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Sample records for break galaxy close

  1. Close Call: Breaking the Rules.

    ERIC Educational Resources Information Center

    Journal of Adventure Education and Outdoor Leadership, 1993

    1993-01-01

    Contrary to a rule to never teach students to lead climb, an instructor taught several youth to lead climb at a parent's request. These students planned to pursue rock climbing on their own after they left school, and preparing them was deemed a safety precaution. Analysis of this "close call" offers guidelines for introducing students to lead…

  2. Record-breaking ancient galaxy clusters

    NASA Astrophysics Data System (ADS)

    2003-12-01

    A tale of two record-breaking clusters hi-res Size hi-res: 768 kb Credits: for RDCS1252: NASA, ESA, J.Blakeslee (Johns Hopkins Univ.), M.Postman (Space Telescope Science Inst.) and P.Rosati, Chris Lidman & Ricardo Demarco (European Southern Observ.) for TNJ1338: NASA, ESA, G.Miley (Leiden Observ.) and R.Overzier (Leiden Obs) A tale of two record-breaking clusters Looking back in time to when the universe was in its formative youth, the Advanced Camera for Surveys (ACS) aboard the NASA/ESA Hubble Space Telescope captured these revealing images of two galaxy clusters. The image at left, which is made with an additional infrared exposure taken with the European Southern Observatory’s Very Large Telescope, shows mature galaxies in a massive cluster that existed when the cosmos was 5000 million years old. The cluster, called RDCS1252.9-2927, is as massive as ‘300 trillion’ suns and is the most massive known cluster for its epoch. The image reveals the core of the cluster and is part of a much larger mosaic of the entire cluster. Dominating the core are a pair of large, reddish elliptical galaxies [near centre of image]. Their red colour indicates an older population of stars. Most of the stars are at least 1000 million years old. The two galaxies appear to be interacting and may eventually merge to form a larger galaxy that is comparable to the brightest galaxies seen in present-day clusters. The red galaxies surrounding the central pair are also cluster members. The cluster probably contains many thousands of galaxies, but only about 50 can be seen in this image. The full mosaic (heic0313d) reveals several hundred cluster members. Many of the other galaxies in the image, including several of the blue galaxies, are foreground or background galaxies. The colour-composite image was assembled from two observations (through i and z filters) taken between May and June 2002 by the ACS Wide Field Camera, and one image with the ISAAC instrument on the VLT taken in 2002

  3. DYNAMICS OF LYMAN BREAK GALAXIES AND THEIR HOST HALOS

    SciTech Connect

    Lowenthal, James D.; Koo, David C.; Van Kampen, Eelco E-mail: koo@ucolick.or E-mail: evkampen@eso.or

    2009-09-20

    We present deep two-dimensional spectra of 22 candidate and confirmed Lyman break galaxies (LBGs) at redshifts 2 < z < 4 in the Hubble Deep Field (HDF) obtained at the Keck II telescope. The targets were preferentially selected with spatial extent and/or multiple knot morphologies, and we used slitmasks and individual slits tilted to optimize measurement of any spatially resolved kinematics. Our sample is more than 1 mag fainter and is at higher redshift than the kinematic LBG targets previously studied by others. The median target magnitude was I {sub 814} = 25.3, and total exposure times ranged from 10 to 50 ks. We measure redshifts, some new, ranging from z = 0.2072 to z = 4.056, including two interlopers at z < 1, and resulting in a sample of 14 LBGs with a median redshift z = 2.424. The morphologies and kinematics of the close pairs and multiple knot sources in our sample are generally inconsistent with galaxy formation scenarios postulating that LBGs occur only at the bottom of the potential wells of massive host halos; rather, they support 'collisional starburst' models with significant major merger rates and a broad halo occupation distribution. For 13 LBGs with possible kinematic signatures, we estimate a simple dynamical mass, subject to numerous caveats and uncertainties, of the galaxies and/or their host dark matter halos. Dynamical mass estimates of individual galaxies range from 4 x 10{sup 9} h {sup -1} M{sub sun} to 1.1 x 10{sup 11} h {sup -1} M{sub sun} and mass estimates of halos, based on close LBG pairs, range from <10{sup 10} h {sup -1} to {approx}10{sup 14} h {sup -1} M{sub sun} with a median value 1 x 10{sup 13} M{sub sun}. Comparison with a recent numerical galaxy formation model implies that indeed the pairwise velocities might not reflect true dynamical masses. We compare our dynamical mass estimates directly to stellar masses estimated for the same galaxies from SEDs, and find no evidence for a strong correlation. The diversity of

  4. Cosmic ray antiprotons in closed galaxy model

    NASA Technical Reports Server (NTRS)

    Protheroe, R.

    1981-01-01

    The flux of secondary antiprotons expected for the leaky-box model was calculated as well as that for the closed galaxy model of Peters and Westergard (1977). The antiproton/proton ratio observed at several GeV is a factor of 4 higher than the prediction for the leaky-box model but is consistent with that predicted for the closed galaxy model. New low energy data is not consistent with either model. The possibility of a primary antiproton component is discussed.

  5. SIZING UP Ly{alpha} AND LYMAN BREAK GALAXIES

    SciTech Connect

    Malhotra, Sangeeta; Rhoads, James E.; McLinden, Emily; Finkelstein, Steven L.; Hathi, Nimish; Nilsson, Kim; Pirzkal, Norbert

    2012-05-10

    We measure the sizes for a sample of 174 Ly{alpha}-selected galaxies with broadband imaging with the Hubble Space Telescope. Over the redshift range 2.25 < z < 6, Ly{alpha}-selected galaxies have a characteristic, constant, small size in rest-frame ultraviolet (UV) light. Coupled with a characteristic star formation intensity (i.e., UV luminosity per unit area), this can explain their non-evolving ultraviolet continuum luminosity function. This is in contrast to Lyman break galaxies (LBGs) over the same redshift range, which have been previously shown to increase in linear size as H(z){sup -1}. The compact physical size seems to be a critical determining factor in whether a galaxy will show Ly{alpha} emission or not. The L{sub *} of LBGs and its evolution with redshift can be derived from a simple model where the star formation intensity has an upper limit set by feedback processes, independent of redshift. The increase in L{sub *} of LBGs is mainly driven by the increase in linear size over redshifts for z = 2-7. Since Ly{alpha} galaxies do not grow in linear size, they do not show an increase in L{sub *}.

  6. The properties of Lyman break galaxies at z~ 5

    NASA Astrophysics Data System (ADS)

    Bremer, M. N.; Lehnert, M. D.; Waddington, I.; Hardcastle, M. J.; Boyce, P. J.; Phillipps, S.

    2004-01-01

    In a recent paper, Lehnert & Bremer have photometrically selected a sample of Lyman break galaxies at z > 4.8 from a single VLT/FORS2 pointing and spectroscopically confirmed half of them to be at 4.8 < z < 5.8. To study the properties of such galaxies further, we have photometrically selected a similar sample (VAB > 28, iAB < 26.3, iAB-zAB > 0) from the Hubble Space Telescope Advanced Camera for Surveys (HST ACS) images of the Chandra Deep Field-South. This selection results in a sample of 44 sources from ~150 arcmin2. We find that such galaxies are often barely resolved in the ACS images, having half-light radii of 0.1-0.3 arcsec (<2 kpc). They show no difference in spatial clustering from sources selected by iAB < 26.3, iAB-zAB > 0, which are generally galaxies of lower redshift. However, their distribution over the field is not uniform and their surface density varies considerably over areas comparable to a single 8-m or HST pointing. A reliable determination of the surface and volume densities of such galaxies requires a sky area considerably larger than the current ACS imaging of this field. No individual Lyman break candidate was detected to a 3σ limit of 6 × 10-17 erg s-1 cm-2 at 0.5-5 keV by Chandra (a limiting luminosity of below 2 × 1043 erg s-1 at z~ 5.3). By summing over all positions, we find that the mean source must be undetected at a level at least a factor of 4 times fainter than this. This rules out anything other than a weak active galactic nucleus (AGN) contribution to the emission from these objects; we conclude that luminous AGNs made little contribution to the final stages of re-ionization of the Universe.

  7. Symmetry Breaking and Optical Negative Index of Closed Nanorings

    NASA Astrophysics Data System (ADS)

    Kante, Boubacar; Park, Yong-Shik; O'Brien, Kevin; Shuldman, Daniel; Lanzillotti-Kimura, Norberto; Wong, Zi; Yin, Xiaobo; Zhang, Xiang; UC Berkeley Team

    2013-03-01

    We report the first experimental demonstration of broadband negative-index metamaterial made solely of closed metallic nanorings. Using symmetry breaking that negatively couples the discrete nanorings, we measured negative phase delay in our composite chess metamaterial. Our approach open avenues towards topological nanophotonics with on demand linear and non-linear responses.

  8. Evolution of Lyman-α Emitters, Lyman-break Galaxies and Elliptical Galaxies

    NASA Astrophysics Data System (ADS)

    Mori, M.; Umemura, M.

    2008-10-01

    High redshift Lyman-α emitters (LAEs) and Lyman-break galaxies (LBGs) possibly provide a significant key for the embryology of galaxies. LBGs have been argued as candidate progenitors of present-day elliptical galaxies in terms of their observed properties. But, what evolutionary stages LBGs correspond to and how they are related to LAEs are still under debate. Here, we present an ultra-high-resolution hydrodynamic simulation of galaxy formation. We show that, at the earliest stages of less than 3×10^8 years, continual supernova explosions produce multitudinous hot bubbles and cooled HI shells in between. The HI shells radiate intense Lyman-α emission like LAEs. We found that the bubbly structures produced are quite similar to the observed features in the Lyman-α surface brightness distribution of the extended LAEs. After 10^9 years, the galaxy emission is dominated by stellar continuum, exhibiting an LBG-like spectrum. Also, we find that, as a result of purely dynamical evolution over 13 billion years, the properties of this galaxy match those of present-day elliptical galaxies well. It is implied that the major episode of star formation and chemical enrichment in elliptical galaxies is almost completed in the evolutionary path from LAEs to LBGs.

  9. X-Ray Emission from Ultraviolet Luminous Galaxies and Lyman Break Galaxies

    NASA Technical Reports Server (NTRS)

    Hornschemeier, Ann; Ptak, A. F.; Salim, S.; Heckman, T. P.; Overzier, R.; Mallery, R.; Rich, M.; Strickland, D.; Grimes, J.

    2009-01-01

    We present results from an XMM mini-survey of GALEX-selected Ultraviolet-Luminous Galaxies (UVLGs) that appear to include an interesting subset that are analogs to the distant (3Break Galaxies (LBGs). The 2-10 kev X-ray emission of LBGs appear to be broadly similar to that of galaxies in the local Universe, possibly indicating similarity in the production of accreting binaries over large evolutionary timescales in the Universe. We have detected luminous X-ray emission from one UVLG that permits basic X-ray spectroscopic analysis, and have direct X-ray constraints on a total of 6 UVLGs. We find evidence for likely large scatter in the assumed X-ray/star-formation rate relation for LBGs.

  10. Symmetry breaking and optical negative index of closed nanorings

    NASA Astrophysics Data System (ADS)

    Kanté, Boubacar; Park, Yong-Shik; O'Brien, Kevin; Shuldman, Daniel; Lanzillotti-Kimura, Norberto D.; Jing Wong, Zi; Yin, Xiaobo; Zhang, Xiang

    2012-11-01

    Metamaterials have extraordinary abilities, such as imaging beyond the diffraction limit and invisibility. Many metamaterials are based on split-ring structures, however, like atomic orbital currents, it has long been believed that closed rings cannot produce negative refractive index. Here we report a low-loss and polarization-independent negative-index metamaterial made solely of closed metallic nanorings. Using symmetry breaking that negatively couples the discrete nanorings, we measured negative phase delay in our composite ‘chess metamaterial’. The formation of an ultra-broad Fano-resonance-induced optical negative-index band, spanning wavelengths from 1.3 to 2.3 μm, is experimentally observed in this structure. This discrete and mono-particle negative-index approach opens exciting avenues towards symmetry-controlled topological nanophotonics with on-demand linear and nonlinear responses.

  11. Disk Galaxy Warp Formation via Close Encounters

    NASA Astrophysics Data System (ADS)

    Kim, Jeonghwan; Peirani, S.; Kim, S.; Yoon, S.

    2012-01-01

    Warped disks appear to be ubiquitous among spiral galaxies. We present a new scenario for the warp formation, in which galactic fly-by encounters are main drivers of the warp structure. Based on N-body simulation using a publicly available code Gadget2, we investigate morphological and kinematical structures of disk galaxies while the galaxies are undergoing fly-by encounters with adjacent dark matter halos. In this study, we find that warps can be excited by impulsive encounters and sustained for a few billion years. We also find that encounters cause the initially spherical halos to deform into intricate shape halos at the inner regions where warps are generated. Most of the warps from the simulation show inclination angles that are comparable to the observations. The creation of warps, their inclination and their lifetimes are governed primarily by the following three parameters: the impact parameter (the minimum distance between two halos), the mass ratio between two galaxies, and the incoming angle of the intruder. We discuss pros and cons about our alternative scenario in comparison with existing explanations.

  12. Cosmic ray antiprotons in the closed galaxy model

    NASA Technical Reports Server (NTRS)

    Protheroe, R. J.

    1981-01-01

    A calculation is made of the flux of secondary antiprotons expected for the leaky box model and for the closed galaxy model of Peters and Westergaard (1977). The antiproton/proton ratio observed at several GeV is a factor of 4 higher than the prediction for the leaky box model but is consistent with that predicted for the closed galaxy model. It is found that new low-energy data are not consistent with either model. Attention is given to the possibility of a primary antiproton component.

  13. Dust properties of Lyman-break galaxies at z ~ 3

    NASA Astrophysics Data System (ADS)

    Álvarez-Márquez, J.; Burgarella, D.; Heinis, S.; Buat, V.; Lo Faro, B.; Béthermin, M.; López-Fortín, C. E.; Cooray, A.; Farrah, D.; Hurley, P.; Ibar, E.; Ilbert, O.; Koekemoer, A. M.; Lemaux, B. C.; Pérez-Fournon, I.; Rodighiero, G.; Salvato, M.; Scott, D.; Taniguchi, Y.; Vieira, J. D.; Wang, L.

    2016-03-01

    Context. Since the mid-1990s, the sample of Lyman-break galaxies (LBGs) has been growing thanks to the increasing sensitivities in the optical and in near-infrared telescopes for objects at z> 2.5. However, the dust properties of the LBGs are poorly known because the samples are small and/or biased against far-infrared (far-IR) or submillimeter (submm) observations. Aims: This work explores from a statistical point of view the far-IR and submm properties of a large sample of LBGs at z ~ 3 that cannot be individually detected from current far-IR observations. Methods: We select a sample of 22, 000 LBGs at 2.5 galaxies included in the sample allows us to split it into several bins as a function of UV luminosity (LFUV), UV continuum slope (βUV), and stellar mass (M∗) to better sample their variety. We stack in PACS (100 and 160 μm) images from PACS Evolution Probe survey (PEP), SPIRE (250, 350 and 500 μm) images from the Herschel Multi-tied Extragalactic Survey (HerMES) programs, and AzTEC (1.1 mm) images from the Atacama Submillimeter Telescope Experiment (ASTE). Our stacking procedure corrects the biases induced by galaxy clustering and incompleteness of our input catalogue in dense regions. Results: We obtain the full infrared spectral energy distributions (SED) of subsamples of LBGs and derive the mean IR luminosity as a function of LFUV, βUV, and M∗. The average IRX (or dust attenuation) is roughly constant over the LFUV range, with a mean of 7.9 (1.8 mag). However, it is correlated with βUV, AFUV = (3.15 ± 0.12) + (1.47 ± 0.14) βUV, and stellar mass, log (IRX) = (0.84 ± 0.11)log (M∗/ 1010.35) + 1.17 ± 0.05. We investigate using a statistically controlled stacking analysis as a function of (M∗, βUV), the dispersion of the IRX-βUV and IRX-M∗ plane. On the one hand, the dust attenuation shows a departure of up to 2.8 mag above the mean IRX-βUV relation when log (M

  14. PRIMUS: Enhanced Specific Star Formation Rates in Close Galaxy Pairs

    NASA Astrophysics Data System (ADS)

    Wong, Kenneth C.; Blanton, Michael R.; Burles, Scott M.; Coil, Alison L.; Cool, Richard J.; Eisenstein, Daniel J.; Moustakas, John; Zhu, Guangtun; Arnouts, Stéphane

    2011-02-01

    Tidal interactions between galaxies can trigger star formation, which contributes to the global star formation rate (SFR) density of the universe and could be a factor in the transformation of blue, star-forming galaxies to red, quiescent galaxies over cosmic time. We investigate tidally triggered star formation in isolated close galaxy pairs drawn from the Prism Multi-Object Survey (PRIMUS), a low-dispersion prism redshift survey that has measured ~120,000 robust galaxy redshifts over 9.1 deg2 out to z ~ 1. We select a sample of galaxies in isolated galaxy pairs at redshifts 0.25 <= z <= 0.75, with no other objects within a projected separation of 300 h -1 kpc and Δz/(1 + z) = 0.01, and compare them to a control sample of isolated galaxies to test for systematic differences in their rest-frame FUV - r and NUV - r colors as a proxy for relative specific star formation rates (SSFRs). We find that galaxies in rp <= 50 h -1 kpc pairs have bluer dust-corrected UV - r colors on average than the control galaxies by -0.134 ± 0.045 mag in FUV - r and -0.075 ± 0.038 mag in NUV - r, corresponding to an ~15%-20% increase in SSFR. This indicates an enhancement in SSFR due to tidal interactions. We also find that this relative enhancement is greater for a subset of rp <= 30 h -1 kpc pair galaxies, for which the average color offsets are -0.193 ± 0.065 mag in FUV - r and -0.159 ± 0.048 mag in NUV - r, corresponding to an ~25%-30% increase in SSFR. We test for evolution in the enhancement of tidally triggered star formation with redshift across our sample redshift range and find marginal evidence for a decrease in SSFR enhancement from 0.25 <= z <= 0.5 to 0.5 <= z <= 0.75. This indicates that a change in enhanced star formation triggered by tidal interactions in low-density environments is not a contributor to the decline in the global SFR density across this redshift range.

  15. LYMAN BREAK GALAXIES AT z approx 5: REST-FRAME UV SPECTRA. III

    SciTech Connect

    Kajino, Hiroki; Ohta, Kouji; Yabe, Kiyoto; Yuma, Suraphong; Iwata, Ikuru; Akiyama, Masayuki; Tamura, Naoyuki; Aoki, Kentaro; Sawicki, Marcin

    2009-10-10

    We present results of optical spectroscopic observations of candidates of Lyman break galaxies (LBGs) at z approx 5 in the region, including the GOODS-N and the J0053+1234 regions by using Gemini Multi-Object Spectrograph North and South, respectively. Among 25 candidates, five objects are identified to be at z approx 5 (two of them were already identified by an earlier study) and one object very close to the color-selection window turned out to be a foreground galaxy. With this spectroscopically identified sample and those from previous studies, we derived the lower limits on the number density of bright (M{sub UV} < -22.0 mag) LBGs at z approx 5. These lower limits are comparable to or slightly smaller than the number densities of UV luminosity functions (UVLFs) that show the smaller number density among z approx 5 UVLFs in literature. However, by considering that there remain many LBG candidates without spectroscopic observations, the number density of bright LBGs is expected to increase by a factor of two or more. The evidence for the deficiency of UV luminous LBGs with large Lyalpha equivalent widths was reinforced. We discuss possible causes for the deficiency and prefer the interpretation of dust absorption.

  16. Comparing Local Starbursts to High-Redshift Galaxies: A Search for Lyman-Break Analogs

    NASA Technical Reports Server (NTRS)

    Petty, Sara M.; de Mello, Duila F.; Gallagher III, John S.; Gardner, Jonathan; Lotz, Jennifer M.; Mountain, C. Matt; Smith, Linda J.

    2008-01-01

    We compare the restframe far-ultraviolet (FUV) morphologies of 8 nearby interacting and starburst galaxies (Arp 269, M 82, Mrk 08, NGC 0520, NGC 1068, NGC 3079, NGC 3310, NGC 7673) with 54 galaxies at z approx.1.5 and 46 galaxies at z approx.4 in the Great Observatories Origins Deep Survey (GOODS) images taken with the Advanced Camera for Surveys onboard the Hubble Space Telescope. We calculate the Gini coefficient (G), the second order moment of 20% of the brightest pixels (M20), and the S ersic index (n). We find that 20% (11/54) of z approx.1.5 and 37% (17/46) of z approx.4 galaxies are bulge-like, using G and M20. We also find approx.70% of the z approx.1.5 and z approx.4 galaxies have exponential disks with n > 0.8. The 2D profile combined with the nonparametric methods provides more detail, concerning the nature of disturbed systems, such as merger and post-merger types. We also provide qualitative descriptions of each galaxy system and at each redshift. We conclude that Mrk 08, NGC 3079, and NGC 7673 have similar morphologies as the starburst FUV restframe galaxies and Lyman-break galaxies at z approx.1.5 and 4, and determine that they are Lyman-break analogs.

  17. Spatially resolved star-formation in nearby analogues of Lyman break galaxies

    NASA Astrophysics Data System (ADS)

    Appel, Sabrina; Baker, Andrew J.; Hall, Kirsten

    2016-01-01

    At redshifts of z > 1.5, UV-selected galaxy populations (such as z ~ 3 Lyman break galaxies = LBGs) have the largest number of spectroscopic redshifts. As a result, LBGs have an important role in our understanding of the history of galaxy formation. However, LBGs are rather poorly understood at longer wavelengths, and thus our understanding of the total star formation rates and (especially) gas masses in such galaxies is incomplete. A common strategy is to assume that the Kennicutt-Schmidt relation between star formation rate (SFR) surface density and gas mass surface density holds, even in these high redshift galaxies where testing the relation directly is not feasible. To help assess the validity of this assumption, we examine the Kennicutt-Schmidt relation in selected nearby (z ~ 0.2) starburst galaxies in the hope of better understanding key questions regarding star formation processes in UV-selected galaxies. Several nearby galaxies with high UV luminosities and surface brightnesses, reminiscent of those found in LBGs, were identified and used for this project. We have obtained new, spatially resolved observations of these nearby analogues in Paschen alpha emission and carbon monoxide emission, from the ESO Very Large Telescope and the IRAM Plateau de Bure Interferometer, respectively. We examine whether the galaxies follow the expected Kennicutt-Schmidt relation, and investigate any implied variation in gas depletion times between and within galaxies. This research has been supported by National Science Foundation grant AST-0955810.

  18. Star formation activity in Balmer break galaxies at z< 1.5

    NASA Astrophysics Data System (ADS)

    Díaz Tello, J.; Donzelli, C.; Padilla, N.; Akiyama, M.; Fujishiro, N.; Yoshikawa, T.; Hanami, H.

    2016-03-01

    Aims: We present a spectroscopic study of the properties of 64 Balmer break galaxies that show signs of star formation. The studied sample of star-forming galaxies spans a redshift range from 0.094 to 1.475 with stellar masses in the range 108-1012M⊙. The sample also includes eight broad emission line galaxies with redshifts between 1.5 break in the correlation, which reveals the presence of massive galaxies with lower SFR values (i.e., decreasing star formation). We also note an anticorrelation for the SSFR with the stellar mass. Again in this case, our data is also consistent with a break in the correlation, revealing the presence of massive star-forming galaxies with lower SSFR values, thereby increasing the anticorrelation. These results might suggest a characteristic mass (M0) at which the red sequence could mostly be assembled. In addition, at a given stellar mass, high-redshift galaxies have on average higher SFR and SSFR values than local galaxies. Finally, we explored whether a similar trend could be observed with redshift in the SSFR-(u - B) color diagram, and we hypothesize that a possible (u - B)0 break color may define a characteristic color for the formation of the red sequence.

  19. Molecular Gas in the Lensed Lyman Break Galaxy cB58

    NASA Astrophysics Data System (ADS)

    Baker, Andrew J.; Tacconi, Linda J.; Genzel, Reinhard; Lehnert, Matthew D.; Lutz, Dieter

    2004-03-01

    We have used the IRAM Plateau de Bure Interferometer to map CO (3-2) emission from the gravitationally lensed Lyman break galaxy MS 1512-cB58. This is the first detection of a molecular emission line in any Lyman break system; its integrated intensity implies a total molecular gas mass of (6.6+5.8-4.3)×109 h-20.7 Msolar, while its width implies a dynamical mass of (1.0+0.6-0.4)×1010csc2i h-10.7 Msolar (for a flat ΩΛ=0.7 cosmology). These estimates are in excellent concordance with nearly all parameters of the system measured at other wavelengths and yield a consistent picture of past and future star formation with no obvious discrepancies requiring explanation by differential lensing. In particular, we find that the age and remaining lifetime of the current episode of star formation are likely to be similar, the surface densities of star formation and molecular gas mass are related by a Schmidt law, and the fraction of baryonic mass already converted into stars is sufficient to account for the observed enrichment of the interstellar medium to 0.4 Zsolar. Barring substantial gas inflow or a major merger, the stars forming in the current episode will have mass and coevality at z=0 similar to those of a spiral bulge. Assuming that cB58 is a typical Lyman break galaxy apart from its magnification, its global parameters suggest that the prescriptions for star formation used in some semianalytic models of galaxy evolution require moderate revision, although the general prediction that gas mass fraction should increase with redshift is validated. The length of cB58's star formation episode relative to the time elapsed over the redshift range 2.5<=z<=3.5 strongly argues against scenarios in which observed LBGs cohabit their halos with a large number of similar but ``dormant'' systems whose starbursts have faded or not yet begun. As a useful empirical result, we find that the observed line/continuum ratio for cB58 is similar to those of high-redshift systems with quite

  20. Lyman Break Galaxies at z ~ 5: Rest-Frame UV Spectra. III.

    NASA Astrophysics Data System (ADS)

    Kajino, Hiroki; Ohta, Kouji; Iwata, Ikuru; Yabe, Kiyoto; Yuma, Suraphong; Akiyama, Masayuki; Tamura, Naoyuki; Aoki, Kentaro; Sawicki, Marcin

    2009-10-01

    We present results of optical spectroscopic observations of candidates of Lyman break galaxies (LBGs) at z ~ 5 in the region, including the GOODS-N and the J0053+1234 regions by using Gemini Multi-Object Spectrograph North and South, respectively. Among 25 candidates, five objects are identified to be at z ~ 5 (two of them were already identified by an earlier study) and one object very close to the color-selection window turned out to be a foreground galaxy. With this spectroscopically identified sample and those from previous studies, we derived the lower limits on the number density of bright (MUV < -22.0 mag) LBGs at z ~ 5. These lower limits are comparable to or slightly smaller than the number densities of UV luminosity functions (UVLFs) that show the smaller number density among z ~ 5 UVLFs in literature. However, by considering that there remain many LBG candidates without spectroscopic observations, the number density of bright LBGs is expected to increase by a factor of two or more. The evidence for the deficiency of UV luminous LBGs with large Lyα equivalent widths was reinforced. We discuss possible causes for the deficiency and prefer the interpretation of dust absorption. 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 National Science Foundation on behalf of the Gemini partnership: the NSF (United States), the Science and Technology Facilities Council (United Kingdom), the National Research Council (Canada), CONICYT (Chile), the Australian Research Council (Australia), Ministério da Ciência e Tecnologia (Brazil), and SECYT (Argentina).

  1. U(1) gauge symmetry breaking in a charged closed universe

    SciTech Connect

    Kim, J.E. ); Lee, T. )

    1990-10-30

    In this paper, the authors obtain the consistency condition on a U(1) gauge boson mass in a charged closed universe, m{sup 2} = 8{pi}GJ{sup 0}J{sub 0}/(R {minus} 2{Lambda}), where J{sup 0} is the charge density.

  2. Determining attenuation laws down to the Lyman break in z~0.3 galaxies

    NASA Astrophysics Data System (ADS)

    Boquien, Mederic

    2013-10-01

    Star formation is the fundamental process transforming baryonic matter in the Universe, and governing the cycling of gas in-and-out of galaxies. Tracing accurately star formation is of critical importance to discriminate between galaxy evolution models.The UV is where massive young stars emit the bulk of their energy and the wavelength of choice to track the evolution of the star formation across cosmic times. Presence of dust, however, impacts the UV emission from galaxies, by dimming and reddening it. Correcting the UV for dust attenuation is thus a crucial requirement to derive the physical parameters of galaxies. Significant variations from the widely used "starburst law" are observed from one galaxy to another, which may reflect systematic variations with stellar populations or galaxy morphology. These uncharacterized variations pose an important limitation to our ability to quantify properties of high-redshift galaxies, a regime where the starburst law is almost universally applied.In order to determine and parametrize attenuation laws in the UV down to the Lyman break we propose to perform COS FUV spectroscopy on a sample of 8 star-forming galaxies at z~0.3. While broadband data can constrain dust masses and optical depth, they cannot reliably constrain the attenuation law itself due to degeneracies between the competing effects of stellar populations and dust. The combination of COS spectra with existing broadband observations will be crucial to address this issue. This will allow us to constrain dust models and will have a broad impact on the study of galaxies from the galactic neighborhood to ultra-high redshifts.

  3. CAN AGN FEEDBACK BREAK THE SELF-SIMILARITY OF GALAXIES, GROUPS, AND CLUSTERS?

    SciTech Connect

    Gaspari, M.; Brighenti, F.; Temi, P.

    2014-03-01

    It is commonly thought that active galactic nucleus (AGN) feedback can break the self-similar scaling relations of galaxies, groups, and clusters. Using high-resolution three-dimensional hydrodynamic simulations, we isolate the impact of AGN feedback on the L {sub x}-T {sub x} relation, testing the two archetypal and common regimes, self-regulated mechanical feedback and a quasar thermal blast. We find that AGN feedback has severe difficulty in breaking the relation in a consistent way. The similarity breaking is directly linked to the gas evacuation within R {sub 500}, while the central cooling times are inversely proportional to the core density. Breaking self-similarity thus implies breaking the cool core, morphing all systems to non-cool-core objects, which is in clear contradiction with the observed data populated by several cool-core systems. Self-regulated feedback, which quenches cooling flows and preserves cool cores, prevents dramatic evacuation and similarity breaking at any scale; the relation scatter is also limited. The impulsive thermal blast can break the core-included L {sub x}-T {sub x} at T {sub 500} ≲ 1 keV, but substantially empties and overheats the halo, generating a perennial non-cool-core group, as experienced by cosmological simulations. Even with partial evacuation, massive systems remain overheated. We show that the action of purely AGN feedback is to lower the luminosity and heat the gas, perpendicular to the fit.

  4. Physical properties of local star-forming analogues to z ˜ 5 Lyman-break galaxies

    NASA Astrophysics Data System (ADS)

    Greis, Stephanie M. L.; Stanway, Elizabeth R.; Davies, Luke J. M.; Levan, Andrew J.

    2016-07-01

    Intense, compact, star-forming galaxies are rare in the local Universe but ubiquitous at high redshift. We interpret the 0.1-22 μm spectral energy distributions of a sample of 180 galaxies at 0.05 < z < 0.25 selected for extremely high surface densities of inferred star formation in the ultraviolet. By comparison with well-established stellar population synthesis models, we find that our sample comprises young (˜60-400 Myr), moderate mass (˜6 × 109 M⊙) star-forming galaxies with little dust extinction (mean stellar continuum extinction Econt(B - V) ˜ 0.1) and find star formation rates of a few tens of solar masses per year. We use our inferred masses to determine a mean specific star formation rate for this sample of ˜10-9 yr-1, and compare this to the specific star formation rates in distant Lyman-break galaxies (LBGs), and in other low-redshift populations. We conclude that our sample's characteristics overlap significantly with those of the z ˜ 5 LBG population, making ours the first local analogue population well tuned to match those high-redshift galaxies. We consider implications for the origin and evolution of early galaxies.

  5. A Resolved Map of the Infrared Excess in a Lyman Break Galaxy at z = 3

    NASA Astrophysics Data System (ADS)

    Koprowski, M. P.; Coppin, K. E. K.; Geach, J. E.; Hine, N. K.; Bremer, M.; Chapman, S.; Davies, L. J. M.; Hayashino, T.; Knudsen, K. K.; Kubo, M.; Lehmer, B. D.; Matsuda, Y.; Smith, D. J. B.; van der Werf, P. P.; Violino, G.; Yamada, T.

    2016-09-01

    We have observed the dust continuum of 10 z = 3.1 Lyman break galaxies with the Atacama Large Millimeter/submillimeter Array at ∼450 mas resolution in Band 7. We detect and resolve the 870 μm emission in one of the targets with a flux density of S 870 = 192 ± 57 μJy, and measure a stacked 3σ signal of S 870 = 67 ± 23 μJy for the remaining nine. The total infrared luminosities are L 8–1000 = (8.4 ± 2.3) × 1010 L ⊙ for the detection and L 8–1000 = (2.9 ± 0.9) × 1010 L ⊙ for the stack. With Hubble Space Telescope Advanced Camera for Surveys I-band imaging we map the rest-frame UV emission on the same scale as the dust, effectively resolving the “infrared excess” (IRX = L FIR/L UV) in a normal galaxy at z = 3. Integrated over the galaxy we measure IRX = 0.56 ± 0.15, and the galaxy-averaged UV slope is β = ‑1.25 ± 0.03. This puts the galaxy a factor of ∼10 below the IRX–β relation for local starburst nuclei of Meurer et al. However, IRX varies by more than a factor of 3 across the galaxy, and we conclude that the complex relative morphology of the dust relative to UV emission is largely responsible for the scatter in the IRX–β relation at high-z. A naive application of a Meurer-like dust correction based on the UV slope would dramatically overestimate the total star formation rate, and our results support growing evidence that when integrated over the galaxy, the typical conditions in high-z star-forming galaxies are not analogous to those in the local starburst nuclei used to establish the Meurer relation.

  6. The Evolutionary History of Lyman Break Galaxies Between Redshift 4 and 6: Observing Successive Generations of Massive Galaxies in Formation

    NASA Astrophysics Data System (ADS)

    Stark, Daniel P.; Ellis, Richard S.; Bunker, Andrew; Bundy, Kevin; Targett, Tom; Benson, Andrew; Lacy, Mark

    2009-06-01

    We present new measurements of the evolution in the Lyman break galaxy (LBG) population between z sime 4 and z sime 6. By utilizing the extensive multiwavelength data sets available in the GOODS fields, we identify 2443 B, 506 V, and 137 i'-band dropout galaxies likely to be at z ≈ 4, 5, and 6. For the subset of dropouts for which reliable Spitzer IRAC photometry is feasible (roughly 35% of the sample), we estimate luminosity-weighted ages and stellar masses. With the goal of understanding the duration of typical star formation episodes in galaxies at z gsim 4, we examine the distribution of stellar masses and ages as a function of cosmic time. We find that at a fixed rest-UV luminosity, the average stellar masses and ages of galaxies do not increase significantly between z sime 6 and 4. In order to maintain this near equilibrium in the average properties of high-redshift LBGs, we argue that there must be a steady flux of young, newly luminous objects at each successive redshift. When considered along with the short duty cycles inferred from clustering measurements, these results may suggest that galaxies are undergoing star formation episodes lasting only several hundred million years. In contrast to the unchanging relationship between the average stellar mass and rest-UV luminosity, we find that the number density of massive galaxies increases considerably with time over 4 lsim z lsim 6. Given this rapid increase of UV luminous massive galaxies, we explore the possibility that a significant fraction of massive (1011 M sun) z sime 2-3 distant red galaxies (DRGs) were in part assembled in an LBG phase at earlier times. Integrating the growth in the stellar mass function of actively forming LBGs over 4 lsim z lsim 6 down to z sime 2, we find that z gsim 3 LBGs could have contributed significantly to the quiescent DRG population, indicating that the intense star-forming systems probed by submillimeter observations are not the only route toward the assembly of DRGs

  7. X-Ray Properties of Lyman Break Galaxies in the Hubble Deep Field North Region

    NASA Technical Reports Server (NTRS)

    Nandra, K.; Mushotzky, R. F.; Arnaud, K.; Steidel, C. C.; Adelberger, K. L.; Gardner, J. P.; Teplitz, H. I.; Windhorst, R. A.; White, Nicholas E. (Technical Monitor)

    2002-01-01

    We describe the X-ray properties of a large sample of z approximately 3 Lyman Break Galaxies (LBGs) in the region of the Hubble Deep Field North, derived from the 1 Ms public Chandra observation. Of our sample of 148 LBGs, four are detected individually. This immediately gives a measure of the bright AGN (active galactic nuclei) fraction in these galaxies of approximately 3 per cent, which is in agreement with that derived from the UV (ultraviolet) spectra. The X-ray color of the detected sources indicates that they are probably moderately obscured. Stacking of the remainder shows a significant detection (6 sigma) with an average luminosity of 3.5 x 10(exp 41) erg/s per galaxy in the rest frame 2-10 keV band. We have also studied a comparison sample of 95 z approximately 1 "Balmer Break" galaxies. Eight of these are detected directly, with at least two clear AGN based on their high X-ray luminosity and very hard X-ray spectra respectively. The remainder are of relatively low luminosity (< 10(exp 42) erg/s, and the X-rays could arise from either AGN or rapid star-formation. The X-ray colors and evidence from other wavebands favor the latter interpretation. Excluding the clear AGN, we deduce a mean X-ray luminosity of 6.6 x 10(exp 40) erg/s, a factor approximately 5 lower than the LBGs. The average ratio of the UV and X-ray luminosities of these star forming galaxies L(sub UV)/L (sub X), however, is approximately the same at z = 1 as it is at z = 3. This scaling implies that the X-ray emission follows the current star formation rate, as measured by the UV luminosity. We use our results to constrain the star formation rate at z approximately 3 from an X-ray perspective. Assuming the locally established correlation between X-ray and far-IR (infrared) luminosity, the average inferred star formation rate in each Lyman break galaxy is found to be approximately 60 solar mass/yr, in excellent agreement with the extinction-corrected UV estimates. This provides an external

  8. Harnessing High Redshift Beacons: IRS Spectra of Lensed Lyman Break Galaxies

    NASA Astrophysics Data System (ADS)

    Siana, Brian; Coppin, Kristen; Ebeling, Harald; Edge, Alastair; Ellis, Richard; Kneib, Jean-Paul; Pettini, Max; Richard, Johan; Smail, Ian; Swinbank, Mark; Teplitz, Harry

    2007-05-01

    Star-formation at high redshift occurs in two types of galaxies: dusty Ultra-Luminous Infrared Galaxies (ULIRGs) and UV-bright Lyman Break Galaxies (LBGs). In both populations dust absorbs most of the ultraviolet (UV) light from young stars and re-emits the energy in the infrared (IR). Therefore, detailed studies of the dust and the infrared SEDs of these galaxies are critical for understanding these important evolutionary stages in galaxy formation. ULIRGs at z ~ 2-3 are luminous enough for both submm detection and Spitzer IRS spectroscopy, so much has been learned recently about their interstellar medium and IR SEDs. LBGs are too faint to be detected with submm imaging or IRS spectroscopy so little can be discovered about their dust content and IR SEDs prior to JWST and ALMA. Fortunately, there exist a few rare examples of LBGs which are strongly lensed by a foreground cluster or galaxy, and are magnified by factors of 10-30. We can therefore study in detail the infrared properties of this otherwise inaccessible population. Our group will obtain (in an approved Cycle-3 program) IRS spectroscopy of the most famous LBG, cB58, but it is clearly dangerous to draw wide-ranging conclusions about the LBG population based on this single object. We therefore propose for a detailed Spitzer study of the only other known bright lensed LBGs: the 'Cosmic Eye' and the '8-O'clock Arc'. The requested program uses IRS spectroscopy, IRS Peak-Up 16 micron, MIPS 70 micron, and IRAC imaging to fully characterize the gas and dust in the ISM of these galaxies and determine the shape of the IR SEDs. Together, the three lensed sources span the full range of star-formation rates and dust attenuation levels observed in LBGs. Therefore, we can correlate these properties with the infrared SEDs and emission-line properties (PAHs) and apply the correlations when examining the entire LBG population.

  9. Optical-to-IR Photometric Properties of Lyman Break Galaxies in the HDF-North

    NASA Astrophysics Data System (ADS)

    Papovich, C.; Dickinson, M.; Ferguson, H.; NICMOS HDF--N GO Team

    1999-12-01

    We present the photometric properties of Lyman Break Galaxies (LBGs) in the Hubble Deep Field North (HDF--N) using deep seven--band photometry from WFPC2 (UBVI, Williams et al. 1996), NICMOS (JH, Dickinson et al. 2000), and newly derived Ks--band photometry from ground--based KPNO data (Dickinson 1997; Papovich & Dickinson 2000). For the 27 HDF galaxies with spectroscopic redshifts 2.0 ≲ z ≲ 3.5, our photometry spans rest frame wavelengths extending from the Lyman limit through rest--frame λ 0 ≳ 5000 Angstroms. In this poster, we compare the spectral energy distributions (SEDs) of the LBGs to empirical spectral templates from Kinney et al. (1996) and Coleman, Wu, & Weedman (1980), and to population synthesis models from Bruzual & Charlot (1996). We consider general constraints on galaxy ages, star formation histories, and extinction. By selection, the LBGs contain strong, blue UV continua. In general, they are well fit by local starburst templates. To fit the SEDs of specific galaxies, most require modest but non--zero reddening. At rest--frame optical wavelengths, many galaxies show evidence for significant contributions from longer lived (A and later) stars, but none appear to be dominated by old (red) stellar populations. In some cases, there may be significant broad band flux contributions from strong nebular emission lines ([N 2]+Hα , [O 3]+Hβ , [O 2]). We discuss the implications for the evolutionary history of these galaxies using these empirical results. Support for this work is provided by NASA through grant GO-07817.01-96A.

  10. A Lyman Break Galaxy in the Epoch of Reionization from Hubble Space Telescope (HST) Grism Spectroscopy

    NASA Technical Reports Server (NTRS)

    Rhoads, James E.; Malhotra, Sangeeta; Stern, Daniel K.; Gardner, Jonathan P.; Dickinson, Mark; Pirzkal, Norbert; Spinrad, Hyron; Reddy, Naveen; Dey, Arjun; Hathi, Nimish; Grogin, Norman; Koekemoer, Anton; Peth, Michael A.; Cohen, Seth; Budavari, Tamas; Ferreras, Ignacio; Gronwall, Caryl; Haiman, Zoltan; Meurer, Gernhardt; Straughn, Amber N.

    2013-01-01

    Slitless grism spectroscopy from space offers dramatic advantages for studying high redshift galaxies: high spatial resolution to match the compact sizes of the targets, a dark and uniform sky background, and simultaneous observation over fields ranging from five square arcminutes (HST) to over 1000 square arcminutes (Euclid). Here we present observations of a galaxy at z = 6.57 the end of the reioinization epoch identified using slitless HST grism spectra from the PEARS survey (Probing Evolution And Reionization Spectroscopically) and reconfirmed with Keck + DEIMOS. This high redshift identification is enabled by the depth of the PEARS survey. Substantially higher redshifts are precluded for PEARS data by the declining sensitivity of the ACS grism at greater than lambda 0.95 micrometers. Spectra of Lyman breaks at yet higher redshifts will be possible using comparably deep observations with IR-sensitive grisms.

  11. SPECTROSCOPIC CONFIRMATION OF z {approx} 7 LYMAN BREAK GALAXIES: PROBING THE EARLIEST GALAXIES AND THE EPOCH OF REIONIZATION

    SciTech Connect

    Pentericci, L.; Fontana, A.; Castellano, M.; Grazian, A.; Boutsia, K.; Giallongo, E.; Maiolino, R.; Paris, D.; Santini, P.; Vanzella, E.; Cristiani, S.; Dijkstra, M.; Dickinson, M.; Giavalisco, M.; Moorwood, A.

    2011-12-20

    We present the final results from our ultra-deep spectroscopic campaign with FORS2 at the ESO Very Large Telescope (VLT) for the confirmation of z {approx_equal} 7 'z-band dropout' candidates selected from our VLT/Hawk-I imaging survey over three independent fields. In particular, we report on two newly discovered galaxies at redshift {approx}6.7 in the New Technology Telescope Deep Field. Both galaxies show an Ly{alpha} emission line with rest-frame equivalent widths (EWs) of the order of 15-20 A and luminosities of (2-4) Multiplication-Sign 10{sup 42} erg s{sup -1}. We also present the results of ultra-deep observations of a sample of i-dropout galaxies, from which we set a solid upper limit on the fraction of interlopers. Out of the 20 z-dropouts observed we confirm 5 galaxies at 6.6 < z < 7.1. This is systematically below the expectations drawn on the basis of lower redshift observations: in particular, there is a significant lack of objects with intermediate Ly{alpha} EWs (between 20 and 55 A). We conclude that the observed trend for the rising fraction of Ly{alpha} emission in Lyman break galaxies from z {approx} 3 to z {approx} 6 is most probably reversed from z {approx} 6 to z {approx} 7. Explaining the observed rapid change in the Ly{alpha} emitter fraction among the dropout population with reionization requires a fast evolution of the neutral fraction of hydrogen in the universe. Assuming that the universe is completely ionized at z = 6 and adopting a set of semi-analytical models, we find that our data require a change of the neutral hydrogen fraction of the order of {Delta}{chi}{sub H{sub i}}{approx}0.6 in a time {Delta}z {approx} 1, provided that the escape fraction does not increase dramatically over the same redshift interval.

  12. FAR-INFRARED PROPERTIES OF LYMAN BREAK GALAXIES FROM COSMOLOGICAL SIMULATIONS

    SciTech Connect

    Cen Renyue

    2011-12-15

    Utilizing state-of-the-art adaptive mesh refinement cosmological hydrodynamic simulations with ultra-high resolution (114 h{sup -1} pc) and a large sample size ({>=}3300 galaxies of stellar mass {>=}10{sup 9} M{sub Sun }), we show how the stellar light of Lyman break galaxies at z = 2 is distributed between optical/ultraviolet (UV) and far-infrared (FIR) bands. With a single scalar parameter for dust obscuration we can simultaneously reproduce the observed UV luminosity function for the entire range (3-100 M{sub Sun} yr{sup -1}) and extant FIR luminosity function at the bright end ({>=}20 M{sub Sun} yr{sup -1}). We quantify that galaxies more massive or having higher star formation rate (SFR) tend to have larger amounts of dust obscuration mostly due to a trend in column density and in a minor part due to a mass (or SFR)-metallicity relation. It is predicted that the FIR luminosity function in the range SFR = 1-100 M{sub Sun} yr{sup -1} is a power law with a slope of about -1.7. We further predict that there is a 'galaxy desert' at SFR{sub FIR} < 0.02(SFR{sub UV}/10 M{sub Sun} yr{sup -1}){sup 2.1} M{sub Sun} yr{sup -1} in the SFR{sub UV} - SFR{sub FIR} plane. Detailed distributions of SFR{sub FIR} at a fixed SFR{sub UV} are presented. Upcoming observations by the Atacama Large Millimeter Array should test this model. If confirmed, it validates the predictions of the standard cold dark matter model and has important implications on the intrinsic SFR function of galaxies at high redshift.

