snapshot Survey

NASA Technical Reports Server (NTRS)

Maoz, D.; Bahcall, J. N.; Doxsey, R.; Schneider, D. P.; Bahcall, N. A.; Lahav, O.; Yanny, B.

1992-01-01

Results from the ongoing HST Snapshot Survey are presented, with emphasis on 152 high-luminosity, z greater than 1 quasars. One quasar among those observed, 1208 + 1011, is a candidate lens system with subarcsecond image separation. Six other quasars have point sources within 6 arcsec. Ground-based observations of five of these cases show that the companion point sources are foreground Galactic stars. The predicted lensing frequency of the sample is calculated for a variety of cosmological models. The effect of uncertainties in some of the observational parameters upon the predictions is discussed. No correlation of the drift rate with time, right ascension, declination, or point error is found.

Clustering of High-Redshift Quasars

NASA Astrophysics Data System (ADS)

Timlin, John D., III

In this work, we investigate the clustering of faint quasars in the early Universe and use the clustering strength to gain a better understanding of quasar feedback mechanisms and the growth of central supermassive black holes at early times in the history of the Universe. It has long been understood (e.g., Hopkins et al. 2007a) that the clustering of distant quasars can be used as a probe of different feedback models; however, until now, there was no sample of faint, high-redshift quasars with sufficient density to accurately measure the clustering strength. Therefore we conducted a new survey to increase the number density of these objects. Here, we describe the Spitzer -IRAC Equatorial Survey (SpIES) which is a moderately deep, large-area Spitzer survey which was designed to discover faint, high-redshift (2.9 ≤ z ≤ 5.1) quasars. SpIES spans 115 deg 2 in the equatorial "Stripe 82" region of the Sloan Digital Sky Survey (SDSS) and probes to 5sigma depths of 6.13 microJy (21.93 AB magnitude) and 5.75 microJy (22.0 AB magnitude) at 3.6 and 4.5 microns. At these depths, SpIES is able to observe faint quasars, and we show that SpIES recovers 94% of the high-redshift (z ≥ 3.5), spectroscopically-confirmed quasars that lie within its footprint. SpIES is also ideally located on Stripe 82 for two reasons: It surrounds existing infrared data from the Spitzer-HETDEX Exploratory Large-area (SHELA) survey which increases the area of infrared coverage, and there is a wide range of multi-wavelength, multi-epoch ancillary data on Stripe 82 which we can use together to select high-redshift quasar candidates. To photometrically identify quasar candidates, we combined the optical data from the Sloan Digital Sky Survey and the infrared data from SpIES and SHELA and employed three machine learning algorithms. These algorithms were trained on the optical/infrared colors of known, high-redshift quasars. Using this method, we generate a sample of 1378 objects that are both faint

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huo, Zhi-Ying; Bai, Zhong-Rui; Chen, Jian-Jun

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 17more » 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

A Chandra Snapshot Survey of Extremely Red Quasars from SDSS BOSS and WISE

NASA Astrophysics Data System (ADS)

Garmire, Gordon

2017-09-01

We propose Chandra snapshot observations of a sample of 15 extremely red and highly luminous quasars at z > 2. These Type 1 objects have recently been discovered via the SDSS BOSS and WISE surveys, and they are among the most-luminous quasars in the Universe. They appear to be part of the missing evolutionary link as merger-induced starburst galaxies transform into typical ultraviolet luminous quasars. Our aim is to efficiently gather X-ray information about a sufficiently large sample of these objects that general conclusions about their basic X-ray properties, especially obscuration level and luminosity, can be drawn reliably. The results will also allow effective targeting of promising objects in longer X-ray spectroscopic observations.

Accurate spectroscopic redshift of the multiply lensed quasar PSOJ0147 from the Pan-STARRS survey

NASA Astrophysics Data System (ADS)

Lee, C.-H.

2017-09-01

Context. The gravitational lensing time delay method provides a one-step determination of the Hubble constant (H0) with an uncertainty level on par with the cosmic distance ladder method. However, to further investigate the nature of the dark energy, a H0 estimate down to 1% level is greatly needed. This requires dozens of strongly lensed quasars that are yet to be delivered by ongoing and forthcoming all-sky surveys. Aims: In this work we aim to determine the spectroscopic redshift of PSOJ0147, the first strongly lensed quasar candidate found in the Pan-STARRS survey. The main goal of our work is to derive an accurate redshift estimate of the background quasar for cosmography. Methods: To obtain timely spectroscopically follow-up, we took advantage of the fast-track service programme that is carried out by the Nordic Optical Telescope. Using a grism covering 3200-9600 Å, we identified prominent emission line features, such as Lyα, N V, O I, C II, Si IV, C IV, and [C III] in the spectra of the background quasar of the PSOJ0147 lens system. This enables us to determine accurately the redshift of the background quasar. Results: The spectrum of the background quasar exhibits prominent absorption features bluewards of the strong emission lines, such as Lyα, N V, and C IV. These blue absorption lines indicate that the background source is a broad absorption line (BAL) quasar. Unfortunately, the BAL features hamper an accurate determination of redshift using the above-mentioned strong emission lines. Nevertheless, we are able to determine a redshift of 2.341 ± 0.001 from three of the four lensed quasar images with the clean forbidden line [C III]. In addition, we also derive a maximum outflow velocity of 9800 km s-1 with the broad absorption features bluewards of the C IV emission line. This value of maximum outflow velocity is in good agreement with other BAL quasars.

The quasar luminosity function at redshift 4 with the Hyper Suprime-Cam Wide Survey

NASA Astrophysics Data System (ADS)

Akiyama, Masayuki; He, Wanqiu; Ikeda, Hiroyuki; Niida, Mana; Nagao, Tohru; Bosch, James; Coupon, Jean; Enoki, Motohiro; Imanishi, Masatoshi; Kashikawa, Nobunari; Kawaguchi, Toshihiro; Komiyama, Yutaka; Lee, Chien-Hsiu; Matsuoka, Yoshiki; Miyazaki, Satoshi; Nishizawa, Atsushi J.; Oguri, Masamune; Ono, Yoshiaki; Onoue, Masafusa; Ouchi, Masami; Schulze, Andreas; Silverman, John D.; Tanaka, Manobu M.; Tanaka, Masayuki; Terashima, Yuichi; Toba, Yoshiki; Ueda, Yoshihiro

2018-01-01

We present the luminosity function of z ˜ 4 quasars based on the Hyper Suprime-Cam Subaru Strategic Program Wide layer imaging data in the g, r, i, z, and y bands covering 339.8 deg2. From stellar objects, 1666 z ˜ 4 quasar candidates are selected via the g-dropout selection down to i = 24.0 mag. Their photometric redshifts cover the redshift range between 3.6 and 4.3, with an average of 3.9. In combination with the quasar sample from the Sloan Digital Sky Survey in the same redshift range, a quasar luminosity function covering the wide luminosity range of M1450 = -22 to -29 mag is constructed. The quasar luminosity function is well described by a double power-law model with a knee at M1450 = -25.36 ± 0.13 mag and a flat faint-end slope with a power-law index of -1.30 ± 0.05. The knee and faint-end slope show no clear evidence of redshift evolution from those seen at z ˜ 2. The flat slope implies that the UV luminosity density of the quasar population is dominated by the quasars around the knee, and does not support the steeper faint-end slope at higher redshifts reported at z > 5. If we convert the M1450 luminosity function to the hard X-ray 2-10 keV luminosity function using the relation between the UV and X-ray luminosity of quasars and its scatter, the number density of UV-selected quasars matches well with that of the X-ray-selected active galactic nuclei (AGNs) above the knee of the luminosity function. Below the knee, the UV-selected quasars show a deficiency compared to the hard X-ray luminosity function. The deficiency can be explained by the lack of obscured AGNs among the UV-selected quasars.

Narrow C IV absorption doublets on quasar spectra of the Baryon Oscillation Spectroscopic Survey

NASA Astrophysics Data System (ADS)

Chen, Zhi-Fu; Gu, Qiu-Sheng; Zhou, Luwenjia; Chen, Yan-Mei

2016-11-01

In this paper, we extend our work of Papers I and II, which are assigned to systematically survey C IV λλ1548,1551 narrow absorption lines (NALs) with zabs ≪ zem on quasar spectra of the Baryon Oscillation Spectroscopic Survey (BOSS) to collect C IV NALs with zabs ≈ zem from blue to red wings of C IV λ1549 emission lines. Together with Papers I and II, we have collected a total number of 41 479 C IV NALs with 1.4544 ≤ zabs ≤ 4.9224 in surveyed spectral region redward of Lyα until red wing of C IV λ1549 emission line. We find that the stronger C IV NALs tend to be the more saturated absorptions, and associated systems (zabs ≈ zem) seem to have larger absorption strengths when compared to intervening ones (zabs ≪ zem). The redshift density evolution behaviour of absorbers (the number of absorbers per redshift path) is similar to the history of the cosmic star formation. When compared to the quasar-frame velocity (β) distribution of Mg II absorbers, the β distribution of C IV absorbers is broader at β ≈ 0, shows longer extended tail, and exhibits a larger dispersion for environmental absorptions. In addition, for associated C IV absorbers, we find that low-luminosity quasars seem to exhibit smaller β and stronger absorptions when compared to high-luminosity quasars.

Reliable samples of quasars and hot stars from a spectrophotometric survey of the U.S. catalogs

NASA Technical Reports Server (NTRS)

Mitchell, Kenneth J.

1987-01-01

The U.S. survey for blue- and ultraviolet-excess starlike objects is reviewed, focusing on the features which have contributed to its accuracy. The spectrophotometric survey is described in terms of the observational setup and procedures. It is suggested that the survey has produced reliably classified samples of quasars and hot evolved stars and that the procedures used in the study provide a means of deriving distance and luminosity information about these objects. Several cumulative number counts and spectra of a DA white dwarf and a quasar with prominent C IV and C III emission are given as examples.

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.

Sloan Digital Sky Survey III photometric quasar clustering: Probing the initial conditions of the Universe

DOE PAGES

Ho, Shirley; Agarwal, Nishant; Myers, Adam D.; ...

2015-05-22

Here, the Sloan Digital Sky Survey has surveyed 14,555 square degrees of the sky, and delivered over a trillion pixels of imaging data. We present the large-scale clustering of 1.6 million quasars between z=0.5 and z=2.5 that have been classified from this imaging, representing the highest density of quasars ever studied for clustering measurements. This data set spans 0~ 11,00 square degrees and probes a volume of 80 h –3 Gpc 3. In principle, such a large volume and medium density of tracers should facilitate high-precision cosmological constraints. We measure the angular clustering of photometrically classified quasars using an optimalmore » quadratic estimator in four redshift slices with an accuracy of ~ 25% over a bin width of δ l ~ 10–15 on scales corresponding to matter-radiation equality and larger (0ℓ ~ 2–3).« less

Finding Hidden Quasars with UKIDSS and AAOmega

NASA Astrophysics Data System (ADS)

Maddox, Natasha; Hewett, P. C.; Warren, S. J.; Croom, S. M.

2007-05-01

The number of luminous quasars that have thus far eluded optical surveys is a subject of ongoing debate. Dust reddening and significant host galaxy light tend to exclude candidates from traditional UV-excess selection. UKIDSS, the near-infrared counterpart to SDSS, has started to provide the large area NIR data required to quantify the number of quasars missing from optical surveys. The quasar candidate list was chosen from the Early Data Release of the UKIDSS Large Area Survey (LAS), which aims to cover 2000 square degrees in two years. Requiring each object to have K<17, J<19.5 (the detection limit of the LAS) and a detection in SDSS were the only restrictions imposed on the candidates. A simple cut in gJK colour space, exploiting the K-band excess of quasars compared to stars, then separates the quasar candidates from the stellar locus. Optical-NIR colour selection with relaxed restrictions on morphology is less sensitive to dust reddening, so provides a more complete candidate list, suitable for follow-up observation with the new AAOmega spectrograph on the Anglo-Australian Telescope. With spectroscopic observations covering nearly 20 square degrees taken at the AAT, this is by far the largest K-band selected quasar sample to date. Many new quasars have been identified, in addition to known quasars being recovered. Several of the newly discovered quasars lie in regions of colour space typically excluded by UV selection. This study highlights the effectiveness of the K-excess technique in selecting quasars that do not necessarily exhibit the classic UV excess, either due to intrinsic SED shape or dust reddening. Combining upcoming UKIDSS data releases with scheduled AAT observations will increase the area surveyed by several times, thus moving closer to fully quantifying the number of luminous, reddened quasars.

A Catalog of Broad Absorption Line Quasars from the Sloan Digital Sky Survey Third Data Release

NASA Astrophysics Data System (ADS)

Trump, Jonathan R.; Hall, Patrick B.; Reichard, Timothy A.; Richards, Gordon T.; Schneider, Donald P.; Vanden Berk, Daniel E.; Knapp, Gillian R.; Anderson, Scott F.; Fan, Xiaohui; Brinkman, J.; Kleinman, S. J.; Nitta, Atsuko

2006-07-01

We present a total of 4784 unique broad absorption line quasars from the Sloan Digital Sky Survey Third Data Release. An automated algorithm was used to match a continuum to each quasar and to identify regions of flux at least 10% below the continuum over a velocity range of at least 1000 km s-1 in the C IV and Mg II absorption regions. The model continuum was selected as the best-fit match from a set of template quasar spectra binned in luminosity, emission line width, and redshift, with the power-law spectral index and amount of dust reddening as additional free parameters. We characterize our sample through the traditional ``balnicity'' index and a revised absorption index, as well as through parameters such as the width, outflow velocity, fractional depth, and number of troughs. From a sample of 16,883 quasars at 1.7<=z<=4.38, we identify 4386 (26.0%) quasars with broad C IV absorption, of which 1756 (10.4%) satisfy traditional selection criteria. From a sample of 34,973 quasars at 0.5<=z<=2.15, we identify 457 (1.31%) quasars with broad Mg II absorption, 191 (0.55%) of which satisfy traditional selection criteria. We also provide a supplementary list of 39 visually identified z>4.38 quasars with broad C IV absorption. We find that broad absorption line quasars may have broader emission lines on average than other quasars.

Quasars, clusters and cosmology

NASA Astrophysics Data System (ADS)

Dhanda, Neelam

PART A: Acceleration of the Universe and Modified Gravity: We study the power of next-generation galaxy cluster surveys (such as eROSITA and WFXT) in constraining the cosmological parameters and especially the growth history of the Universe, using the information from galaxy cluster redshift and mass-function evolution and from cluster power spectrum. We use the Fisher Matrix formalism to evaluate the potential for the galaxy cluster surveys to make predictions about cosmological parameters like the gravitational growth index gamma. The primary purpose of this study has been to check whether we can rule out one or the other of the underlying gravity theories in light of the present uncertainty of mass-observable relations and their scatter evolution. We found that these surveys will provide better constraints on various cosmological parameters even after we admit a lack of complete knowledge about the galaxy cluster structure, and when we combine the information from the cluster number count redshift and mass evolution with that from the cluster power spectrum. Based on this, we studied the ability of different surveys to constrain the growth history of the Universe. It was found that whereas eROSITA surveys will need strong priors on cluster structure evolution to conclusively rule out one or the other of the two gravity models, General Relativity and DGP Braneworld Gravity; WFXT surveys do hold the special promise of differentiating growth and telling us whether it is GR or not, with its wide-field survey having the ability to say so even with 99% confidence. PART B: Chemical Evolution in Quasars: We studied chemical evolution in the broad emission line region (BELR) of nitrogen rich quasars drawn from the SDSS Quasar Catalogue IV. Using tools of emission-line spectroscopy, we made detailed abundance measurements of ˜ 40 quasars and estimated their metallicities using the line-intensity ratio method. It was found that quasars with strong nitrogen lines are

DES J0454-4448: discovery of the first luminous z ≥ 6 quasar from the Dark Energy Survey

DOE Office of Scientific and Technical Information (OSTI.GOV)

Reed, S. L.; McMahon, R. G.; Banerji, M.

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 z AB, Y AB = 20.2, 20.2 (M 1450 = -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 z AB < 21.5 from an area ofmore » ~300 deg 2. 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 W1 AB = 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 deg 2 to Y AB = 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

A Catalog of Quasar Properties from the Baryon Oscillation Spectroscopic Survey

NASA Astrophysics Data System (ADS)

Chen, Zhi-Fu; Pan, Da-Sheng; Pang, Ting-Ting; Huang, Yong

2018-01-01

Using the quasars with z em < 0.9 from the Baryon Oscillation Spectroscopic Survey, we measure the spectral characteristics, including continuum and emission lines, around the Hβ and Hα spectral regions, which are lacking in Quasar Data Release 12 (DR12Q). We estimate the virial black hole mass from broad Hα and/or Hβ, and infer quasar redshifts from [O III] λ5007 emission lines. All the measurements and derived quantities are publicly available. A comparison between [O III] λ5007 redshifts and the visual inspection redshifts included in DR12Q indicates that the visual inspection redshifts are robust. We find that the full widths at half maximum of the broad Hα are consistent with those of the broad Hβ, while both the equivalent widths and line luminosities of the broad Hα are obviously larger than the corresponding quantities of the broad Hβ. We also find that there is an obviously systematic offset between the Hβ and Hα based mass if they are inferred from the empirical relationships in the literature. Using our large quasar sample, we have improved the Hβ and Hα based mass estimators by minimizing the difference between the Hβ- and Hα-based masses. For the black hole mass estimator (Equation (1)), we find that the coefficients (a, b) = (7.00, 0.50) for Hα and (a, b) = (6.96, 0.50) for Hβ are the best choices.

Optical+NIR Quasar Selection with the SDSS and UKIDSS

NASA Astrophysics Data System (ADS)

Mehta, Sajjan S.; Mahon, R. G.; Richards, G. T.; Hewett, P. C.

2010-01-01

We present the details of an optical+near-IR quasar selection technique, which utilizes near-IR data from the UKIDSS Large Area Survey and the optical data from the Sloan Digital Sky Survey in the SDSS's deep "Stripe 82" region, which covers over 200 deg2. Our selection methods primarily consist of isolating potential candidates in giK and gJK color space, in which there exists a significant separation of the stellar locus from the quasar locus. Additionally, we discuss secondary techniques such as comparison of catalog magnitudes with aperture photometry, analysis of SDSS and UKIDSS morphological type classifications, and flag cuts. Our primary color-cut selections include most quasars with redshifts below 3.4, significantly increasing the completeness both to dust reddened quasars and quasars with redshifts z 2.7 in the SDSS footprint. A simple color cut in the UKIDSS LAS Stripe 82 regions reveals 4200 quasar candidates down to K=18. These NIR selections have been used to contribute to the Baryon Oscillation Spectroscopic Survey (BOSS), which is one of the four surveys of the SDSS-III collaboration. We additionally intend to use our NIR techniques to perform an 8-dimensional optical+NIR Bayesian selection of quasars for the AAOmege UKIDSS SDSS (AUS) survey.

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 z AB, Y AB = 20.2, 20.2 (M 1450 = –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 z AB < 21.5 from an area ofmore » ~300 deg 2. 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 W1 AB = 19.68. The discovery of one spectroscopically confirmed quasar with 5.7 < z < 6.5 and z AB ≤ 20.2 is consistent with recent determinations of the luminosity function at z ~ 6. DES when completed will have imaged ~5000 deg 2 to Y AB = 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

DES J0454–4448: Discovery of the first luminous z ≥ 6 quasar from the Dark Energy Survey

DOE Office of Scientific and Technical Information (OSTI.GOV)

Reed, S. L.

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 z AB, Y AB = 20.2, 20.2 (M 1450 = –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 z AB < 21.5 from an area ofmore » ~300 deg 2. 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 W1 AB = 19.68. The discovery of one spectroscopically confirmed quasar with 5.7 < z < 6.5 and z AB ≤ 20.2 is consistent with recent determinations of the luminosity function at z ~ 6. DES when completed will have imaged ~5000 deg 2 to Y AB = 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

The SDSS-XDQSO quasar targeting catalog

NASA Astrophysics Data System (ADS)

Bovy, Jo; Hennawi, J. F.; Hogg, D. W.; Myers, A. D.; Ross, N. P.

2011-01-01

We present the SDSS-XDQSO quasar targeting catalog for efficient flux-based quasar target selection down to the faint limit of the SDSS catalog, even at medium redshifts (2.5 < z < 3). We build models of the distributions of stars and quasars in flux space down to the flux limit by applying the extreme-deconvolution method (XD) to estimate the underlying density. We properly convolve this density with the flux uncertainties when evaluating the probability that an object is a quasar. This results in a targeting algorithm that is more principled, more efficient, and faster than other similar methods. We apply the algorithm to derive low- (z < 2.2), medium- (2.2 <= z 3.5) quasar probabilities for all 160,904,060 point-sources with dereddened i-and magnitude between 17.75 and 22.45 mag in SDSS Data Release 8. The catalog can be used to define a uniformly selected and efficient low- or medium-redshift quasar survey, such as that needed for the SDSS-III Baryon Oscillation Spectroscopic Survey project. We show that the XDQSO technique performs as well as the current best photometric quasar selection technique at low redshift, and out-performs all other flux-based methods for selecting the medium-redshift quasars of our primary interest. Research supported by NASA (grant NNX08AJ48G) and the NSF (grant AST-0908357).

Eight New Luminous z > 6 Quasars Selected via SED Model Fitting of VISTA, WISE and Dark Energy Survey Year 1 Observations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Reed, S.L.; et al.

We present the discovery and spectroscopic confirmation with the ESO NTT and Gemini South telescopes of eight new 6.0 < z < 6.5 quasars with zmore » $$_{AB}$$ < 21.0. These quasars were photometrically selected without any star-galaxy morphological criteria from 1533 deg$$^{2}$$ using SED model fitting to photometric data from the Dark Energy Survey (g, r, i, z, Y), the VISTA Hemisphere Survey (J, H, K) and the Wide-Field Infrared Survey Explorer (W1, W2). The photometric data was fitted with a grid of quasar model SEDs with redshift dependent Lyman-{\\alpha} forest absorption and a range of intrinsic reddening as well as a series of low mass cool star models. Candidates were ranked using on a SED-model based $$\\chi^{2}$$-statistic, which is extendable to other future imaging surveys (e.g. LSST, Euclid). Our spectral confirmation success rate is 100% without the need for follow-up photometric observations as used in other studies of this type. Combined with automatic removal of the main types of non-astrophysical contaminants the method allows large data sets to be processed without human intervention and without being over run by spurious false candidates. We also present a robust parametric redshift estimating technique that gives comparable accuracy to MgII and CO based redshift estimators. We find two z $$\\sim$$ 6.2 quasars with HII near zone sizes < 3 proper Mpc which could indicate that these quasars may be young with ages < 10$^6$ - 10$^7$ years or lie in over dense regions of the IGM. The z = 6.5 quasar VDESJ0224-4711 has J$$_{AB}$$ = 19.75 is the second most luminous quasar known with z > 6.5.« less

Hamburger hazards and emotions.

PubMed

Olsen, Nina Veflen; Røssvoll, Elin; Langsrud, Solveig; Scholderer, Joachim

2014-07-01

Previous studies indicate that many consumers eat rare hamburgers and that information about microbiological hazards related to undercooked meat not necessarily leads to more responsible behavior. With this study we aim to investigate whether consumers' willingness to eat hamburgers depends on the emotions they experience when confronted with the food. A representative sample of 1046 Norwegian consumers participated in an online experiment. In the first part, participants were randomly divided into two groups. One group was confronted with a picture of a rare hamburger, whereas the other group was confronted with a picture of a well-done hamburger. The respondents were instructed to imagine that they were served the hamburger on the picture and then to indicate which emotions they experienced: fear, disgust, surprise, interest, pleasure, or none of these. In part two, all respondents were confronted with four pictures of hamburgers cooked to different degrees of doneness (rare, medium rare, medium well-done, well-done), and were asked to state their likelihood of eating. We analyzed the data by means of a multivariate probit model and two linear fixed-effect models. The results show that confrontation with rare hamburgers evokes more fear and disgust than confrontation with well-done hamburgers, that all hamburgers trigger pleasure and interest, and that a consumer's willingness to eat rare hamburgers depends on the particular type of emotion evoked. These findings indicate that emotions play an important role in a consumer's likelihood of eating risky food, and should be considered when developing food safety strategies. Copyright © 2014 Elsevier Ltd. All rights reserved.

Consumer preferences, internal color and reduction of shigatoxigenic Escherichia coli in cooked hamburgers.

PubMed

Røssvoll, Elin; Sørheim, Oddvin; Heir, Even; Møretrø, Trond; Olsen, Nina Veflen; Langsrud, Solveig

2014-02-01

The aim of this study was to relate consumer preferences and preparation of hamburgers to color change, internal temperature and reduction of shigatoxigenic Escherichia coli (STEC) serogroups O157 and the "Big Six" (O26, O45, O103, O111, O121, O145) under two ground beef packaging scenarios: 75% O2 MAP and vacuum. 75% O2 MAP hamburgers cooked to 60 °C core temperature appeared done and showed less internal red color (lower a*) than corresponding vacuum hamburgers. Similar STEC reduction (<4 log10) was found for both hamburgers at core temperatures ≤ 66 °C. In a representative survey (N=1046) most consumers reported to judge hamburger doneness by the color and many preferred undercooked hamburgers. Premature browning of 75% O2 MAP hamburgers represents a risk of foodborne illness, when considering consumers' food handling practices. The risk is even greater if such ground beef is prepared by consumers who prefer undercooked hamburgers and judge doneness by color. © 2013.

C IV BROAD ABSORPTION LINE ACCELERATION IN SLOAN DIGITAL SKY SURVEY QUASARS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Grier, C. J.; Brandt, W. N.; Trump, J. R.

2016-06-20

We present results from the largest systematic investigation of broad absorption line (BAL) acceleration to date. We use spectra of 140 quasars from three Sloan Digital Sky Survey programs to search for global velocity offsets in BALs over timescales of ≈2.5–5.5 years in the quasar rest frame. We carefully select acceleration candidates by requiring monolithic velocity shifts over the entire BAL trough, avoiding BALs with velocity shifts that might be caused by profile variability. The C iv BALs of two quasars show velocity shifts consistent with the expected signatures of BAL acceleration, and the BAL of one quasar shows amore » velocity-shift signature of deceleration. In our two acceleration candidates, we see evidence that the magnitude of the acceleration is not constant over time; the magnitudes of the change in acceleration for both acceleration candidates are difficult to produce with a standard disk-wind model or via geometric projection effects. We measure upper limits to acceleration and deceleration for 76 additional BAL troughs and find that the majority of BALs are stable to within about 3% of their mean velocities. The lack of widespread acceleration/deceleration could indicate that the gas producing most BALs is located at large radii from the central black hole and/or is not currently strongly interacting with ambient material within the host galaxy along our line of sight.« less

Infrared properties of serendipitous X-ray quasars

NASA Technical Reports Server (NTRS)

Neugebauer, G.; Soifer, B. T.; Matthews, K.; Margon, B.; Chanan, G. A.

1982-01-01

Near infrared measurements were obtained of 30 quasars originally found serendipitously as X-ray sources in fields of other objects. The observations show that the infrared characteristics of these quasars do not differ significantly from those of quasars selected by other criteria. Because this X-ray selected sample is subject to different selection biases than previous radio and optical surveys, this conclusion is useful in validating previous inferences regarding the infrared colors of 'typical' quasars.

Eight new luminous z ≥ 6 quasars discovered via SED model fitting of VISTA, WISE and Dark Energy Survey Year 1 observations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Reed, S. L.; McMahon, R. G.; Martini, P.

Here, we present the discovery and spectroscopic confirmation with the European Southern Observatory New Technology Telescope (NTT) and Gemini South telescopes of eight new, and the rediscovery of two previously known, 6.0 < z < 6.5 quasars with zAB < 21.0. These quasars were photometrically selected without any morphological criteria from 1533 deg2 using spectral energy distribution (SED) model fitting to photometric data from Dark Energy Survey (g, r, i, z, Y), VISTA Hemisphere Survey (J, H, K) and Wide-field Infrared Survey Explorer (W1, W2). The photometric data were fitted with a grid of quasar model SEDs with redshift-dependent Lymore » α forest absorption and a range of intrinsic reddening as well as a series of low-mass cool star models. Candidates were ranked using an SED-model-based χ2-statistic, which is extendable to other future imaging surveys (e.g. LSST and Euclid). Our spectral confirmation success rate is 100 per cent without the need for follow-up photometric observations as used in other studies of this type. Combined with automatic removal of the main types of non-astrophysical contaminants, the method allows large data sets to be processed without human intervention and without being overrun by spurious false candidates. We also present a robust parametric redshift estimator that gives comparable accuracy to Mg ii and CO-based redshift estimators. We find two z ~6.2 quasars with H ii near zone sizes ≤3 proper Mpc that could indicate that these quasars may be young with ages ≲ 10 6-10 7 years or lie in over dense regions of the IGM. The z = 6.5 quasar VDES J0224–4711 has JAB = 19.75 and is the second most luminous quasar known with z ≥ 6.5.« less

Eight new luminous z ≥ 6 quasars discovered via SED model fitting of VISTA, WISE and Dark Energy Survey Year 1 observations

DOE PAGES

Reed, S. L.; McMahon, R. G.; Martini, P.; ...

2017-03-24

Here, we present the discovery and spectroscopic confirmation with the European Southern Observatory New Technology Telescope (NTT) and Gemini South telescopes of eight new, and the rediscovery of two previously known, 6.0 < z < 6.5 quasars with zAB < 21.0. These quasars were photometrically selected without any morphological criteria from 1533 deg2 using spectral energy distribution (SED) model fitting to photometric data from Dark Energy Survey (g, r, i, z, Y), VISTA Hemisphere Survey (J, H, K) and Wide-field Infrared Survey Explorer (W1, W2). The photometric data were fitted with a grid of quasar model SEDs with redshift-dependent Lymore » α forest absorption and a range of intrinsic reddening as well as a series of low-mass cool star models. Candidates were ranked using an SED-model-based χ2-statistic, which is extendable to other future imaging surveys (e.g. LSST and Euclid). Our spectral confirmation success rate is 100 per cent without the need for follow-up photometric observations as used in other studies of this type. Combined with automatic removal of the main types of non-astrophysical contaminants, the method allows large data sets to be processed without human intervention and without being overrun by spurious false candidates. We also present a robust parametric redshift estimator that gives comparable accuracy to Mg ii and CO-based redshift estimators. We find two z ~6.2 quasars with H ii near zone sizes ≤3 proper Mpc that could indicate that these quasars may be young with ages ≲ 10 6-10 7 years or lie in over dense regions of the IGM. The z = 6.5 quasar VDES J0224–4711 has JAB = 19.75 and is the second most luminous quasar known with z ≥ 6.5.« less

Eight new luminous z ≥ 6 quasars discovered via SED model fitting of VISTA, WISE and Dark Energy Survey Year 1 observations

NASA Astrophysics Data System (ADS)

Reed, S. L.; McMahon, R. G.; Martini, P.; Banerji, M.; Auger, M.; Hewett, P. C.; Koposov, S. E.; Gibbons, S. L. J.; Gonzalez-Solares, E.; Ostrovski, F.; Tie, S. S.; Abdalla, F. B.; Allam, S.; Benoit-Lévy, A.; Bertin, E.; Brooks, D.; Buckley-Geer, E.; Burke, D. L.; Carnero Rosell, A.; Carrasco Kind, M.; Carretero, J.; da Costa, L. N.; DePoy, D. L.; Desai, S.; Diehl, H. T.; Doel, P.; Evrard, A. E.; Finley, D. A.; Flaugher, B.; Fosalba, P.; Frieman, J.; García-Bellido, J.; Gaztanaga, E.; Goldstein, D. A.; Gruen, D.; Gruendl, R. A.; Gutierrez, G.; James, D. J.; Kuehn, K.; Kuropatkin, N.; Lahav, O.; Lima, M.; Maia, M. A. G.; Marshall, J. L.; Melchior, P.; Miller, C. J.; Miquel, R.; Nord, B.; Ogando, R.; Plazas, A. A.; Romer, A. K.; Sanchez, E.; Scarpine, V.; Schubnell, M.; Sevilla-Noarbe, I.; Smith, R. C.; Sobreira, F.; Suchyta, E.; Swanson, M. E. C.; Tarle, G.; Tucker, D. L.; Walker, A. R.; Wester, W.

2017-07-01

We present the discovery and spectroscopic confirmation with the European Southern Observatory New Technology Telescope (NTT) and Gemini South telescopes of eight new, and the rediscovery of two previously known, 6.0 < z < 6.5 quasars with zAB < 21.0. These quasars were photometrically selected without any morphological criteria from 1533 deg2 using spectral energy distribution (SED) model fitting to photometric data from Dark Energy Survey (g, r, I, z, Y), VISTA Hemisphere Survey (J, H, K) and Wide-field Infrared Survey Explorer (W1, W2). The photometric data were fitted with a grid of quasar model SEDs with redshift-dependent Ly α forest absorption and a range of intrinsic reddening as well as a series of low-mass cool star models. Candidates were ranked using an SED-model-based χ2-statistic, which is extendable to other future imaging surveys (e.g. LSST and Euclid). Our spectral confirmation success rate is 100 per cent without the need for follow-up photometric observations as used in other studies of this type. Combined with automatic removal of the main types of non-astrophysical contaminants, the method allows large data sets to be processed without human intervention and without being overrun by spurious false candidates. We also present a robust parametric redshift estimator that gives comparable accuracy to Mg II and CO-based redshift estimators. We find two z ˜ 6.2 quasars with H II near zone sizes ≤3 proper Mpc that could indicate that these quasars may be young with ages ≲ 106-107 years or lie in over dense regions of the IGM. The z = 6.5 quasar VDES J0224-4711 has JAB = 19.75 and is the second most luminous quasar known with z ≥ 6.5.

Using the Properties of Broad Absorption Line Quasars to Illuminate Quasar Structure

NASA Astrophysics Data System (ADS)

Yong, Suk Yee; King, Anthea L.; Webster, Rachel L.; Bate, Nicholas F.; O'Dowd, Matthew J.; Labrie, Kathleen

2018-06-01

A key to understanding quasar unification paradigms is the emission properties of broad absorption line quasars (BALQs). The fact that only a small fraction of quasar spectra exhibit deep absorption troughs blueward of the broad permitted emission lines provides a crucial clue to the structure of quasar emitting regions. To learn whether it is possible to discriminate between the BALQ and non-BALQ populations given the observed spectral properties of a quasar, we employ two approaches: one based on statistical methods and the other supervised machine learning classification, applied to quasar samples from the Sloan Digital Sky Survey. The features explored include continuum and emission line properties, in particular the absolute magnitude, redshift, spectral index, line width, asymmetry, strength, and relative velocity offsets of high-ionisation C IV λ1549 and low-ionisation Mg II λ2798 lines. We consider a complete population of quasars, and assume that the statistical distributions of properties represent all angles where the quasar is viewed without obscuration. The distributions of the BALQ and non-BALQ sample properties show few significant differences. None of the observed continuum and emission line features are capable of differentiating between the two samples. Most published narrow disk-wind models are inconsistent with these observations, and an alternative disk-wind model is proposed. The key feature of the proposed model is a disk-wind filling a wide opening angle with multiple radial streams of dense clumps.

THE COLOR VARIABILITY OF QUASARS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schmidt, Kasper B.; Rix, Hans-Walter; Knecht, Matthias

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,more » 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.« less

The Benign Hamburger.

ERIC Educational Resources Information Center

Peaslee, Graham; Lantz, Juliette M.; Walczak, Mary M.

1998-01-01

Uses a case study of food poisoning from hamburgers at the fictitious Jill-at-the-Grill to teach the nuclear science behind food irradiation. Includes case teaching notes on the benign hamburger. (ASK)

Close Companions to Two High-redshift Quasars

NASA Astrophysics Data System (ADS)

McGreer, Ian D.; Fan, Xiaohui; Strauss, Michael A.; Haiman, Zoltàn; Richards, Gordon T.; Jiang, Linhua; Bian, Fuyan; 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 AB = 23.6) located 2'' (12 kpc projected) from the quasar with strong Lyα emission (EW0 ≈ 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 AB = 25) at a separation of 0.''9. The red i 775 - Y 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. Based in part on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with programs #12184 and #12493. Observations were also made with the LBT and MMT.

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

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.

The Sloan Digital Sky Survey Reverberation Mapping Project: Ensemble Spectroscopic Variability of Quasar Broad Emission Lines

NASA Astrophysics Data System (ADS)

Sun, Mouyuan; Trump, Jonathan R.; Shen, Yue; Brandt, W. N.; Dawson, Kyle; Denney, Kelly D.; Hall, Patrick B.; Ho, Luis C.; Horne, Keith; Jiang, Linhua; Richards, Gordon T.; Schneider, Donald P.; Bizyaev, Dmitry; Kinemuchi, Karen; Oravetz, Daniel; Pan, Kaike; Simmons, Audrey

2015-09-01

We explore the variability of quasars in the Mg ii and {{H}}β broad emission lines and ultraviolet/optical continuum emission using the Sloan Digital Sky Survey Reverberation Mapping project (SDSS-RM). This is the largest spectroscopic study of quasar variability to date: our study includes 29 spectroscopic epochs from SDSS-RM over 6 months, containing 357 quasars with Mg ii and 41 quasars with {{H}}β . On longer timescales, the study is also supplemented with two-epoch data from SDSS-I/II. The SDSS-I/II data include an additional 2854 quasars with Mg ii and 572 quasars with {{H}}β . The Mg ii emission line is significantly variable ({{Δ }}f/f∼ 10% on ∼100-day timescales), a necessary prerequisite for its use for reverberation mapping studies. The data also confirm that continuum variability increases with timescale and decreases with luminosity, and the continuum light curves are consistent with a damped random-walk model on rest-frame timescales of ≳ 5 days. We compare the emission-line and continuum variability to investigate the structure of the broad-line region. Broad-line variability shows a shallower increase with timescale compared to the continuum emission, demonstrating that the broad-line transfer function is not a δ-function. {{H}}β is more variable than Mg ii (roughly by a factor of ∼1.5), suggesting different excitation mechanisms, optical depths and/or geometrical configuration for each emission line. The ensemble spectroscopic variability measurements enabled by the SDSS-RM project have important consequences for future studies of reverberation mapping and black hole mass estimation of 1\\lt z\\lt 2 quasars.

VizieR Online Data Catalog: The quasars MMT-BOSS pilot survey (Ross+, 2012)

NASA Astrophysics Data System (ADS)

Ross, N. P.; Myers, A. D.; Sheldon, E. S.; Yeche, C.; Strauss, M. A.; Bovy, J.; Kirkpatrick, J. A.; Richards, G. T.; Aubourg, E.; Blanton, M. R.; Brandt, W. N.; Carithers, W. C.; Croft, R. A. C.; da Silva, R.; Dawson, K.; Eisenstein, D. J.; Hennawi, J. F.; Ho, S.; Hogg, D. W.; Lee, K.-G.; Lundgren, B.; McMahon, R. G.; Miralda-Escude, J.; Palanque-Delabrouille, N.; Paris, I.; Petitjean, P.; Pieri, M. M.; Rich, J.; Roe, N. A.; Schiminovich, D.; Schlegel, D. J.; Schneider, D. P.; Slosar, A. Z.; Suzuki, N.; Tinker, J. L.; Weinberg, D. H.; Weyant, A.; White, M.; Wood-Vasey, W. M.

2012-03-01

The Sloan Digital Sky Survey is now in its third phase (SDSS-III; Eisenstein et al. 2011AJ....142...72E) and is carrying out a combination of four interleaved surveys that will continue until the summer of 2014. One of those surveys, the Baryon Oscillation Spectroscopic Survey (BOSS), commenced operations in late 2009 and is using essentially all the dark time for SDSS-III. BOSS uses the same 2.5m Sloan Foundation telescope that was used in SDSS-I/II, but since BOSS will observe fainter targets, the fiber-fed spectrographs have been significantly upgraded. These upgrades include: new CCDs with improved blue and red response; 1000 2" instead of 640 3" optical diameter fibers; higher throughput gratings over a spectral range of 3600-10000Å at a resolution of about 2000, and improved optics. Prior to the commencement of BOSS spectroscopy, we carried out spectroscopy of quasar candidates selected from co-added photometry in SDSS Stripe 82. Observations of these candidates were carried out in queue mode between 2008 September and 2009 January using the Hectospec multi-fiber spectrograph on the 6.5m Multiple Mirror Telescope (MMT). In Tables 14 and 15, we provide positions, PSF photometry (as observed, uncorrected for Galactic extinction), and redshifts for confirmed quasars from the MMT survey. Objects that are not flagged Primary in the CAS are listed separately (table 15). (2 data files).

First Lensed Quasar Systems from the VST-ATLAS Survey: One Quad, Two Doubles, and Two Pairs of Lensless Twins

NASA Astrophysics Data System (ADS)

Schechter, Paul L.; Morgan, Nicholas D.; Chehade, B.; Metcalfe, N.; Shanks, T.; McDonald, Michael

2017-05-01

We have analyzed images from the VST-ATLAS survey to identify candidate gravitationally lensed quasar systems in a sample of WISE sources with W1-W2> 0.7. Results from follow-up spectroscopy with the Baade 6.5 m telescope are presented for eight systems. One of them is a quadruply lensed quasar, and two are doubly lensed systems. Two are projected superpositions of two quasars at different redshifts. In one system, two quasars, although at the same redshift, have very different emission line profiles and constitute a physical binary. In two systems, the component spectra are consistent with the lensing hypothesis, after allowing for microlensing. However, as no lensing galaxy is detected in these two systems, we classify them as lensless twins. More extensive observations are needed to establish whether they are in fact lensed quasars or physical binaries. This paper includes data gathered with the 6.5 m Magellan telescopes located at Las Campanas Observatory, Chile.

Quasars Probing Quasars. X. The Quasar Pair Spectral Database

NASA Astrophysics Data System (ADS)

Findlay, Joseph R.; Prochaska, J. Xavier; Hennawi, Joseph F.; Fumagalli, Michele; Myers, Adam D.; Bartle, Stephanie; Chehade, Ben; DiPompeo, Michael A.; Shanks, Tom; Lau, Marie Wingyee; Rubin, Kate H. R.

2018-06-01

The rare close projection of two quasars on the sky provides the opportunity to study the host galaxy environment of a foreground quasar in absorption against the continuum emission of a background quasar. For over a decade the “Quasars probing quasars” series has utilized this technique to further the understanding of galaxy formation and evolution in the presence of a quasar at z > 2, resolving scales as small as a galactic disk and from bound gas in the circumgalactic medium to the diffuse environs of intergalactic space. Presented here is the public release of the quasar pair spectral database utilized in these studies. In addition to projected pairs at z > 2, the database also includes quasar pair members at z < 2, gravitational lens candidates, and quasars closely separated in redshift that are useful for small-scale clustering studies. In total, the database catalogs 5627 distinct objects, with 4083 lying within 5‧ of at least one other source. A spectral library contains 3582 optical and near-infrared spectra for 3028 of the cataloged sources. As well as reporting on 54 newly discovered quasar pairs, we outline the key contributions made by this series over the last 10 years, summarize the imaging and spectroscopic data used for target selection, discuss the target selection methodologies, describe the database content, and explore some avenues for future work. Full documentation for the spectral database, including download instructions, is supplied at http://specdb.readthedocs.io/en/latest/.

Sloan Digital Sky Survey III photometric quasar clustering: probing the initial conditions of the Universe

NASA Astrophysics Data System (ADS)

Ho, Shirley; Agarwal, Nishant; Myers, Adam D.; Lyons, Richard; Disbrow, Ashley; Seo, Hee-Jong; Ross, Ashley; Hirata, Christopher; Padmanabhan, Nikhil; O'Connell, Ross; Huff, Eric; Schlegel, David; Slosar, Anže; Weinberg, David; Strauss, Michael; Ross, Nicholas P.; Schneider, Donald P.; Bahcall, Neta; Brinkmann, J.; Palanque-Delabrouille, Nathalie; Yèche, Christophe

2015-05-01

The Sloan Digital Sky Survey has surveyed 14,555 square degrees of the sky, and delivered over a trillion pixels of imaging data. We present the large-scale clustering of 1.6 million quasars between z=0.5 and z=2.5 that have been classified from this imaging, representing the highest density of quasars ever studied for clustering measurements. This data set spans 0~ 11,00 square degrees and probes a volume of 80 h-3 Gpc3. In principle, such a large volume and medium density of tracers should facilitate high-precision cosmological constraints. We measure the angular clustering of photometrically classified quasars using an optimal quadratic estimator in four redshift slices with an accuracy of ~ 25% over a bin width of δl ~ 10-15 on scales corresponding to matter-radiation equality and larger (0l ~ 2-3). Observational systematics can strongly bias clustering measurements on large scales, which can mimic cosmologically relevant signals such as deviations from Gaussianity in the spectrum of primordial perturbations. We account for systematics by employing a new method recently proposed by Agarwal et al. (2014) to the clustering of photometrically classified quasars. We carefully apply our methodology to mitigate known observational systematics and further remove angular bins that are contaminated by unknown systematics. Combining quasar data with the photometric luminous red galaxy (LRG) sample of Ross et al. (2011) and Ho et al. (2012), and marginalizing over all bias and shot noise-like parameters, we obtain a constraint on local primordial non-Gaussianity of fNL = -113+154-154 (1σ error). We next assume that the bias of quasar and galaxy distributions can be obtained independently from quasar/galaxy-CMB lensing cross-correlation measurements (such as those in Sherwin et al. (2013)). This can be facilitated by spectroscopic observations of the sources, enabling the redshift distribution to be completely determined, and allowing precise estimates of the bias

Physical association and periodicity in quasar families with SDSS and 2MRS

NASA Astrophysics Data System (ADS)

Fulton, C. C.; Arp, H. C.; Hartnett, J. G.

2018-07-01

We have used the Sloan Digital Sky Survey (SDSS) data release 7 (DR7) and the 2MASS (Two Micron All Sky Survey) Redshift Survey (2MRS) Ks ≤11.75 mag data release to test for physical association of candidate companion quasars with putative parent galaxies by virtue of Karlsson periodicity in quasar redshifts. We conducted this analysis using the quasar family detection algorithm described in Fulton and Arp (Astrophys. J. 754:134, 2012) and used therein to analyze the 2dF Galaxy Redshift Survey (2dFGRS) and the 2dF Quasar Redshift Survey (2QZ). The SDSS and 2MRS data sets confirm the 2dF results and allow us to examine additional object behaviors also at high significance.

