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Matthew J. O'Dowd,
David Schiminovich,
Benjamin D. Johnson,
Marie A. Treyer,
Christopher D. Martin,
Ted K. Wyder, Stéphane Charlot,
Timothy M. Heckman,
Lucimara P. Martins,
Mark Seibert,
and J. M. van der Hulst
[show abstract]
[hide abstract]
ABSTRACT: The Spitzer-SDSS-GALEX Spectroscopic Survey (SSGSS) provides a new sample of 101 star-forming galaxies at z < 0.2 with unprecedented multi-wavelength coverage. New mid- to far-infrared spectroscopy from the Spitzer Space Telescope is added to a rich suite of previous imaging and spectroscopy, including ROSAT, Galaxy Evolution Explorer, Sloan Digital Sky Survey, Two Micron All Sky Survey, and Spitzer/SWIRE. Sample selection ensures an even coverage of the full range of normal galaxy properties, spanning two orders of magnitude in stellar mass, color, and dust attenuation. In this paper we present the SSGSS data set, describe the science drivers, and detail the sample selection, observations, data reduction, and quality assessment. Also in this paper, we compare the shape of the thermal continuum and the degree of silicate absorption of these typical, star-forming galaxies to those of starburst galaxies. We investigate the link between star formation rate, infrared luminosity, and total polycyclic aromatic hydrocarbon luminosity, with a view to calibrating the latter for spectral energy distribution models in photometric samples and at high redshift. Last, we take advantage of the 5-40 μm spectroscopic and far-infrared photometric coverage of this sample to perform detailed fitting of the Draine et al. dust models, and investigate the link between dust mass and star formation history and active galactic nucleus properties.
The Astrophysical Journal 10/2011; 741(2):79. · 6.02 Impact Factor
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Roderik A. Overzier,
Timothy M. Heckman,
Jing Wang,
Lee Armus,
Veronique Buat,
Justin Howell,
Gerhardt Meurer,
Mark Seibert,
Brian Siana,
Antara Basu-Zych, Stéphane Charlot,
Thiago S. Gonçalves,
D. Christopher Martin,
James D. Neill,
R. Michael Rich,
Samir Salim,
and David Schiminovich
[show abstract]
[hide abstract]
ABSTRACT: We present a new analysis of the dust obscuration in starburst galaxies at low and high redshifts. This study is motivated by our unique sample of the most extreme UV-selected starburst galaxies in the nearby universe (z < 0.3), found to be good analogs of high-redshift Lyman break galaxies (LBGs) in most of their physical properties. We find that the dust properties of the Lyman break analogs (LBAs) are consistent with the relation derived previously by Meurer et al. (M99) that is commonly used to dust-correct star formation rate (SFR) measurements at a very wide range of redshifts. We directly compare our results with high-redshift samples (LBGs, "BzK," and submillimeter galaxies at z ~ 2-3) having IR data either from Spitzer or Herschel. The attenuation in typical LBGs at z ~ 2-3 and LBAs is very similar. Because LBAs are much better analogs to LBGs compared to previous local star-forming samples, including M99, the practice of dust-correcting the SFRs of high-redshift galaxies based on the local calibration is now placed on a much more solid ground. We illustrate the importance of this result by showing how the locally calibrated relation between UV measurements and extinction is used to estimate the integrated, dust-corrected SFR density at z 2-6.