  13. Formation of ring structures in galactic disks during close passages of galaxies

    NASA Astrophysics Data System (ADS)

    Tutukov, A. V.; Fedorova, A. V.

    2016-01-01

    The formation of ring structures in galactic disks is investigated. It is shown that, in addition to the known mechanism of forming rings in "head-on" collisions between galaxies, ring structures can be formed during close passages of galaxies if the perturbing galaxy moves in a plane close to the equatorial plane of the perturbed disk galaxy, opposite to the direction of rotation of the disk. Numerical simulations of the formation of structures in the disk of a massive galaxy undergoing a passage with another galaxy are considered. The results of these cmputations show the formation of pronounced ring structures in the galactic disk when the initial inclination of the trajectory of the perturbing galaxy to the equatorial plane of the perturbed galaxy is no more than ~25°. However, the probability of close passages of galaxies with these parameters is small, as is the probability of head-on collisions. The characteristic time scale for the existence of pronounced rings is of order the dynamical time scale at the edge of the galaxy, 200-300 million years, close to the corresponding time for head-on collisions. The evolution of the rings has the same character in both cases: they gradually expand and move toward the periphery of the galaxy. The results of these simulations can also be applied to a close passage of one star by another star with a protoplanetary disk. According to the computation results, the characteristic time scale for the existence of pronounced rings in such a protoplanetary disk depends mainly on the size of the disk; this time scale can reach several tens of thousands of years for a disk radius of about 1000 AU. The formation of ring structures in such a disk could influence the formation and evolution of planetesimals, and possibly the character of the formation of planets and the distribution of their orbital semi-major axes.

  14. SPECTROSCOPIC CONFIRMATION OF FAINT LYMAN BREAK GALAXIES NEAR REDSHIFT FIVE IN THE HUBBLE ULTRA DEEP FIELD

    SciTech Connect

    Rhoads, James E.; Malhotra, Sangeeta; Cohen, Seth; Grogin, Norman; Hathi, Nimish; Ryan, Russell; Straughn, Amber; Windhorst, Rogier A. Pirzkal, Norbert; Xu Chun; Koekemoer, Anton; Panagia, Nino; Dickinson, Mark; Ferreras, Ignacio; Gronwall, Caryl; Kuemmel, Martin; Walsh, Jeremy; Meurer, Gerhardt; Pasquali, Anna; Yan, H.-J.

    2009-05-20

    We present the faintest spectroscopically confirmed sample of z {approx} 5 Lyman break galaxies (LBGs) to date. The sample is based on slitless grism spectra of the Hubble Ultra Deep Field region from the Grism ACS Program for Extragalactic Science (GRAPES) and Probing Evolution and Reionization Spectroscopically (PEARS) projects, using the G800L grism on the Hubble Space Telescope Advanced Camera for Surveys. We report here confirmations of 39 galaxies, preselected as candidate LBGs using photometric selection criteria. We compare a 'traditional' V-dropout selection, based on the work of Giavalisco et al., to a more liberal one (with V - i > 0.9), and find that the traditional criteria are about 64% complete and 81% reliable. We also study the Ly{alpha} emission properties of our sample. We find that Ly{alpha} emission is detected in {approx}1/4 of the sample, and that the liberal V-dropout color selection includes {approx}55% of previously published line-selected Ly{alpha} sources. Finally, we examine our stacked two-dimensional spectra. We demonstrate that strong, spatially extended ({approx}1'') Ly{alpha} emission is not a generic property of these LBGs, but that a modest extension of the Ly{alpha} photosphere (compared to the starlight) may be present in those galaxies with prominent Ly{alpha} emission.

  15. The clustering and halo occupation distribution of Lyman-break galaxies at z ˜ 4

    NASA Astrophysics Data System (ADS)

    Park, Jaehong; Kim, Han-Seek; Wyithe, J. Stuart B.; Lacey, C. G.; Baugh, C. M.; Barone-Nugent, R. L.; Trenti, M.; Bouwens, R. J.

    2016-09-01

    We investigate the clustering of Lyman-break galaxies (LBGs) at z ˜ 4. Using the hierarchical galaxy formation model GALFORM, we predict, for the first time using a semi-analytical model with feedback from active galactic nuclei (AGN), the angular correlation function (ACF) of LBGs and find agreement within 3σ with new measurements of the ACF from surveys including the Hubble eXtreme Deep Field (XDF) and Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) field. Our simulations confirm the conclusion reached using independent models that although the predicted ACFs reproduce the trend of increased clustering with luminosity, the dependence is less strong than observed. We find that for the detection limits of the XDF field, central LBGs at z ˜ 4 predominantly reside in haloes of mass ˜1011-1012 h-1 M⊙ and that satellites reside in larger haloes of mass ˜1012-1013 h-1 M⊙. The model predicts fewer bright satellite LBGs at z ˜ 4 than is inferred from measurements of the ACF at small scales. By analysing the halo occupation distribution (HOD) predicted by the model, we find evidence that AGN feedback affects the HOD of central LBGs in massive haloes. This is a new high-redshift test of this important feedback mechanism. We investigate the effect of photometric errors in the observations on the ACF predictions. We find that the observational uncertainty in the galaxy luminosity reduces the clustering amplitude and that this effect increases towards faint galaxies, particularly on small scales. To compare properties of model with observed LBGs, this uncertainty must be considered.

  16. The clustering and halo occupation distribution of Lyman-break galaxies at z ˜ 4

    NASA Astrophysics Data System (ADS)

    Park, Jaehong; Kim, Han-Seek; Wyithe, J. Stuart B.; Lacey, C. G.; Baugh, C. M.; Barone-Nugent, R. L.; Trenti, M.; Bouwens, R. J.

    2016-06-01

    We investigate the clustering of Lyman-break galaxies (LBGs) at z ˜ 4. Using the hierarchical galaxy formation model GALFORM, we predict, for the first time using a semi-analytical model with feedback from active galactic nuclei (AGN), the angular correlation function (ACF) of LBGs and find agreement within 3 σ with new measurements of the ACF from surveys including the Hubble eXtreme Deep Field (XDF) and CANDELS field. Our simulations confirm the conclusion reached using independent models that although the predicted ACFs reproduce the trend of increased clustering with luminosity, the dependence is less strong than observed. We find that for the detection limits of the XDF field central LBGs at z ˜ 4 predominantly reside in haloes of mass ˜1011 - 1012h-1M⊙ and that satellites reside in larger haloes of mass ˜1012 - 1013h-1M⊙. The model predicts fewer bright satellite LBGs at z ˜ 4 than is inferred from measurements of the ACF at small scales. By analysing the halo occupation distribution (HOD) predicted by the model, we find evidence that AGN feedback affects the HOD of central LBGs in massive haloes. This is a new high-redshift test of this important feedback mechanism. We investigate the effect of photometric errors in the observations on the ACF predictions. We find that the observational uncertainty in the galaxy luminosity reduces the clustering amplitude and that this effect increases towards faint galaxies, particularly on small scales. To compare properties of model with observed LBGs this uncertainty must be considered.

  17. Bright z ~ 3 Lyman break galaxies in deep wide field surveys

    NASA Astrophysics Data System (ADS)

    Bian, Fuyan

    In my thesis I investigate the luminous z ˜ 3 Lyman break galaxies in deep wide field surveys. In the first part of the thesis, I use the LBT/LUCIFER to observe a lensed high-redshift star-forming galaxy (J0900+2234) at z = 2.03. With the high S/N near-IR spectroscopic observations, I reveal the detailed physical properties of this high-redshift galaxy, including SFR, metallicity, dust extinction, dynamical mass, and electron number density. In the second part of the thesis, I select a large sample of LBGs at z ˜ 3 from our new LBT Bootes field survey, and study the bright end luminosity function (LF), stellar mass function (SMF) and clustering properties of bright LBGs (1L* < L < 2.5L*). Together with other LF and SMF measurements, the evolution of LF and SMF can be well described by continuously rising star formation history model. Using the clustering measurements in this work and other works, a tight relation between the average host galaxy halo mass and the galaxy star formation rate is found, which can be interpreted as arising from cold flow accretion. The relation also suggests that the cosmic star formation efficiency is about 5%-20% of the total cold flow mass. This cosmic star formation efficiency does not evolve with redshift (from z ˜ 5 to z ˜ 3), hosting dark matter halo mass (1011 -- 1013 M⊙ ), or galaxy luminosity (from 0.3L* to 3L* ). In the third and fourth parts, with the spectroscopic follow-up observations of the bright LBGs, I establish a sample of spectroscopically-confirmed ultraluminous LBGs (ULBGs) in NOAO Boo¨tes field. With this new ULBG sample, the rest-frame UV LF of LBG at M1700A = -23.0 was measured for the first time. I find that the ULBGs have larger outflow velocity, broader Lyalpha emission and ISM absorption line profiles, and more prominent C IV P-Cygni profile. This profile may imply a top-heavy IMF in these ULBGs. The ULBGs have larger stellar mass and SFR, but smaller dust extinction than the typical L* LBGs at z ˜ 2

  18. Evidence for Black Hole Growth in Local Analogs to Lyman Break Galaxies

    NASA Technical Reports Server (NTRS)

    Jia, Jianjun; Ptak, Andrew; Heckman, Timothy M.; Overzier, Roderik A.; Hornschemeier, Ann; LaMassa, Stephanie M.

    2011-01-01

    We have used XMM-Newton to observe six Lyman break analogs (LBAs): members of the rare population of local galaxies that have properties that are very similar to distant Lyman break galaxies. Our six targets were specifically selected because they have optical emission-line properties that are intermediate between starbursts and Type 2 (obscured) active galactic nuclei (AGNs). Our new X-ray data provide an important diagnostic of the presence of an AGN. We find X-ray luminosities of order 10(sup 42) erg per second and ratios of X-ray to far-IR lummositles that are higher than values in pure starburst galaxies by factors ranging from approximately 3 to 30. This strongly suggests the presence of an AGN in at least some of the galaxies. The ratios of the luminosities of the hard (2-10 keV) X-ray to [O III] emission line are low by about an order of magnitude compared with Type 1 AGN, but are consistent with the broad range seen in Type 2 AGN. Either the AGN hard X-rays are significantly obscured or the [O III] emission is dominated by the starburst. We searched for an iron emission line at approximately 6.4 ke V, which is a key feature of obscured AGNs, but only detected emission at the approximately 2sigma level. Finally, we find that the ratios of the mid-infrared (24 micrometer) continuum to [O III]lambda 5007 luminosities in these LBAs are higher than the values for Type 2 AGN by an average of 0.8 dex. Combining all these clues, we conclude that an AGN is likely to be present, but that the bolometric luminosity is produced primarily by an intense starburst. If these black holes are radiating at the Eddington limit, their masses would lie in the range of 10(sup 5) - 10(sup 6) solar mass. These objects may offer ideal local laboratories to investigate the processes by which black holes grew in the early universe.

  19. Determining the evolutionary history of galaxies by astrocladistics : some results on close galaxies.

    NASA Astrophysics Data System (ADS)

    Fraix-Burnet, D.

    2006-06-01

    Astrocladistics, a methodology borrowed from biology, is an objective way of understanding galaxy diversity through evolutionary relationships. It is based on the evolution of all the available parameters describing galaxies and thus integrates the complexity of these objects. Through the formalization of the concepts around galaxy formation and evolution, and the identification of the processes of diversification (build up, secular evolution, interaction, merging/accretion, sweeping/ejection), galaxy diversity can be expected to organize itself in a hierarchy. About 500 galaxies described by about 40 observables have now been analysed and several robust trees found. For instance, we show that the Dwarf Galaxies of the Local Group all derive from a common ancestral kind of objects. We identify three evolutionary groups, each one having its own characteristics and own evolution. The Virgo galaxies present a relatively regular diversification, with rather few violent events such as major mergers. Diversification in another sample made of gas-poor galaxies in different environments appears to be slightly more complicated with several diverging evolutionary groups. Work on a large sample of galaxies at non-zero redshifts is in progress and is pioneering a brand new approach to exploit data from the big extragalactic surveys.

  20. BREAKS IN THIN AND THICK DISKS OF EDGE-ON GALAXIES IMAGED IN THE SPITZER SURVEY OF STELLAR STRUCTURE IN GALAXIES (S{sup 4}G)

    SciTech Connect

    Comeron, Sebastien; Salo, Heikki; Laurikainen, Eija; Laine, Jarkko; Elmegreen, Bruce G.; Athanassoula, E.; Bosma, Albert; Knapen, Johan H.; Gadotti, Dimitri A.; Sheth, Kartik; Munoz-Mateos, Juan Carlos; Kim, Taehyun; Hinz, Joannah L.; Regan, Michael W.; Gil de Paz, Armando; Menendez-Delmestre, Karin; Seibert, Mark; Ho, Luis C.; Mizusawa, Trisha; Holwerda, Benne

    2012-11-10

    Breaks in the radial luminosity profiles of galaxies have until now been mostly studied averaged over disks. Here, we study separately breaks in thin and thick disks in 70 edge-on galaxies using imaging from the Spitzer Survey of Stellar Structure in Galaxies. We built luminosity profiles of the thin and thick disks parallel to midplanes and we found that thin disks often truncate (77%). Thick disks truncate less often (31%), but when they do, their break radius is comparable with that in the thin disk. This suggests either two different truncation mechanisms-one of dynamical origin affecting both disks simultaneously and another one only affecting the thin disk-or a single mechanism that creates a truncation in one disk or in both depending on some galaxy property. Thin disks apparently antitruncate in around 40% of galaxies. However, in many cases, these antitruncations are an artifact caused by the superposition of a thin disk and a thick disk, with the latter having a longer scale length. We estimate the real thin disk antitruncation fraction to be less than 15%. We found that the ratio of the thick and thin stellar disk mass is roughly constant (0.2 < M{sub T} /M{sub t} < 0.7) for circular velocities v{sub c} > 120 km s{sup -1}, but becomes much larger at smaller velocities. We hypothesize that this is due to a combination of a high efficiency of supernova feedback and a slower dynamical evolution in lower-mass galaxies causing stellar thin disks to be younger and less massive than in higher-mass galaxies.

  1. Late-time Observations of GRB 080319B: Jet Break, Host Galaxy, and Accompanying Supernova

    NASA Astrophysics Data System (ADS)

    Tanvir, N. R.; Rol, E.; Levan, A. J.; Svensson, K.; Fruchter, A. S.; Granot, J.; O'Brien, P. T.; Wiersema, K.; Starling, R. L. C.; Jakobsson, P.; Fynbo, J.; Hjorth, J.; Curran, P. A.; van der Horst, A. J.; Kouveliotou, C.; Racusin, J. L.; Burrows, D. N.; Genet, F.

    2010-12-01

    The Swift-discovered GRB 080319B was by far the most distant source ever observed at naked-eye brightness, reaching a peak apparent magnitude of 5.3 at a redshift of z = 0.937. We present our late-time optical (Hubble Space Telescope, Gemini, and Very Large Telescope) and X-ray (Chandra) observations, which confirm that an achromatic break occurred in the power-law afterglow light curve at ~11 days post-burst. This most likely indicates that the gamma-ray burst (GRB) outflow was collimated, which for a uniform jet would imply a total energy in the jet E jet >~ 1052 erg. Our observations also show a late-time excess of red light, which is well explained if the GRB was accompanied by a supernova (SN), similar to those seen in some other long-duration GRBs. The latest observations are dominated by light from the host and show that the GRB took place in a faint dwarf galaxy (r(AB) ≈ 27.0, rest frame MB ≈ -17.2). This galaxy is small even by the standards of other GRB hosts, which is suggestive of a low-metallicity environment. Intriguingly, the properties of this extreme event—a small host and bright SN—are entirely typical of the very low luminosity bursts such as GRB 980425 and GRB 060218.

  2. LATE-TIME OBSERVATIONS OF GRB 080319B: JET BREAK, HOST GALAXY, AND ACCOMPANYING SUPERNOVA

    SciTech Connect

    Tanvir, N. R.; O'Brien, P. T.; Wiersema, K.; Starling, R. L. C.; Rol, E.; Levan, A. J.; Svensson, K.; Fruchter, A. S.; Granot, J.; Jakobsson, P.; Fynbo, J.; Hjorth, J.; Curran, P. A.; Burrows, D. N.; Genet, F.

    2010-12-10

    The Swift-discovered GRB 080319B was by far the most distant source ever observed at naked-eye brightness, reaching a peak apparent magnitude of 5.3 at a redshift of z = 0.937. We present our late-time optical (Hubble Space Telescope, Gemini, and Very Large Telescope) and X-ray (Chandra) observations, which confirm that an achromatic break occurred in the power-law afterglow light curve at {approx}11 days post-burst. This most likely indicates that the gamma-ray burst (GRB) outflow was collimated, which for a uniform jet would imply a total energy in the jet E{sub jet} {approx}> 10{sup 52} erg. Our observations also show a late-time excess of red light, which is well explained if the GRB was accompanied by a supernova (SN), similar to those seen in some other long-duration GRBs. The latest observations are dominated by light from the host and show that the GRB took place in a faint dwarf galaxy (r(AB) {approx} 27.0, rest frame M{sub B} {approx} -17.2). This galaxy is small even by the standards of other GRB hosts, which is suggestive of a low-metallicity environment. Intriguingly, the properties of this extreme event-a small host and bright SN-are entirely typical of the very low luminosity bursts such as GRB 980425 and GRB 060218.

  3. INDECENT EXPOSURE IN SEYFERT 2 GALAXIES: A CLOSE LOOK

    SciTech Connect

    Tran, Hien D.; Lyke, J. E.; Mader, Jeff A.

    2011-01-10

    NGC 3147, NGC 4698, and 1ES 1927+654 are active galaxies that are classified as Seyfert 2s, based on the line ratios of strong narrow emission lines in their optical spectra. However, they exhibit rapid X-ray spectral variability and/or little indication of obscuration in X-ray spectral fitting, contrary to expectation from the active galactic nucleus (AGN) unification model. Using optical spectropolarimetry with LRIS and near-infrared spectroscopy with NIRSPEC at the W. M. Keck Observatory, we conducted a deep search for hidden polarized broad H{alpha} and direct broad Pa{beta} or Br{gamma} emission lines in these objects. We found no evidence for any broad emission lines from the active nuclei of these galaxies, suggesting that they are unobscured, completely 'naked' AGNs that intrinsically lack broad-line regions.

  4. Rest-Frame Mid-Infrared Detection of an Extremely Luminous Lyman Break Galaxy with the Spitzer Infrared Spectrograph (IRS)

    NASA Technical Reports Server (NTRS)

    Teplitz, H. I.; Charmandaris, V.; Armus, L.; Appleton, P. N.; Houck, J. R.; Soifer, B. T.; Weedman, D.; Brandl, B. R.; vanCleve, J.; Grillmair, C.; Uchid, K. I.

    2004-01-01

    We present the first rest-frame of approximately 4 microns detection of a Lyman break galaxy. The data were obtained using the 16 microns imaging capability of the Spitzer Infrared Spectrograph. The target object, J134026.44+634433.2, is an extremely luminous Lyman break galaxy at z=2.79, first identified in Sloan Digital Sky Survey (SDSS) spectra (as reported by Bentz et al.). The source is strongly detected with a flux of 0.94 +/- 0.02 mJy. Combining Spitzer and SDSS photometry with supporting ground-based J- and K-band data, we show that the spectral energy distribution is consistent with an actively star-forming galaxy. We also detect other objects in the Spitzer field of view, including a very red mid-infrared source. We find no evidence of a strong lens among the mid-infrared sources.

  5. A LYMAN BREAK GALAXY IN THE EPOCH OF REIONIZATION FROM HUBBLE SPACE TELESCOPE GRISM SPECTROSCOPY

    SciTech Connect

    Rhoads, James E.; Malhotra, Sangeeta; Cohen, Seth; Zheng Zhenya; Stern, Daniel; Dickinson, Mark; Pirzkal, Norbert; Grogin, Norman; Koekemoer, Anton; Peth, Michael A.; Spinrad, Hyron; Reddy, Naveen; Hathi, Nimish; Budavari, Tamas; Ferreras, Ignacio; Gardner, Jonathan P.; Gronwall, Caryl; Haiman, Zoltan; Kuemmel, Martin; Meurer, Gerhardt; and others

    2013-08-10

    We present observations of a luminous galaxy at z = 6.573-the end of the reionization epoch-which has been spectroscopically confirmed twice. The first spectroscopic confirmation comes from slitless Hubble Space Telescope Advanced Camera for Surveys grism spectra from the PEARS survey (Probing Evolution And Reionization Spectroscopically), which show a dramatic continuum break in the spectrum at rest frame 1216 A. The second confirmation is done with Keck + DEIMOS. The continuum is not clearly detected with ground-based spectra, but high wavelength resolution enables the Ly{alpha} emission line profile to be determined. We compare the line profile to composite line profiles at z = 4.5. The Ly{alpha} line profile shows no signature of a damping wing attenuation, confirming that the intergalactic gas is ionized at z = 6.57. Spectra of Lyman breaks at yet higher redshifts will be possible using comparably deep observations with IR-sensitive grisms, even at redshifts where Ly{alpha} is too attenuated by the neutral intergalactic medium to be detectable using traditional spectroscopy from the ground.

  6. Differential evolution of the UV luminosity function of Lyman break galaxies from z ~ 5 to 3

    NASA Astrophysics Data System (ADS)

    Iwata, I.; Ohta, K.; Tamura, N.; Akiyama, M.; Aoki, K.; Ando, M.; Kiuchi, G.; Sawicki, M.

    2007-04-01

    We report the ultraviolet luminosity function (UVLF) of Lyman break galaxies at z ~ 5 derived from a deep and wide survey using the prime focus camera of the 8.2 m Subaru telescope (Suprime-Cam). Target fields consist of two blank regions of the sky, namely, the region including the Hubble Deep Field-North and the J0053+1234 region, and the total effective surveyed area is 1290 arcmin2. Applications of carefully determined colour selection criteria in V - Ic and Ic - z' yield a detection of 853 z ~ 5 candidates with z'AB < 26.5 mag. The UVLF at z ~ 5 based on this sample shows no significant change in the number density of bright (L >~ L*z=3) LBGs from that at z ~ 3, while there is a significant decline in the LF's faint end with increasing look-back time. This result means that the evolution of the number densities is differential with UV luminosity: the number density of UV luminous objects remains almost constant from z ~ 5 to 3 (the cosmic age is about 1.2 to 2.1 Gyr) while the number density of fainter objects gradually increases with cosmic time. This trend becomes apparent thanks to the small uncertainties in number densities both in the bright and faint parts of LFs at different epochs that are made possible by the deep and wide surveys we use. We discuss the origins of this differential evolution of the UVLF along the cosmic time and suggest that our observational findings are consistent with the biased galaxy evolution scenario: a galaxy population hosted by massive dark haloes starts active star formation preferentially at early cosmic time, while less massive galaxies increase their number density later. We also calculated the UV luminosity density by integrating the UVLF and at z ~ 5 found it to be 38.8+6.7-4.1 per cent of that at z ~ 3 for the luminosity range L > 0.1L*z=3. By combining our results with those from the literature, we find that the cosmic UV luminosity density marks its peak at and then slowly declines towards higher redshift. Based on

  7. PHYSICAL PROPERTIES, STAR FORMATION, AND ACTIVE GALACTIC NUCLEUS ACTIVITY IN BALMER BREAK GALAXIES AT 0 < z < 1

    SciTech Connect

    Diaz Tello, J.; Donzelli, C.; Padilla, N.; Fujishiro, N.; Yoshikawa, T.; Hanami, H.; Hatsukade, B.

    2013-07-01

    We present a spectroscopic study with the derivation of the physical properties of 37 Balmer break galaxies, which have the necessary lines to locate them in star-forming-active galactic nuclei (AGNs) diagnostic diagrams. These galaxies span a redshift range from 0.045 to 0.93 and are somewhat less massive than similar samples of previous works. The studied sample has multiwavelength photometric data coverage from the ultraviolet to mid-infrared (MIR) Spitzer bands. We investigate the connection between star formation and AGN activity via optical, mass-excitation (MEx), and MIR diagnostic diagrams. Through optical diagrams, 31 (84%) star-forming galaxies, two (5%) composite galaxies, and three (8%) AGNs were classified, whereas from the MEx diagram only one galaxy was classified as AGN. A total of 19 galaxies have photometry available in all the IRAC/Spitzer bands. Of these, three AGN candidates were not classified as AGN in the optical diagrams, suggesting they are dusty/obscured AGNs, or that nuclear star formation has diluted their contributions. By fitting the spectral energy distribution of the galaxies, we derived the stellar masses, dust reddening E(B - V), ages, and UV star formation rates (SFRs). Furthermore, the relationship between SFR surface density ({Sigma}{sub SFR}) and stellar mass surface density per time unit ({Sigma}{sub M{sub */{tau}}}) as a function of redshift was investigated using the [O II] {lambda}3727, 3729, H{alpha} {lambda}6563 luminosities, which revealed that both quantities are larger for higher redshift galaxies. We also studied the SFR and specific SFR (SSFR) versus stellar mass and color relations, with the more massive galaxies having higher SFR values but lower SSFR values than less massive galaxies. These results are consistent with previous ones showing that, at a given mass, high-redshift galaxies have on average larger SFR and SSFR values than low-redshift galaxies. Finally, bluer galaxies have larger SSFR values than redder

  8. PEP/HerMES/COSMOS: What are the dust properties of z ˜ 3 lyman break galaxies?

    NASA Astrophysics Data System (ADS)

    Álvarez-Márquez, A.; Burgarella, D.; Buat, V.; Heinis, S.; Pep/Hermes/Cosmos Teams

    2015-05-01

    Context. Since the mid-90's, the sample of Lyman break galaxies has been growing up thanks to the deeper and deeper sensitivities of the telescope in optical and in near-infrared for objects at z > 2.5. However, the dust properties of these Lyman break galaxies are still elusive of badly known because the samples are small and/or biased.} Aims. We explore the dust properties in a statistical way of a sample of Lyman break galaxies (LBGs) that can not be individually detected in Herschel maps. Methods. We apply a stacking method in the Herschel and AzTEC maps to LBGs selected at 2.5 < z < 3.5 by dropout technique. Thanks to the size of the sample (˜22 000 LBGs), we can split it in several bins as a function of their ultraviolet luminosity (L_{FUV}), their ultraviolet slope (β_{UV}) and their stellar mass (M_{*}) to better catch their variety. The stacking is corrected for the incompleteness in the priors and for the clustering of the stacked galaxies in ultraviolet. Results. We obtain the full infrared spectral energy distributions of our LBGs as a function of their L_{FUV}, their β_{UV} and their M_* and we can characterize them in terms of their dust attenuation A_{FUV}, their star formation rate (SFR).

  9. WHERE DO WET, DRY, AND MIXED GALAXY MERGERS OCCUR? A STUDY OF THE ENVIRONMENTS OF CLOSE GALAXY PAIRS IN THE DEEP2 GALAXY REDSHIFT SURVEY

    SciTech Connect

    Lin, Lihwai; Cooper, Michael C.; Willmer, Christopher N. A.; Jian, Hung-Yu; Chiueh, Tzihong; Koo, David C.; Guhathakurta, Puragra; Yan, Renbin; Coil, Alison L.; Croton, Darren J.; Gerke, Brian F.; Newman, Jeffrey A.

    2010-08-01

    We study the environments of wet, dry, and mixed galaxy mergers at 0.75 < z < 1.2 using close pairs in the DEEP2 Galaxy Redshift Survey. We find that the typical environment of dry and mixed merger candidates is denser than that of wet mergers, mostly due to the color-density relation. While the galaxy companion rate (N{sub c}) is observed to increase with overdensity, using N-body simulations, we find that the fraction of pairs that will eventually merge decreases with the local density, predominantly because interlopers are more common in dense environments. After taking into account the merger probability of pairs as a function of local density, we find only marginal environment dependence of the galaxy merger rate for wet mergers. On the other hand, the dry and mixed merger rates increase rapidly with local density due to the increased population of red galaxies in dense environments, implying that the dry and mixed mergers are most effective in overdense regions. We also find that the environment distribution of K+A galaxies is similar to that of wet mergers alone and of wet+mixed mergers, suggesting a possible connection between K+A galaxies and wet and/or wet+mixed mergers. Based on our results, we therefore expect that the properties, including structures and masses, of red-sequence galaxies should be different between those in underdense regions and those in overdense regions since the dry mergers are significantly more important in dense environments. We conclude that, as early as z {approx} 1, high-density regions are the preferred environment in which dry mergers occur, and that present-day red-sequence galaxies in overdense environments have, on average, undergone 1.2 {+-} 0.3 dry mergers since this time, accounting for (38 {+-} 10)% of their mass accretion in the last 8 billion years. The main uncertainty in this finding is the conversion from the pair fraction to the galaxy merger rate, which is possibly as large as a factor of 2. Our findings

  10. Lyman Break Galaxies at z˜5: Rest-Frame UV Spectra. II

    NASA Astrophysics Data System (ADS)

    Ando, Masataka; Ohta, Kouji; Iwata, Ikuru; Akiyama, Masayuki; Aoki, Kentaro; Tamura, Naoyuki

    2007-08-01

    We present spectroscopy results of Lyman break galaxies (LBGs) at z˜5 in the J0053+1234 field. Among five bright candidates with z'<25.0mag, two objects are confirmed to be at z˜5. The equivalent widths (EWs) of Lyα emission of the 2 LBGs are not so strong as to be detected as Lyα emitters, and one of them shows strong low-ionization interstellar (LIS) metal absorption lines. Two faint objects with z'geq25.0 mag are also confirmed to be at z˜5, and their spectra show strong Lyα emission in contrast to bright ones. These results suggest a deficiency of strong Lyα emission in bright LBGs at z ˜ 5, as discussed in our previous paper. Combined with our previous spectra of LBGs at z˜5, obtained around the Hubble Deep Field-North (HDF-N), we made a composite spectrum of luminous (M_{1400} leq 21.5mag) LBGs at z˜5. The resultant spectrum shows weak Ly α emission and strong LIS absorptions, which suggest that the bright LBGs at z˜5 have chemically evolved at least to ˜0.1 solar metallicity. For a part of our sample in the HDF-N region, we obtained near-to-mid infrared data, which constrain the stellar masses of these objects. With the stellar mass and the metallicity estimated from the LIS absorptions, the metallicities of the LBGs at z˜5 tend to be lower than those of galaxies with the same stellar mass at z lesssim 2, although the uncertainty is very large.

  11. Star Formation in Damped Lyman-alpha systems and the Outskirts of Lyman Break Galaxies

    NASA Astrophysics Data System (ADS)

    Rafelski, Marc Alexander

    In this thesis we begin to unify two pictures of the high redshift universe: absorption line systems such as damped Lyman alpha systems (DLAs) that provide the fuel for star formation, and compact star forming regions such as Lyman break galaxies (LBGs) which form the majority of stars. Wolfe & Chen (2006) find that the in situ star formation in DLAs is less than 5% of what is expected from the Kennicutt-Schmidt (KS) relation, but they do not constrain DLAs associated with bright star-forming regions such as LBGs. In this work we search for spatially-extended star formation in the outskirts of LBGs at z ∼3. To this end, we create a sample of z ∼3 LBGs in the Hubble Ultra Deep Field (UDF) by using photometric redshifts enabled by the introduction of an extremely deep u -band image. By stacking these galaxies, we find spatially extended low surface brightness emission around LBGs in the V -band image of the UDF, corresponding to the z ∼3 rest-frame far-ultraviolet light, which is a sensitive measure of star formation rates (SFRs). We connect this emission around LBGs to the expected emission from DLAs, and the results suggest that the SFR efficiency in such gas at z ∼3 is between factors of 10 and 50 lower than predictions based on the KS relation. This decreased efficiency is likely due to the lower metallicity of DLA gas. In addition, we measure the metallicity evolution of DLAs out to z ∼5, and find a continued decrease of metallicity with increasing redshift and a metallicity "floor"' around one thousandth of the solar value. We also compare the metallicity distribution and chemistry of DLAs and halo stars, and find that they are not inconsistent. Lastly, we study the photometric variability of stars in the Galactic center in order to further our understanding of the massive young stars forming in the presence of a super massive black hole. All together, these results improve our understanding of star formation and provide constraints for models and

  12. Low-redshift quasars in the SDSS Stripe 82. Host galaxy colours and close environment

    NASA Astrophysics Data System (ADS)

    Bettoni, D.; Falomo, R.; Kotilainen, J. K.; Karhunen, K.; Uslenghi, M.

    2015-12-01

    We present a photometrical and morphological multicolour study of the properties of low-redshift (z < 0.3) quasar hosts based on a large and homogeneous data set of quasars derived from the Sloan Digital Sky Survey (DR7). We used quasars that were imaged in the SDSS Stripe82 that is up to 2 mag deeper than standard Sloan images. This sample is part of a larger data set of ˜400 quasars at z < 0.5 for which both the host galaxies and their galaxy environments were studied. For 52 quasars, we undertake a study of the colour of the host galaxies and of their close environments in the u, g, r, i and z bands. We are able to resolve almost all the quasars in the sample in the filters g, r, i and z and also in u for about 50 per cent of the targets. We found that the mean colours of the QSO host galaxy (g - i = 0.82 ± 0.26; r - i = 0.26 ± 0.16 and u - g = 1.32 ± 0.25) are very similar to the values of a sample of inactive galaxies matched in terms of redshift and galaxy luminosity with the quasar sample. There is a suggestion that the most massive QSO hosts have bluer colours. Both quasar hosts and the comparison sample of inactive galaxies have candidates of close (<50 kpc) companion galaxies for ˜30 per cent of the sources with no significant difference between active and inactive galaxies. We do not find significant correlation between the central black hole (BH) mass and the quasar host luminosity that appears to be extra luminous at a given BH mass with respect to the local relation (MBH - Mhost) for inactive galaxies. This confirms previous suggestion that a substantial disc component, not correlated with the BH mass, is present in the galaxies hosting low-z quasars. These results support a scenario where the activation of the nucleus has negligible effects on the global structural and photometrical properties of the hosting galaxies.

  13. The impact of strong gravitational lensing on observed Lyman-break galaxy numbers at 4 ≤ z ≤ 8 in the GOODS and the XDF blank fields

    NASA Astrophysics Data System (ADS)

    Barone-Nugent, R. L.; Wyithe, J. S. B.; Trenti, M.; Treu, T.; Oesch, P.; Bouwens, R.; Illingworth, G. D.; Schmidt, K. B.

    2015-06-01

    Detections of Lyman-break galaxies (LBGs) at high-redshift are affected by gravitational lensing induced by foreground deflectors not only in galaxy clusters, but also in blank fields. We quantify the impact of strong magnification in the samples of B435, V606, i775 and z850 & Y105 dropouts (4 ≲ z ≲ 8) observed in the eXtreme Deep Field (XDF) and the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) fields by investigating the proximity of dropouts to foreground objects. We find that ˜6 per cent of bright z ˜ 7 LBGs (m_{H_{160}}<26) have been strongly lensed (μ > 2) by foreground objects. This fraction decreases from ˜3.5 per cent at z ˜ 6 to ˜1.5 per cent at z ˜ 4. Since the observed fraction of strongly lensed LBGs is a function of the shape of the luminosity function (LF), it can be used to derive Schechter parameters, α and M⋆, independently from galaxy number counts. Our magnification bias analysis yields Schechter-function parameters in close agreement with those determined from galaxy counts albeit with larger uncertainties. Extrapolation of our analysis to z ≳ 8 suggests that surveys with JWST, WFIRST and Euclid should find excess LBGs at the bright end, over an intrinsic exponential cutoff. Finally, we highlight how the magnification bias measurement near the XDF detection limit can be used to probe the population of galaxies beyond this limit. Preliminary results suggest that the magnification bias at MUV ˜ -18 is weaker than expected if α ≲ -1.7 extends well below the current detection limits. This could imply a flattening of the LF at MUV ≳ -16.5. However, selection effects and completeness estimates are difficult to quantify precisely. Thus, we do not rule out a steep LF extending to MUV ≳ -15.

  14. HerMES: LYMAN BREAK GALAXIES INDIVIDUALLY DETECTED AT 0.7 {<=} z {<=} 2.0 IN GOODS-N WITH HERSCHEL/SPIRE

    SciTech Connect

    Burgarella, D.; Heinis, S.; Buat, V.; Giovannoli, E.; Ilbert, O.; Magdis, G.; Hwang, H. S.; Blain, A.; Bock, J.; Cooray, A.; Brisbin, D.; Chanial, P.; Clements, D. L.; Franceschini, A.; Marchetti, L.; Glenn, J.; Gonzalez Solares, E. A. E-mail: sebastien.heinis@oamp.fr

    2011-06-10

    As part of the Herschel Multi-tiered Extragalactic Survey we have investigated the rest-frame far-infrared (FIR) properties of a sample of more than 4800 Lyman break galaxies (LBGs) in the Great Observatories Origins Deep Survey North field. Most LBGs are not detected individually, but we do detect a sub-sample of 12 objects at 0.7 < z < 1.6 and one object at z = 2.0. The ones detected by Herschel SPIRE have redder observed NUV - U and U - R colors than the others, while the undetected ones have colors consistent with average LBGs at z > 2.5. The UV-to-FIR spectral energy distributions of the objects detected in the rest-frame FIR are investigated using the code CIGALE to estimate physical parameters. We find that LBGs detected by SPIRE are high-mass, luminous infrared galaxies. It appears that LBGs are located in a triangle-shaped region in the A{sub FUV} versus log L{sub FUV} = 0 diagram limited by A{sub FUV} = 0 at the bottom and by a diagonal following the temporal evolution of the most massive galaxies from the bottom right to the top left of the diagram. This upper envelop can be used as upper limits for the UV dust attenuation as a function of L{sub FUV}. The limits of this region are well explained using a closed-box model, where the chemical evolution of galaxies produces metals, which in turn lead to higher dust attenuation when the galaxies age.

  15. Faint Companions in the Close Environment of Starforming Dwarf Galaxies: possible overlooked starburst triggers? (Oral Contribution)

    NASA Astrophysics Data System (ADS)

    Noeske, K. G.; Iglesias-Páramo, J.; Vílchez, J. M.; Papaderos, P.; Fricke, K. J.

    Using the NASA Extragalactic Database, we have searched the close environment of 98 star-forming dwarf galaxies (SFDGs) from field- and low density environments for companion galaxies. Most of the found companions are dwarf galaxies, previously disregarded in environmental studies of SFDGs. Using a subsample at low redshifts, cz < 2000 km/s, i.e. less biased against dwarf companions, we find that 30% of the SFDGs have close companions within a projected linear separation s_p < 100 kpc and a redshift difference of (Delta cz) < 500 km/s. This fraction must be considered a lower limit, given the incompleteness of the available data sets and the non-negligible frequency of HI clouds in the vicinity of SFDGs, so that the majority of SFDGs should not be considered isolated. The redshift differences between companion candidates and sample SFDGs are typically smaller than ~250 km/s and concentrated towards lower values. This is similarly observed for dwarf satellites of spiral galaxies and suggests a physical association between the companion candidates and the sample SFDGs. SFDGs with a close companion do not show significant differences in their H(beta) equivalent widths and B-V colours as compared to isolated ones. However, the available data do not allow to rule out close dwarf companions as an influencing factor for star formation activity.

  16. A close nuclear black-hole pair in the spiral galaxy NGC 3393.

    PubMed

    Fabbiano, G; Wang, Junfeng; Elvis, M; Risaliti, G

    2011-09-22

    The current picture of galaxy evolution advocates co-evolution of galaxies and their nuclear massive black holes, through accretion and galactic merging. Pairs of quasars, each with a massive black hole at the centre of its galaxy, have separations of 6,000 to 300,000 light years (refs 2 and 3; 1 parsec = 3.26 light years) and exemplify the first stages of this gravitational interaction. The final stages of the black-hole merging process, through binary black holes and final collapse into a single black hole with gravitational wave emission, are consistent with the sub-light-year separation inferred from the optical spectra and light-variability of two such quasars. The double active nuclei of a few nearby galaxies with disrupted morphology and intense star formation (such as NGC 6240 with a separation of about 2,600 light years and Mrk 463 with a separation of about 13,000 light years between the nuclei) demonstrate the importance of major mergers of equal-mass spiral galaxies in this evolution; such mergers lead to an elliptical galaxy, as in the case of the double-radio-nucleus elliptical galaxy 0402+379 (with a separation of about 24 light years between the nuclei). Minor mergers of a spiral galaxy with a smaller companion should be a more common occurrence, evolving into spiral galaxies with active massive black-hole pairs, but have hitherto not been seen. Here we report the presence of two active massive black holes, separated by about 490 light years, in the Seyfert galaxy NGC 3393 (50 Mpc, about 160 million light years). The regular spiral morphology and predominantly old circum-nuclear stellar population of this galaxy, and the closeness of the black holes embedded in the bulge, provide a hitherto missing observational point to the study of galaxy/black hole evolution. Comparison of our observations with current theoretical models of mergers suggests that they are the result of minor merger evolution. PMID:21881560

  17. IRAS high resolution studies and modeling of closely interacting galaxies. Galaxy collisions: Infrared observations and analysis of numerical models. UV spectroscopy of massive young stellar populations in interacting galaxies

    NASA Technical Reports Server (NTRS)

    Lamb, Susan A.

    1993-01-01

    The Final Technical Report covering the period from 15 Aug. 1989 to 14 Aug. 1991 is presented. Areas of research included Infrared Astronomy Satellite (IRAS) high resolution studies and modeling of closely interacting galaxies; galaxy collisions: infrared observations and analysis of numerical models; and UV spectroscopy of massive young stellar populations in interacting galaxies. Both observational studies and theoretical modelling of interacting galaxies are covered. As a consequence the report is divided into two parts, one on each aspect of the overall project.

  18. Unveiling the structure of barred galaxies at 3.6 μm with the Spitzer survey of stellar structure in galaxies (S{sup 4}G). I. Disk breaks

    SciTech Connect

    Kim, Taehyun; Lee, Myung Gyoon; Gadotti, Dimitri A.; Muñoz-Mateos, Juan-Carlos; Sheth, Kartik; Madore, Barry F.; Ho, Luis C.; Elmegreen, Bruce; Knapen, Johan H.; Cisternas, Mauricio; Erroz-Ferrer, Santiago; Zaritsky, Dennis; Comerón, Sébastien; Laurikainen, Eija; Salo, Heikki; Holwerda, Benne; Hinz, Joannah L.; Buta, Ron; and others

    2014-02-20

    We have performed two-dimensional multicomponent decomposition of 144 local barred spiral galaxies using 3.6 μm images from the Spitzer Survey of Stellar Structure in Galaxies. Our model fit includes up to four components (bulge, disk, bar, and a point source) and, most importantly, takes into account disk breaks. We find that ignoring the disk break and using a single disk scale length in the model fit for Type II (down-bending) disk galaxies can lead to differences of 40% in the disk scale length, 10% in bulge-to-total luminosity ratio (B/T), and 25% in bar-to-total luminosity ratios. We find that for galaxies with B/T ≥ 0.1, the break radius to bar radius, r {sub br}/R {sub bar}, varies between 1 and 3, but as a function of B/T the ratio remains roughly constant. This suggests that in bulge-dominated galaxies the disk break is likely related to the outer Lindblad resonance of the bar and thus moves outward as the bar grows. For galaxies with small bulges, B/T < 0.1, r {sub br}/R {sub bar} spans a wide range from 1 to 6. This suggests that the mechanism that produces the break in these galaxies may be different from that in galaxies with more massive bulges. Consistent with previous studies, we conclude that disk breaks in galaxies with small bulges may originate from bar resonances that may be also coupled with the spiral arms, or be related to star formation thresholds.

  19. Physical and morphological properties of z ~ 3 Lyman break galaxies: dependence on Lyα line emission

    NASA Astrophysics Data System (ADS)

    Pentericci, L.; Grazian, A.; Scarlata, C.; Fontana, A.; Castellano, M.; Giallongo, E.; Vanzella, E.

    2010-05-01

    Aims: We investigate the physical and morphological properties of Lyman break galaxies (LBGs) at redshift ~2.5 to ~3.5, to determine if and how they depend on the nature and strength of the Lyα emission. Methods: We selected U-dropout galaxies from the z-detected GOODS-MUSIC catalog by adapting the classical Lyman break criteria on the GOODS filter set. We kept only those galaxies with spectroscopic confirmation, mainly from VIMOS and FORS public observations. Using the full multi-wavelength 14-bands information (U to IRAC), we determined the physical properties of the galaxies through a standard spectral energy distribution fitting procedure with the updated Charlot & Bruzual (2009) templates. We also added other relevant observations of the GOODS field, i.e. the 24 μm observations from Spitzer/MIPS and the 2 MSec Chandra X-ray observations. Finally, using non parametric diagnostics (Gini, Concentration, Asymmetry, M20 and ellipticity), we characterized the rest-frame UV morphologies of the galaxies. We then analyzed how these physical and morphological properties correlate with the presence of the Lyα emission line in the optical spectra. Results: We find that unlike at higher redshift, the dependence of physical properties on the Lyα line is milder: galaxies without Lyα in emission tend to be more massive and dustier than the rest of the sample, but all other parameters, ages, star formation rates (SFR), X-ray emission and UV morphology do not depend strongly on the presence of the Lyα emission. A simple scenario where all LBGs have intrinsically high Lyα emission, but where the dust and neutral hydrogen content (which shapes the final appearance of the Lyα) depend on the mass of the galaxies, is able to reproduce the majority of the observed properties at z˜3. Some modification might be needed to account for the observed evolution of these properties with cosmic epoch, which is also discussed.

