Nicholas P. Konidaris

The All-wavelength Extended Groth Strip International Survey (AEGIS) Data Sets

In this the first of a series of Letters, we present a panchromatic data set in the Extended Groth Strip region of the sky. Our survey, the All-Wavelength Extended Groth Strip International Survey (AEGIS), aims to study the physical properties and evolutionary processes of galaxies at z ~ 1. It includes the following deep, wide-field imaging data sets: Chandra/ACIS X-ray, GALEX ultraviolet, CFHT/MegaCam Legacy Survey optical, CFHT/CFH12K optical, Hubble Space Telescope/ACS optical and NICMOS near-infrared, Palomar/WIRC near-infrared, Spitzer/IRAC mid-infrared, Spitzer/MIPS far-infrared, and VLA radio continuum. In addition, this region of the sky has been targeted for extensive spectroscopy using the Deep Imaging Multi-Object Spectrograph (DEIMOS) on the Keck II 10 m telescope. Our survey is compared to other large multiwavelength surveys in terms of depth and sky coverage.

The Deep Evolutionary Exploratory Probe 2 Galaxy Redshift Survey: The Galaxy Luminosity Function to z ~ 1*

The evolution of the B-band galaxy luminosity function is measured using a sample of more than 11,000 galaxies with spectroscopic redshifts from the DEEP2 Redshift Survey. The rest-frame MB versus U - B color-magnitude diagram of DEEP2 galaxies shows that the color-magnitude bimodality seen in galaxies locally is still present at redshifts z > 1. Dividing the sample at the trough of this color bimodality into predominantly red and blue galaxies, we find that the luminosity function of each galaxy color type evolves differently. Blue counts tend to shift to brighter magnitudes at constant number density, while the red counts remain largely constant at a fixed absolute magnitude. Using Schechter functions with fixed faint-end slopes we find that M for blue galaxies brightens by ~1.3 ? 0.14 mag per unit redshift, with no significant evolution in number density. For red galaxies M brightens somewhat less with redshift, while the formal value of * declines. When the population of blue galaxies is subdivided into two halves using the rest-frame color as the criterion, the measured evolution of both blue subpopulations is very similar.The evolution of the B-band galaxy luminosity function is measured using a sample of more than 11,000 galaxies with spectroscopic redshifts from the DEEP2 Redshift Survey. The rest-frame M_B versus U-B color-magnitude diagram of DEEP2 galaxies shows that the color-magnitude bi-modality seen in galaxies locally is still present at redshifts z > 1. Dividing the sample at the trough of this color bimodality into predominantly red and blue galaxies, we find that the luminosity function of each galaxy color type evolves differently. Blue counts tend to shift to brighter magnitudes at constant number density, while the red counts remain largely constant at a fixed absolute magnitude. Using Schechter functions with fixed faint-end slopes we find that M*_B for blue galaxies brightens by ~ 1.3 magnitudes per unit redshift, with no significant evolution in number density. For red galaxies M*_B brightens somewhat less with redshift, while the formal value of phi* declines. When the population of blue galaxies is subdivided into two halves using the rest-frame color as the criterion, the measured evolution of both blue subpopulations is very similar.

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

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 ~ 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 M_B = −20 at z ~ 1 via ~90 nights of observation on the Keck telescope. The survey 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 readily identifiable using BRI photometry and rejected 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 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 ~ 1.45, where the [O ii] 3727 A doublet lies in the infrared. The DEIMOS 1200 line mm^(−1) 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. 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 ~ 1, approaching ~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 ~ 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.