The Astrophysical Journal Letters 12/2010; 726(1):L7. · 5.53 Impact Factor
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Marie Treyer,
David Schiminovich,
Benjamin D. Johnson,
Matt O'Dowd,
Christopher D. Martin,
Ted Wyder, Stéphane Charlot,
Timothy Heckman,
Lucimara Martins,
Mark Seibert,
and J. M. van der Hulst
[show abstract]
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ABSTRACT: We investigate the use of mid-infrared (MIR) polycyclic aromatic hydrocarbon (PAH) bands, the continuum, and emission lines as probes of star formation (SF) and active galactic nucleus (AGN) activity in a sample of 100 "normal" and local (z ~ 0.1) emission-line galaxies. The MIR spectra were obtained with the Spitzer Space Telescope Infrared Spectrograph as part of the Spitzer-SDSS-GALEX Spectroscopic Survey, which includes multi-wavelength photometry from the ultraviolet to the far-infrared and optical spectroscopy. The continuum and features were extracted using PAHFIT, a decomposition code which we find to yield PAH equivalent widths (EWs) up to ~30 times larger than the commonly used spline methods. Despite the lack of extreme objects in our sample (such as strong AGNs, low-metallicity galaxies, or ULIRGs), we find significant variations in PAH, continuum, and emission-line properties, and systematic trends between these MIR properties and optically derived physical properties, such as age, metallicity, and radiation field hardness. We revisit the diagnostic diagram relating PAH EWs and [Ne II]12.8 μm/[O IV]25.9 μm line ratios and find it to be in much better agreement with the standard optical SF/AGN classification than when spline decompositions are used, while also potentially revealing obscured AGNs. The luminosity of individual PAH components, of the continuum, and, with poorer statistics, of the neon emission lines and molecular hydrogen lines are found to be tightly correlated to the total infrared (TIR) luminosity, making individual MIR components good gauges of the total dust emission in SF galaxies. Like the TIR luminosity, these individual components can be used to estimate dust attenuation in the UV and in Hα lines based on energy balance arguments. We also propose average scaling relations between these components and dust-corrected, Hα-derived SF rates.
The Astrophysical Journal 07/2010; 719(2):1191. · 6.02 Impact Factor
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ABSTRACT: We investigate the accretion-driven growth of supermassive black holes in the low-redshift universe using 23,000 narrow-emission-line ("type 2") active galactic nuclei (AGNs) and the complete sample of 123,000 galaxies in the Sloan Digital Sky Survey from which they were drawn. We use the stellar velocity dispersions of the early-type galaxies and AGN hosts to estimate their black hole masses, and we use the AGN [O III] λ5007 emission line luminosities to estimate black hole accretion rates. We find that most present-day accretion occurs onto black holes with masses less than 108 M☉ that reside in moderately massive galaxies (M* ≈ 1010-1011.5 M☉) with high stellar surface mass densities (μ* ≈ 108.5-109.5 M☉ kpc-2) and young stellar populations. The volume-averaged accretion rates of low-mass black holes (<3 × 107 M☉) imply that this population is growing on a timescale that is comparable to the age of the universe. Around half this growth takes place in AGNs that are radiating within a factor of 5 of the Eddington luminosity. Such systems are rare, making up only 0.2% of the low-mass black hole population at the present day. The rest of the growth occurs in lower luminosity AGNs. The growth timescale is more than 2 orders of magnitude longer for the population of the most massive black holes in our sample. The volume-averaged ratio of star formation to black hole accretion in bulge-dominated galaxies is ~1000, in remarkable agreement with the observed ratio of stellar mass to black hole mass in nearby galaxy bulges. We conclude that (1) bulge formation and black hole formation are tightly coupled, even in present-day galaxies, and (2) the evolution of the AGN luminosity function documented in recent optical and X-ray surveys is driven by a decrease in the characteristic mass scale of actively accreting black holes.
The Astrophysical Journal 12/2008; 613(1):109. · 6.02 Impact Factor
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Tamás Budavári,
Alex S. Szalay, Stéphane Charlot,
Mark Seibert,
Ted K. Wyder,
Stéphane Arnouts,
Tom A. Barlow,
Luciana Bianchi,
Yong-Ik Byun,
José Donas, [......],
D. Christopher Martin,
Bruno Milliard,
Patrick Morrissey,
Susan G. Neff,
R. Michael Rich,
David Schiminovich,
Oswald H. W. Siegmund,
Todd Small,
Marie A. Treyer,
and Barry Welsh
[show abstract]
[hide abstract]
ABSTRACT: We present measurements of the UV galaxy luminosity function and the evolution of luminosity density from Galaxy Evolution Explorer (GALEX) observations matched to the Sloan Digital Sky Survey (SDSS). We analyze galaxies in the Medium Imaging Survey overlapping the SDSS First Data Release, with a total coverage of 44 deg2. Using the combined GALEX + SDSS photometry, we compute photometric redshifts and study the luminosity function in three redshift shells between z = 0.07 and 0.25. The Schechter function fits indicate that the faint-end slope α is consistent with -1.1 at all redshifts, but the characteristic UV luminosity M* brightens by 0.2 mag from z = 0.07 to 0.25. In the lowest redshift bin, early- and late-type galaxies are studied separately, and we confirm that red galaxies tend to be brighter and have a shallower slope α than blue ones. The derived luminosity densities are consistent with other GALEX results based on a local spectroscopic sample from the Two-Degree Field, and the evolution follows the trend reported by deeper studies.