  20. TESTING THE EVOLUTIONARY SEQUENCE BETWEEN HIDDEN BROAD-LINE REGION (HBLR) AND NON-HBLR SEYFERT 2 GALAXIES WITH THE 4000 A BREAK STRENGTHS

    SciTech Connect

    Yu, Po-Chieh; Hwang, Chorng-Yuan; Huang, Kui-Yun; Ohyama, Youichi E-mail: hwangcy@astro.ncu.edu.tw E-mail: ohyama@asiaa.sinica.edu.tw

    2013-05-01

    We compare the 4000 A break (D{sub n} (4000)) strength in the central kpc of hidden broad-line region (HBLR) and non-HBLR Seyfert 2 galaxies to investigate the origin of these galaxies. Our results show that the D{sub n} (4000) strengths in the nuclear regions of the non-HBLR Seyfert 2 galaxies are larger than those in the HBLR galaxies. We also show that the D{sub n} (4000) strength is not related to the morphology of host galaxies. These results imply that the non-HBLR Seyfert 2 galaxies have an older stellar population in nuclear regions than the HBLR galaxies. This suggests that an evolutionary connection might exist between non-HBLR and HBLR Seyfert 2 galaxies. We propose a potential evolutionary scenario and a modified unification model for Seyfert galaxies. In this scheme, Seyfert 1 and HBLR Seyfert 2 galaxies evolve into unabsorbed and absorbed non-HBLR Seyfert 2 galaxies. We also discuss the implications of our results in the hydrogen column density distribution of the non-HBLR Seyfert 2 galaxies.

  1. VizieR Online Data Catalog: Balmer break galaxies at z<1.5 star formation (Diaz Tello+, 2016)

    NASA Astrophysics Data System (ADS)

    Diaz Tello, J.; Donzelli, C.; Padilla, N.; Akiyama, M.; Fujishiro, N.; Yoshikawa, T.; Hanami, H.

    2016-05-01

    The galaxies presented in this article come from a sample constructed to study star formation activity of massive galaxies in the redshift range z=0.1-3.0 (Diaz Tello et al., 2013ApJ...771....7D; hereafter D13). The chosen field, the SXDF (RA=02:18:00, DE=-05:00:00; Furusawa et al., 2008, Cat. J/ApJS/176/1) has the advantage that deep photometric data is available in the bands u, B, R, i, z (Subaru), J, H, K (UKIRT), and in all MIR Spitzer bands. The parent sample was selected using the λ3646 Balmer and λ4000 break features as tracers of redshift, as described by Daddi et al. (2004ApJ...617..746D), utilizing the BzK color-color diagram to select star-forming galaxies in a particular redshift range. Furthermore, we used two color-color diagrams to select star-forming galaxies in a lower redshift range than the BzK diagram; these diagrams were presented in Hanami et al. (2012PASJ...64...70H; uVi and uRJ diagrams). (1 data file).

  2. Star formation rate and extinction in faint z ∼ 4 Lyman break galaxies

    SciTech Connect

    To, Chun-Hao; Wang, Wei-Hao; Owen, Frazer N.

    2014-09-10

    We present a statistical detection of 1.5 GHz radio continuum emission from a sample of faint z ∼ 4 Lyman break galaxies (LBGs). To constrain their extinction and intrinsic star formation rate (SFR), we combine the latest ultradeep Very Large Array 1.5 GHz radio image and the Hubble Space Telescope Advanced Camera for Surveys (ACS) optical images in the GOODS-N. We select a large sample of 1771 z ∼ 4 LBGs from the ACS catalog using B {sub F435W}-dropout color criteria. Our LBG samples have I {sub F775W} ∼ 25-28 (AB), ∼0-3 mag fainter than M{sub UV}{sup ⋆} at z ∼ 4. In our stacked radio images, we find the LBGs to be point-like under our 2'' angular resolution. We measure their mean 1.5 GHz flux by stacking the measurements on the individual objects. We achieve a statistical detection of S {sub 1.5} {sub GHz} = 0.210 ± 0.075 μJy at ∼3σ for the first time on such a faint LBG population at z ∼ 4. The measurement takes into account the effects of source size and blending of multiple objects. The detection is visually confirmed by stacking the radio images of the LBGs, and the uncertainty is quantified with Monte Carlo simulations on the radio image. The stacked radio flux corresponds to an obscured SFR of 16.0 ± 5.7 M {sub ☉} yr{sup –1}, and implies a rest-frame UV extinction correction factor of 3.8. This extinction correction is in excellent agreement with that derived from the observed UV continuum spectral slope, using the local calibration of Meurer et al. This result supports the use of the local calibration on high-redshift LBGs to derive the extinction correction and SFR, and also disfavors a steep reddening curve such as that of the Small Magellanic Cloud.

  3. The {open_quotes}leak-before-break{close_quotes} applicability in decision support system {open_quotes}strength{close_quotes}

    SciTech Connect

    Torop, V.M.; Orynyak, I.V.; Kutovoy, O.L.

    1997-04-01

    A software decision support system, STRENGTH, for application of leak before break analysis, is described. The background methodology and sample application are outlined. The program allows multioptional computation of loading parameters for different types of defects, and variable properties for metals and welded joints. Structural strength is assessed, and service life predictions are made. The program is used to analyze specific defects identified by nondestructive testing.

  4. THE MOLECULAR GAS CONTENT OF z = 3 LYMAN BREAK GALAXIES: EVIDENCE OF A NON-EVOLVING GAS FRACTION IN MAIN-SEQUENCE GALAXIES AT z > 2

    SciTech Connect

    Magdis, Georgios E.; Rigopoulou, D.; Daddi, E.; Sargent, M.; Elbaz, D.; Gobat, R.; Tan, Q.; Aussel, H.; Feruglio, C.; Charmandaris, V.; Dickinson, M.; Reddy, N.

    2012-10-10

    We present observations of the CO[J = 3 {yields} 2] emission toward two massive and infrared luminous Lyman break galaxies (LBGs) at z = 3.21 and z = 2.92, using the IRAM Plateau de Bure Interferometer, placing first constraints on the molecular gas masses (M{sub gas}) of non-lensed LBGs. Their overall properties are consistent with those of typical (main-sequence) galaxies at their redshifts, with specific star formation rates {approx}1.6 and {approx}2.2 Gyr{sup -1}, despite their large infrared luminosities (L{sub IR} Almost-Equal-To (2-3) Multiplication-Sign 10{sup 12} L{sub Sun }) derived from Herschel. With one plausible CO detection (spurious detection probability of 10{sup -3}) and one upper limit, we investigate the evolution of the molecular gas-to-stellar mass ratio (M{sub gas}/M{sub *}) with redshift. Our data suggest that the steep evolution of M{sub gas}/M{sub *} of normal galaxies up to z {approx} 2 is followed by a flattening at higher redshifts, providing supporting evidence for the existence of a plateau in the evolution of the specific star formation rate at z > 2.5.

  5. KECK SPECTROSCOPY OF FAINT 3>z>7 LYMAN BREAK GALAXIES: A HIGH FRACTION OF LINE EMITTERS AT REDSHIFT SIX

    SciTech Connect

    Stark, Daniel P.; Ellis, Richard S.; Ouchi, Masami

    2011-02-10

    As Ly{alpha} photons are scattered by neutral hydrogen, a change with redshift in the Ly{alpha} equivalent width (EW) distribution of distant galaxies offers a promising probe of the degree of ionization in the intergalactic medium and hence when cosmic reionization ended. This simple test is complicated by the fact that Ly{alpha} emission can also be affected by variations in the kinematics and dust content of the host galaxies. In the first paper in this series, we demonstrated both a luminosity- and redshift-dependent trend in the fraction of Ly{alpha} emitters seen within color-selected 'Lyman break' galaxies (LBGs) over the range 3 < z < 6; lower luminosity galaxies and those at higher redshift show an increased likelihood of strong emission. Here, we present the results from 12.5 hr exposures with the Keck DEIMOS spectrograph focused primarily on LBGs at z {approx_equal} 6 which enable us to confirm the redshift dependence of line emission more robustly and to higher redshift than was hitherto possible. We find that 54% {+-} 11% of faint z {approx_equal} 6 LBGs show strong (W{sub Ly{alpha},0}>25 A) emission, an increase of 55% from a sample of similarly luminous z {approx_equal} 4 galaxies. With a total sample of 74 z {approx_equal} 6 LBGs, we determine the luminosity-dependent Ly{alpha} EW distribution. Assuming continuity in these trends to the new population of z {approx_equal} 7 sources located with the Hubble WFC3/IR camera, we predict that unless the neutral fraction rises in the intervening 200 Myr, the success rate for spectroscopic confirmation using Ly{alpha} emission should be high.

  6. Rotation of halos in open and closed universes - differentiated merging and natural selection of galaxy types

    SciTech Connect

    Zurek, W.H.; Quinn, P.J.; Salmon, J.K.

    1988-07-01

    Computer simulations are used here to study the properties of galactic halos formed from Gaussian initial density perturbations in both open and closed dark matter universes. It is shown that if galaxies form through gravitational collapse from initial, Gaussian density perturbations, then their luminous parts do not have the original values of either specific angular momentum (ellipticals) or spin parameter lambda (spirals). The rotational properties of a halo depend only weakly on either the halo density or the density of its environment. Variations of the large-scale density of the environment have an expected, dramatic effect on the density of individual halos. Dissipationless merging forces the cores of the merging objects into the core of the merger product. In the process, cores become more bound and lose angular momentum. These findings are extrapolated to propose a model for galaxy formation in which both ellipticals and spirals come into being through mergers. 59 references.

  7. Nurturing Lyman break galaxies: observed link between environment and spectroscopic features

    NASA Astrophysics Data System (ADS)

    Cooke, J.; Omori, Y.; Ryan-Weber, E. V.

    2013-08-01

    We examine the effects of magnitude, colour and Lyα equivalent width (EW) on the spatial distribution of z ˜ 3 Lyman break galaxies (LBGs) and report significant differences in the two-point autocorrelation functions. The results are obtained using samples of ˜10 000-55 000 LBGs from the Canada-France-Hawaii Telescope Legacy Survey Deep Fields. We find that magnitude has a larger effect on the autocorrelation function amplitude on small scales (≲1 h^{-1}_{70} Mpc, the one-halo term) and that colour is more influential on large scales (≳1 h^{-1}_{70} Mpc, the two-halo term). We find the most significant differences between autocorrelation functions for LBGs with dominant net Lyα EW in absorption (aLBGs) and dominant net Lyα EW in emission (eLBGs) determined from ≳95 per cent pure samples of each population using a photometric technique calibrated from ˜1000 spectra. The aLBG autocorrelation function has a higher two-halo amplitude than the full LBG sample and has a one-halo term departure from a power-law fit near ˜1 h^{-1}_{70} Mpc, corresponding to the virial radii of MDM ˜ 1013 M⊙ dark matter haloes. In contrast, the eLBG autocorrelation function has a one-halo term departure at ˜0.12 h^{-1}_{70} Mpc, suggesting parent haloes of MDM ˜ 1011 M⊙ and a two-halo term that exhibits a curious `hump' on intermediate scales that we localize to the faintest, bluest members. The aLBG-eLBG cross-correlation function exhibits an anticorrelation component that reinforces different physical locations for a significant fraction of aLBGs and eLBGs. We introduce a `shell' model for the eLBG autocorrelation function and find that the form can be reproduced assuming that a significant fraction of eLBGs have a shell-like spatial distribution. Based on the analysis of all LBG subsamples, and considering the natural asymmetric distribution of LBGs on the colour-magnitude diagram, we conclude that aLBGs are more likely to reside in group-like environments hosting

  8. Connecting faint-end slopes of the Lyman α emitter and Lyman-break galaxy luminosity functions

    NASA Astrophysics Data System (ADS)

    Gronke, M.; Dijkstra, M.; Trenti, M.; Wyithe, S.

    2015-05-01

    We predict Lyman α (Lyα) luminosity functions (LFs) of Lyα-selected galaxies (Lyα emitters, or LAEs) at z = 3-6 using the phenomenological model. This model combines observed UV-LFs of Lyman-break galaxies (LBGs, or drop-out galaxies), with constraints on their distribution of Lyα line strengths as a function of UV-luminosity and redshift. Our analysis shows that while Lyα LFs of LAEs are generally not Schechter functions, these provide a good description over the luminosity range of log10(Lα/erg s-1) = 41-44. Motivated by this result, we predict Schechter function parameters at z = 3-6. Our analysis further shows that (i) the faint-end slope of the Lyα LF is steeper than that of the UV-LF of LBGs, (with a median αLyα < -2.0 at z ≳ 4), and (ii) a turnover in the Lyα LF of LAEs at Lyα luminosities 1040 ≲ Lα ≲ 1041 erg s-1 may signal a flattening of UV-LF of LBGs at -12 > MUV > -14. We discuss the implications of these results - which can be tested directly with upcoming surveys - for the Epoch of Reionization.

  9. Possible breaking of the FIR-radio correlation in tidally interacting galaxies

    NASA Astrophysics Data System (ADS)

    Donevski, D.; Prodanović, T.

    2015-10-01

    Far-infrared (FIR)-radio correlation is a well-established empirical connection between continuum radio and dust emission of star-forming galaxies, often used as a tool in determining star formation rates. Here we expand the point made by Murphy that in the case of some interacting star-forming galaxies there is a non-thermal emission from the gas bridge in between them, which might cause a dispersion in this correlation. Galactic interactions and mergers have been known to give rise to tidal shocks and disrupt morphologies especially in the smaller of the interacting components. Here we point out that these shocks can also heat the gas and dust and will inevitably accelerate particles and result in a tidal cosmic ray population in addition to standard galactic cosmic rays in the galaxy itself. This would result in a non-thermal emission not only from the gas bridges of interacting systems, but from interacting galaxies as a whole in general. Thus both tidal heating and additional non-thermal radiation will obviously affect the FIR-radio correlation of these systems, the only question is how much. In this scenario the FIR-radio correlation is not stable in interacting galaxies, but rather evolves as the interaction/merger progresses. To test this hypothesis and probe the possible impact of tidal cosmic ray population, we have analysed a sample of 43 infrared-bright star-forming interacting galaxies at different merger stages. We have found that their FIR-radio correlation parameter and radio emission spectral index vary noticeably over different merger stages and behave as it would be expected from our tidal-shock scenario. Important implications of departure of interacting galaxies from the FIR-radio correlation are discussed.

  10. Images From Hubbles's ACS Tell A Tale Of Two Record-Breaking Galaxy Clusters

    NASA Astrophysics Data System (ADS)

    2004-01-01

    Looking back in time nearly 9 billion years, an international team of astronomers found mature galaxies in a young universe. The galaxies are members of a cluster of galaxies that existed when the universe was only 5 billion years old, or about 35 percent of its present age. This compelling evidence that galaxies must have started forming just after the big bang was bolstered by observations made by the same team of astronomers when they peered even farther back in time. The team found embryonic galaxies a mere 1.5 billion years after the birth of the cosmos, or 10 percent of the universe's present age. The "baby galaxies" reside in a still-developing cluster, the most distant proto-cluster ever found. The Advanced Camera for Surveys (ACS) aboard NASA's Hubble Space Telescope was used to make observations of the massive cluster, RDCS 1252.9-2927, and the proto-cluster, TN J1338-1942. Observations by NASA's Chandra X-ray Observatory yielded the mass and heavy element content of RDCS 1252, the most massive known cluster for that epoch. These observations are part of a coordinated effort by the ACS science team to track the formation and evolution of clusters of galaxies over a broad range of cosmic time. The ACS was built especially for studies of such distant objects. These findings further support observations and theories that galaxies formed relatively early in the history of the cosmos. The existence of such massive clusters in the early universe agrees with a cosmological model wherein clusters form from the merger of many sub-clusters in a universe dominated by cold dark matter. The precise nature of cold dark matter, however, is still not known. The first Hubble study estimated that galaxies in RDCS 1252 formed the bulk of their stars more than 11 billion years ago (at redshifts greater than 3). The results were published in the Oct. 20, 2003 issue of the Astrophysical Journal. The paper's lead author is John Blakeslee of the Johns Hopkins University in

  11. Indirect Evidence for Escaping Ionizing Photons in Local Lyman Break Galaxy Analogs

    NASA Astrophysics Data System (ADS)

    Alexandroff, Rachael M.; Heckman, Timothy M.; Borthakur, Sanchayeeta; Overzier, Roderik; Leitherer, Claus

    2015-09-01

    A population of early star-forming galaxies is the leading candidate for the re-ionization of the universe. It is still unclear, however, what conditions and physical processes would enable a significant fraction of the ionizing (Lyman continuum) photons to escape from these gas-rich galaxies. In this paper we present the results of the analysis of Hubble Space Telescope Cosmic Origins Spectrograph far-UV (FUV) spectroscopy plus ancillary multi-waveband data of a sample of 22 low-redshift galaxies that are good analogs to typical star-forming galaxies at high redshift. We measure three parameters that provide indirect evidence of the escape of ionizing radiation (leakiness): (1) the residual intensity in the cores of saturated interstellar low-ionization absorption lines, which indicates incomplete covering by that gas in the galaxy; (2) the relative amount of blueshifted Lyα line emission, which can indicate the existence of holes in the neutral hydrogen on the front-side of the galaxy outflow, and (3) the relative weakness of the [S ii] optical emission lines that trace matter-bounded H ii regions. We show that our residual intensity measures are only negligibly affected by infilling from resonance emission lines. We find all three diagnostics agree well with one another. We use these diagnostics to rank-order our sample in terms of likely leakiness, noting that a direct measure of escaping Lyman continuum has recently been made for one of the leakiest members of our sample. We then examine the correlations between our ranking and other proposed diagnostics of leakiness. We find a good correlation with the equivalent width of the Lyα emission line, but no significant correlations with either the flux ratio of the [O iii]/[O ii] emission lines or the ratio of star-formation rates derived from the (dust-corrected) FUV and Hα luminosities. Turning to galaxy properties, we find the strongest correlations with leakiness are with the compactness of the star

  12. Images From Hubbles's ACS Tell A Tale Of Two Record-Breaking Galaxy Clusters

    NASA Astrophysics Data System (ADS)

    2004-01-01

    Looking back in time nearly 9 billion years, an international team of astronomers found mature galaxies in a young universe. The galaxies are members of a cluster of galaxies that existed when the universe was only 5 billion years old, or about 35 percent of its present age. This compelling evidence that galaxies must have started forming just after the big bang was bolstered by observations made by the same team of astronomers when they peered even farther back in time. The team found embryonic galaxies a mere 1.5 billion years after the birth of the cosmos, or 10 percent of the universe's present age. The "baby galaxies" reside in a still-developing cluster, the most distant proto-cluster ever found. The Advanced Camera for Surveys (ACS) aboard NASA's Hubble Space Telescope was used to make observations of the massive cluster, RDCS 1252.9-2927, and the proto-cluster, TN J1338-1942. Observations by NASA's Chandra X-ray Observatory yielded the mass and heavy element content of RDCS 1252, the most massive known cluster for that epoch. These observations are part of a coordinated effort by the ACS science team to track the formation and evolution of clusters of galaxies over a broad range of cosmic time. The ACS was built especially for studies of such distant objects. These findings further support observations and theories that galaxies formed relatively early in the history of the cosmos. The existence of such massive clusters in the early universe agrees with a cosmological model wherein clusters form from the merger of many sub-clusters in a universe dominated by cold dark matter. The precise nature of cold dark matter, however, is still not known. The first Hubble study estimated that galaxies in RDCS 1252 formed the bulk of their stars more than 11 billion years ago (at redshifts greater than 3). The results were published in the Oct. 20, 2003 issue of the Astrophysical Journal. The paper's lead author is John Blakeslee of the Johns Hopkins University in

  13. Galaxies

    SciTech Connect

    Not Available

    1981-01-01

    Normal galaxies, radio galaxies, and Seyfert galaxies are considered. The large magellanic cloud and the great galaxy in Andromedia are highlighted. Quasars and BL lacertae objects are also discussed and a review of the spectral observations of all of these galaxies and celestial objects is presented.

  14. CO emissions from optically selected galaxies at z ˜ 0.1-0.2: Tight anti-correlation between molecular gas fraction and 4000 Å break strength

    NASA Astrophysics Data System (ADS)

    Morokuma-Matsui, Kana; Baba, Junichi; Sorai, Kazuo; Kuno, Nario

    2015-06-01

    We performed 12CO(J = 1-0) (hereafter, CO) observations toward 12 normal star-forming galaxies with stellar masses of M⋆ = 1010.6-1011.3 M⊙ at z = 0.1-0.2 with the 45 m telescope at the Nobeyama Radio Observatory. The samples were selected with Dn(4000), that is, the strength of the 4000 Å break, instead of the commonly used far-infrared (FIR) flux. We successfully detected the CO emissions from eight galaxies with signal-to-noise ratio larger than three, demonstrating the effectiveness of the Dn(4000)-based sample selection. For the first time, we find a tight anti-correlation between Dn(4000) and molecular gas fraction (fmol) using literature data of nearby galaxies in which the galaxies with more fuel for star formation have younger stellar populations. We find that our CO-detected galaxies at z ˜ 0.1-0.2 also follow the same relation as nearby galaxies. This implies that the galaxies evolve along this Dn(4000)-fmol relation, and that Dn(4000) seems to be able to be used as a proxy for fmol, which requires many time-consuming observations. Based on the comparison with the model calculation with a population synthesis code, we find that star formation from metal enriched gas and its quenching in the early time are necessary to reproduce galaxies with large Dn(4000) and non-zero gas fraction.

  15. Spectral breaks as a signature of cosmic ray induced turbulence in the Galaxy.

    PubMed

    Blasi, Pasquale; Amato, Elena; Serpico, Pasquale D

    2012-08-10

    We show that the complex shape of the cosmic ray (CR) spectrum, as recently measured by PAMELA and inferred from Fermi-LAT γ-ray observations of molecular clouds in the Gould belt, can be naturally understood in terms of basic plasma astrophysics phenomena. A break from a harder to a softer spectrum at rigidity R is approximately equal to 10 GV follows from a transition from transport dominated by advection of particles with Alfvén waves to a regime where diffusion in the turbulence generated by the same CRs is dominant. A second break at R is approximately equal to 200 GV happens when the diffusive propagation is no longer determined by the self-generated turbulence, but rather by the cascading of externally generated turbulence (for instance due to supernova bubbles) from large spatial scales to smaller scales where CRs can resonate. Implications of this scenario for the cosmic ray spectrum, grammage, and anisotropy are discussed. PMID:23006255

  16. A SEARCH FOR LYMAN BREAK GALAXIES IN THE CHANDRA DEEP FIELD SOUTH USING SWIFT ULTRAVIOLET/OPTICAL TELESCOPE

    SciTech Connect

    Basu-Zych, Antara R.; Hornschemeier, Ann E.; Hoversten, Erik A.; Gronwall, Caryl; Lehmer, Bret E-mail: Ann.Hornschemeier@nasa.gov E-mail: caryl@astro.psu.edu

    2011-10-01

    While the Swift satellite is primarily designed to study gamma-ray bursts, its ultraviolet and optical imaging and spectroscopy capabilities are also being used for a variety of scientific programs. In this study, we use the UV/Optical Telescope (UVOT) instrument on board Swift to discover 0.5 < z < 2 Lyman break galaxies (LBGs). UVOT has covered {approx}266 arcmin{sup 2} at >60 ks exposure time, achieving a limiting magnitude of u < 24.5, in the Chandra Deep Field South (CDF-S). Applying UVOT near-ultraviolet color selection, we select 50 UV-dropouts from this UVOT CDF-S data. We match the selected sources with available multiwavelength data from Great Observatories Origins Deep Survey (GOODS) South, Multiwavelength Survey by Yale-Chile, and COMBO-17 to characterize the spectral energy distributions for these galaxies and determine stellar masses, star formation rates (SFRs), and dust attenuations. We compare these properties for LBGs selected in this paper versus z {approx} 3 LBGs and other CDF-S galaxies in the same redshift range (0.5 < z < 2), identified using photometric redshift techniques. The z {approx} 1 LBGs have stellar masses of (logM{sub *}/M{sub sun}) = 9.4 {+-} 0.6, which is slightly lower than z {approx} 3 LBGs ((logM{sub *}/Ms{sub un}) = 10.2 {+-} 0.4) and slightly higher compared with the z {approx} 1 CDF-S galaxies ((logM{sub *}/M{sub sun}) = 8.7 {+-} 0.7). Similarly, our sample of z {approx} 1 LBGs has SFRs (derived using both ultraviolet and infrared data, where available) of (logSFR/(M{sub sun} yr{sup -1})) = 0.7 {+-} 0.6, nearly an order of magnitude lower than z {approx} 3 LBGs ((logSFR/M{sub sun} yr{sup -1}) = 1.5 {+-} 0.4), but slightly higher than the comparison z {approx} 1 sample of CDF-S galaxies ((logSFR/M{sub sun} yr{sup -1}) = 0.2 {+-} 0.7). We find that our z {approx} 1 UV-dropouts have (A{sub FUV}) = 2.0 {+-} 1.0, which is higher than z {approx} 3 LBGs ((A{sub FUV}) = 1.0 {+-} 0.5), but similar to the distribution of dust

  17. Properties of z ~ 3-6 Lyman break galaxies. II. Impact of nebular emission at high redshift

    NASA Astrophysics Data System (ADS)

    de Barros, S.; Schaerer, D.; Stark, D. P.

    2014-03-01

    Context. To gain insight on the mass assembly and place constraints on the star formation history (SFH) of Lyman break galaxies (LBGs), it is important to accurately determine their properties. Aims: We estimate how nebular emission and different SFHs affect parameter estimation of LBGs. Methods: We present a homogeneous, detailed analysis of the spectral energy distribution (SED) of ~1700 LBGs from the GOODS-MUSIC catalogue with deep multi-wavelength photometry from the U band to 8 μm to determine stellar mass, age, dust attenuation, and star formation rate. Using our SED fitting tool, which takes into account nebular emission, we explore a wide parameter space. We also explore a set of different star formation histories. Results: Nebular emission is found to significantly affect the determination of the physical parameters for the majority of z ~ 3-6 LBGs. We identify two populations of galaxies by determining the importance of the contribution of emission lines to broadband fluxes. We find that ~65% of LBGs show detectable signs of emission lines, whereas ~35% show weak or no emission lines. This distribution is found over the entire redshift range. We interpret these groups as actively star-forming and more quiescent LBGs, respectively. We find that it is necessary to considerer SED fits with very young ages (<50 Myr) to reproduce some colours affected by strong emission lines. Other arguments favouring episodic star formation and relatively short star formation timescales are also discussed. Considering nebular emission generally leads to a younger age, lower stellar mass, higher dust attenuation, higher star formation rate, and a large scatter in the SFR-M⋆ relation. Our analysis yields a trend of increasing specific star formation rate with redshift, as predicted by recent galaxy evolution models. Conclusions: The physical parameters of approximately two thirds of high redshift galaxies are significantly modified when we account for nebular emission. The

  18. Cyclopropenium Cations Break the Rules of Attraction to Form Closely Bound Dimers.

    PubMed

    Wallace, Andrew J; Jayasinghe, Chaminda D; Polson, Matthew I J; Curnow, Owen J; Crittenden, Deborah L

    2015-12-16

    The crystal structures of tris(ethylmethylamino)-cyclopropenium chloride and tris(diethylamino)-cyclopropenium iodide reveal the presence of closely bound dicationic dimers formed from two closed-shell monomer units. The distances between the C3 centroids of the staggered monomers are at the short end of those normally found in π-stacked neutral arenes, let alone charged aromatic rings. Computational analysis reveals that short-range interactions are dominated by strong dispersion forces, enabling metastable dicationic dimers to form without covalent intermolecular bonding. Surrounding counterions then provide a background source of charge balance, imparting strong thermodynamic stability to the system. Additionally, these counterions form a weak but attractive electrostatic bridge between the monomer units, contributing to the surprisingly short observed intermolecular C3-C3 centroid distance. PMID:26584632

  19. CO Emissions from Optically Selected Galaxies at z˜0.1-0.2: Tight Anti-Correlation Between Molecular Gas Fraction and 4000 Angstrom Break Strength

    NASA Astrophysics Data System (ADS)

    Morokuma-Matsui, K.; Baba, J.; Sorai, K.; Kuno, N.

    2015-12-01

    We performed 12CO(J=1-0) (hereafter, CO) observations towards 12 normal star-forming galaxies with M⋆=1010.6-1011.3 M⊙ at z=0.1-0.2 with the 45-m telescope at the Nobeyama Radio Observatory (NRO). The samples are selected with Dn(4000) that is a measure of the 4000 Angstrom break strength, instead of commonly used far-infrared (FIR) flux. We detect the CO emissions from 8 galaxies with signal-to-noise ratio (S/N) larger than 3, demonstrating the effectiveness of the Dn(4000)-based sample selection. We find a tight anti-correlation between Dn(4000) and molecular gas fraction (fmol) using literature data of nearby galaxies in which the galaxies with more fuel for star formation have younger stellar populations. CO-detected galaxies at z˜0.1-0.2 also follow the same relation of nearby galaxies, implying 1) the galaxies evolve along this Dn(4000)-fmol relation, and 2) Dn(4000) seems to be used as a proxy for fmol which requires many time-consuming observations1.

  20. USING THE BULLET CLUSTER AS A GRAVITATIONAL TELESCOPE TO STUDY z {approx}> 7 LYMAN BREAK GALAXIES

    SciTech Connect

    Hall, Nicholas; Bradac, Marusa; Gonzalez, Anthony H.; Treu, Tommaso; Clowe, Douglas; Jones, Christine; Stiavelli, Massimo; Zaritsky, Dennis; Cuby, Jean-Gabriel; Clement, Benjamin

    2012-02-01

    We use imaging obtained with the Hubble Space Telescope Wide Field Camera 3 to search for z{sub 850} dropouts at z {approx} 7 and J{sub 110} dropouts at z {approx} 9 lensed by the Bullet Cluster. In total we find 10 z{sub 850} dropouts in our 8.27 arcmin{sup 2} field. Using magnification maps from a combined weak- and strong-lensing mass reconstruction of the Bullet Cluster and correcting for estimated completeness levels, we calculate the surface density and luminosity function of our z{sub 850} dropouts as a function of intrinsic (accounting for magnification) magnitude. We find results consistent with published blank field surveys, despite using much shallower data, and demonstrate the effectiveness of cluster surveys in the search for z {approx} 7 galaxies.

  1. GRB 051008: a long, spectrally hard dust-obscured GRB in a Lyman-break galaxy at z ≈ 2.8

    NASA Astrophysics Data System (ADS)

    Volnova, A. A.; Pozanenko, A. S.; Gorosabel, J.; Perley, D. A.; Frederiks, D. D.; Kann, D. A.; Rumyantsev, V. V.; Biryukov, V. V.; Burkhonov, O.; Castro-Tirado, A. J.; Ferrero, P.; Golenetskii, S. V.; Klose, S.; Loznikov, V. M.; Minaev, P. Yu.; Stecklum, B.; Svinkin, D. S.; Tsvetkova, A. E.; de Ugarte Postigo, A.; Ulanov, M. V.

    2014-08-01

    We present observations of the dark gamma-ray burst GRB 051008 provided by Swift/BAT, Swift/XRT, Konus-WIND, INTEGRAL/SPI-ACS in the high-energy domain and the Shajn, Swift/UVOT, Tautenburg, NOT, Gemini and Keck I telescopes in the optical and near-infrared bands. The burst was detected only in gamma- and X-rays and neither a prompt optical nor a radio afterglow was detected down to deep limits. We identified the host galaxy of the burst, which is a typical Lyman-break galaxy (LBG) with R-magnitude of 24.06 ± 0.10 mag. A redshift of the galaxy of z = 2.77_{-0.20}^{+0.15} is measured photometrically due to the presence of a clear, strong Lyman-break feature. The host galaxy is a small starburst galaxy with moderate intrinsic extinction (AV = 0.3) and has a star formation rate of ˜60 M⊙ yr-1 typical for LBGs. It is one of the few cases where a GRB host has been found to be a classical LBG. Using the redshift we estimate the isotropic-equivalent radiated energy of the burst to be Eiso = (1.15 ± 0.20) × 1054 erg. We also provide evidence in favour of the hypothesis that the darkness of GRB 051008 is due to local absorption resulting from a dense circumburst medium.

  2. Belgian experience in applying the {open_quotes}leak-before-break{close_quotes} concept to the primary loop piping

    SciTech Connect

    Gerard, R.; Malekian, C.; Meessen, O.

    1997-04-01

    The Leak Before Break (LBB) concept allows to eliminate from the design basis the double-ended guillotine break of the primary loop piping, provided it can be demonstrated by a fracture mechanics analysis that a through-wall flaw, of a size giving rise to a leakage still well detectable by the plant leak detection systems, remains stable even under accident conditions (including the Safe Shutdown Earthquake (SSE)). This concept was successfully applied to the primary loop piping of several Belgian Pressurized Water Reactor (PWR) units, operated by the Utility Electrabel. One of the main benefits is to permit justification of supports in the primary loop and justification of the integrity of the reactor pressure vessel and internals in case of a Loss Of Coolant Accident (LOCA) in stretch-out conditions. For two of the Belgian PWR units, the LBB approach also made it possible to reduce the number of large hydraulic snubbers installed on the primary coolant pumps. Last but not least, the LBB concept also facilitates the steam generator replacement operations, by eliminating the need for some pipe whip restraints located close to the steam generator. In addition to the U.S. regulatory requirements, the Belgian safety authorities impose additional requirements which are described in details in a separate paper. An novel aspect of the studies performed in Belgium is the way in which residual loads in the primary loop are taken into account. Such loads may result from displacements imposed to close the primary loop in a steam generator replacement operation, especially when it is performed using the {open_quote}two cuts{close_quotes} technique. The influence of such residual loads on the LBB margins is discussed in details and typical results are presented.

  3. A LOW ESCAPE FRACTION OF IONIZING PHOTONS OF L > L* LYMAN BREAK GALAXIES AT z = 3.3

    SciTech Connect

    Boutsia, K.; Grazian, A.; Giallongo, E.; Fontana, A.; Pentericci, L.; Castellano, M.; Fiore, F.; Gallozzi, S.; Testa, V.; Paris, D.; Santini, P.; Zamorani, G.; Mignoli, M.; Vanzella, E.; Lilly, S. J.

    2011-07-20

    We present an upper limit for the relative escape fraction (f{sup rel}{sub esc}) of ionizing radiation at z {approx} 3.3 using a sample of 11 Lyman break galaxies (LBGs) with deep imaging in the U band obtained with the Large Binocular Camera, mounted on the prime focus of the Large Binocular Telescope. We selected 11 LBGs with secure redshifts in the range 3.27 < z < 3.35, from three independent fields. We stacked the images of our sources in the R and U bands, which correspond to an effective rest-frame wavelength of 1500 A and 900 A, respectively, obtaining a limit in the U band image of {>=}30.7 mag (AB) at 1{sigma}. We derive a 1{sigma} upper limit of f{sup rel}{sub esc} {approx} 5%, which is one of the lowest values found in the literature so far at z {approx} 3.3. Assuming that the upper limit for the escape fraction that we derived from our sample holds for all galaxies at this redshift, the hydrogen ionization rate that we obtain ({Gamma}{sub -12} < 0.3 s{sup -1}) is not enough to keep the intergalactic medium ionized and a substantial contribution to the UV background by faint active galactic nuclei is required. Since our sample is clearly still limited in size, larger z {approx} 3 LBG samples at similar or even greater depths are necessary to confirm these results on a more firm statistical basis.

  4. Resolved Spectroscopy of a Gravitationally Lensed L^{*} Lyman Break Galaxy at z˜5: Evidence for a Starburst-Driven, Galactic-Scale Bi-Polar Outflow

    NASA Astrophysics Data System (ADS)

    Swinbank, M.

    2007-12-01

    We exploit the gravitational potential of a massive, rich cluster as a natural magnifying glass to study the internal properties of the highly magnified galaxy at z=4.88. Using high resolution HST imaging we construct a detailed mass model and, together with optical (VIMOS) and near-infrared (SINFONI) Integral Field Spectroscopy, we have mapped the source-frame morphology of the lensed galaxy behind galaxy cluster RCS0224-002 on 200pc scales to find an ˜L^{*} Lyman-break galaxy with a dynamical mass of 1.0×10^{10} M_{⊙} within 2 kpc and infer an integrated star-formation rate of just 12±2 M_{⊙} yr^{-1}. By combing the spatially resolved velocities from the [O II] and Lyα emission and UV ISM absorption lines we suggest that this galaxy is surrounded by a galactic-scale bi-polar outflow which has recently burst out of the system and is escaping at a speed of ˜500 km s^{-1}. The geometry and velocity of the outflow suggests that the ejected material is travelling far faster than escape velocity and we estimate that it will travel at least 1 Mpc (comoving) before eventually stalling. The enriched, outflowing material is therefore efficient at expelling baryons which are likely to subsequently play no further part in the star-formation history of this galaxy, but rather will pollute the IGM in a volume of at least 3Mpc^{3}.

  5. A DEEP SEARCH FOR MOLECULAR GAS IN TWO MASSIVE LYMAN BREAK GALAXIES AT z = 3 AND 4: VANISHING CO-EMISSION DUE TO LOW METALLICITY?

    SciTech Connect

    Tan, Q.; Gao, Y.; Daddi, E.; Sargent, M.; Béthermin, M.; Bournaud, F.; Elbaz, D.; Pannella, M.; Hodge, J.; Walter, F.; Carilli, C.; Owen, F.; Dannerbauer, H.; Dickinson, M.; Morrison, G.; Riechers, D.

    2013-10-20

    We present deep IRAM Plateau de Bure Interferometer observations, searching for CO-emission toward two massive, non-lensed Lyman break galaxies at z = 3.216 and 4.058. With one low significance CO detection (3.5σ) and one sensitive upper limit, we find that the CO lines are ∼>3-4 times weaker than expected based on the relation between IR and CO luminosities followed by similarly massive galaxies at z = 0-2.5. This is consistent with a scenario in which these galaxies have low metallicity, causing an increased CO-to-H{sub 2} conversion factor, i.e., weaker CO-emission for a given molecular (H{sub 2}) mass. The required metallicities at z > 3 are lower than predicted by the fundamental metallicity relation at these redshifts, consistent with independent evidence. Unless our galaxies are atypical in this respect, detecting molecular gas in normal galaxies at z > 3 may thus remain challenging even with ALMA.

  6. Spitzer UltRa Faint SUrvey Program (SURFS UP). II. IRAC-detected Lyman-Break Galaxies at 6 ≲ z ≲ 10 behind Strong-lensing Clusters

    NASA Astrophysics Data System (ADS)

    Huang, Kuang-Han; Bradač, Maruša; Lemaux, Brian C.; Ryan, R. E., Jr.; Hoag, Austin; Castellano, Marco; Amorín, Ricardo; Fontana, Adriano; Brammer, Gabriel B.; Cain, Benjamin; Lubin, L. M.; Merlin, Emiliano; Schmidt, Kasper B.; Schrabback, Tim; Treu, Tommaso; Gonzalez, Anthony H.; von der Linden, Anja; Knight, Robert I.

    2016-01-01

    We study the stellar population properties of the IRAC-detected 6 ≲ z ≲ 10 galaxy candidates from the Spitzer UltRa Faint SUrvey Program. Using the Lyman Break selection technique, we find a total of 17 galaxy candidates at 6 ≲ z ≲ 10 from Hubble Space Telescope images (including the full-depth images from the Hubble Frontier Fields program for MACS 1149 and MACS 0717) that have detections at signal-to-noise ratios ≥ 3 in at least one of the IRAC 3.6 and 4.5 μm channels. According to the best mass models available for the surveyed galaxy clusters, these IRAC-detected galaxy candidates are magnified by factors of ˜1.2-5.5. Due to the magnification of the foreground galaxy clusters, the rest-frame UV absolute magnitudes M1600 are between -21.2 and -18.9 mag, while their intrinsic stellar masses are between 2 × 108M⊙ and 2.9 × 109M⊙. We identify two Lyα emitters in our sample from the Keck DEIMOS spectra, one at zLyα = 6.76 (in RXJ 1347) and one at zLyα = 6.32 (in MACS 0454). We find that 4 out of 17 z ≳ 6 galaxy candidates are favored by z ≲ 1 solutions when IRAC fluxes are included in photometric redshift fitting. We also show that IRAC [3.6]-[4.5] color, when combined with photometric redshift, can be used to identify galaxies which likely have strong nebular emission lines or obscured active galactic nucleus contributions within certain redshift windows.

  7. MS 1512 cB58: A case study of star formation, metal enrichment and superwinds in Lyman break galaxies

    NASA Astrophysics Data System (ADS)

    Pettini, Max; Rix, Samantha A.; Steidel, Chuck C.; Hunt, Matthew P.; Shapley, Alice E.; Adelberger, Kurt L.

    2002-07-01

    Recent advances in instrumentation and observing techniques have made it possible to begin to study in detail the stellar populations and the interstellar media of galaxies at redshift z = 3, when the universe was still in its ‘teen years’. I illustrate recent progress in this field with the latest observations of the gravitationally lensed galaxy MS 1512- cB58.

  8. Cosmic Evolution of Star Formation Enhancement in Close Major-merger Galaxy Pairs Since z = 1

    NASA Astrophysics Data System (ADS)

    Xu, C. K.; Shupe, D. L.; Béthermin, M.; Aussel, H.; Berta, S.; Bock, J.; Bridge, C.; Conley, A.; Cooray, A.; Elbaz, D.; Franceschini, A.; Le Floc'h, E.; Lu, N.; Lutz, D.; Magnelli, B.; Marsden, G.; Oliver, S. J.; Pozzi, F.; Riguccini, L.; Schulz, B.; Scoville, N.; Vaccari, M.; Vieira, J. D.; Wang, L.; Zemcov, M.

    2012-11-01

    The infrared (IR) emission of "M * galaxies" (1010.4 <= M star <= 1011.0 M ⊙) in galaxy pairs, derived using data obtained in Herschel (PEP/HerMES) and Spitzer (S-COSMOS) surveys, is compared to that of single-disk galaxies in well-matched control samples to study the cosmic evolution of the star formation enhancement induced by galaxy-galaxy interaction. Both the mean IR spectral energy distribution and mean IR luminosity of star-forming galaxies (SFGs) in SFG+SFG (S+S) pairs in the redshift bin of 0.6 < z < 1 are consistent with no star formation enhancement. SFGs in S+S pairs in a lower redshift bin of 0.2 < z < 0.6 show marginal evidence for a weak star formation enhancement. Together with the significant and strong sSFR enhancement shown by SFGs in a local sample of S+S pairs (obtained using previously published Spitzer observations), our results reveal a trend for the star formation enhancement in S+S pairs to decrease with increasing redshift. Between z = 0 and z = 1, this decline of interaction-induced star formation enhancement occurs in parallel with the dramatic increase (by a factor of ~10) of the sSFR of single SFGs, both of which can be explained by the higher gas fraction in higher-z disks. SFGs in mixed pairs (S+E pairs) do not show any significant star formation enhancement at any redshift. The difference between SFGs in S+S pairs and in S+E pairs suggests a modulation of the sSFR by the intergalactic medium (IGM) in the dark matter halos hosting these pairs. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.

  9. COSMIC EVOLUTION OF STAR FORMATION ENHANCEMENT IN CLOSE MAJOR-MERGER GALAXY PAIRS SINCE z = 1

    SciTech Connect

    Xu, C. K.; Shupe, D. L.; Bock, J.; Bridge, C.; Cooray, A.; Lu, N.; Schulz, B.; Bethermin, M.; Aussel, H.; Elbaz, D.; Le Floc'h, E.; Riguccini, L.; Conley, A.; Franceschini, A.; Marsden, G.; Oliver, S. J.; Pozzi, F.; and others

    2012-11-20

    The infrared (IR) emission of 'M {sub *} galaxies' (10{sup 10.4} {<=} M {sub star} {<=} 10{sup 11.0} M {sub Sun }) in galaxy pairs, derived using data obtained in Herschel (PEP/HerMES) and Spitzer (S-COSMOS) surveys, is compared to that of single-disk galaxies in well-matched control samples to study the cosmic evolution of the star formation enhancement induced by galaxy-galaxy interaction. Both the mean IR spectral energy distribution and mean IR luminosity of star-forming galaxies (SFGs) in SFG+SFG (S+S) pairs in the redshift bin of 0.6 < z < 1 are consistent with no star formation enhancement. SFGs in S+S pairs in a lower redshift bin of 0.2 < z < 0.6 show marginal evidence for a weak star formation enhancement. Together with the significant and strong sSFR enhancement shown by SFGs in a local sample of S+S pairs (obtained using previously published Spitzer observations), our results reveal a trend for the star formation enhancement in S+S pairs to decrease with increasing redshift. Between z = 0 and z = 1, this decline of interaction-induced star formation enhancement occurs in parallel with the dramatic increase (by a factor of {approx}10) of the sSFR of single SFGs, both of which can be explained by the higher gas fraction in higher-z disks. SFGs in mixed pairs (S+E pairs) do not show any significant star formation enhancement at any redshift. The difference between SFGs in S+S pairs and in S+E pairs suggests a modulation of the sSFR by the intergalactic medium (IGM) in the dark matter halos hosting these pairs.

  10. KECK SPECTROSCOPY OF FAINT 3 < z < 7 LYMAN BREAK GALAXIES. III. THE MEAN ULTRAVIOLET SPECTRUM AT z {approx_equal} 4

    SciTech Connect

    Jones, Tucker; Ellis, Richard S.; Stark, Daniel P.

    2012-05-20

    We present and discuss the mean rest-frame ultraviolet spectrum for a sample of 81 Lyman break galaxies (LBGs) selected to be B-band dropouts at z {approx_equal} 4. The sample is mostly drawn from our ongoing Keck/DEIMOS survey in the GOODS fields and augmented with archival Very Large Telescope data. In general, we find similar spectroscopic trends to those found in earlier surveys of LBGs at z = 3. Specifically, low-ionization absorption lines which trace neutral outflowing gas are weaker in galaxies with stronger Ly{alpha} emission, bluer UV spectral slopes, lower stellar masses, lower UV luminosities, and smaller half-light radii. This is consistent with a physical picture whereby star formation drives outflows of neutral gas which scatter Ly{alpha} and produce strong low-ionization absorption lines, while increasing galaxy stellar mass, size, metallicity, and dust content. Typical galaxies are thus expected to have stronger Ly{alpha} emission and weaker low-ionization absorption at earlier times, and we indeed find somewhat weaker low-ionization absorption at higher redshifts. In conjunction with earlier results from our survey, we argue that the reduced low-ionization absorption is likely caused by lower covering fraction and/or velocity range of outflowing neutral gas at earlier epochs. Although low-ionization absorption decreases at higher redshift, fine-structure emission lines are stronger, suggesting a greater concentration of neutral gas at small galactocentric radius ({approx}< 5 kpc). Our continuing survey will enable us to extend these diagnostics more reliably to higher redshift and determine the implications for the escape fraction of ionizing photons which governs the role of early galaxies in cosmic reionization.

  11. A XMM-Newton observation of a sample of four close dwarf spheroidal galaxies

    NASA Astrophysics Data System (ADS)

    Manni, L.; Nucita, A. A.; De Paolis, F.; Testa, V.; Ingrosso, G.

