We analyze star formation (SF) as a function of stellar mass (M sub(*)) and redshift z in the All-Wavelength Extended Groth Strip International Survey. For 2905 field galaxies, complete to 10 ...super(10)(10 super(10.8)) M sub((.)) at z < 0.7(1), with Keck spectroscopic redshifts out to z = 1.1, we compile SF rates (SFRs) from emission lines, GALEX, and Spitzer MIPS 24 km photometry, optical-NIR M sub(*) measurements, and HST morphologies. Galaxies with reliable signs of SF form a distinct "main sequence" (MS), with a limited range of SFRs at a given M sub(*) and z (1 s c0.3 dex), and log(SFR) approximately proportional to log M sub(*). The range of log (SFR) remains constant to z > 1, while the MS as a whole moves to higher SFR as z increases. The range of the SFR along the MS constrains the amplitude of episodic variations of SF and the effect of mergers on the SFR. Typical galaxies spend 667%(95%) of their lifetime since z = 1 within a factor of 2(4) of their average SFR at a given M sub(*) and z. The dominant mode of the evolution of SF since z 6 1 is apparently a gradual decline of the average SFR in most individual galaxies, not a decreasing frequency of starburst episodes, or a decreasing factor by which SFRs are enhanced in starbursts. LIRGs at z 6 1 seem to mostly reflect the high SFR typical for massive galaxies at that epoch. The smooth MS may reflect that the same set of few physical processes governs SF prior to additional quenching processes. A gradual process like gas exhaustion may play a dominant role.
We analyze star formation (SF) as a function of stellar mass (M sub(*)) and redshift z in the All-Wavelength Extended Groth Strip International Survey, for star-forming field galaxies with M sub(*) ...10 super(10) M sub((.)) out to z = 1.1. The data indicate that the high specific SF rates (SFRs) of many less massive galaxies do not represent late, irregular or recurrent, starbursts in evolved galaxies. They rather seem to reflect the onset (initial burst) of the dominant SF episode of galaxies, after which SF gradually declines on gigayear timescales to z = 0 and forms the bulk of a galaxy's M sub(*). With decreasing mass, this onset of major SF shifts to decreasing z for an increasing fraction of galaxies (staged galaxy formation). This process may be an important component of the "downsizing" phenomenon. We find that the predominantly gradual decline of SFRs described by Noeske et al. can be reproduced by exponential SF histories (t models), if less massive galaxies have systematically longer e-folding times t, and a later onset of SF (z sub(f)). Our model can provide a first parameterization of SFR as a function of M sub(*) and z, and quantify mass dependences of t and z sub(f) from direct observations of M sub(*) and SFRs up to z> 1. The observed evolution of SF in galaxies can plausibly reflect the dominance of gradual gas exhaustion. The data are also consistent with the history of cosmological accretion onto dark matter halos.
We describe the design and data analysis of the DEEP2 Galaxy Redshift Survey, the densest and largest high-precision redshift survey of galaxies at z approx. 1 completed to date. The survey was ...designed to conduct a comprehensive census of massive galaxies, their properties, environments, and large-scale structure down to absolute magnitude MB = −20 at z approx. 1 via approx.90 nights of observation on the Keck telescope. The survey covers an area of 2.8 Sq. deg divided into four separate fields observed to a limiting apparent magnitude of R(sub AB) = 24.1. Objects with z approx. < 0.7 are readily identifiable using BRI photometry and rejected in three of the four DEEP2 fields, allowing galaxies with z > 0.7 to be targeted approx. 2.5 times more efficiently than in a purely magnitude-limited sample. Approximately 60% of eligible targets are chosen for spectroscopy, yielding nearly 53,000 spectra and more than 38,000 reliable redshift measurements. Most of the targets that fail to yield secure redshifts are blue objects that lie beyond z approx. 1.45, where the O ii 3727 Ang. doublet lies in the infrared. The DEIMOS 1200 line mm(exp −1) grating used for the survey delivers high spectral resolution (R approx. 6000), accurate and secure redshifts, and unique internal kinematic information. Extensive ancillary data are available in the DEEP2 fields, particularly in the Extended Groth Strip, which has evolved into one of the richest multiwavelength regions on the sky. This paper is intended as a handbook for users of the DEEP2 Data Release 4, which includes all DEEP2 spectra and redshifts, as well as for the DEEP2 DEIMOS data reduction pipelines. Extensive details are provided on object selection, mask design, biases in target selection and redshift measurements, the spec2d two-dimensional data-reduction pipeline, the spec1d automated redshift pipeline, and the zspec visual redshift verification process, along with examples of instrumental signatures or other artifacts that in some cases remain after data reduction. Redshift errors and catastrophic failure rates are assessed through more than 2000 objects with duplicate observations. Sky subtraction is essentially photon-limited even under bright OH sky lines; we describe the strategies that permitted this, based on high image stability, accurate wavelength solutions, and powerful B-spline modeling methods. We also investigate the impact of targets that appear to be single objects in ground-based targeting imaging but prove to be composite in Hubble Space Telescope data; they constitute several percent of targets at z approx. 1, approaching approx. 5%-10% at z > 1.5. Summary data are given that demonstrate the superiority of DEEP2 over other deep high-precision redshift surveys at z approx. 1 in terms of redshift accuracy, sample number density, and amount of spectral information. We also provide an overview of the scientific highlights of the DEEP2 survey thus far.