The Astrophysical Journal 12/2008; 619(1):L31. · 6.02 Impact Factor
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Samir Salim,
R. Michael Rich, Stéphane Charlot,
Jarle Brinchmann,
Benjamin D. Johnson,
David Schiminovich,
Mark Seibert,
Ryan Mallery,
Timothy M. Heckman,
Karl Forster, [......],
Todd Small,
Ted K. Wyder,
Luciana Bianchi,
José Donas,
Young-Wook Lee,
Barry F. Madore,
Bruno Milliard,
Alex S. Szalay,
Barry Y. Welsh,
and Sukyoung K. Yi
[show abstract]
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ABSTRACT: We measure star formation rates (SFRs) of 50,000 optically selected galaxies in the local universe (z ≈ 0.1)—from gas-rich dwarfs to massive ellipticals. We obtain dust-corrected SFRs by fitting the GALEX (ultraviolet) and SDSS photometry to a library of dust-attenuated population synthesis models. For star-forming galaxies, our UV-based SFRs compare remarkably well with those from SDSS-measured emission lines (Hα). Deviations from perfect agreement are shown to be due to differences in the dust attenuation estimates. In contrast to Hα measurements, UV provides reliable SFRs for galaxies with weak Hα, and where Hα is contaminated with AGN emission (1/2 of the sample). Using full-SED SFRs, we calibrate a simple prescription that uses GALEX far- and near-UV magnitudes to produce dust-corrected SFRs for normal star-forming galaxies. The specific SFR is considered as a function of stellar mass for (1) star-forming galaxies with no AGNs, (2) those hosting an AGN, and (3) galaxies without Hα emission. We find that the three have distinct star formation histories, with AGNs lying intermediate between the star-forming and the quiescent galaxies. Star-forming galaxies without an AGN lie on a relatively narrow linear sequence. Remarkably, galaxies hosting a strong AGN appear to represent the massive continuation of this sequence. On the other hand, weak AGNs, while also massive, have lower SFRs, sometimes extending to the realm of quiescent galaxies. We propose an evolutionary sequence for massive galaxies that smoothly connects normal star-forming galaxies to quiescent galaxies via strong and weak AGNs. We confirm that some galaxies with no Hα show signs of star formation in the UV. We derive a cosmic star formation density at z = 0.1 with significantly smaller total error than previous measurements.
The Astrophysical Journal Supplement Series 12/2008; 173(2):267. · 13.46 Impact Factor
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Christy A. Tremonti,
Timothy M. Heckman,
Guinevere Kauffmann,
Jarle Brinchmann, Stéphane Charlot,
Simon D. M. White,
Mark Seibert,
Eric W. Peng,
David J. Schlegel,
Alan Uomoto,
Masataka Fukugita,
and Jon Brinkmann
[show abstract]
[hide abstract]
ABSTRACT: We utilize Sloan Digital Sky Survey imaging and spectroscopy of ~53,000 star-forming galaxies at z ~ 0.1 to study the relation between stellar mass and gas-phase metallicity. We derive gas-phase oxygen abundances and stellar masses using new techniques that make use of the latest stellar evolutionary synthesis and photoionization models. We find a tight (±0.1 dex) correlation between stellar mass and metallicity spanning over 3 orders of magnitude in stellar mass and a factor of 10 in metallicity. The relation is relatively steep from 108.5 to 1010.5 M☉ h, in good accord with known trends between luminosity and metallicity, but flattens above 1010.5 M☉. We use indirect estimates of the gas mass based on the Hα luminosity to compare our data to predictions from simple closed box chemical evolution models. We show that metal loss is strongly anticorrelated with baryonic mass, with low-mass dwarf galaxies being 5 times more metal depleted than L* galaxies at z ~ 0.1. Evidence for metal depletion is not confined to dwarf galaxies but is found in galaxies with masses as high as 1010 M☉. We interpret this as strong evidence of both the ubiquity of galactic winds and their effectiveness in removing metals from galaxy potential wells.