    2015-08-01

    We present the results of the analysis of deep archival XMM-Newton observations towards the dwarf spheroidal galaxies Draco, Leo I, Ursa Major II (UMa II) and Ursa Minor (UMi) in the Milky Way neighbourhood. The X-ray source population is characterized and cross-correlated with available databases to infer their nature. We also investigate if intermediate-mass black holes are hosted in the centre of these galaxies. For Draco, we detect 96 high-energy sources, two of them possibly being local stars, while no evidence for any X-ray emitting central compact object is found. Towards the Leo I and UMa II fields of view, we reveal 116 and 49 X-ray sources, respectively. None of them correlates with the putative central black holes and only one is likely associated with a UMa II local source. The study of the UMi dwarf galaxy found 54 high-energy sources and a possible association with a source at the dwarf spheroidal galaxy centre. We put an upper limit on the luminosity of the central compact object of 4.02 × 1033 erg s-1. Furthermore, via the correlation with a radio source near the galactic centre, the putative black hole should have a mass of (2.76^{+32.00}_{-2.54})× 10^6 M_{{{⊙}}} and be radiatively inefficient. This confirms a previous result obtained using Chandra data alone.

  12. Stellar Populations of Lyman Break Galaxies at z approx. to 1-3 in the HST/WFC3 Early Release Science Observations

    NASA Technical Reports Server (NTRS)

    Hathi, N. P.; Cohen, S. H.; Ryan, R. E., Jr.; Finkelstein, S. L.; McCarthy, P. J.; Windhorst, R. A.; Yan, H.; Koekemoer, A. M.; Rutkowski, M. J.; OConnell, R. W.; Straughn, A. N.; Balick, B.; Bond, H. E.; Calzetti, D.; Disney, M. J.; Dopita, M. A.; Frogel, Jay A.; Hall, D. N. B.; Holtzman, J. A.; Kimble, R. A.; Paresce, F.; Saha, A.; Silk, J. I.; Tauger, J. T.; Young, E. T.

    2012-01-01

    We analyze the spectral energy distributions (SEDs) of Lyman break galaxies . (LBGs) at z approx = 1-3 selected using the Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) UVIS channel filters. These HST /WFC3 obse,rvations cover about 50 arcmin2 in the GOODS-South field as a part of the WFC3 Early Release Science program. These LBGs at z approx = 1-3 are selected using dropout selection criteria similar to high redshift LBGs. The deep multi-band photometry in this field is used to identify best-fit SED models, from which we infer the following results: (1) the photometric redshift estimate of these dropout selected LBGs is accurate to within few percent; (2) the UV spectral slope f3 is redder than at high redshift (z > 3), where LBGs are less dusty; (3) on average, LBGs at .z approx = 1-3 are massive, dustier and more highly star-forming, compared to LBGs at higher redshifts with similar luminosities, though their median values are similar within 1a uncertainties. This could imply that identical dropout selection technique, at all. redshifts, find physically similar galaxies; and (4) the stellar masses of these LBGs are directly proportional to their UV luminosities with a logarithmic slope of approx 0.46, and star-formation rates are proportional to their stellar masses with a logarithmic slope of approx 0.90. These relations hold true - within luminosities probed in this study - for LBGs from z approx = 1.5 to 5. The star-forming galaxies selected using other color-based techniques show similar correlations at z approx = 2, but to avoid any selection biases, and for direct comparison with LBGs at z > 3, a true Lyman break selection at z approx = 2 is essential. The future HST UV surveys,. both wider and deeper, covering a large luminosity range are important to better understand LBG properties, and their evolution.

  13. Stellar Populations of Lyman Break Galaxies at z ~= 1-3 in the HST/WFC3 Early Release Science Observations

    NASA Astrophysics Data System (ADS)

    Hathi, N. P.; Cohen, S. H.; Ryan, R. E., Jr.; Finkelstein, S. L.; McCarthy, P. J.; Windhorst, R. A.; Yan, H.; Koekemoer, A. M.; Rutkowski, M. J.; O'Connell, R. W.; Straughn, A. N.; Balick, B.; Bond, H. E.; Calzetti, D.; Disney, M. J.; Dopita, M. A.; Frogel, Jay A.; Hall, D. N. B.; Holtzman, J. A.; Kimble, R. A.; Paresce, F.; Saha, A.; Silk, J. I.; Trauger, J. T.; Walker, A. R.; Whitmore, B. C.; Young, E. T.

    2013-03-01

    We analyze the spectral energy distributions (SEDs) of Lyman break galaxies (LBGs) at z ~= 1-3 selected using the Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) UVIS channel filters. These HST/WFC3 observations cover about 50 arcmin2 in the GOODS-South field as a part of the WFC3 Early Release Science program. These LBGs at z ~= 1-3 are selected using dropout selection criteria similar to high-redshift LBGs. The deep multi-band photometry in this field is used to identify best-fit SED models, from which we infer the following results: (1) the photometric redshift estimate of these dropout-selected LBGs is accurate to within few percent; (2) the UV spectral slope β is redder than at high redshift (z > 3), where LBGs are less dusty; (3) on average, LBGs at z ~= 1-3 are massive, dustier, and more highly star forming, compared to LBGs at higher redshifts with similar luminosities (0.1L* <~ L <~ 2.5L*), though their median values are similar within 1σ uncertainties. This could imply that identical dropout selection technique, at all redshifts, finds physically similar galaxies; and (4) the stellar masses of these LBGs are directly proportional to their UV luminosities with a logarithmic slope of ~0.46, and star formation rates are proportional to their stellar masses with a logarithmic slope of ~0.90. These relations hold true—within luminosities probed in this study—for LBGs from z ~= 1.5 to 5. The star-forming galaxies selected using other color-based techniques show similar correlations at z ~= 2, but to avoid any selection biases, and for direct comparison with LBGs at z > 3, a true Lyman break selection at z ~= 2 is essential. The future HST UV surveys, both wider and deeper, covering a large luminosity range are important to better understand LBG properties and their evolution.

  14. A Study of the Contribution of the Damped Lyman α Systems and Lyman Break Galaxies to the Metal Content of the High-Redshift Universe

    NASA Astrophysics Data System (ADS)

    Lanfranchi, Gustavo; Friaça, Amancio C. S.

    We investigate the evolutionary history of the Universe's metal content through chemical abundances, taken from the literature, and predictions from chemical evolution models. The estimated abundances of several elements (C, N, O, S, Si, Fe, Cr, Zn) were taken from observations of QSOs absorption line systems over a wide range of redshift ( z ˜ 0.5 - 4.5). First, the observational data is analysed with robust statistical methods, which reveals important features: the metallicity of the QSOs absorption line systems increases with N(HI) until it reaches a peak at log(N(HI)) ˜ 20 - 20.5, and then declines suggesting a selection effect; there is an underabundance of Fe and Cr with respect to Zn in Damped Lyman α Systems (DLAS); the [α/Fe] ratio in DLAs is suprasolar; there is a trend of decreasing abundance with increasing N(HI) for Fe, Cr, Zn, Si and S in DLAs. After the statistical analysis, the observational data is compared with predictions of chemical evolution models. We apply different models to these systems due to the uncertainties about the nature of the QSOs absorption line systems. The DLAs are investigated with one zone models describing: a) dwarf galaxies with galactic winds and b) disk galaxies with infall. A chemodynamical model for spheroids is used to study the Lyman Break Galaxies (LBGs). In order to compare the observational data with the models, we use the ratios [N/α] and [α/Fe]. These ratios in DLAs are only partially reproduced by the disk and dwarf galaxy models suggesting that the DLAs come from a variety of morphological types of galaxies and not only one (Lanfranchi & Friaça, in preparation). They also imply a typically long timescale for the star formation in these systems. In contrast, the observational constraints for the LBGs are met by models for spheroid formation with typically short timescales for star formation ( ≈ 10 Gyr^{-1}), giving support to a scenario for galaxy formation in which there is a dichotomy between the

  15. KECK SPECTROSCOPY OF FAINT 3 < z < 8 LYMAN BREAK GALAXIES: EVIDENCE FOR A DECLINING FRACTION OF EMISSION LINE SOURCES IN THE REDSHIFT RANGE 6 < z < 8

    SciTech Connect

    Schenker, Matthew A.; Ellis, Richard S.; Robertson, Brant E.; Stark, Daniel P.; Dunlop, James S.; McLure, Ross J.; Kneib, Jean-Paul; Richard, Johan

    2012-01-10

    Using deep Keck spectroscopy of Lyman break galaxies selected from infrared imaging data taken with the Wide Field Camera 3 on board the Hubble Space Telescope, we present new evidence for a reversal in the redshift-dependent fraction of star-forming galaxies with detectable Lyman alpha (Ly{alpha}) emission in the redshift range 6.3 < z < 8.8. Our earlier surveys with the DEIMOS spectrograph demonstrated a significant increase with redshift in the fraction of line emitting galaxies over the interval 4 < z < 6, particularly for intrinsically faint systems which dominate the luminosity density. Using the longer wavelength sensitivities of Low Resolution Imaging Spectrometer and NIRSPEC, we have targeted 19 Lyman break galaxies selected using recent WFC3/IR data whose photometric redshifts are in the range 6.3 < z < 8.8 and which span a wide range of intrinsic luminosities. Our spectroscopic exposures typically reach a 5{sigma} sensitivity of <50 A for the rest-frame equivalent width (EW) of Ly{alpha} emission. Despite the high fraction of emitters seen only a few hundred million years later, we find only two convincing and one possible line emitter in our more distant sample. Combining with published data on a further seven sources obtained using FORS2 on the ESO Very Large Telescope, and assuming continuity in the trends found at lower redshift, we discuss the significance of this apparent reversal in the redshift-dependent Ly{alpha} fraction in the context of our range in continuum luminosity. Assuming all the targeted sources are at their photometric redshift and our assumptions about the Ly{alpha} EW distribution are correct, we would expect to find so few emitters in less than 1% of the realizations drawn from our lower redshift samples. Our new results provide further support for the suggestion that, at the redshifts now being probed spectroscopically, we are entering the era where the intergalactic medium is partially neutral. With the arrival of more

  16. DISCOVERY OF A CLOSE PAIR OF FAINT DWARF GALAXIES IN THE HALO OF CENTAURUS A

    SciTech Connect

    Crnojević, D.; Sand, D. J.; Caldwell, N.; McLeod, B.; Guhathakurta, P.; Toloba, E.; Simon, J. D.; Strader, J.

    2014-11-10

    As part of the Panoramic Imaging Survey of Centaurus and Sculptor (PISCeS), we report the discovery of a pair of faint dwarf galaxies (CenA-MM-Dw1 and CenA-MM-Dw2) at a projected distance of ∼90 kpc from the nearby elliptical galaxy NGC 5128 (CenA). We measure a tip of the red giant branch distance to each dwarf, finding D = 3.63 ± 0.41 Mpc for CenA-MM-Dw1 and D = 3.60 ± 0.41 Mpc for CenA-MM-Dw2, both of which are consistent with the distance to NGC 5128. A qualitative analysis of the color-magnitude diagrams indicates stellar populations consisting of an old, metal-poor red giant branch (≳12 Gyr, [Fe/H] ∼ –1.7 to –1.9). In addition, CenA-MM-Dw1 seems to host an intermediate-age population as indicated by its candidate asymptotic giant branch stars. The derived luminosities (M{sub V} = –10.9 ± 0.3 for CenA-MM-Dw1 and –8.4 ± 0.6 for CenA-MM-Dw2) and half-light radii (r{sub h} = 1.4 ± 0.04 kpc for CenA-MM-Dw1 and 0.36 ± 0.08 kpc for CenA-MM-Dw2) are consistent with those of Local Group dwarfs. CenA-MM-Dw1's low central surface brightness (μ {sub V,} {sub 0} = 27.3 ± 0.1 mag arcsec{sup –2}) places it among the faintest and most extended M31 satellites. Most intriguingly, CenA-MM-Dw1 and CenA-MM-Dw2 have a projected separation of only 3 arcmin (∼3 kpc): we are possibly observing the first, faint satellite of a satellite in an external group of galaxies.

  17. AN ULTRAVIOLET ULTRA-LUMINOUS LYMAN BREAK GALAXY AT Z = 2.78 IN NDWFS BOOeTES FIELD {sup ,} {sup ,}

    SciTech Connect

    Bian Fuyan; Fan Xiaohui; Jiang Linhua; McGreer, Ian; Wang Ran; Dey, Arjun; Green, Richard F.; Maiolino, Roberto; Walter, Fabian; Lin, Yen-Ting

    2012-10-01

    We present one of the most ultraviolet (UV) luminous Lyman break galaxies (LBGs; J1432+3358) at z = 2.78, discovered in the NOAO Deep Wide-Field Survey Booetes field. The R-band magnitude of J1432+3358 is 22.29 AB, more than two magnitudes brighter than typical L* LBGs at this redshift. The deep z-band image reveals two components of J1432+3358 separated by 1.''0 with a flux ratio of 3:1. The high signal-to-noise ratio rest-frame UV spectrum shows Ly{alpha} emission line and interstellar medium absorption lines. The absence of N V and C IV emission lines, and the non-detection in X-ray and radio wavelengths and mid-infrared (MIR) colors indicates weak or no active galactic nuclei (<10%) in this galaxy. The galaxy shows a broader line profile, with a FWHM of about 1000 km s{sup -1} and a larger outflow velocity ( Almost-Equal-To 500 km s{sup -1}) than those of typical z {approx} 3 LBGs. The physical properties are derived by fitting the spectral energy distribution (SED) with stellar synthesis models. The dust extinction, E(B - V) = 0.12, is similar to that in normal LBGs. The star formation rates (SFRs) derived from the SED fitting and the dust-corrected UV flux are consistent with each other, {approx}300 M{sub Sun} yr{sup -1}, and the stellar mass is (1.3 {+-} 0.3) Multiplication-Sign 10{sup 11} M{sub Sun }. The SFR and stellar mass in J1432+3358 are about an order of magnitude higher than those in normal LBGs. The SED-fitting results support that J1432+3358 has a continuous star formation history, with a star formation episode of 6.3 Multiplication-Sign 10{sup 8} yr. The morphology of J1432+3358 and its physical properties suggest that J1432+3358 is in an early phase of a 3:1 merger process. The unique properties and the low space number density ({approx}10{sup -7} Mpc{sup -3}) are consistent with the interpretation that such galaxies are either found in a short unobscured phase of the star formation or that a small fraction of intensive star-forming galaxies are

  18. Universal IMF versus dark halo response in early-type galaxies: breaking the degeneracy with the Fundamental Plane

    NASA Astrophysics Data System (ADS)

    Dutton, Aaron A.; Macciò, Andrea V.; Mendel, J. Trevor; Simard, Luc

    2013-07-01

    We use the relations between aperture stellar velocity dispersion (σap), stellar mass (MSPS) and galaxy size (Re) for a sample of ˜150 000 early-type galaxies from Sloan Digital Sky Survey/DR7 to place constraints on the stellar initial mass function (IMF) and dark halo response to galaxy formation. We build λ cold dark matter-based mass models that reproduce, by construction, the relations between galaxy size, light concentration and stellar mass, and use the spherical Jeans equations to predict σap. Given our model assumptions (including those in the stellar population synthesis models), we find that reproducing the median σap versus MSPS relation is not possible with both a universal IMF and a universal dark halo response. Significant departures from a universal IMF and/or dark halo response are required, but there is a degeneracy between these two solutions. We show that this degeneracy can be broken using the strength of the correlation between residuals of the velocity-mass (Δlog σap) and size-mass (Δlog Re) relations. The slope of this correlation, ∂VR ≡ Δlog σap/Δlog Re, varies systematically with galaxy mass from ∂VR ≃ -0.45 at MSPS ˜ 1010 M⊙ to ∂VR ≃ -0.15 at MSPS ˜ 1011.6 M⊙. The virial Fundamental Plane (FP) has ∂VR = -1/2, and thus we find that the tilt of the observed FP is mass dependent. Reproducing this tilt requires both a non-universal IMF and a non-universal halo response. Our best model has mass-follows-light at low masses (MSPS ≲ 1011.2 M⊙) and unmodified Navarro, Frenk and White haloes at MSPS ˜ 1011.5 M⊙. The stellar masses imply a mass-dependent IMF which is `lighter' than Salpeter at low masses and `heavier' than Salpeter at high masses.

  19. STELLAR POPULATIONS OF LYMAN BREAK GALAXIES AT z {approx_equal} 1-3 IN THE HST/WFC3 EARLY RELEASE SCIENCE OBSERVATIONS

    SciTech Connect

    Hathi, N. P.; McCarthy, P. J.; Cohen, S. H.; Windhorst, R. A.; Rutkowski, M. J.; Ryan, R. E. Jr.; Koekemoer, A. M.; Bond, H. E.; Finkelstein, S. L.; Yan, H.; O'Connell, R. W.; Straughn, A. N.; Kimble, R. A.; Balick, B.; Calzetti, D.; Disney, M. J.; Dopita, M. A.; Frogel, Jay A.; Hall, D. N. B.; Holtzman, J. A.; and others

    2013-03-10

    We analyze the spectral energy distributions (SEDs) of Lyman break galaxies (LBGs) at z {approx_equal} 1-3 selected using the Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) UVIS channel filters. These HST/WFC3 observations cover about 50 arcmin{sup 2} in the GOODS-South field as a part of the WFC3 Early Release Science program. These LBGs at z {approx_equal} 1-3 are selected using dropout selection criteria similar to high-redshift LBGs. The deep multi-band photometry in this field is used to identify best-fit SED models, from which we infer the following results: (1) the photometric redshift estimate of these dropout-selected LBGs is accurate to within few percent; (2) the UV spectral slope {beta} is redder than at high redshift (z > 3), where LBGs are less dusty; (3) on average, LBGs at z {approx_equal} 1-3 are massive, dustier, and more highly star forming, compared to LBGs at higher redshifts with similar luminosities (0.1L* {approx}< L {approx}< 2.5L*), though their median values are similar within 1{sigma} uncertainties. This could imply that identical dropout selection technique, at all redshifts, finds physically similar galaxies; and (4) the stellar masses of these LBGs are directly proportional to their UV luminosities with a logarithmic slope of {approx}0.46, and star formation rates are proportional to their stellar masses with a logarithmic slope of {approx}0.90. These relations hold true-within luminosities probed in this study-for LBGs from z {approx_equal} 1.5 to 5. The star-forming galaxies selected using other color-based techniques show similar correlations at z {approx_equal} 2, but to avoid any selection biases, and for direct comparison with LBGs at z > 3, a true Lyman break selection at z {approx_equal} 2 is essential. The future HST UV surveys, both wider and deeper, covering a large luminosity range are important to better understand LBG properties and their evolution.

  20. THE GREAT OBSERVATORIES ORIGINS DEEP SURVEY: CONSTRAINTS ON THE LYMAN CONTINUUM ESCAPE FRACTION DISTRIBUTION OF LYMAN-BREAK GALAXIES AT 3.4 < z < 4.5

    SciTech Connect

    Vanzella, E.; Nonino, M.; Fontanot, F.; Cristiani, S.; Tozzi, P.; Giavalisco, M.; Inoue, A. K.; Grazian, A.; Giallongo, E.; Boutsia, K.; Fontana, A.; Pentericci, L.; Dickinson, M.; Stern, D.; Ferguson, H.; Spinrad, H.; Rosati, P.

    2010-12-10

    We use ultra-deep ultraviolet VLT/VIMOS intermediate-band and VLT/FORS1 narrowband imaging in the GOODS Southern field to derive limits on the distribution of the escape fraction (f{sub esc}) of ionizing radiation for L {>=} L*{sub z=3} Lyman-break galaxies (LBGs) at redshift 3.4-4.5. Only one LBG, at redshift z = 3.795, is detected in its Lyman continuum (LyC; S/N {approx_equal} 5.5), the highest redshift galaxy currently known with a direct detection. Its ultraviolet morphology is quite compact (R{sub eff} = 0.8 kpc physical). Three out of seven active galactic nuclei are also detected in their LyC, including one at redshift z = 3.951 and z{sub 850} = 26.1. From stacked data (LBGs), we set an upper limit to the average f{sub esc} in the range 5%-20%, depending on how the data are selected (e.g., by magnitude and/or redshift). We undertake extensive Monte Carlo simulations that take into account intergalactic attenuation, stellar population synthesis models, dust extinction, and photometric noise in order to explore the moments of the distribution of the escaping radiation. Various distributions (exponential, log-normal, and Gaussian) are explored. We find that the median f{sub esc} is lower than {approx_equal}6% with an 84% percentile limit not larger than 20%. If this result remains valid for fainter LBGs down to current observational limits, then the LBG population might be not sufficient to account for the entire photoionization budget at the redshifts considered here, with the exact details dependent upon the assumed ionizing background and QSO contribution thereto. It is possible that f{sub esc} depends on the UV luminosity of the galaxies, with fainter galaxies having higher f{sub esc}, and estimates of f{sub esc} from a sample of faint LBGs from HUDF (i{sub 775} {<=}28.5) are in broad quantitative agreement with such a scenario.

  1. The 8 O'Clock Arc: A Serendipitous Discovery of a Strongly Lensed Lyman Break Galaxy in the SDSS DR4 Imaging Data

    SciTech Connect

    Allam, Sahar S.; Tucker, Douglas L.; Lin, Huan; Diehl, H.Thomas; Annis, James; Buckley-Geer, Elizabeth J.; Frieman, Joshua A.; /Fermilab /Chicago U., Astron. Astrophys. Ctr.

    2006-11-01

    We report on the serendipitous discovery of the brightest Lyman Break Galaxy (LBG) currently known, a galaxy at z = 2.73 that is being strongly lensed by the z = 0.38 Luminous Red Galaxy (LRG) SDSS J002240.91+143110.4. The arc of this gravitational lens system, which we have dubbed the ''8 o'clock arc'' due to its time of discovery, was initially identified in the imaging data of the Sloan Digital Sky Survey Data Release 4 (SDSS DR4); followup observations on the Astrophysical Research Consortium (ARC) 3.5m telescope at Apache Point Observatory confirmed the lensing nature of this system and led to the identification of the arc's spectrum as that of an LBG. The arc has a spectrum and a redshift remarkably similar to those of the previous record-holder for brightest LBG (MS 1512-cB58, a.k.a ''cB58''), but, with an estimated total magnitude of (g,r,i) = (20.0,19.2,19.0) and surface brightness of ({mu}{sub g}, {mu}{sub r}, {mu}{sub i}) = (23.3, 22.5, 22.3) mag arcsec{sup -2}, the 8 o'clock arc is thrice as bright. The 8 o'clock arc, which consists of three lensed images of the LBG, is 162{sup o}(9.6'') long and has a length-to-width ratio of 6:1. A fourth image of the LBG--a counter-image--can also be identified in the ARC 3.5m g-band images. A simple lens model for the system assuming a singular isothermal ellipsoid potential yields an Einstein radius of {theta}{sub Ein} = 2.91'' {+-} 0.14'', a total mass for the lensing LRG (within the 10.6 {+-} 0.5 h{sup -1} kpc enclosed by the lensed images) of 1.04 x 10{sup 12} h{sup -1} M{sub {circle_dot}}, and a magnification factor for the LBG of 12.3{sub -3.6}{sup +15}. The LBG itself is intrinsically quite luminous ({approx} 6 x L{sub *}) and shows indications of massive recent star formation, perhaps as high as 160 h{sup -1} M{sub {circle_dot}} yr{sup -1}.

  2. The UDF05 Follow-up of the HUDF: I. The Faint-End Slope of the Lyman-Break Galaxy Population at zeta approx. 5

    NASA Technical Reports Server (NTRS)

    Oesch, P. A.; Stiavelli, M.; Carollo, C. M.; Bergeron, L. E.; Koekemoer, A.; Lucas, R. A.; Pavlovsky, C. M.; Trenti, M.; Lilly, S. J.; Beckwith, S. V. W.; Dahlen, T.; Ferguson, H. C.; Gardner, J. P.; Lacey, C.; Mobasher, B.; Panagia, N.; Rix, H.-W.

    2007-01-01

    We present the UDF05 project, a HST Large Program of deep ACS (F606W, F775W, F850LP, and NICMOS (Fll0W, Fl60W) imaging of three fields, two of which coincide with the NICP1-4 NICMOS parallel observations of the Hubble Ultra Deep Field (HUDF). In this first paper we use the ACS data for the NICP12 field, as well as the original HUDF ACS data, to measure the UV Luminosity Function (LF) of z approximately 5 Lyman Break Galaxies (LBGs) down to very faint levels. Specifically, based on a V - i, i - z selection criterion, we identify a sample of 101 and 133 candidate z approximately 5 galaxies down to z(sub 850) = 28.5 and 29.25 magnitudes in the NICP12 field and in the HUDF, respectively. Using an extensive set of Monte Carlo simulations we derive corrections for observational biases and selection effects, and construct the rest-frame 1400 Angstroms LBG LF over the range M(sub 1400) = [-22.2, -17.1], i.e. down to approximately 0.04 L(sub *) at z = 5. We show that: (i) Different assumptions for the SED distribution of the LBG population, dust properties and intergalactic absorption result in a 25% variation in the number density of LBGs at z = 5 (ii) Under consistent assumptions for dust properties and intergalactic absorption, the HUDF is about 30% under-dense in z = 5 LBGs relative to the NICP12 field, a variation which is well explained by cosmic variance; (iii) The faint-end slope of the LF is independent of the specific assumptions for the input physical parameters, and has a value of alpha approximately -1.6, similar to the faint-end slope of the LF that has been measured for LBGs at z = 3 and z = 6. Our study therefore supports no variation in the faint-end of the LBG LF over the whole redshift range z = 3 to z = 6. The comparison with theoretical predictions suggests that (a,) the majority of the stars in the z = 5 LBG population are produced with a Top-Heavy IMF in merger-driven starbursts, and that (b) possibly, either the fraction of stellar mass produced in

  3. KECK SPECTROSCOPY OF LYMAN-BREAK GALAXIES AND ITS IMPLICATIONS FOR THE UV-CONTINUUM AND Ly{alpha} LUMINOSITY FUNCTIONS AT z > 6

    SciTech Connect

    Jiang Linhua; Egami, Eiichi; Walth, Gregory; Kashikawa, Nobunari; Matsuda, Yuichi; Shimasaku, Kazuhiro; Nagao, Tohru; Ota, Kazuaki; Ouchi, Masami

    2011-12-10

    We present Keck spectroscopic observations of z > 6 Lyman-break galaxy (LBG) candidates in the Subaru Deep Field (SDF). The candidates were selected as i'-dropout objects down to z' = 27 AB magnitudes from an ultra-deep SDF z'-band image. With the Keck spectroscopy we identified 19 LBGs with prominent Ly{alpha} emission lines at 6 {<=} z {<=} 6.4. The median value of the Ly{alpha} rest-frame equivalent widths (EWs) is {approx}50 A, with four EWs >100 A. This well-defined spectroscopic sample spans a UV-continuum luminosity range of -21.8 {<=} M{sub UV} {<=} -19.5 (0.6 {approx} 5 L*{sub UV}) and a Ly{alpha} luminosity range of (0.3-3) Multiplication-Sign 10{sup 43} erg s{sup -1} (0.3-3 L*{sub Ly{alpha}}). We derive the UV and Ly{alpha} luminosity functions (LFs) from our sample at (z) {approx} 6.2 after we correct for sample incompleteness. We find that our measurement of the UV LF is consistent with the results of previous studies based on photometric LBG samples at 5 < z < 7. Our Ly{alpha} LF is also generally in agreement with the results of Ly{alpha}-emitter surveys at z {approx} 5.7 and 6.6. This study shows that deep spectroscopic observations of LBGs can provide unique constraints on both the UV and Ly{alpha} LFs at z > 6.

  4. Breaking The Quasar L-z Degeneracy Using PDF-weighted Quasar-galaxy Cross-correlations In Deep, Wide NASA Fields

    NASA Astrophysics Data System (ADS)

    Ball, Nicholas M.; Myers, A. D.; White, M.; Hickox, R. C.; Brunner, R. J.

    2010-01-01

    We present a new method for measuring the two-point correlation function, as described by Myers, White, and Ball (2009). The method is an augmentation of previous techniques that use a heterogeneous set of spectroscopic objects to anchor the distance scale, and a well-controlled set of photometric detections to reduce noise. Our new approach weights by the information present in the full photometric redshift probability density function (PDF) to dramatically improve the clustering signal. For instance, an initial test yielded a factor of 5 improvement for quasar clustering in the Sloan Digital Sky Survey. The extra signal arises because we neither express the photometric redshift as a single value nor assign a simplified PDF functional form such as a single Gaussian. Our technique is generally applicable and should be particularly useful where complex spectroscopic data sets (e.g., BOSS) are overlapped by deep photometry (e.g., Pan-STARRS, DES, or LSST). Our method depends only on photometric detections in a single survey, but additional multi-wavelength data can be used to refine the information in the PDF weighting. This makes our approach also highly suited to regions of the sky where deep, multiwavelength space surveys overlap ground-based spectroscopy (e.g., COSMOS or the Bootes Survey). We assign photometric redshift PDFs to photometrically classified galaxies detected in the optical component of COSMOS, and use PDF weights to cross-correlate them against a spectroscopically confirmed AGN sample. We also report on similar results in the Bootes Survey. The deep spectroscopy and photometry in fields such as COSMOS and Bootes will allow new investigations of how AGN cluster as a function of luminosity and type, potentially breaking the so-called L-z degeneracy. Finally, we address the often computationally intensive requirements of utilizing full PDFs. This research was funded in part by NASA ADP grant NNX08AJ28G.

  5. Rest-frame Optical Emission Lines in z ˜ 3.5 Lyman-break-selected Galaxies: The Ubiquity of Unusually High [OIII]/Hβ Ratios at 2 Gyr

    NASA Astrophysics Data System (ADS)

    Holden, B. P.; Oesch, P. A.; González, V. G.; Illingworth, G. D.; Labbé, I.; Bouwens, R.; Franx, M.; van Dokkum, P.; Spitler, L.

    2016-03-01

    We present K-band spectra of rest-frame optical emission lines for 24 star-forming galaxies at z ˜ 3.2-3.7 using MOSFIRE on the Keck I telescope. Strong rest-frame optical [O iii] and Hβ emission lines were detected in 18 Lyman break galaxies (LBGs). The median flux ratio of [O iii]λ5007 to Hβ is {5.1}-0.5+0.5. This is a factor of 5-10 times higher than in local galaxies with similar stellar masses. None of our sources are detected in deep X-ray stacks, ruling out significant contamination by active galactic nuclei. Combining our sample with a variety of LBGs from the literature, including 49 galaxies selected in a very similar manner, we find a high median ratio of [O iii]/Hβ = {4.8}-1.7+0.8. This high ratio seems to be a ubiquitous feature of z ˜ 3-4 LBGs, very different from typical local star-forming galaxies at similar stellar masses. The only comparable systems at z ˜ 0 are those with similarly high specific star formation rates (SSFRs), though ˜5 times lower stellar masses. High SSFRs may result in a higher ionization parameter, higher electron density, or harder ionizing radiation, which, combined different elemental abundances, result in a much higher [O iii]/Hβ line ratio. This implies a strong relation between a global property of a galaxy, the SSFR, and the local conditions of ISM in star-forming regions. Partially based on data obtained with the Hubble Space Telescope operated by AURA, Inc. for NASA under contract NAS5-26555. Partially based on observations with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under NASA contract 1407.

  6. Interaction effects on galaxy pairs with Gemini/GMOS - II: oxygen abundance gradients

    NASA Astrophysics Data System (ADS)

    Rosa, D. A.; Dors, O. L.; Krabbe, A. C.; Hägele, G. F.; Cardaci, M. V.; Pastoriza, M. G.; Rodrigues, I.; Winge, C.

    2014-11-01

    In this paper, we derive oxygen abundance gradients from H II regions located in 11 galaxies in eight systems of close pairs. Long-slit spectra in the range 4400-7300 Å were obtained with the Gemini Multi-Object Spectrograph at Gemini South (GMOS-S). Spatial profiles of oxygen abundance in the gaseous phase along galaxy discs were obtained using calibrations based on strong emission lines (N2 and O3N2). We found oxygen gradients to be significantly flatter for all the studied galaxies than those in typical isolated spiral galaxies. Four objects in our sample, AM 1219A, AM 1256B, AM 2030A and AM 2030B, show a clear break in the oxygen abundance at galactocentric radius R/R25 between 0.2 and 0.5. For AM 1219A and AM 1256B, we found negative slopes for the inner gradients, and for AM 2030B, we found a positive slope. All three cases show a flatter behaviour to the outskirts of the galaxies. For AM 2030A, we found a positive slope for the outer gradient, while the inner gradient is almost compatible with a flat behaviour. We found a decrease of star formation efficiency in the zone that corresponds to the oxygen abundance gradient break for AM 1219A and AM 2030B. For the former, a minimum in the estimated metallicities was found very close to the break zone, which could be associated with a corotation radius. However, AM 1256B and AM 2030A, present a star formation rate maximum but not an extreme oxygen abundance value. All four interacting systems that show oxygen gradient breaks have extreme SFR values located very close to break zones.The H II regions located in close pairs of galaxies follow the same relation between the ionization parameter and the oxygen abundance as those regions in isolated galaxies.

  7. Twins born in different environments? Nuclei of two dSphs: isolated galaxy KKS3 and ESO269-66, a close neighbor of NGC5128

    NASA Astrophysics Data System (ADS)

    Sharina, Margarita; Karachentsev, Igor; Kniazev, Alexei

    2015-08-01

    The close vicinity of giant neighbors determines the environmental mechanisms that have been considered responsible for the evolution of dwarf spheroidal galaxies (dSphs). In the recent years, Karachentsev and collaborators have reported on the discovery of a few truly isolated dSphs in the Local volume. This study focuses on one of these unusual objects, KKs3 (MV=-12.3 mag). It contains a massive globular cluster (GC) (MV=-8.5 mag) near its optical center. We have performed the estimation of its radial velocity using a medium-resolution spectrum obtained with the RSS spectrograph at the Southern African Large Telescope (SALT). The signal-to-noise ratio in the spectrum was sufficient to estimate the age and metallicity for the GC using simple stellar population models, and the methods of full spectrum fitting and Lick index diagnostic diagrams. The results contribute to the knowledge about the origin of massive star clusters and their host dSphs.In the same way we have analyzed another luminous GC (MV=-10) in the center of ESO269-66 (MB=-15.4), a close dSph neighbor of the giant S0 Cen A. The cluster was observed with SALT in the same instrumental configuration. The structure and star formation histories of the two galaxies look rather similar. Both of them have experienced several star-forming events. The most recent ones occurred 1÷2 Gyr ago, and most powerful bursts happened 12÷14 Gyrs ago. Our analysis has shown that both GCs appear to be 1÷2 Gyr younger and 0.2÷0.3 dex more metal-rich than the most ancient metal-poor stars in the host dSphs. We examine signatures of multiple stellar population in the GCs using out data. Since central star-forming bursts were extended in time, the massive clusters might be considered as nuclei of the galaxies.

  8. Cosmological parameter constraints from galaxy-galaxy lensing and galaxy clustering with the SDSS DR7

    NASA Astrophysics Data System (ADS)

    Mandelbaum, Rachel; Slosar, Anže; Baldauf, Tobias; Seljak, Uroš; Hirata, Christopher M.; Nakajima, Reiko; Reyes, Reinabelle; Smith, Robert E.

    2013-06-01

    Recent studies have shown that the cross-correlation coefficient between galaxies and dark matter is very close to unity on scales outside a few virial radii of galaxy haloes, independent of the details of how galaxies populate dark matter haloes. This finding makes it possible to determine the dark matter clustering from measurements of galaxy-galaxy weak lensing and galaxy clustering. We present new cosmological parameter constraints based on large-scale measurements of spectroscopic galaxy samples from the Sloan Digital Sky Survey (SDSS) data release 7. We generalize the approach of Baldauf et al. to remove small-scale information (below 2 and 4 h-1 Mpc for lensing and clustering measurements, respectively), where the cross-correlation coefficient differs from unity. We derive constraints for three galaxy samples covering 7131 deg2, containing 69 150, 62 150 and 35 088 galaxies with mean redshifts of 0.11, 0.28 and 0.40. We clearly detect scale-dependent galaxy bias for the more luminous galaxy samples, at a level consistent with theoretical expectations. When we vary both σ8 and Ωm (and marginalize over non-linear galaxy bias) in a flat Λ cold dark matter model, the best-constrained quantity is σ8(Ωm/0.25)0.57 = 0.80 ± 0.05 (1σ, stat. + sys.), where statistical and systematic errors (photometric redshift and shear calibration) have comparable contributions, and we have fixed ns = 0.96 and h = 0.7. These strong constraints on the matter clustering suggest that this method is competitive with cosmic shear in current data, while having very complementary and in some ways less serious systematics. We therefore expect that this method will play a prominent role in future weak lensing surveys. When we combine these data with Wilkinson Microwave Anisotropy Probe 7-year (WMAP7) cosmic microwave background (CMB) data, constraints on σ8, Ωm, H0, wde and ∑mν become 30-80 per cent tighter than with CMB data alone, since our data break several parameter

  9. First Results from the Faint Infrared Grism Survey (FIGS): First Simultaneous Detection of Lyα Emission and Lyman Break from a Galaxy at z = 7.51

    NASA Astrophysics Data System (ADS)

    Tilvi, V.; Pirzkal, N.; Malhotra, S.; Finkelstein, S. L.; Rhoads, J. E.; Windhorst, R.; Grogin, N. A.; Koekemoer, A.; Zakamska, N. L.; Ryan, R.; Christensen, L.; Hathi, N.; Pharo, J.; Joshi, B.; Yang, H.; Gronwall, C.; Cimatti, A.; Walsh, J.; O’Connell, R.; Straughn, A.; Ostlin, G.; Rothberg, B.; Livermore, R. C.; Hibon, P.; Gardner, Jonathan P.

    2016-08-01

    Galaxies at high redshifts are a valuable tool for studying cosmic dawn, therefore it is crucial to reliably identify these galaxies. Here, we present an unambiguous and first simultaneous detection of both the Lyα emission and the Lyman break from a z=7.512 +/- 0.004 galaxy, observed in the Faint Infrared Grism Survey (FIGS). These spectra, taken with the G102 grism on the Hubble Space Telescope (HST), show a significant emission line detection (6σ ) in two observational position angles (PAs), with Lyα line flux of 1.06+/- 0.19× {10}-17 {erg} {{{s}}}-1 {{cm}}-2. The line flux is nearly a factor of four higher than that in the archival MOSFIRE spectroscopic observations. This is consistent with other recent observations, implying that ground-based near-infrared spectroscopy underestimates the total emission line fluxes, and if confirmed, can have strong implications for reionization studies that are based on ground-based Lyα measurements. A 4σ detection of the NV line in one PA also suggests a weak active galactic nucleus (AGN), and if confirmed, would make this source the highest-redshift AGN yet found. These observations from HST thus clearly demonstrate the sensitivity of the FIGS survey, and the capability of grism spectroscopy for studying the epoch of reionization.

  10. On the dynamical and physical state of the {open_quotes}diffuse ionized medium{close_quotes} in nearby spiral galaxies

    SciTech Connect

    Wang, J.; Heckman, T.M.; Lehnert, M.D.

    1997-12-01

    We report the initial results from a program to study the morphology, physical state, and kinematics of the {open_quotes}diffuse ionized medium{close_quotes} (DIM) in a sample of the nearest and brightest late-type galaxies. For each of five galaxies (NGC 2403, M81, NGC 4395, M51, and M101), we have analyzed deep narrowband H{alpha} images of the entire star-forming disk and long-slit spectra of the inner ({approximately}10kpc) disk with a resolution of 40{endash}75kms{sup {minus}1}. We find that the DIM covers most of the star-forming disk and is morphologically related to the presence of high surface brightness gas (the giant HII regions). The DIM and the giant HII regions differ systematically in their physical and dynamical state. The DIM is characterized by enhanced emission in the low-ionization forbidden lines ([OI], [NII], and [SII]), and even the high-ionization [OIII] {lambda}5007 line is moderately strong in the DIM in at least three cases. This last result contrasts with upper limits on the [OIII] surface brightness in the local DIM of our own Galaxy (the {open_quotes}Reynolds Layer{close_quotes}). We directly verify the inference made by Lehnert and Heckman that the DIM contributes significantly to the spatially integrated (global) emission-line ratios measured in late-type galaxies. We also find that the DIM is more disturbed kinematically than the gas in the giant HII regions. The deconvolved (intrinsic) widths of the H{alpha} and [NII] {lambda}6584 lines range from 30 to 100kms{sup {minus}1} (FWHM) in the DIM compared to 20{endash}50kms{sup {minus}1} in the giant HII regions. The high-ionization gas in the DIM is more kinematically disturbed than the low-ionization gas: the [OIII] {lambda}5007 lines have intrinsic widths of 70{endash}150kms{sup {minus}1}. The differing kinematics implies that the DIM is not a single monolithic phase of the ISM. Instead, it may consist of a {open_quotes}quiescent{close_quotes} DIM with a low ionization state and

  11. Breaking Bat

    ERIC Educational Resources Information Center

    Aguilar, Isaac-Cesar; Kagan, David

    2013-01-01

    The sight of a broken bat in Major League Baseball can produce anything from a humorous dribbler in the infield to a frightening pointed projectile headed for the stands. Bats usually break at the weakest point, typically in the handle. Breaking happens because the wood gets bent beyond the breaking point due to the wave sent down the bat created…

  12. KECK SPECTROSCOPY OF 3 < z < 7 FAINT LYMAN BREAK GALAXIES: THE IMPORTANCE OF NEBULAR EMISSION IN UNDERSTANDING THE SPECIFIC STAR FORMATION RATE AND STELLAR MASS DENSITY

    SciTech Connect

    Stark, Daniel P.; Robertson, Brant; Schenker, Matthew A.; Ellis, Richard; McLure, Ross; Dunlop, James

    2013-02-15

    The physical properties inferred from the spectral energy distributions (SEDs) of z > 3 galaxies have been influential in shaping our understanding of early galaxy formation and the role galaxies may play in cosmic reionization. Of particular importance is the stellar mass density at early times, which represents the integral of earlier star formation. An important puzzle arising from the measurements so far reported is that the specific star formation rates (sSFRs) evolve far less rapidly than expected in most theoretical models. Yet the observations underpinning these results remain very uncertain, owing in part to the possible contamination of rest-optical broadband light from strong nebular emission lines. To quantify the contribution of nebular emission to broadband fluxes, we investigate the SEDs of 92 spectroscopically confirmed galaxies in the redshift range 3.8 < z < 5.0 chosen because the H{alpha} line lies within the Spitzer/IRAC 3.6 {mu}m filter. We demonstrate that the 3.6 {mu}m flux is systematically in excess of that expected from stellar continuum alone, which we derive by fitting the SED with population synthesis models. No such excess is seen in a control sample of spectroscopically confirmed galaxies with 3.1 < z < 3.6 in which there is no nebular contamination in the IRAC filters. From the distribution of our 3.6 {mu}m flux excesses, we derive an H{alpha} equivalent width distribution and consider the implications for both the derived stellar masses and the sSFR evolution. The mean rest-frame H{alpha} equivalent width we infer at 3.8 < z < 5.0 (270 A) indicates that nebular emission contributes at least 30% of the 3.6 {mu}m flux and, by implication, nebular emission is likely to have a much greater impact for galaxies with z {approx_equal} 6-7 where both warm IRAC filters are contaminated. Via our empirically derived equivalent width distribution, we correct the available stellar mass densities and show that the sSFR evolves more rapidly at z

  13. The multifrequency parsec-scale structure of PKS 2254-367 (IC 1459): a luminosity-dependent break in morphology for the precursors of radio galaxies?

    NASA Astrophysics Data System (ADS)

    Tingay, S. J.; Edwards, P. G.

    2015-03-01

    We present the first multifrequency very long baseline interferometry (VLBI) images of PKS 2254-367, a gigahertz-peaked spectrum (GPS) radio source hosted by the nearby galaxy IC 1459 (D = 20.5 Mpc). PKS 2254-367 and the radio source in NGC 1052 (PKS 0238-084; D = 17.2 Mpc) are the two closest GPS radio sources to us, far closer than the next closest example, PKS 1718-649 (D = 59 Mpc). As such, IC 1459 and NGC 1052 offer opportunities to study the details of the parsec-scale radio sources as well as the environments that the radio sources inhabit, across the electromagnetic spectrum. Given that some models for the origin and evolution of GPS radio sources require a strong connection between the radio source morphology and the gaseous nuclear environment, such opportunities for detailed study are important. Our VLBI images of PKS 2254-367 show that the previously identified similarities between IC 1459 and NGC 1052 continue on to the parsec-scale. Both compact radio sources appear to have symmetric jets of approximately the same luminosity, much lower than typically noted in compact double GPS sources. Similarities between PKS 2254-367 and NGC 1052, and differences with respect to other GPS galaxies, lead us to speculate that a sub-class of GPS radio sources, with low luminosity and with jet-dominated morphologies, exists and would be largely absent from radio source surveys with ˜1 Jy flux density cut-offs. We suggest that this possible low-luminosity, jet-dominated population of GPS sources could be an analogue of the Fanaroff-Riley type I (FR I) radio galaxies, with the higher luminosity lobe-dominated GPS sources being the analogue of the FR II radio galaxies.

  14. Deep 15μm AKARI Observations in the CDFS: Estimating Dust Luminosities for a MIR-Selected Sample and for Lyman Break Galaxies and the Evolution of Ldust/LUV with the Redshift

    NASA Astrophysics Data System (ADS)

    Burgarella, Denis; Buat, Véronique; Takeuchi, Tsutomu T.; Wada, Takehiko; Pearson, Chris

    2009-02-01

    Deep observations of the Chandra Deep Field South have been secured at 15μm with AKARI/IRC infrared space telescope. From these observations, we define a sample of mid infrared-selected galaxies at 15μm and we also obtain 15μm flux densities for a sample of Lyman Break Galaxies at z ˜ 1 already observed at 24μm with Spitzer/MIPS. Number counts for the mid infrared-selected sample show a bump around a 15μm flux density of 0.2mJy that can be attributed to galaxies at z > 0.4 and at z > 0.8 for the fainter part of the bump. This bump seems to be shifted as compared to other works and a possible origin can be the Cosmic variance. On the two above samples at z ˜ 1 we have tested the validity of the conversions from luminosities ν.fν at 8νm to total dust luminosities by comparing with luminosities estimated from 12νm data used as a reference. Some calibrations seem better when compared to evaluated from longer wavelength luminosities. We also find that the rest-frame 8μm luminosities provide good estimates of Ldust. By comparing our data to several libraries of spectral energy distributions, we find that models can explain the diversity of the observed f24/f15 ratio quite reasonably. However, when we analyse the luminosity dependence of this ratio, we find important discrepancies. Finally, we revisit the evolution of Ldust/LUV ratio with the redshift z by re-calibrating previous Ldust at z ˜ 2 based on our results and added new data points at higher redshifts. The decreasing trend is amplified as compared to the previous estimate.