A CONSTRAINT ON QUASAR CLUSTERING AT z = 5 FROM A BINARY QUASAR

DOE Office of Scientific and Technical Information (OSTI.GOV)

McGreer, Ian D.; Fan, Xiaohui; Eftekharzadeh, Sarah

2016-03-15

We report the discovery of a quasar pair at z = 5 separated by 21″. Both objects were identified as quasar candidates using simple color selection techniques applied to photometric catalogs from the Canada–France–Hawaii Telescope (CFHT) Legacy Survey (CFHTLS). Spectra obtained with the MMT present no discernible offset in redshift between the two objects; on the other hand, there are clear differences in the emission line profiles and in the multiwavelength spectral energy distributions that strongly disfavor the hypothesis that they are gravitationally lensed images of a single quasar. Both quasars are surprisingly bright given their proximity (a projected separation of ∼135more » kpc), with i = 19.4 and i = 21.4. Previous measurements of the luminosity function demonstrate that luminous quasars are extremely rare at z = 5; the existence of this pair suggests that quasars have strong small-scale clustering at high redshift. Assuming a real-space correlation function of the form ξ(r) ∝ (r/r{sub 0}){sup −2}, this discovery implies a correlation length of r{sub 0} ≳ 20h{sup −1} Mpc, consistent with a rapid strengthening of quasar clustering at high redshift as seen in previous observations and predicted by theoretical models where feedback effects are inefficient at shutting down black hole growth at high redshift.« less

VizieR Online Data Catalog: Australian Dark Energy Survey (OzDES) quasar catalog (Tie+, 2017)

NASA Astrophysics Data System (ADS)

Tie, S. S.; Martini, P.; Mudd, D.; Ostrovski, F.; Reed, S. L.; Lidman, C.; Kochanek, C.; Davis, T. M.; Sharp, R.; Uddin, S.; King, A.; Wester, W.; Tucker, B. E.; Tucker, D. L.; Buckley-Geer, E.; Carollo, D.; Childress, M.; Glazebrook, K.; Hinton, S. R.; Lewis, G.; Macaulay, E.; O'Neill, C. R.; Abbott, T. M. C.; Abdalla, F. B.; Annis, J.; Benoit-Levy, A.; Bertin, E.; Brooks, D.; Carnero Rosell, A.; Carrasco Kind, M.; Carretero, J.; Cunha, C. E.; da Costa, L. N.; Depoy, D. L.; Desai, S.; Doel, P.; Eifler, T. F.; Evrard, A. E.; Finley, D. A.; Flaugher, B.; Fosalba, P.; Frieman, J.; Garcia-Bellido, J.; Gaztanaga, E.; Gerdes, D. W.; Goldstein, D. A.; Gruen, D.; Gruendl, R. A.; Gutierrez, G.; Honscheid, K.; James, D. J.; Kuehn, K.; Kuropatkin, N.; Lima, M.; Maia, M. A. G.; Marshall, J. L.; Menanteau, F.; Miller, C. J.; Miquel, R.; Nichol, R. C.; Nord, B.; Ogando, R.; Plazas, A. A.; Romer, A. K.; 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.; Thomas, D.; Walker, A. R.; DES Collaboration

2017-07-01

The Australian Dark Energy Survey (OzDES; Yuan et al. 2015MNRAS.452.3047Y) is a spectroscopic survey of the DES supernova fields using the AAOmega spectrograph (Smith et al. 2004SPIE.5492..410S) on the Anglo-Australian Telescope (AAT). The field of view of the AAT multi-object fiber-positioning system (Lewis et al. 2002MNRAS.333..279L) is well matched to DECam, making the AAT a well-suited spectroscopic follow-up instrument for DES. OzDES commenced observations at the same time as DES in 2013B and aims to measure redshifts for thousands of host galaxies of Type Ia supernovae and black hole masses for hundreds of AGNs and quasars (King et al. 2015MNRAS.453.1701K) using reverberation mapping (Blandford & McKee 1982ApJ...255..419B; Peterson 1993PASP..105..247P). The observing targets and results of OzDES observations are compiled into a spectroscopic catalog known as the Global Redshift Catalog (GRC). The GRC is updated after every OzDES observing season. In this work, we used the 2016 February version of the OzDES GRC. Here we present the OzDES Quasar Catalog of 1263 OzDES sources with Mi<-22 mag and i<22 mag that are spectroscopically confirmed quasars. (1 data file).

Clustering on very small scales from a large sample of confirmed quasar pairs: does quasar clustering track from Mpc to kpc scales?

NASA Astrophysics Data System (ADS)

Eftekharzadeh, S.; Myers, A. D.; Hennawi, J. F.; Djorgovski, S. G.; Richards, G. T.; Mahabal, A. A.; Graham, M. J.

2017-06-01

We present the most precise estimate to date of the clustering of quasars on very small scales, based on a sample of 47 binary quasars with magnitudes of g < 20.85 and proper transverse separations of ˜25 h-1 kpc. Our sample of binary quasars, which is about six times larger than any previous spectroscopically confirmed sample on these scales, is targeted using a kernel density estimation (KDE) technique applied to Sloan Digital Sky Survey (SDSS) imaging over most of the SDSS area. Our sample is 'complete' in that all of the KDE target pairs with 17.0 ≲ R ≲ 36.2 h-1 kpc in our area of interest have been spectroscopically confirmed from a combination of previous surveys and our own long-slit observational campaign. We catalogue 230 candidate quasar pairs with angular separations of <8 arcsec, from which our binary quasars were identified. We determine the projected correlation function of quasars (\\bar{W}_p) in four bins of proper transverse scale over the range 17.0 ≲ R ≲ 36.2 h-1 kpc. The implied small-scale quasar clustering amplitude from the projected correlation function, integrated across our entire redshift range, is A = 24.1 ± 3.6 at ˜26.6 h-1 kpc. Our sample is the first spectroscopically confirmed sample of quasar pairs that is sufficiently large to study how quasar clustering evolves with redshift at ˜25 h-1 kpc. We find that empirical descriptions of how quasar clustering evolves with redshift at ˜25 h-1 Mpc also adequately describe the evolution of quasar clustering at ˜25 h-1 kpc.

Optimum use of CDOT French and Hamburg data (French and Hamburg tests).

DOT National Transportation Integrated Search

2013-11-01

The Colorado Department of Transportation (CDOT) has been collecting data from the Hamburg Rutter and the : French Rutter for over 20 years. No specifications have been written in that time for either the Hamburg Rutter : or the French Rutter. This r...

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.

Optical+Near-IR Bayesian Classification of Quasars

NASA Astrophysics Data System (ADS)

Mehta, Sajjan S.; Richards, G. T.; Myers, A. D.

2011-05-01

We describe the details of an optimal Bayesian classification of quasars with combined optical+near-IR photometry from the SDSS and UKIDSS LAS surveys. Using only deep co-added SDSS photometry from the "Stripe 82" region and requiring full four-band UKIDSS detections, we reliably identify 2665 quasar candidates with a computed efficiency in excess of 99%. Relaxing the data constraints to combinations of two-band detections yields up to 6424 candidates with minimal trade-off in completeness and efficiency. The completeness and efficiency of the sample are investigated with existing spectra from the SDSS, 2SLAQ, and AUS surveys in addition to recent single-slit observations from Palomar Observatory, which revealed 22 quasars from a subsample of 29 high-z candidates. SDSS-III/BOSS observations will allow further exploration of the completeness/efficiency of the sample over 2.2surveys are particularly incomplete/inefficient.

A study of ten quasars with redshifts greater than four

NASA Technical Reports Server (NTRS)

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

1989-01-01

Four quasars with redshifts greater than four were detected in a low-resolution CCD grism survey. CCD photometry and high S/N, moderate resolution spectra are presented for these quasars and the six other known quasars with redshifts above 4. The M sub B values of nine of the objects are between -27.5 and -25, with the tenth quasar having an M sub B value of -29. The emission lines and shapes of the continua of these ten quasars are similar to those of lower-redshift quasars. The results suggest that the C IV emission lines in high-redshift quasars may be weaker than those in lower-redshift quasars. The continua of all of the high-redshift quasars display strong depressions blueward of the Ly-alpha emission line.

Characterizing Quasar Outflows III: SEDs, and Bolometric Luminosity Estimates

NASA Astrophysics Data System (ADS)

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

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 add photometry from both the Two Micron All-Sky Survey (2MASS) and from the Wide-Field Infrared Survey Explorer (WISE). 2MASS photometry covers the rest-frame optical regime of these qusars, while the WISE W1, W2, and W3 bands cover the rest-frame wavelength ranges 0.9-1.27 micron, 1.35-1.75 micron, and 2.52-5.51 micron, respectively. The preliminary release of WISE data cover 3800 of our quasars. In an accompnying poster, we have subjectively divided 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). Here, we present average SEDs for these subsamples, estimates of bolometric luminosity, and explore changes in SED based on both outflow properties and quasar physical properties. This material is based upon work supported by the National Aeronautics and Space Administration under Grant No. 09-ADP09-0016 issued through the

An ALMA [C II] Survey of 27 Quasars at z > 5.94

NASA Astrophysics Data System (ADS)

Decarli, Roberto; Walter, Fabian; Venemans, Bram P.; Bañados, Eduardo; Bertoldi, Frank; Carilli, Chris; Fan, Xiaohui; Farina, Emanuele Paolo; Mazzucchelli, Chiara; Riechers, Dominik; Rix, Hans-Walter; Strauss, Michael A.; Wang, Ran; Yang, Yujin

2018-02-01

We present a survey of the [C II] 158 μm line and underlying far-infrared (FIR) dust continuum emission in a sample of 27 z≳ 6 quasars using the Atacama Large Millimeter Array (ALMA) at ∼ 1\\prime\\prime resolution. The [C II] line was significantly detected (at > 5-σ) in 23 sources (85%). We find typical line luminosities of {L}[{{C}{{II}}]}={10}9-10 {L}ȯ , and an average line width of ∼385 {km} {{{s}}}-1. The [C II]-to-far-infrared luminosity ratios ([C II]/FIR) in our sources span one order of magnitude, highlighting a variety of conditions in the star-forming medium. Four quasar host galaxies are clearly resolved in their [C II] emission on a few kpc scales. Basic estimates of the dynamical masses of the host galaxies give masses between 2 × 1010 and 2 × 1011 {M}ȯ , i.e., more than an order of magnitude below what is expected from local scaling relations, given the available limits on the masses of the central black holes (> 3× {10}8 {M}ȯ , assuming Eddington-limited accretion). In stacked ALMA [C II] spectra of individual sources in our sample, we find no evidence of a deviation from a single Gaussian profile. The quasar luminosity does not strongly correlate with either the [C II] luminosity or equivalent width. This survey (with typical on-source integration times of 8 minutes) showcases the unparalleled sensitivity of ALMA at millimeter wavelengths, and offers a unique reference sample for the study of the first massive galaxies in the universe.

A SYSTEMATIC SEARCH FOR PERIODICALLY VARYING QUASARS IN PAN-STARRS1: AN EXTENDED BASELINE TEST IN MEDIUM DEEP SURVEY FIELD MD09

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, T.; Gezari, S.; Burgett, W.

We present a systematic search for periodically varying quasars and supermassive black hole binary (SMBHB) candidates in the Pan-STARRS1 (PS1) Medium Deep Survey’s MD09 field. From a color-selected sample of 670 quasars extracted from a multi-band deep-stack catalog of point sources, we locally select variable quasars and look for coherent periods with the Lomb–Scargle periodogram. Three candidates from our sample demonstrate strong variability for more than ∼3 cycles, and their PS1 light curves are well fitted to sinusoidal functions. We test the persistence of the candidates’ apparent periodic variations detected during the 4.2 years of the PS1 survey with archivalmore » photometric data from the SDSS Stripe 82 survey or new monitoring with the Large Monolithic Imager at the Discovery Channel Telescope. None of the three periodic candidates (including PSO J334.2028+1.4075) remain persistent over the extended baseline of 7–14 years, corresponding to a detection rate of <1 in 670 quasars in a search area of ≈5 deg{sup 2}. Even though SMBHBs should be a common product of the hierarchal growth of galaxies, and periodic variability in SMBHBs has been theoretically predicted, a systematic search for such signatures in a large optical survey is strongly limited by its temporal baseline and the “red noise” associated with normal quasar variability. We show that follow-up long-term monitoring (≳5 cycles) is crucial to our search for these systems.« less

SDSS J2222+2745: A GRAVITATIONALLY LENSED SEXTUPLE QUASAR WITH A MAXIMUM IMAGE SEPARATION OF 15.''1 DISCOVERED IN THE SLOAN GIANT ARCS SURVEY

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dahle, H.; Groeneboom, N.; Gladders, M. D.

2013-08-20

We report the discovery of a unique gravitational lens system, SDSS J2222+2745, producing five spectroscopically confirmed images of a z{sub s} = 2.82 quasar lensed by a foreground galaxy cluster at z{sub l} = 0.49. We also present photometric and spectroscopic evidence for a sixth lensed image of the same quasar. The maximum separation between the quasar images is 15.''1. Both the large image separations and the high image multiplicity are in themselves rare among known lensed quasars, and observing the combination of these two factors is an exceptionally unlikely occurrence in present data sets. This is only the thirdmore » known case of a quasar lensed by a cluster, and the only one with six images. The lens system was discovered in the course of the Sloan Giant Arcs Survey, in which we identify candidate lenses in the Sloan Digital Sky Survey and target these for follow-up and verification with the 2.56 m Nordic Optical Telescope. Multi-band photometry obtained over multiple epochs from 2011 September to 2012 September reveals significant variability at the {approx}10%-30% level in some of the quasar images, indicating that measurements of the relative time delay between quasar images will be feasible. In this lens system, we also identify a bright (g = 21.5) giant arc corresponding to a strongly lensed background galaxy at z{sub s} = 2.30. We fit parametric models of the lens system, constrained by the redshift and positions of the quasar images and the redshift and position of the giant arc. The predicted time delays between different pairs of quasar images range from {approx}100 days to {approx}6 yr.« less

Quasar target selection fiber efficiency

NASA Astrophysics Data System (ADS)

Newberg, Heidi; Yanny, Brian

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.

IMPROVED SPECTROPHOTOMETRIC CALIBRATION OF THE SDSS-III BOSS QUASAR SAMPLE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Margala, Daniel; Kirkby, David; Dawson, Kyle

2016-11-10

We present a model for spectrophotometric calibration errors in observations of quasars from the third generation of the Sloan Digital Sky Survey Baryon Oscillation Spectroscopic Survey (BOSS) and describe the correction procedure we have developed and applied to this sample. Calibration errors are primarily due to atmospheric differential refraction and guiding offsets during each exposure. The corrections potentially reduce the systematics for any studies of BOSS quasars, including the measurement of baryon acoustic oscillations using the Ly α forest. Our model suggests that, on average, the observed quasar flux in BOSS is overestimated by ∼19% at 3600 Å and underestimatedmore » by ∼24% at 10,000 Å. Our corrections for the entire BOSS quasar sample are publicly available.« less

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.

Overdensity of galaxies in the environment of quasar pairs

NASA Astrophysics Data System (ADS)

Sandrinelli, A.; Falomo, R.; Treves, A.; Scarpa, R.; Uslenghi, M.

2018-03-01

We report on a study of the galaxy environments of low redshift physical quasars pairs. We selected 20 pairs having projected separation < 0.5 Mpc and difference of systemic velocity < 800 km s-1. Using Sloan Digital Sky Survey images, we evaluated the galaxy overdensity around these quasars in pairs and then compare it with that of a sample of isolated quasars with same redshift and luminosity. It is found that on average there is a systematic larger overdensity of galaxies around quasars in pairs with respect to that of isolated quasars. This may represent a significant link between nuclear activity and galaxy environment. However, at odds with that, the closest quasar pairs seem to inhabit poorer environments. Implications of present results and perspectives for future work are briefly discussed.

The WISSH quasars project. III. X-ray properties of hyper-luminous quasars

NASA Astrophysics Data System (ADS)

Martocchia, S.; Piconcelli, E.; Zappacosta, L.; Duras, F.; Vietri, G.; Vignali, C.; Bianchi, S.; Bischetti, M.; Bongiorno, A.; Brusa, M.; Lanzuisi, G.; Marconi, A.; Mathur, S.; Miniutti, G.; Nicastro, F.; Bruni, G.; Fiore, F.

2017-12-01

We performed a survey of the X-ray properties of 41 objects from the WISE/SDSS selected hyper-luminous (WISSH) quasars sample, which includes 86 broad-line quasars with bolometric luminosity LBol ≳ 2 × 1047 erg s-1 shining at z 2-4. We used both proprietary and archival Chandra and XMM-Newton observations. Twenty-one quasars have sufficient quality data to perform a spectroscopic analysis, while for the remaining sources, X-ray properties are derived through hardness-ratio analysis (apart for six sources that result to be undetected). The bulk ( 70%) of the detected WISSH quasars exhibit NH <5 × 1022 cm-2, in agreement with their optical Type 1 AGN classification. All but three quasars show unabsorbed 2-10 keV luminosities L2-10≥ 1045 erg s-1. Thanks to their extreme radiative output across the mid-IR-to-X-ray range, WISSH quasars therefore offer the opportunity to significantly extend and validate the existing relations involving L2-10. Specifically, we studied the X-ray luminosity as a function of (i) X-ray-to-optical (X/O) flux ratio; (ii) mid-IR luminosity (LMIR); (iii) LBol, and (iv) αOX versus 2500 Å luminosity. We find that the WISSH quasars show (i) unreported very low X/O ( <0.1) compared to typical AGN values; (ii) L2-10/LMIR ratios that are significantly smaller than those derived for AGN with lower luminosity; (iii) a large X-ray bolometric correction, kBol,X ≈ 100-1000; and (iv) steep -2≳αOX≳-1.7. These results lead to a scenario in which the X-ray emission of hyper-luminous quasars is relatively weaker compared to lower luminosity AGN. Models predict that such an X-ray weakness can be relevant for the acceleration of powerful high-ionization, emission-line-driven winds, which are commonly detected in the UV spectra of WISSH quasars and can, in turn, perturb the X-ray corona and weaken its emission. Accordingly, hyper-luminous quasars represent the ideal laboratory to study the link between the AGN energy output and wind acceleration

Insecure Identities: Unaccompanied Minors as Refugees in Hamburg

ERIC Educational Resources Information Center

Schroeder, Joachim

2012-01-01

This paper analyses the financial circumstances and social income of nearly one hundred unaccompanied minors who have come to Hamburg as refugees from various regions of Africa. It is based on extensive qualitative surveys, analysing their objective conditions of life and in particular their legal situation. A wide range of interview material and…

Continuing Long Term Optical and Infrared Reverberation Mapping of 17 Sloan Digital Sky Survey Quasars

NASA Astrophysics Data System (ADS)

Gorjian, Varoujan; Barth, Aaron; Brandt, Niel; Dawson, Kyle; Green, Paul; Ho, Luis; Horne, Keith; Jiang, Linhua; McGreer, Ian; Schneider, Donald; Shen, Yue; Tao, Charling

2018-05-01

Previous Spitzer reverberation monitoring projects searching for UV/optical light absorbed and re-emitted in the IR by dust have been limited to low luminosity active galactic nuclei (AGN) that could potentially show reverberation within a single cycle ( 1 year). Cycle 11-12's two year baseline allowed for the reverberation mapping of 17 high-luminosity quasars from the Sloan Digital Sky Survey Reverberation Mapping project. We continued this monitoring in Cycle 13 and now propose to extend this program in Cycle 14. By combining ground-based monitoring from Pan-STARRS, CFHT, and Steward Observatory telescopes with Spitzer data we have for the first time detected dust reverberation in quasars. By continuing observations with this unqiue combination of resources we should detect reverberation in more objects and reduce the uncertainties for the remaining sources.

The Sloan Digital Sky Survey Reverberation Mapping Project: The C IV Blueshift, Its Variability, and Its Dependence Upon Quasar Properties

NASA Astrophysics Data System (ADS)

Sun, Mouyuan; Xue, Yongquan; Richards, Gordon T.; Trump, Jonathan R.; Shen, Yue; Brandt, W. N.; Schneider, D. P.

2018-02-01

We use the multi-epoch spectra of 362 quasars from the Sloan Digital Sky Survey Reverberation Mapping project to investigate the dependence of the blueshift of C IV relative to Mg II on quasar properties. We confirm that high-blueshift sources tend to have low C IV equivalent widths (EWs), and that the low-EW sources span a range of blueshift. Other high-ionization lines, such as He II, also show similar blueshift properties. The ratio of the line width (measured as both the full width at half maximum and the velocity dispersion) of C IV to that of Mg II increases with blueshift. Quasar variability enhances the connection between the C IV blueshift and quasar properties (e.g., EW). The variability of the Mg II line center (i.e., the wavelength that bisects the cumulative line flux) increases with blueshift. In contrast, the C IV line center shows weaker variability at the extreme blueshifts. Quasars with the high-blueshift C IV lines tend to have less variable continuum emission, when controlling for EW, luminosity, and redshift. Our results support the scenario that high-blueshift sources tend to have large Eddington ratios.

Relativistic redshifts in quasar broad lines

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tremaine, Scott; Shen, Yue; Liu, Xin

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 randomlymore » 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.« less

THE UV-BRIGHT QUASAR SURVEY (UVQS): DR1

DOE Office of Scientific and Technical Information (OSTI.GOV)

Monroe, TalaWanda R.; Tumlinson, Jason; Prochaska, J. Xavier

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 formore » 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.« less

THE SLOAN DIGITAL SKY SURVEY REVERBERATION MAPPING PROJECT: BIASES IN z  > 1.46 REDSHIFTS DUE TO QUASAR DIVERSITY

DOE Office of Scientific and Technical Information (OSTI.GOV)

Denney, K. D.; Peterson, B. M.; Horne, Keith

We use the coadded spectra of 32 epochs of Sloan Digital Sky Survey (SDSS) Reverberation Mapping Project observations of 482 quasars with z  > 1.46 to highlight systematic biases in the SDSS- and Baryon Oscillation Spectroscopic Survey (BOSS)-pipeline redshifts due to the natural diversity of quasar properties. We investigate the characteristics of this bias by comparing the BOSS-pipeline redshifts to an estimate from the centroid of He ii λ 1640. He ii has a low equivalent width but is often well-defined in high-S/N spectra, does not suffer from self-absorption, and has a narrow component which, when present (the case for aboutmore » half of our sources), produces a redshift estimate that, on average, is consistent with that determined from [O ii] to within the He ii and [O ii] centroid measurement uncertainties. The large redshift differences of ∼1000 km s{sup −1}, on average, between the BOSS-pipeline and He ii-centroid redshifts, suggest there are significant biases in a portion of BOSS quasar redshift measurements. Adopting the He ii-based redshifts shows that C iv does not exhibit a ubiquitous blueshift for all quasars, given the precision probed by our measurements. Instead, we find a distribution of C iv-centroid blueshifts across our sample, with a dynamic range that (i) is wider than that previously reported for this line, and (ii) spans C iv centroids from those consistent with the systemic redshift to those with significant blueshifts of thousands of kilometers per second. These results have significant implications for measurement and use of high-redshift quasar properties and redshifts, and studies based thereon.« less

Star Formation in Dusty Quasars

NASA Astrophysics Data System (ADS)

Lumsden, Stuart; Croom, Scott

2012-04-01

Quasar mode feedback is thought to be a crucial ingredient in galaxy formation for luminous merging and star-bursting systems at high redshift. The energy from the active nucleus should cause significant gas outflows, reducing the available free gas reservoir for future star formation. It is currently unknown which observational state best corresponds to the stage at which this "blowout" should occur. We intend to test one possible source population for this transition phase, by studying the molecular gas content in a small, statistically complete sample of 3 K-band selected reddened quasars from the AUS survey. All lie in the redshift range 2quasar activity in typical galaxies, where we also expect the bulk of the stars for form as well.

SUBARU HIGH- z EXPLORATION OF LOW-LUMINOSITY QUASARS (SHELLQs). I. DISCOVERY OF 15 QUASARS AND BRIGHT GALAXIES AT 5.7 < z < 6.9

DOE Office of Scientific and Technical Information (OSTI.GOV)

Matsuoka, Yoshiki; Kashikawa, Nobunari; Imanishi, Masatoshi

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 deg{sup 2} of the survey footprint. The success rate of our photometric selectionmore » is quite high, approaching 100% at the brighter magnitudes (z {sub 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 Ly α 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 {sub 1450} ∼ −22 mag or z {sub AB} ∼ 24 mag. Follow-up studies of the discovered objects as well as further survey observations are ongoing.« less

Quasar Feedback at the Peak of the Galaxy Formation Epoch

NASA Astrophysics Data System (ADS)

Liu, Guilin; Zakamska, Nadia L.; Strauss, Michael A.; Greene, Jenny E.; Alexandroff, Rachael

2014-08-01

The correlations between properties of supermassive black holes and stellar spheroids in galaxies imply a physical connection between these two components. Using Gemini GMOS IFU, we demonstrated that powerful ionized gas winds are ubiquitous in luminous radio-quiet z~ 0.5 quasars. We now extend this study to the era of peak galaxy formation and quasar activity when quasar feedback likely shaped the properties of massive galaxies. Our GMOS IFU observations of 5 quasars at z~ 3 are now underway, and we plan for fall observations. We propose a GMOS IFU survey to map the spatial distribution and kinematics of Ly(alpha) and N V 1240Aemission around 5 obscured quasars at z=3-3.3 that are extremely luminous (L_Ly(alpha)~10^45 erg s^- 1). Obscured quasars likely constitute the majority of the quasar population and represent the early enshrouded phase of black hole growth, luminous obscured quasars are thus the most likely sites of quasar feedback, as we found at low redshifts. We will look for quasar- driven outflows, and directly probe the effects of quasars on their galaxy-wide and intergalactic environments close to the peak of the galaxy formation epoch.

Serendipitous discovery of quadruply imaged quasars: two diamonds

NASA Astrophysics Data System (ADS)

Lucey, John R.; Schechter, Paul L.; Smith, Russell J.; Anguita, T.

2018-05-01

Gravitationally lensed quasars are powerful and versatile astrophysical tools, but they are challengingly rare. In particular, only ˜25 well-characterized quadruple systems are known to date. To refine the target catalogue for the forthcoming Taipan Galaxy Survey, the images of a large number of sources are being visually inspected in order to identify objects that are confused by a foreground star or galaxies that have a distinct multicomponent structure. An unexpected by-product of this work has been the serendipitous discovery of about a dozen galaxies that appear to be lensing quasars, i.e. pairs or quartets of foreground stellar objects in close proximity to the target source. Here, we report two diamond-shaped systems. Follow-up spectroscopy with the IMACS instrument on the 6.5m Magellan Baade telescope confirms one of these as a z = 1.975 quasar quadruply lensed by a double galaxy at z = 0.293. Photometry from publicly available survey images supports the conclusion that the other system is a highly sheared quadruply imaged quasar. In starting with objects thought to be galaxies, our lens finding technique complements the conventional approach of first identifying sources with quasar-like colours and subsequently finding evidence of lensing.

Angular Baryon Acoustic Oscillation measure at z=2.225 from the SDSS quasar survey

NASA Astrophysics Data System (ADS)

de Carvalho, E.; Bernui, A.; Carvalho, G. C.; Novaes, C. P.; Xavier, H. S.

2018-04-01

Following a quasi model-independent approach we measure the transversal BAO mode at high redshift using the two-point angular correlation function (2PACF). The analyses done here are only possible now with the quasar catalogue from the twelfth data release (DR12Q) from the Sloan Digital Sky Survey, because it is spatially dense enough to allow the measurement of the angular BAO signature with moderate statistical significance and acceptable precision. Our analyses with quasars in the redshift interval z in [2.20,2.25] produce the angular BAO scale θBAO = 1.77° ± 0.31° with a statistical significance of 2.12 σ (i.e., 97% confidence level), calculated through a likelihood analysis performed using the theoretical covariance matrix sourced by the analytical power spectra expected in the ΛCDM concordance model. Additionally, we show that the BAO signal is robust—although with less statistical significance—under diverse bin-size choices and under small displacements of the quasars' angular coordinates. Finally, we also performed cosmological parameter analyses comparing the θBAO predictions for wCDM and w(a)CDM models with angular BAO data available in the literature, including the measurement obtained here, jointly with CMB data. The constraints on the parameters ΩM, w0 and wa are in excellent agreement with the ΛCDM concordance model.

Near-infrared Photometric Properties of 130,000 Quasars: An SDSS-UKIDSS-matched Catalog

NASA Astrophysics Data System (ADS)

Peth, Michael A.; Ross, Nicholas P.; Schneider, Donald P.

2011-04-01

We present a catalog of over 130,000 quasar candidates with near-infrared (NIR) photometric properties, with an areal coverage of approximately 1200 deg2. This is achieved by matching the Sloan Digital Sky Survey (SDSS) in the optical ugriz bands to the UKIRT Infrared Digital Sky Survey (UKIDSS) Large Area Survey (LAS) in the NIR YJHK bands. We match the ≈1 million SDSS DR6 Photometric Quasar catalog to Data Release 3 of the UKIDSS LAS (ULAS) and produce a catalog with 130,827 objects with detections in one or more NIR bands, of which 74,351 objects have optical and K-band detections and 42,133 objects have the full nine-band photometry. The majority (~85%) of the SDSS objects were not matched simply because these were not covered by the ULAS. The positional standard deviation of the SDSS Quasar to ULAS matches is δR.A. = 0farcs1370 and δdecl. = 0farcs1314. We find an absolute systematic astrometric offset between the SDSS Quasar catalog and the UKIDSS LAS, of |R.A.offset| = 0farcs025 and |decl.offset| = 0farcs040; we suggest the nature of this offset to be due to the matching of catalog, rather than image, level data. Our matched catalog has a surface density of ≈53 deg-2 for K <= 18.27 objects; tests using our matched catalog, along with data from the UKIDSS Deep Extragalactic Survey, imply that our limiting magnitude is i ≈ 20.6. Color-redshift diagrams, for the optical and NIR, show a close agreement between our matched catalog and recent quasar color models at redshift z <~ 2.0, while at higher redshifts, the models generally appear to be bluer than the mean observed quasar colors. The gJK and giK color spaces are used to examine methods of differentiating between stars and (mid-redshift) quasars, the key to currently ongoing quasar surveys. Finally, we report on the NIR photometric properties of high, z > 4.6, and very high, z > 5.7, redshift previously discovered quasars.

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

Quasar Accretion Disk Sizes With Continuum Reverberation Mapping From the Dark Energy Survey

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mudd, D.; et al.

We present accretion disk size measurements for 15 luminous quasars atmore » $$0.7 \\leq z \\leq 1.9$$ derived from $griz$ light curves from the Dark Energy Survey. We measure the disk sizes with continuum reverberation mapping using two methods, both of which are derived from the expectation that accretion disks have a radial temperature gradient and the continuum emission at a given radius is well-described by a single blackbody. In the first method we measure the relative lags between the multiband light curves, which provides the relative time lag between shorter and longer wavelength variations. The second method fits the model parameters for the canonical Shakura-Sunyaev thin disk directly rather than solving for the individual time lags between the light curves. Our measurements demonstrate good agreement with the sizes predicted by this model for accretion rates between 0.3-1 times the Eddington rate. These results are also in reasonable agreement with disk size measurements from gravitational microlensing studies of strongly lensed quasars, as well as other photometric reverberation mapping results.« less

Discovery of four doubly imaged quasar lenses from the Sloan digital sky survey

DOE Office of Scientific and Technical Information (OSTI.GOV)

Inada, Naohisa; Oguri, Masamune; Rusu, Cristian E.

2014-06-01

We report the discovery of four doubly imaged quasar lenses. All the four systems are selected as lensed quasar candidates from the Sloan Digital Sky Survey data. We confirm their lensing hypothesis with additional imaging and spectroscopic follow-up observations. The discovered lenses are SDSS J0743+2457 with the source redshift z{sub s} = 2.165, the lens redshift z{sub l} = 0.381, and the image separation θ = 1.''034, SDSS J1128+2402 with z{sub s} = 1.608 and θ = 0.''844, SDSS J1405+0959 with z{sub s} = 1.810, z{sub l} ≈ 0.66, and θ = 1.''978, and SDSS J1515+1511 with z{sub s} =more » 2.054, z{sub l} = 0.742, and θ = 1.''989. It is difficult to estimate the lens redshift of SDSS J1128+2402 from the current data. Two of the four systems (SDSS J1405+0959 and SDSS J1515+1511) are included in our final statistical lens sample to derive constraints on dark energy and the evolution of massive galaxies.« less

The Faint End of the z = 5 Quasar Luminosity Function from the CFHTLS

NASA Astrophysics Data System (ADS)

McGreer, Ian D.; Fan, Xiaohui; Jiang, Linhua; Cai, Zheng

2018-03-01

We present results from a spectroscopic survey of z ∼ 5 quasars in the CFHT Legacy Survey. Using both optical color selection and a likelihood method, we select 97 candidates over an area of 105 deg2 to a limit of i AB < 23.2, and 7 candidates in the range 23.2 < i AB < 23.7 over an area of 18.5 deg2. Spectroscopic observations for 43 candidates were obtained with Gemini, MMT, and Large Binocular Telescope, of which 37 are z > 4 quasars. This sample extends measurements of the quasar luminosity function ∼1.5 mag fainter than our previous work in Sloan Digital Sky Survey Stripe 82. The resulting luminosity function is in good agreement with our previous results, and suggests that the faint end slope is not steep. We perform a detailed examination of our survey completeness, particularly the impact of the Lyα emission assumed in our quasar spectral models, and find hints that the observed Lyα emission from faint z ∼ 5 quasars is weaker than for z ∼ 3 quasars at a similar luminosity. Our results strongly disfavor a significant contribution of faint quasars to the hydrogen-ionizing background at z = 5.

Multiwavelength search and studies of active galaxies and quasars

NASA Astrophysics Data System (ADS)

Mickaelian, Areg M.

2017-12-01

The Byurakan Astrophysical Observatory (BAO) has always been one of the centres for surveys and studies of active galaxies. Here we review our search and studies of active galaxies during last 30 years using various wavelength ranges, as well as some recent related works. These projects since late 1980s were focused on multiwavelength search and studies of AGN and Starbursts (SB). 1103 blue stellar objects (BSOs) on the basis of their UV-excess were selected using Markarian Survey (First Byurakan Survey, FBS) plates and Markarian's criteria used for the galaxies. Among many blue stars, QSOs and Seyfert galaxies were found by follow-up observations. 1577 IRAS point sources were optically identified using FBS low-dispersion spectra and many AGN, SB and high-luminosity IR galaxies (LIRG/ULIRG) were discovered. 32 extremely high IR/opt flux ratio galaxies were studies with Spitzer. 2791 ROSAT FSC sources were optically identified using Hamburg Quasar Survey (HQS) low-dispersion spectra and many AGN were discovered by follow-up observations. Fine analysis of emission line spectra was carried out using spectral line decomposition software to establish true profiles and calculate physical parameters for the emitting regions, as well as to study the spectral variability of these objects. X-ray and radio selection criteria were used to find new AGN and variable objects for further studies. We have estimated AGN content of X-ray sources as 52.9%. We have also combined IRAS PSC and FSC catalogs and compiled its extragalactic sample, which allowed us to estimate AGN content among IR sources as 23.7%. Multiwavelength approach allowed revealing many new AGN and SB and obtaining a number of interesting relations using their observational characteristics and physical properties.

Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs). II. Discovery of 32 quasars and luminous galaxies at 5.7 < z ≤ 6.8

NASA Astrophysics Data System (ADS)

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

2018-01-01

We present spectroscopic identification of 32 new quasars and luminous galaxies discovered at 5.7 < z ≤ 6.8. This is the second in a series of papers presenting the results of the Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs) project, which exploits the deep multi-band imaging data produced by the Hyper Suprime-Cam (HSC) Subaru Strategic Program survey. The photometric candidates were selected by a Bayesian probabilistic algorithm, and then observed with spectrographs on the Gran Telescopio Canarias and the Subaru Telescope. Combined with the sample presented in the previous paper of this series, we have now identified 64 HSC sources over about 430 deg2, which include 33 high-z quasars, 14 high-z luminous galaxies, two [O III] emitters at z ˜ 0.8, and 15 Galactic brown dwarfs. The new quasars have considerably lower luminosity (M1450 ˜ -25 to -22 mag) than most of the previously known high-z quasars. Several of these quasars have luminous (>1043 erg s-1) and narrow (< 500 km s-1) Lyα lines, and also a possible mini broad-absorption-line system of N V λ1240 in the composite spectrum, which clearly separate them from typical quasars. On the other hand, the high-z galaxies have extremely high luminosities (M1450 ˜ -24 to -22 mag) compared to other galaxies found at similar redshifts. With the discovery of these new classes of objects, we are opening up new parameter spaces in the high-z Universe. Further survey observations and follow-up studies of the identified objects, including the construction of the quasar luminosity function at z ˜ 6, are ongoing.

VizieR Online Data Catalog: Quasar from SDSS and UKIDSS (Wu+, 2010)

NASA Astrophysics Data System (ADS)

Wu, X.-B.; Jia, Z.

2011-02-01

We cross-identify all quasars in SDSS Data Release 7 (DR7) with the UKIDSS DR3, by finding the closest counterparts within 3-arcsec between the positions in two surveys and requesting all detections in both SDSS ugriz and UKIDSS YJHK bands for each quasar. To do the cross-identifications, we use the CrossID form available at the UKIDSS WFCAM Science Archive web site (http://surveys.roe.ac.uk:8080/wsa/crossID_form.jsp/) and use only the data in UKIDSS Large Area Survey (LAS) in order to avoid the misidentifications in the crowded fields with lower Galactic latitudes. This results in a sample of 8498 quasars with both SDSS and UKIDSS data. (1 data file).

Rapid detection of irradiated frozen hamburgers

NASA Astrophysics Data System (ADS)

Delincée, Henry

2002-03-01

DNA comet assay can be employed as a rapid and inexpensive screening test to check whether frozen ground beef patties (hamburgers) have been irradiated as a means to increase their safety by eliminating pathogenic bacteria, e.g. E. coli O157:H7. Such a detection procedure will provide an additional check on compliance with existing regulations, e.g. enforcement of labelling and rules in international trade. Frozen ready prepared hamburgers from the market place were `electron irradiated' with doses of 0, 1.3, 2.7, 4.5 and 7.2kGy covering the range of potential commercial irradiation. DNA fragmentation in the hamburgers was made visible within a few hours using the comet assay, and non-irradiated hamburgers could be easily discerned from the irradiated ones. Even after 9 months of frozen storage, irradiated hamburgers could be identified. Since DNA fragmentation may also occur with other food processes (e.g. temperature abuse), positive screening tests shall be confirmed using a validated method to specifically prove an irradiation treatment, e.g. EN 1784 or EN 1785.

The Frequency of Intrinsic X-Ray Weakness among Broad Absorption Line Quasars

NASA Astrophysics Data System (ADS)

Liu, Hezhen; Luo, B.; Brandt, W. N.; Gallagher, S. C.; Garmire, G. P.

2018-06-01

We present combined ≈14–37 ks Chandra observations of seven z = 1.6–2.7 broad absorption line (BAL) quasars selected from the Large Bright Quasar Survey (LBQS). These seven objects are high-ionization BAL (HiBAL) quasars, and they were undetected in the Chandra hard band (2–8 keV) in previous observations. The stacking analyses of previous Chandra observations suggested that these seven objects likely contain some candidates for intrinsically X-ray weak BAL quasars. With the new Chandra observations, six targets are detected. We calculate their effective power-law photon indices and hard-band flux weakness, and find that two objects, LBQS 1203+1530 and LBQS 1442–0011, show soft/steep spectral shapes ({{{Γ }}}eff}={2.2}-0.9+0.9 and {1.9}-0.8+0.9) and significant X-ray weakness in the hard band (by factors of ≈15 and 12). We conclude that the two HiBAL quasars are good candidates for intrinsically X-ray weak BAL quasars. The mid-infrared-to-ultraviolet spectral energy distributions of the two candidates are consistent with those of typical quasars. We constrain the fraction of intrinsically X-ray weak active galactic nuclei (AGNs) among HiBAL quasars to be ≈7%–10% (2/29–3/29), and we estimate it is ≈6%–23% (2/35–8/35) among the general BAL quasar population. Such a fraction is considerably larger than that among non-BAL quasars, and we suggest that intrinsically X-ray weak quasars are preferentially observed as BAL quasars. Intrinsically X-ray weak AGNs likely comprise a small minority of the luminous type 1 AGN population, and they should not affect significantly the completeness of these AGNs found in deep X-ray surveys.

NuSTAR Observations of Heavily Obscured Quasars Selected by WISE

NASA Astrophysics Data System (ADS)

Yan, Wei

2017-08-01

A key goal of the Nuclear Spectroscopic Telescope Array (NuSTAR) program is to find and characterize heavily obscured quasars, luminous accreting supermassive black holes hidden by gas and dust. Based on mid-infrared (IR) photometry from Wide-Field Infrared Survey Explorer (WISE) and optical photometry from the Sloan Digital Sky Surveys, we have selected a large population of obscured quasars; here we report the NuSTAR observations of four WISE-selected heavily obscured quasars for which we have optical spectroscopy from the Southern African Large Telescope and KECK Telescope. Three of four objects are undetected with NuSTAR, while the fourth has only a marginal detection. We confirm our objects have observed hard X-ray (10-40 keV) luminosities at or below ~1043 erg s-1. We compare IR and X-ray luminosities to obtain estimates of hydrogen column NH based on the suppression of the hard X-ray emission. We estimate NH to be at or greater than 1025 cm-2, confirming that WISE and optical selection can identify very heavily obscured quasars that may be missed in X-ray surveys.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Xue-Bing; Zuo, Wenwen; Yang, Jinyi

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 ourmore » 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

NEAR-INFRARED PHOTOMETRIC PROPERTIES OF 130,000 QUASARS: AN SDSS-UKIDSS-MATCHED CATALOG

DOE Office of Scientific and Technical Information (OSTI.GOV)

Peth, Michael A.; Ross, Nicholas P.; Schneider, Donald P., E-mail: npross@lbl.gov

2011-04-15

We present a catalog of over 130,000 quasar candidates with near-infrared (NIR) photometric properties, with an areal coverage of approximately 1200 deg{sup 2}. This is achieved by matching the Sloan Digital Sky Survey (SDSS) in the optical ugriz bands to the UKIRT Infrared Digital Sky Survey (UKIDSS) Large Area Survey (LAS) in the NIR YJHK bands. We match the {approx}1 million SDSS DR6 Photometric Quasar catalog to Data Release 3 of the UKIDSS LAS (ULAS) and produce a catalog with 130,827 objects with detections in one or more NIR bands, of which 74,351 objects have optical and K-band detections andmore » 42,133 objects have the full nine-band photometry. The majority ({approx}85%) of the SDSS objects were not matched simply because these were not covered by the ULAS. The positional standard deviation of the SDSS Quasar to ULAS matches is {delta}{sub R.A.} = 0.''1370 and {delta}{sub decl.} = 0.''1314. We find an absolute systematic astrometric offset between the SDSS Quasar catalog and the UKIDSS LAS, of |R.A.{sub offset}| = 0.''025 and |decl.{sub offset}| = 0.''040; we suggest the nature of this offset to be due to the matching of catalog, rather than image, level data. Our matched catalog has a surface density of {approx}53 deg{sup -2} for K {<=} 18.27 objects; tests using our matched catalog, along with data from the UKIDSS Deep Extragalactic Survey, imply that our limiting magnitude is i {approx} 20.6. Color-redshift diagrams, for the optical and NIR, show a close agreement between our matched catalog and recent quasar color models at redshift z {approx}< 2.0, while at higher redshifts, the models generally appear to be bluer than the mean observed quasar colors. The gJK and giK color spaces are used to examine methods of differentiating between stars and (mid-redshift) quasars, the key to currently ongoing quasar surveys. Finally, we report on the NIR photometric properties of high, z > 4.6, and very high, z > 5.7, redshift previously discovered quasars.« less

Weak bump quasars

NASA Technical Reports Server (NTRS)

Wilkes, B. J.; Mcdowell, J.

1994-01-01

Research into the optical, ultraviolet and infrared continuum emission from quasars and their host galaxies was carried out. The main results were the discovery of quasars with unusually weak infrared emission and the construction of a quantitative estimate of the dispersion in quasar continuum properties. One of the major uncertainties in the measurement of quasar continuum strength is the contribution to the continuum of the quasar host galaxy as a function of wavelength. Continuum templates were constructed for different types of host galaxy and individual estimates made of the decomposed quasar and host continua based on existing observations of the target quasars. The results are that host galaxy contamination is worse than previously suspected, and some apparent weak bump quasars are really normal quasars with strong host galaxies. However, the existence of true weak bump quasars such as PHL 909 was confirmed. The study of the link between the bump strength and other wavebands was continued by comparing with IRAS data. There is evidence that excess far infrared radiation is correlated with weaker ultraviolet bumps. This argues against an orientation effect and implies a probable link with the host galaxy environment, for instance the presence of a luminous starburst. However, the evidence still favors the idea that reddening is not important in those objects with ultraviolet weak bumps. The same work has led to the discovery of a class of infrared weak quasars. Pushing another part of the envelope of quasar continuum parameter space, the IR-weak quasars have implications for understanding the effects of reddening internal to the quasars, the reality of ultraviolet turnovers, and may allow further tests of the Phinney dust model for the IR continuum. They will also be important objects for studying the claimed IR to x-ray continuum correlation.

Quasar populations in a cosmological constant-dominated flat universe

NASA Technical Reports Server (NTRS)

Malhotra, Sangeeta; Turner, Edwin L.

1995-01-01

Most physical properties derived for quasars, as single entities or as a population, depend upon the cosmology assumed. In this paper, we calculate the quasar luminosity function and some related quantities for a flat universe dominated by a cosmological constant Lambda (Lambda = 0.9, Omega = 0.1) and compare them with those deduced for a flat universe with zero cosmological constant (Lambda = 0, Omega = 1). We use the ATT quasar survey data (Boyle et al. 1990) as input in both cases. The data are fitted well by a pure luminosity evolution model for both the cosmologies but with different evolutionary parameters. From the luminosity function, we predict (extrapolate) a greater number of quasars at faint apparent magnitudes (twice the number at B = 24, z is less than 2.2) for the Lambda-dominated universe. This population of faint quasars at high redshift would result in a higher incidence of gravitational lensing. The total luminosity of the quasar population and the total mass tied up in black hole remnants of quasars is not sensitive to the cosmology. However, for a Lambda cosmology, this mass is tied up in fewer but more massive black holes.

Flooding near Hamburg, Iowa

NASA Image and Video Library

2017-12-08

NASA image acquired July 17, 2011 In mid-July 2011, more than a month after the Missouri River broke through two levees and flooded fields near Hamburg, Iowa, muddy water lingered near the city. Hamburg residents were relieved, however, that a newly built levee had spared the town from flooding. On July 17, 2011, the Advanced Land Imager (ALI) on NASA’s Earth Observing-1 (EO-1) satellite captured this natural-color image. Compared to an image acquired on June 24, flooding has apparently receded slightly in some areas. Sediment-choked water nevertheless lingers on large swaths of land. On July 13, 2011, KETV of Omaha, Nebraska, reported that a newly built, 2-mile levee designed to protect Hamburg already exceeded federal standards. The U.S. Army Corps of Engineers handed control of the levee over to city officials on July 12. In the end, the levee was expected to cost the Army Corps $6 million, and the city of Hamburg about $800,000. On July 18, 2011, the Advanced Hydrological Prediction Service reported moderate flooding along the Missouri River not far from Hamburg, Iowa. In the northwest, the river reached 24.37 feet (7.43 meters) at Nebraska City. In the southeast, the river reached 38.98 feet (11.88 meters) at Brownville, Nebraska. NASA Earth Observatory image created by Jesse Allen and Robert Simmon, using EO-1 ALI data provided courtesy of the NASA EO-1 team. Caption by Michon Scott. Instrument: EO-1 - ALI Credit: NASA Earth Observatory NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

Quasars at Cosmic Dawn: Discoveries and Probes of the Early Universe

NASA Astrophysics Data System (ADS)

Wang, Feige; Wu, Xue-Bing; Fan, Xiaohui; Yang, Jinyi; Bian, Fuyan; McGreer, Ian D.; Green, Richard F.; Yang, Qian; Jiang, Linhua; Wang, Ran; DECaLS Team; UHS Team

2017-01-01

High redshift quasars, as the most luminous non-transient objects in the early universe, are the most promising tracers to address the history of cosmic reionization and how the origins of super-massive black hole (SMBH) are linked to galaxy formation and evolution. Over the last fifteen years, more than 100 quasars within the first billion years after the Big Bang have been discovered with the highest redshift at 7.1. We have developed a new method to select z>~6 quasars with both high efficiency and high completeness by combing optical and mid-IR Wide-field Infrared Survey Explorer (WISE) photometric data. We have applied this method to SDSS footprint and resulted in the discovery of the most luminous z>6 quasar ever discovered, which hosts a twelve billion solar mass black hole. I will present detailed follow-up observations of the host galaxies and environment of the most luminous quasars using HST, LBT and ALMA, in order to constrain early black hole growth and black hole/galaxy co-evolution at the highest redshift. I will also present initial results from a new quasar survey, which utilizes optical data from DECaLS, which is imaging 6700 deg^2 of sky down to z_AB˜23.0, and neaar-IR data from UHS and UKIDSS, which maps the whole northern sky at Decl.<+60deg. The combination of these datasets allows us to discover quasars at redshift z>~7 and to conduct a complete census of the faint quasar population at z~6.