The Astrophysical Journal 12/2008; 613(2):898. · 6.02 Impact Factor
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Roderik A. Overzier,
Timothy M. Heckman,
Guinevere Kauffmann,
Mark Seibert,
R. Michael Rich,
Antara Basu-Zych,
Jennifer Lotz,
Alessandra Aloisi, Stéphane Charlot,
C. Hoopes,
D. Christopher Martin,
David Schiminovich,
and Barry Madore
[show abstract]
[hide abstract]
ABSTRACT: Heckman and coworkers used the GALEX UV imaging survey to show that there exists a rare population of nearby compact UV-luminous galaxies (UVLGs) that closely resemble high-redshift Lyman break galaxies (LBGs). We present HST images in the UV, optical, and Hα and resimulate them at the depth and resolution of the GOODS/UDF fields to show that the morphologies of UVLGs are also similar to those of LBGs. Our sample of eight LBG analogs thus provides detailed insight into the connection between star formation and LBG morphology. Faint tidal features or companions can be seen in all of the rest-frame optical images, suggesting that the starbursts are the result of a merger or interaction. The UV/optical light is dominated by unresolved (~100-300 pc) super starburst regions (SSBs). A detailed comparison with the galaxies Haro 11 and VV 114 at z = 0.02 indicates that the SSBs themselves consist of diffuse stars and (super) star clusters. The structural features revealed by the new HST images occur on very small physical scales and are thus not detectable in images of high-redshift LBGs, except in a few cases where they are magnified by gravitational lensing. We propose, therefore, that LBGs are mergers of gas-rich, relatively low-mass (M* ~ 1010 M☉) systems, and that the mergers trigger the formation of SSBs. If galaxies at high redshifts are dominated by SSBs, then the faint-end slope of the luminosity function is predicted to have slope α ~ 2. Our results are the most direct confirmation to date of models that predict that the main mode of star formation in the early universe was highly collisional.
The Astrophysical Journal 12/2008; 677(1):37. · 6.02 Impact Factor
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Samir Salim, Stéphane Charlot,
R. Michael Rich,
Guinevere Kauffmann,
Timothy M. Heckman,
Tom A. Barlow,
Luciana Bianchi,
Yong-Ik Byun,
Jose Donas,
Karl Forster, [......],
Bruno Milliard,
Patrick Morrissey,
Susan G. Neff,
David Schiminovich,
Mark Seibert,
Oswald H. W. Siegmund,
Todd Small,
Alex S. Szalay,
Barry Y. Welsh,
and Ted K. Wyder
[show abstract]
[hide abstract]
ABSTRACT: We derive a variety of physical parameters including star formation rates (SFRs), dust attenuation, and burst mass fractions for 6472 galaxies observed by the Galaxy Evolution Explorer (GALEX) and present in the Sloan Digital Sky Survey Data Release 1 (SDSS DR1) main spectroscopic sample. Parameters are estimated in a statistical way by comparing each observed broadband spectral energy distribution (SED) (two GALEX and five SDSS bands) with an extensive library of model galaxy SEDs, which cover a wide range of star formation histories and include stochastic starbursts. We compare the constraints derived using SDSS bands only with those derived using the combination of SDSS and GALEX photometry. We find that the addition of the GALEX bands leads to significant improvement in the estimation of both the dust optical depth and the star formation rate over timescales of 100 Myr to 1 Gyr in a galaxy. We attain sensitivity to SFRs as low as 10-3 M☉ yr-1, and we find that low levels of star formation (SF) are mostly associated with early-type, red galaxies. The least massive galaxies have ratios of current to past-averaged SF rates (b-parameter) consistent with constant SF over a Hubble time. For late-type galaxies, this ratio on average decreases with mass. We find that b correlates tightly with NUV - r color, implying that the SF history of a galaxy can be constrained on the basis of the NUV - r color alone. The fraction of galaxies that have undergone a significant starburst episode within the last 1 Gyr steeply declines with mass, from ~20% for galaxies with ~108 M☉ to ~5% for ~1011 M☉ galaxies.