  15. THE LBT BOOeTES FIELD SURVEY. I. THE REST-FRAME ULTRAVIOLET AND NEAR-INFRARED LUMINOSITY FUNCTIONS AND CLUSTERING OF BRIGHT LYMAN BREAK GALAXIES AT Z {approx} 3

    SciTech Connect

    Bian Fuyan; Fan Xiaohui; Jiang Linhua; McGreer, Ian; Dave, Romeel; Dey, Arjun; Green, Richard F.; Maiolino, Roberto; Walter, Fabian; Lee, Kyoung-Soo

    2013-09-01

    We present a deep LBT/LBC U{sub spec}-band imaging survey (9 deg{sup 2}) covering the NOAO Booetes field. A total of 14,485 Lyman break galaxies (LBGs) at z {approx} 3 are selected, which are used to measure the rest-frame UV luminosity function (LF). The large sample size and survey area reduce the LF uncertainties due to Poisson statistics and cosmic variance by {>=}3 compared to previous studies. At the bright end, the LF shows excess power compared to the best-fit Schechter function, which can be attributed to the contribution of z {approx} 3 quasars. We compute the rest-frame near-infrared LF and stellar mass function (SMF) of z {approx} 3 LBGs based on the R-band and [4.5 {mu}m]-band flux relation. We investigate the evolution of the UV LFs and SMFs between z {approx} 7 and z {approx} 3, which supports a rising star formation history in the LBGs. We study the spatial correlation function of two bright LBG samples and estimate their average host halo mass. We find a tight relation between the host halo mass and the galaxy star formation rate (SFR), which follows the trend predicted by the baryonic accretion rate onto the halo, suggesting that the star formation in LBGs is fueled by baryonic accretion through the cosmic web. By comparing the SFRs with the total baryonic accretion rates, we find that cosmic star formation efficiency is about 5%-20% and it does not evolve significantly with redshift, halo mass, or galaxy luminosity.

  16. Ring Galaxies

    NASA Astrophysics Data System (ADS)

    Dennefeld, M.; Materne, J.

    1980-09-01

    Among the 338 exotic, intriguing and/or fascinating objects contained in Arp's catalogue of peculiar galaxies, two, Arp 146 and 147, are calling special attention as a presumably separate class of objects displaying closed rings with almost empty interior. It is difficult to find out when, historically speaking, attention was called first to this type of object as a peculiar class, but certainly ga1axies with rings were widely found and recognized in the early sixties, ul}der others by Vorontsov-Velyaminov (1960), Sandage (1961) in the Hubble Atlas or de Vaucouleurs (1964) in the first reference catalogue of ga1axies. The most recent estimates by Arp and Madore (1977) from a search on about 200 Schmidt plates covering 7,000 square degrees give 3.6 per cent of ring galaxies among 2,784 peculiar galaxies found. However, despite the mythological perfection associated with a circle, some ordering is necessary before trying to understand the nature of such objects. This is particularly true because a large fraction of those galaxies with rings are probably normal spiral galaxies of type RS or S(r) as defined by de Vaucouleurs, where the spiral arms are simply "closing the circle". A good example of such "ordinary" galaxy is NGC 3081 in the Hubble Atlas .

  17. Closing in on a Short-Hard Burst Progenitor: Constraints From Early-Time Optical Imaging and Spectroscopy of a Possible Host Galaxy of GRB 050509b

    SciTech Connect

    Bloom, Joshua S.; Prochaska, J.X.; Pooley, D.; Blake, C.W.; Foley, R.J.; Jha, S.; Ramirez-Ruiz, E.; Granot, J.; Filippenko, A.V.; Sigurdsson, S.; Barth, A.J.; Chen, H.-W.; Cooper, M.C.; Falco, E.E.; Gal, R.R.; Gerke, B.F.; Gladders, M.D.; Greene, J.E.; Hennanwi, J.; Ho, L.C.; Hurley, K.; /UC, Berkeley, Astron. Dept. /Lick Observ. /Harvard-Smithsonian Ctr. Astrophys. /Princeton, Inst. Advanced Study /KIPAC, Menlo Park /Penn State U., Astron. Astrophys. /UC, Irvine /MIT, MKI /UC, Davis /UC, Berkeley /Carnegie Inst. Observ. /UC, Berkeley, Space Sci. Dept. /Michigan U. /LBL, Berkeley /Spitzer Space Telescope

    2005-06-07

    The localization of the short-duration, hard-spectrum gamma-ray burst GRB050509b by the Swift satellite was a watershed event. Never before had a member of this mysterious subclass of classic GRBs been rapidly and precisely positioned in a sky accessible to the bevy of ground-based follow-up facilities. Thanks to the nearly immediate relay of the GRB position by Swift, we began imaging the GRB field 8 minutes after the burst and have continued during the 8 days since. Though the Swift X-ray Telescope (XRT) discovered an X-ray afterglow of GRB050509b, the first ever of a short-hard burst, thus far no convincing optical/infrared candidate afterglow or supernova has been found for the object. We present a re-analysis of the XRT afterglow and find an absolute position of R.A. = 12h36m13.59s, Decl. = +28{sup o}59'04.9'' (J2000), with a 1{sigma} uncertainty of 3.68'' in R.A., 3.52'' in Decl.; this is about 4'' to the west of the XRT position reported previously. Close to this position is a bright elliptical galaxy with redshift z = 0.2248 {+-} 0.0002, about 1' from the center of a rich cluster of galaxies. This cluster has detectable diffuse emission, with a temperature of kT = 5.25{sub -1.68}{sup +3.36} keV. We also find several ({approx}11) much fainter galaxies consistent with the XRT position from deep Keck imaging and have obtained Gemini spectra of several of these sources. Nevertheless we argue, based on positional coincidences, that the GRB and the bright elliptical are likely to be physically related. We thus have discovered reasonable evidence that at least some short-duration, hard-spectra GRBs are at cosmological distances. We also explore the connection of the properties of the burst and the afterglow, finding that GRB050509b was underluminous in both of these relative to long-duration GRBs. However, we also demonstrate that the ratio of the blast-wave energy to the {gamma}-ray energy is consistent with that of long-duration GRBs. We thus find plausible

  18. A dusty, normal galaxy in the epoch of reionization

    NASA Astrophysics Data System (ADS)

    Watson, Darach; Christensen, Lise; Knudsen, Kirsten Kraiberg; Richard, Johan; Gallazzi, Anna; Michałowski, Michał Jerzy

    2015-03-01

    Candidates for the modest galaxies that formed most of the stars in the early Universe, at redshifts z > 7, have been found in large numbers with extremely deep restframe-ultraviolet imaging. But it has proved difficult for existing spectrographs to characterize them using their ultraviolet light. The detailed properties of these galaxies could be measured from dust and cool gas emission at far-infrared wavelengths if the galaxies have become sufficiently enriched in dust and metals. So far, however, the most distant galaxy discovered via its ultraviolet emission and subsequently detected in dust emission is only at z = 3.2 (ref. 5), and recent results have cast doubt on whether dust and molecules can be found in typical galaxies at z >= 7. Here we report thermal dust emission from an archetypal early Universe star-forming galaxy, A1689-zD1. We detect its stellar continuum in spectroscopy and determine its redshift to be z = 7.5 +/- 0.2 from a spectroscopic detection of the Lyman-α break. A1689-zD1 is representative of the star-forming population during the epoch of reionization, with a total star-formation rate of about 12 solar masses per year. The galaxy is highly evolved: it has a large stellar mass and is heavily enriched in dust, with a dust-to-gas ratio close to that of the Milky Way. Dusty, evolved galaxies are thus present among the fainter star-forming population at z > 7.

  19. Transient etiolation: protochlorophyll(ide) and chlorophyll forms in differentiating plastids of closed and breaking leaf buds of horse chestnut (Aesculus hippocastanum).

    PubMed

    Solymosi, Katalin; Bóka, Károly; Böddi, Béla

    2006-08-01

    An accompanying paper reports the accumulation of photoactive protochlorophyllide (Pchlide) in the innermost leaf primordia of buds of many tree species. In this paper, we describe plastid differentiation, changes in pigment concentrations and spectral properties of bud scales and leaf primordia of horse chestnut (Aesculus hippocastanum L.) from January until the end of bud break in April. The bud scales contained plastids with grana, stroma thylakoids characteristic of chloroplasts and large dense bodies within the stroma. In January, proplastids and young chloroplasts were present in the leaf primordia, and the fluorescence spectra of the primordia were similar to those of green leaves except for a minor band at 630 nm, indicative of a protochlorophyll(ide). During bud break, the pigment concentrations of the green bud scales and the outermost leaf primordia increased, and Pchlide forms with emission maxima at 633, 644 and 655 nm accumulated in the middle and innermost leaf primordia. Depending on the position of the leaf primordia within the bud, their plastids and their pigment concentrations varied. Etio-chloroplasts with prolamellar bodies (PLBs) and prothylakoids with developing grana were observed in the innermost leaves. Besides the above-mentioned Pchlide forms, the middle and innnermost leaf primordia contained only a Chl band with an emission maximum at 686 nm. The outermost leaf primordia contained etio-chloroplasts with well-developed grana and small, narrow-type PLBs. These outermost leaves contained only chlorophyll forms like the mature green leaves. No Pchlide accumulation was observed after bud break, indicating that etiolation of the innermost and middle leaves is transient. The Pchlide forms and the plastid types of the primordia in buds grown in nature were similar to those of leaves of dark-germinated seedlings and to those of the leaf primordia of dark-forced buds. We conclude that transient etiolation occurs under natural conditions. The

  20. Structural Properties of Barred Galaxies

    NASA Astrophysics Data System (ADS)

    Kim, Taehyun; Gadotti, D. A.; Sheth, K.; Lee, M.; S4G Team

    2014-01-01

    We have performed two-dimensional multicomponent decomposition of 144 local barred spiral galaxies using 3.6 micron images from the Spitzer Survey of Stellar Structure in Galaxies. Our model fit includes up to four components (bulge, disk, bar, and a point source) and, most importantly, takes into account disk breaks. We present that ignoring the disk break and using a single disk scale length in the model fit for Type II (down- bending) disk galaxies can lead to differences of 40% in the disk scale length, 10% in bulge-to-total luminosity ratio (B/T), and 25% in bar-to-total luminosity ratios. We show that for galaxies with B/T > 0.1, the break radius to bar radius, r_br/R_bar, varies between 1 and 3, but as a function of B/T the ratio remains roughly constant. This suggests that in bulge-dominated galaxies the disk break is likely related to the outer Lindblad Resonance (OLR) of the bar, and thus the OLR also moves outwards at the same rate as the bar grows. For galaxies with B/T < 0.1, r_br/R_bar, spans a wide range from 1 to 6. This suggests that the mechanism that produces the break in these galaxies may be different from that in galaxies with more massive bulges. Consistent with previous studies, we conclude that disk breaks in galaxies with small bulges may originate from bar resonances that may be also coupled with the spiral arms, or be related to star formation thresholds. We quantifiy shapes of bar radial surface brightness profiles by measuring their Sersic indices and show that bars in higher B/T galaxies have flatter radial surface brightness profile than bulgeless galaxies do. In particular, bulgeless galaxies mostly have bars with steep profiles. We show that the normalized bar length is correlated with B/T, which is consistent with bars growing longer with time.

  1. Improved limit on the neutrino mass with CMB and redshift-dependent halo bias-mass relations from SDSS, DEEP2, and Lyman-break galaxies

    SciTech Connect

    De Bernardis, Francesco; Serra, Paolo; Cooray, Asantha; Melchiorri, Alessandro

    2008-10-15

    We use measurements of luminosity-dependent galaxy bias at several different redshifts, SDSS at z=0.05, DEEP2 at z=1, and LBGs at z=3.8, combined with WMAP 5-year cosmic microwave background anisotropy data and SDSS Red Luminous Galaxy survey three-dimensional clustering power spectrum to put constraints on cosmological parameters. Fitting this combined dataset, we show that the luminosity-dependent bias data that probe the relation between halo bias and halo mass and its redshift evolution are very sensitive to sum of the neutrino masses: in particular, we obtain the upper limit of at the 95% confidence level for a {lambda}CDM+m{sub {nu}} model, with a {sigma}{sub 8} equal to {sigma}{sub 8}=0.759{+-}0.025 (1{sigma}). When we allow the dark energy equation-of-state parameter w to vary, we find w=-1.30{+-}0.19 for a general wCDM+m{sub {nu}} model with the 95% confidence level upper limit on the neutrino masses at . The constraint on the dark energy equation of state further improves to w=-1.125{+-}0.092 when using also ACBAR and supernovae Union data, in addition to above, with a prior on the Hubble constant from the Hubble Space Telescope.

  2. Breaking Bat

    NASA Astrophysics Data System (ADS)

    Aguilar, Isaac-Cesar; Kagan, David

    2013-02-01

    The sight of a broken bat in Major League Baseball can produce anything from a humorous dribbler in the infield to a frightening pointed projectile headed for the stands. Bats usually break at the weakest point, typically in the handle. Breaking happens because the wood gets bent beyond the breaking point due to the wave sent down the bat created by the collision with the ball. The kind of wood that is used plays a role in the manner in which the bat breaks—-its "failure mode." We report on a simple experiment to compare the breaking strength and failure modes of ash and maple dowels. The results illustrate some of the features of breaking bats under game conditions.

  3. CARS: the CFHTLS-Archive-Research Survey. II. Weighing dark matter halos of Lyman-break galaxies at z = 3-5

    NASA Astrophysics Data System (ADS)

    Hildebrandt, H.; Pielorz, J.; Erben, T.; van Waerbeke, L.; Simon, P.; Capak, P.

    2009-05-01

    Aims: We measure the clustering properties for a large samples of u- (z˜3), g- (z˜4), and r- (z˜5) dropouts from the Canada-France-Hawaii Telescope Legacy Survey (CFHTLS) Deep fields. Methods: Photometric redshift distributions along with simulations allow us to de-project the angular correlation measurements and estimate physical quantities such as the correlation length, halo mass, galaxy bias, and halo occupation as a function of UV luminosity. Results: For the first time we detect a significant one-halo term in the correlation function at z˜5. The comoving correlation lengths and halo masses of LBGs are found to decrease with decreasing rest-frame UV-luminosity. No significant redshift evolution is found in either quantity. The typical halo mass hosting an LBG is M⪆1012~h-1~M_⊙ and the halos are typically occupied by less than one galaxy. Clustering segregation with UV luminosity is clearly observed in the dropout samples, however redshift evolution cannot clearly be disentangled from systematic uncertainties introduced by the redshift distributions. We study a range of possible redshift distributions to illustrate the effect of this choice. Spectroscopy of representative subsamples is required to make high-accuracy absolute measurements of high-z halo masses. Based on observations obtained with MegaPrime/MegaCam, a joint project of CFHT and CEA/DAPNIA, at the Canada-France-Hawaii Telescope (CFHT) which is operated by the National Research Council (NRC) of Canada, the Institut National des Sciences de l'Univers of the Centre National de la Recherche Scientifique (CNRS) of France, and the University of Hawaii. This work is based in part on data products produced at TERAPIX and the Canadian Astronomy Data Centre as part of the Canada-France-Hawaii Telescope Legacy Survey, a collaborative project of NRC and CNRS. Based on zCOSMOS and VVDS observations carried out using the Very Large Telescope at the ESO Paranal Observatory under Programme IDs: LP175.A

  4. A SIMPLE TECHNIQUE FOR PREDICTING HIGH-REDSHIFT GALAXY EVOLUTION

    SciTech Connect

    Behroozi, Peter S.; Silk, Joseph

    2015-01-20

    We show that the ratio of galaxies' specific star formation rates (SSFRs) to their host halos' specific mass accretion rates (SMARs) strongly constrains how the galaxies' stellar masses, SSFRs, and host halo masses evolve over cosmic time. This evolutionary constraint provides a simple way to probe z > 8 galaxy populations without direct observations. Tests of the method with galaxy properties at z = 4 successfully reproduce the known evolution of the stellar mass-halo mass (SMHM) relation, galaxy SSFRs, and the cosmic star formation rate (CSFR) for 5 < z < 8. We then predict the continued evolution of these properties for 8 < z < 15. In contrast to the nonevolution in the SMHM relation at z < 4, the median galaxy mass at fixed halo mass increases strongly at z > 4. We show that this result is closely linked to the flattening in galaxy SSFRs at z > 2 compared to halo SMARs; we expect that average galaxy SSFRs at fixed stellar mass will continue their mild evolution to z ∼ 15. The expected CSFR shows no breaks or features at z > 8.5; this constrains both reionization and the possibility of a steep falloff in the CSFR at z = 9-10. Finally, we make predictions for stellar mass and luminosity functions for the James Webb Space Telescope, which should be able to observe one galaxy with M {sub *} ≳ 10{sup 8} M {sub ☉} per 10{sup 3} Mpc{sup 3} at z = 9.6 and one such galaxy per 10{sup 4} Mpc{sup 3} at z = 15.

  5. How do galaxies get their gas?

    NASA Astrophysics Data System (ADS)

    Kereš, Dušan; Katz, Neal; Weinberg, David H.; Davé, Romeel

    2005-10-01

    We examine the temperature history of gas accreted by forming galaxies in smoothed particle hydrodynamics simulations. About half of the gas follows the track expected in the conventional picture of galaxy formation, shock heating to roughly the virial temperature of the galaxy potential well (T~ 106 K for a Milky Way type galaxy) before cooling, condensing and forming stars. However, the other half radiates its acquired gravitational energy at much lower temperatures, typically T < 105 K, and the histogram of maximum gas temperatures is clearly bimodal. The `cold mode' of gas accretion dominates for low-mass galaxies (baryonic mass Mgal<~ 1010.3Msolar or halo mass Mhalo<~ 1011.4Msolar), while the conventional `hot mode' dominates the growth of high-mass systems. Cold accretion is often directed along filaments, allowing galaxies to efficiently draw gas from large distances, while hot accretion is quasi-spherical. The galaxy and halo mass dependence leads to redshift and environment dependence of cold and hot accretion rates, with the cold mode dominating at high redshift and in low-density regions today, and the hot mode dominating in group and cluster environments at low redshift. The simulations reproduce an important feature of the observed relation between the galaxy star formation rate (SFR) and the environment, namely a break in star formation rates at surface densities Σ~ 1h275 Mpc-2, outside the virial radii of large groups and clusters. The cosmic SFR tracks the overall history of gas accretion, and its decline at low redshift follows the combined decline of cold and hot accretion rates. The drop in cold accretion is driven by the decreasing infall rate on to haloes, while for hot accretion this slower mass growth is further modified by the longer cooling times within haloes. If we allowed hot accretion to be suppressed by conduction or active galactic nuclei feedback, then the simulation predictions would change in interesting ways, perhaps resolving

  6. Whirlpool Galaxy

    NASA Technical Reports Server (NTRS)

    1999-01-01

    Scientists are seeing unprecedented detail of the spiral arms and dust clouds in the nearby Whirlpool galaxy, thanks to a new Hubble Space Telescope image, available at http://www.jpl.nasa.gov/pictures/wfpc/wfpc.html. The image uses data collected January 15 and 24, 1995, and July 21, 1999, by Hubble's Wide Field and Planetary Camera 2, designed and built by JPL. Using the image, a research group led by Dr. Nick Scoville of the California Institute of Technology, Pasadena, clearly defined the structure of the galaxy's cold dust clouds and hot hydrogen, and they linked star clusters within the galaxy to their parent dust clouds.

    The Whirlpool galaxy is one of the most photogenic galaxies. This celestial beauty is easily seen and photographed with smaller telescopes and studied extensively from large ground- and space-based observatories. The new composite image shows visible starlight and light from the emission of glowing hydrogen, which is associated with the most luminous young stars in the spiral arms.

    The galaxy is having a close encounter with a nearby companion galaxy, NGC 5195, just off the upper edge of the image. The companion's gravitational pull is triggering star formation in the main galaxy, lit up by numerous clusters of young and energetic stars in brilliant detail. Luminous clusters are highlighted in red by their associated emission from glowing hydrogen gas.

    This image was composed by the Hubble Heritage Team from Hubble archive data and was superimposed onto data taken by Dr. Travis Rector of the National Optical Astronomy Observatory at the .9-meter (35-inch) telescope at the National Science Foundation's Kitt Peak National Observatory, Tucson, Ariz. Scoville's team includes M. Polletta of the University of Geneva, Switzerland; S. Ewald and S. Stolovy of Caltech; and R. Thompson and M. Rieke of the University of Arizona, Tucson.

    The Space Telescope Science Institute, Baltimore, Md., manages space operations for the Hubble Space

  7. Radio Galaxies.

    ERIC Educational Resources Information Center

    Downes, Ann

    1986-01-01

    Provides background information on radio galaxies. Topic areas addressed include: what produces the radio emission; radio telescopes; locating radio galaxies; how distances to radio galaxies are found; physics of radio galaxies; computer simulations of radio galaxies; and the evolution of radio galaxies with cosmic time. (JN)

  8. MCG+00-32-16: An Irregular Galaxy Close to the Lowest Redshift Absorber on the 3C 273 Line of Sight

    NASA Technical Reports Server (NTRS)

    Hoffman, G. L.; Lu, N. Y.; Salpeter, E. E.; Connell, B. M.; Fromhold-Treu, R.

    1998-01-01

    We present H I synthesis array mapping and CCD photometry in B and R for MCG+00-32-16. The H I disk is rotating in such a way that the side of the galaxy closer to the sight-line to the quasar has the larger velocity difference from the absorber.

  9. A dusty, normal galaxy in the epoch of reionization.

    PubMed

    Watson, Darach; Christensen, Lise; Knudsen, Kirsten Kraiberg; Richard, Johan; Gallazzi, Anna; Michałowski, Michał Jerzy

    2015-03-19

    Candidates for the modest galaxies that formed most of the stars in the early Universe, at redshifts z > 7, have been found in large numbers with extremely deep restframe-ultraviolet imaging. But it has proved difficult for existing spectrographs to characterize them using their ultraviolet light. The detailed properties of these galaxies could be measured from dust and cool gas emission at far-infrared wavelengths if the galaxies have become sufficiently enriched in dust and metals. So far, however, the most distant galaxy discovered via its ultraviolet emission and subsequently detected in dust emission is only at z = 3.2 (ref. 5), and recent results have cast doubt on whether dust and molecules can be found in typical galaxies at z ≥ 7. Here we report thermal dust emission from an archetypal early Universe star-forming galaxy, A1689-zD1. We detect its stellar continuum in spectroscopy and determine its redshift to be z = 7.5 ± 0.2 from a spectroscopic detection of the Lyman-α break. A1689-zD1 is representative of the star-forming population during the epoch of reionization, with a total star-formation rate of about 12 solar masses per year. The galaxy is highly evolved: it has a large stellar mass and is heavily enriched in dust, with a dust-to-gas ratio close to that of the Milky Way. Dusty, evolved galaxies are thus present among the fainter star-forming population at z > 7. PMID:25731171

  10. Spontaneous chiral symmetry breaking by hydromagnetic buoyancy

    NASA Astrophysics Data System (ADS)

    Chatterjee, Piyali; Mitra, Dhrubaditya; Brandenburg, Axel; Rheinhardt, Matthias

    2011-08-01

    Evidence for the parity-breaking nature of the magnetic buoyancy instability in a stably stratified gas is reported. In the absence of rotation, no helicity is produced, but the nonhelical state is found to be unstable to small helical perturbations during the development of the instability. The parity-breaking nature of this magnetohydrodynamic instability appears to be the first of its kind and has properties similar to those in chiral symmetry breaking in biochemistry. Applications to the production of mean fields in galaxy clusters are discussed.

  11. Insights on galaxy formation

    NASA Astrophysics Data System (ADS)

    Bullock, James Steven

    1999-12-01

    Recent advances in theoretical modeling coupled with a wealth of new observational data, provide a unique opportunity for gaining insight into process of galaxy formation. I present results which test and develop current theories. The analysis utilizes state of the art theoretical modeling and makes predictions aimed at comparisons with some of the latest and upcoming observational data sets. In part I, I discuss an analysis of the structure and properties of dark matter halos (believed to govern the dynamical evolution of galaxies). The results make use of very high-resolution N-body simulations, and are derived from a new hierarchical halo finder, designed especially for these projects and to complement advancements in simulation technology. I present information on the dark matter halo substructure, density profiles, angular momentum structure, and collision rates. In part II, I discuss some aspects of galaxy formation theory in light of new observational data. The discussion includes an investigation of the nature of high-redshift galaxies, the local velocity function of galaxies, and the use of gamma ray telescopes to probe the extra-galactic background light-the latter analysis is done in the context of semi-analytic modeling of galaxy formation. The most important conclusions of this thesis are as follows. (1)Dark matter halos at high redshift are much less concentrated than previously believed. implying that quiescently star-forming galaxies at high redshift are larger and dimmer than expected. (2)The observed bright. abundant. and highly clustered high- redshift (Lyman-break) galaxies are likely starbursts driven by collisions between relatively small galaxies at z ~ 3. And (3)there is a real possibility of using the growing advances in γ-ray astronomy to probe many poorly constrained processes of galaxy formation, including the stellar initial mass function and the star formation history of the universe.

  12. The evolution of galaxies from primeval irregulars to present-day ellipticals.

    PubMed

    Mori, Masao; Umemura, Masayuki

    2006-03-30

    Galaxy formation is believed to proceed in a 'bottom up' manner, starting with the formation of small clumps of gas and stars that then merge hierarchically into giant systems. The baryonic gas loses thermal energy by radiative cooling and falls towards the centres of the new galaxies, while supernovae blow gas out. Any realistic model therefore requires a proper treatment of these processes, but hitherto this has been far from satisfactory. Here we report a simulation that follows evolution from the earliest stages of galaxy formation through the period of dynamical relaxation, at which point the resulting galaxy is in its final form. The bubble structures of gas revealed in our simulation (for times of less than 3 x 10(8) years) resemble closely high-redshift Lyman-alpha emitters. After 10(9) years, these bodies are dominated by stellar continuum radiation and then resemble the Lyman break galaxies, which are high-redshift star-forming galaxies. At this point, the abundance of elements heavier than helium ('metallicity') appears to be solar. After 1.3 x 10(10) years, these galaxies resemble present-day ellipticals. PMID:16572164

  13. STUDYING LARGE- AND SMALL-SCALE ENVIRONMENTS OF ULTRAVIOLET LUMINOUS GALAXIES

    SciTech Connect

    Basu-Zych, Antara R.; Schiminovich, David; Heinis, Sebastien; Heckman, Tim; Bianchi, Luciana; Overzier, Roderik; Zamojski, Michel; Barlow, Tom A.; Conrow, Tim; Forster, Karl G.; Friedman, Peter G.; Martin, D. Christopher; Morrissey, Patrick; Ilbert, Olivier; Koekemoer, Anton M.; Donas, Jose; Milliard, Bruno; Lee, Young-Wook; Madore, Barry F.; Neff, Susan G.

    2009-07-10

    Studying the environments of 0.4 < z < 1.2 ultraviolet (UV)-selected galaxies, as examples of extreme star-forming galaxies (with star formation rates (SFRs) in the range of 3-30 M{sub sun} yr{sup -1}), we explore the relationship between high rates of star formation, host halo mass, and pair fractions. We study the large- and small-scale environments of local ultraviolet luminous galaxies (UVLGs) by measuring angular correlation functions. We cross-correlate these systems with other galaxy samples: a volume-limited sample (ALL), a blue luminous galaxy sample, and a luminous red galaxy (LRG) sample. We determine the UVLG comoving correlation length to be r{sub 0} = 4.8{sup +11.6}{sub -2.4} h {sup -1} Mpc at (z) = 1.0, which is unable to constrain the halo mass for this sample. However, we find that UVLGs form close (separation <30 kpc) pairs with the ALL sample, but do not frequently form pairs with LRGs. A rare subset of UVLGs, those with the highest FUV surface brightnesses, are believed to be local analogs of high-redshift Lyman break galaxies (LBGs) and are called Lyman break analogs (LBAs). LBGs and LBAs share similar characteristics (i.e., color, size, surface brightness, specific SFRs, metallicities, and dust content). Recent Hubble Space Telescope images of z {approx} 0.2 LBAs show disturbed morphologies, signs of mergers and interactions. UVLGs may be influenced by interactions with other galaxies and we discuss this result in terms of other high star-forming, merging systems.

  14. Constraining inflation with future galaxy redshift surveys

    SciTech Connect

    Huang, Zhiqi; Vernizzi, Filippo; Verde, Licia E-mail: liciaverde@icc.ub.edu

    2012-04-01

    With future galaxy surveys, a huge number of Fourier modes of the distribution of the large scale structures in the Universe will become available. These modes are complementary to those of the CMB and can be used to set constraints on models of the early universe, such as inflation. Using a MCMC analysis, we compare the power of the CMB with that of the combination of CMB and galaxy survey data, to constrain the power spectrum of primordial fluctuations generated during inflation. We base our analysis on the Planck satellite and a spectroscopic redshift survey with configuration parameters close to those of the Euclid mission as examples. We first consider models of slow-roll inflation, and show that the inclusion of large scale structure data improves the constraints by nearly halving the error bars on the scalar spectral index and its running. If we attempt to reconstruct the inflationary single-field potential, a similar conclusion can be reached on the parameters characterizing the potential. We then study models with features in the power spectrum. In particular, we consider ringing features produced by a break in the potential and oscillations such as in axion monodromy. Adding large scale structures improves the constraints on features by more than a factor of two. In axion monodromy we show that there are oscillations with small amplitude and frequency in momentum space that are undetected by CMB alone but can be measured by including galaxy surveys in the analysis.

  15. Searches for High Redshift Galaxies

    NASA Astrophysics Data System (ADS)

    Stevens, R.

    In recent years, the technique of Lyman break imaging has proven very effective at identifying large numbers of galaxies at high redshifts through deep multicolour imaging (Steidel et al 1996b; Steidel et al 1999). The combination of an intrinsic break in the spectra of star-forming galaxies below the rest-frame wavelength of Lyman-alpha and attenuation by intervening HI systems on the line of sight to high redshifts makes for a pronounced drop in the flux of high redshift galaxies between 912 Å and 1216 Å in the rest-frame. At redshifts z> 3, the break is shifted sufficiently far into the optical window accessible to ground-based telescopes for galaxies at such redshift to be distinguished from the foreground galaxy population through photometry alone. Through modelling of the expected colours of a wide range of galaxy types, ages and redshifts, taking into account the effects of reddening (Calzetti, Kinney and Storchi-Bergmann 1994) and intergalactic attenuation (Madau 1995), we assess the likely colours of high redshift galaxies and determine the redshift ranges most effectively probed by the imaging filters. We obtain multicolour imaging of the fields of four high redshift radio galaxies, covering around 40 arcmin2 in each, allowing us to attempt to find ordinary galaxies at similar redshifts to the central radio galaxies through photometric colour selection techniques. Some idea as to the effectiveness comes through additional colour and morphological information obtained from high-resolution Hubble Space Telescope images and from data taken in the near infra-red. While we do not have spectroscopic evidence for the redshifts of our candidates, given the available evidence we conclude that the number densities of Lyman break galaxies in the radio galaxy fields are in broad agreement with the data of Steidel et al (1999). Finally, we assess the prospects for future studies of the high redshift Universe, in particular the potential of the Oxford Deep Wide Field

  16. Gas in void galaxies

    NASA Astrophysics Data System (ADS)

    Kreckel, Kathryn Joyce

    . We find that the void galaxies are ! generally gas rich, low luminosity, blue disk galaxies, but identify three as early type galaxies. The void galaxy optical and H I properties are not unusual for their luminosity and morphology. The small scale clustering in the void is similar to that in higher density regions, and we identify 18 H I rich neighboring galaxies in the voids. Two of these are systems of three galaxies linearly aligned and joined by a H I bridge, suggestive of filamentary formation within the void. We find no population of H I rich low luminosity galaxies within the observed voids that are not close companions of the targeted sample. Finally, to put these observations in a theoretical context, we analyze a (120 h^-1 Mpc)^3 adaptive mesh refinement hydrodynamic simulation that contains a high resolution subvolume centered on a ~30 Mpc diameter void. We construct mock observations with ~1 kpc resolution of the stellar and gas properties of these systems which reproduce the range of colors and luminosities observed in the SDSS for nearby galaxies, however we find no strong trends with density. We also make predictions for a significant population of low luminosity (M_r = -14) dwarf galaxies that is preferentially located in low density regions and specifically in the void center.

  17. Closed reduction of a fractured bone

    MedlinePlus

    Fracture reduction - closed ... Closed reduction is a procedure to set (reduce) a broken bone without surgery. This allows the bone ... soon as possible after the bone breaks. A closed reduction can be done by an orthopedic surgeon ( ...

  18. Supernovae in paired host galaxies

    NASA Astrophysics Data System (ADS)

    Nazaryan, T. A.; Petrosian, A. R.; Hakobyan, A. A.; Adibekyan, V. Zh.; Kunth, D.; Mamon, G. A.; Turatto, M.; Aramyan, L. S.

    2014-12-01

    We investigate the influence of close neighbor galaxies on the properties of supernovae (SNe) and their host galaxies using 56 SNe located in pairs of galaxies with different levels of star formation (SF) and nuclear activity. The mean distance of type II SNe from nuclei of hosts is greater by about a factor of 2 than that of type Ibc SNe. For the first time it is shown that SNe Ibc are located in pairs with significantly smaller difference of radial velocities between components than pairs containing SNe Ia and II. We consider this as a result of higher star formation rate (SFR) of these closer systems of galaxies. SN types are not correlated with the luminosity ratio of host and neighbor galaxies in pairs. The orientation of SNe with respect to the preferred direction toward neighbor galaxy is found to be isotropic and independent of kinematical properties of the galaxy pair.

  19. Isolated galaxies, pairs, and groups of galaxies

    NASA Technical Reports Server (NTRS)

    Kuneva, I.; Kalinkov, M.

    1990-01-01

    The authors searched for isolated galaxies, pairs and groups of galaxies in the CfA survey (Huchra et al. 1983). It was assumed that the distances to galaxies are given by R = V/H sub o, where H sub o = 100 km s(exp -1) Mpc(exp -1) and R greater than 6 Mpc. The searching procedure is close to those, applied to find superclusters of galaxies (Kalinkov and Kuneva 1985, 1986). A sphere with fixed radius r (asterisk) is described around each galaxy. The mean spatial density in the sphere is m. Let G (sup 1) be any galaxy and G (sup 2) be its nearest neighbor at a distance R sub 2. If R sub 2 exceeds the 95 percent quintile in the distribution of the distances of the second neighbors, then G (sup 1) is an isolated galaxy. Let the midpoint of G (sup 1) and G (sup 2) be O sub 2 and r sub 2=R sub 2/2. For the volume V sub 2, defined with the radius r sub 2, the density D sub 2 less than k mu, the galaxy G (sup 2) is a single one and the procedure for searching for pairs and groups, beginning with this object is over and we have to pass to another object. Here the authors present the groups - isolated and nonisolated - with n greater than 3, found in the CfA survey in the Northern galactic hemisphere. The parameters used are k = 10 and r (asterisk) = 5 Mpc. Table 1 contains: (1) the group number, (2) the galaxy, nearest to the multiplet center, (3) multiplicity n, (4) the brightest galaxy if it is not listed in (2); (5) and (6) are R.A. and Dec. (1950), (7) - mean distance D in Mpc. Further there are the mean density rho (8) of the multiplet (galaxies Mpc (exp -3), (9) the density rho (asterisk) for r (asterisk) = 5 Mpc and (10) the density rho sub g for the group with its nearest neighbor. The parenthesized digits for densities in the last three columns are powers of ten.

  20. JSPAM: Interacting galaxies modeller

    NASA Astrophysics Data System (ADS)

    Wallin, John F.; Holincheck, Anthony; Harvey, Allen

    2015-11-01

    JSPAM models galaxy collisions using a restricted n-body approach to speed up computation. Instead of using a softened point-mass potential, the software supports a modified version of the three component potential created by Hernquist (1994, ApJS 86, 389). Although spherically symmetric gravitationally potentials and a Gaussian model for the bulge are used to increase computational efficiency, the potential mimics that of a fully consistent n-body model of a galaxy. Dynamical friction has been implemented in the code to improve the accuracy of close approaches between galaxies. Simulations using this code using thousands of particles over the typical interaction times of a galaxy interaction take a few seconds on modern desktop workstations, making it ideal for rapidly prototyping the dynamics of colliding galaxies. Extensive testing of the code has shown that it produces nearly identical tidal features to those from hierarchical tree codes such as Gadget but using a fraction of the computational resources. This code was used in the Galaxy Zoo: Mergers project and is very well suited for automated fitting of galaxy mergers with automated pattern fitting approaches such as genetic algorithms. Java and Fortran versions of the code are available.

  1. Supernovae in paired galaxies

    NASA Astrophysics Data System (ADS)

    Nazaryan, T. A.; Petrosian, A. R.; Hakobyan, A. A.; Adibekyan, V. Zh.; Kunth, D.; Mamon, G. A.; Turatto, M.; Aramyan, L. S.

    2014-07-01

    We investigate the influence of close neighbor galaxies on the properties of supernovae (SNe) and their host galaxies using 56 SNe located in pairs of galaxies with different levels of star formation (SF) and nuclear activity. The mean distance of type II SNe from nuclei of hosts is greater by about a factor of 2 than that of type Ibc SNe. The distributions and mean distances of SNe are consistent with previous results compiled with the larger sample. For the first time it is shown that SNe Ibc are located in pairs with significantly smaller difference of radial velocities between components than pairs containing SNe Ia and II. We consider this as a result of higher star formation rate (SFR) of these closer systems of galaxies.

  2. An Imaging Survey of Late-Type Galaxies: Local Benchmarks of Galaxy Evolution

    NASA Astrophysics Data System (ADS)

    Taylor, V. A.

    2005-12-01

    Nearby (z ˜ 0) irregular, peculiar, and merging galaxies resemble the majority of galaxy types observed at high redshift. Since optical observations of galaxies at high redshift cover their rest-frame ultraviolet emission, imaging of local late-type galaxies in the ultraviolet and optical will provide a necessary basis for understanding high-redshift galaxies and their implications for galaxy formation and evolution. For this purpose, I present an analysis of a unique, panchromatic sample of 199 mostly late-type, irregular, peculiar, and merging nearby galaxies observed in a combination of 10 different pass-bands from the far ultraviolet through the infrared. I first present results of a study of the color gradients of these galaxies. I find that although elliptical through mid-type spiral galaxies are redder in their centers than their outskirts, most late-type spirals, irregular, and merging galaxies are bluer in their centers, becoming increasingly redder at larger radii. This indicates that late-type galaxies have a significant halo or thick disk of older stars, while young UV-bright stars dominate their inner regions. These results are consistent with models of hierarchical galaxy formation. I also present measurements of the concentration, asymmetry, and clumpiness ("CAS") parameters of these galaxies. These fundamental galaxy parameters can be used for galaxy classification, and studying and identifying merging and perturbed galaxies. The dependence of these parameters on wavelength yields a quantitative measure of the "morphological k-correction," which describes how the appearance of a galaxy changes with rest-frame wavelength. I find that the CAS parameters depend on galaxy type, and vary significantly with rest-frame wavelength, especially short-ward of the Balmer break. Galaxies generally become less concentrated and more asymmetric and clumpy at shorter wavelengths. Funded by NASA grants GO-8645.01-A, GO-9124.01-A and GO-9824.01-A, GALEXGI04

  3. Galaxy collisions - A preliminary study

    NASA Technical Reports Server (NTRS)

    Miller, R. H.; Smith, B. F.

    1980-01-01

    Collisions of spherical galaxies were studied in a series of numerical experiments to see what happens when galaxies collide. Each experiment starts with two model galaxies, each consisting of 50,000 stars, moving toward each other along a specified orbit. The series of experiments provides a systematic sampling of the parameter space spanned by the initial orbital energy and the initial angular momentum. Deeply penetrating collisions are emphasized. The collisions reported here scale to relative velocities as great as 500 km/s, well into the range for collisions within clusters of galaxies. It is found that: (1) the galaxies contract momentarily to about half their original sizes shortly after close passage; and (2) the initial galaxies blend into a single dynamical system while they are near each other.

  4. EXTREME GAS FRACTIONS IN CLUMPY, TURBULENT DISK GALAXIES AT z ∼ 0.1

    SciTech Connect

    Fisher, David B.; Glazebrook, Karl; Bassett, Robert; Bolatto, Alberto; Obreschkow, Danail; Cooper, Erin Mentuch; Wisnioski, Emily; Abraham, Roberto G.; Damjanov, Ivana; Green, Andy; McGregor, Peter

    2014-08-01

    In this Letter, we report the discovery of CO fluxes, suggesting very high gas fractions in three disk galaxies seen in the nearby universe (z ∼ 0.1). These galaxies were investigated as part of the DYnamics of Newly Assembled Massive Objects (DYNAMO) survey. High-resolution Hubble Space Telescope imaging of these objects reveals the presence of large star forming clumps in the bodies of the galaxies, while spatially resolved spectroscopy of redshifted Hα reveals the presence of high dispersion rotating disks. The internal dynamical state of these galaxies resembles that of disk systems seen at much higher redshifts (1 < z < 3). Using CO(1-0) observations made with the Plateau de Bure Interferometer, we find gas fractions of 20%-30% and depletion times of t {sub dep} ∼ 0.5 Gyr (assuming a Milky-Way-like α{sub CO}). These properties are unlike those expected for low-redshift galaxies of comparable specific star formation rate, but they are normal for their high-z counterparts. DYNAMO galaxies break the degeneracy between gas fraction and redshift, and we show that the depletion time per specific star formation rate for galaxies is closely tied to gas fraction, independent of redshift. We also show that the gas dynamics of two of our local targets corresponds to those expected from unstable disks, again resembling the dynamics of high-z disks. These results provide evidence that DYNAMO galaxies are local analogs to the clumpy, turbulent disks, which are often found at high redshift.

  5. Triple Scoop from Galaxy Hunter

    NASA Technical Reports Server (NTRS)

    2006-01-01

    [figure removed for brevity, see original site] [figure removed for brevity, see original site] [figure removed for brevity, see original site] Figure 1Figure 2Figure 3

    Silver Dollar Galaxy: NGC 253 (figure 1) Located 10 million light-years away in the southern constellation Sculptor, the Silver Dollar galaxy, or NGC 253, is one of the brightest spiral galaxies in the night sky. In this edge-on view from NASA's Galaxy Evolution Explorer, the wisps of blue represent relatively dustless areas of the galaxy that are actively forming stars. Areas of the galaxy with a soft golden glow indicate regions where the far-ultraviolet is heavily obscured by dust particles.

    Gravitational Dance: NGC 1512 and NGC 1510 (figure 2) In this image, the wide ultraviolet eyes of NASA's Galaxy Evolution Explorer show spiral galaxy NGC 1512 sitting slightly northwest of elliptical galaxy NGC 1510. The two galaxies are currently separated by a mere 68,000 light-years, leading many astronomers to suspect that a close encounter is currently in progress.

    The overlapping of two tightly wound spiral arm segments makes up the light blue inner ring of NGC 1512. Meanwhile, the galaxy's outer spiral arm is being distorted by strong gravitational interactions with NGC 1510.

    Galaxy Trio: NGC 5566, NGC 5560, and NGC 5569 (figure 3) NASA's Galaxy Evolution Explorer shows a triplet of galaxies in the Virgo cluster: NGC 5560 (top galaxy), NGC 5566 (middle galaxy), and NGC 5569 (bottom galaxy).

    The inner ring in NGC 5566 is formed by two nearly overlapping bright arms, which themselves spring from the ends of a central bar. The bar is not visible in ultraviolet because it consists of older stars or low mass stars that do not emit energy at ultraviolet wavelengths. The outer disk of NGC 5566 appears warped, and the disk of NGC 5560 is clearly disturbed. Unlike its galactic neighbors, the disk of NGC 5569 does not appear to have been distorted by any passing

  6. Growing Galaxies Gently

    NASA Astrophysics Data System (ADS)

    2010-10-01

    of the flow of pristine gas from the surrounding space and the associated formation of new stars. They were very careful to make sure that their specimen galaxies had not been disturbed by interactions with other galaxies. The selected galaxies were very regular, smoothly rotating discs, similar to the Milky Way, and they were seen about two billion years after the Big Bang (at a redshift of around three). In galaxies in the modern Universe the heavy elements [1] are more abundant close to the centre. But when Cresci's team mapped their selected distant galaxies with the SINFONI spectrograph on the VLT [2] they were excited to see that in all three cases there was a patch of the galaxy, close to the centre, with fewer heavy elements, but hosting vigorously forming stars, suggesting that the material to fuel the star formation was coming from the surrounding pristine gas that is low in heavy elements. This was the smoking gun that provided the best evidence yet of young galaxies accreting primitive gas and using it to form new generations of stars. As Cresci concludes: "This study has only been possible because of the outstanding performance of the SINFONI instrument on the VLT. It has opened a new window for studying the chemical properties of very distant galaxies. SINFONI provides information not only in two spatial dimensions, but also in a third, spectral dimension, which allows us to see the internal motions inside galaxies and study the chemical composition of the interstellar gas." Notes [1] The gas filling the early Universe was almost all hydrogen and helium. The first generations of stars processed this primitive material to create heavier elements such as oxygen, nitrogen and carbon by nuclear fusion. When this material was subsequently spewed back into space by intense particle winds from massive young stars and supernova explosions the amounts of heavy elements in the galaxy gradually increased. Astronomers refer to elements other than hydrogen and

  7. First Observational Support for Overlapping Reionized Bubbles Generated by a Galaxy Overdensity

    NASA Astrophysics Data System (ADS)

    Castellano, M.; Dayal, P.; Pentericci, L.; Fontana, A.; Hutter, A.; Brammer, G.; Merlin, E.; Grazian, A.; Pilo, S.; Amorin, R.; Cristiani, S.; Dickinson, M.; Ferrara, A.; Gallerani, S.; Giallongo, E.; Giavalisco, M.; Guaita, L.; Koekemoer, A.; Maiolino, R.; Paris, D.; Santini, P.; Vallini, L.; Vanzella, E.; Wagg, J.