Space Density of Optically Selected Type 2 Quasars

NASA Astrophysics Data System (ADS)

Reyes, Reinabelle; Zakamska, Nadia L.; Strauss, Michael A.; Green, Joshua; Krolik, Julian H.; Shen, Yue; Richards, Gordon T.; Anderson, Scott F.; Schneider, Donald P.

2008-12-01

Type 2 quasars are luminous active galactic nuclei whose central regions are obscured by large amounts of gas and dust. In this paper, we present a catalog of type 2 quasars from the Sloan Digital Sky Survey, selected based on their optical emission lines. The catalog contains 887 objects with redshifts z < 0.83; this is 6 times larger than the previous version and is by far the largest sample of type 2 quasars in the literature. We derive the [O III]5007 luminosity function (LF) for 108.3 L sun < L [O III] < 1010 L sun (corresponding to intrinsic luminosities up to M[2500 Å] ~= -28 mag or bolometric luminosities up to 4 × 1047 erg s-1). This LF provides robust lower limits to the actual space density of obscured quasars due to our selection criteria, the details of the spectroscopic target selection, and other effects. We derive the equivalent LF for the complete sample of type 1 (unobscured) quasars and determine the ratio of type 2 to type 1 quasar number densities. Our data constrain this ratio to be at least ~1.5:1 for 108.3 L sun < L [O III] < 109.5 L sun at z < 0.3, and at least ~1.2:1 for L [O III] ~ 1010 L sun at 0.3 < z < 0.83. Type 2 quasars are at least as abundant as type 1 quasars in the relatively nearby universe (z <~ 0.8) for the highest luminosities.

THE HALO OCCUPATION DISTRIBUTION OF SDSS QUASARS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Richardson, Jonathan; Chatterjee, Suchetana; Nagai, Daisuke

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 measurementsmore » 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

Extremely red quasars from SDSS, BOSS and WISE: classification of optical spectra

NASA Astrophysics Data System (ADS)

Ross, Nicholas P.; Hamann, Fred; Zakamska, Nadia L.; Richards, Gordon T.; Villforth, Carolin; Strauss, Michael A.; Greene, Jenny E.; Alexandroff, Rachael; Brandt, W. Niel; Liu, Guilin; Myers, Adam D.; Pâris, Isabelle; Schneider, Donald P.

2015-11-01

Quasars with extremely red infrared-to-optical colours are an interesting population that can test ideas about quasar evolution as well as orientation, obscuration and geometric effects in the so-called AGN unified model. To identify such a population, we match the quasar catalogues of the Sloan Digital Sky Survey (SDSS), the Baryon Oscillation Spectroscopic Survey (BOSS) to the Wide-Field Infrared Survey Explorer (WISE) to identify quasars with extremely high infrared-to-optical ratios. We identify 65 objects with rAB - W4Vega > 14 mag (i.e. Fν(22 μm)/Fν(r) ≳ 1000). This sample spans a redshift range of 0.28 < z < 4.36 and has a bimodal distribution, with peaks at z ˜ 0.8 and z ˜ 2.5. It includes three z > 2.6 objects that are detected in the W4 band but not W1 or W2 (i.e. `W1W2 dropouts'). The SDSS/BOSS spectra show that the majority of the objects are reddened type 1 quasars, type 2 quasars (both at low and high redshift) or objects with deep low-ionization broad absorption lines (BALs) that suppress the observed r-band flux. In addition, we identify a class of type 1 permitted broad emission-line objects at z ≃ 2-3 which are characterized by emission line rest-frame equivalent widths (REWs) of ≳150 Å, much larger than those of typical quasars. In particular, 55 per cent (45 per cent) of the non-BAL type 1s with measurable C IV in our sample have REW(C IV) > 100 (150) Å, compared to only 5.8 per cent (1.3 per cent) for non-BAL quasars in BOSS. These objects often also have unusual line ratios, such as very high N V/Ly α ratios. These large REWs might be caused by suppressed continuum emission analogous to type 2 quasars; however, there is no obvious mechanism in standard unified models to suppress the continuum without also obscuring the broad emission lines.

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.

A search for changing look quasars in second epoch imaging

NASA Astrophysics Data System (ADS)

Findlay, Joseph; Myers, Adam; McGreer, Ian

2018-01-01

Over nearly two decades, the Sloan Digital Sky Survey has compiled a catalog of over half a million confirmed quasars. During that period approximately ten percent of these objects have been spectroscopically observed in two or more epochs over baselines of ten or more years. This led recently to the discovery of the largest change in luminosity ever before observed in a quasar. The dimming emission was a reflection of very significant changes in continuum and broad line properties, the source had effectively transitioned from a Type I quasar to a Type II AGN. Since then several more "changing look" quasars have been discovered in multi-epoch SDSS spectroscopy. Among them are objects with rising and falling luminosities, appearing and disappearing broad lines. The origin of this behavior is still very uncertain, currently favored is the scenario in which an accreting black hole is simply starved of fuel. Other plausible scenarios include flaring due to stellar tidal disruption close to the black hole or large changes in accretion flow, which can occur during transitions between radiatively efficient and inefficient accretion regimes. Monitoring of larger numbers of changing look quasars will help to elucidate these ideas.In this poster, we report on the progress of a pilot study in which we hope to learn how to select changing look quasars in multi-epoch imaging. This will allow us to take advantage of the entire SDSS quasar catalog rather than just the ten percent of objects with multi-epoch spectroscopy. Comparing archival SDSS and more recent Legacy Survey imaging over ten-year baselines we select objects whose photometry is consistent with the large changes in luminosity expected in changing look quasars. We aim to build up a catalog of both transitioned and transitioning objects for future monitoring.

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.

Quasar Feedback at the Peak of Galaxy Formation Epoch

NASA Astrophysics Data System (ADS)

Liu, Guilin; Zakamska, Nadia L.; Strauss, Michael A.; Greene, Jenny E.; Alexandroff, Rachael

2013-02-01

The correlations between properties of supermassive black holes and stellar spheroids in galaxies imply a physical connection between these two components in spite of their vastly different masses and physical scales. Using Gemini GMOS IFU, we demonstrated that powerful ionized gas winds are a ubiquitous feature in luminous radio-quiet obscured z 0.5 quasars. We now plan to extend this discovery to the era of peak galaxy formation and quasar activity - to the epoch when feedback was most prominent and the galaxy vs. black hole correlations were established. We propose a GMOS IFU survey to map the spatial distribution and the kinematics of Ly(alpha) and N sc v 1240Å emission around 5 obscured quasars at z=3-3.4. We will use Ly(alpha) observations to directly probe the effects of ionizing radiation of obscured quasars on their large-scale environments and N sc v observations to look for signatures of unbound quasar-driven outflows. We will observe in the g-band on sub-galactic and galaxy- wide scales (spatial resolution 3-6 kpc, field of view 40times50 kpc^2 at z=3). Obscured quasars likely constitute the majority of the quasar population and may represent the relatively early enshrouded phase of black hole growth; thus, luminous obscured quasars are the most likely sites of quasar ionization- and wind-feedback, as we found at low redshifts. Our proposed GMOS observations will provide a definitive probe of the effects of quasars on their galaxy-wide and large-scale environments close to the peak of galaxy formation epoch.

Statistical Detection of the He II Transverse Proximity Effect: Evidence for Sustained Quasar Activity for >25 Million Years

NASA Astrophysics Data System (ADS)

Schmidt, Tobias M.; Worseck, Gabor; Hennawi, Joseph F.; Prochaska, J. Xavier; Crighton, Neil H. M.

2017-09-01

The He II transverse proximity effect—enhanced He II {Ly}α transmission in a background sightline caused by the ionizing radiation of a foreground quasar—offers a unique opportunity to probe the morphology of quasar-driven He II reionization. We conduct a comprehensive spectroscopic survey to find z˜ 3 quasars in the foreground of 22 background quasar sightlines with Hubble Space Telescope/COS He II {Ly}α transmission spectra. With our two-tiered survey strategy, consisting of a deep pencil-beam survey and a shallow wide-field survey, we discover 131 new quasars, which we complement with known SDSS/BOSS quasars in our fields. Using a restricted sample of 66 foreground quasars with inferred He II photoionization rates greater than the expected UV background at these redshifts ({{{Γ }}}{QSO}{He {{II}}}> 5× {10}-16 {{{s}}}-1) we perform the first statistical analysis of the He II transverse proximity effect. Our results show qualitative evidence for a large object-to-object variance: among the four foreground quasars with the highest {{{Γ }}}{QSO}{He {{II}}} only one (previously known) quasar is associated with a significant He II transmission spike. We perform a stacking analysis to average down these fluctuations, and detect an excess in the average He II transmission near the foreground quasars at 3σ significance. This statistical evidence for the transverse proximity effect is corroborated by a clear dependence of the signal strength on {{{Γ }}}{QSO}{He {{II}}}. Our detection places a purely geometrical lower limit on the quasar lifetime of {t}{{Q}}> 25 {Myr}. Improved modeling would additionally constrain quasar obscuration and the mean free path of He II-ionizing photons.

Quasars with P v broad absorption in BOSS data release 9

NASA Astrophysics Data System (ADS)

Capellupo, D. M.; Hamann, F.; Herbst, H.; Brandt, W. N.; Ge, J.; Pâris, I.; Petitjean, P.; Schneider, D. P.; Streblyanska, A.; York, D.

2017-07-01

Broad absorption lines (BALs) found in a significant fraction of quasar spectra identify high-velocity outflows that might be present in all quasars and could be a major factor in feedback to galaxy evolution. Understanding the nature of these flows requires further constraints on their physical properties, including their column densities, for which well-studied BALs, such as C IV λλ1548,1551, typically provide only a lower limit because of saturation effects. Low-abundance lines, such as P v λλ1118,1128, indicate large column densities, implying that outflows more powerful than measurements of C IV alone would indicate. We search through a sample of 2694 BAL quasars from the Sloan Digital Sky Survey III/Baryon Oscillation Spectroscopic Survey data release 9 quasar catalogue for such absorption, and we identify 81 'definite' and 86 'probable' detections of P v broad absorption, yielding a firm lower limit of 3.0-6.2 per cent for the incidence of such absorption among BAL quasars. The P v-detected quasars tend to have stronger C IV and Si IV absorption, as well as a higher incidence of LoBAL absorption, than the overall BAL quasar population. Many of the P v-detected quasars have C IV troughs that do not reach zero intensity (at velocities where P v is detected), confirming that the outflow gas only partially covers the UV continuum source. P v appears significantly in a composite spectrum of non-P v-detected BAL quasars, indicating that P v absorption (and large column densities) is much more common than indicated by our search results. Our sample of P v detections significantly increases the number of known P v detections, providing opportunities for follow-up studies to better understand BAL outflow energetics.

[Active and healthy living in old age--results from a representative survey of community-dwelling senior citizens in Hamburg].

PubMed

Dapp, Ulrike; Lorentz, Ch; Laub, S; Anders, J; von Renteln-Kruse, W; Minder, Ch; Dirksen-Fischer, M

2009-06-01

The majority of community-dwelling people 60 years and older are independent and live actively. However, there is little information about elderly persons' views on aging, health and health promotion. Therefore, an anonymous, written questionnaire survey was performed in a representative sample of inhabitants from a section of the city of Hamburg, 60 years and older; 5 year intervals, 14 subsamples according to 7 age groups of females and males. Questionnaires from 950 participants (29% response) could be evaluated: mean age 71.5 years, 58% women, 34% living alone, 5% with professional healthcare needs as indicated by status according to German nursing care insurance. Senior citizens' positive attitudes towards aging and health were predominant: 69% of respondents felt young, 85% worried about loss of autonomy in old age. The results provide evidence indicating potential for improving health-promoting lifestyles in parts of the older population by evaluating and strengthening older persons' competencies and by considering their concerns seriously. These results provide valuable information for future plans in the public-health sector in the city of Hamburg where particular health-promoting actions for elderly persons will be considered.

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.

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.

Extremely red quasars in BOSS

NASA Astrophysics Data System (ADS)

Hamann, Fred; Zakamska, Nadia L.; Ross, Nicholas; Paris, Isabelle; Alexandroff, Rachael M.; Villforth, Carolin; Richards, Gordon T.; Herbst, Hanna; Brandt, W. Niel; Cook, Ben; Denney, Kelly D.; Greene, Jenny E.; Schneider, Donald P.; Strauss, Michael A.

2017-01-01

Red quasars are candidate young objects in an early transition stage of massive galaxy evolution. Our team recently discovered a population of extremely red quasars (ERQs) in the Baryon Oscillation Spectroscopic Survey (BOSS) that has a suite of peculiar emission-line properties including large rest equivalent widths (REWs), unusual `wingless' line profiles, large N V/Lyα, N V/C IV, Si IV/C IV and other flux ratios, and very broad and blueshifted [O III] λ5007. Here we present a new catalogue of C IV and N V emission-line data for 216 188 BOSS quasars to characterize the ERQ line properties further. We show that they depend sharply on UV-to-mid-IR colour, secondarily on REW(C IV), and not at all on luminosity or the Baldwin Effect. We identify a `core' sample of 97 ERQs with nearly uniform peculiar properties selected via I-W3 ≥ 4.6 (AB) and REW(C IV) ≥ 100 Å at redshifts 2.0-3.4. A broader search finds 235 more red quasars with similar unusual characteristics. The core ERQs have median luminosity ˜ 47.1, sky density 0.010 deg-2, surprisingly flat/blue UV spectra given their red UV-to-mid-IR colours, and common outflow signatures including BALs or BAL-like features and large C IV emission-line blueshifts. Their SEDs and line properties are inconsistent with normal quasars behind a dust reddening screen. We argue that the core ERQs are a unique obscured quasar population with extreme physical conditions related to powerful outflows across the line-forming regions. Patchy obscuration by small dusty clouds could produce the observed UV extinctions without substantial UV reddening.

Mean Occupation Function of High-redshift Quasars from the Planck Cluster Catalog

NASA Astrophysics Data System (ADS)

Chakraborty, Priyanka; Chatterjee, Suchetana; Dutta, Alankar; Myers, Adam D.

2018-06-01

We characterize the distribution of quasars within dark matter halos using a direct measurement technique for the first time at redshifts as high as z ∼ 1. Using the Planck Sunyaev-Zeldovich (SZ) catalog for galaxy groups and the Sloan Digital Sky Survey (SDSS) DR12 quasar data set, we assign host clusters/groups to the quasars and make a measurement of the mean number of quasars within dark matter halos as a function of halo mass. We find that a simple power-law fit of {log}< N> =(2.11+/- 0.01) {log}(M)-(32.77+/- 0.11) can be used to model the quasar fraction in dark matter halos. This suggests that the quasar fraction increases monotonically as a function of halo mass even to redshifts as high as z ∼ 1.

MEASURING LENSING MAGNIFICATION OF QUASARS BY LARGE SCALE STRUCTURE USING THE VARIABILITY-LUMINOSITY RELATION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bauer, Anne H.; Seitz, Stella; Jerke, Jonathan

2011-05-10

We introduce a technique to measure gravitational lensing magnification using the variability of type I quasars. Quasars' variability amplitudes and luminosities are tightly correlated, on average. Magnification due to gravitational lensing increases the quasars' apparent luminosity, while leaving the variability amplitude unchanged. Therefore, the mean magnification of an ensemble of quasars can be measured through the mean shift in the variability-luminosity relation. As a proof of principle, we use this technique to measure the magnification of quasars spectroscopically identified in the Sloan Digital Sky Survey (SDSS), due to gravitational lensing by galaxy clusters in the SDSS MaxBCG catalog. The Palomar-QUESTmore » Variability Survey, reduced using the DeepSky pipeline, provides variability data for the sources. We measure the average quasar magnification as a function of scaled distance (r/R{sub 200}) from the nearest cluster; our measurements are consistent with expectations assuming Navarro-Frenk-White cluster profiles, particularly after accounting for the known uncertainty in the clusters' centers. Variability-based lensing measurements are a valuable complement to shape-based techniques because their systematic errors are very different, and also because the variability measurements are amenable to photometric errors of a few percent and to depths seen in current wide-field surveys. Given the volume data of the expected from current and upcoming surveys, this new technique has the potential to be competitive with weak lensing shear measurements of large-scale structure.« less

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.

Enhancement of galaxy overdensity around quasar pairs at z < 3.6 based on the Hyper Suprime-Cam Subaru Strategic Program Survey

NASA Astrophysics Data System (ADS)

Onoue, Masafusa; Kashikawa, Nobunari; Uchiyama, Hisakazu; Akiyama, Masayuki; Harikane, Yuichi; Imanishi, Masatoshi; Komiyama, Yutaka; Matsuoka, Yoshiki; Nagao, Tohru; Nishizawa, Atsushi J.; Oguri, Masamune; Ouchi, Masami; Tanaka, Masayuki; Toba, Yoshiki; Toshikawa, Jun

2018-01-01

We investigate the galaxy overdensity around proto-cluster scale quasar pairs at high (z > 3) and low (z ˜ 1) redshift based on the unprecedentedly wide and deep optical survey of the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP). Using the first-year survey data covering effectively ˜121 deg2 with the 5σ depth of i ˜ 26.4 and the SDSS DR12Q catalog, we find two luminous pairs at z ˜ 3.3 and 3.6 which reside in >5σ overdensity regions of g-dropout galaxies at i < 25. The projected separations of the two pairs are R⊥ = 1.75 and 1.04 proper Mpc (pMpc), and their velocity offsets are ΔV = 692 and 1448 km s-1, respectively. This result is in clear contrast to the average z ˜ 4 quasar environments as discussed in Uchiyama et al. (2018, PASJ 70, S32) and implies that the quasar activities of the pair members are triggered via major mergers in proto-clusters, unlike the vast majority of isolated quasars in general fields that may turn on via non-merger events such as bar and disk instabilities. At z ˜ 1, we find 37 pairs with R⊥ < 2 pMpc and ΔV < 2300 km s-1 in the current HSC-Wide coverage, including four from Hennawi et al. (2006, AJ, 131, 1). The distribution of the peak overdensity significance within two arcminutes around the pairs has a long tail toward high-density (>4σ) regions. Thanks to the large sample size, we find statistical evidence that this excess is unique to the pair environments when compared to single-quasar and randomly selected galaxy environments at the same redshift range. Moreover, there are nine small-scale (R⊥ < 1 pMpc) pairs, two of which are found to reside in cluster fields. Our results demonstrate that <2 pMpc scale quasar pairs at both redshift ranges tend to occur in massive haloes, although perhaps not the most massive ones, and that they are useful in searching for rare density peaks.

The Clustering of High-Redshift (2.9 < z < 5.4) Quasars in SDSS Stripe 82

NASA Astrophysics Data System (ADS)

Timlin, John; Ross, Nicolas; Richards, Gordon; Myers, Adam; Bauer, Franz Erik; Lacy, Mark; Schneider, Donald; Wollack, Edward; Zakamska, Nadia

2018-01-01

We present the data from the Spitzer IRAC Equatorial Survey (SpIES) along with our first high-redshift (2.9quasar clustering results using these data. SpIES is a mid-infrared survey covering ~100 square degrees of the Sloan Digital Sky Survey (SDSS) Stripe 82 (S82) field. The SpIES field is optimally located to overlap with the optical data from SDSS and to complement the area of the pre-existing Spitzer data from the Spitzer-HETDEX Exploratory Large-area (SHELA) survey, which adds ~20 square degrees of infrared coverage on S82. SpIES probes magnitudes significantly fainter than WISE; depth that is crucial to detect faint, high-redshift quasars. Using the infrared data from SpIES and SHELA, and the deep optical data from SDSS, we employ multi-dimensional empirical selection algorithms to identify high-redshift quasar candidates in this field. We then combine these candidates with spectroscopically confirmed high-redshift quasars and measure the angular correlation function. Using these results, we compute the linear bias to try to constrain quasar feedback models akin to those in Hopkins et al. 2007.

There Are (super)Giants in the Sky: Searching for Misidentified Massive Stars in Algorithmically-Selected Quasar Catalogs

NASA Astrophysics Data System (ADS)

Dorn-Wallenstein, Trevor Z.; Levesque, Emily

2017-11-01

Thanks to incredible advances in instrumentation, surveys like the Sloan Digital Sky Survey have been able to find and catalog billions of objects, ranging from local M dwarfs to distant quasars. Machine learning algorithms have greatly aided in the effort to classify these objects; however, there are regimes where these algorithms fail, where interesting oddities may be found. We present here an X-ray bright quasar misidentified as a red supergiant/X-ray binary, and a subsequent search of the SDSS quasar catalog for X-ray bright stars misidentified as quasars.

Physical Properties of 15 Quasars at z ≳ 6.5

NASA Astrophysics Data System (ADS)

Mazzucchelli, C.; Bañados, E.; Venemans, B. P.; Decarli, R.; Farina, E. P.; Walter, F.; Eilers, A.-C.; Rix, H.-W.; Simcoe, R.; Stern, D.; Fan, X.; Schlafly, E.; De Rosa, G.; Hennawi, J.; Chambers, K. C.; Greiner, J.; Burgett, W.; Draper, P. W.; Kaiser, N.; Kudritzki, R.-P.; Magnier, E.; Metcalfe, N.; Waters, C.; Wainscoat, R. J.

2017-11-01

Quasars are galaxies hosting accreting supermassive black holes; due to their brightness, they are unique probes of the early universe. To date, only a few quasars have been reported at z> 6.5 (<800 Myr after the big bang). In this work, we present six additional z≳ 6.5 quasars discovered using the Pan-STARRS1 survey. We use a sample of 15 z≳ 6.5 quasars to perform a homogeneous and comprehensive analysis of this highest-redshift quasar population. We report four main results: (1) the majority of z≳ 6.5 quasars show large blueshifts of the broad C IV λ1549 emission line compared to the systemic redshift of the quasars, with a median value ˜3× higher than a quasar sample at z˜ 1; (2) we estimate the quasars’ black hole masses ({M}{BH} ˜ (0.3-5) × 109 M ⊙) via modeling of the Mg II λ2798 emission line and rest-frame UV continuum and find that quasars at high redshift accrete their material (with < ({L}{bol}/{L}{Edd})> =0.39) at a rate comparable to a luminosity-matched sample at lower redshift, albeit with significant scatter (0.4 dex); (3) we recover no evolution of the Fe II/Mg II abundance ratio with cosmic time; and (4) we derive near-zone sizes and, together with measurements for z˜ 6 quasars from recent work, confirm a shallow evolution of the decreasing quasar near-zone sizes with redshift. Finally, we present new millimeter observations of the [C II] 158 μm emission line and underlying dust continuum from NOEMA for four quasars and provide new accurate redshifts and [C II]/infrared luminosity estimates. The analysis presented here shows the large range of properties of the most distant quasars.

Composite Spectral Energy Distributions and Infrared-Optical Colors of Type 1 and Type 2 Quasars

NASA Astrophysics Data System (ADS)

Hickox, Ryan C.; Myers, Adam D.; Greene, Jenny E.; Hainline, Kevin N.; Zakamska, Nadia L.; DiPompeo, Michael A.

2017-11-01

We present observed mid-infrared and optical colors and composite spectral energy distributions (SEDs) of type 1 (broad-line) and 2 (narrow-line) quasars selected from Sloan Digital Sky Survey (SDSS) spectroscopy. A significant fraction of powerful quasars are obscured by dust and are difficult to detect in optical photometric or spectroscopic surveys. However, these may be more easily identified on the basis of mid-infrared (MIR) colors and SEDs. Using samples of SDSS type 1 and 2 matched in redshift and [O III] luminosity, we produce composite rest-frame 0.2-15 μm SEDs based on SDSS, UKIDSS, and Wide-field Infrared Survey Explorer photometry and perform model fits using simple galaxy and quasar SED templates. The SEDs of type 1 and 2 quasars are remarkably similar, with the differences explained primarily by the extinction of the quasar component in the type 2 systems. For both types of quasar, the flux of the active galactic nucleus (AGN) relative to the host galaxy increases with AGN luminosity ({L}[{{O}{{III}}]}) and redder observed MIR color, but we find only weak dependencies of the composite SEDs on mechanical jet power as determined through radio luminosity. We conclude that luminous quasars can be effectively selected using simple MIR color criteria similar to those identified previously ({{W}}1{--}{{W}}2> 0.7; Vega), although these criteria miss many heavily obscured objects. Obscured quasars can be further identified based on optical-IR colors (for example, (u{--}{{W}}3 [{AB}])> 1.4({{W}}1{--}{{W}}2 [{Vega}])+3.2). These results illustrate the power of large statistical studies of obscured quasars selected on the basis of MIR and optical photometry.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ikeda, H.; Nagao, T.; Matsuoka, K.

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 quasarmore » 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.« less

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

DISCOVERY OF A FAINT QUASAR AT z ∼ 6 AND IMPLICATIONS FOR COSMIC REIONIZATION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kim, Yongjung; Im, Myungshin; Jeon, Yiseul

2015-11-10

Recent studies suggest that faint active galactic nuclei may be responsible for the reionization of the universe. Confirmation of this scenario requires spectroscopic identification of faint quasars (M{sub 1450} > −24 mag) at z ≳ 6, but only a very small number of such quasars have been spectroscopically identified so far. Here, we report the discovery of a faint quasar IMS J220417.92+011144.8 at z ∼ 6 in a 12.5 deg{sup 2} region of the SA22 field of the Infrared Medium-deep Survey (IMS). The spectrum of the quasar shows a sharp break at ∼8443 Å, with emission lines redshifted to zmore » = 5.944 ± 0.002 and rest-frame ultraviolet continuum magnitude M{sub 1450} = −23.59 ± 0.10 AB mag. The discovery of IMS J220417.92+011144.8 is consistent with the expected number of quasars at z ∼ 6 estimated from quasar luminosity functions based on previous observations of spectroscopically identified low-luminosity quasars. This suggests that the number of M{sub 1450} ∼ −23 mag quasars at z ∼ 6 may not be high enough to fully account for the reionization of the universe. In addition, our study demonstrates that faint quasars in the early universe can be identified effectively with a moderately wide and deep near-infrared survey such as the IMS.« less

Broad NE 8 lambda 774 emission from quasars in the HST-FOS snapshot survey (ABSNAP)

NASA Technical Reports Server (NTRS)

Hamann, Fred; Zuo, Lin; Tytler, David

1995-01-01

We discuss the strength and frequency of broad Ne VIII lambda 774 emission from quasars measured in the Hubble Space Telescope Faint Object Spectrograph (HST-FOS) snapshot survey (Absnap). Five sources in the survey have suitable redshifts (0.86 less than or equal to Z(sub em) less than or equal to 1.31), signal-to-noise ratios and no Lyman limit absorptions. Three of the five sources have a strong broad emission line near 774 A (rest), and the remaining two sources have a less securely measured line near this wavelength. We identify these lines with Ne VIII lambda 774 based on the measured wavelengths and theoretical estimates of various line fluxes (Hamann et al. 1995a). Secure Ne VIII detections occur in both radio-loud and radio-quiet sources. We tentatively conclude that broad Ne VIII lambda 774 emission is common in quasars, with typical strengths between approximately 25% and approximately 200% of O VI lambda 1034. These Ne VIII lambda 774 measurements imply that the broad emission line regions have a much hotter and more highly ionized component than previously recognized. They also suggest that quasar continua have substantial ionizing flux out to energies greater than 207 eV (greater than 15.2 ryd, lambda less than 60 A). Photoionization calculations using standard incident spectra indicate that the Ne VIII emission requires ionization parameters U greater than or = 5, total column densities N(sub H) greater than or = 10(sub 22)/sq cm and covering factors greater than or = 25%. The temperatures could be as high as approximately 10(exp 5) K. If the gas is instead collisionally ionized, strong Ne VIII would imply equilibrium temperatures in the range approximately 400,000 less than or approximately = T(sub e) less than or approximately = 10(exp 6) K. In either case, the highly ionized Ne VIII emission regions would appear as X-ray 'warm absorbers' if they lie along our line of sight to the X-ray continuum source.

A quasar discovered at redshift 6.6 from Pan-STARRS1

NASA Astrophysics Data System (ADS)

Tang, Ji-Jia; Goto, Tomotsugu; Ohyama, Youichi; Chen, Wen-Ping; Walter, Fabian; Venemans, Bram; Chambers, Kenneth C.; Bañados, Eduardo; Decarli, Roberto; Fan, Xiaohui; Farina, Emanuele; Mazzucchelli, Chiara; Kaiser, Nick; Magnier, Eugene A.

2017-04-01

Luminous high-redshift quasars can be used to probe of the intergalactic medium in the early universe because their UV light is absorbed by the neutral hydrogen along the line of sight. They help us to measure the neutral hydrogen fraction of the high-z universe, shedding light on the end of reionization epoch. In this paper, we present a discovery of a new quasar (PSO J006.1240+39.2219) at redshift z = 6.61 ± 0.02 from Panoramic Survey Telescope & Rapid Response System 1. Including this quasar, there are nine quasars above z > 6.5 up to date. The estimated continuum brightness is M1450 = -25.96 ± 0.08. PSO J006.1240+39.2219 has a strong Ly α emission compared with typical low-redshift quasars, but the measured near-zone region size is RNZ = 3.2 ± 1.1 proper megaparsecs, which is consistent with other quasars at z ˜ 6.

Camera for Quasars in the Early Universe (CQUEAN)

NASA Astrophysics Data System (ADS)

Kim, Eunbin; Park, W.; Lim, J.; Jeong, H.; Kim, J.; Oh, H.; Pak, S.; Im, M.; Kuehne, J.

2010-05-01

The early universe of z ɳ is where the first stars, galaxies, and quasars formed, starting the re-ionization of the universe. The discovery and the study of quasars in the early universe allow us to witness the beginning of history of astronomical objects. In order to perform a medium-deep, medium-wide, imaging survey of quasars, we are developing an optical CCD camera, CQUEAN (Camera for QUasars in EArly uNiverse) which uses a 1024*1024 pixel deep-depletion CCD. It has an enhanced QE than conventional CCD at wavelength band around 1μm, thus it will be an efficient tool for observation of quasars at z > 7. It will be attached to the 2.1m telescope at McDonald Observatory, USA. A focal reducer is designed to secure a larger field of view at the cassegrain focus of 2.1m telescope. For long stable exposures, auto-guiding system will be implemented by using another CCD camera viewing an off-axis field. All these instruments will be controlled by the software written in python on linux platform. CQUEAN is expected to see the first light during summer in 2010.

Two more, bright, z > 6 quasars from VST ATLAS and WISE

NASA Astrophysics Data System (ADS)

Chehade, B.; Carnall, A. C.; Shanks, T.; Diener, C.; Fumagalli, M.; Findlay, J. R.; Metcalfe, N.; Hennawi, J.; Leibler, C.; Murphy, D. N. A.; Prochaska, J. X.; Irwin, M. J.; Gonzalez-Solares, E.

2018-03-01

Recently, Carnall et al. discovered two bright high redshift quasars using the combination of the VST ATLAS and WISE surveys. The technique involved using the 3-D colour plane i - z: z - W1: W1 - W2 with the WISE W1(3.4 micron) and W2 (4.5 micron) bands taking the place of the usual NIR J band to help decrease stellar dwarf contamination. Here we report on our continued search for 5.7 < z < 6.4 quasars over an ≈2 × larger area of ≈3577 deg2 of the Southern Hemisphere. We have found two further z > 6 quasars, VST-ATLAS J158.6938-14.4211 at z = 6.07 and J332.8017-32.1036 at z = 6.32 with magnitudes of zAB = 19.4 and 19.7 mag respectively. J158.6938-14.4211 was confirmed by Keck LRIS observations and J332.8017-32.1036 was confirmed by ESO NTT EFOSC-2 observations. Here we present VLT X-shooter Visible and NIR spectra for the four ATLAS quasars. We have further independently rediscovered two z > 5.7 quasars previously found by the VIKING/KiDS and PanSTARRS surveys. This means that in ATLAS we have now discovered a total of six quasars in our target 5.7 < z < 6.4 redshift range. Making approximate corrections for incompleteness, we find that our quasar space density agrees with the SDSS results of Jiang et al. at M1450Å ≈ -27. Preliminary virial mass estimates based on the CIV and MgII emission lines give black hole masses in the range MBH ≈ 1 - 6 × 109M⊙ for the four ATLAS quasars.

Quasars Probing Quasars. IX. The Kinematics of the Circumgalactic Medium Surrounding z ∼ 2 Quasars

NASA Astrophysics Data System (ADS)

Lau, Marie Wingyee; Prochaska, J. Xavier; Hennawi, Joseph F.

2018-04-01

We examine the kinematics of the gas in the environments of galaxies hosting quasars at z ∼ 2. We employ 148 projected quasar pairs to study the circumgalactic gas of the foreground quasars in absorption. The sample selects foreground quasars with precise redshift measurements, using emission lines with precision ≲300 km s‑1 and average offsets from the systemic redshift ≲ | 100 {km} {{{s}}}-1| . We stack the background quasar spectra at the foreground quasar’s systemic redshift to study the mean absorption in C II, C IV, and Mg II. We find that the mean absorptions exhibit large velocity widths σv ≈ 300 km s‑1. Further, the mean absorptions appear to be asymmetric about the systemic redshifts. The mean absorption centroids exhibit small redshift relative to the systemic δv ≈ +200 km s‑1, with large intrinsic scatter in the centroid velocities of the individual absorption systems. We find the observed widths are consistent with gas in gravitational motion and Hubble flow. However, while the observation of large widths alone does not require galactic-scale outflows, the observed offsets suggest that the gas is on average outflowing from the galaxy. The observed offsets also suggest that the ionizing radiation from the foreground quasars is anisotropic and/or intermittent.

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

VLBI survey of compact broad absorption line quasars with balnicity index BI = 0

NASA Astrophysics Data System (ADS)

Cegłowski, M.; Kunert-Bajraszewska, M.; Roskowiński, C.

2015-06-01

We present high-resolution observations, using both the European VLBI Network (EVN) at 1.7 GHz and the Very Long Baseline Array (VLBA) at 5 and 8.4 GHz, to image radio structures of 14 compact sources classified as broad absorption line (BAL) quasars based on the absorption index (AI). All sources but one were resolved, with the majority showing core-jet morphology typical for radio-loud quasars. We discuss in detail the most interesting cases. The high radio luminosities and small linear sizes of the observed objects indicate they are strong young active galactic nuclei. Nevertheless, the distribution of the radio-loudness parameter, log RI, of a larger sample of AI quasars shows that the objects observed by us constitute the most luminous, small subgroup of the AI population. Additionally, we report that for the radio-loudness parameter, the distribution of AI quasars and that for those selected using the traditional balnicity index differ significantly. Strong absorption is connected with lower log RI and thus probably larger viewing angles. Since the AI quasars have on average larger log RI, the orientation can mean that we see them less absorbed. However, we suggest that the orientation is not the only parameter that affects the detected absorption. That the strong absorption is associated with the weak radio emission is equally important and worth exploring.

A Quasar Turns On

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2017-02-01

The intermediate Palomar Transient Factory (iPTF) has discovered a quasar the brightly-shining, active nucleus of a galaxy abruptly turning on in what appears to be the fastest such transition ever seen in such an object.A Rapid TransitionQuasars are expected to show variations in brightness on timescales of hours to millions of years, but its not often that we get to study their major variability in real time! So far, weve discovered only a dozen changing-look quasars active galactic nuclei that exhibit major changes in their spectral class and brightness between observations. Roughly half of these were quasars that turned on and half were quasars that turned off, generally on timescales of maybe 5 or 10 years.The dramatic change in spectrum of iPTF 16bco between the archival SDSS data from 2004 (bottom) and the follow-up spectroscopy from Keck 2+DEIMOS in 2016 (top). [Adapted from Gezari et al. 2017]In June 2016, however, a team of scientists led by Suvi Gezari (University of Maryland) discovered iPTF 16bco, a nuclear transient that wasnt there the last time Palomar checked in 2012. A search through archival Sloan Digital Sky Survey and GALEX data in addition to some follow-up X-ray imaging and spectroscopic observations told the team what they needed to know: iPTF 16bco is a quasar that only just turned on within the 500 days preceding the iPTF observations.This source, in fact, is a 100-million-solar-mass black hole located at the center of a galaxy at a redshift of z= 0.237. In just over a year, the source changed classification from a galaxy with weak narrow-line emission to a quasar with characteristic strong, broad emission lines and a ten-fold increase in continuum brightness! What caused this sudden transition?Instabilities at Fault?iPTF 16bco and the other known changing-look quasars with disappearing (red circles) and appearing (blue circles) broad-line emission. [Adapted from Gezari et al. 2017]Gezari and collaborators used the large number of recent

Investigating the Fraction of Radio-Loud Quasars with High Velocity Broad Emission LInes

NASA Astrophysics Data System (ADS)

Bhattacharjee, Anirban; Gilbert, Miranda; Brotherton, Michael S.

2018-06-01

Quasars show a bimodal distribution in their radio emission, with some having powerful radio-emitting jets (radio-loud), and most having weak or no jets (radio-quiet). Surveys have shown around 10% of of quasars have detectable radio emissions. These quasars are called radio-loud. Several multiwavelength studies have shown that radio-loud quasars have different properties than radio-quiet quasars. This fraction of radio-loud quasars to radio-quiet quasars has been assumed to be constant across all parameter space. In this study, we breakdown the parameter space with respect to the increasing velocity dispersion of broad emission lines. Our sample has been drawn from 2011 Shen et al. catalog of more than 100,000 quasars. In this study, we demonstrate that this fraction varies with respect to the increasing velocity dispersion (FWHM) of broad emission lines. We compare three different emission lines: H-Beta, MgII, and CIV. We observe with increasing FWHM of these three emission lines, fraction of radio-loud quasars within the subset increases. This poster presents our initial results into investigating whether the fraction of RL quasars remains 10% in different parameter space.

Probabilistic selection of high-redshift quasars

NASA Astrophysics Data System (ADS)

Mortlock, Daniel J.; Patel, Mitesh; Warren, Stephen J.; Hewett, Paul C.; Venemans, Bram P.; McMahon, Richard G.; Simpson, Chris

2012-01-01

High-redshift quasars (HZQs) with redshifts of z ≳ 6 are so rare that any photometrically selected sample of sources with HZQ-like colours is likely to be dominated by Galactic stars and brown dwarfs scattered from the stellar locus. It is impractical to re-observe all such candidates, so an alternative approach was developed in which Bayesian model comparison techniques are used to calculate the probability that a candidate is a HZQ, Pq, by combining models of the quasar and star populations with the photometric measurements of the object. This method was motivated specifically by the large number of HZQ candidates identified by cross-matching the UKIRT (United Kingdom Infrared Telescope) Infrared Deep Sky Survey (UKIDSS) Large Area Survey (LAS) to the Sloan Digital Sky Survey (SDSS): in the ? covered by the LAS in the UKIDSS Eighth Data Release (DR8) there are ˜9 × 103 real astronomical point sources with the measured colours of the target quasars, of which only ˜10 are expected to be HZQs. Applying Bayesian model comparison to the sample reveals that most sources with HZQ-like colours have Pq≲ 0.1 and can be confidently rejected without the need for any further observations. In the case of the UKIDSS DR8 LAS, there were just 107 candidates with Pq≥ 0.1; these objects were prioritized for re-observation by ranking according to Pq (and their likely redshift, which was also inferred from the photometric data). Most candidates were rejected after one or two (moderate-depth) photometric measurements by recalculating Pq using the new data. That left 12 confirmed HZQs, six of which were previously identified in the SDSS and six of which were new UKIDSS discoveries. The high efficiency of this Bayesian selection method suggests that it could usefully be extended to other HZQ surveys (e.g. searches by the Panoramic Survey Telescope And Rapid Response System, Pan-STARRS, or the Visible and Infrared Survey Telescope for Astronomy, VISTA) as well as to other

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.

[Galaxy/quasar classification based on nearest neighbor method].

PubMed

Li, Xiang-Ru; Lu, Yu; Zhou, Jian-Ming; Wang, Yong-Jun

2011-09-01

With the wide application of high-quality CCD in celestial spectrum imagery and the implementation of many large sky survey programs (e. g., Sloan Digital Sky Survey (SDSS), Two-degree-Field Galaxy Redshift Survey (2dF), Spectroscopic Survey Telescope (SST), Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) program and Large Synoptic Survey Telescope (LSST) program, etc.), celestial observational data are coming into the world like torrential rain. Therefore, to utilize them effectively and fully, research on automated processing methods for celestial data is imperative. In the present work, we investigated how to recognizing galaxies and quasars from spectra based on nearest neighbor method. Galaxies and quasars are extragalactic objects, they are far away from earth, and their spectra are usually contaminated by various noise. Therefore, it is a typical problem to recognize these two types of spectra in automatic spectra classification. Furthermore, the utilized method, nearest neighbor, is one of the most typical, classic, mature algorithms in pattern recognition and data mining, and often is used as a benchmark in developing novel algorithm. For applicability in practice, it is shown that the recognition ratio of nearest neighbor method (NN) is comparable to the best results reported in the literature based on more complicated methods, and the superiority of NN is that this method does not need to be trained, which is useful in incremental learning and parallel computation in mass spectral data processing. In conclusion, the results in this work are helpful for studying galaxies and quasars spectra classification.

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.

The K-Band Quasar Luminosity Function from an SDSS and UKIDSS Matched Catalog

NASA Astrophysics Data System (ADS)

Peth, Michael; Ross, N. P.; Schneider, D. P.

2010-01-01

We match the 1,015,082 quasars from the Sloan Digital Sky Survey (SDSS) DR6 Photometric Quasar catalog to the UKIRT Infrared Digital Sky Survey (UKIDSS) Large Area Survey (LAS) DR3 to produce a catalog of 130,827 objects with optical (ugriz) and infrared (YJHK) measurements over an area of 1,200 sq. deg. A matching radius of 1'’ is used; the positional standard deviations of SDSS DR6 quasars and UKIDSS LAS is δRA = 0.137'’ and δDec = 0.131''. The catalog contains 74,351 K-band detections and 42,133 objects have coverage in all four NIR bands. In addition to the catalog, we present optical and NIR color-redshift and color-color plots. The photometric vs. spectroscopic redshift plots demonstrate how unreliable high reported photometric redshifts can be. This forces us to focus on z4.6 quasars are compared to our highest redshift objects. The giK color-color plot demonstrates that stellar contamination only affects a small sample of the objects. Distributions for Y,J,H,K and i-bands reveal insights into the flux limits in each magnitude. We investigate the distribution of redshifts from different data sets and investigate the legitimacy of certain measured photometric redshift regions. For in-depth analysis, we focus on the 300 sq. deg area equatorial SDSS region designated as Stripe 82. We measure the observed K-band quasar luminosity function (QLF) for a subset of 9,872, z<2.2 objects. We find the shape of the K-band QLF is very similar to that of the optical QLF, over the considered redshift ranges. Our calculated K-Band QLFs broadly match previous optical QLFs calculated from the SDSS and 2SLAQ QSO surveys and should provide important constraints linking unobscured optical quasars to Mid-Infrared detected, dusty and obscured AGNs at high-redshift.

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

Quasar microlensing models with constraints on the Quasar light curves

NASA Astrophysics Data System (ADS)

Tie, S. S.; Kochanek, C. S.

2018-01-01

Quasar microlensing analyses implicitly generate a model of the variability of the source quasar. The implied source variability may be unrealistic yet its likelihood is generally not evaluated. We used the damped random walk (DRW) model for quasar variability to evaluate the likelihood of the source variability and applied the revized algorithm to a microlensing analysis of the lensed quasar RX J1131-1231. We compared estimates of the size of the quasar disc and the average stellar mass of the lens galaxy with and without applying the DRW likelihoods for the source variability model and found no significant effect on the estimated physical parameters. The most likely explanation is that unreliastic source light-curve models are generally associated with poor microlensing fits that already make a negligible contribution to the probability distributions of the derived parameters.

DISSECTING THE QUASAR MAIN SEQUENCE: INSIGHT FROM HOST GALAXY PROPERTIES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sun, Jiayi; Shen, Yue

2015-05-01

The diverse properties of broad-line quasars appear to follow a well-defined main sequence along which the optical Fe ii strength increases. It has been suggested that this sequence is mainly driven by the Eddington ratio (L/L{sub Edd}) of the black hole (BH) accretion. Shen and Ho demonstrated with quasar clustering analysis that the average BH mass decreases with increasing Fe ii strength when quasar luminosity is fixed, consistent with this suggestion. Here we perform an independent test by measuring the stellar velocity dispersion σ{sub *} (hence, the BH mass via the M–σ{sub *} relation) from decomposed host spectra in low-redshiftmore » Sloan Digital Sky Survey quasars. We found that at fixed quasar luminosity, σ{sub *} systematically decreases with increasing Fe ii strength, confirming that the Eddington ratio increases with Fe ii strength. We also found that at fixed luminosity and Fe ii strength, there is little dependence of σ{sub *} on the broad Hβ FWHM. These new results reinforce the framework that the Eddington ratio and orientation govern most of the diversity seen in broad-line quasar properties.« less

Evaluating and improving the redshifts of z > 2.2 quasars

NASA Astrophysics Data System (ADS)

Mason, Michelle; Brotherton, Michael S.; Myers, Adam

2017-08-01

Quasar redshifts require the best possible precision and accuracy for a number of applications, such as setting the velocity scale for outflows as well as measuring small-scale quasar-quasar clustering. The most reliable redshift standard in luminous quasars is arguably the narrow [O III] λλ4959, 5007 emission line doublet in the rest-frame optical. We use previously published [O III] redshifts obtained using near-infrared spectra in a sample of 45 high-redshift (z > 2.2) quasars to evaluate redshift measurement techniques based on rest-frame ultraviolet spectra. At redshifts above z = 2.2, the Mg II λ2798 emission line is not available in observed-frame optical spectra and the most prominent unblended and unabsorbed spectral feature available is usually C IV λ1549. Peak and centroid measurements of the C IV profile are often blueshifted relative to the rest-frame of the quasar, which can significantly bias redshift determinations. We show that redshift determinations for these high-redshift quasars are significantly correlated with the emission-line properties of C IV (I.e. the equivalent width, or EW, and the full width at half-maximum, or FWHM) as well as the luminosity, which we take from the Sloan Digital Sky Survey Data Release 7. We demonstrate that empirical corrections based on multiple regression analyses yield significant improvements in both the precision and accuracy of the redshifts of the most distant quasars and are required to establish consistency with redshifts determined in more local quasars.

The End of Hamburg's Anglophilia: Wilhelmine Hamburg Attitudes Viewed through School Examination Essays and a University Lecture (1912-1914)

ERIC Educational Resources Information Center

Gärtner, Niko

2014-01-01

Late nineteenth-century German-English rivalry changed attitudes in Hamburg. Previously, the once fiercely independent city and its burgeoning mercantile middle class had developed an Anglophilia that justified Hamburg being labelled a "London suburb" and "the most British town on the Continent". The affinity for all things…

Space Density Of Optically-Selected Type II Quasars From The SDSS

NASA Astrophysics Data System (ADS)

Reyes, Reinabelle; Zakamska, N. L.; Strauss, M. A.; Green, J.; Krolik, J. H.; Shen, Y.; Richards, G. T.

2007-12-01

Type II quasars are luminous Active Galactic Nuclei (AGN) whose central regions are obscured by large amounts of gas and dust. In this poster, we present a catalog of 887 type II quasars with redshifts z<0.83 from the Sloan Digital Sky Survey (SDSS), selected based on their emission lines, and derive the 1/Vmax [OIII] 5007 luminosity function from this sample. Since some objects may not be included in the sample because they lack strong emission lines, the derived luminosity function is only a lower limit. We also derive the [OIII] 5007 luminosity function for a sample of type I (broad-line) quasars in the same redshift range. Taking [OIII] 5007 luminosity as a tracer of intrinsic luminosity in both type I and type II quasars, we obtain lower limits to the type II quasar fraction as a function of [OIII] 5007 luminosity, from L[OIII] = 108.3 to 1010 Lsun, which roughly correspond to bolometric luminosities of 1044 to 1046 erg/s.