The Astrophysical Journal 12/2008; 619(1):L39. · 6.02 Impact Factor
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[hide abstract]
ABSTRACT: [Abridged] We investigate trends between the recent star formation history and black hole growth in galaxy bulges in the Sloan Digital Sky Survey (SDSS). The galaxies lie at 0.01<z<0.07 where the fibre aperture covers only the central 0.6-4.0kpc diameter of the galaxy. We find strong trends between black hole growth, as measured by dust-attenuation-corrected OIII luminosity, and the recent star formation history of the bulges. We conclude that our results support the popular hypothesis for black hole growth occurring through gas inflow into the central regions of galaxies, followed by a starburst and triggering of the AGN. However, while this is a significant pathway for the growth of black holes, it is not the dominant one in the present-day Universe. More unspectacular processes are apparently responsible for the majority of this growth. In order to arrive at these conclusions we have developed a set of new high signal-to-noise ratio (SNR) optical spectral indicators, designed to allow a detailed study of stellar populations which have undergone recent enhanced star formation. Working in the rest-frame wavelength range 3750-4150AA, ideally suited to many recent and ongoing spectroscopic surveys at low and high redshift, the first two indices are equivalent to the previously well studied 4000AA break strength and Hdelta equivalent width. The primary advantage of this new method is a greatly improved SNR for the latter index, allowing the present study to use spectra with SNR-per-pixel as low as 8. Comment: 27 pages, submitted to MNRAS. Due to astro-ph size restrictions 6 figures in appendix are available as separate files. Full version, with full resolution figures available at http://www.mpa-garching.mpg.de/~vwild/HDelta/Hd_PCAmethod.pdf
06/2007;
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[hide abstract]
ABSTRACT: We exploit recent constraints on the ages and metallicities of early-type galaxies in the Sloan Digital Sky Survey (SDSS) to gain new insight into the physical origin of two fundamental relations obeyed by these galaxies: the colour–magnitude and the Mg2–σV relations. Our sample consists of 26 003 galaxies selected from the SDSS Data Release 2 (DR2) on the basis of their concentrated light profiles, for which we have previously derived median-likelihood estimates of stellar metallicity, light-weighted age and stellar mass. Our analysis provides the most unambiguous demonstration to date of the fact that both the colour–magnitude and the Mg2–σV relations are primarily sequences in stellar mass and that total stellar metallicity, α-elements-to-iron abundance ratio and light-weighted age all increase with mass along the two relations. For high-mass ellipticals, the dispersion in age is small and consistent with the error. At the low-mass end, there is a tail towards younger ages, which dominates the scatter in colour and index strength at fixed mass. A small, but detectable, intrinsic scatter in the mass–metallicity relation also contributes to the scatter in the two observational scaling relations, even at high masses. Our results suggest that the chemical composition of an early-type galaxy is more tightly related to its dynamical mass (including stars and dark matter) than to its stellar mass. The ratio between stellar mass and dynamical mass appears to decrease from the least massive to the most massive galaxies in our sample.