    2016-02-01

    We present an analysis of deep Hubble Space Telescope (HST) multi-band imaging of the BDF field specifically designed to identify faint companions around two of the few Lyα emitting galaxies spectroscopically confirmed at z ˜ 7. Although separated by only 4.4 proper Mpc these galaxies cannot generate H ii regions large enough to explain the visibility of their Lyα lines, thus requiring a population of fainter ionizing sources in their vicinity. We use deep HST and VLT-Hawk-I data to select z ˜ 7 Lyman break galaxies around the emitters. We select six new robust z ˜ 7 LBGs at Y ˜ 26.5-27.5 whose average spectral energy distribution is consistent with the objects being at the redshift of the close-by Lyα emitters. The resulting number density of z ˜ 7 LBGs in the BDF field is a factor of approximately three to four higher than expected in random pointings of the same size. We compare these findings with cosmological hydrodynamic plus radiative transfer simulations of a universe with a half neutral IGM: we find that indeed Lyα emitter pairs are only found in completely ionized regions characterized by significant LBG overdensities. Our findings match the theoretical prediction that the first ionization fronts are generated within significant galaxy overdensities and support a scenario where faint, “normal” star-forming galaxies are responsible for reionization.

  8. Statistics of associations among IR galaxies

    NASA Technical Reports Server (NTRS)

    Gallimore, Jack F.; Keel, William C.

    1990-01-01

    In the course of expanding the search of Kleinmann et. al. (1988) for distant, infrared-luminous objects, the authors noticed (as is often remarked) that a large number of infrared-selected galaxies have close neighbors or show merger characteristics (e.g., tidal tails, distorted disks). Because the sample size is large (567 infrared galaxies and 2182 field galaxies), this sample is ideal for statistically examining the importance of interactions among infrared galaxies. In particular, the authors compare the nearest-neighbor distribution and the two-point correlation function of their sample with that of a control sample of field galaxies.

  9. Galaxy masses

    NASA Astrophysics Data System (ADS)

    Courteau, Stéphane; Cappellari, Michele; de Jong, Roelof S.; Dutton, Aaron A.; Emsellem, Eric; Hoekstra, Henk; Koopmans, L. V. E.; Mamon, Gary A.; Maraston, Claudia; Treu, Tommaso; Widrow, Lawrence M.

    2014-01-01

    Galaxy masses play a fundamental role in our understanding of structure formation models. This review addresses the variety and reliability of mass estimators that pertain to stars, gas, and dark matter. The different sections on masses from stellar populations, dynamical masses of gas-rich and gas-poor galaxies, with some attention paid to our Milky Way, and masses from weak and strong lensing methods all provide review material on galaxy masses in a self-consistent manner.

  10. Galaxy and Mass Assembly (GAMA): merging galaxies and their properties

    NASA Astrophysics Data System (ADS)

    De Propris, Roberto; Baldry, Ivan K.; Bland-Hawthorn, Joss; Brough, Sarah; Driver, Simon P.; Hopkins, Andrew M.; Kelvin, Lee; Loveday, Jon; Phillipps, Steve; Robotham, Aaron S. G.

    2014-11-01

    We derive the close pair fractions and volume merger rates for galaxies in the Galaxy and Mass Assembly (GAMA) survey with -23 < Mr < -17 (ΩM = 0.27, ΩΛ = 0.73, H0 = 100 km s-1 Mpc-1) at 0.01 < z < 0.22 (look-back time of <2 Gyr). The merger fraction is approximately 1.5 per cent Gyr-1 at all luminosities (assuming 50 per cent of pairs merge) and the volume merger rate is ≈3.5 × 10-4 Mpc-3 Gyr-1. We examine how the merger rate varies by luminosity and morphology. Dry mergers (between red/spheroidal galaxies) are found to be uncommon and to decrease with decreasing luminosity. Fainter mergers are wet, between blue/discy galaxies. Damp mergers (one of each type) follow the average of dry and wet mergers. In the brighter luminosity bin (-23 < Mr < -20), the merger rate evolution is flat, irrespective of colour or morphology, out to z ˜ 0.2. The makeup of the merging population does not appear to change over this redshift range. Galaxy growth by major mergers appears comparatively unimportant and dry mergers are unlikely to be significant in the buildup of the red sequence over the past 2 Gyr. We compare the colour, morphology, environmental density and degree of activity (BPT class, Baldwin, Phillips & Terlevich) of galaxies in pairs to those of more isolated objects in the same volume. Galaxies in close pairs tend to be both redder and slightly more spheroid dominated than the comparison sample. We suggest that this may be due to `harassment' in multiple previous passes prior to the current close interaction. Galaxy pairs do not appear to prefer significantly denser environments. There is no evidence of an enhancement in the AGN fraction in pairs, compared to other galaxies in the same volume.

  11. Starburst galaxies

    NASA Technical Reports Server (NTRS)

    Weedman, Daniel W.

    1987-01-01

    The infrared properties of star-forming galaxies, primarily as determined by the Infrared Astronomy Satellite (IRAS), are compared to X-ray, optical, and radio properties. Luminosity functions are reviewed and combined with those derived from optically discovered samples using 487 Markarian galaxies with redshifts and published IRAS 60 micron fluxes, and 1074 such galaxies in the Center for Astrophysics redshift survey. It is found that the majority of infrared galaxies which could be detected are low luminosity sources already known from the optical samples, but non-infrared surveys have found only a very small fraction of the highest luminosity sources. Distributions of infrared to optical fluxes and available spectra indicate that the majority of IRAS-selected galaxies are starburst galaxies. Having a census of starburst galaxies and associated dust allow severl important global calculations. The source counts are predicted as a function of flux limits for both infrared and radio fluxes. These galaxies are found to be important radio sources at faint flux limits. Taking the integrated flux to z = 3 indicates that such galaxies are a significant component of the diffuse X-ray background, and could be the the dominant component depending on the nature of the X-ray spectra and source evolution.

  12. Andromeda Galaxy

    NASA Technical Reports Server (NTRS)

    2003-01-01

    [figure removed for brevity, see original site]

    This image is a Galaxy Evolution Explorer observation of the large galaxy in Andromeda, Messier 31. The Andromeda galaxy is the most massive in the local group of galaxies that includes our Milky Way. Andromeda is the nearest large galaxy to our own. The image is a mosaic of 10 separate Galaxy Evolution Explorer images taken in September, 2003. The color image (with near ultraviolet shown by red and far ultraviolet shown by blue) shows blue regions of young, hot, high mass stars tracing out the spiral arms where star formation is occurring, and the central orange-white 'bulge' of old, cooler stars formed long ago. The star forming arms of Messier 31 are unusual in being quite circular rather than the usual spiral shape. Several companion galaxies can also be seen. These include Messier 32, a dwarf elliptical galaxy directly below the central bulge and just outside the spiral arms, and Messier 110 (M110), which is above and to the right of the center. M110 has an unusual far ultraviolet bright core in an otherwise 'red,' old star halo. Many other regions of star formation can be seen far outside the main body of the galaxy.

  13. Galaxy Evolution Across The Redshift Desert

    NASA Astrophysics Data System (ADS)

    Kotulla, Ralf

    2010-01-01

    GALEV evolutionary synthesis models are an ideal tool to study the formation and evolution of galaxies. I present a large model grid that contains undisturbed E and Sa-Sd type galaxies as well as a wide range of models undergoing starbursts of various strengths and at different times and also includes the subsequent post-starburst phases for these galaxies. This model grid not only allows to describe and refine currently used color selection criteria for Lyman Break Galaxies, BzK galaxies, Extremely Red Objects (ERO) and both Distant and Luminous Red Galaxies (DRG, LRG). It also gives accurate stellar masses, gas fractions, star formation rates, metallicities and burst strengths for an unprecedentedly large sample of galaxies with multi-band photometry. We find, amongst other things, that LBGs are most likely progenitors of local early type spiral galaxies and low-mass ellipticals. We are for the first time able to reproduce E+A features in EROs by post-starbursts as an alternative to dusty starforming galaxies and predict how to discriminate between these scenarios. Our results from photometric analyses perfectly agree with all available spectroscopic information and open up a much wider perspective, including the bulk of the less luminous and more typical galaxy population, in the redshift desert and beyond. All model data are available online at http://www.galev.org.

  14. Radio Galaxies in Abell Rich Clusters

    NASA Astrophysics Data System (ADS)

    Ledlow, M. J.

    1994-05-01

    We have defined a complete sample of radio galaxies chosen from Abell's northern catalog consisting of all clusters with measured redshifts < 0.09. This sample consists of nearly 300 clusters. A multiwavelength survey including optical CCD R-Band imaging, optical spectroscopy, and VLA 20 cm radio maps has been compiled. I have used this database to study the optical/radio properties of radio galaxies in the cluster environment. In particular, optical properties have been compared to a radio-quiet selected sample to look for optical signatures which may distinguish radio galaxies from normal radio-quiet ellipticals. The correlations between radio morphology and galaxy type, the optical dependence of the FR I/II break, and the univariate and bivariate luminosity functions have been examined for this sample. This study is aimed at understanding radio galaxies as a population and examining their status in the AGN heirarchy. The results of this work will be applied to models of radio source evolution. The results from the optical data analysis suggest that radio galaxies, as a class, cannot be distinguished from non-radio selected elliptical galaxies. The magnitude/size relationship, the surface-brightness profiles, the fundamental plane, and the intrinsic shape of the radio galaxies are consistent between our radio galaxy and control sample. The radio galaxies also trace the elliptical galaxy optical luminosity function in clusters very well; with many more L(*) galaxies than brightest cluster members. Combined with the results of the spectroscopy, the data are consistent with the idea that all elliptical galaxies may at some point in their lifetimes become radio sources. In conclusion, I present a new observational picture for radio galaxies and discuss the important properties which may determine the evolution of individual sources.

  15. Ring Around a Galaxy

    NASA Technical Reports Server (NTRS)

    1999-01-01

    Space Telescope Science Institute astronomers are giving the public chances to decide where to aim NASA's Hubble Space Telescope. Guided by 8,000 Internet voters, Hubble has already been used to take a close-up, multi-color picture of the most popular object from a list of candidates, the extraordinary 'polar-ring' galaxy NGC 4650A. Located about 130 million light-years away, NGC 4650A is one of only 100 known polar-ring galaxies. Their unusual disk-ring structure is not yet understood fully. One possibility is that polar rings are the remnants of colossal collisions between two galaxies sometime in the distant past, probably at least 1 billion years ago. What is left of one galaxy has become the rotating inner disk of old red stars in the center. Meanwhile, another smaller galaxy which ventured too close was probably severely damaged or destroyed. The bright bluish clumps, which are especially prominent in the outer parts of the ring, are regions containing luminous young stars, examples of stellar rebirth from the remnants of an ancient galactic disaster. The polar ring appears to be highly distorted. No regular spiral pattern stands out in the main part of the ring, and the presence of young stars below the main ring on one side and above on the other shows that the ring is warped and does not lie in one plane. Determining the typical ages of the stars in the polar ring is an initial goal of our Polar Ring Science Team that can provide a clue to the evolution of this unusual galaxy. The HST exposures were acquired by the Hubble Heritage Team, consisting of Keith Noll, Howard Bond, Carol Christian, Jayanne English, Lisa Frattare, Forrest Hamilton, Anne Kinney and Zolt Levay, and guest collaborators Jay Gallagher (University of Wisconsin-Madison), Lynn Matthews (National Radio Astronomy Observatory-Charlottesville), and Linda Sparke (University of Wisconsin-Madison).

  16. Dark-matter halos and evolution of high-z early-type galaxies

    NASA Astrophysics Data System (ADS)

    Koopmans, Leon

    2004-07-01

    Gravitational lensing and stellar dynamics provide two complementary methods to determine the mass distribution and evolution of luminous and dark-matter in early-type {E/S0} galaxies. The combined study of stellar dynamics and gravitational lensing allows one to break degeneracies inherent to each method separately, providing a clean probe of the internal structure of massive galaxies. Since most lens galaxies are at redshifts z=0.1-1.0, they also provide the required look-back time to study their structural and stellar-population evolution. We recently analyzed 5 E/S0 lens galaxies between z=0.5 and 1.0, combining exquisite Hubble Space Telescope imaging data with kinematic data from ground-based Keck spectroscopy, placing the first precise constraints on the dark-matter mass fraction and its inner slope beyond the local Universe. To expand the sample to 30 systems - required to study potential trends and evolution in the E/S0 mass profiles - we propose to target the 49 E/S0 lens-galaxy candidates discovered by Bolton et al. {2004} from the Sloan Digital Sky Survey {SDSS}. With the average lens rate being 40% and some systems having a lensing probability close to unity, we expect to discover 20 strong gravitational lenses from the sample. This will triple the current sample of 9 E/S0 systems, with data in hand. With the sample of 30 systems, we will be able to determine the average slope of the dark-matter and total mass profile of E/S0 galaxies to 10% and 4% accuracy, respectively. If present, we can simultaneously detect 10% evolution in the total mass slope with 95% confidence. This will provide unprecedented constraints on E/S0 galaxies beyond the local Universe and allow a stringent test of their formation scenarios and the standard cosmological model.

  17. SHELS: OPTICAL SPECTRAL PROPERTIES OF WISE 22 {mu}m SELECTED GALAXIES

    SciTech Connect

    Hwang, Ho Seong; Geller, Margaret J.; Kurtz, Michael J.; Fabricant, Daniel G.; Dell'Antonio, Ian P. E-mail: mgeller@cfa.harvard.edu E-mail: dfabricant@cfa.harvard.edu

    2012-10-10

    We use a dense, complete redshift survey, the Smithsonian Hectospec Lensing Survey (SHELS), covering a 4 deg{sup 2} region of a deep imaging survey, the Deep Lens Survey (DLS), to study the optical spectral properties of Wide-field Infrared Survey Explorer (WISE) 22 {mu}m selected galaxies. Among 507 WISE 22 {mu}m selected sources with (S/N){sub 22{mu}m} {>=} 3 ( Almost-Equal-To S{sub 22{mu}m} {approx}> 2.5 mJy), we identify the optical counterparts of 481 sources ({approx}98%) at R < 25.2 in the very deep, DLS R-band source catalog. Among them, 337 galaxies at R < 21 have SHELS spectroscopic data. Most of these objects are at z < 0.8. The infrared (IR) luminosities are in the range 4.5 Multiplication-Sign 10{sup 8}(L{sub Sun }) {approx}< L{sub IR} {approx}< 5.4 Multiplication-Sign 10{sup 12}(L{sub Sun }). Most 22 {mu}m selected galaxies are dusty star-forming galaxies with a small (<1.5) 4000 A break. The stacked spectra of the 22 {mu}m selected galaxies binned in IR luminosity show that the strength of the [O III] line relative to H{beta} grows with increasing IR luminosity. The optical spectra of the 22 {mu}m selected galaxies also show that there are some ({approx}2.8%) unusual galaxies with very strong [Ne III] {lambda}3869, 3968 emission lines that require hard ionizing radiation such as active galactic nuclei (AGNs) or extremely young massive stars. The specific star formation rates (sSFRs) derived from the 3.6 and 22 {mu}m flux densities are enhanced if the 22 {mu}m selected galaxies have close late-type neighbors. The sSFR distribution of the 22 {mu}m selected galaxies containing AGNs is similar to the distribution for star-forming galaxies without AGNs. We identify 48 dust-obscured galaxy candidates with large ({approx}> 1000) mid-IR to optical flux density ratio. The combination of deep photometric and spectroscopic data with WISE data suggests that WISE can probe the universe to z {approx} 2.

  18. Galaxy And Mass Assembly (GAMA): the life and times of L★ galaxies

    NASA Astrophysics Data System (ADS)

    Robotham, A. S. G.; Liske, J.; Driver, S. P.; Sansom, A. E.; Baldry, I. K.; Bauer, A. E.; Bland-Hawthorn, J.; Brough, S.; Brown, M. J. I.; Colless, M.; Christodoulou, L.; Drinkwater, M. J.; Grootes, M. W.; Hopkins, A. M.; Kelvin, L. S.; Norberg, P.; Loveday, J.; Phillipps, S.; Sharp, R.; Taylor, E. N.; Tuffs, R. J.

    2013-05-01

    In this work, we investigate in detail the effects the local environment (groups and pairs) has on galaxies with stellar mass similar to the Milky Way (L* galaxies). A volume limited sample of 6150 galaxies are visually classified to determine the emission features, morphological type and presence of a disc. This large sample allows for the significant characteristics of galaxies to be isolated (e.g. stellar mass and group halo mass), and their codependencies determined. We observe that galaxy-galaxy interactions play the most important role in shaping the evolution within a group halo; the main role of halo mass is in gathering the galaxies together to encourage such interactions. Dominant pair galaxies find their overall star formation enhanced when the pair's mass ratio is close to 1; otherwise, we observe the same galaxies as we would in an unpaired system. The minor galaxy in a pair is greatly affected by its companion galaxy, and while the star-forming fraction is always suppressed relative to equivalent stellar mass unpaired galaxies, it becomes lower still when the mass ratio of a pair system increases. We find that, in general, the close galaxy-galaxy interaction rate drops as a function of halo mass for a given amount of stellar mass. We find evidence of a local peak of interactions for Milky Way stellar mass galaxies in Milky Way halo mass groups. Low-mass haloes, and in particular Local Group mass haloes, are an important environment for understanding the typical evolutionary path of a unit of stellar mass. We find compelling evidence for galaxy conformity in both groups and pairs, where morphological type conformity is dominant in groups, and emission class conformity is dominant in pairs. This suggests that group scale conformity is the result of many galaxy encounters over an extended period of time, while pair conformity is a fairly instantaneous response to a transitory interaction.

  19. Growing Galaxies Gently

    NASA Astrophysics Data System (ADS)

    2010-10-01

    of the flow of pristine gas from the surrounding space and the associated formation of new stars. They were very careful to make sure that their specimen galaxies had not been disturbed by interactions with other galaxies. The selected galaxies were very regular, smoothly rotating discs, similar to the Milky Way, and they were seen about two billion years after the Big Bang (at a redshift of around three). In galaxies in the modern Universe the heavy elements [1] are more abundant close to the centre. But when Cresci's team mapped their selected distant galaxies with the SINFONI spectrograph on the VLT [2] they were excited to see that in all three cases there was a patch of the galaxy, close to the centre, with fewer heavy elements, but hosting vigorously forming stars, suggesting that the material to fuel the star formation was coming from the surrounding pristine gas that is low in heavy elements. This was the smoking gun that provided the best evidence yet of young galaxies accreting primitive gas and using it to form new generations of stars. As Cresci concludes: "This study has only been possible because of the outstanding performance of the SINFONI instrument on the VLT. It has opened a new window for studying the chemical properties of very distant galaxies. SINFONI provides information not only in two spatial dimensions, but also in a third, spectral dimension, which allows us to see the internal motions inside galaxies and study the chemical composition of the interstellar gas." Notes [1] The gas filling the early Universe was almost all hydrogen and helium. The first generations of stars processed this primitive material to create heavier elements such as oxygen, nitrogen and carbon by nuclear fusion. When this material was subsequently spewed back into space by intense particle winds from massive young stars and supernova explosions the amounts of heavy elements in the galaxy gradually increased. Astronomers refer to elements other than hydrogen and

  20. Breaking waves, turbulence and bubbles

    NASA Astrophysics Data System (ADS)

    Gemmrich, Johannes; Vagle, Svein; Thomson, Jim

    2014-05-01

    The air-sea fluxes of heat, momentum, and gases are to a large extent affected by wave-induced turbulence in the near-surface ocean layer, and are generally increased over the fluxes in a law-of-the-wall type boundary layer. However, air-bubbles generated during the wave breaking process may affect the density stratification and in turn reduce turbulence intensity in the near-surface layer. The turbulence field beneath surface waves is rather complex and provides great challenges for detailed observations. We obtained high resolution near-surface velocity profiles, bubble cloud measurements and video recordings of the breaking activity in a coastal strait. Conditions ranged from moderate to strong wind forcing with wind speed ranging from 5 m/s to 20 m/s. Estimates of the dissipation rates of turbulence kinetic energy are calculated from the in-situ velocity measurements. We find dissipation rates, fluctuating by more than two orders of magnitude, are closely linked to the air-fraction associated with micro-bubbles. Combining these turbulence estimates and the bubble cloud characteristics we infer differences in the strength of wave breaking and its effect on wave-induced mixing and air-sea exchange processes.

  1. A MINUET OF GALAXIES

    NASA Technical Reports Server (NTRS)

    2002-01-01

    This troupe of four galaxies, known as Hickson Compact Group 87 (HCG 87), is performing an intricate dance orchestrated by the mutual gravitational forces acting between them. The dance is a slow, graceful minuet, occurring over a time span of hundreds of millions of years. The Wide Field and Planetary Camera 2 on NASA's Hubble Space Telescope (HST) provides a striking improvement in resolution over previous ground-based imaging. In particular, this image reveals complex details in the dust lanes of the group's largest galaxy member (HCG 87a), which is actually disk-shaped, but tilted so that we see it nearly edge-on. Both 87a and its elliptically shaped nearest neighbor (87b) have active galactic nuclei which are believed to harbor black holes that are consuming gas. A third group member, the nearby spiral galaxy 87c, may be undergoing a burst of active star formation. Gas flows within galaxies can be intensified by the gravitational tidal forces between interacting galaxies. So interactions can provide fresh fuel for both active nuclei and starburst phenomena. These three galaxies are so close to each other that gravitational forces disrupt their structure and alter their evolution. From the analysis of its spectra, the small spiral near the center of the group could either be a fourth member or perhaps an unrelated background object. The HST image was made by combining images taken in four different color filters in order to create a three-color picture. Regions of active star formation are blue (hot stars) and also pinkish if hot hydrogen gas is present. The complex dark bands across the large edge-on disk galaxy are due to interstellar dust silhouetted against the galaxy's background starlight. A faint tidal bridge of stars can be seen between the edge-on and elliptical galaxies. HCG 87 was selected for Hubble imaging by members of the public who visited the Hubble Heritage website (http://heritage.stsci.edu) during the month of May and registered their votes

  2. Les galaxies

    NASA Astrophysics Data System (ADS)

    Combes, Francoise

    2016-08-01

    Considerable progress has been made on galaxy formation and evolution in recent years, and new issues. The old Hubble classification according to the tuning fork of spirals, lenticulars and ellipticals, is still useful but has given place to the red sequence, the blue cloud and the green valley, showing a real bimodality of types between star forming galaxies (blue) and quenched ones (red). Large surveys have shown that stellar mass and environment density are the two main factors of the evolution from blue to red sequences. Evolution is followed directly with redshift through a look-back time of more than 12 billion years. The most distant galaxy at z=11. has already a stellar mass of a billion suns. In an apparent anti-hierarchical scenario, the most massive galaxies form stars early on, while essentially dwarf galaxies are actively star-formers now. This downsizing feature also applies to the growth of super-massive black holes at the heart of each bulgy galaxy. The feedback from active nuclei is essential to explain the distribution of mass in galaxies, and in particular to explain why the fraction of baryonic matter is so low, lower by more than a factor 5 than the baryonic fraction of the Universe. New instruments just entering in operation, like MUSE and ALMA, provide a new and rich data flow, which is developed in this series of articles.

  3. Disrupted Stars in Unusual Galaxies

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2016-03-01

    Tidal disruption events (TDEs) occur when a star passes a little too close to a supermassive black hole at the center of a galaxy. Tidal forces from the black hole cause the passing star to be torn apart, resulting in a brief flare of radiation as the stars material accretes onto the black hole. A recent study asks the following question: do TDEs occur most frequently in an unusual type of galaxy?A Trend in DisruptionsSo far, we have data from eight candidate TDEs that peaked in optical and ultraviolet wavelengths. The spectra from these observations have shown an intriguing trend: many of these TDEs host galaxies exhibit weak line emission (indicating little or no current star-formation activity), and yet they show strong Balmer absorption lines (indicating star formation activity occurred within the last Gyr). These quiescent, Balmer-strong galaxies likely underwent a period of intense star formation that recently ended.To determine if TDEs are overrepresented in such galaxies, a team of scientists led by Decker French (Steward Observatory, University of Arizona) has quantified the fraction of galaxies in the Sloan Digital Sky Survey (SDSS) that exhibit similar properties to those of TDE hosts.Quantifying OverrepresentationSpectral characteristics of SDSS galaxies (gray) and TDE candidate host galaxies (colored points): line emission vs. Balmer absorption. The lower right-hand box identifies thequiescent, Balmer-strong galaxies which contain most TDE events, yet are uncommon among the galaxy sample as a whole. Click for a better look! [French et al. 2016]French and collaborators compare the optical spectra of the TDE host galaxies to those of nearly 600,000 SDSS galaxies, using two different cutoffs for the Balmer absorption the indicator of past star formation. Their strictest cut, filtering for very high Balmer absorption, selected only 0.2% of the SDSS galaxies, yet 38% of the TDEs are hosted in such galaxies. Using a more relaxed cutoff selects 2.3% of

  4. Midsummer's Dream Galaxies

    NASA Astrophysics Data System (ADS)

    2005-08-01

    -years away in the constellation Coma Berenices (Berenice's Hair). It displays a bright yellowish central bulge that juts out above most impressive dust lanes. Because it is relatively close (it is only 12 times farther away than Messier 31, the Andromeda galaxy, which is the major galaxy closest to us) and relatively large (roughly one third larger than the Milky Way), it does not fit entirely into the field of view of the FORS instrument (about 7 x 7 arcmin2). Many background galaxies are also visible in this FORS image, giving full meaning to their nickname of "island universes". Messier 83 If our Milky Way were to resemble this one, we certainly would be proud of our home! The beautiful spiral galaxy Messier 83 [4] is located in the southern constellation Hydra (the Water Snake) and is also known as NGC 5236 and as the Southern Pinwheel galaxy. Its distance is about 15 million light-years. Being about twice as small as the Milky Way, its size on the sky is 11x10 arcmin2. The image show clumpy, well-defined spiral arms that are rich in young stars, while the disc reveals a complex system of intricate dust lanes. This galaxy is known to be a site of vigorous star formation.

  5. DEEP NEAR-INFRARED SPECTROSCOPY OF PASSIVELY EVOLVING GALAXIES AT z {approx}> 1.4

    SciTech Connect

    Onodera, M.; Carollo, M.; Lilly, S.; Renzini, A.; Mancini, C.; Cappellari, M.; Strazzullo, V.; Daddi, E.; Gobat, R.; McCracken, H. J.; Ilbert, O.; Capak, P.; Cimatti, A.; Giavalisco, M.; Koekemoer, A. M.; Kong, X.; Motohara, K.; Ohta, K.; and others

    2012-08-10

    We present the results of new near-IR spectroscopic observations of passive galaxies at z {approx}> 1.4 in a concentration of BzK-selected galaxies in the COSMOS field. The observations have been conducted with Subaru/MOIRCS, and have resulted in absorption lines and/or continuum detection for 18 out of 34 objects. This allows us to measure spectroscopic redshifts for a sample that is almost complete to K{sub AB} = 21. COSMOS photometric redshifts are found in fair agreement overall with the spectroscopic redshifts, with a standard deviation of {approx}0.05; however, {approx}30% of objects have photometric redshifts systematically underestimated by up to {approx}25%. We show that these systematic offsets in photometric redshifts can be removed by using these objects as a training set. All galaxies fall in four distinct redshift spikes at z = 1.43, 1.53, 1.67, and 1.82, with this latter one including seven galaxies. SED fits to broadband fluxes indicate stellar masses in the range of {approx}4-40 Multiplication-Sign 10{sup 10} M{sub Sun} and that star formation was quenched {approx}1 Gyr before the cosmic epoch at which they are observed. The spectra of several individual galaxies have allowed us to measure their H{delta}{sub F} indices and the strengths of the 4000 A break, which confirms their identification as passive galaxies, as does a composite spectrum resulting from the co-addition of 17 individual spectra. The effective radii of the galaxies have been measured on the COSMOS HST/ACS i{sub F814W}-band image, confirming the coexistence at these redshifts of passive galaxies, which are substantially more compact than their local counterparts with others that follow the local effective radius-stellar mass relation. For the galaxy with the best signal-to-noise spectrum we were able to measure a velocity dispersion of 270 {+-} 105 km s{sup -1} (error bar including systematic errors), indicating that this galaxy lies closely on the virial relation given its stellar

  6. GOODS-Herschel: the impact of galaxy-galaxy interactions on the far-infrared properties of galaxies

    NASA Astrophysics Data System (ADS)

    Hwang, H. S.; Elbaz, D.; Dickinson, M.; Charmandaris, V.; Daddi, E.; Le Borgne, D.; Buat, V.; Magdis, G. E.; Altieri, B.; Aussel, H.; Coia, D.; Dannerbauer, H.; Dasyra, K.; Kartaltepe, J.; Leiton, R.; Magnelli, B.; Popesso, P.; Valtchanov, I.

    2011-11-01

    Aims: We study the impact of galaxy-galaxy interactions on the far-infrared properties of galaxies and its evolution at 0 < z < 1.2. Methods: Using the high-z galaxies in the fields of Great Observatories Origins Deep Survey (GOODS) observed by the Herschel Space Observatory in the framework of the GOODS-Herschel key program and the local IRAS or AKARI-selected galaxies in the field of Sloan Digital Sky Survey Data Release 7, we investigate the dependence of galaxy properties on the morphology of and the distance to the nearest neighbor galaxy. Results: We find that the star-formation rates (SFRs) and the specific SFRs (SSFRs) of galaxies on average depend on the morphology of and the distance to the nearest neighbor galaxy in this redshift range. When a late-type galaxy has a close neighbor galaxy, the SFR and the SSFR increase as it approaches a late-type neighbor, which is supported by Kolmogorov-Smirnov (K-S) and Monte Carlo (MC) tests with a significance level of >99%. However, the SFR and the SSFR decrease or do not change much as the galaxy approaches an early-type neighbor. The bifurcations of SFRs and SSFRs depending on the neighbor's morphology seem to occur at Rn ≈ 0.5rvir,nei (virial radius of the neighbor), which is supported by K-S and MC tests with a significance level of >98%. For all redshift bins, the SSFRs of late-type galaxies interacting with late-type neighbors are increased by factors of about 1.8 ± 0.7 and 4.0 ± 1.2 compared to those of non-interacting galaxies when the pair separation is smaller than 0.5rvir,nei and 0.1rvir,nei, respectively. The dust temperature of both local and high-z late-type galaxies that strongly interact with late-type neighbors (i.e. Rn ≤ 0.1rvir,nei) appears to be higher than that of non-interacting galaxies with a significance level of 96-99%. However, the dust temperature of local late-type galaxies that strongly interact with early-type neighbors seems to be lower than or similar to that of non

  7. Galaxy dynamics in clustered environments

    NASA Astrophysics Data System (ADS)

    Pereira, Maria J. R. R.

    Galaxy orientations have been studied statistically for over 70 years now, but it is only recently that alignments have been found on scales larger than those of close interacting pairs. Large scale alignments between galaxies and their surrounding tidal fields are expected to occur during formation, but what happens when these galaxies fall into larger systems? Can their orientations tell us anything about the accretion process itself? In this dissertation I will focus on the radial alignment of satellite galaxies, in which a satellite's long axis points preferentially toward the center of its host. I present observational evidence for this type of galaxy alignment in the SDSS DR3 using a sample of X-ray selected massive clusters. Then, using results from N-body cosmological simulations, I will argue that this effect is the result of a secular tidal interaction between the galaxies and their host potential. The analysis shows that subhalos are effectively torqued by their host throughout their orbits, so that their major axes tend to be aligned with the gradient of the host potential. The significant discrepancy between the magnitude of the effect as seen in these simulations and that detected in observations motivates the work of the next chapter, where I perform numerical experiments on idealized, high resolution N-body models of elliptical galaxies. These experiments show that the more centrally concentrated luminous components of galaxies take longer to react to the external torque, and, in the particular case of mildly eccentric orbits, their orientations can figure rotate in periodic patterns that are not radially aligned on average. The mechanism is more effective on galaxies that have larger triaxialities, but the overall effect of torquing is to make galaxies rounder, since radially misaligned galaxies tend to become more spherical as they are torqued towards equilibrium. In the last chapter, I briefly discuss the impact of these results for galaxy

  8. Local Group dwarf galaxies: nature and nurture

    NASA Astrophysics Data System (ADS)

    Sawala, Till; Scannapieco, Cecilia; White, Simon

    2012-02-01

    We investigate the formation and evolution of dwarf galaxies in a high-resolution, hydrodynamical cosmological simulation of a Milky Way sized halo and its environment. Our simulation includes gas cooling, star formation, supernova feedback, metal enrichment and ultraviolet heating. In total, 90 satellites and more than 400 isolated dwarf galaxies are formed in the simulation, allowing a systematic study of the internal and environmental processes that determine their evolution. We find that 95 per cent of satellite galaxies are gas free at z= 0, and identify three mechanisms for gas loss: supernova feedback, tidal stripping and photoevaporation due to re-ionization. Gas-rich satellite galaxies are only found with total masses above ˜5 × 109 M⊙. In contrast, for isolated dwarf galaxies, a total mass of ˜109 M⊙ constitutes a sharp transition; less massive galaxies are predominantly gas free at z= 0, more massive, isolated dwarf galaxies are often able to retain their gas. In general, we find that the total mass of a dwarf galaxy is the main factor which determines its star formation, metal enrichment and its gas content, but that stripping may explain the observed difference in gas content between field dwarf galaxies and satellites with total masses close to 109 M⊙. We also find that a morphological transformation via tidal stripping of infalling, luminous dwarf galaxies whose dark matter is less concentrated than their stars cannot explain the high total mass-to-light ratios of the faint dwarf spheroidal galaxies.

  9. 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.

  10. Andromeda Galaxy

    NASA Astrophysics Data System (ADS)

    Walterbos, R.; Murdin, P.

    2000-11-01

    The Andromeda galaxy is the closest SPIRAL GALAXY to the MILKY WAY, just visible to the naked eye on a dark night as a faint smudge of light in the constellation Andromeda. The earliest records of the Andromeda nebula, as it is still often referred to, date back to AD 964, to the `Book of the Fixed Stars' published by the Persian astronomer AL-SÛFI. The first European to officially note the Andro...

  11. HUBBLE'S INFRARED GALAXY GALLERY

    NASA Technical Reports Server (NTRS)

    2002-01-01

    Astronomers have used the NASA Hubble Space Telescope to produce an infrared 'photo essay' of spiral galaxies. By penetrating the dust clouds swirling around the centers of these galaxies, the telescope's infrared vision is offering fresh views of star birth. These six images, taken with the Near Infrared Camera and Multi-Object Spectrometer, showcase different views of spiral galaxies, from a face-on image of an entire galaxy to a close-up of a core. The top row shows spirals at diverse angles, from face-on, (left); to slightly tilted, (center); to edge-on, (right). The bottom row shows close-ups of the hubs of three galaxies. In these images, red corresponds to glowing hydrogen, the raw material for star birth. The red knots outlining the curving spiral arms in NGC 5653 and NGC 3593, for example, pinpoint rich star-forming regions where the surrounding hydrogen gas is heated by intense ultraviolet radiation from young, massive stars. In visible light, many of these regions can be hidden from view by the clouds of gas and dust in which they were born. The glowing hydrogen found inside the cores of these galaxies, as in NGC 6946, may be due to star birth; radiation from active galactic nuclei (AGN), which are powered by massive black holes; or a combination of both. White is light from middle-age stars. Clusters of stars appear as white dots, as in NGC 2903. The galaxy cores are mostly white because of their dense concentration of stars. The dark material seen in these images is dust. These galaxies are part of a Hubble census of about 100 spiral galaxies. Astronomers at Space Telescope Science Institute took these images to fill gaps in the scheduling of a campaign using the NICMOS-3 camera. The data were non-proprietary, and were made available to the entire astronomical community. Filters: Three filters were used: red, blue, and green. Red represents emission at the Paschen Alpha line (light from glowing hydrogen) at a wavelength of 1.87 microns. Blue shows the

  12. Breaking the Hermetic Seal.

    ERIC Educational Resources Information Center

    Hill, Paul

    2001-01-01

    The key to handling persistent challenges (increased accountability demands, unstable superintendencies, educator shortages, minority underachievement, and resistant high schools) is breaking down institutional barriers separating today's schools from their surrounding communities. Tapping human and cultural resources and offering better…

  13. Stellar populations in spiral galaxies: broadband versus spectroscopic viewpoints

    NASA Astrophysics Data System (ADS)

    MacArthur, Lauren Anne

    2006-06-01

    This thesis addresses the stellar population content in the bulges and disks of spiral galaxies using broad-band and spectroscopic data. The results can be used to constrain models of galaxy formation in addition to establishing a comprehensive, model-independent, picture of colour and line-index gradients in spiral galaxies. Building upon my Masters study of structural parameters in spiral galaxies, I use the largest collection of multi-band (optical and IR) surface brightness profiles for face-on and moderately-tilted galaxies to extract radial colour profiles. The colour gradients are then translated into age and metallicity gradients by comparison with stellar population synthesis (SPS) models considering a range of star formation histories, including recent bursts. Based on their integrated light, we find that high surface brightness (SB) regions of galaxies formed their stars earlier than lower SB ones, or at a similar epoch but on shorter timescale. At a given SB level, the star formation histories are modulated by the overall potential of the galaxy such that brighter/higher rotational velocity galaxies formed earlier. This formation "down-sizing" implied by our results is inconsistent with current implementations of semi-analytic structure formation models. In order to alleviate concerns that our colour gradients could be affected by dust reddening, we designed a similar spectroscopic investigation and explored the dust sensitivity of absorption-line indices. The latter test makes use of the latest SPS, models incorporating a multi-component model for the line and continuum attenuation due to dust. For quiescent stellar populations (e.g. spheroids and globular clusters), dust extinction effects are small for most indices with the exception of the 4000 Å break. For models with current star formation, many indices may suffer from dust reddening and any departures depend on age, dust distribution, and the effective optical depth. However, a number of useful

  14. Stellar populations in spiral galaxies: Broadband versus spectroscopic viewpoints

    NASA Astrophysics Data System (ADS)

    MacArthur, Lauren Anne

    This thesis addresses the stellar population content in the bulges and disks of spiral galaxies using broad-band and spectroscopic data. The results can be used to constrain models of galaxy formation in addition to establishing a comprehensive, model-independent, picture of colour and line-index gradients in spiral galaxies. Building upon my Masters study of structural parameters in spiral galaxies, I use the largest collection of multi-band (optical and IR) surface brightness profiles for face-on and moderately-tilted galaxies to extract radial colour profiles. The colour gradients are then translated into age and metallicity gradients by comparison with stellar population synthesis (SPS) models considering a range of star formation histories, including recent bursts. Based on their integrated light, we find that high surface brightness (SB) regions of galaxies formed their stars earlier than lower SB ones, or at a similar epoch but on shorter timescale. At a given SB level, the star formation histories are modulated by the overall potential of the galaxy such that brighter/higher rotational velocity galaxies formed earlier. This formation "down-sizing" implied by our results is inconsistent with current implementations of semi-analytic structure formation models. In order to alleviate concerns that our colour gradients could be affected by dust reddening, we designed a similar spectroscopic investigation and explored the dust sensitivity of absorption-line indices. The latter test makes use of the latest SPS, models incorporating a multi-component model for the line and continuum attenuation due to dust. For quiescent stellar populations (e.g. spheroids and globular clusters), dust extinction effects are small for most indices with the exception of the 4000 Å break. For models with current star formation, many indices may suffer from dust reddening and any departures depend on age, dust distribution, and the effective optical depth. However, a number of useful

  15. DISTANT CLUSTER OF GALAXIES [left

    NASA Technical Reports Server (NTRS)

    2002-01-01

    One of the deepest images to date of the universe, taken with NASA's Hubble Space Telescope (HST), reveals thousands of faint galaxies at the detection limit of present day telescopes. Peering across a large volume of the observable cosmos, Hubble resolves thousands of galaxies from five to twelve billion light-years away. The light from these remote objects has taken billions of years to cross the expanding universe, making these distant galaxies fossil evidence' of events that happened when the universe was one-third its present age. A fraction of the galaxies in this image belong to a cluster located nine billion light-years away. Though the field of view (at the cluster's distance) is only two million light-years across, it contains a multitude of fragmentary objects. (By comparison, the two million light-years between our Milky Way galaxy and its nearest large companion galaxy, in the constellation Andromeda, is essentially empty space!) Very few of the cluster's members are recognizable as normal spiral galaxies (like our Milky Way), although some elongated members might be edge-on disks. Among this zoo of odd galaxies are ``tadpole-like'' objects, disturbed and apparently merging systems dubbed 'train-wrecks,' and a multitude of faint, tiny shards and fragments, dwarf galaxies or possibly an unknown population of objects. However, the cluster also contains red galaxies that resemble mature examples of today's elliptical galaxies. Their red color comes from older stars that must have formed shortly after the Big Bang. The image is the full field view of the Wide Field and Planetary Camera-2. The picture was taken in intervals between May 11 and June 15, 1994 and required an 18-hour long exposure, over 32 orbits of HST, to reveal objects down to 29th magnitude. [bottom right] A close up view of the peculiar radio galaxy 3C324 used to locate the cluster. The galaxy is nine billion light-years away as measured by its spectral redshift (z=1.2), and located in the

  16. The Hooked Galaxy

    NASA Astrophysics Data System (ADS)

    2006-06-01

    Life is not easy, even for galaxies. Some indeed get so close to their neighbours that they get rather distorted. But such encounters between galaxies have another effect: they spawn new generations of stars, some of which explode. ESO's VLT has obtained a unique vista of a pair of entangled galaxies, in which a star exploded. Because of the importance of exploding stars, and particularly of supernovae of Type Ia [1], for cosmological studies (e.g. relating to claims of an accelerated cosmic expansion and the existence of a new, unknown, constituent of the universe - the so called 'Dark Energy'), they are a preferred target of study for astronomers. Thus, on several occasions, they pointed ESO's Very Large Telescope (VLT) towards a region of the sky that portrays a trio of amazing galaxies. MCG-01-39-003 (bottom right) is a peculiar spiral galaxy, with a telephone number name, that presents a hook at one side, most probably due to the interaction with its neighbour, the spiral galaxy NGC 5917 (upper right). In fact, further enhancement of the image reveals that matter is pulled off MCG-01-39-003 by NGC 5917. Both these galaxies are located at similar distances, about 87 million light-years away, towards the constellation of Libra (The Balance). ESO PR Photo 22/06 ESO PR Photo 22/06 The Hooked Galaxy and its Companion NGC 5917 (also known as Arp 254 and MCG-01-39-002) is about 750 times fainter than can be seen by the unaided eye and is about 40,000 light-years across. It was discovered in 1835 by William Herschel, who strangely enough, seems to have missed its hooked companion, only 2.5 times fainter. As seen at the bottom left of this exceptional VLT image, a still fainter and nameless, but intricately beautiful, barred spiral galaxy looks from a distance the entangled pair, while many 'island universes' perform a cosmic dance in the background. But this is not the reason why astronomers look at this region. Last year, a star exploded in the vicinity of the hook

  17. An imaging survey of late-type galaxies: Local benchmarks of galaxy evolution

    NASA Astrophysics Data System (ADS)

    Taylor, Violet

    The majority of galaxies observed at high redshift display structures and morphologies resembling those of nearby (z ~ 0) irregular, peculiar and merging galaxies. To better understand galaxy assembly and evolution, the properties of such nearby galaxies must be compared with distant ones in the rest-frame ultraviolet (UV), where the highest resolution and deepest observations of high-redshift galaxies were taken. To evaluate the possible dependence of galaxy structure and morphology on rest-frame wavelength, it is necessary to study the nearby galaxies in redder bands as well. For this purpose, a panchromatic imaging survey was conducted in the far-UV through the near- infrared of 199 nearby, mostly late-type, irregular, peculiar, and merging galaxies. An analysis is presented here of the color gradients, and the wavelength- dependent quantitative morphology of this sample. Whereas ellipticals and early- to mid-type spiral galaxies tend to become bluer at larger radial distances from their centers, most late-type spiral, irregular, and merging galaxies become increasingly redder at larger radii. This may indicate that late-type galaxies have a significant halo or thick disk of older stars, while their inner regions are dominated by younger, UV-bright stars. This result is consistent with recent numerical models of hierarchical galaxy assembly. Galaxy morphology is also quantitatively analyzed, as parametrized with measurements of concentration index, asymmetry, and clumpiness (CAS) parameters. These CAS parameters depend on both galaxy type and the wavelength of observation, and can be used to measure the "morphological k-correction", i.e., the change in appearance of a galaxy with rest-frame wavelength. Whereas early-type galaxies (E-S0) appear the same at all wavelengths longward of the Balmer break, there is a significant wavelength-dependence of the CAS parameters for galaxies of types later than S0, which generally become less concentrated and more asymmetric

  18. Experimental breaking of an adiabatic invariant

    NASA Astrophysics Data System (ADS)

    Notte, J.; Fajans, J.; Chu, R.; Wurtele, J. S.

    1993-06-01

    When a cylindrical pure electron plasma is displaced from the center of the trap, it performs a bulk circular orbital motion known as the l=1 diocotron mode. The slow application of a perturbing potential to a patch on the trap wall distorts the orbit into a noncircular closed path. Experiments and a simple theoretical model indicate that the area by the loop is an adiabatic invariant. Detailed studies are made of the breaking of the invariant when perturbations are rapidly applied. When the perturbation is applied with discontinuous time derivatives, the invariant breaking greatly exceeds the predictions of the standard theory for smooth perturbations.

  19. Fire within the Antennae Galaxies

    NASA Technical Reports Server (NTRS)

    2004-01-01

    This false-color image composite from NASA's Spitzer Space Telescope reveals hidden populations of newborn stars at the heart of the colliding 'Antennae' galaxies. These two galaxies, known individually as NGC 4038 and 4039, are located around 68 million light-years away and have been merging together for about the last 800 million years. The latest Spitzer observations provide a snapshot of the tremendous burst of star formation triggered in the process of this collision, particularly at the site where the two galaxies overlap.

    The image is a composite of infrared data from Spitzer and visible-light data from Kitt Peak National Observatory, Tucson, Ariz. Visible light from stars in the galaxies (blue and green) is shown together with infrared light from warm dust clouds heated by newborn stars (red).

    The two nuclei, or centers, of the merging galaxies show up as yellow-white areas, one above the other. The brightest clouds of forming stars lie in the overlap region between and left of the nuclei.

    Throughout the sky, astronomers have identified many of these so-called 'interacting' galaxies, whose spiral discs have been stretched and distorted by their mutual gravity as they pass close to one another. The distances involved are so large that the interactions evolve on timescales comparable to geologic changes on Earth. Observations of such galaxies, combined with computer models of these collisions, show that the galaxies often become forever bound to one another, eventually merging into a single, spheroidal-shaped galaxy.

    Wavelengths of 0.44 microns are represented in blue, .70 microns in green and 8.0 microns in red. This image was taken on Dec. 24, 2003.

