The DEEP2 Galaxy Redshift Survey: Design, Observations, Data Reduction, and Redshifts

TL;DR

DEEP2 delivers a large, high-resolution spectroscopic census of galaxies near $z\sim1$ with ~53,000 spectra and ~38,000 secure redshifts across four wide fields. The design emphasizes a simple, well-characterized selection function, dense sampling for environmental and clustering studies, and high spectral resolution ($R\sim6000$) to resolve kinematic features via the [O II] 3727 doublet. A comprehensive data-reduction pipeline (spec2d/spec1d) and an interactive redshift verification tool (zspec) yield robust redshifts with quantified completeness and reliability, all publicly available in Data Release 4 (DR4). Key science highlights include growth of the red sequence, the star-formation main sequence, halo-mass–dependent quenching, and detailed clustering and environmental analyses at $z\sim1$, supported by rich multiwavelength ancillary data in the DEEP2 fields. The work establishes a legacy dataset for galaxy evolution and large-scale structure studies, with future extensions (e.g., DEEP3) planned to extend spectral coverage and sample size.

Abstract

We describe the design and data sample from the DEEP2 Galaxy Redshift Survey, the densest and largest precision-redshift survey of galaxies at z ~ 1 completed to date. The survey has conducted a comprehensive census of massive galaxies, their properties, environments, and large-scale structure down to absolute magnitude M_B = -20 at z ~ 1 via ~90 nights of observation on the DEIMOS spectrograph at Keck Observatory. DEEP2 covers an area of 2.8 deg^2 divided into four separate fields, observed to a limiting apparent magnitude of R_AB=24.1. Objects with z < 0.7 are rejected based on BRI photometry in three of the four DEEP2 fields, allowing galaxies with z > 0.7 to be targeted ~2.5 times more efficiently than in a purely magnitude-limited sample. Approximately sixty percent of eligible targets are chosen for spectroscopy, yielding nearly 53,000 spectra and more than 38,000 reliable redshift measurements. Most of the targets which fail to yield secure redshifts are blue objects that lie beyond z ~ 1.45. The DEIMOS 1200-line/mm grating used for the survey delivers high spectral resolution (R~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. DEEP2 surpasses other deep precision-redshift surveys at z ~ 1 in terms of galaxy numbers, 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. 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 publicly-available DEEP2 DEIMOS data reduction pipelines. [Abridged]

Figures (51)

• Figure 1: 2-d redshift completeness maps, $w( , )$, in DEEP2 Fields 2, 3, and 4, updated from Cooper et al. (2006). The boundaries for each pointing of the DEEP2 CFHT 12K $BRI$ photometry are indicated by the dashed lines, labelled by the pointing number (e.g., pointing 21 is the first pointing in DEEP2 Field 2). The grey scale at each point represents the probability that a galaxy in that mask meeting the DEEP2 sample selection criteria was targeted for spectroscopy and that a $Q=3$ or $Q=4$ redshift was measured. Most of the slitmasks for each pointing are in two rows of approximately 20 masks each. The small white lines correspond to gaps between the DEIMOS CCDs. The darker regions show areas where masks overlap and objects are therefore observed with higher probability. At the intersection of the top and bottom rows, objects may be observed twice, allowing verification of redshift repeatability, etc.; however, the vertical masks filling in the "fishtails" at the east end of each pointing do not contain duplicate objects.
• Figure 2: As Figure \ref{['cooper.deep2.wfn.eps']}, but for the Extended Groth Strip (DEEP2 Field 1). Pointing boundaries for the CFHT 12K $BRI$ photometry catalog are again shown as dashed lines. Masks were designed in eight blocks along the long direction of the Strip. Each block has 15 masks, eight perpendicular to the strip and 7 parallel. Masks overlap extensively but unlike in Fields 2, 3, and 4 there are very few duplicate observations built into the design. DEEP2 pointing 14 is omitted here, as mask design in that region followed different algorithms to account for its poorer photometry. Pointing 14 is therefore not included in any DEEP2 large-scale structure analyses.
• Figure 3: Initial data in the Extended Groth Strip (DEEP2 Field 1). Details of the individual data sets are given in Table \ref{['table.otherdata']}. The CFHT 12K imaging provides the $BRI$pcat photometry used for DEEP2 target selection. The HST/ACS mosaic is one of the largest two-color $V+I$ mosaics on the sky. The Guaranteed Time Observation Spitzer/IRAC data and the Chandra 200 ksec data are the deepest/widest of their kind, and the CFHT Legacy Survey provides valuable synoptic variability data. EGS has also been imaged deeply with the VLA at 20 cm and with the GMRT (not shown) at 50 cm.
• Figure 4: Data in the Extended Groth Strip are continually expanding. Details of the individual data sets are given in Table \ref{['table.otherdata']}. The FIDEL Spitzer/MIPS, AEGIS-X Chandra/ACIS, and GALEX/FUV+NUV imaging are the deepest exposures of their size on the sky. The ongoing DEEP3 survey (Cooper et al. 2012, in prep) will increase the number of DEEP2 spectra by 50% and triple the weight of environmental data in the upper three fields of EGS. The Warm Spitzer Deep Extragalactic Survey (SEDS) will provide a total of 10 hours of integration time per pointing in IRAC Channels 1 and 2 (centered at 3.6 and 4.5 $$m). The NEWFIRM survey will provide $JK$ photometry to $\sim$24 AB mag, while the NEWFIRM Intermediate Band Survey (PI: Pieter van Dokkum; cf. van Dokkum et al. 2009) will measure photoz's to roughly $K_{\rm AB} \sim 23.4$. In addition (not shown), EGS is a deep SCUBA-2 Legacy field and a deep field for the Herschel HERMES survey with the PACS and SPIRE instruments.
• Figure 5: Number of redshifts vs. volume sampled for major spectroscopic redshift surveys out to $z \sim 1$. For all surveys except zCOSMOS-bright, we use the number of redshifts and areas covered to date (as given in Table \ref{['table.othersurveys']} for the distant surveys). For zCOSMOS-bright, which is still in progress, design data are used. Numbers in all cases use reliable redshifts only (those with probabilities of being correct $\ge$95%). Volumes covered are computed from the field areas and magnitude limits of each survey as described in §\ref{['surveyparameters']}. The TKRS survey is omitted from this figure (although included in Table \ref{['table.othersurveys']}) due to the relatively small sample size and volume. PRIMUS has low-resolution spectra, and provides coarser redshift information for brighter samples than the other higher-$z$ surveys shown. If it is set aside, DEEP2 leads amongst distant surveys in both volume surveyed and number of reliable redshifts.