Monthly Notices of the Royal Astronomical Society 06/2006; 370(3):1106 - 1124. · 4.90 Impact Factor
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ABSTRACT: We have compiled a sample of 2728 nearby ($z<0.08$) elliptical galaxies with photometry in the $g,r,i,z$ bands from the Sloan Digital Sky Survey (SDSS) and $J,H,K$ photometry from the Two Micron All Sky Survey (2MASS). Stellar masses, stellar velocity dispersions and structural parameters such as sizes and surface mass densities are also available for these objects. In order to correct the aperture mismatch between SDSS and 2MASS, we correct the SDSS magnitudes to the isophotal circular radius where the 2MASS magnitudes are measured. We compare the correlations between optical, optical-infrared and infrared colours and galaxy luminosity, stellar mass, velocity dispersion and surface mass density. We find that all galaxy colours correlate more strongly with stellar mass and velocity dispersion than with any other structural parameter. The dispersion about these two relations is also smaller. We also study the correlations between a variety of stellar absorption line indices and the same set of galaxy parameters and we reach very similar conclusions. Finally, we analyze correlations between absorption line indices and colour. Our results suggest that the optical colours of elliptical galaxies are sensitive to a combination of age, metallicity and $\alpha$-enhancement, while the optical-infrared colours are sensitive to metallicity and to $\alpha$-enhancement, but are somewhat less sensitive to age. Comment: 13 pages, 8 figures, accepted by MNRAS
02/2005;
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Guinevere Kauffmann,
Timothy M. Heckman,
Christy Tremonti,
Jarle Brinchmann, Stéphane Charlot,
Simon D. M. White,
Susan E. Ridgway,
Jon Brinkmann,
Masataka Fukugita,
Patrick B. Hall,
Željko Ivezić,
Gordon T. Richards,
Donald P. Schneider
[show abstract]
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ABSTRACT: We examine the properties of the host galaxies of 22 623 narrow-line active galactic nuclei (AGN) with 0.02 < z < 0.3 selected from a complete sample of 122 808 galaxies from the Sloan Digital Sky Survey. We focus on the luminosity of the [O iii]λ5007 emission line as a tracer of the strength of activity in the nucleus. We study how AGN host properties compare with those of normal galaxies and how they depend on L[O iii]. We find that AGN of all luminosities reside almost exclusively in massive galaxies and have distributions of sizes, stellar surface mass densities and concentrations that are similar to those of ordinary early-type galaxies in our sample. The host galaxies of low-luminosity AGN have stellar populations similar to normal early types. The hosts of high-luminosity AGN have much younger mean stellar ages. The young stars are not preferentially located near the nucleus of the galaxy, but are spread out over scales of at least several kiloparsecs. A significant fraction of high-luminosity AGN have strong Hδ absorption-line equivalent widths, indicating that they experienced a burst of star formation in the recent past. We have also examined the stellar populations of the host galaxies of a sample of broad-line AGN. We conclude that there is no significant difference in stellar content between type 2 Seyfert hosts and quasars (QSOs) with the same [O iii] luminosity and redshift. This establishes that a young stellar population is a general property of AGN with high [O iii] luminosities.
Monthly Notices of the Royal Astronomical Society 12/2003; 346(4):1055 - 1077. · 4.90 Impact Factor
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Guinevere Kauffmann,
Timothy M. Heckman,
Simon D. M. White, Stéphane Charlot,
Christy Tremonti,
Eric W. Peng,
Mark Seibert,
Jon Brinkmann,
Robert C. Nichol,
Mark SubbaRao,
Don York
[show abstract]
[hide abstract]
ABSTRACT: We study the relations between stellar mass, star formation history, size and internal structure for a complete sample of 122 808 galaxies drawn from the Sloan Digital Sky Survey. We show that low-redshift galaxies divide into two distinct families at a stellar mass of 3 × 1010 M⊙. Lower-mass galaxies have young stellar populations, low surface mass densities and the low concentrations typical of discs. Their star formation histories are more strongly correlated with surface mass density than with stellar mass. A significant fraction of the lowest-mass galaxies in our sample have experienced recent starbursts. At given stellar mass, the sizes of low-mass galaxies are lognormally distributed with dispersion σ(ln R50) ∼ 0.5, in excellent agreement with the idea that they form with little angular momentum loss through cooling and condensation in a gravitationally dominant dark matter halo. Their median stellar surface mass density scales with stellar mass as μ*∝M0.54*, suggesting that the stellar mass of a disc galaxy is proportional to the three halves power of its halo mass. All of this suggests that the efficiency of the conversion of baryons into stars in low-mass galaxies increases in proportion to halo mass, perhaps as a result of supernova feedback processes. At stellar masses above 3 × 1010 M⊙, there is a rapidly increasing fraction of galaxies with old stellar populations, high surface mass densities and the high concentrations typical of bulges. In this regime, the size distribution remains lognormal, but its dispersion decreases rapidly with increasing mass and the median stellar mass surface density is approximately constant. This suggests that the star formation efficiency decreases in the highest-mass haloes, and that little star formation occurs in massive galaxies after they have assembled.