  20. Galaxy Clusters

    NASA Astrophysics Data System (ADS)

    Miller, Christopher J. Miller

    2012-03-01

    There are many examples of clustering in astronomy. Stars in our own galaxy are often seen as being gravitationally bound into tight globular or open clusters. The Solar System's Trojan asteroids cluster at the gravitational Langrangian in front of Jupiter’s orbit. On the largest of scales, we find gravitationally bound clusters of galaxies, the Virgo cluster (in the constellation of Virgo at a distance of ˜50 million light years) being a prime nearby example. The Virgo cluster subtends an angle of nearly 8◦ on the sky and is known to contain over a thousand member galaxies. Galaxy clusters play an important role in our understanding of theUniverse. Clusters exist at peaks in the three-dimensional large-scale matter density field. Their sky (2D) locations are easy to detect in astronomical imaging data and their mean galaxy redshifts (redshift is related to the third spatial dimension: distance) are often better (spectroscopically) and cheaper (photometrically) when compared with the entire galaxy population in large sky surveys. Photometric redshift (z) [Photometric techniques use the broad band filter magnitudes of a galaxy to estimate the redshift. Spectroscopic techniques use the galaxy spectra and emission/absorption line features to measure the redshift] determinations of galaxies within clusters are accurate to better than delta_z = 0.05 [7] and when studied as a cluster population, the central galaxies form a line in color-magnitude space (called the the E/S0 ridgeline and visible in Figure 16.3) that contains galaxies with similar stellar populations [15]. The shape of this E/S0 ridgeline enables astronomers to measure the cluster redshift to within delta_z = 0.01 [23]. The most accurate cluster redshift determinations come from spectroscopy of the member galaxies, where only a fraction of the members need to be spectroscopically observed [25,42] to get an accurate redshift to the whole system. If light traces mass in the Universe, then the locations

  1. Nature of multiple-nucleus cluster galaxies

    SciTech Connect

    Merritt, D.

    1984-05-01

    In models for the evolution of galaxy clusters which include dynamical friction with the dark binding matter, the distribution of galaxies becomes more concentrated to the cluster center with time. In a cluster like Coma, this evolution could increase by a factor of approximately 3 the probability of finding a galaxy very close to the cluster center, without decreasing the typical velocity of such a galaxy significantly below the cluster mean. Such an enhancement is roughly what is needed to explain the large number of first-ranked cluster galaxies which are observed to have extra ''nuclei''; it is also consistent with the high velocities typically measured for these ''nuclei.'' Unlike the cannibalism model, this model predicts that the majority of multiple-nucleus systems are transient phenomena, and not galaxies in the process of merging.

  2. Extended Source/Galaxy All Sky 2

    NASA Technical Reports Server (NTRS)

    2003-01-01

    This panoramic view encompasses the entire sky and reveals the distribution of galaxies beyond the Milky Way galaxy, which astronomers call extended sources, as observed by Two Micron All-Sky Survey. The image is assembled from a database of over 1.6 million galaxies listed in the survey's All-Sky Survey Extended Source Catalog,; more than half of the galaxies have never before been catalogued. The colors represent how the many galaxies appear at three distinct wavelengths of infrared light (blue at 1.2 microns, green at 1.6 microns, and red at 2.2 microns). Quite evident are the many galactic clusters and superclusters, as well as some streamers composing the large-scale structure of the nearby universe. The blue overlay represents the very close and bright stars from our own Milky Way galaxy. In this projection, the bluish Milky Way lies predominantly toward the upper middle and edges of the image.

  3. Baby Galaxies in the Adult Universe

    NASA Technical Reports Server (NTRS)

    2004-01-01

    [figure removed for brevity, see original site] Figure 1

    This artist's conception illustrates the decline in our universe's 'birth-rate' over time. When the universe was young, massive galaxies were forming regularly, like baby bees in a bustling hive. In time, the universe bore fewer and fewer 'offspring,' and newborn galaxies (white circles) matured into older ones more like our own Milky Way (spirals).

    Previously, astronomers thought that the universe had ceased to give rise to massive, young galaxies, but findings from NASA's Galaxy Evolution Explorer suggest that may not be the case. Surveying thousands of nearby galaxies with its highly sensitive ultraviolet eyes, the telescope spotted three dozen that greatly resemble youthful galaxies from billions of years ago. In this illustration, those galaxies are represented as white circles on the right, or 'today' side of the timeline.

    The discovery not only suggests that our universe may still be alive with youth, but also offers astronomers their first close-up look at what appear to be baby galaxies. Prior to the new result, astronomers had to peer about 11 billion light-years into the distant universe to see newborn galaxies. The newfound galaxies are only about 2 to 4 billion light-years away.

  4. Galaxy formation

    SciTech Connect

    Silk, J.

    1984-11-01

    Implications of the isotropy of the cosmic microwave background on large and small angular scales for galaxy formation are reviewed. In primeval adiabatic fluctuations, a universe dominated by cold, weakly interacting nonbaryonic matter, e.g., the massive photino is postulated. A possible signature of photino annihilation in our galactic halo involves production of cosmic ray antiprotons. If the density is near its closure value, it is necessary to invoke a biasing mechanism for suppressing galaxy formation throughout most of the universe in order to reconcile the dark matter density with the lower astronomical determinations of the mean cosmological density. A mechanism utilizing the onset of primordial massive star formation to strip gaseous protogalaxies is described. Only the densest, early collapsing systems form luminous galaxies. (ESA)

  5. Electroweak symmetry breaking

    SciTech Connect

    Chanowitz, M.S.

    1990-09-01

    The Higgs mechanism is reviewed in its most general form, requiring the existence of a new symmetry-breaking force and associated particles, which need not however be Higgs bosons. The first lecture reviews the essential elements of the Higgs mechanism, which suffice to establish low energy theorems for the scattering of longitudinally polarized W and Z gauge bosons. An upper bound on the scale of the symmetry-breaking physics then follows from the low energy theorems and partial wave unitarity. The second lecture reviews particular models, with and without Higgs bosons, paying special attention to how the general features discussed in lecture 1 are realized in each model. The third lecture focuses on the experimental signals of strong WW scattering that can be observed at the SSC above 1 TeV in the WW subenergy, which will allow direct measurement of the strength of the symmetry-breaking force. 52 refs., 10 figs.

  6. Stellar Populations and Radial Migrations in Virgo Disk Galaxies

    NASA Astrophysics Data System (ADS)

    Roediger, Joel C.; Courteau, Stéphane; Sánchez-Blázquez, Patricia; McDonald, Michael

    2012-10-01

    We present new stellar age profiles, derived from well-resolved optical and near-infrared images of 64 Virgo cluster disk galaxies, whose analysis poses a challenge for current disk galaxy formation models. Our ability to break the age-metallicity degeneracy and the significant size of our sample represent key improvements over complementary studies of field disk galaxies. Our results can be summarized as follows: first, and contrary to observations of disk galaxies in the field, these cluster galaxies are distributed almost equally amongst the three main types of disk galaxy luminosity profiles (I/II/III), indicating that the formation and/or survival of Type II breaks is suppressed within the cluster environment. Second, we find examples of statistically significant inversions ("U-shapes") in the age profiles of all three disk galaxy types, reminiscent of predictions from high-resolution simulations of classically truncated Type II disks in the field. These features characterize the age profiles for only about a third (<=36%) of each disk galaxy type in our sample. An even smaller fraction of cluster disks (~11% of the total sample) exhibit age profiles that decrease outward (i.e., negative age gradients). Instead, flat and/or positive age gradients prevail (>=50%) within our Type I, II, and III subsamples. These observations thus suggest that while stellar migrations and inside-out growth can play a significant role in the evolution of all disk galaxy types, other factors contributing to the evolution of galaxies can overwhelm the predicted signatures of these processes. We interpret our observations through a scenario whereby Virgo cluster disk galaxies formed initially like their brethren in the field but which, upon falling into the cluster, were transformed into their present state through external processes linked to the environment (e.g., ram-pressure stripping and harassment). Current disk galaxy formation models, which have largely focused on field

  7. STELLAR POPULATIONS AND RADIAL MIGRATIONS IN VIRGO DISK GALAXIES

    SciTech Connect

    Roediger, Joel C.; Courteau, Stephane; Sanchez-Blazquez, Patricia; McDonald, Michael E-mail: courteau@astro.queensu.ca E-mail: mcdonald@space.mit.edu

    2012-10-10

    We present new stellar age profiles, derived from well-resolved optical and near-infrared images of 64 Virgo cluster disk galaxies, whose analysis poses a challenge for current disk galaxy formation models. Our ability to break the age-metallicity degeneracy and the significant size of our sample represent key improvements over complementary studies of field disk galaxies. Our results can be summarized as follows: first, and contrary to observations of disk galaxies in the field, these cluster galaxies are distributed almost equally amongst the three main types of disk galaxy luminosity profiles (I/II/III), indicating that the formation and/or survival of Type II breaks is suppressed within the cluster environment. Second, we find examples of statistically significant inversions ({sup U}-shapes{sup )} in the age profiles of all three disk galaxy types, reminiscent of predictions from high-resolution simulations of classically truncated Type II disks in the field. These features characterize the age profiles for only about a third ({<=}36%) of each disk galaxy type in our sample. An even smaller fraction of cluster disks ({approx}11% of the total sample) exhibit age profiles that decrease outward (i.e., negative age gradients). Instead, flat and/or positive age gradients prevail ({>=}50%) within our Type I, II, and III subsamples. These observations thus suggest that while stellar migrations and inside-out growth can play a significant role in the evolution of all disk galaxy types, other factors contributing to the evolution of galaxies can overwhelm the predicted signatures of these processes. We interpret our observations through a scenario whereby Virgo cluster disk galaxies formed initially like their brethren in the field but which, upon falling into the cluster, were transformed into their present state through external processes linked to the environment (e.g., ram-pressure stripping and harassment). Current disk galaxy formation models, which have largely

  8. Bar Formation from Galaxy Flybys

    NASA Astrophysics Data System (ADS)

    Holley-Bockelmann, Kelly; Lang, Meagan; Sinha, Manodeep

    2016-05-01

    Both simulations and observations reveal that flybys—fast, one-time interactions between two galaxy halos—are surprisingly common, comparable to galaxy mergers. Since these are rapid, transient events with the closest approach well outside the galaxy disk, it is unclear if flybys can transform the galaxy in a lasting way. We conduct collisionless N-body simulations of three coplanar flyby interactions between pure-disk galaxies to take a first look at the effects flybys have on disk structure, with particular focus on stellar bar formation. We find that some flybys are capable of inciting a bar; bars form in both galaxies during our 1:1 interaction and in the secondary during our 10:1 interaction. The bars formed have ellipticities >0.5, sizes on the order of the scale length of the disk, and persist to the end of our simulations, ~5 Gyr after pericenter. The ability of flybys to incite bar formation implies that many processes associated with secular bar evolution may be more closely tied with flyby interactions than previously thought.

  9. BAR FORMATION FROM GALAXY FLYBYS

    SciTech Connect

    Lang, Meagan; Holley-Bockelmann, Kelly; Sinha, Manodeep E-mail: k.holley@vanderbilt.edu

    2014-08-01

    Recently, both simulations and observations have revealed that flybys—fast, one-time interactions between two galaxy halos—are surprisingly common, nearing/comparable to galaxy mergers. Since these are rapid, transient events with the closest approach well outside the galaxy disk, it is unclear if flybys can transform the galaxy in a lasting way. We conduct collisionless N-body simulations of three coplanar flyby interactions between pure-disk galaxies to take a first look at the effects flybys have on disk structure, with particular focus on stellar bar formation. We find that some flybys are capable of inciting a bar with bars forming in both galaxies during our 1:1 interaction and in the secondary during our 10:1 interaction. The bars formed have ellipticities ≳ 0.5, sizes on the order of the host disk's scale length, and persist to the end of our simulations, ∼5 Gyr after pericenter. The ability of flybys to incite bar formation implies that many processes associated with secular bar evolution may be more closely tied with interactions than previously thought.

  10. Discovering Teenage Galaxies

    NASA Astrophysics Data System (ADS)

    2007-11-01

    Staring for the equivalent of every night for two weeks at the same little patch of sky with ESO's Very Large Telescope, an international team of astronomers has found the extremely faint light from teenage galaxies billions of light years away. These galaxies, which the research team believes are the building blocks of normal galaxies like our Milky Way, had eluded detection for three decades, despite intensive searches. ESO PR Photo 52/07 ESO PR Photo 52/07 A 92-hour long spectrum Two-dimensional spectrum obtained in 92 hours of exposure time, showing the line emitter candidates. The quasar absorption lines are visible close to the centre of the image. The team, led by Martin Haehnelt of the University of Cambridge, UK, Michael Rauch and George Becker of the Observatories of the Carnegie Institution, USA, and Andy Bunker of the Anglo-Australian Observatory, reports their results in the 1 March 2008 issue of the Astrophysical Journal. "This is the first time that the sky has been searched to this depth and the unrivalled sensitivity of the picture taken with the VLT was key to succeeding," says Haehnelt. Experts have long speculated that galaxies like ours were created by the amalgamation of proto-galaxies early in the history of the Universe, but the light from these fragments was so faint that astronomers had struggled to prove they were there at all. Astronomers thought that the teenage galaxies must be out there because they were blocking part of the light from objects even further away in space. "Previous attempts have usually been frustrated by the difficulty of detecting extremely faint objects: the amount of time required even with an 8-metre class telescope like the VLT considerably exceeds typical observing time awards. We have thus exploited the periods of less good weather with the FORS2 spectrograph at the VLT, taking advantage of the service observing mode," says Becker. In service mode, ESO staff astronomers at Paranal are responsible for carrying

  11. Comparing Stellar Populations of Galaxies across the Hubble Sequence

    NASA Astrophysics Data System (ADS)

    Kaleida, Catherine C.; Parkash, Vaishali; Jansen, Rolf

    2014-08-01

    We propose to investigate the spatial distributions of stellar populations within a statistically significant set of galaxies, representing the full range of luminosity and morphological type. By obtaining new, near-infrared images of these galaxies to complement existing optical and near-UV data, we can self-consistently probe the older stellar populations, dust extinction, and metallicity, and ultimately determine ages of and age variations within the stellar components of these galaxies. This information can then be used to compare stellar populations between luminous and faint galaxies of the same Hubble type, and between similar luminosity galaxies of different types. Galaxy candidates for this study were drawn from the Nearby Field Galaxy Survey (Jansen 2000), which provides U, B, and R optical images and both nuclear and globally integrated spectra. Near- infrared J, H, and K_s surface photometry can break the age-dust- metallicity degeneracy in galaxy spectral energy distributions (SEDs), but existing 2MASS image data is not sufficiently deep for this purpose. We therefore request observing time on the Infrared Side Port Imager (ISPI) on the CTIO 4-m Blanco telescope to secure J, H, and K_s images reaching out to the optical radius for 19 NFGS galaxies observable from Cerro Tololo in 2014B. Specific results expected from this sample are the distributions of age, dust, and metallicity across galaxies of differing type and luminosity. These distributions will allow us to address systematic trends in assembly history that can confront simulations of hierarchical galaxy formation.

  12. Comparing Stellar Populations of Galaxies across the Hubble Sequence

    NASA Astrophysics Data System (ADS)

    Kaleida, Catherine C.; Parkash, Vaishali; Jansen, Rolf

    2014-02-01

    We propose to investigate the spatial distributions of stellar populations within a statistically significant set of galaxies, representing the full range of luminosity and morphological type. By obtaining new, near-infrared images of these galaxies to complement existing optical and near-UV data, we can self-consistently probe the older stellar populations, dust extinction, and metallicity, and ultimately determine ages of and age variations within the stellar components of these galaxies. This information can then be used to compare stellar populations between luminous and faint galaxies of the same Hubble type, and between similar luminosity galaxies of different types. Galaxy candidates for this study were drawn from the Nearby Field Galaxy Survey (Jansen 2000), which provides U, B, and R optical images and both nuclear and globally integrated spectra. Near- infrared J, H, and K_s surface photometry can break the age-dust- metallicity degeneracy in galaxy spectral energy distributions (SEDs), but existing 2MASS image data is not sufficiently deep for this purpose. We therefore request observing time on the Infrared Side Port Imager (ISPI) on the CTIO 4-m Blanco telescope to secure J, H, and K_s images reaching out to the optical radius for 12 NFGS galaxies observable from Cerro Tololo in 2014A. Specific results expected from this sample are the distributions of age, dust, and metallicity across galaxies of differing type and luminosity. These distributions will allow us to address systematic trends in assembly history that can confront simulations of hierarchical galaxy formation.

  13. Model Breaking Points Conceptualized

    ERIC Educational Resources Information Center

    Vig, Rozy; Murray, Eileen; Star, Jon R.

    2014-01-01

    Current curriculum initiatives (e.g., National Governors Association Center for Best Practices and Council of Chief State School Officers 2010) advocate that models be used in the mathematics classroom. However, despite their apparent promise, there comes a point when models break, a point in the mathematical problem space where the model cannot,…

  14. Cosmology with equivalence principle breaking in the dark sector

    SciTech Connect

    Keselman, Jose Ariel; Nusser, Adi; Peebles, P. J. E.

    2010-03-15

    A long-range force acting only between nonbaryonic particles would be associated with a large violation of the weak equivalence principle. We explore cosmological consequences of this idea, which we label ReBEL (daRk Breaking Equivalence principLe). A high resolution hydrodynamical simulation of the distributions of baryons and dark matter confirms our previous findings that a ReBEL force of comparable strength to gravity on comoving scales of about 1 h{sup -1} Mpc causes voids between the concentrations of large galaxies to be more nearly empty, suppresses accretion of intergalactic matter onto galaxies at low redshift, and produces an early generation of dense dark-matter halos. A preliminary analysis indicates the ReBEL scenario is consistent with the one-dimensional power spectrum of the Lyman-Alpha forest and the three-dimensional galaxy autocorrelation function. Segregation of baryons and DM in galaxies and systems of galaxies is a strong prediction of ReBEL. ReBEL naturally correlates the baryon mass fraction in groups and clusters of galaxies with the system mass, in agreement with recent measurements.

  15. Extragalatic zoo. I. [New galaxies

    SciTech Connect

    Schorn, R.A.

    1988-01-01

    The characteristics of various types of extragalactic objects are described. Consideration is given to cD galaxies, D galaxies, N galaxies, Markarian galaxies, liners, starburst galaxies, and megamasers. Emphasis is also placed on the isolated extragalatic H I region; the isolated extragalatic H II region; primeval galaxies or photogalaxies; peculiar galaxies; Arp galaxies; interacting galaxies; ring galaxies; and polar-ring galaxies. Diagrams of these objects are provided.

  16. The ionizing photon production efficiency of compact z ~ 0.3 Lyman continuum leakers and comparison with high-redshift galaxies

    NASA Astrophysics Data System (ADS)

    Schaerer, D.; Izotov, Y. I.; Verhamme, A.; Orlitová, I.; Thuan, T. X.; Worseck, G.; Guseva, N. G.

    2016-06-01

    We have recently discovered five Lyman continuum leaking galaxies at z ~ 0.3 that were selected for their compactness, intense star formation, and high [O iii]λ5007/[O ii] λ3727 ratio. Here we derive their ionizing photon production efficiency, ξion, a fundamental quantity for inferring the number of photons available to reionize the Universe. This is the first time this is done for galaxies with confirmed strong Lyman continuum escape (fesc ~ 6-13%). We find an ionizing photon production per unit UV luminosity, ξion, that is higher by a factor 2-6 than the canonical value when reported to their observed UV luminosity. After correction for extinction, this value is close to the canonical value. The properties of our five Lyman continuum leakers are found to be very similar to those of the previously reported confirmed z = 3.218 leaker Ion2 and very similar to those of typical star-forming galaxies at z ≳ 6. Our results suggest that UV bright galaxies at high-z such as Lyman-break galaxies can be Lyman continuum leakers and that their contribution to cosmic reionization may be underestimated.

  17. Secular Evolution in Disk Galaxies

    NASA Astrophysics Data System (ADS)

    Kormendy, John

    2013-10-01

    Self-gravitating systems evolve toward the most tightly bound configuration that is reachable via the evolution processes that are available to them. They do this by spreading -- the inner parts shrink while the outer parts expand -- provided that some physical process efficiently transports energy or angular momentum outward. The reason is that self-gravitating systems have negative specific heats. As a result, the evolution of stars, star clusters, protostellar and protoplanetary disks, black hole accretion disks and galaxy disks are fundamentally similar. How evolution proceeds then depends on the evolution processes that are available to each kind of self-gravitating system. These processes and their consequences for galaxy disks are the subjects of my lectures and of this Canary Islands Winter School. I begin with a review of the formation, growth and death of bars. Then I review the slow (`secular') rearrangement of energy, angular momentum, and mass that results from interactions between stars or gas clouds and collective phenomena such as bars, oval disks, spiral structure and triaxial dark haloes. The `existence-proof' phase of this work is largely over: we have a good heuristic understanding of how nonaxisymmetric structures rearrange disk gas into outer rings, inner rings and stuff dumped onto the centre. The results of simulations correspond closely to the morphology of barred and oval galaxies. Gas that is transported to small radii reaches high densities. Observations confirm that many barred and oval galaxies have dense central concentrations of gas and star formation. The result is to grow, on timescales of a few Gyr, dense central components that are frequently mistaken for classical (elliptical-galaxy-like) bulges but that were grown slowly out of the disk (not made rapidly by major mergers). The resulting picture of secular galaxy evolution accounts for the richness observed in galaxy structure. We can distinguish between classical and pseudo

  18. Crashing galaxies, cosmic fireworks

    SciTech Connect

    Keel, W.C.

    1989-01-01

    The study of binary systems is reviewed. The history of the study of interacting galaxies, the behavior of gas in binary systems, studies to identify the processes that occur when galaxies interact, and the relationship of Seyfert galaxies and quasars to binary systems are discussed. The development of an atlas of peculiar galaxies (Arp, 1966) and methods for modeling galaxy interactions are examined.

  19. REEXAMINATION OF THE RADIAL ABUNDANCE GRADIENT BREAK IN NGC 3359

    SciTech Connect

    Zahid, H. J.; Bresolin, F.

    2011-06-15

    In this contribution, we reexamine the radial oxygen abundance gradient in the strongly barred spiral galaxy NGC 3359, for which, using an imaging spectrophotometric technique, Martin and Roy detected a break near the effective radius of the galaxy. We have new emission line flux measurements of H II regions in NGC 3359 from spectra obtained with the Subaru telescope to further investigate this claim. We find that there are small systematic variations in the line ratios determined from narrowband imaging as compared to our spectroscopic measurements. We derive and apply a correction to the line ratios found by Martin and Roy and statistically examine the validity of the gradient break proposed for NGC 3359 using recently developed metallicity diagnostics. We find that, with a high degree of confidence, a model with a break fits the data significantly better than one without it. This suggests that the presence of a strong bar in spiral galaxies can generate measurable changes in the radial distribution of metals.

  20. EXPLORING THE z = 3-4 MASSIVE GALAXY POPULATION WITH ZFOURGE: THE PREVALENCE OF DUSTY AND QUIESCENT GALAXIES

    SciTech Connect

    Spitler, Lee R.; Rees, Glen; Straatman, Caroline M. S.; Labbé, Ivo; Glazebrook, Karl; Kacprzak, Glenn G.; Nanayakkara, Themiya; Tran, Kim-Vy H.; Papovich, Casey; Kawinwanichakij, Lalitwadee; Mehrtens, Nicola; Tilvi, Vithal; Tomczak, Adam R.; Quadri, Ryan F.; Persson, S. Eric; Kelson, Daniel D.; McCarthy, Patrick J.; Monson, Andrew J.; Van Dokkum, Pieter; Allen, Rebecca

    2014-06-01

    Our understanding of the redshift z > 3 galaxy population relies largely on samples selected using the popular ''dropout'' technique, typically consisting of UV-bright galaxies with blue colors and prominent Lyman breaks. As it is currently unknown if these galaxies are representative of the massive galaxy population, we here use the FOURSTAR Galaxy Evolution (ZFOURGE) survey to create a stellar mass-limited sample at z = 3-4. Uniquely, ZFOURGE uses deep near-infrared medium-bandwidth filters to derive accurate photometric redshifts and stellar population properties. The mass-complete sample consists of 57 galaxies with log M >10.6, reaching below M {sup *} at z = 3-4. On average, the massive z = 3-4 galaxies are extremely faint in the observed optical with median R{sub tot}{sup AB}=27.48±0.41 (rest-frame M {sub 1700} = –18.05 ± 0.37). They lie far below the UV luminosity-stellar mass relation for Lyman break galaxies and are about ∼100 × fainter at the same mass. The massive galaxies are red (R – K {sub s} {sub AB} = 3.9 ± 0.2; rest-frame UV-slope β = –0.2 ± 0.3) likely from dust or old stellar ages. We classify the galaxy spectral energy distributions by their rest-frame U–V and V–J colors and find a diverse population: 46{sub −6−17}{sup +6+10}% of the massive galaxies are quiescent, 40{sub −6−5}{sup +6+7}% are dusty star-forming galaxies, and only 14{sub −3−4}{sup +3+10}% resemble luminous blue star-forming Lyman break galaxies. This study clearly demonstrates an inherent diversity among massive galaxies at higher redshift than previously known. Furthermore, we uncover a reservoir of dusty star-forming galaxies with 4 × lower specific star-formation rates compared to submillimeter-selected starbursts at z > 3. With 5 × higher numbers, the dusty galaxies may represent a more typical mode of star formation compared to submillimeter-bright starbursts.

  1. Understanding the SEDS of Massive Stars and Radiative Feedback from Starburst Galaxies

    NASA Astrophysics Data System (ADS)

    Zastrow, Jordan A.; Oey, M. S.; Pellegrini, E. W.; Veilleux, S.; McDonald, M.; Martin, C. L.

    2013-01-01

    Massive stars strongly influence the properties of their interstellar and intergalactic environments through radiative feedback. The resulting HII regions are used as diagnostics for many galaxy properties, and the radiation from massive stars is thought to be a source for reionization in the early universe. Yet, there are still unanswered questions about the shape of the massive star spectral energy distribution and how far the radiation propagates in a galaxy. We use the emission-line spectra of a sample of single-star HII regions, in conjunction with photoionization simulations, to evaluate the predictions of widely used stellar atmosphere models. The model atmospheres generate simulated HII region spectra that agree well with the observations, except at the highest energy transitions, provided that the nebular density distributions are inhomogeneous. WM-basic atmospheres are better at reproducing the observed nebular spectrum, while TLUSTY atmospheres more closely match the observed rate of ionizing photons. Based on the results of our detailed CLOUDY simulations, we create a new spectral type to stellar effective temperature calibration. We also investigate the galactic parameters that control the propagation of ionizing radiation out of a galaxy by searching for extended, photoionized emission in a sample of nearby, dwarf starburst galaxies. Using narrowband emission-line images taken with the Maryland-Magellan Tunable Filter, we create ionization parameter maps of the starbursts. In NGC 5253, we detect an optically thin ionization cone extending from the central starburst, which is suggestive of the escape of ionizing radiation. The narrow morphology of the cone supports the scenario that an orientation bias contributes to the challenge of detecting Lyman continuum in starbursts and Lyman Break Galaxies.

  2. Local starburst galaxies and their descendants. Statistics from the Sloan Digital Sky Survey

    NASA Technical Reports Server (NTRS)

    Bergvall, Nils; Marquart, Thomas; Way, Michael J.; Blomqvist, Anna; Holst, Emma; Ostlin, Goran; Zackrisson, Erik

    2016-01-01

    Despite strong interest in the starburst phenomenon in extragalactic astronomy, the concept remains ill-defined. Here we use a strict definition of starburst to examine the statistical properties of starburst galaxies in the local universe. We also seek to establish links between starburst galaxies, post-starburst (hereafter postburst) galaxies, and active galaxies. Data were selected from the Sloan Digital Sky Survey DR7. We applied a novel method of treating dust attenuation and derive star formation rates, ages, and stellar masses assuming a two-component stellar population model. Dynamical masses are calculated from the width of the H-alpha line. These masses agree excellently with the photometric masses. The mass (gas+stars) range is approximately 10( exp 9) - 10(exp 11.5) solar mass. As a selection criterion for starburst galaxies, we use, the birthrate parameter, b = SFR/SFR, requiring that b is greater than 3. For postburst galaxies, we use, the equivalent width of Hdelta in absorption with the criterion EW (sub Hdelta_abs) is greater than 6 A. Results. We find that only 1% of star-forming galaxies are starburst galaxies. They contribute 3-6% to the stellar production and are therefore unimportant for the local star formation activity. The median starburst age is 70 Myr roughly independent of mass, indicating that star formation is mainly regulated by local feedback processes. The b-parameter strongly depends on burst age. Values close to b = 60 are found at ages approximately 10 Myr, while almost no starbursts are found at ages greater than 1 Gyr. The median baryonic burst mass fraction of sub-L galaxies is 5% and decreases slowly towards high masses. The median mass fraction of the recent burst in the postburst sample is 5-10%. A smaller fraction of the postburst galaxies, however, originates in non-bursting galaxies. The age-mass distribution of the postburst progenitors (with mass fractions is greater than 3%) is bimodal with a break at logM(solar mass

  3. Which String Breaks? Revisited

    NASA Astrophysics Data System (ADS)

    Frye, Christopher

    2011-03-01

    Many have seen the common introductory physics demonstration in which a heavy ball hangs from a string, with another identical string hanging freely from the ball. When the instructor pulls the bottom string slowly, the top string breaks. However, when the instructor pulls the bottom string very rapidly, the bottom string breaks. This simple experiment is used to demonstrate inertia and Newton's laws. In The Physics Teacher of November 1996, there is an article in which the authors create a model of this problem in an attempt to explain the outcomes quantitatively. However, their analysis gave strange results. Using an improved model, I will show that the results of this demonstration can be obtained using only simple calculations. This work was funded by a RAMP grant from the University of Central Florida.

  4. Shaping galaxy evolution with galaxy structure

    NASA Astrophysics Data System (ADS)

    Cheung, Edmond

    A fundamental pursuit of astronomy is to understand galaxy evolution. The enormous scales and complex physics involved in this endeavor guarantees a never-ending journey that has enamored both astronomers and laymen alike. But despite the difficulty of this task, astronomers have still attempted to further this goal. Among of these astronomers is Edwin Hubble. His work, which includes the famous Hubble sequence, has immeasurably influenced our understanding of galaxy evolution. In this thesis, we present three works that continues Hubble's line of study by using galaxy structure to learn about galaxy evolution. First, we examine the dependence of galaxy quiescence on inner galactic structure with the AEGIS/ DEEP2 survey at 0.5In this thesis, we present three works that continues Hubble's line of study by using galaxy structure to learn about galaxy evolution. First, we examine the dependence of galaxy quiescence on inner galactic structure with the AEGIS/ DEEP2 survey at 0.5galaxies from quiescent galaxies. Our method indicates that the inner stellar mass is the most correlated parameter of quenching, implying that the process that quenches galaxies must also buildup their inner structure. Second, we explore the relationship between galactic bars and their host galaxies with Galaxy Zoo 2 at z˜0. The correlations of bar properties and galaxy properties are consistent with simulations of bar formation and evolution, indicating that bars affect their host galaxies. Finally, we investigate whether bars can drive supermassive black hole growth with data from Chandra and Galaxy Zoo: Hubble at 0.2galaxies to a matched sample of inactive, control galaxies shows that there is no statistically significant excess of bars in active hosts. Our result shows that bars are not the primary fueling mechanism of supermassive black hole

  5. Predicting appointment breaking.

    PubMed

    Bean, A G; Talaga, J

    1995-01-01

    The goal of physician referral services is to schedule appointments, but if too many patients fail to show up, the value of the service will be compromised. The authors found that appointment breaking can be predicted by the number of days to the scheduled appointment, the doctor's specialty, and the patient's age and gender. They also offer specific suggestions for modifying the marketing mix to reduce the incidence of no-shows. PMID:10142384

  6. Submillimeter Galaxies

    NASA Astrophysics Data System (ADS)

    Blain, A. W.

    2009-12-01

    The Universe was a more exciting place at moderate to high redshifts z˜3, after reionization took place, but before the present day galaxy properties were firmly established. From a wide variety of directions, we are gaining insight into the Universe at these epochs. Less gas was sequestered into stars and had been ejected into the interstellar medium as weakly emitting, slowly cooling debris, because a significant amount of star formation and supermassive blackhole growth in active galactic nuclei (AGNs) was still to occur. Furthermore, the processes that shape today’s galaxies were at work, and can be seen in real time with the appropriate tools. The most active regions of galaxies at these redshifts are deeply obscured at ultraviolet and optical wavelengths by an opaque interstellar medium (ISM) that absorbs most of their radiation, and then re-emits at far-infrared (IR) wavelengths. This emission provides us with a very powerful probe of the regions within galaxies where the most intense activity takes place; both their total energy output, and from spectroscopy, about the physics and chemistry of the atomic and molecular gas that fuels, hides and surrounds these regions. This information is unique, but not complete: radio, mid- and near-IR, optical and X-ray observations each provide unique complementary views. Nevertheless, probing the obscured Universe, with the Atacama Large (Sub-)Millimeter Array (ALMA), James Webb Space Telescope (JWST), Herschel Space Observatory, Wide Field Infrared Survey Explorer (WISE), and missions and telescopes that are not yet in construction, like an actively cooled sub-10-m class IR space telescope and a 25-m class ground-based submillimeter/THz telescope (CCAT) will provide a more complete picture of in which neighborhoods, by what means and how quickly the most vigorous bursts of activity take place.

  7. Dwarf spheroidal galaxies: Keystones of galaxy evolution

    NASA Technical Reports Server (NTRS)

    Gallagher, John S., III; Wyse, Rosemary F. G.

    1994-01-01

    Dwarf spheroidal galaxies are the most insignificant extragalactic stellar systems in terms of their visibility, but potentially very significant in terms of their role in the formation and evolution of much more luminous galaxies. We discuss the present observational data and their implications for theories of the formation and evolution of both dwarf and giant galaxies. The putative dark-matter content of these low-surface-brightness systems is of particular interest, as is their chemical evolution. Surveys for new dwarf spheroidals hidden behind the stars of our Galaxy and those which are not bound to giant galaxies may give new clues as to the origins of this unique class of galaxy.

  8. THE PROPERTIES OF TYPE Ia SUPERNOVA HOST GALAXIES FROM THE SLOAN DIGITAL SKY SURVEY

    SciTech Connect

    Han, Du-Hwan; Park, Myeong-Gu; Park, Changbom; Choi, Yun-Young E-mail: mgp@knu.ac.k E-mail: yychoi@khu.ac.k

    2010-11-20

    We investigate the properties and environments of Type Ia Supernova (SN Ia) host galaxies in the Stripe 82 of the Sloan Digital Sky Survey-II Supernova Survey centered on the celestial equator. Host galaxies are defined as the galaxy nearest to the supernova (SN) in terms of angular distance whose velocity difference from the SN is less than 1000 km s{sup -1}. Eighty seven SN Ia host galaxies are selected from the SDSS Main galaxy sample with the apparent r-band magnitude m{sub r} < 17.77, and compared with the SDSS Main galaxies. The SN Ia rates for early- and late-type galaxies are 0.81 {+-} 0.19 SN (100 yr){sup -1} and 0.99 {+-} 0.21 SN (100 yr){sup -1}, respectively. We find that the host galaxies have a color distribution consistent with that of the Main galaxies, regardless of their morphology. However, host galaxies are on average brighter than the Main galaxies by {approx}0.3 mag over the range of -18.3>M{sub r} > - 21.3. But the brighter ends of their luminosity distributions are similar. The distribution of the distance to the nearest neighbor galaxy shows that SNe Ia are more likely to occur in isolated galaxies without close neighbors. We also find that the SN Ia host galaxies are preferentially located in a region close to massive galaxy clusters compared to the Main galaxies.

  9. RADIO GALAXY FEEDBACK IN X-RAY-SELECTED GROUPS FROM COSMOS: THE EFFECT ON THE INTRACLUSTER MEDIUM

    SciTech Connect

    Giodini, S.; Finoguenov, A.; Boehringer, H.; Pierini, D.; Smolcic, V.; Massey, R.; BIrzan, L.; Zamorani, G.; Oklopcic, A.; Pratt, G. W.; Koekemoer, A. M.; Salvato, M.; Sanders, D. B.; Kartaltepe, J. S.; Thompson, D.

    2010-05-01

    We quantify the importance of the mechanical energy released by radio galaxies inside galaxy groups. We use scaling relations to estimate the mechanical energy released by 16 radio-active galactic nuclei located inside X-ray-detected galaxy groups in the COSMOS field. By comparing this energy output to the host groups' gravitational binding energy, we find that radio galaxies produce sufficient energy to unbind a significant fraction of the intragroup medium. This unbinding effect is negligible in massive galaxy clusters with deeper potential wells. Our results correctly reproduce the breaking of self-similarity observed in the scaling relation between entropy and temperature for galaxy groups.

  10. A study of massive and evolved galaxies at high redshift

    SciTech Connect

    Nayyeri, H.; Mobasher, B.; Hemmati, S.; De Barros, S.; Ferguson, H. C.; Wiklind, T.; Dahlen, T.; Kassin, S.; Koekemoer, A.; Dickinson, M.; Giavalisco, M.; Fontana, A.; Paris, D.; Ashby, M.; Willner, S.; Barro, G.; Guo, Y.; Hathi, N. P.; Dunlop, J. S.; Targett, T. A.

    2014-10-10

    We use data taken as part of Hubble Space Telescope (HST)/Wide Field Camera 3 (WFC3) observations of the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) to identify massive and evolved galaxies at 3 < z < 4.5. This is performed using the strength of the Balmer break feature at rest-frame 3648 Å, which is a diagnostic of the age of the stellar population in galaxies. Using the WFC3 H-band-selected catalog for the CANDELS GOODS-S field and deep multi-waveband photometry from optical (HST) to mid-infrared (Spitzer) wavelengths, we identify a population of old and evolved post-starburst galaxies based on the strength of their Balmer breaks (Balmer break galaxies, BBGs). The galaxies are also selected to be bright in rest-frame near-IR wavelengths and hence massive. We identify a total of 16 BBGs. Fitting the spectral energy distribution of the BBGs shows that the candidate galaxies have average estimated ages of ∼800 Myr and average stellar masses of ∼5 × 10{sup 10} M {sub ☉}, consistent with being old and massive systems. Two of our BBG candidates are also identified by the criteria that are sensitive to star-forming galaxies (Lyman break galaxy selection). We find a number density of ∼3.2 × 10{sup –5} Mpc{sup –3} for the BBGs, corresponding to a mass density of ∼2.0 × 10{sup 6} M {sub ☉} Mpc{sup –3} in the redshift range covering the survey. Given the old age and the passive evolution, it is argued that some of these objects formed the bulk of their mass only a few hundred million years after the big bang.

  11. Secular Evolution in Disk Galaxies

    NASA Astrophysics Data System (ADS)

    Kormendy, John

    2013-10-01

    Self-gravitating systems evolve toward the most tightly bound configuration that is reachable via the evolution processes that are available to them. They do this by spreading -- the inner parts shrink while the outer parts expand -- provided that some physical process efficiently transports energy or angular momentum outward. The reason is that self-gravitating systems have negative specific heats. As a result, the evolution of stars, star clusters, protostellar and protoplanetary disks, black hole accretion disks and galaxy disks are fundamentally similar. How evolution proceeds then depends on the evolution processes that are available to each kind of self-gravitating system. These processes and their consequences for galaxy disks are the subjects of my lectures and of this Canary Islands Winter School. I begin with a review of the formation, growth and death of bars. Then I review the slow (`secular') rearrangement of energy, angular momentum, and mass that results from interactions between stars or gas clouds and collective phenomena such as bars, oval disks, spiral structure and triaxial dark haloes. The `existence-proof' phase of this work is largely over: we have a good heuristic understanding of how nonaxisymmetric structures rearrange disk gas into outer rings, inner rings and stuff dumped onto the centre. The results of simulations correspond closely to the morphology of barred and oval galaxies. Gas that is transported to small radii reaches high densities. Observations confirm that many barred and oval galaxies have dense central concentrations of gas and star formation. The result is to grow, on timescales of a few Gyr, dense central components that are frequently mistaken for classical (elliptical-galaxy-like) bulges but that were grown slowly out of the disk (not made rapidly by major mergers). The resulting picture of secular galaxy evolution accounts for the richness observed in galaxy structure. We can distinguish between classical and pseudo

  12. Local Analogs for High-redshift Galaxies: Resembling the Physical Conditions of the Interstellar Medium in High-redshift Galaxies

    NASA Astrophysics Data System (ADS)

    Bian, Fuyan; Kewley, Lisa J.; Dopita, Michael A.; Juneau, Stephanie

    2016-05-01

    We present a sample of local analogs for high-redshift galaxies selected in the Sloan Digital Sky Survey (SDSS). The physical conditions of the interstellar medium (ISM) in these local analogs resemble those in high-redshift galaxies. These galaxies are selected based on their positions in the [O iii]/Hβ versus [N ii]/Hα nebular emission-line diagnostic diagram. We show that these local analogs share similar physical properties with high-redshift galaxies, including high specific star formation rates (sSFRs), flat UV continuums, and compact galaxy sizes. In particular, the ionization parameters and electron densities in these analogs are comparable to those in z ≃ 2–3 galaxies, but higher than those in normal SDSS galaxies by ≃0.6 dex and ≃0.9 dex, respectively. The mass–metallicity relation (MZR) in these local analogs shows ‑0.2 dex offset from that in SDSS star-forming galaxies at the low-mass end, which is consistent with the MZR of the z˜ 2{--}3 galaxies. We compare the local analogs in this study with those in other studies, including Lyman break analogs (LBA) and green pea (GP) galaxies. The analogs in this study share a similar star formation surface density with LBAs, but the ionization parameters and electron density in our analogs are higher than those in LBAs by factors of 1.5 and 3, respectively. The analogs in this study have comparable ionization parameters and electron densities to the GP galaxies, but our method can select galaxies in a wider redshift range. We find the high sSFR and SFR surface density can increase the electron density and ionization parameters, but still cannot fully explain the difference in ISM condition between nearby galaxies and the local analogs/high-redshift galaxies.

  13. Local Analogs for High-redshift Galaxies: Resembling the Physical Conditions of the Interstellar Medium in High-redshift Galaxies

    NASA Astrophysics Data System (ADS)

    Bian, Fuyan; Kewley, Lisa J.; Dopita, Michael A.; Juneau, Stephanie

    2016-05-01

    We present a sample of local analogs for high-redshift galaxies selected in the Sloan Digital Sky Survey (SDSS). The physical conditions of the interstellar medium (ISM) in these local analogs resemble those in high-redshift galaxies. These galaxies are selected based on their positions in the [O iii]/Hβ versus [N ii]/Hα nebular emission-line diagnostic diagram. We show that these local analogs share similar physical properties with high-redshift galaxies, including high specific star formation rates (sSFRs), flat UV continuums, and compact galaxy sizes. In particular, the ionization parameters and electron densities in these analogs are comparable to those in z ≃ 2–3 galaxies, but higher than those in normal SDSS galaxies by ≃0.6 dex and ≃0.9 dex, respectively. The mass–metallicity relation (MZR) in these local analogs shows ‑0.2 dex offset from that in SDSS star-forming galaxies at the low-mass end, which is consistent with the MZR of the z∼ 2{--}3 galaxies. We compare the local analogs in this study with those in other studies, including Lyman break analogs (LBA) and green pea (GP) galaxies. The analogs in this study share a similar star formation surface density with LBAs, but the ionization parameters and electron density in our analogs are higher than those in LBAs by factors of 1.5 and 3, respectively. The analogs in this study have comparable ionization parameters and electron densities to the GP galaxies, but our method can select galaxies in a wider redshift range. We find the high sSFR and SFR surface density can increase the electron density and ionization parameters, but still cannot fully explain the difference in ISM condition between nearby galaxies and the local analogs/high-redshift galaxies.

  14. 76 FR 61760 - Post Office Closing

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-10-05

    ... [Docket No. A2011-88; Order No. 880 Post Office Closing AGENCY: Postal Regulatory Commission. ACTION... post office has been filed. It identifies preliminary steps and provides a procedural schedule... received a petition for review of the Postal Service's determination to close the Breaks post office...

  15. BOOK REVIEW: Symmetry Breaking

    NASA Astrophysics Data System (ADS)

    Ryder, L. H.

    2005-11-01

    One of the most fruitful and enduring advances in theoretical physics during the last half century has been the development of the role played by symmetries. One needs only to consider SU(3) and the classification of elementary particles, the Yang Mills enlargement of Maxwell's electrodynamics to the symmetry group SU(2), and indeed the tremendous activity surrounding the discovery of parity violation in the weak interactions in the late 1950s. This last example is one of a broken symmetry, though the symmetry in question is a discrete one. It was clear to Gell-Mann, who first clarified the role of SU(3) in particle physics, that this symmetry was not exact. If it had been, it would have been much easier to discover; for example, the proton, neutron, Σ, Λ and Ξ particles would all have had the same mass. For many years the SU(3) symmetry breaking was assigned a mathematical form, but the importance of this formulation fell away when the quark model began to be taken seriously; the reason the SU(3) symmetry was not exact was simply that the (three, in those days) quarks had different masses. At the same time, and in a different context, symmetry breaking of a different type was being investigated. This went by the name of `spontaneous symmetry breaking' and its characteristic was that the ground state of a given system was not invariant under the symmetry transformation, though the interactions (the Hamiltonian, in effect) was. A classic example is ferromagnetism. In a ferromagnet the atomic spins are aligned in one direction only—this is the ground state of the system. It is clearly not invariant under a rotation, for that would change the ground state into a (similar but) different one, with the spins aligned in a different direction; this is the phenomenon of a degenerate vacuum. The contribution of the spin interaction, s1.s2, to the Hamiltonian, however, is actually invariant under rotations. As Coleman remarked, a little man living in a ferromagnet would

  16. Galaxies Collide to Create Hot, Huge Galaxy

    NASA Technical Reports Server (NTRS)

    2009-01-01

    This image of a pair of colliding galaxies called NGC 6240 shows them in a rare, short-lived phase of their evolution just before they merge into a single, larger galaxy. The prolonged, violent collision has drastically altered the appearance of both galaxies and created huge amounts of heat turning NGC 6240 into an 'infrared luminous' active galaxy.

    A rich variety of active galaxies, with different shapes, luminosities and radiation profiles exist. These galaxies may be related astronomers have suspected that they may represent an evolutionary sequence. By catching different galaxies in different stages of merging, a story emerges as one type of active galaxy changes into another. NGC 6240 provides an important 'missing link' in this process.

    This image was created from combined data from the infrared array camera of NASA's Spitzer Space Telescope at 3.6 and 8.0 microns (red) and visible light from NASA's Hubble Space Telescope (green and blue).