We characterize the mass-dependent evolution of more than 8000 galaxies using spectroscopic redshifts from the DEEP2 Galaxy Redshift Survey in the range 0.4 < z < 1.4 and stellar masses calculated ...from K-band photometry obtained at Palomar Observatory. This sample spans more than 1.5 deg super(2) in four independent fields. Using rest-frame U - B color and O II equivalent widths, we distinguish star-forming from passive populations in order to explore the nature of "downsizing"--a pattern in which the sites of active star formation shift from high-mass galaxies at early times to lower mass systems at later epochs. We identify a mass limit, M sub(Q), above which star formation appears to be quenched and show that the physical mechanisms responsible for downsizing can thus be empirically quantified by charting the evolution in this threshold mass. We find that M sub(Q) decreases with time by a factor of 63 across our redshift range according to M sub(Q) 8(1 + z) super(3.5). To further constrain possible quenching mechanisms, we investigate how downsizing depends on local galaxy environment using the projected third-nearest-neighbor statistic D sub(p,3). For the majority of galaxies near the median density, there is no significant correlation between downsizing and environment. However, a trend is observed in the comparison between environments that are more than 3 times overdense or underdense relative to the median. Here, downsizing appears accelerated in overdense regions that host higher numbers of massive, early-type galaxies as compared to the underdense regions. Our results significantly constrain recent suggestions for the origin of downsizing and indicate that the process for quenching star formation must, primarily, be internally driven.
Strong nebular emission lines are a sensitive probe of star formation and extinction in galaxies, and the O II line detects star-forming populations out to z > 1. However, star formation rates from ...emission lines depend on calibration of extinction and the O II/Ha line ratio, and separating star formation from AGN emission. We use calibrated line luminosities from the DEEP2 survey and Palomar K magnitudes to show that the behavior of emission-line ratios depends on galaxy magnitude and color. For galaxies on the blue side of the color bimodality, the vast majority show emission signatures of star formation, and there are strong correlations of extinction and O II/Ha with rest-frame H magnitude. The conversion of O II to extinction-corrected Ha and thus to star formation rate has a significant slope with M sub(H), 0.23 dex mag super(-1). Red galaxies with emission lines have a much higher scatter in their line ratios, and more than half show AGN signatures. We use 24 km fluxes from Spitzer MIPS to demonstrate the differing populations probed by nebular emission and by mid-IR luminosity. Although extinction is correlated with luminosity, 98% of IR-luminous galaxies at z 6 1 are still detected in the O II line. Mid-IR-detected galaxies are mostly bright and intermediate color, while fainter, bluer galaxies with high O II luminosity are rarely detected at 24 km.
We combine newly measured rotation velocities, velocity dispersions, and stellar masses to construct stellar mass Tully-Fisher relations (M sub(*)TFRs) for 544 galaxies with strong emission lines at ...0.1 z 1.2 from the All-Wavelength Extended Groth Strip International Survey (AEGIS) and the Deep Extragalactic Evolutionary Probe 2 (DEEP2) survey. The conventional M sub(*)TFR using only rotation velocity (V sub(rot)) shows large scatter (61.5 dex in velocity). The scatter and residuals are correlated with morphology in the sense that disturbed, compact, and major merger galaxies have lower velocities for their masses. We construct an M sub(*)TFR using the kinematic estimator S sub(0.5), which is defined as (0.5V super(2) sub(rot) + s super(2) sub(g)) super(1/2) and accounts for disordered or noncircular motions through the gas velocity dispersion (s sub(g)). The new M sub(*)TFR, termed S sub(0.5)/M sub(*)TFR, is remarkably tight over 0.1 < z < 1.2, with no detectable evolution of its intercept or slope with redshift. The average best-fit relation has 0.47 dex scatter in stellar mass, corresponding to 61.2 "magnitudes," assuming a constant mass-to-light ratio. Interestingly, the S sub(0.5)/M sub(*)TFR is consistent with the absorption-line-based stellar mass Faber-Jackson relation for nearby elliptical galaxies in terms of slope and intercept, which might suggest a physical connection between the two relations.
We present a ground-based optical spectroscopic and HST U, V, I photometric study of the blue compact dwarf (BCD) galaxy Pox 186. It is found that the emission of the low-surface brightness (LSB) ...component in Pox 186 at radii $\la$3´´ ($\la$270 pc in linear scale) is mainly gaseous in origin. We detect Hα emission out to radii as large as 6´´. At radii $\ga$3´´ the light of the LSB component is contaminated by the emission of background galaxies complicating the study of the outermost regions. The surface brightness distribution in the LSB component can be approximated by an exponential law with a scale length $\alpha \la 120$ pc. This places Pox 186 among the most compact dwarf galaxies known. The derived α is likely to be an upper limit to the scale length of the LSB component because of the strong contribution of the gaseous emission. The oxygen abundance in the bright H ii region derived from the 4.5 m Multiple Mirror Telescope (MMT) and 3.6 m ESO telescope spectra are $12 + \log\,{\rm (O/H)} = 7.76 \pm 0.02$ and $7.74 \pm 0.01$ (~$Z_\odot$/15), respectively, in accordance with previous determinations. The helium mass fractions found in this region are $Y = 0.248 \pm 0.009$ (MMT) and $Y = 0.248 \pm 0.004$ (3.6 m) suggesting a high primordial helium abundance.
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