Characterizing the evolution of WISE-selected obscured and unobscured quasars using HOD models.

NASA Astrophysics Data System (ADS)

Myers, Adam D.; DiPompeo, Michael A.; Mitra, Kaustav; Hickox, Ryan C.; Chatterjee, Suchetana; Whalen, Kelly

2018-06-01

Large-area imaging surveys in the infrared are now beginning to unlock the links between the activity of supermassive black holes and the cosmic evolution of dark matter halos during the significant times when black hole growth is enshrouded in dust. With data from the Wide-Field Infrared Survey Explorer (WISE) and complementary optical photometry, we construct samples of nearly half-a-million obscured and unobscured quasars around redshift 1. We study the dark matter halos of these populations using both angular autocorrelation functions and CMB lensing cross-correlations, carefully characterizing the redshift distribution of the obscured quasar sample using cross-correlations. Independent of our measurement technique, we find that obscured quasars occupy dark matter halos a few times more massive than their unobscured counterparts, despite being matched in luminosity at 12 and 22 microns. Modeling the two-point correlation function using a four-parameter Halo Occupation Distribution (HOD) formalism, we determine that purely optically selected quasars reside in dark matter halos that are about half the mass of WISE-selected obscured quasars, and that satellite fractions are somewhat larger for obscured quasars. We investigate scenarios such as merger-driven fueling and Eddington-dependent obscuration to explore what combinations of physical effects can reproduce our observed halo mass measurements. This work was, in part, supported by NASA ADAP award NNX16AN48G.

VizieR Online Data Catalog: Radio-loud and radio-quiet quasars sample (Gupta+, 2016)

NASA Astrophysics Data System (ADS)

Gupta, M.; Sikora, M.; Nalewajko, K.

2017-11-01

We performed matching of the FR II quasar sample of van Velzen et al. (2015, Cat. J/MNRAS/446/2985) (1108 sources) with the SDSS DR7 quasar catalogue (Schneider et al., 2010AJ....139.2360S, Cat. VII/260) (105 783 sources). We used a matching radius of 5 arcsec and obtained 899 objects. This resulting sample of FR II quasars was then matched with the sample of SDSS DR7 quasars detected by the Wide-field Infrared Survey Explorer (WISE) (Wu et al., 2012, Cat. J/AJ/144/49). This gave us 895 FR II quasars detected in the MIR band. The RQ sample with MIR data is constructed by matching the DR7 quasar catalogue (Schneider et al., 2010AJ....139.2360S, Cat. VII/260) and Wise all-sky catalogue (Wu et al., 2012, Cat. J/AJ/144/49), using a matching radius of 1 arcsec, resulting in 101 853 objects. From these we remove the 899 RL quasars matched with the catalogue by van Velzen et al. (2015, Cat. J/MNRAS/446/2985), this leaves us with 100 958 quasars. We then remove objects that were detected by the FIRST survey (Becker et al. 1995ApJ...450..559B, Cat. VIII/92), this gives us 92 648. We repeat the same process with the NVSS (Condon, Cotton & Broderick, 1998AJ....115.1693C, Cat. VIII/65) and end up with 92 445 objects. We also removed those objects that were outside the FIRST observation region. (2 data files).

On the selection of high-z quasars using LOFAR observations

NASA Astrophysics Data System (ADS)

Retana-Montenegro, Edwin; Röttgering, Huub

2018-03-01

We present a method to identify candidate quasars which combines optical/infrared color selection with radio detections from the Low Frequency ARray (LOFAR) at 150MHz. We apply this {method} in a region of 9 square degrees located in the Boötes field, with a wealth of multi-wavelength data. Our LOFAR imaging in the central region reaches a rms noise of ˜50μJy with a resolution of 5''. This is so deep that we also routinely, `radio-quiet' quasars. We use quasar spectroscopy from the literature to calculate the completeness and efficiency of our selection method. We conduct our analysis in two redshift intervals, 1quasars, and 80% of our candidates are in the spectroscopic sample; while for objects at 2.0quasars. For this purpose, we calculate the spectral index between 1400MHz and 150MHz, by combining our LOFAR-Boötes data with 1.4GHz imaging of the Boötes field obtained with the Westerbork Synthesis Radio Telescope (WSRT), which has a rms noise of σ˜28μJy with a resolution of 13''×27''. We find that 27% of the candidate quasars are detected at 1400 MHz, and that these detected objects have a spectral index distribution with a median value of α=-0.73±0.07. Using a flux density threshold of S_{150MHz}=1.50mJy, so that all the α>-1.0 sources can be detected in the WSRT-Boötes map, we find that the spectral index distribution of the 21 quasars in the resulting sample is steeper than the general LOFAR-WSRT spectral index distribution with a median of α=-0.80±0.06. As the upcoming LOFAR wide area surveys are much deeper than the traditional 1.4GHz surveys like NVSS and FIRST, this indicates that LOFAR in combination with optical and infrared will be an excellent fishing ground to obtain large samples of quasars.

Biopreservation of hamburgers by essential oil of Zataria multiflora.

PubMed

Samadi, N; Sharifan, A; Emam-Djomeh, Z; Sormaghi, M H Salehi

2012-01-01

Hamburgers with high nutrient supply and a loosely-packed structure present favourable conditions for microbial growth. In this study, the chemical composition and antimicrobial activity of the essential oil of Zataria multiflora and its potential application as a natural preservative in reducing the indigenous microbial population of hamburgers were investigated. Carvacrol, thymol and linalool were found to be the most abundant constituents of the essential oil using GC-MS analysis. The essential oil exhibited strong antibacterial activity against Gram-positive and Gram-negative bacteria. Addition of Z. multiflora essential oil in concentrations higher than MIC values influenced the microbial population of hamburgers stored at 25°C, 4°C and -12°C. The significant results of this study are our observations that the use of Z. multiflora essential oil at 0.05% v/w increases the time needed for the natural microflora of hamburgers to reach concentrations able to produce a perceivable spoilage at refrigerator and room temperatures without any inverse effect on their sensory attributes. Freezing of essential oil-treated hamburgers may also reduce the risk of diseases associated with consumption of under-cooked hamburgers through significant microbial reduction by more than 3 log.

[A method for obtaining redshifts of quasars based on wavelet multi-scaling feature matching].

PubMed

Liu, Zhong-Tian; Li, Xiang-Ru; Wu, Fu-Chao; Zhao, Yong-Heng

2006-09-01

The LAMOST project, the world's largest sky survey project being implemented in China, is expected to obtain 10(5) quasar spectra. The main objective of the present article is to explore methods that can be used to estimate the redshifts of quasar spectra from LAMOST. Firstly, the features of the broad emission lines are extracted from the quasar spectra to overcome the disadvantage of low signal-to-noise ratio. Then the redshifts of quasar spectra can be estimated by using the multi-scaling feature matching. The experiment with the 15, 715 quasars from the SDSS DR2 shows that the correct rate of redshift estimated by the method is 95.13% within an error range of 0. 02. This method was designed to obtain the redshifts of quasar spectra with relative flux and a low signal-to-noise ratio, which is applicable to the LAMOST data and helps to study quasars and the large-scale structure of the universe etc.

The Gaseous Environments of Quasars: Outflows, Feedback & Cold Mode Accretion

NASA Astrophysics Data System (ADS)

Chen, Chen; Hamann, Fred

2018-06-01

The early stages of massive galaxy evolution can involve galaxy-scale outflows driven by a starburst or a central quasar and cold-mode accretion (infall) that adds to the mass buildup in the galaxies. I will describe three related studies that use quasar absorption lines to measure outflows, infall, and the general gaseous environments of quasars across a range of spatial scales. The three studies are: 1) High-resolution spectroscopy with Keck-HIRES and VLT-UVES to study associated absorption lines (AALs) that have redshifts greater than the emission redshifts indicating infall and/or rich multi-component AAL complexes that might be interstellar clouds in the host galaxies that have been shredded and dispersed by a fast unseen quasar-driven wind. The data provide strong constraints on the gas kinematics, spatial structure, column densities, metallicities, and energetics. 2) A complete inventory of high-velocity CIV 1548,1550 mini-BAL outflows in quasars using high-resolution high signal-to-noise spectra in the public VLT-UVES and Keck-HIRES archives. This sensitive mini-BAL survey fills an important niche between previous work on narrow absorption lines (NALs) and the much-studied broad absorption lines (BALs) to build a more complete picture of quasar outflows. I will report of the mini-BAL statistics, the diversity of lines detected, and some tests for correlations with the quasar properties. We find, for example, that mini-BALs at v > 4000 km/s in at least 10% of 511 quasars studied, including 1% at v > 0.1 c. Finally, 3) Use the much larger database of NALs measured in 262,449 BOSS quasars by York et al. (in prep.) to study their potential relationships to the quasars and, specifically, their origins in quasar outflows. This involves primarily comparisons of the incidence and properties of NALs at different velocity shifts to other measured properties of the quasars such as BAL outflows, emission line characteristics, radio-loudness, and red colors. We find

VizieR Online Data Catalog: The UV-bright Quasar Survey (UVQS) DR1 (Monroe+, 2016)

NASA Astrophysics Data System (ADS)

Monroe, T. R.; Prochaska, J. X.; Tejos, N.; Worseck, G.; Hennawi, J. F.; Schmidt, T.; Tumlinson, J.; Shen, Y.

2016-09-01

We have performed an all-sky survey for z~1, FUV-bright quasars selected from GALEX and WISE photometry. We generated a list of 1450 primary candidates (Table1). In several of the observing runs, conditions were unexpectedly favorable and we exhausted the primary candidates at certain right ascension ranges. To fill the remaining observing time, we generated a secondary candidate list. This secondary set of candidates is provided in Table2. We proceeded to obtain discovery-quality longslit spectra (i.e., low-dispersion, large wavelength coverage, modest signal-to-noise ratio (S/N) of our UV-bright Quasar Survey (UVQS) candidates in one calendar year. Our principal facilities were: (i) the dual Kast spectrometer on the 3m Shane telescope at the Lick Observatory; (ii) the Boller & Chivens (BCS) spectrometer on the Irenee du Pont 100'' telescope at the Las Campanas Observatory; and (iii) the Calar Alto Faint Object Spectrograph on the CAHA 2.2m telescope at the Calar Alto Observatory (CAHA). We acquired an additional ~20 spectra on larger aperture telescopes (Keck/ESI, MMT/MBC, Magellan/MagE) during twilight or under poor observing conditions. Typical exposure times were limited to <~200s, with adjustments for fainter sources or sub-optimal observing conditions. Table3 provides a list of the observed candidates. There are 93 sources with a good quality spectrum for which we cannot recover a secure redshift. The majority of these have been previously cataloged as blazars (or BL Lac objects). Table6 lists the sample of these unknowns. (6 data files).

The Clustering of High-redshift (2.9 ≤ z ≤ 5.1) Quasars in SDSS Stripe 82

NASA Astrophysics Data System (ADS)

Timlin, John D.; Ross, Nicholas P.; Richards, Gordon T.; Myers, Adam D.; Pellegrino, Andrew; Bauer, Franz E.; Lacy, Mark; Schneider, Donald P.; Wollack, Edward J.; Zakamska, Nadia L.

2018-05-01

We present a measurement of the two-point autocorrelation function of photometrically selected high-z quasars over ∼100 deg2 on the Sloan Digital Sky Survey Stripe 82 field. Selection is performed using three machine-learning algorithms in a six-dimensional optical/mid-infrared color space. Optical data from the Sloan Digital Sky Survey are combined with overlapping deep mid-infrared data from the Spitzer IRAC Equatorial Survey and the Spitzer-HETDEX Exploratory Large-Area survey. Our selection algorithms are trained on the colors of known high-z quasars. The selected quasar sample consists of 1378 objects and contains both spectroscopically confirmed quasars and photometrically selected quasar candidates. These objects span a redshift range of 2.9 ≤ z ≤ 5.1 and are generally fainter than i = 20.2, a regime that has lacked sufficient number density to perform autocorrelation function measurements of photometrically classified quasars. We compute the angular correlation function of these data, marginally detecting quasar clustering. We fit a single power law with an index of δ = 1.39 ± 0.618 and amplitude of θ 0 = 0.‧71 ± 0.‧546 . A dark matter model is fit to the angular correlation function to estimate the linear bias. At the average redshift of our survey (< z> =3.38), the bias is b = 6.78 ± 1.79. Using this bias, we calculate a characteristic dark matter halo mass of 1.70–9.83× {10}12{h}-1 {M}ȯ . Our bias estimate suggests that quasar feedback intermittently shuts down the accretion of gas onto the central supermassive black hole at early times. If confirmed, these results hint at a level of luminosity dependence in the clustering of quasars at high-z.

Discovery of a z = 0.65 post-starburst BAL quasar in the DES supernova fields

DOE PAGES

Mudd, Dale; Martini, Paul; Tie, Suk Sien; ...

2017-03-23

In this paper, we present the discovery of a z = 0.65 low-ionization broad absorption line (LoBAL) quasar in a post-starburst galaxy in data from the Dark Energy Survey (DES) and spectroscopy from the Australian Dark Energy Survey (OzDES). LoBAL quasars are a minority of all BALs, and rarer still is that this object also exhibits broad Fe ii (an FeLoBAL) and Balmer absorption. This is the first BAL quasar that has signatures of recently truncated star formation, which we estimate ended about 40 Myr ago. The characteristic signatures of an FeLoBAL require high column densities, which could be explainedmore » by the emergence of a young quasar from an early, dust-enshrouded phase, or by clouds compressed by a blast wave. Finally, the age of the starburst component is comparable to estimates of the lifetime of quasars, so if we assume the quasar activity is related to the truncation of the star formation, this object is better explained by the blast wave scenario.« less

Discovery of a z = 0.65 post-starburst BAL quasar in the DES supernova fields

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mudd, Dale; Martini, Paul; Tie, Suk Sien

We present the discovery of a z=0.65 low-ionization broad absorption line (LoBAL) quasar in a post-starburst galaxy in data from the Dark Energy Survey (DES) and spectroscopy from the Australian Dark Energy Survey (OzDES). LoBAL quasars are a minority of all BALs, and rarer still is that this object also exhibits broad FeII (an FeLoBAL) and Balmer absorption. This is the first BAL quasar that has signatures of recently truncated star formation, which we estimate ended about 40 Myr ago. The characteristic signatures of an FeLoBAL require high column densities, which could be explained by the emergence of a youngmore » quasar from an early, dust-enshrouded phase, or by clouds compressed by a blast wave. The age of the starburst component is comparable to estimates of the lifetime of quasars, so if we assume the quasar activity is related to the truncation of the star formation, this object is better explained by the blast wave scenario.« less

Discovery of a z = 0.65 post-starburst BAL quasar in the DES supernova fields

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mudd, Dale; Martini, Paul; Tie, Suk Sien

In this paper, we present the discovery of a z = 0.65 low-ionization broad absorption line (LoBAL) quasar in a post-starburst galaxy in data from the Dark Energy Survey (DES) and spectroscopy from the Australian Dark Energy Survey (OzDES). LoBAL quasars are a minority of all BALs, and rarer still is that this object also exhibits broad Fe ii (an FeLoBAL) and Balmer absorption. This is the first BAL quasar that has signatures of recently truncated star formation, which we estimate ended about 40 Myr ago. The characteristic signatures of an FeLoBAL require high column densities, which could be explainedmore » by the emergence of a young quasar from an early, dust-enshrouded phase, or by clouds compressed by a blast wave. Finally, the age of the starburst component is comparable to estimates of the lifetime of quasars, so if we assume the quasar activity is related to the truncation of the star formation, this object is better explained by the blast wave scenario.« less

The WISSH quasars project. II. Giant star nurseries in hyper-luminous quasars

NASA Astrophysics Data System (ADS)

Duras, F.; Bongiorno, A.; Piconcelli, E.; Bianchi, S.; Pappalardo, C.; Valiante, R.; Bischetti, M.; Feruglio, C.; Martocchia, S.; Schneider, R.; Vietri, G.; Vignali, C.; Zappacosta, L.; La Franca, F.; Fiore, F.

2017-08-01

Context. Studying the coupling between the energy output produced by the central quasar and the host galaxy is fundamental to fully understand galaxy evolution. Quasar feedback is indeed supposed to dramatically affect the galaxy properties by depositing large amounts of energy and momentum into the interstellar medium (ISM). Aims: In order to gain further insights on this process, we study the spectral energy distributions (SEDs) of sources at the brightest end of the quasar luminosity function, for which the feedback mechanism is assumed to be at its maximum, given their high efficiency in driving powerful outflows. Methods: We modelled the rest-frame UV-to-far-IR SEDs of 16 WISE-SDSS Selected Hyper-luminous (WISSH) quasars at 1.8 < z < 4.6 based on SDSS, 2MASS, WISE and Herschel/SPIRE data. Through an accurate SED-fitting procedure, we separate the different emission components by deriving physical parameters of both the nuclear component (I.e. bolometric and monochromatic luminosities) and the host galaxy (I.e. star formation rate, mass, and temperature of the cold dust). We also use a radiative transfer code to account for the contribution of the quasar-related emission to the far-IR fluxes. Results: Most SEDs are well described by a standard combination of accretion disc plus torus and cold dust emission. However, about 30% of SEDs require an additional emission component in the near-IR, with temperatures peaking at 750 K, which indicates that a hotter dust component is present in these powerful quasars. We measure extreme values of both AGN bolometric luminosity (LBOL > 1047 erg/s) and star formation rate (up to 2000 M⊙/yr) based on the quasar-corrected, IR luminosity of the host galaxy. A new relation between quasar and star formation luminosity is derived (LSF ∝ L0.73QSO) by combining several Herschel-detected quasar samples from z 0 to 4. WISSH quasars have masses ( 108M⊙) and temperatures ( 50 K) of cold dust in agreement with those found for other

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hennawi, Joseph F.; Prochaska, J. Xavier, E-mail: xavier@ucolick.org

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 (predominantlymore » 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

Measuring the Clustering Around Normal and Dust-Obscured Quasars at 2 in the Spitzer Extragalactic Representative Volume Survey (SERVS)

NASA Astrophysics Data System (ADS)

Jones, Kristen M.; Lacy, M.; Spitzer Extragalactic Representative Volume Survey Team

2014-01-01

Little is known about the environments of high redshift quasars, particularly those obscured by dust. Previous work suggests that dust-shrouded (type 2) quasars are at least as common as un-obscured optical (type 1) quasars; therefore, in order to fully understand the role quasars play in the evolutionary history of the universe, we must understand both types of objects. This project seeks to explore the environments in which obscured quasars form. In this poster, we present mid-infrared clustering measurements for a sample of 45 quasars with 1.3 < z < 2.5, a redshift range that is unexplored in the literature. The objects were selected using IRAC multi-color criteria to remove low-redshift starburst and quiescent galaxies, and subsequently had spectroscopy carried out to both obtain redshifts, and to distinguish between type 1 and type 2 quasars; the high-redshift sample presented in this paper is roughly evenly distributed between the two types. We use the SERVS galaxy catalogs to estimate the cross-correlation between each quasar and its surrounding galaxies. The amplitude of this function gives us the richness of the environments in which these quasars are found, and we compare our results with a matched sample with z < 1.3.

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.

The clustering of the SDSS-IV extended Baryon Oscillation Spectroscopic Survey DR14 quasar sample: anisotropic Baryon Acoustic Oscillations measurements in Fourier-space with optimal redshift weights

NASA Astrophysics Data System (ADS)

Wang, Dandan; Zhao, Gong-Bo; Wang, Yuting; Percival, Will J.; Ruggeri, Rossana; Zhu, Fangzhou; Tojeiro, Rita; Myers, Adam D.; Chuang, Chia-Hsun; Baumgarten, Falk; Zhao, Cheng; Gil-Marín, Héctor; Ross, Ashley J.; Burtin, Etienne; Zarrouk, Pauline; Bautista, Julian; Brinkmann, Jonathan; Dawson, Kyle; Brownstein, Joel R.; de la Macorra, Axel; Schneider, Donald P.; Shafieloo, Arman

2018-06-01

We present a measurement of the anisotropic and isotropic Baryon Acoustic Oscillations (BAO) from the extended Baryon Oscillation Spectroscopic Survey Data Release 14 quasar sample with optimal redshift weights. Applying the redshift weights improves the constraint on the BAO dilation parameter α(zeff) by 17 per cent. We reconstruct the evolution history of the BAO distance indicators in the redshift range of 0.8 < z < 2.2. This paper is part of a set that analyses the eBOSS DR14 quasar sample.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu Xuebing; Wang Ran; Bian Fuyan

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 partsmore » 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.« less

A Full Year's Chandra Exposure on Sloan Digital Sky Survey Quasars from the Chandra Multiwavelength Project

NASA Astrophysics Data System (ADS)

Green, Paul J.; Aldcroft, T. L.; Richards, G. T.; Barkhouse, W. A.; Constantin, A.; Haggard, D.; Karovska, M.; Kim, D.-W.; Kim, M.; Vikhlinin, A.; Anderson, S. F.; Mossman, A.; Kashyap, V.; Myers, A. D.; Silverman, J. D.; Wilkes, B. J.; Tananbaum, H.

2009-01-01

We study the spectral energy distributions and evolution of a large sample of optically selected quasars from the Sloan Digital Sky Survey that were observed in 323 Chandra images analyzed by the Chandra Multiwavelength Project. Our highest-confidence matched sample includes 1135 X-ray detected quasars in the redshift range 0.2 < z < 5.4, representing some 36 Msec of effective exposure. We provide catalogs of QSO properties, and describe our novel method of calculating X-ray flux upper limits and effective sky coverage. Spectroscopic redshifts are available for about 1/3 of the detected sample; elsewhere, redshifts are estimated photometrically. We detect 56 QSOs with redshift z > 3, substantially expanding the known sample. We find no evidence for evolution out to z ~ 5 for either the X-ray photon index Γ or for the ratio of optical/UV to X-ray flux αox. About 10% of detected QSOs show best-fit intrinsic absorbing columns greater than 1022 cm-2, but the fraction might reach ~1/3 if most nondetections are absorbed. We confirm a significant correlation between αox and optical luminosity, but it flattens or disappears for fainter (MB gsim -23) active galactic nucleus (AGN) alone. We report significant hardening of Γ both toward higher X-ray luminosity, and for relatively X-ray loud quasars. These trends may represent a relative increase in nonthermal X-ray emission, and our findings thereby strengthen analogies between Galactic black hole binaries and AGN. For uniformly selected subsamples of narrow-line Seyfert 1s and narrow absorption line QSOs, we find no evidence for unusual distributions of either αox or Γ.

Gravitationally Lensed Quasars in Gaia: II. Discovery of 24 Lensed Quasars

NASA Astrophysics Data System (ADS)

Lemon, Cameron A.; Auger, Matthew W.; McMahon, Richard G.; Ostrovski, Fernanda

2018-04-01

We report the discovery, spectroscopic confirmation and preliminary characterisation of 24 gravitationally lensed quasars identified using Gaia observations. Candidates were selected in the Pan-STARRS footprint with quasar-like WISE colours or as photometric quasars from SDSS, requiring either multiple detections in Gaia or a single Gaia detection near a morphological galaxy. The Pan-STARRS grizY images were modelled for the most promising candidates and 60 candidate systems were followed up with the William Herschel Telescope. 13 of the lenses were discovered as Gaia multiples and 10 as single Gaia detections near galaxies. We also discover 1 lens identified through a quasar emission line in an SDSS galaxy spectrum. The lenses have median image separation 2.13″ and the source redshifts range from 1.06 to 3.36. 4 systems are quadruply-imaged and 20 are doubly-imaged. Deep CFHT data reveal an Einstein ring in one double system. We also report 12 quasar pairs, 10 of which have components at the same redshift and require further follow-up to rule out the lensing hypothesis. We compare the properties of these lenses and other known lenses recovered by our search method to a complete sample of simulated lenses to show the lenses we are missing are mainly those with small separations and higher source redshifts. The initial Gaia data release only catalogues all images of ˜ 30% of known bright lensed quasars, however the improved completeness of Gaia data release 2 will help find all bright lensed quasars on the sky.

Minor Contribution of Quasars to Ionizing Photon Budget at z ˜ 6: Update on Quasar Luminosity Function at the Faint End with Subaru/Suprime-Cam

NASA Astrophysics Data System (ADS)

Onoue, Masafusa; Kashikawa, Nobunari; Willott, Chris J.; Hibon, Pascale; Im, Myungshin; Furusawa, Hisanori; Harikane, Yuichi; Imanishi, Masatoshi; Ishikawa, Shogo; Kikuta, Satoshi; Matsuoka, Yoshiki; Nagao, Tohru; Niino, Yuu; Ono, Yoshiaki; Ouchi, Masami; Tanaka, Masayuki; Tang, Ji-Jia; Toshikawa, Jun; Uchiyama, Hisakazu

2017-10-01

We constrain the quasar contribution to the cosmic reionization based on our deep optical survey of z ˜ 6 quasars down to z R = 24.15 using Subaru/Suprime-Cam in three UKIDSS-DXS fields covering 6.5 deg2. In Kashikawa et al. (2015), we select 17 quasar candidates and report our initial discovery of two low-luminosity quasars ({M}1450˜ -23) from seven targets, one of which might be a Lyα-emitting galaxy. From an additional optical spectroscopy, none of the four candidates out of the remaining 10 turn out to be genuine quasars. Moreover, the deeper optical photometry provided by the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP) shows that, unlike the two already-known quasars, the I - z and z - y colors of the last six candidates are consistent with M- or L-type brown dwarfs. Therefore, the quasar luminosity function (QLF) measurement in the previous paper is confirmed. Compiling the QLF measurements from the literature over a wide magnitude range, including an extremely faint AGN candidate from Parsa et al. (2017), to fit them with a double power law, we find that the best-fit faint-end slope is α =-{2.04}-0.18+0.33 (-{1.98}-0.21+0.48) and characteristic magnitude is {M}1450* =-{25.8}-1.9+1.1 (-{25.7}-1.8+1.0) in the case of two (one) quasar detection. Our result suggests that, if the QLF is integrated down to {M}1450=-18, quasars produce ˜1%-12% of the ionizing photons required to fully ionize the universe at z ˜ 6 with a 2σ confidence level, assuming that the escape fraction is {f}{esc}=1 and the intergalactic medium clumpy factor is C = 3. Even when the systematic uncertainties are taken into account, our result supports the scenario that quasars are the minor contributors of the reionization.

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.

The Black Hole Masses and Eddington Ratios of Type 2 Quasars

NASA Astrophysics Data System (ADS)

Kong, Minzhi; Ho, Luis C.

2018-06-01

Type 2 quasars are an important constituent of active galaxies, possibly representing the evolutionary precursors of traditionally studied type 1 quasars. We characterize the black hole (BH) mass (M BH) and Eddington ratio (L bol/L Edd) for 669 type 2 quasars selected from the Sloan Digital Sky Survey, using BH masses estimated from the M BH–σ * relation and bolometric corrections scaled from the extinction-corrected [O III] λ5007 luminosity. When stellar velocity dispersions cannot be measured directly from the spectra, we estimate them from the core velocity dispersions of the narrow emission lines [O II] λλ3726, 3729, [S II] λλ6716, 6731, and [O III] λ5007, which are shown to trace the gravitational potential of the stars. Energy input from the active nucleus still imparts significant perturbations to the gas kinematics, especially to high-velocity, blueshifted wings. Nonvirial motions in the gas become most noticeable in systems with high Eddington ratios. The BH masses of our sample of type 2 quasars range from M BH ≈ 106.5 to 1010.4 M ⊙ (median 108.2 M ⊙). Type 2 quasars have characteristically large Eddington ratios (L bol/L Edd ≈ 10‑2.9–101.8 median 10‑0.7), slightly higher than in type 1 quasars of similar redshift; the luminosities of ∼20% of the sample formally exceed the Eddington limit. The high Eddington ratios may be consistent with the notion that obscured quasars evolve into unobscured quasars.

SDSS J102111.02+491330.4: A Newly Discovered Gravitationally Lensed Quasar

NASA Astrophysics Data System (ADS)

Pindor, Bart; Eisenstein, Daniel J.; Gregg, Michael D.; Becker, Robert H.; Inada, Naohisa; Oguri, Masamune; Hall, Patrick B.; Johnston, David E.; Richards, Gordon T.; Schneider, Donald P.; Turner, Edwin L.; Brasi, Guido; Hinz, Philip M.; Kenworthy, Matthew A.; Miller, Doug; Barentine, J. C.; Brewington, Howard J.; Brinkmann, J.; Harvanek, Michael; Kleinman, S. J.; Krzesinski, Jurek; Long, Dan; Neilsen, Eric H., Jr.; Newman, Peter R.; Nitta, Atsuko; Snedden, Stephanie A.; York, Donald G.

2006-01-01

We report follow-up observations of two gravitational lens candidates identified in the Sloan Digital Sky Survey (SDSS) data set. We have confirmed that SDSS J102111.02+491330.4 is a previously unknown gravitationally lensed quasar. This lens system exhibits two images of a z=1.72 quasar, with an image separation of 1.14"+/-0.04". Optical and near-IR imaging of the system reveals the presence of the lensing galaxy between the two quasar images. Observations of SDSS J112012.12+671116.0 indicate that it is more likely a binary quasar than a gravitational lens. This system has two quasars at a redshift of z=1.49, with an angular separation of 1.49"+/-0.02". However, the two quasars have markedly different spectral energy distributions, and no lens galaxy is apparent in optical and near-IR images of this system. We also present a list of 31 SDSS lens candidates that follow-up observations have confirmed are not gravitational lenses. Observations reported here were obtained at the MMT Observatory, a joint facility of the University of Arizona and the Smithsonian Institution.

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.

Clustering of quasars in a wide luminosity range at redshift 4 with Subaru Hyper Suprime-Cam Wide-field imaging

NASA Astrophysics Data System (ADS)

He, Wanqiu; Akiyama, Masayuki; Bosch, James; Enoki, Motohiro; Harikane, Yuichi; Ikeda, Hiroyuki; Kashikawa, Nobunari; Kawaguchi, Toshihiro; Komiyama, Yutaka; Lee, Chien-Hsiu; Matsuoka, Yoshiki; Miyazaki, Satoshi; Nagao, Tohru; Nagashima, Masahiro; Niida, Mana; Nishizawa, Atsushi J.; Oguri, Masamune; Onoue, Masafusa; Oogi, Taira; Ouchi, Masami; Schulze, Andreas; Shirasaki, Yuji; Silverman, John D.; Tanaka, Manobu M.; Tanaka, Masayuki; Toba, Yoshiki; Uchiyama, Hisakazu; Yamashita, Takuji

2018-01-01

We examine the clustering of quasars over a wide luminosity range, by utilizing 901 quasars at \\overline{z}_phot˜ 3.8 with -24.73 < M1450 < -22.23 photometrically selected from the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP) S16A Wide2 date release and 342 more luminous quasars at 3.4 < zspec < 4.6 with -28.0 < M1450 < -23.95 from the Sloan Digital Sky Survey that fall in the HSC survey fields. We measure the bias factors of two quasar samples by evaluating the cross-correlation functions (CCFs) between the quasar samples and 25790 bright z ˜ 4 Lyman break galaxies in M1450 < -21.25 photometrically selected from the HSC dataset. Over an angular scale of 10.0" to 1000.0", the bias factors are 5.93+1.34-1.43 and 2.73+2.44-2.55 for the low- and high-luminosity quasars, respectively, indicating no significant luminosity dependence of quasar clustering at z ˜ 4. It is noted that the bias factor of the luminous quasars estimated by the CCF is smaller than that estimated by the auto-correlation function over a similar redshift range, especially on scales below 40.0". Moreover, the bias factor of the less-luminous quasars implies the minimal mass of their host dark matter halos is 0.3-2 × 1012 h-1 M⊙, corresponding to a quasar duty cycle of 0.001-0.06.

Composite Spectra of Broad Absorption Line Quasars in SDSS-III BOSS

NASA Astrophysics Data System (ADS)

Herbst, Hanna; Hamann, Fred; Paris, Isabelle; Capellupo, Daniel M.

2017-01-01

We present preliminary results from a study of broad absorption line (BAL) quasars in the SDSS-III BOSS survey. We’re particularly interested in BALs because they arise from quasar outflows, which may be a source of feedback to the host galaxy. We analyze median composite spectra for BOSS QSOs in the redshift range 2.1 to 3.4 sorted by the strength of the BAL absorption troughs, parameterized by the Balnicity Index (BI), to study trends in the emission and absorption properties of BAL quasars. The wavelength coverage and high number of quasars observed in the BOSS survey allow us to examine BALs in the Lyman forest. Our main preliminary results when sorting the quasars by BI are 1) doublet absorption lines such as P V 1128A show a 1:1 ratio across all BI, indicating large column densities at all BI. This suggests that weaker BAL troughs result from smaller covering fractions rather than lower column densities. 2) The He II emission line, which is a measure of the far-UV/near-UV hardness of the ionizing continuum, is weaker in the larger BI composite spectra, indicating a far-UV spectral softening correlated with BI. This is consistent with the radiatively-driven BAL outflows being helped by intrinsically weaker ionizing continuum shapes (e.g., Baskin, Laor, and Hamann 2013). We also find a trend for slightly redder continuum slopes in the larger BI composite spectra, suggesting that the slope differences in the near-UV are also intrinsic.

A Glimpse at Quasar Host Galaxy Far-UV Emission, Using Damped Lyα's as Natural Coronagraphs

DOE PAGES

Cai, Zheng; Fan, Xiaohui; Noterdaeme, Pasquier; ...

2014-09-16

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. Here, we have stacked the spectra of ~2000 DLA systems (N HI > 10 20.6cm –2) with a median absorption redshiftmore » $$\\langle$$z$$\\rangle$$ = 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 $$\\langle$$z$$\\rangle$$ = 3.1) that is not blocked by the intervening DLA. Finally, assuming that all of the detected flux originates from quasar hosts, for the highest quasar luminosity bin ($$\\langle$$L$$\\rangle$$ = 2.5 × 10 13 L ⊙), the host galaxy has an FUV intensity of 1.5 ± 0.2 × 10 40 erg s –1 Å –1; this corresponds to an unobscured UV star formation rate of 9 M ⊙ yr –1.« less

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ikeda, H.; Matsuoka, K.; Kajisawa, M.

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. Inmore » 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.« less

Microlensing of Relativistic Knots in the Quasar HE 1104-1805 AB

NASA Astrophysics Data System (ADS)

Schechter, Paul L.; Udalski, A.; Szymański, M.; Kubiak, M.; Pietrzyński, G.; Soszyński, I.; Woźniak, P.; Żebruń, K.; Szewczyk, O.; Wyrzykowski, Ł.

2003-02-01

We present 3 years of photometry of the ``Double Hamburger'' lensed quasar, HE 1104-1805 AB, obtained on 102 separate nights using the Optical Gravitational Lensing Experiment 1.3 m telescope. Both the A and B images show variations, but with substantial differences in the light curves at all time delays. At the 310 day delay reported by Wisotzki and collaborators, the difference light curve has an rms amplitude of 0.060 mag. The structure functions for the A and B images are quite different, with image A more than twice as variable as image B (a factor of 4 in structure function) on timescales of less than a month. Adopting microlensing as a working hypothesis for the uncorrelated variability, the short timescale argues for the relativistic motion of one or more components of the source. We argue that the small amplitude of the fluctuations is due to the finite size of the source with respect to the microlenses.

Solving the puzzle of discrepant quasar variability on monthly time-scales implied by SDSS and CRTS data sets

NASA Astrophysics Data System (ADS)

Suberlak, Krzysztof; Ivezić, Željko; MacLeod, Chelsea L.; Graham, Matthew; Sesar, Branimir

2017-12-01

We present an improved photometric error analysis for the 7 100 CRTS (Catalina Real-Time Transient Survey) optical light curves for quasars from the SDSS (Sloan Digital Sky Survey) Stripe 82 catalogue. The SDSS imaging survey has provided a time-resolved photometric data set, which greatly improved our understanding of the quasar optical continuum variability: Data for monthly and longer time-scales are consistent with a damped random walk (DRW). Recently, newer data obtained by CRTS provided puzzling evidence for enhanced variability, compared to SDSS results, on monthly time-scales. Quantitatively, SDSS results predict about 0.06 mag root-mean-square (rms) variability for monthly time-scales, while CRTS data show about a factor of 2 larger rms, for spectroscopically confirmed SDSS quasars. Our analysis has successfully resolved this discrepancy as due to slightly underestimated photometric uncertainties from the CRTS image processing pipelines. As a result, the correction for observational noise is too small and the implied quasar variability is too large. The CRTS photometric error correction factors, derived from detailed analysis of non-variable SDSS standard stars that were re-observed by CRTS, are about 20-30 per cent, and result in reconciling quasar variability behaviour implied by the CRTS data with earlier SDSS results. An additional analysis based on independent light curve data for the same objects obtained by the Palomar Transient Factory provides further support for this conclusion. In summary, the quasar variability constraints on weekly and monthly time-scales from SDSS, CRTS and PTF surveys are mutually compatible, as well as consistent with DRW model.

Sunyaev–Zel’Dovich Signal from Quasar Hosts: Implications for Detection of Quasar Feedback

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chowdhury, Dhruba Dutta; Chatterjee, Suchetana, E-mail: dhruba.duttachowdhury@yale.edu

2017-04-10

Several analytic and numerical studies have indicated that the interstellar medium of a quasar host galaxy heated by feedback can contribute to a substantial secondary signal in the cosmic microwave background (CMB) through the thermal Sunyaev–Zel’dovich (SZ) effect. Recently, many groups have tried to detect this signal by cross-correlating CMB maps with quasar catalogs. Using a self-similar model for the gas in the intra-cluster medium and a realistic halo occupation distribution (HOD) prescription for quasars, we estimate the level of SZ signal from gravitational heating of quasar hosts. The bias in the host halo signal estimation due to an unconstrainedmore » high mass HOD tail and yet unknown redshift dependence of the quasar HOD restricts us from drawing any robust conclusions at low redshift ( z < 1.5) from our analysis. However, at higher redshifts ( z > 2.5), we find an excess signal in recent observations than what is predicted from our model. The excess signal could be potentially generated from additional heating due to quasar feedback.« less

Deep learning approach for classifying, detecting and predicting photometric redshifts of quasars in the Sloan Digital Sky Survey stripe 82

NASA Astrophysics Data System (ADS)

Pasquet-Itam, J.; Pasquet, J.

2018-04-01

We have applied a convolutional neural network (CNN) to classify and detect quasars in the Sloan Digital Sky Survey Stripe 82 and also to predict the photometric redshifts of quasars. The network takes the variability of objects into account by converting light curves into images. The width of the images, noted w, corresponds to the five magnitudes ugriz and the height of the images, noted h, represents the date of the observation. The CNN provides good results since its precision is 0.988 for a recall of 0.90, compared to a precision of 0.985 for the same recall with a random forest classifier. Moreover 175 new quasar candidates are found with the CNN considering a fixed recall of 0.97. The combination of probabilities given by the CNN and the random forest makes good performance even better with a precision of 0.99 for a recall of 0.90. For the redshift predictions, the CNN presents excellent results which are higher than those obtained with a feature extraction step and different classifiers (a K-nearest-neighbors, a support vector machine, a random forest and a Gaussian process classifier). Indeed, the accuracy of the CNN within |Δz| < 0.1 can reach 78.09%, within |Δz| < 0.2 reaches 86.15%, within |Δz| < 0.3 reaches 91.2% and the value of root mean square (rms) is 0.359. The performance of the KNN decreases for the three |Δz| regions, since within the accuracy of |Δz| < 0.1, |Δz| < 0.2, and |Δz| < 0.3 is 73.72%, 82.46%, and 90.09% respectively, and the value of rms amounts to 0.395. So the CNN successfully reduces the dispersion and the catastrophic redshifts of quasars. This new method is very promising for the future of big databases such as the Large Synoptic Survey Telescope. A table of the candidates is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/611/A97

X-raying the most luminous quasars at cosmic noon

NASA Astrophysics Data System (ADS)

Piconcelli, E.; Martocchia, S.; Zappacosta, L.

2017-10-01

The WISE/SDSS hyper-luminous (log L_Bol > 47) quasar (WISSH) survey is performing a multi-band systematic exploration of the most luminous AGN shining at the golden epoch of AGN activity (i.e. z ˜ 2-4). This gives the opportunity of overcoming the luminosity bias in the exploration of the accretion phenomenon and the impact of AGN radiative output on the host. In this talk, I present the results of our study of the X-ray spectra of 40 WISSH quasars. I report on the correlations between the X-ray and Optical, UV and MIR properties, and the behavior of the X-ray bolometric correction at the brightest end of the luminosity function. I discuss the relative X-ray weakness of these very powerful quasars compared to less luminous AGN. This X-ray weakness can be a key ingredient for accelerating powerful ionized outflows (ubiquitously revealed in the UV/optical spectra of WISSH quasars) and, furthermore, radiation-driven winds can be effective in destroying the X-ray corona and quenching the X-ray emission. The potential offered by Athena in studying this extreme class of AGN is also discussed.

Toward a Prescription for Feedback from Quasar Outflows

NASA Astrophysics Data System (ADS)

Ganguly, Rajib; Bourjaily, M.; Munsell, J.; Brotherton, M. S.; Bhattacharjee, A.; Runnoe, J.; Charlton, J. C.; Eracleous, M.

2011-01-01

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, distance, 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 14000 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) estimates of the quasar black hole mass. To this, we are adding photometry from GALEX, 2MASS, and ROSAT in an effort to characterize more fully the quasar SEDs. ROSAT photometry provides estimates of the level of soft X-ray absorption, which helps regulate the velocity of outflows. GALEX photometry samples the extreme ultraviolet range where several high ionization species, that may be present in the outflows, absorb light. 2MASS photometry samples the rest-frame optical, where the effects of absorption and dust reddening are minimal, yield better estimates of the bolometric luminosity (hence, Eddington ratio). In this poster, we will present preliminary measurements of the amount of absorption in the soft X-ray and extreme ultraviolet bands as a function of both outflow properties and quasar physical properties. This material is based upon work supported by the National Aeronautics and Space Administration under Grant No. 09-ADP09-0016 issued through the Astrophysics Data Analysis Program.

Understanding extreme quasar optical variability with CRTS - I. Major AGN flares

NASA Astrophysics Data System (ADS)

Graham, Matthew J.; Djorgovski, S. G.; Drake, Andrew J.; Stern, Daniel; Mahabal, Ashish A.; Glikman, Eilat; Larson, Steve; Christensen, Eric

2017-10-01

There is a large degree of variety in the optical variability of quasars and it is unclear whether this is all attributable to a single (set of) physical mechanism(s). We present the results of a systematic search for major flares in active galactic nucleus (AGN) in the Catalina Real-time Transient Survey as part of a broader study into extreme quasar variability. Such flares are defined in a quantitative manner as being atop of the normal, stochastic variability of quasars. We have identified 51 events from over 900 000 known quasars and high-probability quasar candidates, typically lasting 900 d and with a median peak amplitude of Δm = 1.25 mag. Characterizing the flare profile with a Weibull distribution, we find that nine of the sources are well described by a single-point single-lens model. This supports the proposal by Lawrence et al. that microlensing is a plausible physical mechanism for extreme variability. However, we attribute the majority of our events to explosive stellar-related activity in the accretion disc: superluminous supernovae, tidal disruption events and mergers of stellar mass black holes.

Mining the Infrared Sky for High-Redshift Quasars

NASA Astrophysics Data System (ADS)

Richards, Gordon

The Spitzer and WISE satellites have opened up new avenues for the study of active galactic nuclei (AGN) by peering through the dust shrouding half (or more) of AGNs. However, despite being more sensitive to shrouded AGNs, current selection methods being used in the mid-IR are still largely blind to the highest redshift quasars-both those that are shrouded and those that are not (and should therefore be easy to find). We describe projects to identify both unobscured (at z>3) and obscured quasars (at z>2) that have heretofore been missed in significant numbers. Finding the high-z obscured quasars in large numbers is crucial for fulfilling the legacy of NASA missions in the IR and X-ray. With these quasars we will be able to perform clustering analyses that break the degeneracy of models describing how black holes can ``feed back" energy to the large-scale host galaxy, significantly influencing its evolution. We will further trace the luminosity function of galaxies undergoing active accretion from low-luminosity AGNs to luminous quasars—probing the growth of the supermassive black holes that we see today in the local universe. Our new insights come about from leveraging new Spitzer data, primarily from the PI's SpitzerIRAC Equatorial Survey (SpIES). The Spitzer data are 2.5 magnitudes deeper than the "AllWISE" survey in a 125 square degree, multiwavelength-rich, equatorial region known as SDSS "Stripe 82". These data are crucial for extending mid-IR investigations to higher redshifts, both for unobscured and obscured sources. The PI's team are among the world's experts in using the proposed machine learning techniques to find both unobscured (type-1) and obscured (type- 2) quasars and in using quasar clustering and luminosity functions to do cutting-edge science. The luminosity function and clustering algorithms are already in place, allowing for timely completion of this project once the multi-wavelength NASA data have been incorporated. This project is directly

EVLA observations of radio-loud quasars selected to study radio orientation

NASA Astrophysics Data System (ADS)

Maithil, Jaya; Brotherton, Michael S.; Runnoe, Jessie; Wardle, John F. C.; DiPompeo, Michael; De Breuck, Carlos; Wills, Beverley J.

2018-06-01

We present preliminary work to develop an unbiased sample of radio-loud quasars to test orientation indicators. We have obtained radio data of 147 radio-loud quasars using EVLA at 10 GHz and with the A-array. With this high-resolution data we have measured the uncontaminated core flux density to determine orientation indicators based on radio core dominance. The radio cores of quasars have a flat spectrum over a broad range of frequencies, so we expect that the core flux density at the FIRST and the observed frequencies should be the same in the absence of variability. Jackson & Brown (2012) pointed out that the survey measurements of core flux density, like FIRST, often doesn't have the spatial resolution to distinguish cores from extended emission. Our measurements show that at FIRST spatial resolution, core flux measurements are indeed systematically high. Our results establish that orientation studies need high-resolution radio data as compared to survey data, and that the optical emission is a better normalization than the extended radio emission for a core dominance parameter to track orientation.

Constraints on the temperature inhomogeneity in quasar accretion discs from the ultraviolet-optical spectral variability

NASA Astrophysics Data System (ADS)

Kokubo, Mitsuru

2015-05-01

The physical mechanisms of the quasar ultraviolet (UV)-optical variability are not well understood despite the long history of observations. Recently, Dexter & Agol presented a model of quasar UV-optical variability, which assumes large local temperature fluctuations in the quasar accretion discs. This inhomogeneous accretion disc model is claimed to describe not only the single-band variability amplitude, but also microlensing size constraints and the quasar composite spectral shape. In this work, we examine the validity of the inhomogeneous accretion disc model in the light of quasar UV-optical spectral variability by using five-band multi-epoch light curves for nearly 9 000 quasars in the Sloan Digital Sky Survey (SDSS) Stripe 82 region. By comparing the values of the intrinsic scatter σint of the two-band magnitude-magnitude plots for the SDSS quasar light curves and for the simulated light curves, we show that Dexter & Agol's inhomogeneous accretion disc model cannot explain the tight inter-band correlation often observed in the SDSS quasar light curves. This result leads us to conclude that the local temperature fluctuations in the accretion discs are not the main driver of the several years' UV-optical variability of quasars, and consequently, that the assumption that the quasar accretion discs have large localized temperature fluctuations is not preferred from the viewpoint of the UV-optical spectral variability.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cai, Zheng; Fan, Xiaohui; Wang, Ran

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 fluxmore » 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}.« less

Characterizing Quasar Outflows II: The Incidence of the Highest Velocity Outflows

NASA Astrophysics Data System (ADS)

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

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 an accompanying poster, we subjectively divide these quasars into four categories (broad absorption-line quasars, associated absorption-line quasars, reddened quasars, and unabsorbed/unreddened quasars). This subjective scheme is limited with regard to classifying narrow absorption-line systems (NALs). With single epoch, low dispersion SDSS spectra, we cannot distinguish between cosmologically intervening NALs, and intrinsic NALs that appear at large velocity offsets. In this poster, we tackle this uncertainty statistically by considering the incidence of both CIV and MgII NALs as a function of velocity, and how this distribution changes with quasar properties. We expect that absorption by intervening structures should not vary with quasar property. Other accompanying posters add photometry from rest-frame X-ray through the infrared (WISE) to complete the SED, which we utilize in these efforts. This material is based upon work supported by the National Aeronautics and Space Administration under

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.