  17. Galaxy NGC 55

    NASA Technical Reports Server (NTRS)

    2003-01-01

    This image of the nearby edge-on spiral galaxy NGC 55 was taken by Galaxy Evolution Explorer on September 14, 2003, during 2 orbits. This galaxy lies 5.4 million light years from our Milky Way galaxy and is a member of the 'local group' of galaxies that also includes the Andromeda galaxy (M31), the Magellanic clouds, and 40 other galaxies. The spiral disk of NGC 55 is inclined to our line of sight by approximately 80 degrees and so this galaxy looks cigar-shaped. This picture is a combination of Galaxy Evolution Explorer images taken with the far ultraviolet (colored blue) and near ultraviolet detectors, (colored red). The bright blue regions in this image are areas of active star formation detected in the ultraviolet by Galaxy Evolution Explorer. The red stars in this image are foreground stars in our own Milky Way galaxy.

  18. Atmospheric noise of a breaking tidal bore.

    PubMed

    Chanson, Hubert

    2016-01-01

    A tidal bore is a surge of waters propagating upstream in an estuary as the tidal flow turns to rising and the flood tide propagates into a funnel-shaped system. Large tidal bores have a marked breaking roller. The sounds generated by breaking tidal bores were herein investigated in the field (Qiantang River) and in laboratory. The sound pressure record showed two dominant periods, with some similarity with an earlier study [Chanson (2009). J. Acoust. Soc. Am. 125(6), 3561-3568]. The two distinct phases were the incoming tidal bore when the sound amplitude increased with the approaching bore, and the passage of the tidal bore in front of the microphone when loud and powerful noises were heard. The dominant frequency ranged from 57 to 131 Hz in the Qiantang River bore. A comparison between laboratory and prototype tidal bores illustrated both common features and differences. The low pitch sound of the breaking bore had a dominant frequency close to the collective oscillations of bubble clouds, which could be modeled with a bubble cloud model using a transverse dimension of the bore roller. The findings suggest that this model might be over simplistic in the case of a powerful breaking bore, like that of the Qiantang River. PMID:26827000

  19. Breaking a vicious cycle.

    PubMed

    Hayes, Daniel F; Allen, Jeff; Compton, Carolyn; Gustavsen, Gary; Leonard, Debra G B; McCormack, Robert; Newcomer, Lee; Pothier, Kristin; Ransohoff, David; Schilsky, Richard L; Sigal, Ellen; Taube, Sheila E; Tunis, Sean R

    2013-07-31

    Despite prodigious advances in tumor biology research, few tumor-biomarker tests have been adopted as standard clinical practice. This lack of reliable tests stems from a vicious cycle of undervaluation, resulting from inconsistent regulatory standards and reimbursement, as well as insufficient investment in research and development, scrutiny of biomarker publications by journals, and evidence of analytical validity and clinical utility. We offer recommendations designed to serve as a roadmap to break this vicious cycle and call for a national dialogue, as changes in regulation, reimbursement, investment, peer review, and guidelines development require the participation of all stakeholders. PMID:23903752

  20. Ion wave breaking acceleration

    NASA Astrophysics Data System (ADS)

    Liu, B.; Meyer-ter-Vehn, J.; Bamberg, K.-U.; Ma, W. J.; Liu, J.; He, X. T.; Yan, X. Q.; Ruhl, H.

    2016-07-01

    Laser driven ion wave breaking acceleration (IWBA) in plasma wakefields is investigated by means of a one-dimensional (1D) model and 1D/3D particle-in-cell (PIC) simulations. IWBA operates in relativistic transparent plasma for laser intensities in the range of 1020- 1023 W /cm2 . The threshold for IWBA is identified in the plane of plasma density and laser amplitude. In the region just beyond the threshold, self-injection takes place only for a fraction of ions and in a limited time period. This leads to well collimated ion pulses with peaked energy spectra, in particular for 3D geometry.

  1. Multicolor surface photometry of powerful radio galaxies

    SciTech Connect

    Smith, E.P.

    1988-01-01

    CCD images of 72 powerful radio galaxies have been obtained with the KPNO 2.1m, 4m and CTIO 4m telescopes utilizing B, V, and R filters to study the colors and other photometric properties of these large systems. The GASP software package was used for the data reduction and detailed 2-d surface photometry. In addition, image modeling techniques were employed to investigate the contributions to galaxy properties by point-like nuclear sources seen in some of these galaxies. It was found that powerful radio galaxies show a much higher frequency than normal bright ellipticals of having optical morphologies which deviate from elliptical symmetry. Approximately 50% of the sample exhibit non-elliptically symmetric isophotes. These prominent distortions are present at surface brightness levels of {le} 25 V mag/(arc sec){sup 2}. In addition, a large fraction ({approximately}50%) of the remaining radio galaxies without the aforementioned morphological peculiarities have large isophotal twists ({Delta}P.A. {ge} 10{degree}) or ellipticity gradients. Significantly {approximately}50% of the galaxies with strong optical emission lines in their spectra display optically peculiar structures very similar to those found by Toomre and Toomre (1972) in their simulations of interacting disk galaxies. The galaxies with weak emission lines in their spectra are less frequently ({approximately}10%) distorted from elliptical shape. Those that are exhibit features like isophote twists, double nuclei and close companion galaxies embedded in the radio galaxy optical isophotes. The (B-V) colors of many of the powerful radio galaxies with strong emission lines are blue relative to normal giant ellipticals at the same redshift.

  2. The DEEP2 Galaxy Redshift Survey: Clustering of Galaxies in Early Data

    NASA Astrophysics Data System (ADS)

    Coil, Alison L.; Davis, Marc; Madgwick, Darren S.; Newman, Jeffrey A.; Conselice, Christopher J.; Cooper, Michael; Ellis, Richard S.; Faber, S. M.; Finkbeiner, Douglas P.; Guhathakurta, Puragra; Kaiser, Nick; Koo, David C.; Phillips, Andrew C.; Steidel, Charles C.; Weiner, Benjamin J.; Willmer, Christopher N. A.; Yan, Renbin

    2004-07-01

    We measure the two-point correlation function ξ(rp,π) in a sample of 2219 galaxies between z=0.7 and 1.35 to a magnitude limit of RAB=24.1 from the first season of the DEEP2 Galaxy Redshift Survey. From ξ(rp,π) we recover the real-space correlation function, ξ(r), which we find can be approximated within the errors by a power law, ξ(r)=(r/r0)-γ, on scales ~0.1-10 h-1 Mpc. In a sample with an effective redshift of zeff=0.82, for a ΛCDM cosmology we find r0=3.53+/-0.81 h-1 Mpc (comoving) and γ=1.66+/-0.12, while in a higher redshift sample with zeff=1.14 we find r0=3.12+/-0.72 h-1 Mpc and γ=1.66+/-0.12. These errors are estimated from mock galaxy catalogs and are dominated by the cosmic variance present in the current data sample. We find that red, absorption-dominated, passively evolving galaxies have a larger clustering scale length, r0, than blue, emission-line, actively star-forming galaxies. Intrinsically brighter galaxies also cluster more strongly than fainter galaxies at z~=1. Our results imply that the DEEP2 galaxies have an effective bias b=0.96+/-0.13 if σ8DM=1 today or b=1.19+/-0.16 if σ8DM=0.8 today. This bias is lower than that predicted by semianalytic simulations at z~=1, which may be the result of our R-band target selection. We discuss possible evolutionary effects within our survey volume, and we compare our results with galaxy-clustering studies at other redshifts, noting that our star-forming sample at z~=1 has selection criteria very similar to the Lyman break galaxies at z~=3 and that our red, absorption-line sample displays a clustering strength comparable to the expected clustering of the Lyman break galaxy descendants at z~=1. Our results demonstrate that galaxy-clustering properties as a function of color, spectral type, and luminosity seen in the local universe were largely in place by z~=1.

  3. Enhancement of galaxy images for improved classification

    NASA Astrophysics Data System (ADS)

    Jenkinson, John; Grigoryan, Artyom M.; Agaian, Sos S.

    2015-03-01

    In this paper, the classification accuracy of galaxy images is demonstrated to be improved by enhancing the galaxy images. Galaxy images often contain faint regions that are of similar intensity to stars and the image background, resulting in data loss during background subtraction and galaxy segmentation. Enhancement darkens these faint regions, enabling them to be distinguished from other objects in the image and the image background, relative to their original intensities. The heap transform is employed for the purpose of enhancement. Segmentation then produces a galaxy image which closely resembles the structure of the original galaxy image, and one that is suitable for further processing and classification. 6 Morphological feature descriptors are applied to the segmented images after a preprocessing stage and used to extract the galaxy image structure for use in training the classifier. The support vector machine learning algorithm performs training and validation of the original and enhanced data, and a comparison between the classification accuracy of each data set is included. Principal component analysis is used to compress the data sets for the purpose of classification visualization and a comparison between the reduced and original feature spaces. Future directions for this research include galaxy image enhancement by various methods, and classification performed with the use of a sparse dictionary. Both future directions are introduced.

  4. APEX Snaps First Close-up of Star Factories in Distant Universe

    NASA Astrophysics Data System (ADS)

    2010-03-01

    For the first time, astronomers have made direct measurements of the size and brightness of regions of star-birth in a very distant galaxy, thanks to a chance discovery with the APEX telescope. The galaxy is so distant, and its light has taken so long to reach us, that we see it as it was 10 billion years ago. A cosmic "gravitational lens" is magnifying the galaxy, giving us a close-up view that would otherwise be impossible. This lucky break reveals a hectic and vigorous star-forming life for galaxies in the early Universe, with stellar nurseries forming one hundred times faster than in more recent galaxies. The research is published online today in the journal Nature. Astronomers were observing a massive galaxy cluster [1] with the Atacama Pathfinder Experiment (APEX) telescope, using submillimetre wavelengths of light, when they found a new and uniquely bright galaxy, more distant than the cluster and the brightest very distant galaxy ever seen at submillimetre wavelengths. It is so bright because the cosmic dust grains in the galaxy are glowing after being heated by starlight. The new galaxy has been given the name SMM J2135-0102. "We were stunned to find a surprisingly bright object that wasn't at the expected position. We soon realised it was a previously unknown and more distant galaxy being magnified by the closer galaxy cluster," says Carlos De Breuck from ESO, a member of the team. De Breuck was making the observations at the APEX telescope on the plateau of Chajnantor at an altitude of 5000 m in the Chilean Andes. The new galaxy SMM J2135-0102 is so bright because of the massive galaxy cluster that lies in the foreground. The vast mass of this cluster bends the light of the more distant galaxy, acting as a gravitational lens [2]. As with a telescope, it magnifies and brightens our view of the distant galaxy. Thanks to a fortuitous alignment between the cluster and the distant galaxy, the latter is strongly magnified by a factor of 32. "The magnification

  5. SAMI Galaxy Survey: Spectrally Dissecting 3400 Galaxies By the Dozen

    NASA Astrophysics Data System (ADS)

    Cecil, Gerald N.; Croom, S.; The SAMI Galaxy Survey Team

    2014-01-01

    More than 440 mapped, less than 3000 to go in the Sydney-AAO Multi-object IFU (SAMI) Galaxy Survey! SAMI uses novel, photonic fused-optical fiber “hexabundles” that were developed successfully at The University of Sydney and the Australian Astronomical Observatory AAO), with support from the Australian Research Council Centre of Excellence for All-Sky Astrophysics (CAASTRO). The SAMI Galaxy Survey, led by Assoc. Prof. Croom, is backed by an international team. This spectro-bolometric survey mitigates against “aperture effects” that may mislead when stacking single-fiber galaxy spectra. We seek to answer questions such as “what is the physical role of environment in galaxy evolution? How is stellar mass growth and angular momentum development related in galaxies? How does gas get into and out of galaxies, and how do such flows drive star formation?” SAMI maps stellar and gas properties with 13 integral-field units (IFU) plugged onto a dozen galaxies over the 1° field of the AAT prime-focus corrector. 78% of each bundle's area is filled by sixty-one 1.6-arcsec diameter fibers that are packed closely into concentric circles then their etched, thinned cladding is fused without deforming their cores. The fiber hexabundles route to the bench-mounted AAOmega double-beam spectrograph to cover simultaneously 373-570 nm at R=1730 and 620-735 nm at R=4500. Full spatial resolution of the observing site is recovered by dithered exposures totaling 3.5 hours per field. Target stellar masses generally exceed 108 M⊙, and span a range of environments: ˜650 are within clusters of virial mass 1014-15 M⊙ at 0.03 < z < 0.06, the rest are in the z < 0.1 field with extensive frequency data ancillary to the GAMA Survey. We display some key early results of major science themes being addressed by the SAMI survey team, from rotation curve dependence on group halo mass, through galaxy winds and AGN feedback mechanisms, to oxygen abundance gradients, kinematic decomposition

  6. Mapping stellar content to dark matter haloes using galaxy clustering and galaxy-galaxy lensing in the SDSS DR7

    NASA Astrophysics Data System (ADS)

    Zu, Ying; Mandelbaum, Rachel

    2015-12-01

    The mapping between the distributions of the observed galaxy stellar mass and the underlying dark matter haloes provides the crucial link from theories of large-scale structure formation to interpreting the complex phenomena of galaxy formation and evolution. We develop a novel statistical method, based on the halo occupation distribution (HOD) model, to solve for this mapping by jointly fitting the galaxy clustering and the galaxy-galaxy lensing from the Sloan Digital Sky Survey (SDSS). The method, called the iHOD model, extracts maximum information from the survey by including ˜80 per cent more galaxies than the traditional HOD methods, accounting for the incompleteness of the stellar mass samples self-consistently. The derived stellar-to-halo mass relation (SHMR) explains the clustering and lensing of SDSS galaxies over four decades in stellar mass, while successfully predicting the observed stellar mass functions (SMFs). By modelling significantly more galaxies, the iHOD breaks the degeneracy between the logarithmic scatter in the stellar mass at fixed halo mass and the slope of the mean SHMR at high masses, without assuming a strong prior on the scatter and/or using the SMF as an input. We detect a decline of the scatter with halo mass, from 0.22_{-0.01}^{+0.02} dex below 1012 h-1 M⊙ to 0.18 ± 0.01 dex at 1014 h-1 M⊙. The model predicts a departure of satellite SMFs from the Schechter form in massive haloes and a linear scaling of satellite number with halo mass. The iHOD model can be easily applied to other spectroscopic data sets, greatly improving statistical constraints on the SHMR compared to traditional HOD methods within the same survey.

  7. Spontaneous breaking of supersymmetry

    SciTech Connect

    Zumino, B.

    1981-12-01

    There has been recently a revival of interest in supersymmetric gauge theories, stimulated by the hope that supersymmetry might help in clarifying some of the questions which remain unanswered in the so called Grand Unified Theories and in particular the gauge hierarchy problem. In a Grand Unified Theory one has two widely different mass scales: the unification mass M approx. = 10/sup 15/GeV at which the unification group (e.g. SU(5)) breaks down to SU(3) x SU(2) x U(1) and the mass ..mu.. approx. = 100 GeV at which SU(2) x U(1) is broken down to the U(1) of electromagnetism. There is at present no theoretical understanding of the extreme smallness of the ratio ..mu../M of these two numbers. This is the gauge hierarchy problem. This lecture attempts to review the various mechanisms for spontaneous supersymmetry breaking in gauge theories. Most of the discussions are concerned with the tree approximation, but what is presently known about radiative correction is also reviewed.

  8. Galaxy Groups

    NASA Astrophysics Data System (ADS)

    Tully, R. Brent

    2015-02-01

    Galaxy groups can be characterized by the radius of decoupling from cosmic expansion, the radius of the caustic of second turnaround, and the velocity dispersion of galaxies within this latter radius. These parameters can be a challenge to measure, especially for small groups with few members. In this study, results are gathered pertaining to particularly well-studied groups over four decades in group mass. Scaling relations anticipated from theory are demonstrated and coefficients of the relationships are specified. There is an update of the relationship between light and mass for groups, confirming that groups with mass of a few times {{10}12}{{M}⊙ } are the most lit up while groups with more and less mass are darker. It is demonstrated that there is an interesting one-to-one correlation between the number of dwarf satellites in a group and the group mass. There is the suggestion that small variations in the slope of the luminosity function in groups are caused by the degree of depletion of intermediate luminosity systems rather than variations in the number per unit mass of dwarfs. Finally, returning to the characteristic radii of groups, the ratio of first to second turnaround depends on the dark matter and dark energy content of the universe and a crude estimate can be made from the current observations of {{Ω}matter}˜ 0.15 in a flat topology, with a 68% probability of being less than 0.44.

  9. Galaxy groups

    SciTech Connect

    Brent Tully, R.

    2015-02-01

    Galaxy groups can be characterized by the radius of decoupling from cosmic expansion, the radius of the caustic of second turnaround, and the velocity dispersion of galaxies within this latter radius. These parameters can be a challenge to measure, especially for small groups with few members. In this study, results are gathered pertaining to particularly well-studied groups over four decades in group mass. Scaling relations anticipated from theory are demonstrated and coefficients of the relationships are specified. There is an update of the relationship between light and mass for groups, confirming that groups with mass of a few times 10{sup 12}M{sub ⊙} are the most lit up while groups with more and less mass are darker. It is demonstrated that there is an interesting one-to-one correlation between the number of dwarf satellites in a group and the group mass. There is the suggestion that small variations in the slope of the luminosity function in groups are caused by the degree of depletion of intermediate luminosity systems rather than variations in the number per unit mass of dwarfs. Finally, returning to the characteristic radii of groups, the ratio of first to second turnaround depends on the dark matter and dark energy content of the universe and a crude estimate can be made from the current observations of Ω{sub matter}∼0.15 in a flat topology, with a 68% probability of being less than 0.44.

  10. Application of break preclusion concept in German nuclear power plants

    SciTech Connect

    Roos, E.; Maier, V.; Nagel, G.

    1997-04-01

    The break preclusion concept is based on {open_quotes}KTA rules{close_quotes}, {open_quotes}RSK guidelines{close_quotes} and {open_quotes}Rahmenspeziflkation Basissicherheit{close_quotes}. These fundamental rules containing for example requirements on material, design, calculation, manufacturing and testing procedures are explained and the technical realisation is shown by means of examples. The proof of the quality of these piping systems can be executed by means of fracture mechanics calculations by showing that in every case the leakage monitoring system already detect cracks which are clearly smaller than the critical crack. Thus the leak before break behavior and the break preclusion concept is implicitly affirmed. In order to further diminish conservativities in the fracture mechanics procedures, specific research projects are executed which are explained in this contribution.

  11. Interpreting the Clustering of Distant Red Galaxies

    SciTech Connect

    Tinker, Jeremy L.; Wechsler, Risa H.; Zheng, Zheng; /Princeton, Inst. Advanced Study

    2009-08-03

    We analyze the angular clustering of z {approx} 2.3 distant red galaxies (DRGs) measured by Quadri et al. (2008). We find that, with robust estimates of the measurement errors and realistic halo occupation distribution modeling, the measured clustering can be well fit within standard halo occupation models, in contrast to previous results. However, in order to fit the strong break in w({theta}) at {theta} = 10{double_prime}, nearly all satellite galaxies in the DRG luminosity range are required to be DRGs. Within this luminosity-threshold sample, the fraction of galaxies that are DRGs is {approx} 44%, implying that the formation of DRGs is more efficient for satellite galaxies than for central galaxies. Despite the evolved stellar populations contained within DRGs at z = 2.3, 90% of satellite galaxies in the DRG luminosity range have been accreted within 500 Myr. Thus, satellite DRGs must have known they would become satellites well before the time of their accretion. This implies that the formation of DRGs correlates with large-scale environment at fixed halo mass, although the large-scale bias of DRGs can be well fit without such assumptions. Further data are required to resolve this issue. Using the observational estimate that {approx} 30% of DRGs have no ongoing star formation, we infer a timescale for star formation quenching for satellite galaxies of 450 Myr, although the uncertainty on this number is large. However, unless all non-star forming satellite DRGs were quenched before accretion, the quenching timescale is significantly shorter than z {approx} 0 estimates. Down to the completeness limit of the Quadri et al sample, we find that the halo masses of central DRGs are {approx} 50% higher than non-DRGs in the same luminosity range, but at the highest halo masses the central galaxies are DRGs only {approx} 2/3 of the time.

  12. Interpreting the Clustering of Distant Red Galaxies

    NASA Astrophysics Data System (ADS)

    Tinker, Jeremy L.; Wechsler, Risa H.; Zheng, Zheng

    2010-01-01

    We analyze the angular clustering of z ~ 2.3 distant red galaxies (DRGs) measured by Quardi et al. We find that, with robust estimates of the measurement errors and realistic halo occupation distribution modeling, the measured clustering can be well fit within standard halo occupation models, in contrast to previous results. However, in order to fit the strong break in w(θ) at θ = 10'', nearly all satellite galaxies in the DRG luminosity range are required to be DRGs. Within this luminosity-threshold sample, the fraction of galaxies that are DRGs is ~44%, implying that the formation of DRGs is more efficient for satellite galaxies than for central galaxies. Despite the evolved stellar populations contained within DRGs at z = 2.3, 90% of satellite galaxies in the DRG luminosity range have been accreted within 500 Myr. Thus, satellite DRGs must have known they would become satellites well before the time of their accretion. This implies that the formation of DRGs correlates with large-scale environment at fixed halo mass, although the large-scale bias of DRGs can be well fit without such assumptions. Further data are required to resolve this issue. Using the observational estimate that ~30% of DRGs have no ongoing star formation, we infer a timescale for star formation quenching for satellite galaxies of 450 Myr, although the uncertainty on this number is large. However, unless all non-star-forming satellite DRGs were quenched before accretion, the quenching timescale is significantly shorter than z ~ 0 estimates. Down to the completeness limit of the Quadri et al. sample, we find that the halo masses of central DRGs are ~50% higher than non-DRGs in the same luminosity range, but at the highest halo masses the central galaxies are DRGs only ~2/3 of the time.

  13. STRUCTURES OF LOCAL GALAXIES COMPARED TO HIGH-REDSHIFT STAR-FORMING GALAXIES

    SciTech Connect

    Petty, Sara M.; De Mello, DuIlia F.; Gallagher, John S.; Gardner, Jonathan P.; Lotz, Jennifer M.; Matt Mountain, C.; Smith, Linda J.

    2009-08-15

    The rest-frame far-ultraviolet morphologies of eight nearby interacting and starburst galaxies (Arp 269, M 82, Mrk 8, NGC 520, NGC 1068, NGC 3079, NGC 3310, and NGC 7673) are compared with 54 galaxies at z {approx} 1.5 and 46 galaxies at z {approx} 4 observed in the Great Observatories Origins Deep Survey (GOODS) taken with the Advanced Camera for Surveys onboard the Hubble Space Telescope. The nearby sample is artificially redshifted to z {approx} 1.5 and 4 by applying luminosity and size scaling. We compare the simulated galaxy morphologies to real z {approx} 1.5 and 4 UV-bright galaxy morphologies. We calculate the Gini coefficient (G), the second-order moment of the brightest 20% of the galaxy's flux (M {sub 20}), and the Sersic index (n). We explore the use of nonparametric methods with two-dimensional profile fitting and find the combination of M {sub 20} with n an efficient method to classify galaxies as having merger, exponential disk, or bulge-like morphologies. When classified according to G and M {sub 20} 20/30% of real/simulated galaxies at z {approx} 1.5 and 37/12% at z {approx} 4 have bulge-like morphologies. The rest have merger-like or intermediate distributions. Alternatively, when classified according to the Sersic index, 70% of the z {approx} 1.5 and z {approx} 4 real galaxies are exponential disks or bulge-like with n>0.8, and {approx} 30% of the real galaxies are classified as mergers. The artificially redshifted galaxies have n values with {approx} 35% bulge or exponential at z {approx} 1.5 and 4. Therefore, {approx} 20%-30% of Lyman-break galaxies have structures similar to local starburst mergers, and may be driven by similar processes. We assume merger-like or clumpy star-forming galaxies in the GOODS field have morphological structure with values n < 0.8 and M {sub 20}> - 1.7. We conclude that Mrk 8, NGC 3079, and NGC 7673 have structures similar to those of merger-like and clumpy star-forming galaxies observed at z {approx} 1.5 and 4.

  14. SURFACE BRIGHTNESS PROFILES OF DWARF GALAXIES. I. PROFILES AND STATISTICS

    SciTech Connect

    Herrmann, Kimberly A.; Hunter, Deidre A.; Elmegreen, Bruce G. E-mail: dah@lowell.edu

    2013-11-01

    Radial surface brightness profiles of spiral galaxies are classified into three types: (I) single exponential, or the light falls off with one exponential to a break before falling off (II) more steeply, or (III) less steeply. Profile breaks are also found in dwarf disks, but some dwarf Type IIs are flat or increasing out to a break before falling off. Here we re-examine the stellar disk profiles of 141 dwarfs: 96 dwarf irregulars (dIms), 26 Blue Compact Dwarfs (BCDs), and 19 Magellanic-type spirals (Sms). We fit single, double, or even triple exponential profiles in up to 11 passbands: GALEX FUV and NUV, ground-based UBVJHK and Hα, and Spitzer 3.6 and 4.5 μm. We find that more luminous galaxies have brighter centers, larger inner and outer scale lengths, and breaks at larger radii; dwarf trends with M{sub B} extend to spirals. However, the V-band break surface brightness is independent of break type, M{sub B} , and Hubble type. Dwarf Type II and III profiles fall off similarly beyond the breaks but have different interiors and IIs break ∼twice as far as IIIs. Outer Type II and III scale lengths may have weak trends with wavelength, but pure Type II inner scale lengths clearly decrease from the FUV to visible bands whereas Type III inner scale lengths increase with redder bands. This suggests the influence of different star formation histories on profile type, but nonetheless the break location is approximately the same in all passbands. Dwarfs continue trends between profile and Hubble types such that later-type galaxies have more Type II but fewer Type I and III profiles than early-type spirals. BCDs and Sms are over-represented as Types III and II, respectively, compared to dIms.

  15. GALAXY GROWTH BY MERGING IN THE NEARBY UNIVERSE

    SciTech Connect

    Jiang Tao; Hogg, David W.; Blanton, Michael R.

    2012-11-10

    We measure the mass growth rate by merging for a wide range of galaxy types. We present the small-scale (0.014 h {sup -1} {sub 70} Mpc < r < 11 h {sub 70} {sup -1} Mpc) projected cross-correlation functions w(r {sub p}) of galaxy subsamples from the spectroscopic sample of the NYU Value-Added Galaxy Catalog (5 Multiplication-Sign 10{sup 5} galaxies of redshifts 0.03 < z < 0.15) with galaxy subsamples from the Sloan Digital Sky Survey imaging (4 Multiplication-Sign 10{sup 7} galaxies). We use smooth fits to de-project the two-dimensional functions w(r {sub p}) to obtain smooth three-dimensional real-space cross-correlation functions {xi}(r) for each of several spectroscopic subsamples with each of several imaging subsamples. Because close pairs are expected to merge, the three-space functions and dynamical evolution time estimates provide galaxy accretion rates. We find that the accretion onto massive blue galaxies and onto red galaxies is dominated by red companions, and that onto small-mass blue galaxies, red and blue galaxies make comparable contributions. We integrate over all types of companions and find that at fixed stellar mass, the total fractional accretion rates onto red galaxies ({approx}3 h {sub 70} percent per Gyr) are greater than that onto blue galaxies ({approx}1 h {sub 70} percent per Gyr). These rates are almost certainly overestimates because we have assumed that all close pairs merge as quickly as the merger time that we used. One conclusion of this work is that if the total growth of red galaxies from z = 1 to z = 0 is mainly due to merging, the merger rates must have been higher in the past.

  16. Merging Galaxies Create a Binary Quasar

    NASA Astrophysics Data System (ADS)

    2010-02-01

    Observatory in California indicated that the object was likely a binary quasar in the midst of a galaxy merger. Carnegie's Mulchaey then used the 6.5 meter Baade-Magellan telescope at the Las Campanas observatory in Chile to obtain deeper images and more detailed spectroscopy of the merging galaxies. "Just because you see two galaxies that are close to each other in the sky doesn't mean they are merging," says Mulchaey. "But from the Magellan images we can actually see tidal tails, one from each galaxy, which suggests that the galaxies are in fact interacting and are in the process of merging." Thomas Cox, now a fellow at the Carnegie Observatories, corroborated this conclusion using computer simulations of the merging galaxies. When Cox's model galaxies merged, they showed features remarkably similar to what Mulchaey observed in the Magellan images. "The model verifies the merger origin for this binary quasar system," he says. "It also hints that this kind of galaxy interaction is a key component of the growth of black holes and production of quasars throughout our universe." * The authors of the paper published in the Astrophysical Journal are Paul J. Green of the Harvard-Smithsonian Center for Astrophysics, Adam D. Myers of the University of Illinois at Urbana-Champaign, Wayne A. Barkhouse of the University of North Dakota, John S. Mulchaey of the Observatories of the Carnegie Institution for Science, Vardha N. Bennert of the Department of Physics, University of California, Santa Barbara, Thomas J. Cox of the Observatories of the Carnegie Institution for Science, Thomas L. Aldcroft of the Harvard-Smithsonian Center for Astrophysics, and Joan M. Wrobel of National Radio Astronomy Observatory, Socorro, NM. More information, including images and other multimedia, can be found at: http://chandra.harvard.edu and http://chandra.nasa.gov

  17. Star-formation rates, molecular clouds, and the origin of the far-infrared luminosity of isolated and interacting galaxies

    NASA Technical Reports Server (NTRS)

    Solomon, P. M.; Sage, L. J.

    1988-01-01

    The CO luminosities of 93 galaxies have been determined and are compared with their IRAS FIR luminosities. Strongly interacting/merging galaxies have L(FIR)/L(CO) substantially higher than that of isolated galaxies or galactic giant molecular clouds (GMCs). Galaxies with tidal tails/bridges are the most extreme type with L(FIR)/L(CO) nine times as high as isolated galaxies. Interactions between close pairs of galaxies do not have much effect on the molecular content and global star-formation rate. If the high ratio L(FIR)/L(CO) in strongly interacting galaxies is due to star formation then the efficiency of this process is higher than that of any galactic GMC. Isolated galaxies, distant pairs, and close pairs have an FIR/CO luminosity ratio which is within a factor of two of galactic GMCs with H II regions. The CO luminosities of FIR-luminous galaxies are among the highest observed for any spiral galaxies.

  18. Ergodicity breaking and localization.

    PubMed

    Geneston, Elvis; Tuladhar, Rohisha; Beig, M T; Bologna, Mauro; Grigolini, Paolo

    2016-07-01

    We study the joint action of the non-Poisson renewal events (NPR) yielding Continuous-time random walk (CTRW) with index α<1 and two different generators of Hurst coefficient H≠0.5, one generating fractional Brownian motion (FBM) and another scaled Brownian motion (SBM). We discuss the ergodicity breaking emerging from these joint actions and we find that in both cases the adoption of time averages leads to localization. In the case of the joint action of NPR and SBM, localization occurs when SBM would produce subdiffusion. The joint action of NPR and FBM, on the contrary, may lead to localization when FBM is a source of superdiffusion. The joint action of NPR and FBM is equivalent to extending the CTRW to the case where the jumps of the runner are correlated and we argue that the the memory-induced localization requires a refinement of the theoretical perspective about determinism and randomness. PMID:27575105

  19. Ergodicity breaking and localization

    NASA Astrophysics Data System (ADS)

    Geneston, Elvis; Tuladhar, Rohisha; Beig, M. T.; Bologna, Mauro; Grigolini, Paolo

    2016-07-01

    We study the joint action of the non-Poisson renewal events (NPR) yielding Continuous-time random walk (CTRW) with index α <1 and two different generators of Hurst coefficient H ≠0.5 , one generating fractional Brownian motion (FBM) and another scaled Brownian motion (SBM). We discuss the ergodicity breaking emerging from these joint actions and we find that in both cases the adoption of time averages leads to localization. In the case of the joint action of NPR and SBM, localization occurs when SBM would produce subdiffusion. The joint action of NPR and FBM, on the contrary, may lead to localization when FBM is a source of superdiffusion. The joint action of NPR and FBM is equivalent to extending the CTRW to the case where the jumps of the runner are correlated and we argue that the the memory-induced localization requires a refinement of the theoretical perspective about determinism and randomness.

  20. Galaxy pairs in the Sloan Digital Sky Survey - X. Does gas content alter star formation rate enhancement in galaxy interactions?

    NASA Astrophysics Data System (ADS)

    Scudder, Jillian M.; Ellison, Sara L.; Momjian, Emmanuel; Rosenberg, Jessica L.; Torrey, Paul; Patton, David R.; Fertig, Derek; Mendel, J. Trevor

    2015-06-01

    New spectral line observations, obtained with the Jansky Very Large Array (VLA), of a sample of 34 galaxies in 17 close pairs are presented in this paper. The sample of galaxy pairs is selected to contain galaxies in close, major interactions (i.e. projected separations <30 h_{70}^{-1} kpc, and mass ratios less extreme than 4:1), while still having a sufficiently large angular separation that the VLA can spatially resolve both galaxies in the pair. Of the 34 galaxies, 17 are detected at >3σ. We compare the H I gas fraction of the galaxies with the triggered star formation present in that galaxy. When compared to the star formation rates (SFRs) of non-pair galaxies matched in mass, redshift, and local environment, we find that the star formation enhancement is weakly positively correlated (˜2.5σ) with H I gas fraction. In order to help understand the physical mechanisms driving this weak correlation, we also present results from a small suite of binary galaxy merger simulations with varying gas fractions. The simulated galaxies indicate that larger initial gas fractions are associated with lower levels of interaction-triggered star formation (relative to an identical galaxy in isolation), but also show that high gas fraction galaxies have higher absolute SFRs prior to an interaction. We show that when interaction-driven SFR enhancements are calculated relative to a galaxy with an average gas fraction for its stellar mass, the relationship between SFR and initial gas fraction dominates over the SFR enhancements driven by the interaction. Simulated galaxy interactions that are matched in stellar mass but not in gas fraction, like our VLA sample, yield the same general positive correlation between SFR enhancement and gas fraction that we observe.

  1. Tracking star formation in dwarf cluster galaxies

    NASA Astrophysics Data System (ADS)

    Rude, Cody Millard

    The evolution of galaxies in dense environments can be affected by close encounters with neighboring galaxies and interactions with the intracluster medium (ICM). Dwarf galaxies may be especially susceptible to these effects due to their low mass. The goal of my dissertation research is to look for signs of star formation in cluster dwarf galaxies by measuring and comparing the r- and u-band luminosity functions of 15 low redshift Abell galaxy clusters using archival data from the Canada-France-Hawaii Telescope (CFHT). Luminosity functions, dwarf-to-giant ratios, and blue fractions are measured in four cluster-centric annuli from stacked cluster data. To account for differences in cluster optical richness, each cluster is scaled according to r200, where r200 is the radius of a sphere, centered on the cluster, whose average density is 200 times the critical density of the universe. The outer region of the cluster sample shows an increase in the faint-end slope of the u-band luminosity function relative to the r-band, indicating star formation in dwarf galaxies. The blue fraction for dwarf galaxies steadily rises with increasing cluster-centric radii. The change in the blue fraction of giant galaxies also increases, but at a lower rate. Additionally, the inner regions of clusters ranging from 0.185 < z < 0.7 from the "Cluster Lensing and Supernova survey with Hubble (CLASH)" are used to generate blue- and red-band luminosity functions, dwarf-to-giant ratios, and blue fractions. Comparisons of the inner region of the CLASH and CFHT clusters show an increase in the blue fraction of dwarf galaxies with redshift that is not present in giant galaxies.

  2. Tidal Disruption Events Prefer Unusual Host Galaxies

    NASA Astrophysics Data System (ADS)

    French, K. Decker; Arcavi, Iair; Zabludoff, Ann

    2016-02-01

    Tidal Disruption Events (TDEs) are transient events observed when a star passes close enough to a supermassive black hole to be tidally destroyed. Many TDE candidates have been discovered in host galaxies whose spectra have weak or no line emission yet strong Balmer line absorption, indicating a period of intense star formation that has recently ended. As such, TDE host galaxies fall into the rare class of quiescent Balmer-strong galaxies. Here, we quantify the fraction of galaxies in the Sloan Digital Sky Survey (SDSS) with spectral properties like those of TDE hosts, determining the extent to which TDEs are over-represented in such galaxies. Galaxies whose spectra have Balmer absorption {{H}}{δ }{{A}} - σ(H{δ }{{A}}) > 4 Å (where σ(H{δ }{{A}}) is the error in the Lick {{H}}{δ }{{A}} index) and Hα emission equivalent width (EW) < 3 Å have had a strong starburst in the last ˜Gyr. They represent 0.2% of the local galaxy population, yet host 3 of 8 (37.5%) optical/UV-selected TDE candidates. A broader cut, {{H}}{δ }{{A}}\\quad \\gt 1.31 Å and Hα EW < 3 Å, nets only 2.3% of SDSS galaxies, but 6 of 8 (75%) optical/UV TDE hosts. Thus, quiescent Balmer-strong galaxies are over-represented among the TDE hosts by a factor of 33-190. The high-energy-selected TDE Swift J1644 also lies in a galaxy with strong Balmer lines and weak Hα emission, implying a \\gt 80× enhancement in such hosts and providing an observational link between the γ/X-ray-bright and optical/UV-bright TDE classes.

  3. Encounters of spherical galaxies. I - Galaxy models with one stellar population. II - Galaxy models with two stellar populations

    NASA Technical Reports Server (NTRS)

    Biermann, P.; Silk, J.

    1976-01-01

    Close encounters between two spherical galaxies of equal size and consisting of only one stellar population are calculated using models of elliptical galaxies constructed according to King's (1966) method. The mass loss and the change in internal energy are computed under the assumption that the stars do not change their velocity or density distributions during the encounters. The results for a specific case are compared with the calculations of Gallagher and Ostriker (1972), who employed the observed brightness distribution and the derived density distribution of the E1 galaxy NGC 3379. For models with one stellar population, the results suggest that the radius of a galactic halo would have to be at least 200 kpc for appreciable mass loss to occur over the history of a galaxy in a rich cluster. The calculations are then extended to include a halo population characterized by a high central velocity dispersion. In this case, it is found that the halo population of sufficiently large galaxies can be dispersed without appreciably affecting the main population. It is suggested that the missing mass of many clusters of galaxies may be located in an intergalactic sea of faint stars making up an envelope for the centrally located gE galaxies.

  4. THE ACS NEARBY GALAXY SURVEY TREASURY. XI. THE REMARKABLY UNDISTURBED NGC 2403 DISK

    SciTech Connect

    Williams, Benjamin F.; Dalcanton, Julianne J.; Stilp, Adrienne; Radburn-Smith, David; Dolphin, Andrew; Skillman, Evan D. E-mail: jd@astro.washington.edu E-mail: dolphin@raytheon.com

    2013-03-10

    We present detailed analysis of color-magnitude diagrams of NGC 2403, obtained from a deep (m {approx}< 28) Hubble Space Telescope (HST) Wide Field Planetary Camera 2 observation of the outer disk of NGC 2403, supplemented by several shallow (m {approx}< 26) HST Advanced Camera for Surveys fields. We derive the spatially resolved star formation history of NGC 2403 out to 11 disk scale lengths. In the inner portions of the galaxy, we compare the recent star formation rates (SFRs) we derive from the resolved stars with those measured using GALEX FUV + Spitzer 24{mu} fluxes, finding excellent agreement between the methods. Our measurements also show that the radial gradient in recent SFR mirrors the disk exponential profile to 11 scale lengths with no break, extending to SFR densities a factor of {approx}100 lower than those that can be measured with GALEX and Spitzer ({approx}2 Multiplication-Sign 10{sup -6} M{sub Sun} yr{sup -1} kpc{sup -2}). Furthermore, we find that the cumulative stellar mass of the disk was formed at similar times at all radii. We compare these characteristics of NGC 2403 to those of its ''morphological twins'', NGC 300 and M 33, showing that the structure and age distributions of the NGC 2403 disk are more similar to those of the relatively isolated system NGC 300 than to those of the Local Group analog M 33. We also discuss the environments and HI morphologies of these three nearby galaxies, comparing them to integrated light studies of larger samples of more distant galaxy disks. Taken together, the physical properties and evolutionary history of NGC 2403 suggest that the galaxy has had no close encounters with other M 81 group members and may be falling into the group for the first time.

  5. Measuring the Red Sequence Slope in a Distant Galaxy Cluster

    NASA Astrophysics Data System (ADS)

    Schultz, Erin; Rudnick, G.

    2013-01-01

    Our project goal is to constrain the possible stellar mass dependence of galaxy ages for red sequence galaxies. We use the Y, J, and K-band data collected from the Very Large Telescope in Chile of the z = 1.62 galaxy cluster XMM-LSS J02182-051020. This spectroscopically confirmed galaxy cluster is one of the only known massive clusters at an epoch close to the time when stars stopped forming within red sequence galaxies. For red sequence galaxies, which have little recent star formation and little dust, the color is an indicator of the luminosity weighted age of the stars. This is in turn correlated to the last epoch of significant star formation. At the same time, the mass of such a galaxy is correlated to its magnitude. The more stars a galaxy contains, the more massive and brighter the galaxy. The slope of the red sequence in color-magnitude space, therefore, gives an indication of the dependence of galaxy age on stellar mass. We use the age-sensitive Y-J color and measure a slope of zero for the red sequence in Y-J vs. J. We interpret this to mean that the age does not depend strongly on the mass of the galaxy. We will present the limits on the slope of the color-magnitude relation and will discuss what limits this corresponds to on the age dependence with mass.

  6. Revealing the nature of star forming blue early-type galaxies at low redshift

    NASA Astrophysics Data System (ADS)

    George, Koshy; Zingade, Kshama

    2015-11-01

    Context. Star forming early-type galaxies with blue optical colours at low redshift can be used to test our current understanding of galaxy formation and evolution. Aims: We want to reveal the fuel and triggering mechanism for star formation in these otherwise passively evolving red and dead stellar systems. Methods: We undertook an optical and ultraviolet study of 55 star forming blue early-type galaxies, searching for signatures of recent interactions that could be driving the molecular gas into the galaxy and potentially triggering the star formation. Results: We report here our results on star forming blue early-type galaxies with tidal trails and in close proximity to neighbouring galaxies that are evidence of ongoing or recent interactions between galaxies. There are 12 galaxies with close companions with similar redshifts, among which two galaxies are having ongoing interactions that potentially trigger the star formation. Two galaxies show a jet feature that could be due to the complete tidal disruption of the companion galaxy. The interacting galaxies have high star formation rates and very blue optical colours. Galaxies with no companion could have undergone a minor merger in the recent past. Conclusions: The recent or ongoing interaction with a gas-rich neighbouring galaxy could be responsible for bringing cold gas to an otherwise passively evolving early-type galaxy. The sudden gas supply could trigger the star formation, eventually creating a blue early-type galaxy. The galaxies with ongoing tidal interaction are blue and star forming, thereby implying that blue early-type galaxies can exist even when the companion is on flyby so does not end up in a merger. Based on data compiled from Galaxy Zoo project, and the volunteers contribution are acknowledged at http://www.galaxyzoo.org/Volunteers.aspx

  7. Star Formation in Irregular Galaxies.

    ERIC Educational Resources Information Center

    Hunter, Deidre; Wolff, Sidney

    1985-01-01

    Examines mechanisms of how stars are formed in irregular galaxies. Formation in giant irregular galaxies, formation in dwarf irregular galaxies, and comparisons with larger star-forming regions found in spiral galaxies are considered separately. (JN)

  8. The AMIGA sample of isolated galaxies. X. A first look at isolated galaxy colors

    NASA Astrophysics Data System (ADS)

    Fernández Lorenzo, M.; Sulentic, J.; Verdes-Montenegro, L.; Ruiz, J. E.; Sabater, J.; Sánchez, S.

    2012-04-01

    Context. The basic properties of galaxies can be affected by both nature (internal processes) or nurture (interactions and effects of environment). Deconvolving the two effects is an important current effort in astrophysics. Observed properties of a sample of isolated galaxies should be mainly the result of internal (natural) evolution. It follows that nurture-induced galaxy evolution can only be understood through a comparative study of galaxies in different environments. Aims: We take a first look at SDSS (g - r) colors of galaxies in the AMIGA sample, which consists of many of the most isolated galaxies in the local Universe. This alerted us at the same time to the pitfalls of using automated SDSS colors. Methods: We focused on median values for the principal morphological subtypes found in the AMIGA sample (E/S0 and Sb-Sc) and compared them with equivalent measures obtained for galaxies in denser environments. Results: We find a weak tendency for AMIGA spiral galaxies to be redder than objects in close pairs. We find no clear difference when we compared this with galaxies in other (e.g. group) environments. However, the (g - r) color of isolated galaxies shows a Gaussian distribution, as might be expected assuming nurture-free evolution. We find a smaller median absolute deviation in colors for isolated galaxies compared to both wide and close pairs. The majority of the deviation on median colors for spiral subtypes is caused by a color-luminosity correlation. Surprisingly, isolated and non-isolated early-type galaxies show similar (g - r). We see little evidence for a green valley in our sample because most spirals redder than (g - r) = 0.7 have spurious colors. Conclusions: The redder colors of AMIGA spirals and lower color dispersions for AMIGA subtypes - compared with close pairs - are likely caused by a more passive star formation in very isolated galaxies. Full Tables 1 and 2 are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130

  9. Core break-off mechanism

    NASA Technical Reports Server (NTRS)

    Myrick, Thomas M. (Inventor)

    2003-01-01

    A mechanism for breaking off and retaining a core sample of a drill drilled into a ground substrate has an outer drill tube and an inner core break-off tube sleeved inside the drill tube. The break-off tube breaks off and retains the core sample by a varying geometric relationship of inner and outer diameters with the drill tube. The inside diameter (ID) of the drill tube is offset by a given amount with respect to its outer diameter (OD). Similarly, the outside diameter (OD) of the break-off tube is offset by the same amount with respect to its inner diameter (ID). When the break-off tube and drill tube are in one rotational alignment, the two offsets cancel each other such that the drill can operate the two tubes together in alignment with the drill axis. When the tubes are rotated 180 degrees to another positional alignment, the two offsets add together causing the core sample in the break-off tube to be displaced from the drill axis and applying shear forces to break off the core sample.

  10. Simple Stringy Dynamical SUSY Breaking

    SciTech Connect

    Aharony, Ofer; Kachru, Shamit; Silverstein, Eva; /Stanford U., Phys. Dept. /SLAC

    2007-08-08

    We present simple string models which dynamically break supersymmetry without non-Abelian gauge dynamics. The Fayet model, the Polonyi model, and the O'Raifeartaigh model each arise from D-branes at a specific type of singularity. D-brane instanton effects generate the requisite exponentially small scale of supersymmetry breaking.