Monthly Notices of the Royal Astronomical Society 04/2003; 341(1):54 - 69. · 4.90 Impact Factor
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Guinevere Kauffmann,
Timothy M. Heckman,
Simon D. M. White, Stéphane Charlot,
Christy Tremonti,
Jarle Brinchmann,
Gustavo Bruzual,
Eric W. Peng,
Mark Seibert,
Mariangela Bernardi, [......],
Francisco Castander,
Istvan Csábai,
Masataka Fukugita,
Zeljko Ivezic,
Jeffrey A. Munn,
Robert C. Nichol,
Nikhil Padmanabhan,
Aniruddha R. Thakar,
David H. Weinberg,
Donald York
[show abstract]
[hide abstract]
ABSTRACT: We develop a new method to constrain the star formation histories, dust attenuation and stellar masses of galaxies. It is based on two stellar absorption-line indices, the 4000-Å break strength and the Balmer absorption-line index HδA. Together, these indices allow us to constrain the mean stellar ages of galaxies and the fractional stellar mass formed in bursts over the past few Gyr. A comparison with broad-band photometry then yields estimates of dust attenuation and of stellar mass. We generate a large library of Monte Carlo realizations of different star formation histories, including starbursts of varying strength and a range of metallicities. We use this library to generate median likelihood estimates of burst mass fractions, dust attenuation strengths, stellar masses and stellar mass-to-light ratios for a sample of 122 808 galaxies drawn from the Sloan Digital Sky Survey. The typical 95 per cent confidence range in our estimated stellar masses is ±40 per cent. We study how the stellar mass-to-light ratios of galaxies vary as a function of absolute magnitude, concentration index and photometric passband and how dust attenuation varies as a function of absolute magnitude and 4000- Å break strength. We also calculate how the total stellar mass of the present Universe is distributed over galaxies as a function of their mass, size, concentration, colour, burst mass fraction and surface mass density. We find that most of the stellar mass in the local Universe resides in galaxies that have, to within a factor of approximately 2, stellar masses ∼5× 1010 M⊙, half-light radii ∼3 kpc and half-light surface mass densities ∼109 M⊙ kpc−2. The distribution of Dn(4000) is strongly bimodal, showing a clear division between galaxies dominated by old stellar populations and galaxies with more recent star formation.
Monthly Notices of the Royal Astronomical Society 04/2003; 341(1):33 - 53. · 4.90 Impact Factor
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ABSTRACT: There is accumulating observational evidence suggesting that damped Ly$\alpha$ absorption systems systems are the progenitors of present-day spiral galaxies. We use the observed properties of these systems to place constraints on the history of star formation in galactic disks, and on cosmological theories of structure formation in the universe. We show that the observed increase in $\Omega_{HI}$ contributed by damped Ly$\alpha$ systems at high redshift implies that star formation must have been considerably less efficient in the past. We also show that the data can constrain cosmological models in which structure forms at late epochs. A mixed dark matter (MDM) model with $\Omega_{\nu}=0.3$ is unable to reproduce the mass densities of cold gas seen at high redshift, even in the absence of any star formation. We show that at redshifts greater than 3, this model predicts that the total baryonic mass contained in dark matter halos with circular velocities $V_c > 35$ km s$^{-1}$ is less than the observed mass of HI in damped systems. At these redshifts, the photo-ionizing background would prevent gas from dissipating and collapsing to form high column density systems in halos smaller than 35 km s$^{-1}$. MDM models are thus ruled out by the observations. Comment: Latex file
02/1994;
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[show abstract]
[hide abstract]
ABSTRACT: We investigate trends between the recent star formation history and black hole growth in galaxy bulges in the Sloan Digital Sky Survey. The galaxies lie at 0.01 < z < 0.07 where the fibre aperture covers only the central 0.6-4.0 kpc diameter of the galaxy. We find strong trends between black hole growth, as measured by dust-attenuation-corrected [O III] luminosity, and the recent star formation history of the bulges. 