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.

The Halo Occupation Distribution of obscured quasars: revisiting the unification model

NASA Astrophysics Data System (ADS)

Mitra, Kaustav; Chatterjee, Suchetana; DiPompeo, Michael A.; Myers, Adam D.; Zheng, Zheng

2018-06-01

We model the projected angular two-point correlation function (2PCF) of obscured and unobscured quasars selected using the Wide-field Infrared Survey Explorer (WISE), at a median redshift of z ˜ 1 using a five parameter Halo Occupation Distribution (HOD) parametrization, derived from a cosmological hydrodynamic simulation by Chatterjee et al. The HOD parametrization was previously used to model the 2PCF of optically selected quasars and X-ray bright active galactic nuclei (AGNs) at z ˜ 1. The current work shows that a single HOD parametrization can be used to model the population of different kinds of AGN in dark matter haloes suggesting the universality of the relationship between AGN and their host dark matter haloes. Our results show that the median halo mass of central quasar hosts increases from optically selected (4.1^{+0.3}_{-0.4} × 10^{12} h^{-1} M_{⊙}) and infra-red (IR) bright unobscured populations (6.3^{+6.2}_{-2.3} × 10^{12} h^{-1} M_{⊙}) to obscured quasars (10.0^{+2.6}_{-3.7} × 10^{12} h^{-1} M_{⊙}), signifying an increase in the degree of clustering. The projected satellite fractions also increase from optically bright to obscured quasars and tend to disfavour a simple `orientation only' theory of active galactic nuclei unification. Our results also show that future measurements of the small-scale clustering of obscured quasars can constrain current theories of galaxy evolution where quasars evolve from an IR-bright obscured phase to the optically bright unobscured phase.

X-ray properties of quasars

NASA Technical Reports Server (NTRS)

Ku, W. H.-M.; Helfand, D. J.; Lucy, L. B.

1980-01-01

The X-ray properties of 111 catalogued quasars have been examined with the imaging proportional counter on board the Einstein Observatory. Thirty-five of the objects, of redshift between 0.064 and 3.53, were detected as X-ray sources. The 0.5-4.5-keV X-ray properties of these quasars are correlated with their optical and radio continuum properties and with their redshifts and variability characteristics. The X-ray luminosity of quasars tends to be highest for those objects which are bright in the optical and radio regimes and which exhibit optically violent variability. These observations suggest that quasars should be divided into two classes on the basis of radio luminosities, spectra, evolution and underlying morphology and that quasars can make up a significant portion of the diffuse soft X-ray background only if the slope of the optical quasar log N-log S relation is steeper than 2 to m sub b of about 21.5.

A study on rate of infestation to Sarcocystis cysts in supplied raw hamburgers.

PubMed

Nematollahia, Ahmad; Khoshkerdar, Afsaneh; Helan, Javad Ashrafi; Shahbazi, Parisa; Hassanzadeh, Parviz

2015-06-01

This study was carried on for determination of presence of Sarcocystis cysts in raw hamburgers in Tabriz North West of Iran. Ninety-six samples of industrial (70 % meat content) and traditional (30 % meat content) hamburgers (80 samples industrial and 16 samples traditional) were obtained from retail fast food stores. The samples were examined by gross examination, and microscopic examination methods consist impression smear and peptic digestion. Macroscopic cysts did not observed in any of the samples in gross examination. Microscopic study showed that from 96 samples 54 (56.25 %) samples were infected by at least one bradyzoites of Sarcocystis. From 54 infected samples, 45 industrial hamburgers and nine traditional hamburgers samples were infected. Statistical analysis showed that there was not significant differences between industrial and traditional hamburgers in infection to Sarcocystis. Infestation of hamburgers to Sarcocystis in summer was higher than other seasons but this difference was not significant. In Iran, beef meat is used for preparation of 70 % of hamburger and infestation of cattle to sarcocystosis was reported in many investigations in Iran. With regard to the high prevalence of Sarcocystis infection in meat products such as hamburgers in this study, it is strongly recommended to avoid eating raw or under-cooked hamburgers or keep them at freezing temperature for at least 3-5 days.

A Search for Nontoroidal Topological Lensing in the Sloan Digital Sky Survey Quasar Catalog

NASA Astrophysics Data System (ADS)

Fujii, Hirokazu; Yoshii, Yuzuru

2013-08-01

Flat space models with multiply connected topology, which have compact dimensions, are tested against the distribution of high-redshift (z >= 4) quasars of the Sloan Digital Sky Survey (SDSS). When the compact dimensions are smaller in size than the observed universe, topological lensing occurs, in which multiple images of single objects (ghost images) are observed. We improve on the recently introduced method to identify ghost images by means of four-point statistics. Our method is valid for any of the 17 multiply connected flat models, including nontoroidal ones that are compacted by screw motions or glide reflection. Applying the method to the data revealed one possible case of topological lensing caused by sixth-turn screw motion, however, it is consistent with the simply connected model by this test alone. Moreover, simulations suggest that we cannot exclude the other space models despite the absence of their signatures. This uncertainty mainly originates from the patchy coverage of SDSS in the south Galactic cap, and this situation will be improved by future wide-field spectroscopic surveys.

Ten More New Sightlines for the Study of Intergalactic Helium, and Hundreds of Far-Ultraviolet-Bright Quasars, from the Sloan Digital Sky Survey, Galaxy Evolution Explorer, and Hubble Space Telescope

NASA Astrophysics Data System (ADS)

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

2009-11-01

Absorption along quasar sightlines remains among the most sensitive direct measures of He II reionization in much of the intergalactic medium (IGM). Until recently, fewer than a half-dozen unobscured quasar sightlines suitable for the He II 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 He II 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 He II Lyα, substantially expanding the number of known clean He II 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 He II quasars, quintupling the sample. These provide substantial progress toward a sample of He II 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. Based on observations with the NASA/ESA Hubble Space Telescope obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc

The Atacama Cosmology Telescope: Cross-Correlation of Cosmic Microwave Background Lensing and Quasars

NASA Technical Reports Server (NTRS)

Sherwin, Blake D; Das, Sudeep; Haijian, Amir; Addison, Graeme; Bond, Richard; Crichton, Devin; Devlin, Mark J.; Dunkley, Joanna; Gralla, Megan B.; Halpern, Mark;

Luminous quasars do not live in the most overdense regions of galaxies at z ˜ 4

NASA Astrophysics Data System (ADS)

Uchiyama, Hisakazu; Toshikawa, Jun; Kashikawa, Nobunari; Overzier, Roderik; Chiang, Yi-Kuan; Marinello, Murilo; Tanaka, Masayuki; Niino, Yuu; Ishikawa, Shogo; Onoue, Masafusa; Ichikawa, Kohei; Akiyama, Masayuki; Coupon, Jean; Harikane, Yuichi; Imanishi, Masatoshi; Kodama, Tadayuki; Komiyama, Yutaka; Lee, Chien-Hsiu; Lin, Yen-Ting; Miyazaki, Satoshi; Nagao, Tohru; Nishizawa, Atsushi J.; Ono, Yoshiaki; Ouchi, Masami; Wang, Shiang-Yu

2018-01-01

We present the cross-correlation between 151 luminous quasars (MUV < -26) and 179 protocluster candidates at z ˜ 3.8, extracted from the Wide imaging survey (˜121 deg2) performed as part of the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP). We find that only two out of 151 quasars reside in regions that are more overdense compared to the average field at >4 σ. The distributions of the distances between quasars and the nearest protoclusters and the significance of the overdensity at the positions of quasars are statistically identical to those found for g-dropout galaxies, suggesting that quasars tend to reside in almost the same environment as star-forming galaxies at this redshift. Using stacking analysis, we find that the average density of g-dropout galaxies around quasars is slightly higher than that around g-dropout galaxies on 1.0-2.5 pMpc scales, while at <0.5 pMpc that around quasars tends to be lower. We also find that quasars with higher UV luminosity or with more massive black holes tend to avoid the most overdense regions, and that the quasar near-zone sizes are anti-correlated with overdensity. These findings are consistent with a scenario in which luminous quasars at z ˜ 4 reside in structures that are less massive than those expected for the progenitors of today's rich clusters of galaxies, and possibly that luminous quasars may be suppressing star formation in their close vicinity.

VizieR Online Data Catalog: Quasars narrow absorption lines from SDSS (Chen+, 2015)

NASA Astrophysics Data System (ADS)

Chen, Z.-F.; Gu, Q.-S.; Chen, Y.-M.; Cao, Y.

2017-11-01

The Baryon Oscillation Spectroscopic Survey (BOSS: Eisenstein et al. 2011AJ....142...72E; Paris et al. 2012, Cat. VII/269) is the main dark-time legacy survey of the third stage of the SDSS, which used the same 2.5-m telescope (Gunn et al. 2006AJ....131.2332G; Ross et al. 2012, J/ApJS/199/3) as the first and second stages of the SDSS (hereafter SDSS-I/II). SDSS-I/II spectra have a wavelength coverage from 3800-9200Å with a spectral resolution of 1800-2200 (e.g. York et al. 2000AJ....120.1579Y). BOSS spectra span a range from 3600-10500Å at a resolution of 1300-2500 (Paris et al. 2012, Cat. VII/269). During the first two years, BOSS detected 87822 quasars over an area of 3275 deg2, including 7932 quasars that were observed by SDSS-I/II as well. Quasars observed by both SDSS-I/II and BOSS provide a remarkable chance to study the variabilities of absorption lines in a large population. Throughout this work, we take the quasar emission redshifts provided by Hewett & Wild (2010, J/MNRAS/405/2302, http://das.sdss.org/va/HewettWilddr7qso_newz/) directly. (2 data files).

A luminous quasar at a redshift of z = 7.085.

PubMed

Mortlock, Daniel J; Warren, Stephen J; Venemans, Bram P; Patel, Mitesh; Hewett, Paul C; McMahon, Richard G; Simpson, Chris; Theuns, Tom; Gonzáles-Solares, Eduardo A; Adamson, Andy; Dye, Simon; Hambly, Nigel C; Hirst, Paul; Irwin, Mike J; Kuiper, Ernst; Lawrence, Andy; Röttgering, Huub J A

2011-06-29

The intergalactic medium was not completely reionized until approximately a billion years after the Big Bang, as revealed by observations of quasars with redshifts of less than 6.5. It has been difficult to probe to higher redshifts, however, because quasars have historically been identified in optical surveys, which are insensitive to sources at redshifts exceeding 6.5. Here we report observations of a quasar (ULAS J112001.48+064124.3) at a redshift of 7.085, which is 0.77 billion years after the Big Bang. ULAS J1120+0641 has a luminosity of 6.3 × 10(13)L(⊙) and hosts a black hole with a mass of 2 × 10(9)M(⊙) (where L(⊙) and M(⊙) are the luminosity and mass of the Sun). The measured radius of the ionized near zone around ULAS J1120+0641 is 1.9 megaparsecs, a factor of three smaller than is typical for quasars at redshifts between 6.0 and 6.4. The near-zone transmission profile is consistent with a Lyα damping wing, suggesting that the neutral fraction of the intergalactic medium in front of ULAS J1120+0641 exceeded 0.1.

Erratum: "Space Density of Optically Selected Type 2 Quasars" (2008, AJ, 136, 2373)

NASA Astrophysics Data System (ADS)

Reyes, Reinabelle; Zakamska, Nadia L.; Strauss, Michael A.; Green, Joshua; Krolik, Julian H.; Shen, Yue; Richards, Gordon T.; Anderson, Scott F.; Schneider, Donald P.

2010-03-01

Figure 12 of the paper "Space Density of Optically Selected Type 2 Quasars" compares the obscured quasar fractions derived in our work with those of other studies. Unfortunately, some of the points from these other studies were shown incorrectly. Specifically, the results from X-ray data—Hasinger (2004; open circles) and Ueda et al. (2003; open squares)—which we had taken from Figure 16 of Hopkins et al. (2006), were affected by a luminosity conversion error, in the sense that the displayed luminosities for these data were too high by ~1 dex. With this erratum, we correct this problem and update the figure. The new version (Figure 12) shows more recent results from Hasinger (2008), in lieu of the Hasinger (2004) data points. These are based on data in the redshift range z = 0.2-3.2 (open circles) in that work. The best linear fit to these data (black dashed line) is consistent with that derived for the redshift slice z = 0.4-0.8, which overlaps with the highest redshift bin in our study, and is higher than that derived for redshifts smaller than 0.4 (corresponding to a shift of ~0.7 dex in luminosity). Figure 12 also shows estimates of the obscured quasar fraction derived from the ratio of IR to bolometric luminosities of an AGN sample at redshift z ~ 1 (Treister et al. 2008; filled triangles). Because the obscured quasar fractions derived from our analysis (colored arrows) are strict lower limits, there was already a hint in the previous version of Figure 12 that at high quasar luminosities, we find higher obscured quasar fractions than X-ray surveys. The correction and updates of Figure 12 strengthen this conclusion. At face value, our derived obscured quasar fractions are consistent with those from IR data (Treister et al. 2008; filled triangles). However, we find that they are significantly higher than those derived from X-ray surveys at L_[O\\,\\mathsc {iii]}\\gtrsim 10^{9.5}\\;L_{\\odot }, especially those from the recent analysis by Hasinger (2008). This

Rapidly star-forming galaxies adjacent to quasars at redshifts exceeding 6

PubMed Central

Decarli, R.; Walter, F.; Venemans, B.P.; Bañados, E.; Bertoldi, F.; Carilli, C.; Fan, X.; Farina, E.P.; Mazzucchelli, C.; Riechers, D.; Rix, H.-W.; Strauss, M.A.; Wang, R.; Yang, Y.

2017-01-01

The existence of massive (1011 Msun) elliptical galaxies by redshift z~4[1,2,3] (when the Universe was 1.5 billion years old) necessitates the presence of galaxies with star formation rates SFR>100 Msun/yr at z>6 (corresponding to an age of the Universe of less than 1 billion years). Surveys have discovered hundreds of galaxies at these early cosmic epochs, but their star formation rates are more than an order of magnitude lower[4]. The only known examples of very high rate galaxies at z>6 are, with only one exception[5], quasar host galaxies[6,7,8,9], i.e. galaxies that host an accreting supermassive (~109 Msun) black hole that likely affects the host properties. Here we report observations of the [CII] 158 μm line in 4 galaxies that are companions of quasars, with velocity offsets of less than 600 kilometres per second and linear offsets of less than 100 kiloparsecs. The discovery of these four galaxies was serendipitous; they are close to their companion quasars and appear bright in the far-infrared. Based upon the [CII] measurements, we estimate star formation rates of >100 Msun/yr. These sources are similar to the quasar hosts in [CII] brightness, line width and implied dynamical masses, but do not show evidence for accreting supermassive black holes. Similar systems have previously been found at lower redshift[10,11,12]. We find such close companions in 4 out of 25 z>6 quasars surveyed, a fraction that needs to be accounted for in simulations[13,14]. If representative of the bright end of the [CII] luminosity function, they can account for the population of massive elliptical galaxies at z~4 in terms of cosmic space density. PMID:28541326

Environments of strong/ultrastrong, ultraviolet Fe II emitting quasars

NASA Astrophysics Data System (ADS)

Clowes, Roger G.; Raghunathan, Srinivasan; Söchting, Ilona K.; Graham, Matthew J.; Campusano, Luis E.

2013-08-01

We have investigated the strength of ultraviolet (UV) Fe II emission from quasars within the environments of large quasar groups (LQGs) in comparison with quasars elsewhere, for 1.1 ≤ zLQG ≤ 1.7, using the DR7QSO catalogue of the Sloan Digital Sky Survey. We use the Weymann et al. W2400 equivalent width, defined between the rest-frame continuum windows 2240-2255 and 2665-2695 Å, as the measure of the UV Fe II emission. We find a significant shift of the W2400 distribution to higher values for quasars within LQGs, predominantly for those LQGs with 1.1 ≤ zLQG ≤ 1.5. There is a tentative indication that the shift to higher values increases with the quasar i magnitude. We find evidence that within LQGs the ultrastrong emitters with W2400 ≥ 45 Å (more precisely, ultrastrong plus with W2400 ≥ 44 Å) have preferred nearest-neighbour separations of ˜30-50 Mpc to the adjacent quasar of any W2400 strength. No such effect is seen for the ultrastrong emitters that are not in LQGs. The possibilities for increasing the strength of the Fe II emission appear to be iron abundance, Lyα fluorescence and microturbulence, and probably all of these operate. The dense environment of the LQGs may have led to an increased rate of star formation and an enhanced abundance of iron in the nuclei of galaxies. Similarly, the dense environment may have led to more active blackholes and increased Lyα fluorescence. The preferred nearest-neighbour separation for the stronger emitters would appear to suggest a dynamical component, such as microturbulence. In one particular LQG, the Huge-LQG (the largest structure known in the early Universe), six of the seven strongest emitters very obviously form three pairings within the total of 73 members.

Quasars Probing Quasars. VII. The Pinnacle of the Cool Circumgalactic Medium Surrounds Massive z ~ 2 Galaxies

NASA Astrophysics Data System (ADS)

Prochaska, J. Xavier; Lau, Marie Wingyee; Hennawi, Joseph F.

2014-12-01

We survey the incidence and absorption strength of the metal-line transitions C II 1334 and C IV 1548 from the circumgalactic medium (CGM) surrounding z ~ 2 quasars, which act as signposts for massive dark matter halos M halo ≈ 1012.5 M ⊙. On scales of the virial radius (r vir ≈ 160 kpc), we measure a high covering fraction fC = 0.73 ± 0.10 to strong C II 1334 absorption (rest equivalent width W 1334 >= 0.2 Å), implying a massive reservoir of cool (T ~ 104 K) metal enriched gas. We conservatively estimate a metal mass exceeding 108 M ⊙. We propose that these metals trace enrichment of the incipient intragroup/intracluster medium that these halos eventually inhabit. This cool CGM around quasars is the pinnacle among galaxies observed at all epochs, as regards covering the fraction and average equivalent width of H I Lyα and low-ion metal absorption. We argue that the properties of this cool CGM primarily reflect the halo mass, and that other factors such as feedback, star-formation rate, and accretion from the intergalactic medium are secondary. We further estimate that the CGM of massive, z ~ 2 galaxies accounts for the majority of strong Mg II absorption along random quasar sightlines. Last, we detect an excess of strong C IV 1548 absorption (W 1548 >= 0.3 Å) over random incidence to the 1 Mpc physical impact parameter and measure the quasar-C IV cross-correlation function: ξ C \\scriptsize{IV-Q}(r) = (r/r_0)-γ with r0 = 7.5+2.8-1.4 h-1 Mpc and γ = 1.7+0.1-0.2. Consistent with previous work on larger scales, we infer that this highly ionized C IV gas traces massive (1012 M ⊙) halos.

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.

Imprints of quasar duty cycle on the 21cm signal from the Epoch of Reionization

NASA Astrophysics Data System (ADS)

Bolgar, Florian; Eames, Evan; Hottier, Clément; Semelin, Benoit

2018-05-01

Quasars contribute to the 21-cm signal from the Epoch of Reionization (EoR) primarily through their ionizing UV and X-ray emission. However, their radio continuum and Lyman-band emission also regulates the 21-cm signal in their direct environment, potentially leaving the imprint of their duty cycle. We develop a model for the radio and UV luminosity functions of quasars from the EoR, and constrain it using recent observations. Our model is consistent with the recent discovery of the quasar J1342+0928 at redshift ˜7.5, and also predicts only a few quasars suitable for 21-cm forest observations (˜10 mJy) in the sky. We exhibit a new effect on the 21-cm signal observed against the CMB: a radio-loud quasar can leave the imprint of its duty cycle on the 21-cm tomography. We apply this effect in a cosmological simulation and conclude that the effect of typical radio-loud quasars is most likely negligible in an SKA field of view. For a ˜10mJy quasar the effect is stronger though hardly observable at SKA resolution. Then we study the contribution of the lyman band (Ly-α to Ly-β) emission of quasars to the Wouthuisen-Field coupling. The collective effect of quasars on the 21-cm power spectrum is larger than the thermal noise at low k, though featureless. However, a distinctive pattern around the brightest quasars in an SKA field of view may be observable in the tomography, encoding the duration of their duty cycle. This pattern has a high signal-to-noise ratio for the brightest quasar in a typical SKA shallow survey.

Mean and extreme radio properties of quasars and the origin of radio emission

DOE Office of Scientific and Technical Information (OSTI.GOV)

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 increasemore » 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.« less

A main sequence for quasars

NASA Astrophysics Data System (ADS)

Marziani, Paola; Dultzin, Deborah; Sulentic, Jack W.; Del Olmo, Ascensión; Negrete, C. A.; Martínez-Aldama, Mary L.; D'Onofrio, Mauro; Bon, Edi; Bon, Natasa; Stirpe, Giovanna M.

2018-03-01

The last 25 years saw a major step forward in the analysis of optical and UV spectroscopic data of large quasar samples. Multivariate statistical approaches have led to the definition of systematic trends in observational properties that are the basis of physical and dynamical modeling of quasar structure. We discuss the empirical correlates of the so-called “main sequence” associated with the quasar Eigenvector 1, its governing physical parameters and several implications on our view of the quasar structure, as well as some luminosity effects associated with the virialized component of the line emitting regions. We also briefly discuss quasars in a segment of the main sequence that includes the strongest FeII emitters. These sources show a small dispersion around a well-defined Eddington ratio value, a property which makes them potential Eddington standard candles.

Broad Absorption Line Quasars with Polar Outflows

NASA Astrophysics Data System (ADS)

Wang, Junxian

2005-10-01

It is widely accepted that the broad absorption line (BAL) outflow exists in most (if not all) quasars with a small covering factor. Various evidences show that equatorial outflows are responsible for the BALs in most BAL QSOs. By searching for radio variable quasars in SDSS, we built the first sample of 6 BAL QSOs with polar BAL outflows. It is very likely that polar outflows are associated with relativistic jets, and their origins should be different from the equatorial outflows in the majority of BAL QSOs. We propose an XMM snapshot survey to a) check whether strong X-ray absorption, one of the most prominent characteristics of most BAL QSOs, also exist in the polar outflows b) check whether face-on BAL QSOs are otherwise X-ray normal c) provide a baseline for future extensive X-ray studies.

Extreme Variability in a Broad Absorption Line Quasar

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stern, Daniel; Jun, Hyunsung D.; Graham, Matthew J.

CRTS J084133.15+200525.8 is an optically bright quasar at z = 2.345 that has shown extreme spectral variability over the past decade. Photometrically, the source had a visual magnitude of V ∼ 17.3 between 2002 and 2008. Then, over the following five years, the source slowly brightened by approximately one magnitude, to V ∼ 16.2. Only ∼1 in 10,000 quasars show such extreme variability, as quantified by the extreme parameters derived for this quasar assuming a damped random walk model. A combination of archival and newly acquired spectra reveal the source to be an iron low-ionization broad absorption line quasar withmore » extreme changes in its absorption spectrum. Some absorption features completely disappear over the 9 years of optical spectra, while other features remain essentially unchanged. We report the first definitive redshift for this source, based on the detection of broad H α in a Keck/MOSFIRE spectrum. Absorption systems separated by several 1000 km s{sup −1} in velocity show coordinated weakening in the depths of their troughs as the continuum flux increases. We interpret the broad absorption line variability to be due to changes in photoionization, rather than due to motion of material along our line of sight. This source highlights one sort of rare transition object that astronomy will now be finding through dedicated time-domain surveys.« less

The Hunt for Red Quasars: Luminous Obscured Black Hole Growth Unveiled in the Stripe 82 X-Ray Survey

NASA Astrophysics Data System (ADS)

LaMassa, Stephanie M.; Glikman, Eilat; Brusa, Marcella; Rigby, Jane R.; Tasnim Ananna, Tonima; Stern, Daniel; Lira, Paulina; Urry, C. Megan; Salvato, Mara; Alexandroff, Rachael; Allevato, Viola; Cardamone, Carolin; Civano, Francesca; Coppi, Paolo; Farrah, Duncan; Komossa, S.; Lanzuisi, Giorgio; Marchesi, Stefano; Richards, Gordon; Trakhtenbrot, Benny; Treister, Ezequiel

2017-10-01

We present results of a ground-based near-infrared campaign with Palomar TripleSpec, Keck NIRSPEC, and Gemini GNIRS to target two samples of reddened active galactic nucleus (AGN) candidates from the 31 deg2 Stripe 82 X-ray survey. One sample, which is ˜89% complete to K< 16 (Vega), consists of eight confirmed AGNs, four of which were identified with our follow-up program, and is selected to have red R - K colors (> 4, Vega). The fainter sample (K> 17, Vega) represents a pilot program to follow-up four sources from a parent sample of 34 that are not detected in the single-epoch SDSS catalog and have WISE quasar colors. All 12 sources are broad-line AGNs (at least one permitted emission line has an FWHM exceeding 1300 km s-1) and span a redshift range 0.59< z< 2.5. Half the (R - K)-selected AGNs have features in their spectra suggestive of outflows. When comparing these sources to a matched sample of blue Type 1 AGNs, we find that the reddened AGNs are more distant (z> 0.5), and a greater percentage have high X-ray luminosities ({L}{{X},{full}}> {10}44 erg s-1). Such outflows and high luminosities may be consistent with the paradigm that reddened broad-line AGNs represent a transitory phase in AGN evolution as described by the major merger model for black hole growth. Results from our pilot program demonstrate proof of concept that our selection technique is successful in discovering reddened quasars at z> 1 missed by optical surveys.

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.

The Identification of Z-dropouts in Pan-STARRS1: Three Quasars at 6.5< z< 6.7

NASA Astrophysics Data System (ADS)

Venemans, B. P.; Bañados, E.; Decarli, R.; Farina, E. P.; Walter, F.; Chambers, K. C.; Fan, X.; Rix, H.-W.; Schlafly, E.; McMahon, R. G.; Simcoe, R.; Stern, D.; Burgett, W. S.; Draper, P. W.; Flewelling, H.; Hodapp, K. W.; Kaiser, N.; Magnier, E. A.; Metcalfe, N.; Morgan, J. S.; Price, P. A.; Tonry, J. L.; Waters, C.; AlSayyad, Y.; Banerji, M.; Chen, S. S.; González-Solares, E. A.; Greiner, J.; Mazzucchelli, C.; McGreer, I.; Miller, D. R.; Reed, S.; Sullivan, P. W.

2015-03-01

Luminous distant quasars are unique probes of the high-redshift intergalactic medium (IGM) and of the growth of massive galaxies and black holes in the early universe. Absorption due to neutral hydrogen in the IGM makes quasars beyond a redshift of z≃ 6.5 very faint in the optical z band, thus locating quasars at higher redshifts requires large surveys that are sensitive above 1 micron. We report the discovery of three new z\\gt 6.5 quasars, corresponding to an age of the universe of \\lt 850 Myr, selected as z-band dropouts in the Pan-STARRS1 survey. This increases the number of known z\\gt 6.5 quasars from four to seven. The quasars have redshifts of z = 6.50, 6.52, and 6.66, and include the brightest z-dropout quasar reported to date, PSO J036.5078 + 03.0498 with {{M}1450}=-27.4. We obtained near-infrared spectroscopy for the quasars, and from the Mg ii line, we estimate that the central black holes have masses between 5 × 108 and 4 × 109 {{M}⊙ } and are accreting close to the Eddington limit ({{L}Bol}/{{L}Edd}=0.13-1.2). We investigate the ionized regions around the quasars and find near-zone radii of {{R}NZ}=1.5-5.2 proper Mpc, confirming the trend of decreasing near-zone sizes with increasing redshift found for quasars at 5.7\\lt z\\lt 6.4. By combining RNZ of the PS1 quasars with those of 5.7\\lt z\\lt 7.1 quasars in the literature, we derive a luminosity-corrected redshift evolution of {{R}NZ,corrected}=(7.2+/- 0.2)-(6.1+/- 0.7)× (z-6) Mpc. However, the large spread in RNZ in the new quasars implies a wide range in quasar ages and/or a large variation in the neutral hydrogen fraction along different lines of sight. Based in part on observations collected at the European Southern Observatory, Chile, programs 179.A-2010, 092.A-0150, 093.A-0863, and 093.A-0574, and at the Centro Astronómico Hispano Alemán (CAHA) at Calar Alto, operated jointly by the Max-Planck Institut für Astronomie and the Instituto de Astrofísica de Andalucía (CSIC). This paper

The stellar content of the Hamburg/ESO survey. IV. Selection of candidate metal-poor stars

NASA Astrophysics Data System (ADS)

Christlieb, N.; Schörck, T.; Frebel, A.; Beers, T. C.; Wisotzki, L.; Reimers, D.

2008-06-01

We present the quantitative methods used for selecting candidate metal-poor stars in the Hamburg/ESO objective-prism survey (HES). The selection is based on the strength of the Ca II K line, B-V colors (both measured directly from the digital HES spectra), as well as J-K colors from the 2 Micron All Sky Survey. The KP index for Ca II K can be measured from the HES spectra with an accuracy of 1.0 Å, and a calibration of the HES B-V colors, using CCD photometry, yields a 1-σ uncertainty of 0.07 mag for stars in the color range 0.3 < B-V < 1.4. These accuracies make it possible to reliably reject stars with [Fe/H] > -2.0 without sacrificing completeness at the lowest metallicities. A test of the selection using 1121 stars of the HK survey of Beers, Preston, and Shectman present on HES plates suggests that the completeness at [Fe/H] < -3.5 is close to 100% and that, at the same time, the contamination of the candidate sample with false positives is low: 50% of all stars with [Fe/H] > -2.5 and 97% of all stars with [Fe/H] > -2.0 are rejected. The selection was applied to 379 HES fields, covering a nominal area of 8853 deg2 of the southern high Galactic latitude sky. The candidate sample consists of 20 271 stars in the magnitude range 10 ≲ B ≲ 18. A comparison of the magnitude distribution with that of the HK survey shows that the magnitude limit of the HES sample is about 2 mag fainter. Taking the overlap of the sky areas covered by both surveys into account, it follows that the survey volume for metal-poor stars has been increased by the HES by about a factor of 10 with respect to the HK survey. We have already identified several very rare objects with the HES, including, e.g., the three most heavy-element deficient stars currently known. Based on observations collected at the European Southern Observatory, Chile (Proposal ID 145.B-0009). Tables A.1 and A.2 are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or

AN APPARENT REDSHIFT DEPENDENCE OF QUASAR CONTINUUM: IMPLICATION FOR COSMIC DUST EXTINCTION?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xie, Xiaoyi; Shen, Shiyin; Shao, Zhengyi

We investigate the luminosity and redshift dependence of the quasar continuum by means of the composite spectrum using a large non-BAL radio-quiet quasar sample drawn from the Sloan Digital Sky Survey. Quasar continuum slopes in the UV-Opt band are measured at two different wavelength ranges, i.e., α{sub ν12} (1000 ∼ 2000 Å) and α{sub ν24} (2000 ∼ 4000 Å) derived from a power-law fitting. Generally, the UV spectra slope becomes harder (higher α{sub ν}) toward higher bolometric luminosity. On the other hand, when quasars are further grouped into luminosity bins, we find that both α{sub ν12} and α{sub ν24} show significant anti-correlationsmore » with redshift (i.e., the quasar continuum becomes redder toward higher redshift). We suggest that the cosmic dust extinction is very likely the cause of this observed α{sub ν} − z relation. We build a simple cosmic dust extinction model to quantify the observed reddening tendency and find an effective dust density nσ{sub v} ∼ 10{sup −5}h Mpc{sup −1} at z < 1.5. The other possibilities that could produce such a reddening effect have also been discussed.« less

Optical Variability and Classification of High Redshift (3.5 < z < 5.5) Quasars on SDSS Stripe 82

NASA Astrophysics Data System (ADS)

AlSayyad, Yusra; McGreer, Ian D.; Fan, Xiaohui; Connolly, Andrew J.; Ivezic, Zeljko; Becker, Andrew C.

2015-01-01

Recent studies have shown promise in combining optical colors with variability to efficiently select and estimate the redshifts of low- to mid-redshift quasars in upcoming ground-based time-domain surveys. We extend these studies to fainter and less abundant high-redshift quasars using light curves from 235 sq. deg. and 10 years of Stripe 82 imaging reprocessed with the prototype LSST data management stack. Sources are detected on the i-band co-adds (5σ: i ~ 24) but measured on the single-epoch (ugriz) images, generating complete and unbiased lightcurves for sources fainter than the single-epoch detection threshold. Using these forced photometry lightcurves, we explore optical variability characteristics of high redshift quasars and validate classification methods with particular attention to the low signal limit. In this low SNR limit, we quantify the degradation of the uncertainties and biases on variability parameters using simulated light curves. Completeness/efficiency and redshift accuracy are verified with new spectroscopic observations on the MMT and APO 3.5m. These preliminary results are part of a survey to measure the z~4 luminosity function for quasars (i < 23) on Stripe 82 and to validate purely photometric classification techniques for high redshift quasars in LSST.

A Main Sequence For Quasars

NASA Astrophysics Data System (ADS)

Marziani, Paola; Sulentic, J. W.; Dultzin, D.; Negrete, A.; del Olmo, A.; Martínez-Carballo, M. A.; Stirpe, G. M.; D'Onofrio, M.; Perea, J.

2016-10-01

The 4D eigenvector 1 parameter space defined by Sulentic et al. may be seen as a surrogate H-R diagram for quasars. As in the stellar H-R diagram, a source sequence can be easily identified. In the case of quasars, the main sequence appears to be mainly driven by Eddington ratio. A transition Eddington ratio may in part explain the striking observational differences between quasars at opposite ends of the main sequence. The eigenvector-1 approach opens the door towards properly contextualized models of quasar physics, geometry and kinematics. We review some of the progress that has been made over the past 15 years, and point out still unsolved issues.

A Study of Galaxies and Quasars in the Background of the Andromeda Galaxy

NASA Astrophysics Data System (ADS)

Dhara, Atirath; McConnell, Kaela; Guhathakurta, Puragra; Roy, Namrata; Waite, Jurij

2018-01-01

The SPLASH (Spectroscopic and Photometric Landscape of Andromeda’s Stellar Halo) survey is based on wide-field ground-based optical images (KPNO 4-m/Mosaic, CFHT 3.6-m/MegaCam imager, and Subaru 8-m/Suprime-Cam), deep Hubble Space Telescope ultraviolet/optical/near infrared images (ACS and WFC3), and medium resolution spectra (Keck II 10-m/DEIMOS). The SPLASH survey data set contains two main categories of (non-M31) contaminants (SPLASH trash, if you will): foreground Milky Way stars and compact background galaxies/quasars. In this poster, we present the discovery and characterization of galaxies and quasars behind M31. Such objects were identified based on the presence of redshifted emission lines and other galaxy/quasar spectral features (e.g., Ca H+K absorption and IGM absorption). The redshift of each galaxy was measured by cross-correlating its spectrum against an emission line galaxy spectral template. The cross-correlation results (spectrum and best-fit template) were visually inspected to identify cases of incorrect matching of emission lines. Many of these incorrect redshift estimates were corrected by using the second or third highest cross-correlation peak. Quasar redshifts were determined based on cross-correlation against a quasar spectral template. Most of the galaxies in our sample are star forming galaxies with strong emission lines. We analyze their emission line flux ratios in a BPT diagram to learn more about the ionization source and metallicity. Finally, the properties of these compact galaxies behind M31 are compared to those of galaxies selected in a more standard way in the DEEP2 redshift survey to explore the effects of morphological pre-selection (compact vs. extended) on the properties of the resulting galaxy sample.This research was supported by NASA/STScI and the National Science Foundation. Most of this work was carried out by high school students working under the auspices of the Science Internship Program (SIP) at UC Santa Cruz.

A closer look at the quadruply lensed quasar PSOJ0147: spectroscopic redshifts and microlensing effect

NASA Astrophysics Data System (ADS)

Lee, Chien-Hsiu

2018-04-01

I present a timely spectroscopic follow-up of the newly discovered, quadruply lensed quasar PSOJ0147 from the Pan-STARRS 1 survey. The newly acquired optical spectra with GMOS onboard the Gemini North Telescope allow us to pin down the redshifts of both the foreground lensing galaxy and the background lensed quasar to be z = 0.572 and 2.341, providing a firm basis for cosmography with future high-cadence photometric monitoring. I also inspect difference spectra from two of the quasar images, revealing the microlensing effect. Long-term spectroscopic follow-ups will shed lights on the structure of the active galactic nucleus and its environment.

OPTIMAL TIME-SERIES SELECTION OF QUASARS

DOE Office of Scientific and Technical Information (OSTI.GOV)

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% completenessmore » 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.« less

Near-infrared properties of quasar and Seyfert host galaxies

NASA Astrophysics Data System (ADS)

McLeod, Kim Katris

1994-01-01

We present near-infrared images of nearly 100 host galaxies of Active Galactic Nuclei (AGN). Our quasar sample is comprised of the 50 quasars from the Palomar Green Bright Quasar Survey with redshifts z less than or equal to 0.3. We have restricted the redshift range to ensure adequate spatial resolution, galaxy detectability, and minimal distance-dependent effects, while still giving a large sample of objects. For lower-luminosity AGN we have chosen to image the CfA Seyfert sample. This sample is composed of 48 Seyferts, roughly equally divided among types 1, 1.5-1.9, and 2. This sample was spectroscopically selected, and, therefore, is not biased towards Seyferts with significant star formation. Taken together, these samples allow a statistical look at the continuity of host galaxy properties over a factor of 10,000 in nuclear luminosity. We find the near-infrared light to be a good tracer of luminous mass in these galaxies. The Seyferts are found in galaxies of type SO to Sc. The radio quiet quasars live in similar kinds of galaxies spanning the same range of mass centered around L(*). However, for the most luminous quasars, there is a correlation between the minimum host galaxy mass and the luminosity of the active nucleus. Radio-loud quasars are generally found in hosts more massive than an L(*) galaxy. We also detect a population of low mass host galaxies with very low luminosity Seyfert nuclei. The low luminosity quasars and the Seyferts both tend to lie in host galaxies seen preferentially face-on, which suggests there is a substantial amount of obscuration coplanar with the galaxian disk. The obscuration must be geometrically thick (thickness-to-radius approximately 1) and must cover a significant fraction of the narrow line region (r greater than 100 pc). We have examined our images for signs of perturbations that could drive fuel toward the galaxy nucleus, but there are none we can identify at a significant level. The critical element for fueling is

Near-Infrared Properties of Quasar and Seyfert Host Galaxies

NASA Astrophysics Data System (ADS)

McLeod, Kim Katris

1995-01-01

We present near-infrared images of nearly 100 host galaxies of Active Galactic Nuclei (AGN). Our quasar sample is comprised of the 50 quasars from the Palomar Green Bright Quasar Survey with redshifts z\\<= 0.3. We have restricted the redshift range to ensure adequate spatial resolution, galaxy detectability, and minimal distance-dependent effects, while still giving a large sample of objects. For lower-luminosity AGN we have chosen to image the CfA Seyfert sample. This sample is composed of 48 Seyferts, roughly equally divided among types 1, 1.5-1.9, and 2. This sample was spectroscopically selected, and, therefore, is not biased towards Seyferts with significant star formation. Taken together, these samples allow a statistical look at the continuity of host-galaxy properties over a factor of 10,000 in nuclear luminosity. We find the near-infrared light to be a good tracer of luminous mass in these galaxies. The Seyferts are found in galaxies of type S0 to Sc. The radio quiet quasars live in similar kinds of galaxies spanning the same range of mass centered around L*. However, for the most luminous quasars, there is a correlation between the minimum host-galaxy mass and the luminosity of the active nucleus. Radio-loud quasars are generally found in hosts more massive than an L* galaxy. We also detect a population of low-mass host galaxies with very low-luminosity Seyfert nuclei. The low luminosity quasars and the Seyferts both tend to lie in host galaxies seen preferentially face-on, which suggests there is a substantial amount of obscuration coplanar with the galaxian disk. The obscuration must be geometrically thick (thickness-to-radius ~1) and must cover a significant fraction of the narrow line region (r>100 pc). We have examined our images for signs of perturbations that could drive fuel toward the galaxy nucleus, but there are none we can identify at a significant level. The critical element for fueling is evidently not reflected clearly in the large scale

Crowdsourcing Broad Absorption Line Properties and Other Features of Quasar Outflow Using Zooniverse Citizen Science Project Platform

NASA Astrophysics Data System (ADS)

Crowe, Cassie; Lundgren, Britt; Grier, Catherine

2018-01-01

The Sloan Digital Sky Survey (SDSS) regularly publishes vast catalogs of quasars and other astronomical objects. Previously, the SDSS collaboration has used visual inspection to check quasar redshift validity and flag instances of broad absorption lines (BALs). This information helps researchers to easily single out the quasars with BAL properties and study their outflows and other intervening gas clouds. Due to the ever-growing number of new SDSS quasar observations, visual inspections are no longer possible using previous methods. Currently, BAL information is being determined entirely computationally, and the accuracy of that information is not precisely known. This project uses the Zooniverse citizen science platform to visually inspect quasar spectra for BAL properties, to check the accuracy of the current autonomous methods, and to flag multi-phase outflows and find candidates for in-falling gas into the quasar central engine. The layout and format of a Zooniverse project provides an easier way to inspect and record data on each spectrum and share the workload via crowdsourcing. Work done by the SDSS collaboration members is serving as a beta test for a public project upon the official release of the DR14 quasar catalog by SDSS.

Deep learning of quasar spectra to discover and characterize damped Lyα systems

NASA Astrophysics Data System (ADS)

Parks, David; Prochaska, J. Xavier; Dong, Shawfeng; Cai, Zheng

2018-05-01

We have designed, developed, and applied a convolutional neural network (CNN) architecture using multi-task learning to search for and characterize strong H I Lyα absorption in quasar spectra. Without any explicit modelling of the quasar continuum or application of the predicted line profile for Lyα from quantum mechanics, our algorithm predicts the presence of strong H I absorption and estimates the corresponding redshift zabs and H I column density N_{H I}, with emphasis on damped Lyα systems (DLAs, absorbers with N_{H I}≥ 2 × 10^{20} cm^{-2}). We tuned the CNN model using a custom training set of DLAs injected into DLA-free quasar spectra from the Sloan Digital Sky Survey (SDSS), data release 5 (DR5). Testing on a held-back validation set demonstrates a high incidence of DLAs recovered by the algorithm (97.4 per cent as DLAs and 99 per cent as an H I absorber with N_{H I}> 10^{19.5} cm^{-2}) and excellent estimates for zabs and N_{H I}. Similar results are obtained against a human-generated survey of the SDSS DR5 data set. The algorithm yields a low incidence of false positives and negatives but is challenged by overlapping DLAs and/or very high N_{H I} systems. We have applied this CNN model to the quasar spectra of SDSS DR7 and the Baryon Oscillation Spectroscopic Survey (data release 12) and provide catalogues of 4913 and 50 969 DLAs, respectively (including 1659 and 9230 high-confidence DLAs that were previously unpublished). This work validates the application of deep learning techniques to astronomical spectra for both classification and quantitative measurements.

A Time-domain Analysis of Nitrogen-rich Quasars.

NASA Astrophysics Data System (ADS)

Dittmann, Alexander; Liu, Xin; Shen, Yue; Jiang, Linhua

2018-01-01

A small population of quasars exhibit anomalously high nitrogen-to-carbon ratios (N/C) in their emission lines. These “nitrogen-rich” (N-rich) quasars have been difficult to explain. Few of the possible mechanism are natural, since stellar populations with abnormally high metallicities are required to produce an N-rich interstellar medium. N-rich quasars are also more likely to be “radio-loud” than average quasars, which is difficult to explain by invoking higher metallicity alone. Recently, tidal disruption events (TDEs) have been proposed as a mechanism for N-rich quasars. Such a TDE would occur between a supersolar mass star and a supermassive black hole. The CNO cycle creates a surplus of N-rich and carbon-deficient material that could naturally explain the N/C observed in N-rich quasars. The TDE hypothesis explains N-rich quasars without requiring extremely exotic stellar populations. A testable difference differentiating the TDE explanation and exotic stellar population scenarios is that TDEs do not produce enough N-rich material to pollute the quasar environment for extended periods of time, in which case N-rich phenomena in quasars would be transient. By analyzing changes in nitrogen and carbon line widths in time-separated spectra of N-rich quasars, we have studied nitrogen abundance in quasars which had previously been identified as nitrogen rich. We have found that over time-frames of greater than one year in the quasar rest frame, nitrogen abundance tends to systematically decrease. The observed decrease is larger than our estimate of the effects of noise based on spectra separated by smaller time frames. Additionally, x-ray observations of one N-rich quasar have demonstrated that its x-ray emission is an outlier among the quasar population, but similar to confirmed TDEs.

