We study the mean environment of galaxies in the DEEP2 Galaxy Redshift Survey as a function of rest-frame colour, luminosity, and O-ii 3727-Å equivalent width. The local galaxy overdensity for ...>14-000 galaxies at 0.75 < z < 1.35 is estimated using the projected third-nearest-neighbour surface density. Of the galaxy properties studied, mean environment is found to depend most strongly on galaxy colour; all major features of the correlation between mean overdensity and rest-frame colour observed in the local universe were already in place at z∼ 1. In contrast to local results, we find a substantial slope in the mean dependence of environment on luminosity for blue, star forming galaxies at z∼ 1, with brighter blue galaxies being found on average in regions of greater overdensity. We discuss the roles of galaxy clusters and groups in establishing the observed correlations between environment and galaxy properties at high redshift, and we also explore the evidence for a 'downsizing of quenching' from z∼ 1 to ∼0. Our results add weight to existing evidence that the mechanism(s) that result in star formation quenching are efficient in group environments as well as clusters. This work is the first of its kind at high redshift and represents the first in a series of papers addressing the role of environment in galaxy formation at 0 < z < 1.
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 study the applicability of several galaxy environment measures (nth-nearest neighbor distance, counts in an aperture, and Voronoi volume) within deep redshift surveys. Mock galaxy catalogs are ...employed to mimic representative photometric and spectroscopic surveys at high redshift (z 61). We investigate the effects of survey edges, redshift precision, redshift-space distortions, and target selection on each environment measure. We find that even optimistic photometric redshift errors (s super(z) = 0.02) smear out the line-of-sight galaxy distribution irretrievably on small scales; this significantly limits the application of photometric redshift surveys to environment studies. Edges and holes in a survey field dramatically affect the estimation of environment, with the impact of edge effects depending on the adopted environment measure. These edge effects considerably limit the usefulness of smaller survey fields (e.g., the GOODS fields) for studies of galaxy environment. In even the poorest groups and clusters, redshift-space distortions limit the effectiveness of each environment statistic; measuring density in projection (e.g., using counts in a cylindrical aperture or a projected nth-nearest neighbor distance measure) significantly improves the accuracy of measures in such overdense environments. For the DEEP2 Galaxy Redshift Survey, we conclude that among the environment estimators tested the projected nth-nearest neighbor distance measure provides the most accurate estimate of local galaxy density over a continuous and broad range of scales.
We calculate the optical bJ luminosity function (LF) of the 2dF Galaxy Redshift Survey (2dFGRS) for different subsets defined by their spectral properties. These spectrally selected subsets are ...defined using a new parameter, η, which is a linear combination of the first two projections derived from a Principal Component Analysis. This parameter η identifies the average emission- and absorption-line strength in the galaxy rest frame spectrum, and hence is a useful indicator of the present star formation. We use a total of 75 000 galaxies in our calculations, chosen from a sample of high signal-to-noise ratio, low-redshift galaxies observed before 2001 January. We find that there is a systematic steepening of the faint-end slope (α) as one moves from passive (α=-0.54) to active (α=-1.50) star-forming galaxies, and that there is also a corresponding faintening of the rest frame characteristic magnitude M*-5 log10(h) (from −19.6 to −19.2). We also show that the Schechter function provides a poor fit to the quiescent (Type 1) LF for very faint galaxies M-5 log10(h) fainter than −16.0, perhaps suggesting the presence of a significant dwarf population. The LFs presented here give a precise confirmation of the trends seen previously in a much smaller preliminary 2dFGRS sample, and in other surveys. We also present a new procedure for determining self-consistent k-corrections, and investigate possible fibre-aperture biases.
We measure the two-point correlation function xi(r sub(@)p, pi) in a sample of 2219 galaxies between z = 0.7 and 1.35 to a magnitude limit of R sub(AB) = 24.1 from the first season of the DEEP2 ...Galaxy Redshift Survey. From xi(r sub(p), pi) we recover the real-space correlation function, xi(r), which we find can be approximated within the errors by a power law, xi(r) = (r/r sub(0)) super(-gamma), on scales approx0.1-10 h super(-1) Mpc. In a sample with an effective redshift of z sub(eff) = 0.82, for a lambda CDM cosmology we find r sub(0) = 3.53 plus or minus 0.81 h super(-1) Mpc (comoving) and gamma = 1.66 plus or minus 0.12, while in a higher redshift sample with z sub(eff) = 1.14 we find r sub(0) = 3.12 plus or minus 0.72 h super(-1) Mpc and gamma = 1.66 plus or minus 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, r sub(0), 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 plus or minus 0.13 if capital sigma sub(8DM) = 1 today or b = 1.19 plus or minus 0.16 if capital sigma sub(8DM) = 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.
We present the results of a novel new search of the first data-release from the Sloan Digital Sky Survey(SDSS-DR1) for the spectra of supernovae. The use of large spectroscopic galaxy surveys offers ...the prospect of obtaining improved estimates of the local supernova rate, with the added benefit of a very different selection function to that of conventional photometric surveys. In this Letter we present an overview of our search methodology and the details of 19 Type Ia supernovae found in SDSS-DR1. The supernovae sample is used to make a preliminary estimate Gamma{sub Ia} = 0.4 +- 0.2h2 SNu, of the cosmological SNe rate.
We have cross-matched the 1.4-GHz NRAO VLA Sky Survey (NVSS) with the first 210 fields observed in the 2dF Galaxy Redshift Survey (2dFGRS), covering an effective area of 325deg2 (about 20 per cent of ...the final 2dFGRS area). This yields a set of optical spectra of 912 candidate NVSS counterparts, of which we identify 757 as genuine radio identifications – the largest and most homogeneous set of radio source spectra ever obtained. The 2dFGRS radio sources span the redshift range to 0.438, and are a mixture of active galaxies (60 per cent) and star-forming galaxies (40 per cent). About 25 per cent of the 2dFGRS radio sources are spatially resolved by NVSS, and the sample includes three giant radio galaxies with projected linear size greater than 1Mpc. The high quality of the 2dF spectra means we can usually distinguish unambiguously between AGN and star-forming galaxies. We make a new determination of the local radio luminosity function at 1.4GHz for both active and star-forming galaxies, and derive a local star formation density of .
The correlation between the morphology of a galaxy and its observed optical spectrum is investigated. As an example, 4000 galaxies from the 2dF Galaxy Redshift Survey, which possess both good quality ...spectra and have visually determined morphologies, are analysed. Of particular use is the separation of early- and late-type galaxies present in a redshift survey since these can then be used in their respective redshift-independent distance estimators (Dn−σ and Tully-Fisher). It is determined that galaxies in this sample can be relatively successfully separated into these two types by the use of various statistical methods. These methods are briefly outlined in this paper and are also compared to the default 2dFGRS spectral classification η. In addition it is found that the 4000-Å break in the spectrum is the best discriminant in determining its morphological type.
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