56 per cent of the bulges are quiescent with no signs of recent or ongoing star formation and, while almost half of all active galactic nuclei (AGN) lie within these bulges, they contribute only ~10 per cent to the total black hole growth in the local Universe. At the other extreme, the AGN contained within the ~4 per cent of galaxy bulges that are undergoing or have recently undergone the strongest starbursts, contribute at least 10-20 per cent of the total black hole growth. Much of this growth occurs in AGN with high amounts of dust extinction and thus the precise numbers remain uncertain. The remainder of the black hole growth (>60 per cent) is contributed by bulges with more moderate recent or ongoing star formation. The strongest accreting black holes reside in bulges with a wide range in recent star formation history. We conclude that our results support the popular hypothesis for black hole growth occurring through gas inflow into the central regions of galaxies, followed by a starburst and triggering of the AGN. However, while this is a significant pathway for the growth of black holes, it is not the dominant one in the present-day Universe. More unspectacular processes are apparently responsible for the majority of this growth. In order to arrive at these conclusions we have developed a set of new high signal-to-noise ratio (S/N) optical spectral indicators, designed to allow a detailed study of stellar populations which have undergone recent enhanced star formation. Working in the rest-frame wavelength range 3750-4150 Å, ideally suited to many recent and ongoing spectroscopic surveys at low and high redshift, the first two indices are equivalent to the previously well-studied 4000-Å break strength and Hdelta equivalent width. The primary advantage of this new method is a greatly improved S/N for the latter index, allowing the present study to use spectra with S/N per pixel as low as 8. The third index measures the excess strength of Ca II (H&K), which is particularly sensitive to the transition of a post-starburst spectrum from A to F stars, and allows the degeneracy between time of burst and strength of burst to be broken.
Monthly Notices of the Royal Astronomical Society, v.381, 543-572 (2007).
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ABSTRACT: We combine stellar metallicity and stellar mass estimates for a large sample of galaxies drawn from the Sloan Digital Sky Survey Data Release 2 (SDSS DR2) spanning wide ranges in physical properties, in order to derive an inventory of the total mass of metals and baryons locked up in stars in the local Universe. Physical parameter estimates are derived from galaxy spectra with high signal-to-noise ratio (S/N) (of at least 20). Co-added spectra of galaxies with similar velocity dispersions, absolute r-band magnitudes and 4000-Ã
break values are used for those regions of parameter space where individual spectra have lower S/N. We estimate the total density of metals rhoZ and of baryons rho* in stars and, from these two quantities, we obtain a mass- and volume-averaged stellar metallicity of <Z*> = 1.04 +/- 0.14Zsolar, i.e. consistent with solar. We also study how metals are distributed in galaxies according to different properties, such as mass, morphology, mass- and light-weighted age, and we then compare these distributions with the corresponding distributions of stellar mass. We find that the bulk of metals locked up in stars in the local Universe reside in massive, bulge-dominated galaxies, with red colours and high 4000-Ã
break values corresponding to old stellar populations. Bulge-dominated and disc-dominated galaxies contribute similar amounts to the total stellar mass density, but have different fractional contributions to the mass density of metals in stars, in agreement with the mass-metallicity relation. Bulge-dominated galaxies contain roughly 40 per cent of the total amount of metals in stars, while disc-dominated galaxies less than 25 per cent. Finally, at a given galaxy stellar mass, we define two characteristic ages as the median of the distributions of mass and metals as a function of age. These characteristic ages decrease progressively from high-mass to low-mass galaxies, consistent with the high formation epochs of stars in massive galaxies.
Monthly Notices of the Royal Astronomical Society, v.383, 1439-1458 (2008).
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Christy Tremonti,
Timothy Heckman,
Guinevere Kauffmann,
Jarle Brinchmann, Stéphane Charlot,
Simon White,
Mark Seibert,
Eric Peng,
David Schlegel,
Alan Uomoto,
Masataka Fukugita,
Jon Brinkmann
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Christy A. Tremonti,
Timothy M. Heckman,
Guinevere Kauffmann,
Jarle Brinchmann, Stéphane Charlot,
Simon D. M. White,
Mark Seibert,
Eric W. Peng,
David J. Schlegel,
Alan Uomoto,
Masataka Fukugita,
Jon Brinkmann
The Astrophysical Journal, v.613, 898-913 (2004).