Color-Space Outliers in DPOSS: Quasars and Peculiar Objects

NASA Astrophysics Data System (ADS)

Djorgovski, S. G.; Gal, R. R.; Mahabal, A.; Brunner, R.; Castro, S. M.; Odewahn, S. C.; de Carvalho, R. R.; DPOSS Team

2000-12-01

The processing of DPOSS, a digital version of the POSS-II sky atlas, is now nearly complete. The resulting Palomar--Norris Sky Catalog (PNSC) is expected to contain > 5 x 107 galaxies and > 109 stars, including large numbers of quasars and other unresolved sources. For objects morphologically classified as stellar (i.e., PSF-like), colors and magnitudes provide the only additional source of discriminating information. We investigate the distribution of objects in the parameter space of (g-r) and (r-i) colors as a function of magnitude. Normal stars form a well-defined (temperature) sequence in this parameter space, and we explore the nature of the objects which deviate significantly from this stellar locus. The causes of the deviations include: non-thermal or peculiar spectra, interagalactic absorption (for high-z quasars), presence of strong emission lines in one or more of the bandpasses, or strong variability (because the plates are taken at widely separated epochs). In addition to minor contamination by misclassified compact galaxies, we find the following: (1) Quasars at z > 4; to date, ~ 100 of these objects have been found, and used for a variety of follow-up studies. They are made publicly available immediately after discovery, through http://astro.caltech.edu/ ~george/z4.qsos. (2) Type-2 quasars in the redshift interval z ~ 0.31 - 0.38. (3) Other quasars, starburst and emission-line galaxies, and emission-line stars. (4) Objects with highly peculiar spectra, some or all of which may be rare subtypes of BAL QSOs. (5) Highly variable stars and optical transients, some of which may be GRB ``orphan afterglows''. To date, systematic searches have been made only for (1) and (2); other types of objects were found serendipitously. However, we plan to explore systematically all of the statistically significant outliers in this parameter space. This illustrates the potential of large digital sky surveys for discovery of rare types of objects, both known (e.g., high

Evidence for the Thermal Sunyaev Zeldovich Effect Associated with Quasar Feedback

NASA Technical Reports Server (NTRS)

Crichton, Devin; Gralla, Megan B.; Hall, Kirsten; Marriage, Tobias A.; Zakamska, Nadia L.; Battaglia, Nick; Bond, J. Richard; Devlin, Mark J.; Hill, J. Colin; Hilton, Matt;

The clustering of the SDSS-IV extended Baryon Oscillation Spectroscopic Survey DR14 quasar sample: structure growth rate measurement from the anisotropic quasar power spectrum in the redshift range 0.8 < z < 2.2

NASA Astrophysics Data System (ADS)

Gil-Marín, Héctor; Guy, Julien; Zarrouk, Pauline; Burtin, Etienne; Chuang, Chia-Hsun; Percival, Will J.; Ross, Ashley J.; Ruggeri, Rossana; Tojerio, Rita; Zhao, Gong-Bo; Wang, Yuting; Bautista, Julian; Hou, Jiamin; Sánchez, Ariel G.; Pâris, Isabelle; Baumgarten, Falk; Brownstein, Joel R.; Dawson, Kyle S.; Eftekharzadeh, Sarah; González-Pérez, Violeta; Habib, Salman; Heitmann, Katrin; Myers, Adam D.; Rossi, Graziano; Schneider, Donald P.; Seo, Hee-Jong; Tinker, Jeremy L.; Zhao, Cheng

2018-06-01

We analyse the clustering of the Sloan Digital Sky Survey IV extended Baryon Oscillation Spectroscopic Survey Data Release 14 quasar sample (DR14Q). We measure the redshift space distortions using the power-spectrum monopole, quadrupole, and hexadecapole inferred from 148 659 quasars between redshifts 0.8 and 2.2, covering a total sky footprint of 2112.9 deg2. We constrain the logarithmic growth of structure times the amplitude of dark matter density fluctuations, fσ8, and the Alcock-Paczynski dilation scales that allow constraints to be placed on the angular diameter distance DA(z) and the Hubble H(z) parameter. At the effective redshift of zeff = 1.52, fσ8(zeff) = 0.420 ± 0.076, H(z_eff)=[162± 12] (r_s^fid/r_s) {km s}^{-1} Mpc^{-1}, and D_A(z_eff)=[1.85± 0.11]× 10^3 (r_s/r_s^fid) Mpc, where rs is the comoving sound horizon at the baryon drag epoch and the superscript `fid' stands for its fiducial value. The errors take into account the full error budget, including systematics and statistical contributions. These results are in full agreement with the current Λ-Cold Dark Matter cosmological model inferred from Planck measurements. Finally, we compare our measurements with other eBOSS companion papers and find excellent agreement, demonstrating the consistency and complementarity of the different methods used for analysing the data.

The WISSH quasars project. I. Powerful ionised outflows in hyper-luminous quasars

NASA Astrophysics Data System (ADS)

Bischetti, M.; Piconcelli, E.; Vietri, G.; Bongiorno, A.; Fiore, F.; Sani, E.; Marconi, A.; Duras, F.; Zappacosta, L.; Brusa, M.; Comastri, A.; Cresci, G.; Feruglio, C.; Giallongo, E.; La Franca, F.; Mainieri, V.; Mannucci, F.; Martocchia, S.; Ricci, F.; Schneider, R.; Testa, V.; Vignali, C.

2017-02-01

Models and observations suggest that both the power and effects of AGN feedback should be maximised in hyper-luminous (LBol > 1047 erg s-1) quasars, I.e. objects at the brightest end of the AGN luminosity function. In this paper, we present the first results of a multiwavelength observing programme, focusing on a sample of WISE/SDSS selected hyper-luminous (WISSH) broad-line quasars at z ≈ 1.5-5. The WISSH quasars project has been designed to reveal the most energetic AGN-driven outflows, estimate their occurrence at the peak of quasar activity, and extend the study of correlations between outflows and nuclear properties up to poorly investigated, extreme AGN luminosities, I.e. LBol 1047 - 1048 erg s-1. We present near-infrared, long-slit LBT/LUCI1 spectroscopy of five WISSH quasars at z ≈ 2.3 - 3.5, showing prominent [OIII] emission lines with broad (FWHM 1200-2200 km s-1) and skewed profiles. The luminosities of these broad [OIII] wings are the highest measured so far, with L[OIII]broad ≳ 5 × 1044 erg s-1, and reveal the presence of powerful ionised outflows with associated mass outflow rates Ṁ ≳ 1700M⊙ yr-1 and kinetic powers Ėkin ≳ 1045 erg s-1. Although these estimates are affected by large uncertainties because of the use of [OIII] as a tracer of ionised outflows and the very basic outflow model adopted here, these results suggest that in our hyper-luminous targets the AGN is highly efficient at pushing large amounts of ionised gas outwards. Furthermore, the mechanical outflow luminosities measured for WISSH quasars correspond to higher percentages ( 1-3%) of LBol than those derived for AGN with lower LBol. Our targets host very massive (MBH ≳ 2 × 109M⊙) black holes that are still accreting at a high rate (I.e. a factor of 0.4-3 of the Eddington limit). These findings clearly demonstrate that WISSH quasars offer the opportunity to probe the extreme end of both luminosity and supermassive black holes (SMBH) mass functions and revealing

Rapidly star-forming galaxies adjacent to quasars at redshifts exceeding 6

NASA Astrophysics Data System (ADS)

Decarli, R.; Walter, F.; Venemans, B. P.; Bañados, E.; Bertoldi, F.; Carilli, C.; Fan, X.; Farina, E. P.; Mazzucchelli, C.; Riechers, D.; Rix, H.-W.; Strauss, M. A.; Wang, R.; Yang, Y.

2017-05-01

The existence of massive (1011 solar masses) elliptical galaxies by redshift z ≈ 4 (refs 1, 2, 3; when the Universe was 1.5 billion years old) necessitates the presence of galaxies with star-formation rates exceeding 100 solar masses per year at z > 6 (corresponding to an age of the Universe of less than 1 billion years). Surveys have discovered hundreds of galaxies at these early cosmic epochs, but their star-formation rates are more than an order of magnitude lower. The only known galaxies with very high star-formation rates at z > 6 are, with one exception, the host galaxies of quasars, but these galaxies also host accreting supermassive (more than 109 solar masses) black holes, which probably affect the properties of the galaxies. Here we report observations of an emission line of singly ionized carbon ([C II] at a wavelength of 158 micrometres) in four galaxies at z > 6 that are companions of quasars, with velocity offsets of less than 600 kilometres per second and linear offsets of less than 100 kiloparsecs. The discovery of these four galaxies was serendipitous; they are close to their companion quasars and appear bright in the far-infrared. On the basis of the [C II] measurements, we estimate star-formation rates in the companions of more than 100 solar masses per year. These sources are similar to the host galaxies of the quasars in [C II] brightness, linewidth and implied dynamical mass, but do not show evidence for accreting supermassive black holes. Similar systems have previously been found at lower redshift. We find such close companions in four out of the twenty-five z > 6 quasars surveyed, a fraction that needs to be accounted for in simulations. If they are representative of the bright end of the [C II] luminosity function, then they can account for the population of massive elliptical galaxies at z ≈ 4 in terms of the density of cosmic space.

Rapidly star-forming galaxies adjacent to quasars at redshifts exceeding 6.

PubMed

Decarli, R; Walter, F; Venemans, B P; Bañados, E; Bertoldi, F; Carilli, C; Fan, X; Farina, E P; Mazzucchelli, C; Riechers, D; Rix, H-W; Strauss, M A; Wang, R; Yang, Y

2017-05-24

The existence of massive (10 11 solar masses) elliptical galaxies by redshift z ≈ 4 (refs 1, 2, 3; when the Universe was 1.5 billion years old) necessitates the presence of galaxies with star-formation rates exceeding 100 solar masses per year at z > 6 (corresponding to an age of the Universe of less than 1 billion years). Surveys have discovered hundreds of galaxies at these early cosmic epochs, but their star-formation rates are more than an order of magnitude lower. The only known galaxies with very high star-formation rates at z > 6 are, with one exception, the host galaxies of quasars, but these galaxies also host accreting supermassive (more than 10 9 solar masses) black holes, which probably affect the properties of the galaxies. Here we report observations of an emission line of singly ionized carbon ([C ii] at a wavelength of 158 micrometres) in four galaxies at z > 6 that are companions of quasars, with velocity offsets of less than 600 kilometres per second and linear offsets of less than 100 kiloparsecs. The discovery of these four galaxies was serendipitous; they are close to their companion quasars and appear bright in the far-infrared. On the basis of the [C ii] measurements, we estimate star-formation rates in the companions of more than 100 solar masses per year. These sources are similar to the host galaxies of the quasars in [C ii] brightness, linewidth and implied dynamical mass, but do not show evidence for accreting supermassive black holes. Similar systems have previously been found at lower redshift. We find such close companions in four out of the twenty-five z > 6 quasars surveyed, a fraction that needs to be accounted for in simulations. If they are representative of the bright end of the [C ii] luminosity function, then they can account for the population of massive elliptical galaxies at z ≈ 4 in terms of the density of cosmic space.

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.

Reduction and analysis of VLA maps for 281 radio-loud quasars using the UNLV Cray Y-MP supercomputer

NASA Technical Reports Server (NTRS)

Ding, Ailian; Hintzen, Paul; Weistrop, Donna; Owen, Frazer

1993-01-01

The identification of distorted radio-loud quasars provides a potentially very powerful tool for basic cosmological studies. If large morphological distortions are correlated with membership of the quasars in rich clusters of galaxies, optical observations can be used to identify rich clusters of galaxies at large redshifts. Hintzen, Ulvestad, and Owen (1983, HUO) undertook a VLA A array snapshot survey at 20 cm of 123 radio-loud quasars, and they found that among triple sources in their sample, 17 percent had radio axes which were bent more than 20 deg and 5 percent were bent more than 40 deg. Their subsequent optical observations showed that excess galaxy densities within 30 arcsec of 6 low-redshift distorted quasars were on average 3 times as great as those around undistorted quasars (Hintzen 1984). At least one of the distorted quasars observed, 3C275.1, apparently lies in the first-ranked galaxy at the center of a rich cluster of galaxies (Hintzen and Romanishin, 1986). Although their sample was small, these results indicated that observations of distorted quasars could be used to identify clusters of galaxies at large redshifts. The purpose of this project is to increase the available sample of distorted quasars to allow optical detection of a significant sample of quasar-associated clusters of galaxies at large redshifts.

Phylogenetic Analyses of Quasars and Galaxies

NASA Astrophysics Data System (ADS)

Fraix-Burnet, Didier; D'Onofrio, Mauro; Marziani, Paola

2017-10-01

Phylogenetic approaches have proven to be useful in astrophysics. We have recently published a Maximum Parsimony (or cladistics) analysis on two samples of 215 and 85 low-z quasars (z < 0.7) which offer a satisfactory coverage of the Eigenvector 1-derived main sequence. Cladistics is not only able to group sources radiating at higher Eddington ratios, to separate radio-quiet (RQ) and radio-loud (RL) quasars and properly distinguishes core-dominated and lobe-dominated quasars, but it suggests a black hole mass threshold for powerful radio emission as already proposed elsewhere. An interesting interpretation from this work is that the phylogeny of quasars may be represented by the ontogeny of their central black hole, i.e. the increase of the black hole mass. However these exciting results are based on a small sample of low-z quasars, so that the work must be extended. We are here faced with two difficulties. The first one is the current lack of a larger sample with similar observables. The second one is the prohibitive computation time to perform a cladistic analysis on more that about one thousand objects. We show in this paper an experimental strategy on about 1500 galaxies to get around this difficulty. Even if it not related to the quasar study, it is interesting by itself and opens new pathways to generalize the quasar findings.

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.

iPTF Discovery of the Rapid “Turn-on” of a Luminous Quasar

DOE PAGES

Gezari, S.; Hung, T.; Cenko, S. B.; ...

2017-01-24

We present a radio-quiet quasar at z = 0.237 discovered "turning on" by the intermediate Palomar Transient Factory (iPTF). The transient, iPTF 16bco, was detected by iPTF in the nucleus of a galaxy with an archival Sloan Digital Sky Survey spectrum with weak narrow-line emission characteristic of a low-ionization nuclear emission-line region (LINER). Our follow-up spectra show the dramatic appearance of broad Balmer lines and a power-law continuum characteristic of a luminous ( L bol ≈ 10 45 erg s -1) type 1 quasar 12 yr later. Our photometric monitoring with PTF from 2009-2012 and serendipitous X-ray observations from themore » XMM-Newton Slew Survey in 2011 and 2015 constrain the change of state to have occurred less than 500 days before the iPTF detection. An enhanced broad Hα/[O iii] λ5007 line ratio in the type 1 state relative to other changing-look quasars also is suggestive of the most rapid change of state yet observed in a quasar. Here, we argue that the > 10 increase in Eddington ratio inferred from the brightening in UV and X-ray continuum flux is more likely due to an intrinsic change in the accretion rate of a preexisting accretion disk than an external mechanism such as variable obscuration, microlensing, or the tidal disruption of a star. However, further monitoring will be helpful in better constraining the mechanism driving this change of state. The rapid "turn-on" of the quasar is much shorter than the viscous infall timescale of an accretion disk and requires a disk instability that can develop around a ~ 10 8 M ⊙ black hole on timescales less than 1 yr.« less

Discovery of the Lensed Quasar System DES J0408-5354

DOE PAGES

Lin, H.; Buckley-Geer, E.; Agnello, A.; ...

2017-03-27

We report the discovery and spectroscopic confirmation of the quad-like lensed quasar system DES J0408-5354 found in the Dark Energy Survey (DES) Year 1 (Y1) data. This system was discovered during a search for DES Y1 strong lensing systems using a method that identified candidates as red galaxies with multiple blue neighbors. DES J0408-5354 consists of a central red galaxy surrounded by three bright (more » $$i\\lt 20$$) blue objects and a fourth red object. Subsequent spectroscopic observations using the Gemini South telescope confirmed that the three blue objects are indeed the lensed images of a quasar with redshift z = 2.375, and that the central red object is an early-type lensing galaxy with redshift z = 0.597. DES J0408-5354 is the first quad lensed quasar system to be found in DES and begins to demonstrate the potential of DES to discover and dramatically increase the sample size of these very rare objects.« less

Discovery of the Lensed Quasar System DES J0408-5354

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lin, H.; Buckley-Geer, E.; Agnello, A.

We report the discovery and spectroscopic confirmation of the quad-like lensed quasar system DES J0408-5354 found in the Dark Energy Survey (DES) Year 1 (Y1) data. This system was discovered during a search for DES Y1 strong lensing systems using a method that identified candidates as red galaxies with multiple blue neighbors. DES J0408-5354 consists of a central red galaxy surrounded by three bright (more » $$i\\lt 20$$) blue objects and a fourth red object. Subsequent spectroscopic observations using the Gemini South telescope confirmed that the three blue objects are indeed the lensed images of a quasar with redshift z = 2.375, and that the central red object is an early-type lensing galaxy with redshift z = 0.597. DES J0408-5354 is the first quad lensed quasar system to be found in DES and begins to demonstrate the potential of DES to discover and dramatically increase the sample size of these very rare objects.« less

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.

The Time-domain Spectroscopic Survey: Target Selection for Repeat Spectroscopy

NASA Astrophysics Data System (ADS)

MacLeod, Chelsea L.; Green, Paul J.; Anderson, Scott F.; Eracleous, Michael; Ruan, John J.; Runnoe, Jessie; Nielsen Brandt, William; Badenes, Carles; Greene, Jenny; Morganson, Eric; Schmidt, Sarah J.; Schwope, Axel; Shen, Yue; Amaro, Rachael; Lebleu, Amy; Filiz Ak, Nurten; Grier, Catherine J.; Hoover, Daniel; McGraw, Sean M.; Dawson, Kyle; Hall, Patrick B.; Hawley, Suzanne L.; Mariappan, Vivek; Myers, Adam D.; Pâris, Isabelle; Schneider, Donald P.; Stassun, Keivan G.; Bershady, Matthew A.; Blanton, Michael R.; Seo, Hee-Jong; Tinker, Jeremy; Fernández-Trincado, J. G.; Chambers, Kenneth; Kaiser, Nick; Kudritzki, R.-P.; Magnier, Eugene; Metcalfe, Nigel; Waters, Chris Z.

2018-01-01

As astronomers increasingly exploit the information available in the time domain, spectroscopic variability in particular opens broad new channels of investigation. Here we describe the selection algorithms for all targets intended for repeat spectroscopy in the Time Domain Spectroscopic Survey (TDSS), part of the extended Baryon Oscillation Spectroscopic Survey within the Sloan Digital Sky Survey (SDSS)-IV. Also discussed are the scientific rationale and technical constraints leading to these target selections. The TDSS includes a large “repeat quasar spectroscopy” (RQS) program delivering ∼13,000 repeat spectra of confirmed SDSS quasars, and several smaller “few-epoch spectroscopy” (FES) programs targeting specific classes of quasars as well as stars. The RQS program aims to provide a large and diverse quasar data set for studying variations in quasar spectra on timescales of years, a comparison sample for the FES quasar programs, and an opportunity for discovering rare, serendipitous events. The FES programs cover a wide variety of phenomena in both quasars and stars. Quasar FES programs target broad absorption line quasars, high signal-to-noise ratio normal broad line quasars, quasars with double-peaked or very asymmetric broad emission line profiles, binary supermassive black hole candidates, and the most photometrically variable quasars. Strongly variable stars are also targeted for repeat spectroscopy, encompassing many types of eclipsing binary systems, and classical pulsators like RR Lyrae. Other stellar FES programs allow spectroscopic variability studies of active ultracool dwarf stars, dwarf carbon stars, and white dwarf/M dwarf spectroscopic binaries. We present example TDSS spectra and describe anticipated sample sizes and results.

Galaxy evolution. Quasar quartet embedded in giant nebula reveals rare massive structure in distant universe.

PubMed

Hennawi, Joseph F; Prochaska, J Xavier; Cantalupo, Sebastiano; Arrigoni-Battaia, Fabrizio

2015-05-15

All galaxies once passed through a hyperluminous quasar phase powered by accretion onto a supermassive black hole. But because these episodes are brief, quasars are rare objects typically separated by cosmological distances. In a survey for Lyman-α emission at redshift z ≈ 2, we discovered a physical association of four quasars embedded in a giant nebula. Located within a substantial overdensity of galaxies, this system is probably the progenitor of a massive galaxy cluster. The chance probability of finding a quadruple quasar is estimated to be ∼10(-7), implying a physical connection between Lyman-α nebulae and the locations of rare protoclusters. Our findings imply that the most massive structures in the distant universe have a tremendous supply (≃10(11) solar masses) of cool dense (volume density ≃ 1 cm(-3)) gas, which is in conflict with current cosmological simulations. Copyright © 2015, American Association for the Advancement of Science.

Highly Accreting Quasars at High Redshift

NASA Astrophysics Data System (ADS)

Martínez-Aldama, Mary L.; Del Olmo, Ascensión; Marziani, Paola; Sulentic, Jack W.; Negrete, C. Alenka; Dultzin, Deborah; Perea, Jaime; D'Onofrio, Mauro

2017-12-01

We present preliminary results of a spectroscopic analysis for a sample of type 1 highly accreting quasars (LLedd>0.2) at high redshift, z 2-3. The quasars were observed with the OSIRIS spectrograph on the GTC 10.4 m telescope located at the Observatorio del Roque de los Muchachos in La Palma. The highly accreting quasars were identified using the 4D Eigenvector 1 formalism, which is able to organize type 1 quasars over a broad range of redshift and luminosity. The kinematic and physical properties of the broad line region have been derived by fitting the profiles of strong UV emission lines such as AlIII, SiIII and CIII. The majority of our sources show strong blueshifts in the high-ionization lines and high Eddington ratios which are related with the productions of outflows. The importance of highly accreting quasars goes beyond a detailed understanding of their physics: their extreme Eddington ratio makes them candidates standard candles for cosmological studies.

Using quasars as standard clocks for measuring cosmological redshift.

PubMed

Dai, De-Chang; Starkman, Glenn D; Stojkovic, Branislav; Stojkovic, Dejan; Weltman, Amanda

2012-06-08

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.

NO OVERDENSITY OF LYMAN-ALPHA EMITTING GALAXIES AROUND A QUASAR AT z  ∼ 5.7

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mazzucchelli, C.; Bañados, E.; Decarli, R.

2017-01-01

Bright quasars, observed when the universe was less than one billion years old ( z  > 5.5), are known to host massive black holes (∼10{sup 9} M {sub ⊙}) and are thought to reside in the center of massive dark matter overdensities. In this picture, overdensities of galaxies are expected around high-redshift quasars. However, observations based on the detection of Lyman-break galaxies (LBGs) around these quasars do not offer a clear picture: this may be due to the uncertain redshift constraints of LBGs, which are solely selected through broadband filters. To circumvent such uncertainties, we here perform a search for Lyman-alphamore » emitting galaxies (LAEs) in the field of the quasar PSO J215.1512–16.0417 at z  ∼ 5.73, through narrowband deep imaging with FORS2 at the Very Large Telescope. We study an area of 37 arcmin{sup 2}, i.e., ∼206 comoving Mpc{sup 2} at the redshift of the quasar. We find no evidence of an overdensity of LAEs in the quasar field with respect to blank-field studies. Possible explanations for these findings may be that our survey volume is too small, or that the strong ionizing radiation from the quasar hinders galaxy formation in its immediate proximity. Another possibility is that these quasars are not situated in the dense environments predicted by some simulations.« less

Various Approaches for Targeting Quasar Candidates

NASA Astrophysics Data System (ADS)

Zhang, Y.; Zhao, Y.

2015-09-01

With the establishment and development of space-based and ground-based observational facilities, the improvement of scientific output of high-cost facilities is still a hot issue for astronomers. The discovery of new and rare quasars attracts much attention. Different methods to select quasar candidates are in bloom. Among them, some are based on color cuts, some are from multiwavelength data, some rely on variability of quasars, some are based on data mining, and some depend on ensemble methods.

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.

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.

The triply-ionized carbon forest from eBOSS: cosmological correlations with quasars in SDSS-IV DR14

NASA Astrophysics Data System (ADS)

Blomqvist, Michael; Pieri, Matthew M.; du Mas des Bourboux, Hélion; Busca, Nicolás G.; Slosar, Anže; Bautista, Julian E.; Brinkmann, Jonathan; Brownstein, Joel R.; Dawson, Kyle; de Sainte Agathe, Victoria; Guy, Julien; Percival, Will J.; Pérez-Ràfols, Ignasi; Rich, James; Schneider, Donald P.

2018-05-01

We present measurements of the cross-correlation of the triply-ionized carbon (CIV) forest with quasars using Sloan Digital Sky Survey Data Release 14. The study exploits a large sample of new quasars from the first two years of observations by the Extended Baryon Oscillation Spectroscopic Survey (eBOSS). The CIV forest is a weaker tracer of large-scale structure than the Lyα forest, but benefits from being accessible at redshifts z<2 where the quasar number density from eBOSS is high. Our data sample consists of 287,651 CIV forest quasars in the redshift range 1.4quasars with 1.2quasar rest-frame wavelength bands of the spectra referred to as the CIV forest, the SiIV forest and the Lyα forest. From the combined fit to the quasar-CIV cross-correlations for the CIV forest and the SiIV forest, the CIV redshift-space distortion parameter is βCIV=0.27 ‑0.14 ‑0.26 +0.16 +0.34 and its combination with the CIV linear transmission bias parameter is bCIV(1+βCIV)=‑0.0183 ‑0.0014 ‑0.0029 +0.0013 +0.0025 (1σ and 2σ statistical errors) at the mean redshift z=2.00. Splitting the sample at z=2.2 to constrain the bias evolution with redshift yields the power-law exponent γ=0.60±0.63, indicating a significantly weaker redshift-evolution than for the Lyα forest linear transmission bias. Additionally, we demonstrate that CIV absorption has the potential to be used as a probe of baryon acoustic oscillations (BAO). While the current data set is insufficient for a detection of the BAO peak feature, the final quasar samples for redshifts 1.4

AGN radiative feedback in dusty quasar populations

NASA Astrophysics Data System (ADS)

Ishibashi, W.; Banerji, M.; Fabian, A. C.

2017-08-01

New populations of hyper-luminous, dust-obscured quasars have been recently discovered around the peak epoch of galaxy formation (z ˜ 2-3), in addition to similar sources found at lower redshifts. Such dusty quasars are often interpreted as sources 'in transition', from dust-enshrouded starbursts to unobscured luminous quasars, along the evolutionary sequence. Here we consider the role of the active galactic nucleus (AGN) radiative feedback, driven by radiation pressure on dust, in high-luminosity, dust-obscured sources. We analyse how the radiation pressure-driven dusty shell models, with different shell mass configurations, may be applied to the different populations of dusty quasars reported in recent observations. We find that expanding shells, sweeping up matter from the surrounding environment, may account for prolonged obscuration in dusty quasars, e.g. for a central luminosity of L ˜ 1047 erg s-1, a typical obscured phase (with extinction in the range AV ˜ 1-10 mag) may last a few ˜106 yr. On the other hand, fixed-mass shells, coupled with high dust-to-gas ratios, may explain the extreme outflows recently discovered in red quasars at high redshifts. We discuss how the interaction between AGN radiative feedback and the ambient medium at different temporal stages in the evolutionary sequence may contribute to shape the observational appearance of dusty quasar populations.

Recurrent hamburger thyrotoxicosis

PubMed Central

Parmar, Malvinder S.; Sturge, Cecil

2003-01-01

RECURRENT EPISODES OF SPONTANEOUSLY RESOLVING HYPERTHYROIDISM may be caused by release of preformed hormone from the thyroid gland after it has been damaged by inflammation (recurrent silent thyroiditis) or by exogenous administration of thyroid hormone, which might be intentional or surreptitious (thyrotoxicosis factitia). Community-wide outbreaks of “hamburger thyrotoxicosis” resulting from inadvertent consumption of beef contaminated with bovine thyroid gland have been previously reported. Here we describe a single patient who experienced recurrent episodes of this phenomenon over an 11-year period and present an approach to systematically evaluating patients with recurrent hyperthyroidism. PMID:12952802

Luminosity correlations in quasars

NASA Technical Reports Server (NTRS)

Chanan, G. A.

1983-01-01

Simulations are conducted with and without flux thresholds in an investigation of quasar luminosity correlations by means of a Monte Carlo analysis, for various model distributions of quasars in X-rays and optical luminosity. For the case where the X-ray photons are primary, an anticorrelation between X-ray-to-optical luminosity ratio and optical luminosity arises as a natural consequence which resembles observations. The low optical luminosities of X-ray selected quasars can be understood as a consequence of the same effect, and similar conclusions may hold if the X-ray and optical luminosities are determined independently by a third parameter, although they do not hold if the optical photons are primary. The importance of such considerations is demonstrated through a reanalysis of the published X-ray-to-optical flux ratios for the 3CR sample.

VizieR Online Data Catalog: Large area KX quasar catalogue (Maddox+, 2012)

NASA Astrophysics Data System (ADS)

Maddox, N.; Hewett, P. C.; Peroux, C.; Nestor, D. B.; Wisotzki, L.

2013-05-01

In order to maximize the dynamic range of the survey in absolute magnitude at fixed redshift, while ensuring adequate sampling of the brightest quasars, a 'wedding cake' survey geometry is adopted. Thus, the entire survey area is complete to the brightest limits, with a smaller subregion complete to fainter magnitudes and the smallest subregion complete to the faintest limits. Observations of the survey area utilized four telescopes (NTT, VLT, CA 2.2m and CA 3.5m) over three observing semesters between 2009 May and 2010 July. (2 data files).

The clustering of the SDSS-IV extended Baryon Oscillation Spectroscopic Survey DR14 quasar sample: First measurement of Baryon Acoustic Oscillations between redshift 0.8 and 2.2

DOE PAGES

Ata, Metin

2017-06-20

Here, we present measurements of the Baryon Acoustic Oscillation (BAO) scale in redshift-space using the clustering of quasars. We consider a sample of 147,000 quasars from the extended Baryon Oscillation Spectroscopic Survey (eBOSS) distributed over 2044 square degrees with redshifts 0.8 < z < 2.2 and measure their spherically-averaged clustering in both configuration and Fourier space. Our observational dataset and the 1400 simulated realizations of the dataset allow us to detect a preference for BAO that is greater than 2.5σ . We determine the spherically averaged BAO distance to z = 1.52 to 4.4 per cent precision: D V (zmore » = 1:52) = 3855 170 (r d/r d,fid) Mpc. This is the first time the location of the BAO feature has been measured between redshifts 1 and 2. Our result is fully consistent with the prediction obtained by extrapolating the Planck flat CDM best-fit cosmology. All of our results are consistent with basic large-scale structure (LSS) theory, confirming quasars to be a reliable tracer of LSS, and provide a starting point for numerous cosmological tests to be performed with eBOSS quasar samples. We combine our result with previous, independent, BAO distance measurements to construct an updated BAO distance-ladder. Bu using these BAO data alone and marginalizing over the length of the standard ruler, we find Ω Λ > 0 at 6.5σ significance when testing a CDM model with free curvature.« less

The clustering of the SDSS-IV extended Baryon Oscillation Spectroscopic Survey DR14 quasar sample: First measurement of Baryon Acoustic Oscillations between redshift 0.8 and 2.2

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ata, Metin

Here, we present measurements of the Baryon Acoustic Oscillation (BAO) scale in redshift-space using the clustering of quasars. We consider a sample of 147,000 quasars from the extended Baryon Oscillation Spectroscopic Survey (eBOSS) distributed over 2044 square degrees with redshifts 0.8 < z < 2.2 and measure their spherically-averaged clustering in both configuration and Fourier space. Our observational dataset and the 1400 simulated realizations of the dataset allow us to detect a preference for BAO that is greater than 2.5σ . We determine the spherically averaged BAO distance to z = 1.52 to 4.4 per cent precision: D V (zmore » = 1:52) = 3855 170 (r d/r d,fid) Mpc. This is the first time the location of the BAO feature has been measured between redshifts 1 and 2. Our result is fully consistent with the prediction obtained by extrapolating the Planck flat CDM best-fit cosmology. All of our results are consistent with basic large-scale structure (LSS) theory, confirming quasars to be a reliable tracer of LSS, and provide a starting point for numerous cosmological tests to be performed with eBOSS quasar samples. We combine our result with previous, independent, BAO distance measurements to construct an updated BAO distance-ladder. Bu using these BAO data alone and marginalizing over the length of the standard ruler, we find Ω Λ > 0 at 6.5σ significance when testing a CDM model with free curvature.« less

The clustering of the SDSS-IV extended Baryon Oscillation Spectroscopic Survey DR14 quasar sample: first measurement of baryon acoustic oscillations between redshift 0.8 and 2.2

NASA Astrophysics Data System (ADS)

Ata, Metin; Baumgarten, Falk; Bautista, Julian; Beutler, Florian; Bizyaev, Dmitry; Blanton, Michael R.; Blazek, Jonathan A.; Bolton, Adam S.; Brinkmann, Jonathan; Brownstein, Joel R.; Burtin, Etienne; Chuang, Chia-Hsun; Comparat, Johan; Dawson, Kyle S.; de la Macorra, Axel; Du, Wei; du Mas des Bourboux, Hélion; Eisenstein, Daniel J.; Gil-Marín, Héctor; Grabowski, Katie; Guy, Julien; Hand, Nick; Ho, Shirley; Hutchinson, Timothy A.; Ivanov, Mikhail M.; Kitaura, Francisco-Shu; Kneib, Jean-Paul; Laurent, Pierre; Le Goff, Jean-Marc; McEwen, Joseph E.; Mueller, Eva-Maria; Myers, Adam D.; Newman, Jeffrey A.; Palanque-Delabrouille, Nathalie; Pan, Kaike; Pâris, Isabelle; Pellejero-Ibanez, Marcos; Percival, Will J.; Petitjean, Patrick; Prada, Francisco; Prakash, Abhishek; Rodríguez-Torres, Sergio A.; Ross, Ashley J.; Rossi, Graziano; Ruggeri, Rossana; Sánchez, Ariel G.; Satpathy, Siddharth; Schlegel, David J.; Schneider, Donald P.; Seo, Hee-Jong; Slosar, Anže; Streblyanska, Alina; Tinker, Jeremy L.; Tojeiro, Rita; Vargas Magaña, Mariana; Vivek, M.; Wang, Yuting; Yèche, Christophe; Yu, Liang; Zarrouk, Pauline; Zhao, Cheng; Zhao, Gong-Bo; Zhu, Fangzhou

2018-02-01

We present measurements of the Baryon Acoustic Oscillation (BAO) scale in redshift-space using the clustering of quasars. We consider a sample of 147 000 quasars from the extended Baryon Oscillation Spectroscopic Survey (eBOSS) distributed over 2044 square degrees with redshifts 0.8 < z < 2.2 and measure their spherically averaged clustering in both configuration and Fourier space. Our observational data set and the 1400 simulated realizations of the data set allow us to detect a preference for BAO that is greater than 2.8σ. We determine the spherically averaged BAO distance to z = 1.52 to 3.8 per cent precision: DV(z = 1.52) = 3843 ± 147(rd/rd, fid)Mpc. This is the first time the location of the BAO feature has been measured between redshifts 1 and 2. Our result is fully consistent with the prediction obtained by extrapolating the Planck flat ΛCDM best-fitting cosmology. All of our results are consistent with basic large-scale structure (LSS) theory, confirming quasars to be a reliable tracer of LSS, and provide a starting point for numerous cosmological tests to be performed with eBOSS quasar samples. We combine our result with previous, independent, BAO distance measurements to construct an updated BAO distance-ladder. Using these BAO data alone and marginalizing over the length of the standard ruler, we find ΩΛ > 0 at 6.6σ significance when testing a ΛCDM model with free curvature.

First identification of Sarcocystis hominis in Iranian traditional hamburger.

PubMed

Ahmadi, M Moghaddam; Hajimohammadi, B; Eslami, G; Oryan, A; Yasini Ardakani, S A; Zohourtabar, A; Zare, S

2015-12-01

Zoonotic concerns of cattle sarcocystosis are of importance, because humans are the final host for Sarcocystis hominis. Therefore the meat products containing beef may encompass sarcocysts which endanger food safety. In this study, we described the first report of molecular identification of S. hominis in Iranian traditional hamburgers using PCR-RFLP. Throughout a pilot research that was carried out to setup a molecular approach to identify the Sarcocystis spp., using PCR-RFLP, a sample of raw Iranian traditional hamburger was purchased from a street food seller located in Yazd, central Iran in May 2013. DNA extraction was done, by salting out method; briefly, the sample was lysed with NET buffer. The DNA purification and precipitation was then performed. Amplicon and digestion results were analyzed, using gel agarose electrophoresis. The results showed a PCR product with 926 bp in length after amplification and 376 and 550 bp in length after digestion. This product was identified as S. hominis. To the best of our knowledge, this is the first report of S. hominis infection in Iranian hamburger.

Hubble Space Telescope Images of Nearby Luminous Quasars. 2; Results for Eight Quasars and Tests of the Detection Sensitivity

NASA Technical Reports Server (NTRS)

Bahcall, John N.; Kirhakos, Sofia; Schneider, Donald P.

1995-01-01

Observations with the Wide-Field Camera of the Hubble Space Telescope (HST) are presented for eight intrinsically luminous quasars with redshifts between 0.16 and 0.29. These observations, when combined with a similar HST study of the quasar PKS 2349-014, show that luminous nearby quasars exist in a variety of environments. Seven companion galaxies brighter than M(V) = 16.5 (H(sub 0) = 100 km s(sup -1) Mpc(sup -1), Omega(sub 0) = 1.0) lie within a projected distance of 25 kpc of the quasars; three of the companions are located closer than 3'' (6 kpc projected distance) from the quasars, well within the volume that would be enclosed by a typical L* host galaxy. The observed association of quasars and companion galaxies is statistically significant and may he an important element in the luminous-quasar phenomenon. Apparent host galaxies are detected for three of the quasars: PG 1116+215, 3C 273, and PG 1444+407; the hosts have an average absolute magnitude of about 0.6 mag brighter than L*. The agreement between the previously published major-axis directions in ground-based images and in the present HST images of 3C 273 and PG 1444+407 constitutes important evidence supporting the reality of these candidate host galaxies. Upper limits are placed on the visual-band brightnesses of representative galactic hosts for all the quasars. These limits are established by placing galaxy images obtained with HST underneath the quasars and measuring at what faintness level the known galaxies are detected. On average, the HST spirals would have been detected if they were as faint as 1 mag below L*, and the early-type galaxies could have been detected down to a brightness level of about L*, where L* is the Schechter characteristic luminosity of field galaxies. Smooth, featureless galaxy models (exponential disks or de Vaucouleurs profiles) are fitted to the residual light after a best-fitting point source is subtracted from the quasar images. The results show that smooth spiral

ACCRETION RATES OF RED QUASARS FROM THE HYDROGEN Pβ LINE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kim, Dohyeong; Im, Myungshin; Glikman, Eilat

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, whichmore » 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.« less

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.

Quasars at the High Redshift Frontier

NASA Astrophysics Data System (ADS)

Bosman, Sarah E. I.

2017-11-01

In recent years the formation of primordial galaxies, cosmic metal enrichment, and hydrogen reionisation have been studied using both refined observations and powerful numerical simulations. High-redshift quasars have become a ubiquitous tool in the study of this era with more than 115 quasars now spectroscopically confirmed at z>6.0. In this thesis, I use spectra of high-redshift quasars to provide improved observational constraints through a mixture of existing and new techniques. I first investigate the claim of neutral gas around the most distant known quasar, ULASJ1120+0641(J1120), with a cosmological redshift of z=7.1. Its spectrum shows a relatively weak Lyman-α emission line, which has been interpreted as evidence of absorption by neutral gas. Attributing this to a Gunn-Peterson damping wing has led to claims that the intergalactic medium is at least 10% neutral at that redshift. However, these claims rely on a reconstruction of the unabsorbed quasar emission. Initial attempts using composite spectra of lower-redshift quasars mismatched the CIV emission line of J1120, a feature known to correlate with Lyman-α and which is strongly blueshifted in J1120. I attempt to establish whether this mismatch could explain the apparently weak Lyman-α emission line. I find that among a C IV-matched sample the Lyman-α line of J1120 is not anomalous. This raises doubts as to the interpretation of absorbed Lyman-α emission lines in the context of reionisation. I then use a high quality X-Shooter spectrum of the same z=7 quasar to measure the abundances of diffuse metals within one billion years of the Big Bang. I measure the occurrence rates of CIV, CII, SiII, FeII and MgII, producing the first measurement at z>6 for many of these ions. I find that the incidence of CIV systems is consistent with a continuing decline in the total mass density of highly ionized metals, a trend seen at lower redshifts. The ratio CII/CIV, however, seems to remain constant or increase with

VizieR Online Data Catalog: ROSAT detected quasars. II. (Yuan+ 1998)

NASA Astrophysics Data System (ADS)

Yuan, W.; Brinkmann, W.; Siebert, J.; Voges, W.

1997-11-01

We have compiled a sample of all radio-quiet quasars or quasars without radio detection from the Veron-Cetty - Veron catalogue (1993, VV93, Cat. ) detected by ROSAT in the ALL-SKY SURVEY (RASS, Voges 1992, in Proc. of the ISY Conference `Space Science', ESA ISY-3, ESA Publications, p.9, See Cat. ), as targets of pointed observations, or as serendipitous sources from pointed observations publicly available from the ROSAT point source catalogue (ROSAT-SRC, Voges et al. 1995, Cat. ). For all sources we used the results of the Standard Analysis Software System (SASS, Voges et al. 1992, in Proc. of the ISY Conference `Space Science', ESA ISY-3, ESA Publications, p.223), employing the most recent processing for the Survey data (RASS-II, Voges et al. 1996, Cat. ). The total number of quasars is 846. 69 of the radio-quiet objects with radio detections have already been presented in a previous paper (Brinkmann, Yuan, & Siebert 1997, Cat. ) using the RASS-I results. 17 objects were found to be radio-loud from recent radio surveys and were marked in the table. When available, the power law photon indices and the corresponding absorption column densities (NH) were estimated from the two hardness ratios given by the SASS, both with free fitted NH and for Galactic absorption. The unabsorbed X-ray flux densities in the ROSAT band (0.1-2.4keV) were calculated from the count rates using the energy to counts conversion factor for power law spectra and Galactic absorption. As the photon index we used the value obtained for the individual source if the estimated 1-σ error is smaller than 0.5, otherwise we used the redshift-dependent mean value (see the paper for details). (1 data file).

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.

Models of the strongly lensed quasar DES J0408-5354

NASA Astrophysics Data System (ADS)

Agnello, A.; Lin, H.; Buckley-Geer, L.; Treu, T.; Bonvin, V.; Courbin, F.; Lemon, C.; Morishita, T.; Amara, A.; Auger, M. W.; Birrer, S.; Chan, J.; Collett, T.; More, A.; Fassnacht, C. D.; Frieman, J.; Marshall, P. J.; McMahon, R. G.; Meylan, G.; Suyu, S. H.; Castander, F.; Finley, D.; Howell, A.; Kochanek, C.; Makler, M.; Martini, P.; Morgan, N.; Nord, B.; Ostrovski, F.; Schechter, P.; Tucker, D.; Wechsler, R.; Abbott, T. M. C.; Abdalla, F. B.; Allam, S.; Benoit-Lévy, A.; Bertin, E.; Brooks, D.; Burke, D. L.; Rosell, A. Carnero; Kind, M. Carrasco; Carretero, J.; Crocce, M.; Cunha, C. E.; D'Andrea, C. B.; da Costa, L. N.; Desai, S.; Dietrich, J. P.; Eifler, T. F.; Flaugher, B.; Fosalba, P.; García-Bellido, J.; Gaztanaga, E.; Gill, M. S.; Goldstein, D. A.; Gruen, D.; Gruendl, R. A.; Gschwend, J.; Gutierrez, G.; Honscheid, K.; James, D. J.; Kuehn, K.; Kuropatkin, N.; Li, T. S.; Lima, M.; Maia, M. A. G.; March, M.; Marshall, J. L.; Melchior, P.; Menanteau, F.; Miquel, R.; Ogando, R. L. C.; Plazas, A. A.; Romer, A. K.; Sanchez, E.; Schindler, R.; Schubnell, M.; Sevilla-Noarbe, I.; Smith, M.; Smith, R. C.; Sobreira, F.; Suchyta, E.; Swanson, M. E. C.; Tarle, G.; Thomas, D.; Walker, A. R.

2017-12-01

We present detailed modelling of the recently discovered, quadruply lensed quasar J0408-5354, with the aim of interpreting its remarkable configuration: besides three quasar images (A,B,D) around the main deflector (G1), a fourth image (C) is significantly reddened and dimmed by a perturber (G2) which is not detected in the Dark Energy Survey imaging data. From lens models incorporating (dust-corrected) flux ratios, we find a perturber Einstein radius 0.04 arcsec ≲ RE, G2 ≲ 0.2 arcsec and enclosed mass Mp(RE, G2) ≲ 1.0 × 1010 M⊙. The main deflector has stellar mass log _{10}(M_{\\star }/M_{⊙})=11.49^{+0.46}_{-0.32}, a projected mass Mp(RE, G1) ≈ 6 × 1011 M⊙ within its Einstein radius RE, G1 = (1.85 ± 0.15) arcsec and predicted velocity dispersion 267-280 km s-1. Follow-up images from a companion monitoring campaign show additional components, including a candidate second source at a redshift between the quasar and G1. Models with free perturbers, and dust-corrected and delay-corrected flux ratios, are also explored. The predicted time-delays (ΔtAB = (135.0 ± 12.6) d, ΔtBD = (21.0 ± 3.5) d) roughly agree with those measured, but better imaging is required for proper modelling and comparison. We also discuss some lessons learnt from J0408-5354 on lensed quasar finding strategies, due to its chromaticity and morphology.

The Associated Absorption Features in Quasar Spectra of the Sloan Digital Sky Survey. I. Mg II Absorption Doublets

NASA Astrophysics Data System (ADS)

Chen, Zhi-Fu; Huang, Wei-Rong; Pang, Ting-Ting; Huang, Hong-Yan; Pan, Da-Sheng; Yao, Min; Nong, Wei-Jing; Lu, Mei-Mei

2018-03-01

Using the SDSS spectra of quasars included in the DR7Q or DR12Q catalogs, we search for Mg II λλ2796, 2803 narrow absorption doublets in the spectra data around Mg II λ2798 emission lines. We obtain 17,316 Mg II doublets, within the redshift range of 0.3299 ≤ z abs ≤ 2.5663. We find that a velocity offset of υ r < 6000 km s‑1 is a safe boundary to constrain the vast majority of associated Mg II systems, although we find some doublets at υ r > 6000 km s‑1. If associated Mg II absorbers are defined by υ r < 6000 km s‑1, ∼33.3% of the absorbers are supposed to be contaminants of intervening systems. Removing the 33.3% contaminants, ∼4.5% of the quasars present at least one associated Mg II system with {W}{{r}}λ 2796≥slant 0.2 \\mathringA . The fraction of associated Mg II systems with high-velocity outflows correlates with the average luminosities of their central quasars, indicating a relationship between outflows and the quasar feedback power. The υ r distribution of the outflow Mg II absorbers is peaked at 1023 km s‑1, which is smaller than the corresponding value of the outflow C IV absorbers. The redshift number density evolution of absorbers (dn/dz) limited by υ r > ‑3000 km s‑1 differs from that of absorbers constrained by υ r > 2000 km s‑1. Absorbers limited by υ r > 2000 km s‑1 and higher values exhibit profiles similar to dn/dz. In addition, the dn/dz is smaller when absorbers are constrained with larger υ r . The distributions of equivalent widths, and the ratio of {W}rλ 2796/{W}rλ 2803, are the same for associated and intervening systems, and independent of quasar luminosity.

Discovery of a new blue quasar: SDSS J022218.03-062511.1

DOE PAGES

Fix, Mees B.; Smith, J. Allyn; Tucker, Douglas L.; ...

2015-07-29

We report the discovery of a bright blue quasar: SDSS J022218.03–062511.1. This object was discovered spectroscopically while searching for hot white dwarfs that may be used as calibration sources for large sky surveys such as the Dark Energy Survey or the Large Synoptic Survey Telescope project. In addition, we present the calibrated spectrum, spectral line shifts and report a redshift of z = 0.521 ± 0.0015 and a rest-frame g-band luminosity of 8.71 × 10 11 L ⊙.

Constraints on Primordial Non-Gaussianity from 800 000 Photometric Quasars.

PubMed

Leistedt, Boris; Peiris, Hiranya V; Roth, Nina

2014-11-28

We derive robust constraints on primordial non-Gaussianity (PNG) using the clustering of 800 000 photometric quasars from the Sloan Digital Sky Survey in the redshift range 0.5quasar halo bias at the largest scales, while discarding as little as possible of the data. The standard local-type PNG parameters f_{NL} and g_{NL} both imprint a k^{-2} scale-dependent effect in the bias. Constraining these individually, we obtain -49quasar clustering to the underlying dark matter. These are the strongest constraints obtained to date on PNG using a single population of large-scale structure tracers, and are already at the level of pre-Planck constraints from the cosmic microwave background. A conservative forecast for a Large Synoptic Survey Telescope (LSST)-like survey incorporating mode projection yields σ(f_{NL})∼5-competitive with the Planck result-highlighting the power of upcoming large scale structure surveys to probe the initial conditions of the Universe.

