Guangtun Zhu

PRIMUS: Constraints on Star Formation Quenching and Galaxy Merging, and the Evolution of the Stellar Mass Function From z=0-1

We measure the evolution of the stellar mass function (SMF) from z = 0−1 using multi-wavelength imaging and spectroscopic redshifts from the PRism MUlti-object Survey (PRIMUS) and the Sloan Digital Sky Survey (SDSS). From PRIMUS we construct an i < 23 flux-limited sample of ∼ 40,000 galaxies at z = 0.2 − 1.0 over five fields totaling ≈ 5.5 deg 2 , and from the SDSS we select ∼ 170,000 galaxies atz = 0.01−0.2 that we analyze consistently with respect to PRIMUS to minimize systematic errors in our evolutionary measurements. We find that the SMF of all galaxies evolves relatively little since z = 1, although we do find evidence for mass assembly downsizing; we measure a ≈ 30% increase in the number density of ∼ 10 10 M⊙ galaxies sincez ≈ 0.6, and a . 10% change in the number density of all & 10 11 M⊙ galaxies since z ≈ 1. Dividing the sample into star-forming and quiescent using an evolving cut in specific star-formation rate, we find that the number density of ∼ 10 10 M⊙ star-forming galaxies stays relatively constant since z ≈ 0.6, whereas the space-density of & 10 11 M⊙ star-forming galaxies decreases by ≈ 50% between z ≈ 1 and z ≈ 0. Meanwhile, the number density of ∼ 10 10 M⊙ quiescent galaxies increases steeply towards low redshift, by a factor of ∼ 2 − 3 since z ≈ 0.6, while the number of massive quiescent galaxies remains approximately constant since z ≈ 1. These results suggest that the rate at which star-forming galaxies are quenched increases with decreasing stellar mass, but that the bulk of the stellar mass buildup within the quiescent population occurs around ∼ 10 10.8 M⊙. In addition, we conclude that mergers do not appear to be a dominant channel for the stellar mass buildup of galaxies at z < 1, even among massive (& 10 11 M⊙) quiescent galaxies. Subject headings: Surveys – galaxies: evolution – galaxies: high-redshift – cosmology: large-scale structure of universe

THE JHU-SDSS METAL ABSORPTION LINE CATALOG: REDSHIFT EVOLUTION AND PROPERTIES OF Mg II ABSORBERS

We present a generic and fully automatic method aimed at detecting absorption lines in the spectra of astronomical objects. The algorithm estimates the source continuum flux using a dimensionality reduction technique and nonnegative matrix factorization, and then detects and identifies metal absorption lines. We apply it to a sample of ~105 quasar spectra from the Sloan Digital Sky Survey and compile a sample of ~40,000 Mg II- and Fe II-absorber systems, spanning the redshift range 0.4 < z < 2.3. The corresponding catalog is publicly available. We study the statistical properties of these absorber systems and find that the rest equivalent width distribution of strong Mg II absorbers follows an exponential distribution at all redshifts, confirming previous studies. Combining our results with recent near-infrared observations of Mg II absorbers, we introduce a new parameterization that fully describes the incidence rate of these systems up to z ~ 5. We find the redshift evolution of strong Mg II absorbers to be remarkably similar to the cosmic star formation history over 0.4 < z < 5.5 (the entire redshift range covered by observations), suggesting a physical link between these two quantities.

THE PRISM MULTI-OBJECT SURVEY (PRIMUS). II. DATA REDUCTION AND REDSHIFT FITTING

The PRIsm MUlti-object Survey (PRIMUS) is a spectroscopic galaxy redshift survey to z ~ 1 completed with a low-dispersion prism and slitmasks allowing for simultaneous observations of ~2500 objects over 0.18 deg2. The final PRIMUS catalog includes ~130,000 robust redshifts over 9.1 deg2. In this paper, we summarize the PRIMUS observational strategy and present the data reduction details used to measure redshifts, redshift precision, and survey completeness. The survey motivation, observational techniques, fields, target selection, slitmask design, and observations are presented in Coil et al. Comparisons to existing higher-resolution spectroscopic measurements show a typical precision of σ z /(1 + z) = 0.005. PRIMUS, both in area and number of redshifts, is the largest faint galaxy redshift survey completed to date and is allowing for precise measurements of the relationship between active galactic nuclei and their hosts, the effects of environment on galaxy evolution, and the build up of galactic systems over the latter half of cosmic history.