Host galaxy properties of calcium II and sodium I quasar absorption-line systems

NASA Astrophysics Data System (ADS)

Cherinka, Brian

Many questions remain within the areas of galaxy formation and evolution. Understanding the origin of gas in galaxy environments, whether as tidal debris, infalling High Velocity Clouds, galaxy outflows, or as gaseous material residing in galaxy disks, is an important step in answering those questions. Quasar absorption-lines can often be used to probe the environments of intervening galaxies. Traditionally, quasar absorption-lines are studied independently of the host galaxy but this method denies us the exploration of the connection between galaxy and environment. Instead, one can select pairs of known galaxies and quasars. This gives much more information regarding the host galaxy and allows us to better connect galaxy properties with associated absorbers. We use the seventh data release of the Sloan Digital Sky Survey to generate a sample of spectroscopic galaxy-quasar pairs. We cross-correlated a sample of 105,000 quasars and ˜800,000 galaxies to produce ˜98,000 galaxy-quasar pairs, with the quasar projected within 100 kpc of the galaxy. Adopting an automated line-finding algorithm and using the galaxy redshift as a prior, we search through all quasar spectra and identify Ca II and Na I absorption due to the intervening galaxy. This procedure produced 1745 Ca II absorbers and 4500 Na I absorbers detected at or above 2σ. Stacking analysis of a subset of absorbers at z > 0.01, with significances at or above 3σ, showed strong Ca II and Na I features around external galaxies. Using the same subset of absorbers at z > 0.01, we looked for correlations between absorber and galaxy properties and examined differences in galaxy properties between the absorbers and non-absorbers. We found no correlations with absorber strength or differences between many galaxy properties at the 3σ level. The lack of correlations and differences between absorbers and non-absorbers suggest a ubiquitous nature for Ca II and Na I around all types of galaxies, with the absorbers showing

The Tidbinbilla-U.K. Schmidt radio quasar identification program

NASA Technical Reports Server (NTRS)

Jauncey, D. L.; Batty, M. J.; Savage, A.; Gulkis, S.

1983-01-01

A program is under way at Tidbinbilla to measure accurate (up to 2 arcsec r.m.s) radio positions for compact sources in the Parkes 2.7 GHz survey south of declination -30 deg. Optical identifications are being made on the basis of radio-optical position coincidence alone, without regard to colour or morphology, using the U.K. Schmidt IIIa-J sky survey to a limiting magnitude of 22.5. This program is aimed at producing an evaluation of the radio quasar redshift distribution with particular emphasis on those objects with redshifts greater than 3.0.

The QUASAR facility

NASA Astrophysics Data System (ADS)

Gates, David

2013-10-01

The QUAsi-Axisymmetric Research (QUASAR) stellarator is a new facility which can solve two critical problems for fusion, disruptions and steady-state, and which provides new insights into the role of magnetic symmetry in plasma confinement. If constructed it will be the only quasi-axisymmetric stellarator in the world. The innovative principle of quasi-axisymmetry (QA) will be used in QUASAR to study how ``tokamak-like'' systems can be made: 1) Disruption-free, 2) Steady-state with low recirculating power, while preserving or improving upon features of axisymmetric tokamaks, such as 1) Stable at high pressure simultaneous with 2) High confinement (similar to tokamaks), and 3) Scalable to a compact reactor Stellarator research is critical to fusion research in order to establish the physics basis for a magnetic confinement device that can operate efficiently in steady-state, without disruptions at reactor-relevant parameters. The two large stellarator experiments - LHD in Japan and W7-X under construction in Germany are pioneering facilities capable of developing 3D physics understanding at large scale and for very long pulses. The QUASAR design is unique in being QA and optimized for confinement, stability, and moderate aspect ratio (4.5). It projects to a reactor with a major radius of ~8 m similar to advanced tokamak concepts. It is striking that (a) the EU DEMO is a pulsed (~2.5 hour) tokamak with major R ~ 9 m and (b) the ITER physics scenarios do not presume steady-state behavior. Accordingly, QUASAR fills a critical gap in the world stellarator program. This work supported by DoE Contract No. DEAC02-76CH03073.

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.

Mid-infrared luminous quasars in the GOODS-Herschel fields: a large population of heavily obscured, Compton-thick quasars at z ≈ 2

NASA Astrophysics Data System (ADS)

Del Moro, A.; Alexander, D. M.; Bauer, F. E.; Daddi, E.; Kocevski, D. D.; McIntosh, D. H.; Stanley, F.; Brandt, W. N.; Elbaz, D.; Harrison, C. M.; Luo, B.; Mullaney, J. R.; Xue, Y. Q.

2016-02-01

We present the infrared (IR) and X-ray properties of a sample of 33 mid-IR luminous quasars (νL6 μm ≥ 6 × 1044 erg s-1) at redshift z ≈ 1-3, identified through detailed spectral energy distribution analyses of distant star-forming galaxies, using the deepest IR data from Spitzer and Herschel in the GOODS-Herschel fields. The aim is to constrain the fraction of obscured, and Compton-thick (CT, NH > 1.5 × 1024 cm-2) quasars at the peak era of nuclear and star formation activities. Despite being very bright in the mid-IR band, ≈30 per cent of these quasars are not detected in the extremely deep 2 and 4 Ms Chandra X-ray data available in these fields. X-ray spectral analysis of the detected sources reveals that the majority (≈67 per cent) are obscured by column densities NH > 1022 cm-2; this fraction reaches ≈80 per cent when including the X-ray-undetected sources (9 out of 33), which are likely to be the most heavily obscured, CT quasars. We constrain the fraction of CT quasars in our sample to be ≈24-48 per cent, and their space density to be Φ = (6.7 ± 2.2) × 10-6 Mpc-3. From the investigation of the quasar host galaxies in terms of star formation rates (SFRs) and morphological distortions, as a sign of galaxy mergers/interactions, we do not find any direct relation between SFRs and quasar luminosity or X-ray obscuration. On the other hand, there is tentative evidence that the most heavily obscured quasars have, on average, more disturbed morphologies than the unobscured/moderately obscured quasar hosts, which preferentially live in undisturbed systems. However, the fraction of quasars with disturbed morphology amongst the whole sample is ≈40 per cent, suggesting that galaxy mergers are not the main fuelling mechanism of quasars at z ≈ 2.

An automated algorithm for determining photometric redshifts of quasars

NASA Astrophysics Data System (ADS)

Wang, Dan; Zhang, Yanxia; Zhao, Yongheng

2010-07-01

We employ k-nearest neighbor algorithm (KNN) for photometric redshift measurement of quasars with the Fifth Data Release (DR5) of the Sloan Digital Sky Survey (SDSS). KNN is an instance learning algorithm where the result of new instance query is predicted based on the closest training samples. The regressor do not use any model to fit and only based on memory. Given a query quasar, we find the known quasars or (training points) closest to the query point, whose redshift value is simply assigned to be the average of the values of its k nearest neighbors. Three kinds of different colors (PSF, Model or Fiber) and spectral redshifts are used as input parameters, separatively. The combination of the three kinds of colors is also taken as input. The experimental results indicate that the best input pattern is PSF + Model + Fiber colors in all experiments. With this pattern, 59.24%, 77.34% and 84.68% of photometric redshifts are obtained within ▵z < 0.1, 0.2 and 0.3, respectively. If only using one kind of colors as input, the model colors achieve the best performance. However, when using two kinds of colors, the best result is achieved by PSF + Fiber colors. In addition, nearest neighbor method (k = 1) shows its superiority compared to KNN (k ≠ 1) for the given sample.

Yacare caiman (Caiman yacare) trim hamburger and sausage subjected to different smoking techniques.

PubMed

Fernandes, Vitória Regina Takeuchi; Souza Franco, Maria Luiza Rodrigues; Mikcha, Jane Martha Graton; de Souza, Vera Lúcia Ferreira; Gasparino, Eliane; Coutinho, Marcos Eduardo; Tanamati, Augusto; Del Vesco, Ana Paula

2014-02-01

Caiman, as well as having skin that, after tanning, produces leather of high added value, exceptional quality and good market value, also possesses a meat with a remarkably smooth taste and appearance. This study aimed to characterize hamburger and sausages made from Yacare caiman (Caiman yacare) meat trim. Hot smoked products contained less moisture than the unsmoked products. Protein and ash were higher, respectively, for hot smoked hamburger and sausage. Lipids had greater presence in hot smoked sausage (9.72%), whereas in the burgers they were higher in the liquid smoked burgers (6.71%). The hot smoked products had lower water activity. Hot smoked products displayed less luminance, but the a* and b* chroma were higher in smoked hamburgers. Taste, texture and general acceptability were significant for the hamburger, whereas for the sausage there was a significant effect for texture, salt and purchase intent. For all the products, the hot smoking resulted in the lowest acceptability. © 2013 Society of Chemical Industry.

The diversity of soft X-ray spectra in quasars

NASA Technical Reports Server (NTRS)

Elvis, M.; Wilkes, B. J.; Tananbaum, H.

1985-01-01

Soft X-ray spectra for three quasars obtained with the Einstein Imaging Proportional Counter covering the 0.1-4.0 keV band are reported. Power-law fits to these spectra have best-fit energy indices of 1.2 +0.6 or -0.2, for the quasar NAB 0205 + 024, 0.6 +0.3 or -0.2 for the quasar B2 1028 + 313, and 2.2 + or -0.4 for the quasar PG 1211 + 143. None of the quasars shows any evidence for a column density of cold matter in excess of the galactic values. The derived spectra demonstrate that there is no single universal power law slope for quasar X-ray spectra. The implications of these results for the X-ray background, X-ray continuum emission mechanisms, and the production of the optical/UV emission lines are briefly discussed.

The clustering of the SDSS-IV extended Baryon Oscillation Spectroscopic Survey DR14 quasar sample: First measurement of Baryon Acoustic Oscillations between redshift 0.8 and 2.2

DOE PAGES

Ata, Metin; Baumgarten, Falk; Bautista, Julian; ...

2017-10-11

We present measurements of the Baryon Acoustic Oscillation (BAO) scale in redshift-space using the clustering of quasars. We consider a sample of 147,000 quasars from the extended Baryon Oscillation Spectroscopic Survey (eBOSS) distributed over 2044 square degrees with redshiftsmore » $0.8 < z < 2.2$ and measure their spherically-averaged clustering in both configuration and Fourier space. Our observational dataset and the 1400 simulated realizations of the dataset allow us to detect a preference for BAO that is greater than 2.5$$\\sigma$$. We determine the spherically averaged BAO distance to $z = 1.52$ to 4.4 per cent precision: $$D_V(z=1.52)=3855\\pm170 \\left(r_{\\rm d}/r_{\\rm d, fid}\\right)\\ $$Mpc. This is the first time the location of the BAO feature has been measured between redshifts 1 and 2. Our result is fully consistent with the prediction obtained by extrapolating the Planck flat $$\\Lambda$$CDM best-fit cosmology. All of our results are consistent with basic large-scale structure (LSS) theory, confirming quasars to be a reliable tracer of LSS, and provide a starting point for numerous cosmological tests to be performed with eBOSS quasar samples. We combine our result with previous, independent, BAO distance measurements to construct an updated BAO distance-ladder. Using these BAO data alone and marginalizing over the length of the standard ruler, we find $$\\Omega_{\\Lambda} > 0$$ at 6.5$$\\sigma$$ significance when testing a $$\\Lambda$$CDM model with free curvature.« less

Testing the Triggering Mechanism for Luminous, Radio-Quiet Red Quasars in the Clearing Phase: A Comparison to Radio-Loud Red Quasars

NASA Astrophysics Data System (ADS)

Glikman, Eliat

2016-10-01

We propose to conduct a controlled study of the relationship between radio emission and host galaxy morphology for a new sample of radio-quiet dust-reddened quasars selected by their infrared colors in WISE and 2MASS (W2M). These sources are the radio-quiet analogs to the FIRST-2MASS (F2M) red quasars, which we found to be predominantly driven by major mergers. F2M red quasars are accreting at very high rates and exhibit broad absorption lines associated with outflows and feedback. Their properties are consistent with buried quasars expelling their dusty shrouds in an an evolutionary phase predicted by merger-driven co-evolution models. The quasars in both samples are the most intrinsically luminous objects in the Universe - the regime where we expect mergers to dominate. However, recent lines of evidence suggest that radio emission may be linked to AGN reddening and merging hosts. We will use WFC3/IR and ACS to image the host galaxies of W2M quasars in the two redshift regimes that our previous studies probed, z 0.7 and z 2, testing the merger-driven quasar paradigm across the full radio range with a minimum of selection effects or other biases that plague many studies comparing different samples. The images proposed here will sample the host galaxies in rest-frame visible and UV light to look for merger signatures. Evidence for mergers in these quasar hosts would support a picture in which luminous quasars and galaxies co-evolve through major-mergers, independent of their radio properties. The absence of mergers in our data would link radio emission to mergers and require an alternate explanation for the extreme properties of these radio-quiet sources.

A Hungry Quasar Caught in the Act

NASA Astrophysics Data System (ADS)

2001-05-01

The VLT Secures Spectacular Image of Distant Gravitational Interaction Summary A new image of a distant quasar (the luminous core of an "active" galaxy) shows that it is engaged in a gravitational battle with its neighbouring galaxies . It also provides information on how supermassive black holes present in the center of quasars are fed. Using the FORS2 multi-mode instrument at the ESO 8.2-m VLT KUEYEN telescope on Paranal (Chile), a team of German astronomers [1] obtained a spectacular image of the close and complex environment of the distant quasar "HE 1013-2136", located some 10 billion light-years away [2]. The remarkable structures revealed in this photo lend support to the hypothesis that quasar activity is connected to gravitational interaction between galaxies, already at this early epoch of the Universe (about 5 billion years after the Big Bang). PR Photo 20a/01 : A VLT image of the Quasar HE 1013-2136 . PR Photo 20b/01 : A sharpened version of the same image. Feeding the Black Hole "Quasars" (Quasi-Stellar Objects) were first discovered by Dutch-American astronomer Maarten Schmidt in 1963 as distant, energetic objects of star-like appearance. Since then, more than 15,000 quasars have been found and we now know that they are the luminous cores at the heart of distant galaxies. Such "Active Galactic Nuclei (AGN)" are thought to host Supermassive Black Holes of up to one billion solar masses at their centres. Black Holes represent the densest possible state of matter; if the Earth were to become one, it would measure no more than a few millimetres across. The Black Hole in a galaxy gobbles up the gas and dust of its host, a process that efficiently powers the luminous core that we observe as a point-like "quasar". A Black Hole must be continuously fed to remain active. During an active phase of typically 100 million years, the Black Hole in a quasar swallows material with a total weight of up to 10 solar masses every year. This may be predominantly in the

A 14 h-3 Gpc3 study of cosmic homogeneity using BOSS DR12 quasar sample

NASA Astrophysics Data System (ADS)

Laurent, Pierre; Le Goff, Jean-Marc; Burtin, Etienne; Hamilton, Jean-Christophe; Hogg, David W.; Myers, Adam; Ntelis, Pierros; Pâris, Isabelle; Rich, James; Aubourg, Eric; Bautista, Julian; Delubac, Timothée; du Mas des Bourboux, Hélion; Eftekharzadeh, Sarah; Palanque Delabrouille, Nathalie; Petitjean, Patrick; Rossi, Graziano; Schneider, Donald P.; Yeche, Christophe

2016-11-01

The BOSS quasar sample is used to study cosmic homogeneity with a 3D survey in the redshift range 2.2 < z < 2.8. We measure the count-in-sphere, N(< r), i.e. the average number of objects around a given object, and its logarithmic derivative, the fractal correlation dimension, D2(r). For a homogeneous distribution N(< r) propto r3 and D2(r) = 3. Due to the uncertainty on tracer density evolution, 3D surveys can only probe homogeneity up to a redshift dependence, i.e. they probe so-called ``spatial isotropy". Our data demonstrate spatial isotropy of the quasar distribution in the redshift range 2.2 < z < 2.8 in a model-independent way, independent of any FLRW fiducial cosmology, resulting in 3 - langleD2rangle < 1.7 × 10-3 (2 σ) over the range 250 < r < 1200 h-1 Mpc for the quasar distribution. If we assume that quasars do not have a bias much less than unity, this implies spatial isotropy of the matter distribution on large scales. Then, combining with the Copernican principle, we finally get homogeneity of the matter distribution on large scales. Alternatively, using a flat ΛCDM fiducial cosmology with CMB-derived parameters, and measuring the quasar bias relative to this ΛCDM model, our data provide a consistency check of the model, in terms of how homogeneous the Universe is on different scales. D2(r) is found to be compatible with our ΛCDM model on the whole 10 < r < 1200 h-1 Mpc range. For the matter distribution we obtain 3 - langleD2rangle < 5 × 10-5 (2 σ) over the range 250 < r < 1200 h-1 Mpc, consistent with homogeneity on large scales.

A search for optical variability of type 2 quasars in SDSS stripe 82

DOE Office of Scientific and Technical Information (OSTI.GOV)

Barth, Aaron J.; Carson, Daniel J.; Voevodkin, Alexey

Hundreds of Type 2 quasars have been identified in Sloan Digital Sky Survey (SDSS) data, and there is substantial evidence that they are generally galaxies with highly obscured central engines, in accord with unified models for active galactic nuclei (AGNs). A straightforward expectation of unified models is that highly obscured Type 2 AGNs should show little or no optical variability on timescales of days to years. As a test of this prediction, we have carried out a search for variability in Type 2 quasars in SDSS Stripe 82 using difference-imaging photometry. Starting with the Type 2 AGN catalogs of Zakamskamore » et al. and Reyes et al., we find evidence of significant g-band variability in 17 out of 173 objects for which light curves could be measured from the Stripe 82 data. To determine the nature of this variability, we obtained new Keck spectropolarimetry observations for seven of these variable AGNs. The Keck data show that these objects have low continuum polarizations (p ≲ 1% in most cases) and all seven have broad Hα and/or Mg II emission lines in their total (unpolarized) spectra, indicating that they should actually be classified as Type 1 AGNs. We conclude that the primary reason variability is found in the SDSS-selected Type 2 AGN samples is that these samples contain a small fraction of Type 1 AGNs as contaminants, and it is not necessary to invoke more exotic possible explanations such as a population of 'naked' or unobscured Type 2 quasars. Aside from misclassified Type 1 objects, the Type 2 quasars do not generally show detectable optical variability over the duration of the Stripe 82 survey.« less

Insights into quasar UV spectra using unsupervised clustering analysis

NASA Astrophysics Data System (ADS)

Tammour, A.; Gallagher, S. C.; Daley, M.; Richards, G. T.

2016-06-01

Machine learning techniques can provide powerful tools to detect patterns in multidimensional parameter space. We use K-means - a simple yet powerful unsupervised clustering algorithm which picks out structure in unlabelled data - to study a sample of quasar UV spectra from the Quasar Catalog of the 10th Data Release of the Sloan Digital Sky Survey (SDSS-DR10) of Paris et al. Detecting patterns in large data sets helps us gain insights into the physical conditions and processes giving rise to the observed properties of quasars. We use K-means to find clusters in the parameter space of the equivalent width (EW), the blue- and red-half-width at half-maximum (HWHM) of the Mg II 2800 Å line, the C IV 1549 Å line, and the C III] 1908 Å blend in samples of broad absorption line (BAL) and non-BAL quasars at redshift 1.6-2.1. Using this method, we successfully recover correlations well-known in the UV regime such as the anti-correlation between the EW and blueshift of the C IV emission line and the shape of the ionizing spectra energy distribution (SED) probed by the strength of He II and the Si III]/C III] ratio. We find this to be particularly evident when the properties of C III] are used to find the clusters, while those of Mg II proved to be less strongly correlated with the properties of the other lines in the spectra such as the width of C IV or the Si III]/C III] ratio. We conclude that unsupervised clustering methods (such as K-means) are powerful methods for finding `natural' binning boundaries in multidimensional data sets and discuss caveats and future work.

High Redshift QSOs in the UKIDSS Large Area Survey

NASA Astrophysics Data System (ADS)

Venemans, B. P.

2007-12-01

In this proceeding, I will present the first results on our ongoing search for z⪆6 quasars in the UKIDSS Large Area Survey (LAS). The unique infrared sky coverage of the LAS combined with SDSS i and z observations allows us to efficiently search for high redshift quasars with minimal contamination from foreground objects, e.g. galactic cool stars. Analysis of 106 deg^2 of sky from UKIDSS Data Release 1 (DR1) has resulted in the discovery of ULAS J020332.38+001229.2, a luminous (J_{AB}=20.0, M_{1450}=-26.2) quasar at z=5.86. The quasar is not present in the SDSS DR5 catalogue and the continuum spectral index of α=-1.4 (F_{ν}∝ν^{α}) is redder than a composite of SDSS quasars at similar redshifts (α=-0.5). Although it is difficult to draw any strong conclusions regarding the space density of quasars from one object, the discovery of this quasar in ˜100 deg^2 in a complete sample within our selection criteria down to a median depth of Y_{AB}=20.4 (7σ) is consistent with existing SDSS results. Finally, I will present the expected number density of high redshift z>6.5 quasars using future infrared surveys with VISTA.

The clustering of the SDSS-IV extended Baryon Oscillation Spectroscopic Survey DR14 quasar sample: measurement of the growth rate of structure from the anisotropic correlation function between redshift 0.8 and 2.2

NASA Astrophysics Data System (ADS)

Zarrouk, Pauline; Burtin, Etienne; Gil-Marín, Héctor; Ross, Ashley J.; Tojeiro, Rita; Pâris, Isabelle; Dawson, Kyle S.; Myers, Adam D.; Percival, Will J.; Chuang, Chia-Hsun; Zhao, Gong-Bo; Bautista, Julian; Comparat, Johan; González-Pérez, Violeta; Habib, Salman; Heitmann, Katrin; Hou, Jiamin; Laurent, Pierre; Le Goff, Jean-Marc; Prada, Francisco; Rodríguez-Torres, Sergio A.; Rossi, Graziano; Ruggeri, Rossana; Sánchez, Ariel G.; Schneider, Donald P.; Tinker, Jeremy L.; Wang, Yuting; Yèche, Christophe; Baumgarten, Falk; Brownstein, Joel R.; de la Torre, Sylvain; du Mas des Bourboux, Hélion; Kneib, Jean-Paul; Mariappan, Vivek; Palanque-Delabrouille, Nathalie; Peacock, John; Petitjean, Patrick; Seo, Hee-Jong; Zhao, Cheng

2018-06-01

We present the clustering measurements of quasars in configuration space based on the Data Release 14 (DR14) of the Sloan Digital Sky Survey IV extended Baryon Oscillation Spectroscopic Survey (eBOSS). This data set includes 148 659 quasars spread over the redshift range 0.8 ≤ z ≤ 2.2 and spanning 2112.9 deg2. We use the Convolution Lagrangian Perturbation Theory approach with a Gaussian Streaming model for the redshift space distortions of the correlation function and demonstrate its applicability for dark matter haloes hosting eBOSS quasar tracers. At the effective redshift zeff = 1.52, we measure the linear growth rate of structure fσ8(zeff) = 0.426 ± 0.077, the expansion rate H(z_eff)= 159^{+12}_{-13}(rs^fid/r_s) {{}km s}^{-1} Mpc^{-1}, and the angular diameter distance DA(z_eff)=1850^{+90}_{-115} (r_s/rs^fid) {}Mpc, where rs is the sound horizon at the end of the baryon drag epoch and rs^fid is its value in the fiducial cosmology. The quoted uncertainties include both systematic and statistical contributions. The results on the evolution of distances are consistent with the predictions of flat Λ-cold dark matter cosmology with Planck parameters, and the measurement of fσ8 extends the validity of General Relativity to higher redshifts (z > 1). This paper is released with companion papers using the same sample. The results on the cosmological parameters of the studies are found to be in very good agreement, providing clear evidence of the complementarity and of the robustness of the first full-shape clustering measurements with the eBOSS DR14 quasar sample.

Quasar Photometric Redshifts and Candidate Selection: A New Algorithm Based on Optical and Mid-infrared Photometric Data

NASA Astrophysics Data System (ADS)

Yang, Qian; Wu, Xue-Bing; Fan, Xiaohui; Jiang, Linhua; McGreer, Ian; Green, Richard; Yang, Jinyi; Schindler, Jan-Torge; Wang, Feige; Zuo, Wenwen; Fu, Yuming

2017-12-01

We present a new algorithm to estimate quasar photometric redshifts (photo-zs), by considering the asymmetries in the relative flux distributions of quasars. The relative flux models are built with multivariate Skew-t distributions in the multidimensional space of relative fluxes as a function of redshift and magnitude. For 151,392 quasars in the SDSS, we achieve a photo-z accuracy, defined as the fraction of quasars with the difference between the photo-z z p and the spectroscopic redshift z s , | {{Δ }}z| =| {z}s-{z}p| /(1+{z}s) within 0.1, of 74%. Combining the WISE W1 and W2 infrared data with the SDSS data, the photo-z accuracy is enhanced to 87%. Using the Pan-STARRS1 or DECaLS photometry with WISE W1 and W2 data, the photo-z accuracies are 79% and 72%, respectively. The prior probabilities as a function of magnitude for quasars, stars, and galaxies are calculated, respectively, based on (1) the quasar luminosity function, (2) the Milky Way synthetic simulation with the Besançon model, and (3) the Bayesian Galaxy Photometric Redshift estimation. The relative fluxes of stars are obtained with the Padova isochrones, and the relative fluxes of galaxies are modeled through galaxy templates. We test our classification method to select quasars using the DECaLS g, r, z, and WISE W1 and W2 photometry. The quasar selection completeness is higher than 70% for a wide redshift range 0.5< z< 4.5, and a wide magnitude range 18< r< 21.5 mag. Our photo-z regression and classification method has the potential to extend to future surveys. The photo-z code will be publicly available.

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.

Models of the strongly lensed quasar DES J0408-5354

DOE Office of Scientific and Technical Information (OSTI.GOV)

Agnello, A.; Lin, H.; Buckley-Geer, L.

We present detailed modelling of the recently discovered, quadruply lensed quasar J0408-5354, with the aim of interpreting its remarkable configuration: besides three quasar images (A,B,D) around the main deflector (G1), a fourth image (C) is significantly reddened and dimmed by a perturber (G2) which is not detected in the Dark Energy Survey imaging data. From lens models incorporating (dust-corrected) flux ratios, we find a perturber Einstein radius 0.04 arcsec ≲ RE, G2 ≲ 0.2 arcsec and enclosed mass M p(R E, G2) ≲ 1.0 × 10 10 M⊙. The main deflector has stellar mass log10 (M */M⊙) =11.49more » $$+0.46\\atop{-0.32}$$ log10 (M */M⊙)=11.49-0.32+0.46 , a projected mass M p(R E, G1) ≈ 6 × 10 11 M⊙ within its Einstein radius R E, G1 = (1.85 ± 0.15) arcsec and predicted velocity dispersion 267–280 km s -1. Follow-up images from a companion monitoring campaign show additional components, including a candidate second source at a redshift between the quasar and G1. Models with free perturbers, and dust-corrected and delay-corrected flux ratios, are also explored. The predicted time-delays (Δt AB = (135.0 ± 12.6) d, Δt BD = (21.0 ± 3.5) d) roughly agree with those measured, but better imaging is required for proper modelling and comparison. Lastly, we also discuss some lessons learnt from J0408-5354 on lensed quasar finding strategies, due to its chromaticity and morphology.« less

Models of the strongly lensed quasar DES J0408-5354

DOE PAGES

Agnello, A.; Lin, H.; Buckley-Geer, L.; ...

2017-09-07

We present detailed modelling of the recently discovered, quadruply lensed quasar J0408-5354, with the aim of interpreting its remarkable configuration: besides three quasar images (A,B,D) around the main deflector (G1), a fourth image (C) is significantly reddened and dimmed by a perturber (G2) which is not detected in the Dark Energy Survey imaging data. From lens models incorporating (dust-corrected) flux ratios, we find a perturber Einstein radius 0.04 arcsec ≲ RE, G2 ≲ 0.2 arcsec and enclosed mass M p(R E, G2) ≲ 1.0 × 10 10 M⊙. The main deflector has stellar mass log10 (M */M⊙) =11.49more » $$+0.46\\atop{-0.32}$$ log10 (M */M⊙)=11.49-0.32+0.46 , a projected mass M p(R E, G1) ≈ 6 × 10 11 M⊙ within its Einstein radius R E, G1 = (1.85 ± 0.15) arcsec and predicted velocity dispersion 267–280 km s -1. Follow-up images from a companion monitoring campaign show additional components, including a candidate second source at a redshift between the quasar and G1. Models with free perturbers, and dust-corrected and delay-corrected flux ratios, are also explored. The predicted time-delays (Δt AB = (135.0 ± 12.6) d, Δt BD = (21.0 ± 3.5) d) roughly agree with those measured, but better imaging is required for proper modelling and comparison. Lastly, we also discuss some lessons learnt from J0408-5354 on lensed quasar finding strategies, due to its chromaticity and morphology.« less

ASERA: A spectrum eye recognition assistant for quasar spectra

NASA Astrophysics Data System (ADS)

Yuan, Hailong; Zhang, Haotong; Zhang, Yanxia; Lei, Yajuan; Dong, Yiqiao; Zhao, Yongheng

2013-11-01

Spectral type recognition is an important and fundamental step of large sky survey projects in the data reduction for further scientific research, like parameter measurement and statistic work. It tends out to be a huge job to manually inspect the low quality spectra produced from the massive spectroscopic survey, where the automatic pipeline may not provide confident type classification results. In order to improve the efficiency and effectiveness of spectral classification, we develop a semi-automated toolkit named ASERA, ASpectrum Eye Recognition Assistant. The main purpose of ASERA is to help the user in quasar spectral recognition and redshift measurement. Furthermore it can also be used to recognize various types of spectra of stars, galaxies and AGNs (Active Galactic Nucleus). It is an interactive software allowing the user to visualize observed spectra, superimpose template spectra from the Sloan Digital Sky Survey (SDSS), and interactively access related spectral line information. It is an efficient and user-friendly toolkit for the accurate classification of spectra observed by LAMOST (the Large Sky Area Multi-object Fiber Spectroscopic Telescope). The toolkit is available in two modes: a Java standalone application and a Java applet. ASERA has a few functions, such as wavelength and flux scale setting, zoom in and out, redshift estimation, spectral line identification, which helps user to improve the spectral classification accuracy especially for low quality spectra and reduce the labor of eyeball check. The function and performance of this tool is displayed through the recognition of several quasar spectra and a late type stellar spectrum from the LAMOST Pilot survey. Its future expansion capabilities are discussed.

SpIES: The Spitzer IRAC Equatorial Survey

NASA Technical Reports Server (NTRS)

Timlin, John D.; Ross, Nicholas P.; Richards, Gordon, T.; Lacy, Mark; Ryan, Erin L.; Stone, Robert B.; Bauer, Franz, E.; Brandt, W. N.; Fan, Xiaohui; Glikman, Eilat;

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

New Constraints on the Hard Ionizing Photon Budget and the Lifetime and Obscuration of Quasars During the Epoch of Helium Reionization

NASA Astrophysics Data System (ADS)

Davies, Frederick

2017-08-01

The epoch of helium reionization was a major milestone in the history of the Universe, a direct consequence of supermassive black hole growth and the cumulative output of hard ionizing photons by quasars. Our observations of the He II Ly-alpha forest with HST/COS in 26 quasar sightlines show strong fluctuations at z 3, consistent with our state-of-the-art simulations of the He II reionization epoch. However, our detection of transmission at z > 3.5 is inconsistent with all He II reionization models. Resolving this puzzle requires an extensive parameter study of He II reionization, which we propose to carry out using our fast, efficient simulations. The He II Ly-alpha forest is also sensitive to the effect of quasar radiation illuminating the intergalactic medium, known as the proximity effect. We have performed an ambitious ground-based imaging and spectroscopic survey for z 3 quasars in the foreground of HeII sightlines observed with HST/COS, and statistically detected the transverse proximity effect for the first time. The strength of this effect depends on both the quasar lifetime and the opening angle of quasar emission (or the fraction of obscured quasars), and we propose to use our He II reionization simulations to interpret this new measurement. Finally, the line-of-sight proximity effect due to the background quasar provides an independent constraint on the quasar lifetime. Our preliminary comparison of He II spectra to our radiative transfer simulations suggests a quasar lifetime > 10 Myr. We propose to use our He II reionization simulations to model this diverse set of observations and fully capitalize on the far-UV legacy of HST.

Cosmic Infrared Background Sources Clustered Around Quasars

NASA Astrophysics Data System (ADS)

Hall, Kirsten R.; Zakamska, Nadia; Marriage, Tobias; Crichton, Devin; Gralla, Megan

2017-06-01

Powerful quasars can be seen out to large distances. As they reside in massive dark matter halos, they provide a useful tracer of large scale structure. We stack Herschel-SPIRE images at 250, 350, and 500 microns at the locations of 13,000 quasars in redshift bins spanning 0.5 < z < 3.5. While the detected signal is dominated on instrumental beam scales by the unresolved dust emission of the quasar and its host galaxy, at z 2 the extended emission is clearly spatially resolved on Mpc scales. This emission is due to star-forming galaxies clustered around the dark matter halos hosting quasars. We measure radial surface brightness profiles of the stacked images to compute the angular correlation function of dusty star-forming galaxies correlated with quasars. We generate a halo occupation distribution model in order to determine the masses of the dark matter halos in which dusty star forming galaxies reside. We are probing potential changes in the halo mass most efficient at hosting star forming galaxies, and assessing any evidence that this halo mass evolved with redshift in the context of "cosmic downsizing".

Predicting the Quasar Photometric Reshift with the Sloan Digital Sky Survey Filter System

NASA Astrophysics Data System (ADS)

Laubacher, Emily M.; York, Donald G.

1999-10-01

Photometric data were obtained for a set of known quasars (QSOs) in five bands with the Sloan Digital Sky Survey (SDSS) filter system for the purpose of testing the ability of the SDSS system to accurately predict the photometric redshift of QSOs. The initial plot of the SDSS photometric redshift versus the measured redshift shows a good relationship, but a lot of scatter. A literature search was conducted on a selected sampling of 49 QSOs, 26 with redshift z <= 0.5 and 23 with 0.5 < z < 2.6, to confirm their accurate identifications as QSOs with their advertised redshifts. This search revealed 10 rejected QSOs which were not QSOs but rather Seyfert galaxies or Narrow Line Objects. Additionally, 11 QSOs were either Broad Absorption Line Systems or had spectra that were in some way incomplete, and therefore, their QSO identification could not be confirmed. The revised plot, with the rejected and unconfirmed QSOs removed, gives an excellent straight line with very little scatter. Although these results are preliminary and for only a small sampling of QSOs, they show that further study of the relationship is warranted and that eventually the SDSS method may be used to accurately predict the photometric redshift of QSOs.

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.

Implications of z ~ 6 Quasar Proximity Zones for the Epoch of Reionization and Quasar Lifetimes

DOE PAGES

Eilers, Anna-Christina; Davies, Frederick B.; Hennawi, Joseph F.; ...

2017-05-02

In this paper, we study quasar proximity zones in the redshift rangemore » $$5.77\\leqslant z\\leqslant 6.54$$ by homogeneously analyzing 34 medium-resolution spectra, encompassing both archival and newly obtained data, and exploiting recently updated systemic redshift and magnitude measurements. Whereas previous studies found strong evolution of proximity zone sizes with redshift and argued that this provides evidence for a rapidly evolving intergalactic medium (IGM) neutral fraction during reionization, we measure a much shallower trend $$\\propto {(1+z)}^{-1.44}$$. We compare our measured proximity zone sizes to predictions from hydrodynamical simulations post-processed with one-dimensional radiative transfer and find good agreement between observations and theory, irrespective of the ionization state of the ambient IGM. This insensitivity to IGM ionization state has been previously noted, and results from the fact that the definition of proximity zone size as the first drop of the smoothed quasar spectrum below the 10% flux transmission level probes locations where the ionizing radiation from the quasar is an order of magnitude larger than the expected ultraviolet ionizing background that sets the neutral fraction of the IGM. Our analysis also uncovered three objects with exceptionally small proximity zones (two have $${R}_{p}\\lt 1$$ proper Mpc), which constitute outliers from the observed distribution and are challenging to explain with our radiative transfer simulations. Finally, we consider various explanations for their origin, such as strong absorption line systems associated with the quasar or patchy reionization, but find that the most compelling scenario is that these quasars have been shining for ≲10 5 years.« less

[Habitus, capital and fields: the search for an acting head of the Hamburg Asylum Friedrichsberg in 1897].

PubMed

Sammet, Kai

2005-01-01

In 1897 Hamburg was in search of an Oberarzt for the asylum Friedrichsberg who should function as the acting head of the head Wilhelm Reye (1833-1912). This search was part of the intended reformation of the outmoded psychiatric care in Hamburg. During this application procedure the Hamburg Physikus John Wahncau examined all possible candidates and applicants. The article explores the election process by using some sociological categories developed by Pierre Bourdieu (habitus, capital, field). The author argues that not only meritocratic attributes led to the choice of one candidate, but also his functional "fitting" into the field in Hamburg.

Spread of Measles Virus D4-Hamburg, Europe, 2008–2011

PubMed Central

Mihneva, Zefira; Gold, Hermann; Baumgarte, Sigrid; Baillot, Armin; Helble, Rudolph; Roggendorf, Hedwig; Bosevska, Golubinka; Nedeljkovic, Jasminka; Makowka, Agata; Hutse, Veronik; Holzmann, Heidemarie; Aberle, Stefan W.; Cordey, Samuel; Necula, Gheorghe; Mentis, Andreas; Korukluoğlu, Gulay; Carr, Michael; Brown, Kevin E.; Hübschen, Judith M.; Muller, Claude P.; Mulders, Mick N.; Santibanez, Sabine

2011-01-01

A new strain of measles virus, D4-Hamburg, was imported from London to Hamburg in December 2008 and subsequently spread to Bulgaria, where an outbreak of >24,300 cases was observed. We analyzed spread of the virus to demonstrate the importance of addressing hard-to-reach communities within the World Health Organization European Region regarding access to medical care and vaccination campaigns. The D4-Hamburg strain appeared during 2009–2011 in Poland, Ireland, Northern Ireland, Austria, Greece, Romania, Turkey, Macedonia, Serbia, Switzerland, and Belgium and was repeatedly reimported to Germany. The strain was present in Europe for >27 months and led to >25,000 cases in 12 countries. Spread of the virus was prevalently but not exclusively associated with travel by persons in the Roma ethnic group; because this travel extends beyond the borders of any European country, measures to prevent the spread of measles should be implemented by the region as a whole. PMID:21801615

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hainline, Kevin N.; Hickox, Ryan C.; Carroll, Christopher M.

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 thatmore » 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.« less

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.;

The SCUBA-2 850 μm Follow-up of WISE-selected, Luminous Dust-obscured Quasars

NASA Astrophysics Data System (ADS)

Fan, Lulu; Jones, Suzy F.; Han, Yunkun; Knudsen, Kirsten K.

2017-12-01

Hot dust-obscured galaxies (Hot DOGs) are a new population recently discovered in the Wide-field Infrared Survey Explorer All-Sky survey. Multiwavelength follow-up observations suggest that they are luminous, dust-obscured quasars at high redshift. Here we present the JCMT SCUBA-2 850 μm follow-up observations of 10 Hot DOGs. Four out of ten Hot DOGs have been detected at >3σ level. Based on the IR SED decomposition approach, we derive the IR luminosities of AGN torus and cold dust components. Hot DOGs in our sample are extremely luminous with most of them having {L}{IR}{tot}> {10}14 {L}⊙ . The torus emissions dominate the total IR energy output. However, the cold dust contribution is still non-negligible, with the fraction of the cold dust contribution to the total IR luminosity (˜8%-24%) being dependent on the choice of torus model. The derived cold dust temperatures in Hot DOGs are comparable to those in UV bright quasars with similar IR luminosity, but much higher than those in SMGs. Higher dust temperatures in Hot DOGs may be due to the more intense radiation field caused by intense starburst and obscured AGN activities. Fourteen and five submillimeter serendipitous sources in the 10 SCUBA-2 fields around Hot DOGs have been detected at >3σ and >3.5σ levels, respectively. By estimating their cumulative number counts, we confirm the previous argument that Hot DOGs lie in dense environments. Our results support the scenario in which Hot DOGs are luminous, dust-obscured quasars lying in dense environments, and being in the transition phase between extreme starburst and UV-bright quasars.

High-z X-ray Obscured Quasars in Galaxies with Extreme Mid-IR/Optical Colors

NASA Astrophysics Data System (ADS)

Piconcelli, E.; Lanzuisi, G.; Fiore, F.; Feruglio, C.; Vignali, C.; Salvato, M.; Grappioni, C.

2009-05-01

Extreme Optical/Mid-IR color cuts have been used to uncover a population of dust-enshrouded, mid-IR luminous galaxies at high redshifts. Several lines of evidence point towards the presence of an heavily absorbed, possibly Compton-thick quasar at the heart of these systems. Nonetheless, the X-ray spectral properties of these intriguing sources still remain largely unexplored. Here we present an X-ray spectroscopic study of a large sample of 44 extreme dust-obscured galaxies (EDOGs) with F24 μm/FR>2000 and F24 μm>1.3 mJy selected from a 6 deg2 region in the SWIRE fields. The application of our selection criteria to a wide area survey has been capable of unveiling a population of X-ray luminous, absorbed z>1 quasars which is mostly missed in the traditional optical/X-ray surveys performed so far. Advances in the understanding of the X-ray properties of these recently-discovered sources by Simbol-X observations will be also discussed.

Measuring the ISM Content of Optically Luminous Type 2 Quasars

NASA Astrophysics Data System (ADS)

Marshall, Jameeka; Petric, Andreea; Flagey, Nicolas; Lacy, Mark; Omont, Alain

2018-01-01

There is a connection between black holes (BH) and the surrounding bulge stars. Measuring the cold interstellar medium (ISM) content of host galaxies is essential to understand the coevolution of galaxies and BHs. The ISM measurement is important because gas constitutes the raw material from which BHs grow and stars form. Quasars are extremely luminous active galaxies fueled by accreting supermassive black holes. Type 2 quasars have narrow spectral lines whereas type 1 quasars have broad spectral lines. Not only can the ISM measurements provide empirical data to help further clarify quasar models but it is also crucial in distinguishing the physical differences between type 1 and type 2 quasars. Observations of twenty type 2 quasars were made using IRAM, a single dish 30 meter radio telescope, to measure 12CO (1-0) and 12CO (2-1) emission. We used line widths to constrain the dynamical mass and gravitational potential of the host galaxy. Star formation rate (SFR) measured in the infrared (IR) and SFR derived from optical spectra were used to estimate star formation efficiency and gas depletion time scale (M H2/star formation rate). Preliminary analysis suggests that star formation efficiency in type 2 quasars is slightly higher than in type 1 quasars.

GREEN BANK TELESCOPE DETECTION OF POLARIZATION-DEPENDENT H I ABSORPTION AND H I OUTFLOWS IN LOCAL ULIRGs AND QUASARS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Teng, Stacy H.; Veilleux, Sylvain; Baker, Andrew J., E-mail: stacy.h.teng@nasa.gov

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%)more » 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.« less

IRAS observations of radio-quiet and radio-loud quasars

NASA Technical Reports Server (NTRS)

Neugebauer, G.; Soifer, B. T.; Miley, G.; Habing, H. J.; Young, E.; Low, F. J.; Beichman, C. A.; Clegg, P. E.; Harris, S.; Rowan-Robinson, M.

1984-01-01

Observations from 12 to 100 microns are presented of two radio-quiet and three radio-loud quasars. Over this wavelength range, all five have grossly similar continuum energy distributions. The continua of the radio-loud quasars are consistent with synchrotron radiation. There is an indication, however, of excess 100 micron emission in the two radio-quiet quasars.

QUASAR PG1115+080 AND GRAVITATIONAL LENS

NASA Technical Reports Server (NTRS)

2002-01-01

Left: The light from the single quasar PG 1115+080 is split and distorted in this infrared image. PG 1115+080 is at a distance of about 8 billion light years in the constellation Leo, and it is viewed through an elliptical galaxy lens at a distance of 3 billion light years. The NICMOS frame is taken at a wavelength of 1.6 microns and it shows the four images of the quasar (the two on the left are nearly merging) surrounding the galaxy that causes the light to be lensed. The quasar is a variable light source and the light in each image travels a different path to reach the Earth. The time delay of the variations allows the distance scale to be measured directly. The linear streaks on the image are diffraction artifacts in the NICMOS instrument (NASA/Space Telescope Science Institute). Right: In this NICMOS image, the four quasar images and the lens galaxy have been subtracted, revealing a nearly complete ring of infrared light. This ring is the stretched and amplified starlight of the galaxy that contains the quasar, some 8 billion light years away. (NASA/Space Telescope Science Institute). Credit: Christopher D. Impey (University of Arizona)

Characterizing the WISE-selected heavily obscured quasar population with optical spectroscopy from the Southern African Large Telescope

NASA Astrophysics Data System (ADS)

Hviding, Raphael E.; Hickox, Ryan C.; Hainline, Kevin N.; Carroll, Christopher M.; DiPompeo, Michael A.; Yan, Wei; Jones, Mackenzie L.

2018-02-01

We present the results of an optical spectroscopic survey of 46 heavily obscured quasar candidates. Objects are selected using their mid-infrared (mid-IR) colours and magnitudes from the Wide-Field Infrared Survey Explorer (WISE) anzd their optical magnitudes from the Sloan Digital Sky Survey. Candidate Active Galactic Nuclei (AGNs) are selected to have mid-IR colours indicative of quasar activity and lie in a region of mid-IR colour space outside previously published X-ray based selection regions. We obtain optical spectra for our sample using the Robert Stobie Spectrograph on the Southern African Large Telescope. 30 objects (65 per cent) have identifiable emission lines, allowing for the determination of spectroscopic redshifts. Other than one object at z ˜ 2.6, candidates have moderate redshifts ranging from z = 0.1 to 0.8 with a median of 0.3. 21 (70 per cent) of our objects with identified redshift (46 per cent of the whole sample) are identified as AGNs through common optical diagnostics. We model the spectral energy distributions of our sample and found that all require a strong AGN component, with an average intrinsic AGN fraction at 8 μm of 0.91. Additionally, the fits require large extinction coefficients with an average E(B - V)AGN = 17.8 (average A(V)AGN = 53.4). By focusing on the area outside traditional mid-IR photometric cuts, we are able to capture and characterize a population of deeply buried quasars that were previously unattainable through X-ray surveys alone.

HUBBLE'S 100,000TH EXPOSURE CAPTURES IMAGE OF DISTANT QUASAR

NASA Technical Reports Server (NTRS)

2002-01-01

The Hubble Space Telescope achieved its 100,000th exposure June 22 with a snapshot of a quasar that is about 9 billion light-years from Earth. The Wide Field and Planetary Camera 2 clicked this image of the quasar, the bright object in the center of the photo. The fainter object just above it is an elliptical galaxy. Although the two objects appear to be close to each other, they are actually separated by about 2 billion light-years. Located about 7 billion light-years away, the galaxy is almost directly in front of the quasar. Astronomer Charles Steidel of the California Institute of Technology in Pasadena, Calif., indirectly discovered the galaxy when he examined the quasar's light, which contained information about the galaxy's chemical composition. The reason, Steidel found, was that the galaxy was absorbing the light at certain frequencies. The astronomer is examining other background quasars to determine which kinds of galaxies absorb light at the same frequencies. Steidel also was somewhat surprised to discover that the galaxy is an elliptical, rather than a spiral. Elliptical galaxies are generally believed to contain very little gas. However, this elliptical has a gaseous 'halo' and contains no visible stars. Part of the halo is directly in front of the quasar. The bright object to the right of the quasar is a foreground star. The quasar and star are separated by billions of light-years. The quasar looks as bright as the star because it produces a tremendous amount of light from a compact source. The 'disturbed-looking' double spiral galaxy above the quasar also is in the foreground. Credit: Charles Steidel (California Institute of Technology, Pasadena, CA) and NASA. Image files in GIF and JPEG format and captions may be accessed on Internet via anonymous ftp from ftp.stsci.edu in /pubinfo.

X-ray studies of quasars with the Einstein Observatory. II

NASA Technical Reports Server (NTRS)

Zamorani, G.; Maccacaro, T.; Henry, J. P.; Tananbaum, H.; Soltan, A.; Liebert, J.; Stocke, J.; Strittmatter, P. A.; Weymann, R. J.; Smith, M. G.

1981-01-01

X-ray observations of 107 quasars have been carried out with the Einstein Observatory, and 79 have been detected. A correlation between optical emission and X-ray emission is found; and for radio-loud quasars, the data show a correlation between radio emission and X-ray emission. For a given optical luminosity, the average X-ray emission of radio-loud quasars is about three times higher than that of radio-quiet quasars. The data also suggest that the ratio of X-ray to optical luminosity is decreasing with increasing redshift and/or optical luminosity. The data support the picture in which luminosity evolution, rather than pure density evolution, describes the quasar behavior as a function of redshift.

Quasar 2175 Å dust absorbers - I. Metallicity, depletion pattern and kinematics

NASA Astrophysics Data System (ADS)

Ma, Jingzhe; Ge, Jian; Zhao, Yinan; Prochaska, J. Xavier; Zhang, Shaohua; Ji, Tuo; Schneider, Donald P.

2017-12-01

We present 13 new 2175 Å dust absorbers at zabs = 1.0-2.2 towards background quasars from the Sloan Digital Sky Survey. These absorbers are examined in detail using data from the Echelle Spectrograph and Imager (ESI) on the Keck II telescope. Many low-ionization lines including Fe II, Zn II, Mg II, Si II, Al II, Ni II, Mn II, Cr II, Ti II and Ca II are present in the same absorber that gives rise to the 2175 Å bump. The relative metal abundances (with respect to Zn) demonstrate that the depletion patterns of our 2175 Å dust absorbers resemble that of the Milky Way clouds although some are disc-like and some are halo-like. The 2175 Å dust absorbers have significantly higher depletion levels compared to literature damped Lyman α absorbers (DLAs) and sub-DLAs. The dust depletion level indicator [Fe/Zn] tends to anticorrelate with bump strengths. The velocity profiles from the Keck/ESI spectra also provide kinematical information on the dust absorbers. The dust absorbers are found to have multiple velocity components with velocity widths extending from ∼100 to ∼600 km s-1, which are larger than those of most DLAs and sub-DLAs. Assuming the velocity width is a reliable tracer of stellar mass, the host galaxies of 2175 Å dust absorbers are expected to be more massive than DLA/sub-DLA hosts. Not all of the 2175 Å dust absorbers are intervening systems towards background quasars. The absorbers towards quasars J1006+1538 and J1047+3423 are proximate systems that could be associated with the quasar itself or the host galaxy.

Compton scattering of the microwave background by quasar-blown bubbles

NASA Technical Reports Server (NTRS)

Voit, G. Mark

1994-01-01

At least 10% of quasars drive rapid outflows from the central regions of their host galaxies. The mass and energy flow rates in these winds are difficult to measure, but their kinetic luminosities probably exceed 10(exp 45) ergs/s. This kind of outflow easily sunders the interstellar medium of the host and blows a bubble in the intergalactic medium. After the quasar shuts off, the hot bubble continues to shock intergalactic gas until its leading edge merges with the Hubble flow. The interior hot gas Compton scatters microwave background photons, potentially providing a way to detect these bubbles. Assuming that quasar kinetic luminosities scale with their blue luminosities, we integrate over the quasar luminosity function to find the total distortion (y) of the microwave background produced by the entire population of quasar wind bubbles. This calculation of y distortion is remarkably insensitive to the properties of the intergalactic medium (IGM), quasar lifetimes, and cosmological parameters. Current Cosmic Background Explorer (COBE) limits on y constrain the kinetic luminosities of quasars to be less than several times their bolometric radiative luminosities. Within this constraint, quasars can still expel enough kinetic luminosity to shock the entire IGM by z = 0, but cannot heat and ionize the IGM by z = 4 unless omega(sub IGM) much less than 10(exp -2).

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

The Hamburger War. Instructor's Guide [and] Student Materials. Business Issues in the Classroom. Revised.

ERIC Educational Resources Information Center

Maxey, Phyllis F.; Meier, Stephen C.

One of a series of units on business issues for high school students, this packet uses the example of hamburger wars ("price wars" between hamburger stands) to introduce students to the ways in which businesses operate in a competitive environment. A teacher's guide and student materials are provided in two separate sections. Following…

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.

The Spectral and Environment Properties of z ∼ 2.0–2.5 Quasar Pairs

NASA Astrophysics Data System (ADS)

Lusso, Elisabeta; Fumagalli, Michele; Rafelski, Marc; Neeleman, Marcel; Prochaska, Jason X.; Hennawi, Joseph F.; O’Meara, John M.; Theuns, Tom

2018-06-01

We present the first results from our survey of intervening and proximate Lyman limit systems (LLSs) at z ∼ 2.0–2.5 using the Wide Field Camera 3 on board the Hubble Space Telescope. The quasars in our sample are projected pairs with proper transverse separations R ⊥ ≤ 150 kpc and line-of-sight velocity separations ≲11,000 km s‑1. We construct a stacked ultraviolet (rest-frame wavelengths 700–2000 Å) spectrum of pairs corrected for the intervening Lyman forest and Lyman continuum absorption. The observed spectral composite presents a moderate flux excess for the most prominent broad emission lines, a ∼30% decrease in flux at λ = 800–900 Å compared to a stack of brighter quasars not in pairs at similar redshifts, and lower values of the mean free path of the H I ionizing radiation for pairs ({λ }mfp}912 = 140.7 ± 20.2 {h}70-1 Mpc) compared to single quasars ({λ }mfp}912 = 213.8 ± 28 {h}70-1 Mpc) at the average redshift z ≃ 2.44. From the modeling of LLS absorption in these pairs, we find a higher (∼20%) incidence of proximate LLSs with log {N}{{H}{{I}}} ≥ 17.2 at δv < 5000 km s‑1 compared to single quasars (∼6%). These two rates are different at the 5σ level. Moreover, we find that optically thick absorbers are equally shared between foreground and background quasars. Based on these pieces of evidence, we conclude that there is a moderate excess of gas-absorbing Lyman continuum photons in our closely projected quasar pairs compared to single quasars. We argue that this gas arises mostly within large-scale structures or partially neutral regions inside the dark matter halos where these close pairs reside.

X-RAYS FROM A RADIO-LOUD COMPACT BROAD ABSORPTION LINE QUASAR 1045+352 AND THE NATURE OF OUTFLOWS IN RADIO-LOUD BROAD ABSORPTION LINE QUASARS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kunert-Bajraszewska, Magdalena; Katarzynski, Krzysztof; Siemiginowska, Aneta

2009-11-10

We present new results on X-ray properties of radio-loud broad absorption line (BAL) quasars and focus on broadband spectral properties of a high-ionization BAL (HiBAL) compact steep spectrum (CSS) radio-loud quasar 1045+352. This HiBAL quasar has a very complex radio morphology indicating either strong interactions between a radio jet and the surrounding interstellar medium or a possible re-start of the jet activity. We detected 1045+352 quasar in a short 5 ksec Chandra ACIS-S observation. We applied theoretical models to explain spectral energy distribution of 1045+352 and argue that non-thermal, inverse-Compton (IC) emission from the innermost parts of the radio jetmore » can account for a large fraction of the observed X-ray emission. In our analysis, we also consider a scenario in which the observed X-ray emission from radio-loud BAL quasars can be a sum of IC jet X-ray emission and optically thin corona X-ray emission. We compiled a sample of radio-loud BAL quasars that were observed in X-rays to date and report no correlation between their X-ray and radio luminosity. However, the radio-loud BAL quasars show a large range of X-ray luminosities and absorption columns. This is consistent with the results obtained earlier for radio-quiet BAL quasars and may indicate an orientation effect in BAL quasars or more complex dependence between X-ray emission, radio emission, and an orientation based on the radio morphology.« less

An annotated type catalogue of the camel spiders (Arachnida: Solifugae) held in the Zoological Museum Hamburg.

PubMed

Harms, Danilo; DupÉrrÉ, Nadine

2018-01-23

Solifuges are an enigmatic and poorly studied group of arachnids. Commonly referred to as camel spiders or sun spiders, these animals are voracious predators of small animals and found in arid biomes of the Old World and the Americas. In this paper, we provide a catalogue for the solifuges (Arachnida: Solifugae) that are held at the Center of Natural History in Hamburg. The collections in Hamburg are predominantly historical and were accumulated by Karl Kraepelin between 1889 and 1914 with the help of other famous arachnologists such as Ferdinant Karsch and Eugène Simon. The re-study of these collections indicates that there are 38 type species and 65 type specimens from 10 families. We provide a detailed account of this material, including collection data, taxonomic updates, measurements and high-resolution images for species that are either poorly or not at all illustrated. Most specimens (70%) were collected in Africa as part of colonial expeditions or field surveys but there are also types from Western Asia (11%), and North and South America (19%). We provide an overview of the history of this collection, including a summary of the field surveys during which the specimens were collected and the arachnologists who described the material. Overall, this is the third-largest collection of solifuges in Germany with a distinct biogeographical focus and one of the largest collections of camel spiders in Europe.

Magnification of light from many distant quasars by gravitational lenses.

PubMed

Wyithe, J Stuart B; Loeb, Abraham

2002-06-27

Exceptionally bright quasars with redshifts up to z = 6.28 have recently been discovered. Quasars are thought to be powered by the accretion of gas onto supermassive black holes at the centres of galaxies. Their maximum (Eddington) luminosity depends on the mass of the black hole, and the brighter quasars are inferred to have black holes with masses of more than a few billion solar masses. The existence of such massive black holes poses a challenge to models for the formation of structures in the early Universe, as it requires their formation within one billion years of the Big Bang. Here we show that up to one-third of known quasars with z approximately equal to 6 will have had their observed flux magnified by a factor of ten or more, as a consequence of gravitational lensing by galaxies along the line of sight. The inferred abundance of quasar host galaxies, as well as the luminosity density provided by the quasars, has therefore been substantially overestimated.

Near-IR Spectroscopy of Luminous LoBAL Quasars at 1 < z < 2.5

NASA Astrophysics Data System (ADS)

Schulze, Andreas; Schramm, Malte; Zuo, Wenwen; Wu, Xue-Bing; Urrutia, Tanya; Kotilainen, Jari; Reynolds, Thomas; Terao, Koki; Nagao, Tohru; Izumiura, Hideyuki

2017-10-01

We present near-IR spectroscopy of 22 luminous low-ionization broad absorption line quasars (LoBAL QSOs) at redshift 1.3< z< 2.5, with 12 objects at z ˜ 1.5 and 10 at z ˜ 2.3. The spectra cover the rest-frame Hα and Hβ line regions, allowing us to obtain robust black hole mass estimates based on the broad Hα line. We use these data, augmented by a lower-redshift sample from the Sloan Digital Sky Survey, to test the proposed youth scenario for LoBALs, which suggests that LoBALs constitute an early short-lived evolutionary stage of quasar activity, by probing for any difference in their masses, Eddington ratios, or rest-frame optical spectroscopic properties compared to normal quasars. In addition, we construct the UV to mid-IR spectral energy distributions (SEDs) for the LoBAL sample and a matched non-BAL quasar sample. We do not find any statistically significant difference between LoBAL QSOs and non-BAL QSOs in their black hole mass or Eddington ratio distributions. The mean UV to mid-IR SED of the LoBAL QSOs is consistent with non-BAL QSOs, apart from their stronger reddening. At z> 1 there is no clear difference in their optical emission line properties. We do not see particularly weak [O III] or strong Fe II emission. The LoBAL QSOs do not show a stronger prevalence of ionized gas outflows as traced by the [O III] line, compared to normal QSOs of similar luminosity. We conclude that the optical-MIR properties of LoBAL QSOs are consistent with the general quasar population and do not support them to constitute a special phase of active galactic nucleus evolution.

Inspiraling halo accretion mapped in Ly α emission around a z ˜ 3 quasar

NASA Astrophysics Data System (ADS)

Arrigoni Battaia, Fabrizio; Prochaska, J. Xavier; Hennawi, Joseph F.; Obreja, Aura; Buck, Tobias; Cantalupo, Sebastiano; Dutton, Aaron A.; Macciò, Andrea V.

2018-01-01

In an effort to search for Ly α emission from circum- and intergalactic gas on scales of hundreds of kpc around z ∼ 3 quasars, and thus characterize the physical properties of the gas in emission, we have initiated an extensive fast survey with the Multi-Unit Spectroscopic Explorer (MUSE): Quasar Snapshot Observations with MUse: Search for Extended Ultraviolet eMission (QSO MUSEUM). In this work, we report the discovery of an enormous Ly α nebula (ELAN) around the quasar SDSS J102009.99+104002.7 at z = 3.164, which we followed-up with deeper MUSE observations. This ELAN spans ∼297 projected kpc, has an average Ly α surface brightness SBLy α ∼ 6.04 × 10-18 erg s-1 cm-2 arcsec-2(within the 2σ isophote) and is associated with an additional four previously unknown embedded sources: two Ly α emitters and two faint active galactic nuclei (one type-1 and one type-2 quasar). By mapping at high significance, the line-of-sight velocity in the entirety of the observed structure, we unveiled a large-scale coherent rotation-like pattern spanning ∼300 km s-1 with a velocity dispersion of <270 km s-1, which we interpret as a signature of the inspiraling accretion of substructures within the quasar's host halo. Future multiwavelength data will complement our MUSE observations and are definitely needed to fully characterize such a complex system. None the less, our observations reveal the potential of new sensitive integral-field spectrographs to characterize the dynamical state of diffuse gas on large scales in the young Universe, and thereby witness the assembly of galaxies.

Nearby Quasars Result From Galactic Encounters, VLA Studies Indicate

NASA Astrophysics Data System (ADS)

1998-12-01

Astronomers using the National Science Foundation's Very Large Array (VLA) radio telescope have found previously unseen evidence that galaxy collisions trigger energetic quasar activity in relatively nearby galaxies. New radio images of galaxies with bright quasar cores show that, though the galaxies appear normal in visible-light images, their gas has been disrupted by encounters with other galaxies. "This is what theorists have believed for years, but even the best images from optical telescopes, including the Hubble Space Telescope, failed to show any direct evidence of interactions with other galaxies in many cases," said Jeremy Lim, of the Academia Sinica Institute of Astronomy & Astrophysics in Taipei, Taiwan. Lim, along with Paul Ho of the Harvard-Smithsonian Center for Astrophysics in Cambridge, MA, reported their findings in the January 1 issue of Astrophysical Journal Letters. Quasars are among the most luminous objects in the universe, and generally are believed to be powered by material being drawn into a supermassive black hole at the center of a galaxy, releasing large amounts of energy. Many quasars are found at extremely great distances from Earth, billions of light-years away. Because the light from these quasars took billions of years to reach our telescopes, we see them as they were when they were much younger objects. These distant quasars are thought to "turn on" when the host galaxy's central black hole is "fueled" by material drawn in during an early stage of the galaxy's development, before the galaxy "settles down" to a more sedate life. However, other galaxies with quasar cores are much closer, and thus are older, more mature galaxies. Their quasar activity has been attributed to encounters with nearby galaxies -- encounters that disrupt material and provide new "fuel" to the black hole. The problem for this scenario was the lack of evidence for such galactic encounters in optical images of many nearby quasars. "Our VLA studies are the

The kinetically dominated quasar 3C 418

NASA Astrophysics Data System (ADS)

Punsly, Brian; Kharb, Preeti

2017-06-01

The existence of quasars that are kinetically dominated, where the jet kinetic luminosity, Q, is larger than the total (infrared to X-ray) thermal luminosity of the accretion flow, Lbol, provides a strong constraint on the fundamental physics of relativistic jet formation. Since quasars have high values of Lbol by definition, only ˜10 kinetically dominated quasars (with \\overline{Q}/L_{bol}>1) have been found, where \\overline{Q} is the long-term time-averaged jet power. We use low-frequency (151 MHz-1.66 GHz) observations of the quasar 3C 418 to determine \\overline{Q}≈ 5.5 ± 1.3 × 10^{46} {erg s^{-1}}. Analysis of the rest-frame ultraviolet spectrum indicates that this equates to 0.57 ± 0.28 times the Eddington luminosity of the central supermassive black hole and \\overline{Q}/L_{bol} ≈ 4.8 ± 3.1, making 3C 418 one of the most kinetically dominated quasars found to date. It is shown that this maximal \\overline{Q}/L_{bol} is consistent with models of magnetically arrested accretion of jet production in which the jet production reproduces the observed trend of a decrement in the extreme ultraviolet continuum as the jet power increases. This maximal condition corresponds to an almost complete saturation of the inner accretion flow with vertical large-scale magnetic flux (maximum saturation).

Quasar-mode Feedback in Nearby Type 1 Quasars: Ubiquitous Kiloparsec-scale Outflows and Correlations with Black Hole Properties

NASA Astrophysics Data System (ADS)

Rupke, David S. N.; Gültekin, Kayhan; Veilleux, Sylvain

2017-11-01

The prevalence and properties of kiloparsec-scale outflows in nearby Type 1 quasars have been the subject of little previous attention. This work presents Gemini integral field spectroscopy of 10 Type 1 radio-quiet quasars at z< 0.3. The excellent image quality, coupled with a new technique to remove the point-spread function using spectral information, allows the fitting of the underlying host on a spaxel-by-spaxel basis. Fits to stars, line-emitting gas, and interstellar absorption show that 100% of the sample hosts warm ionized and/or cool neutral outflows with spatially averaged velocities (< {v}98 % > \\equiv < v+2σ > ) of 200-1300 {km} {{{s}}}-1 and peak velocities (maximum {v}98 % ) of 500-2600 {km} {{{s}}}-1. These minor-axis outflows are powered primarily by the central active galactic nucleus, reach scales of 3-12 kpc, and often fill the field of view. Including molecular data and Type 2 quasar measurements, nearby quasars show a wide range in mass outflow rates ({dM}/{dt}=1 to > 1000 {M}⊙ {{yr}}-1) and momentum boosts [(c {dp}/{dt})/{L}{AGN}=0.01{--}20]. After extending the mass scale to Seyferts, dM/dt and dE/dt correlate with black hole mass ({dM}/{dt}˜ {M}{BH}0.7+/- 0.3 and {dE}/{dt}˜ {M}{BH}1.3+/- 0.5). Thus, the most massive black holes in the local universe power the most massive and energetic quasar-mode winds.

A Wealth of Dust Grains in Quasar Winds

NASA Technical Reports Server (NTRS)

2007-01-01

[figure removed for brevity, see original site] Click on image for larger poster version

This plot of data captured by NASA's Spitzer Space Telescope reveals dust entrained in the winds rushing away from a quasar, or growing black hole. The quasar, called PG2112+059, is located deep inside a galaxy 8 billion light-years away. Astronomers believe the dust might have been forged in the winds, which would help explain where dust in the very early universe came from.

The data were captured by Spitzer's infrared spectrograph, an instrument that splits apart light from the quasar into a spectrum that reveals telltale signs of different minerals. Each type of mineral, or dust grain, has a unique signature, as can be seen in the graph, or spectrum, above.

The strongest features are from the mineral amorphous olivine, or glass (purple); the mineral forsterite found in sand (blue); and the mineral corundum found in rubies (light blue). The detection of forsterite and corundum is highly unusual in galaxies without quasars. Therefore, their presence is a key clue that these grains might have been created in the quasar winds and not by dying stars as they are in our Milky Way galaxy. Forsterite is destroyed quickly in normal galaxies by radiation, so it must be continually produced to be detected by Spitzer.

Corundum is hard, and provides a seed that softer, more common minerals usually cover up. As a result, corundum is usually not seen in spectra of galaxies. Since Spitzer did detect the mineral, it is probably forming in a clumpy environment, which is expected in quasar winds. All together, the signatures of the unusual minerals in this spectrum point towards dust grains forming in the winds blowing away from quasars.

First neutral atomic hydrogen images of quasar host galaxies.

NASA Astrophysics Data System (ADS)

Lim, J.; Ho, P. T. P.

1999-12-01

Violent galactic encounters or mergers are the leading contenders for triggering luminous quasar activity at low redshifts: such interactions can lead to the concentration of gas in the host galactic nucleus, thus fueling the suspected central supermassive black hole. Here the authors image quasar host galaxies in the redshifted 21-cm line emission of neutral atomic hydrogen (H I) gas, which in nearby galaxies has proven to be a particularly sensitive as well as enduring tracer of tidal interactions. The three quasars studied have different optical environments normally seen around low-redshift quasars, ranging from a perhaps mildly interacting system to a relatively undisturbed host with a projected neighbouring galaxy to an isolated and apparently serene host galaxy. By contrast with their optical appearences, all three quasar host galaxies exhibit ongoing or remnant tidal H I disruptions tracing galactic encounters or mergers. These observations provide a better understanding of the likely stage of their interaction.

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.

VizieR Online Data Catalog: ROSAT detected quasars. I. (Brinkmann+ 1997)

NASA Astrophysics Data System (ADS)

Brinkmann, W.; Yuan, W.

1996-09-01

We have compiled a sample of all quasars with measured radio emission from the Veron-Cetty - Veron catalogue (1993, VV93 ) detected by ROSAT in the ALL-SKY SURVEY (RASS, Voges 1992), as targets of pointed observations, or as serendipitous sources from pointed observations as publicly available from the ROSAT point source catalogue (ROSAT-SRC, Voges et al. 1995). The total number of ROSAT detected radio quasars from the above three sources is 654 objects. 69 of the objects are classified as radio-quiet using the defining line at a radio-loudness of 1.0, and 10 objects have no classification. The 5GHz data are from the 87GB radio survey, the NED database, or from the Veron-Cetty - Veron catalogue. The power law indices and their errors are estimated from the two hardness ratios given by the SASS assuming Galactic absorption. The X-ray flux densities in the ROSAT band (0.1-2.4keV) are calculated from the count rates using the energy to counts conversion factor for power law spectra and Galactic absorption. For the photon index we use the value obtained for a individual source if the estimated 1 sigma error is smaller than 0.5, otherwise we use the mean value 2.14. (1 data file).

A search for quasars in the Virgo cluster region

NASA Technical Reports Server (NTRS)

He, X.-T.; Cannon, R. D.; Peacock, J. A.; Smith, M. G.; Oke, J. B.

1984-01-01

Using objective-prism plates taken with the 44-arcmin objective prism mounted on the UK Schmidt telescope, 53 emission-line quasar candidates and 29 ultraviolet-excess objects (possible low-redshift quasars) have been found in a 5 x 5-degree field centered on 12 h 27 m, + 13 deg 30 min (1950) in the Virgo cluster of galaxies. Eighteen of these 82 candidates were observed using the double spectrograph on the Palomar 5-meter telescope; 13 of the observed objects proved to be quasars. The broad-absorption-line QSO Q1232 + 134 is the first example of the class to show broad low-ionization absorption lines (such as Mg II 2798 A) in addition to the usual high-excitation lines such as Nv 1240 A. Although no conclusive evidence for quasar-galaxy associations is found in this field, there do exist nonuniformities in the distribution of the quasar candidates which may merit further investigation. These objects will provide a useful network of probes for absorbing material in the Virgo cluster. The lines-of-sight to two of the confirmed quasars pass very close to NGC galaxies; the respective projected QSO-galaxy separations are only 4 and 11 kpc at the assumed distance of the Virgo cluster.

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.

Probing Extragalactic Planets Using Quasar Microlensing

NASA Astrophysics Data System (ADS)

Dai, Xinyu; Guerras, Eduardo

2018-02-01

Previously, planets have been detected only in the Milky Way galaxy. Here, we show that quasar microlensing provides a means to probe extragalactic planets in the lens galaxy, by studying the microlensing properties of emission close to the event horizon of the supermassive black hole of the background quasar, using the current generation telescopes. We show that a population of unbound planets between stars with masses ranging from Moon to Jupiter masses is needed to explain the frequent Fe Kα line energy shifts observed in the gravitationally lensed quasar RXJ 1131–1231 at a lens redshift of z = 0.295 or 3.8 billion lt-yr away. We constrain the planet mass-fraction to be larger than 0.0001 of the halo mass, which is equivalent to 2000 objects ranging from Moon to Jupiter mass per main-sequence star.

A 14 h {sup −3} Gpc{sup 3} study of cosmic homogeneity using BOSS DR12 quasar sample

DOE Office of Scientific and Technical Information (OSTI.GOV)

Laurent, Pierre; Goff, Jean-Marc Le; Burtin, Etienne

2016-11-01

The BOSS quasar sample is used to study cosmic homogeneity with a 3D survey in the redshift range 2.2 < z < 2.8. We measure the count-in-sphere, N (< r ), i.e. the average number of objects around a given object, and its logarithmic derivative, the fractal correlation dimension, D {sub 2}( r ). For a homogeneous distribution N (< r ) ∝ r {sup 3} and D {sub 2}( r ) = 3. Due to the uncertainty on tracer density evolution, 3D surveys can only probe homogeneity up to a redshift dependence, i.e. they probe so-called ''spatial isotropy'. Ourmore » data demonstrate spatial isotropy of the quasar distribution in the redshift range 2.2 < z < 2.8 in a model-independent way, independent of any FLRW fiducial cosmology, resulting in 3 − ( D {sub 2}) < 1.7 × 10{sup −3} (2 σ) over the range 250 < r < 1200 h {sup −1} Mpc for the quasar distribution. If we assume that quasars do not have a bias much less than unity, this implies spatial isotropy of the matter distribution on large scales. Then, combining with the Copernican principle, we finally get homogeneity of the matter distribution on large scales. Alternatively, using a flat ΛCDM fiducial cosmology with CMB-derived parameters, and measuring the quasar bias relative to this ΛCDM model, our data provide a consistency check of the model, in terms of how homogeneous the Universe is on different scales. D {sub 2}( r ) is found to be compatible with our ΛCDM model on the whole 10 < r < 1200 h {sup −1} Mpc range. For the matter distribution we obtain 3 − ( D {sub 2}) < 5 × 10{sup −5} (2 σ) over the range 250 < r < 1200 h {sup −1} Mpc, consistent with homogeneity on large scales.« less

An Archival Chandra and XMM-Newton Survey of Type 2 Quasars

NASA Technical Reports Server (NTRS)

Jia, Jianjun; Ptak, Andrew Francis; Heckman, Timothy; Zakamska, Nadia L.

2013-01-01

In order to investigate obscuration in high-luminosity type 2 active galactic nuclei (AGNs), we analyzed Chandra and XMM-Newton archival observations for 71 type 2 quasars detected at 0.05 < z < 0.73, which were selected based on their [O III] lambda5007 emission lines. For 54 objects with good spectral fits, the observed hard X-ray luminosity ranges from 2 × 10(exp 41) to 5.3 × 10(exp 44) erg s(exp -1), with a median of 1.1 × 10(exp 43) erg s(exp -1). We find that the means of the column density and photon index of our sample are log N(sub H) = 22.9 cm(exp -2) and gamma = 1.87, respectively. From simulations using a more physically realistic model, we find that the absorbing column density estimates based on simple power-law models significantly underestimate the actual absorption in approximately half of the sources. Eleven sources show a prominent Fe K alpha emission line (EW>100 eV in the rest frame) and we detect this line in the other sources through a joint fit (spectral stacking). The correlation between the Fe K alpha and [O III] fluxes and the inverse correlation of the equivalent width of the Fe Ka line with the ratio of hard X-ray and [O III] fluxes is consistent with previous results for lower luminosity Seyfert 2 galaxies. We conclude that obscuration is the cause of the weak hard X-ray emission rather than intrinsically low X-ray luminosities. We find that about half of the population of optically selected type 2 quasars are likely to be Compton thick. We also find no evidence that the amount of X-ray obscuration depends on the AGN luminosity (over a range of more than three orders of magnitude in luminosity).

A large sample of Kohonen-selected SDSS quasars with weak emission lines: selection effects and statistical properties

NASA Astrophysics Data System (ADS)

Meusinger, H.; Balafkan, N.

2014-08-01

Aims: A tiny fraction of the quasar population shows remarkably weak emission lines. Several hypotheses have been developed, but the weak line quasar (WLQ) phenomenon still remains puzzling. The aim of this study was to create a sizeable sample of WLQs and WLQ-like objects and to evaluate various properties of this sample. Methods: We performed a search for WLQs in the spectroscopic data from the Sloan Digital Sky Survey Data Release 7 based on Kohonen self-organising maps for nearly 105 quasar spectra. The final sample consists of 365 quasars in the redshift range z = 0.6 - 4.2 (z¯ = 1.50 ± 0.45) and includes in particular a subsample of 46 WLQs with equivalent widths WMg ii< 11 Å and WC iv< 4.8 Å. We compared the luminosities, black hole masses, Eddington ratios, accretion rates, variability, spectral slopes, and radio properties of the WLQs with those of control samples of ordinary quasars. Particular attention was paid to selection effects. Results: The WLQs have, on average, significantly higher luminosities, Eddington ratios, and accretion rates. About half of the excess comes from a selection bias, but an intrinsic excess remains probably caused primarily by higher accretion rates. The spectral energy distribution shows a bluer continuum at rest-frame wavelengths ≳1500 Å. The variability in the optical and UV is relatively low, even taking the variability-luminosity anti-correlation into account. The percentage of radio detected quasars and of core-dominant radio sources is significantly higher than for the control sample, whereas the mean radio-loudness is lower. Conclusions: The properties of our WLQ sample can be consistently understood assuming that it consists of a mix of quasars at the beginning of a stage of increased accretion activity and of beamed radio-quiet quasars. The higher luminosities and Eddington ratios in combination with a bluer spectral energy distribution can be explained by hotter continua, i.e. higher accretion rates. If

VDES J2325-5229 a z = 2.7 gravitationally lensed quasar discovered using morphology-independent supervised machine learning

NASA Astrophysics Data System (ADS)

Ostrovski, Fernanda; McMahon, Richard G.; Connolly, Andrew J.; Lemon, Cameron A.; Auger, Matthew W.; Banerji, Manda; Hung, Johnathan M.; Koposov, Sergey E.; Lidman, Christopher E.; Reed, Sophie L.; Allam, Sahar; Benoit-Lévy, Aurélien; Bertin, Emmanuel; Brooks, David; Buckley-Geer, Elizabeth; Carnero Rosell, Aurelio; Carrasco Kind, Matias; Carretero, Jorge; Cunha, Carlos E.; da Costa, Luiz N.; Desai, Shantanu; Diehl, H. Thomas; Dietrich, Jörg P.; Evrard, August E.; Finley, David A.; Flaugher, Brenna; Fosalba, Pablo; Frieman, Josh; Gerdes, David W.; Goldstein, Daniel A.; Gruen, Daniel; Gruendl, Robert A.; Gutierrez, Gaston; Honscheid, Klaus; James, David J.; Kuehn, Kyler; Kuropatkin, Nikolay; Lima, Marcos; Lin, Huan; Maia, Marcio A. G.; Marshall, Jennifer L.; Martini, Paul; Melchior, Peter; Miquel, Ramon; Ogando, Ricardo; Plazas Malagón, Andrés; Reil, Kevin; Romer, Kathy; Sanchez, Eusebio; Santiago, Basilio; Scarpine, Vic; Sevilla-Noarbe, Ignacio; Soares-Santos, Marcelle; Sobreira, Flavia; Suchyta, Eric; Tarle, Gregory; Thomas, Daniel; Tucker, Douglas L.; Walker, Alistair R.

2017-03-01

We present the discovery and preliminary characterization of a gravitationally lensed quasar with a source redshift zs = 2.74 and image separation of 2.9 arcsec lensed by a foreground zl = 0.40 elliptical galaxy. Since optical observations of gravitationally lensed quasars show the lens system as a superposition of multiple point sources and a foreground lensing galaxy, we have developed a morphology-independent multi-wavelength approach to the photometric selection of lensed quasar candidates based on Gaussian Mixture Models (GMM) supervised machine learning. Using this technique and gi multicolour photometric observations from the Dark Energy Survey (DES), near-IR JK photometry from the VISTA Hemisphere Survey (VHS) and WISE mid-IR photometry, we have identified a candidate system with two catalogue components with IAB = 18.61 and IAB = 20.44 comprising an elliptical galaxy and two blue point sources. Spectroscopic follow-up with NTT and the use of an archival AAT spectrum show that the point sources can be identified as a lensed quasar with an emission line redshift of z = 2.739 ± 0.003 and a foreground early-type galaxy with z = 0.400 ± 0.002. We model the system as a single isothermal ellipsoid and find the Einstein radius θE ˜ 1.47 arcsec, enclosed mass Menc ˜ 4 × 1011 M⊙ and a time delay of ˜52 d. The relatively wide separation, month scale time delay duration and high redshift make this an ideal system for constraining the expansion rate beyond a redshift of 1.

Dust-deficient Palomar-Green Quasars and the Diversity of AGN Intrinsic IR Emission

NASA Astrophysics Data System (ADS)

Lyu, Jianwei; Rieke, G. H.; Shi, Yong

2017-02-01

To elucidate the intrinsic broadband infrared (IR) emission properties of active galactic nuclei (AGNs), we analyze the spectral energy distributions (SEDs) of 87 z ≲ 0.5 Palomar-Green (PG) quasars. While the Elvis AGN template with a moderate far-IR correction can reasonably match the SEDs of the AGN components in ˜60% of the sample (and is superior to alternatives such as that by Assef), it fails on two quasar populations: (1) hot-dust-deficient (HDD) quasars that show very weak emission thoroughly from the near-IR to the far-IR, and (2) warm-dust-deficient (WDD) quasars that have similar hot dust emission as normal quasars but are relatively faint in the mid- and far-IR. After building composite AGN templates for these dust-deficient quasars, we successfully fit the 0.3-500 μm SEDs of the PG sample with the appropriate AGN template, an infrared template of a star-forming galaxy, and a host galaxy stellar template. 20 HDD and 12 WDD quasars are identified from the SED decomposition, including seven ambiguous cases. Compared with normal quasars, the HDD quasars have AGNs with relatively low Eddington ratios and the fraction of WDD quasars increases with AGN luminosity. Moreover, both the HDD and WDD quasar populations show relatively stronger mid-IR silicate emission. Virtually identical SED properties are also found in some quasars from z = 0.5 to 6. We propose a conceptual model to demonstrate that the observed dust deficiency of quasars can result from a change of structures of the circumnuclear tori that can occur at any cosmic epoch.

The Stacked LYα Emission Profile from the Circum-Galactic Medium of z ˜ 2 Quasars

NASA Astrophysics Data System (ADS)

Arrigoni Battaia, Fabrizio; Hennawi, Joseph F.; Cantalupo, Sebastiano; Prochaska, J. Xavier

2016-09-01

In the context of the FLASHLIGHT survey, we obtained deep narrowband images of 15 z ˜ 2 quasars with the Gemini Multi-object Spectrograph on Gemini South in an effort to measure Lyα emission from circum- and intergalactic gas on scales of hundreds of kpc from the central quasar. We do not detect bright giant Lyα nebulae (SB ˜ 10-17 erg s-1 cm-2 arcsec-2 at distances >50 kpc) around any of our sources, although we routinely (≃47%) detect smaller-scale <50 kpc Lyα emission at this surface brightness level emerging from either the extended narrow emission line regions powered by the quasars or by star formation in their host galaxies. We stack our 15 deep images to study the average extended Lyα surface brightness profile around z ˜ 2 quasars, carefully PSF-subtracting the unresolved emission component and paying close attention to sources of systematic error. Our analysis, which achieves an unprecedented depth, reveals a surface brightness of SBLyα ˜ 10-19 erg s-1 cm-2 arcsec-2 at ˜200 kpc, with a 2.3σ detection of Lyα emission at SB {}{Lyα }=(5.5+/- 3.1)× {10}-20 erg s-1 cm-2 arcsec-2 within an annulus spanning 50 kpc < R < 500 kpc from the quasars. Assuming that this Lyα emission is powered by fluorescence from highly ionized gas illuminated by the bright central quasar, we deduce an average volume density of n H = 0.6 × 10-2 cm-3 on these large scales. Our results are in broad agreement with the densities suggested by cosmological hydrodynamical simulations of massive (M ≃ 1012.5 M ⊙) quasar hosts; however, they indicate that the typical quasars at these redshifts are surrounded by gas that is a factor of ˜100 times less dense than the (˜1 cm-3) gas responsible for the giant bright Lyα nebulae around quasars recently discovered by our group. Based 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

Cross-Correlations in Quasar Radio Emission

NASA Astrophysics Data System (ADS)

Nefedyev, Yuri; Panischev, Oleg; Demin, Sergey

The main factors forming the complex evolution of the accretive astrophysical systems are nonlinearity, intermittency, nonstationarity and also collective phenomena. To discover the dynamic processes in these objects and to detain understanding their properties we need to use all the applicable analyzing methods. Here we use the Flicker-Noise Spectroscopy (FNS) as a phenomenological approach to analyzing and parameterizing the auto- and cross-correlations in time series of astrophysical objects dynamics. As an example we consider the quasar flux radio spectral density at frequencies 2.7 GHz and 8.1 GHz. Data have been observed by Dr. N. Tanizuka (Laboratory for Complex Systems Analysis, Osaka Prefecture University) in a period of 1979 to 1988 (3 309 days). According to mental habits quasar is a very energetic and distant active galactic nucleus containing a supermassive black hole by size 10-10,000 times the Schwarzschild radius. The quasar is powered by an accretion disc around the black hole. The accretion disc material layers, moving around the black hole, are under the influence of gravitational and frictional forces. It results in raising the high temperature and arising the resonant and collective phenomena reflected in quasar emission dynamics. Radio emission dynamics of the quasar 0215p015 is characterized by three quasi-periodic processes, which are prevalent in considering dynamics. By contrast the 1641p399's emission dynamics have not any distinguish processes. It means the presence of high intermittency in accretive modes. The second difference moment allows comparing the degree of manifesting of resonant and chaotic components in initial time series of the quasar radio emission. The comparative analysis shows the dominating of chaotic part of 1641p399's dynamics whereas the radio emission of 0215p015 has the predominance of resonant component. Analyzing the collective features of the quasar radio emission intensity demonstrates the significant

Absorption in X-ray spectra of high-redshift quasars

NASA Technical Reports Server (NTRS)

Elvis, Martin; Fiore, Fabrizio; Wilkes, Belinda; Mcdowell, Jonathan; Bechtold, Jill

1994-01-01

We present evidence that X-ray absorption is common in high-redshift quasars. We have studied six high-redshift (z approximately 3) quasars with the ROSAT Position Sensitive Proportional Counter (PSPC) of which four are in directions of low Galactic N(sub H). Three out of these four show excess absorption, while only three in approximately 50 z approximately less than 0.4 quasars do, indicating that such absorption must be common, but not ubiquitous, at high redshifts, and that the absorbers must lie at z greater than 0.4. The six quasars were: S5 0014+81, Q0420-388, PKS 0438-436, S4 0636+680. PKS 2000-330, PKS 2126-158, which have redshifts between 2.85 and 3.78. PKS 0438-436 and PKS 2126-158 show evidence for absorption above the local Galactic value at better than 99.999% confidence level. If the absorber is at the redshift of the quasar, then values of N(sub H) = (0.86(+0.49, -0.28)) x 10(exp 22) atoms/sq cm for PKS 0438-436, and N(sub H) = (1.45(+1.20, -0.64)) x 10(exp 22) atoms/ sq cm for PKS 2126-158, are implied, assuming solar abundances. The spectrum of S4 0636+680 also suggests the presence of a similarly large absorption column density at the 98% confidence level. This absorption reverses the trend for the most luminous active galactic nuclei (AGN) to have the least X-ray absorption, so a new mechanism is likely to be responsible. Intervening absorption due to damped Lyman(alpha) systems is a plausible cause. We also suggest, as an intrinsic model, that intracluster material, e.g., a cooling flow, around the quasar could account for both the X-ray spectrum and other properties of these quasars. All the quasars are radio-loud and three are gigahertz peaked (two of the three showing absorption). No excess absorption above the Galactic value is seen toward Q0420-388. This quasar has two damped Lyman(alpha) systems at z = 3.08. The limit on the X-ray column density implies a low ionization fraction, N(H I)/N(H) approximately greater than 4 x 10(exp -3) (3

Learning by Doing: Science Education at the Hamburg Observatory

ERIC Educational Resources Information Center

Wolfschmidt, Gudrun

2015-01-01

In my contribution I would like to offer three different examples: the activities of the association "Förderverein Hamburger Sternwarte", science education in the "astronomy workshop", and the teaching of the history of science and technology for university students.

Surface density of quasars in two high-latitude fields

NASA Technical Reports Server (NTRS)

Usher, P. D.; Green, R. F.; Huang, K. L.; Warnock, A., III

1983-01-01

Fourty-four objects selected for ultraviolet excess have been identified spectroscopically. The objects lie in two Palomar 1.2 m Schmidt fields in the north galactic polar cap, one of 7.7 sq deg centered on Kapteyn Selected Area 29, the other of 36 sq deg centered on SA 55. The objects are characterized by Color Classes (CC) 1A, 1, 1B, 1C, 2, and 3. Quasars comprise 75 percent of the CC 1A objects and 44 percent of the objects in the SA 29 field. Twelve quasars in the SA 29 field comprise a complete sample to B = 18.5 mag, and given an uncorrected surface density of 1.6 quasars/sq deg. This value is essentially that derived by Sandage (1969). Corrections are applied to account for the lack of high redshift quasars. An empirical correction is derived to account for lack of simultaneity in selection and photometry. A corrected lower limit to the surface density is estimated to be 1.85 quasars/sq deg to B = 18.5 mag.

Doppler interpretation of quasar red shifts.

PubMed

Zapolsky, H S

1966-08-05

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.

Modernization of the graphics post-processors of the Hamburg German Climate Computer Center Carbon Cycle Codes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stevens, E.J.; McNeilly, G.S.

The existing National Center for Atmospheric Research (NCAR) code in the Hamburg Oceanic Carbon Cycle Circulation Model and the Hamburg Large-Scale Geostrophic Ocean General Circulation Model was modernized and reduced in size while still producing an equivalent end result. A reduction in the size of the existing code from more than 50,000 lines to approximately 7,500 lines in the new code has made the new code much easier to maintain. The existing code in Hamburg model uses legacy NCAR (including even emulated CALCOMP subrountines) graphics to display graphical output. The new code uses only current (version 3.1) NCAR subrountines.

Evaluation of bias in the Hamburg wheel tracking device.

DOT National Transportation Integrated Search

2013-09-01

As the list of states adopting the Hamburg Wheel Tracking Device (HWTD) continues to grow, there is a need to evaluate how results are utilized. American Association of State Highway and Transportation Officials T 324 does not standardize the analysi...

How fast do quasar emission lines vary? First results from a program to monitor the Balmer lines of the Palomar-Green Quasars

NASA Technical Reports Server (NTRS)

Maoz, Dan; Smith, Paul S.; Jannuzi, Buell T.; Kaspi, Shai; Netzer, Hagai

1994-01-01

We have monitored spectrophotometrically a subsample (28) of the Palomar-Green Bright Quasar Sample for 2 years in order to test for correlations between continuum and emission-line variations and to determine the timescales relevant to mapping the broad-line regions of high-luminosity active galactic nuclei (AGNs). Half of the quasars showed optical continuum variations with amplitudes in the range 20-75%. The rise and fall time for the continuum variations is typically 0.5-2 years. In most of the objects with continuum variations, we detect correlated variations in the broad H-alpha and H-beta emission lines. The amplitude of the line variations is usually 2-4 times smaller than the optical continuum fluctuations. We present light curves and analyze spectra for six of the variable quasars with 1000-10,000 A luminosity in the range 0.3-4 x 10(exp 45) ergs/s. In four of these objects the lines respond to the continuum variations with a lag that is smaller than or comparable to our typical sampling interval (a few months). Although continued monitoring is required to confirm these results and increase their accuracy, the present evidence indicates that quasars with the above luminosities have broad-line regions smaller than about 1 1t-yr. Two of the quasars monitored show no detectable line variations despite relatively large-amplitude continuum changes. This could be a stronger manifestation of the low-amplitude line-response phenomenon we observe in the other quasars.

The nature of X-ray selected star candidates

NASA Astrophysics Data System (ADS)

Mickaelian, A. M.; Paronyan, G. M.; Abrahamyan, H. V.; Gigoyan, K. S.; Gyulzadyan, M. V.; Kostandyan, G. R.

2016-12-01

The joint HRC/BHRC catalogue of optical identifications of ROSAT BSC and FSC X-ray sources is based on merging the Hamburg-ROSAT Catalogue (HRC) and Byurakan-Hamburg-ROSAT Catalogue (BHRC). Both have been made by optical identifications of X-ray sources based on low-dispersion spectra of the Hamburg QuasarSurvey (HQS) using the ROSAT Catalogues. HRC/BHRC contains a sample of 8132 (5341+2791) optically identified X-ray sources with count rate (CR) of photons ≥ 0.04 ct/s in the area of the low-dispersion Hamburg Quasar Survey (HQS), |b| ≥ 20° and δ ≥ 0°. Based on low-dispersion spectral classification, there are 4253 AGN, 492 galaxies, 1800 stars and 1587 unknown objects in the sample. 1800 star candidates include 1429 objects listed in SDSS DR12 photometric catalogue and 433 given in SDSS spectroscopic catalogue. Using these spectra, we have carried out classification of these star candidates to reveal new interesting objects, as well as to define the true content of our sample. 34 cataclysmic variables (including 7 new ones), 19 white dwarfs, 19 late-type stars (K-M and C types), 16 early type stars (O-B), 40 hot coronal stars (A-F types), 2 composite spectrum objects, and 17 bright stars have been revealed, as well as 286 objects which turned out to be extragalactic ones; 75 emission-line galaxies (HII/SB and AGN, including QSOs, Seyferts, and LINERs) and 211 absorption line galaxies were revealed (wrong classifications in HRC/BHRC due to their faint images and low-quality spectra). We have retrieved multiwavelength data from recent catalogues and carried out statistical investigations of the multiwavelength properties for the whole sample of stars. All stars have been found in GSC 2.3.2, as well as most of them are in GALEX, USNO-B1.0, 2MASS and WISE catalogues. Relations between the radiation fluxes in different bands from X-ray to radio for different types of sources are studied and analysis of their characteristics is made. X-ray selected stars are an

Formación estelar y AGNs en los entornos de quasars

NASA Astrophysics Data System (ADS)

Coldwell, G.; García Lambas, D.

En este trabajo utilizamos las galaxias del catálogo 2dF (2dF public 100K data release) y muestras de quasars tomados del catálogo Verón-Cetty & Verón (2001) para estudiar la naturaleza de estas galaxias en los entornos de quasars con redshift en el rango 0.1< z < 0.2. Estudiamos la distribución de índices espectrales, η, de galaxias a distintas distancias proyectadas de quasars y con diferencias de velocidad radial Δ V <= 500 km s-1. Por comparación, realizamos el mismo análisis en una muestra de galaxias random del catálogo 2dF y en una muestra de cúmulos Abell con similar distribución de redshift que los quasars. Los resultados indican que existe una gran fracción de galaxias con fuertes líneas de emisión, eta > 3.5, en los entornos de quasars comparado con la fracción presente en las vecindades de galaxias típicas del 2dF. Analizamos las distribuciones de luminosidad para estas galaxias (eta > 3.5) encontrando un exceso de galaxias mas luminosas que M ˜ -19.5 en las vecindades de quasars, indicativo de la posible presencia de AGNs. Por otro lado, estimamos la tasa de formación estelar promedio para objetos a distintas distancias de quasars, galaxias y cúmulos de galaxias detectando una actividad de formacion estelar significativamente alta dentro de 1.5 Mpc h-1 de quasars con respecto a las galaxias del 2dF. Estos resultados proveen evidencia de un particular entorno de galaxias alrededor de Quasars.

Is there any evidence that ionized outflows quench star formation in type 1 quasars at z < 1?

NASA Astrophysics Data System (ADS)

Balmaverde, B.; Marconi, A.; Brusa, M.; Carniani, S.; Cresci, G.; Lusso, E.; Maiolino, R.; Mannucci, F.; Nagao, T.

2016-01-01