STELLAR POPULATIONS OF ELLIPTICAL GALAXIES IN THE LOCAL UNIVERSE

We study the stellar populations of 1923 elliptical galaxies at z < 0.05 selected from the Sloan Digital Sky Survey as a function of velocity dispersion, σ, and environment. Our sample constitutes among the largest high-fidelity samples of elliptical galaxies with uniform imaging and optical spectroscopy assembled to date. Confirming previous studies, we find that elliptical galaxies dominate at high luminosities (L*), and that the highest-σ ellipticals favor high-density environments. We construct average, high signal-to-noise spectra in bins of σ and environment and find the following: (1) lower-σ galaxies have a bluer optical continuum and stronger (but still weak) emission lines; (2) at fixed σ, field ellipticals have a slightly bluer stellar continuum, especially at wavelengths 4000 A, and have stronger (but still weak) emission lines compared with their group counterparts, although this environmental dependence is strongest for low-σ ellipticals and the highest-σ ellipticals are much less affected. Based on Lick indices measured from both the individual and average spectra, we find that (1) at a given σ, elliptical galaxies in groups have systematically weaker Balmer absorption than their field counterparts, although this environmental dependence is most pronounced at low σ; (2) there is no clear environmental dependence of Fe, while the α-element absorption indices such as Mg b are only slightly stronger in galaxies belonging to rich groups. An analysis based on simple stellar populations (SSPs) reveals that more massive elliptical galaxies are older, more metal-rich, and more strongly α-enhanced. We also find that (1) the SSP-equivalent ages of galaxies in rich groups are, on average, ~1 Gyr older than in the field, although once again this effect is strongest at low σ; (2) galaxies in rich groups have slightly lower [Fe/H] and are marginally more strongly α-enhanced; and (3) there is no significant environmental dependence of total metallicity, [Z/H]. Our results are generally consistent with stronger low-level recent star formation in field ellipticals at low σ, similar to recent results based on ultraviolet and infrared observations. We conclude with a brief discussion of our results in the context of recent theoretical models of elliptical galaxy formation.

THE [O II] λ3727 LUMINOSITY FUNCTION AT z ∼ 1

We measure the evolution of the [O II] λ3727 luminosity function (LF) at 0.75 < z < 1.45 using high-resolution spectroscopy of ~14,000 galaxies observed by the Deep Extragalactic Evolutionary Probe 2 galaxy redshift survey. We find that brighter than the LF is well represented by a power law dN/dL L α with slope α ~ –3. The number density of [O II]-emitting galaxies above this luminosity declines by a factor of 2.5 between z ~ 1.35 and z ~ 0.84. In the limit of no number-density evolution, the characteristic [O II] luminosity, , defined as the luminosity where the space density equals 10–3.5 dex-1 Mpc–3, declines by a factor of ~1.8 over the same redshift interval. Assuming that is proportional to the star formation rate (SFR), and negligible change in the typical dust attenuation in galaxies at fixed [O II] luminosity, the measured decline in implies a ~25% per Gyr decrease in the amount of star formation in galaxies during this epoch. Adopting a faint-end power-law slope of –1.3 ± 0.2, we derive the comoving SFR density in four redshift bins centered around z ~ 1 by integrating the observed [O II] LF using a local, empirical calibration between and SFR, which statistically accounts for variations in dust attenuation and metallicity among galaxies. We find that our estimate of the SFR density at z ~ 1 is consistent with previous measurements based on a variety of independent SFR indicators.

PRIMUS: The Relationship between Star Formation and AGN Accretion

We study the evidence for a connection between active galactic nuclei (AGN) fueling and star formation by investigating the relationship between the X-ray luminosities of AGN and the star formation rates (SFRs) of their host galaxies. We identify a sample of 309 AGN with

PRIMUS: GALAXY CLUSTERING AS A FUNCTION OF LUMINOSITY AND COLOR AT 0.2 <z< 1

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PRIMUS: An Observationally Motivated Model to Connect the Evolution of the Active Galactic Nucleus and Galaxy Populations out to z ~ 1

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The large-scale distribution of cool gas around luminous red galaxies

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PRIMUS: ENHANCED SPECIFIC STAR FORMATION RATES IN CLOSE GALAXY PAIRS

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