On the Origin of [O II] Emission in Red-Sequence and Poststarburst Galaxies

We investigate the emission-line properties of galaxies with red rest-frame colors (compared to the g - r color bimodality) using spectra from SDSS DR4. Emission lines are detected in more than half of the red galaxies. We focus on the relationship between two emission lines commonly used as star formation rate indicators: Hα and [O II] λ3727. There is a strong bimodality in [O II]/Hα ratio in the SDSS sample that closely corresponds to the bimodality in rest-frame color. Nearly all of the line-emitting red galaxies have line ratios typical of various types of AGNs—most commonly LINERs, a small fraction of transition objects, and, more rarely, Seyferts. Only ~6% of red galaxies display star-forming line ratios. A straight line in the [O II]-Hα EW diagram separates LINER-like galaxies from other categories. Quiescent galaxies with no detectable emission lines and LINER-like galaxies combine to form a single, tight red sequence in color-magnitude-concentration space. [O II] EWs in LINER- and AGN-like galaxies can be as large as those in star-forming galaxies. Thus, unless objects with AGN/LINER-like line ratios are excluded, [O II] emission cannot be used directly as a proxy for star formation rate; this is a particular issue for red galaxies. Lack of [O II] emission is generally used to indicate a lack of star formation when poststarburst galaxies are selected at high redshift. Our results imply, however, that these samples have been cut on AGN properties, as well as star formation, and therefore may provide seriously incomplete sets of poststarburst galaxies. Furthermore, poststarburst galaxies identified in SDSS by requiring minimal Hα EW generally exhibit weak but nonzero line emission with ratios typical of AGNs; few of them show residual star formation. This suggests that most poststarburst galaxies may harbor AGNs/LINERs.

The Lyα Properties of Faint Galaxies at z ~ 2-3 with Systemic Redshifts and Velocity Dispersions from Keck-MOSFIRE

We study the Lya profiles of 36 spectroscopically-detected Lya-emitters (LAEs) at z2-3, using Keck MOSFIRE to measure systemic redshifts and velocity dispersions from rest-frame optical nebular emission lines. The sample has a median optical magnitude R=26.0, and ranges from R23 to R>27, corresponding to rest-frame UV absolute magnitudes M_UV-22 to M_UV>-18.2. Dynamical masses range from M_dyn 3 sigma significance: brighter galaxies with larger velocity dispersions tend to have larger values of dv_Lya. We also make use of a comparison sample of 122 UV-color-selected R<25.5 galaxies at z2, all with Lya emission and systemic redshifts measured from nebular emission lines. Using the combined LAE and comparison samples for a total of 158 individual galaxies, we find that dv_Lya is anti-correlated with the Lya equivalent width with 7 sigma significance. Our results are consistent with a scenario in which the Lya profile is determined primarily by the properties of the gas near the systemic redshift; in such a scenario, the opacity to Lya photons in lower mass galaxies may be reduced if large gaseous disks have not yet developed and if the gas is ionized by the harder spectrum of young, low metallicity stars.

The DEEP2 galaxy redshift survey : Mean ages and metallicities of red field galaxies at z ∼ 0.9 from stacked keck DEIMOS spectra

Version: Aug 29, 2006 A Preprint typeset using L TEX style emulateapj v. 04/21/05 THE DEEP2 GALAXY REDSHIFT SURVEY: MEAN AGES AND METALLICITIES OF RED FIELD GALAXIES AT Z ∼ 0.9 FROM STACKED KECK/DEIMOS SPECTRA 1 Ricardo P. Schiavon 2 , S. M. Faber 3 , Nicholas Konidaris 3 , Genevieve Graves 3 , Christopher N.A. Willmer 3,4 , Benjamin J. Weiner 5 , Alison L. Coil 4,6,8 , Michael C. Cooper 6 , Marc Davis 6 , Justin Harker 3 , David C. Koo 3 , Jeffrey A. Newman 6,7,8 & Renbin Yan 6 2 Department of Astronomy, University of Virginia, P.O. Box 3818, Charlottesville, VA 22903-0818 UCO/Lick Observatory/Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 4 Steward Observatory, University of Arizona, Tucson, AZ 85721 5 Department of Astronomy, University of Maryland, College Park, MD 20742-2421 6 Department of Astronomy, University of California, Berkeley, 601 Campbell Hall, Berkeley, CA 94720-3411 7 Lawrence Berkeley National Laboratory, Berkeley, CA 94720 and 8 Hubble Fellow Version: Aug 29, 2006 ABSTRACT As part of the DEEP2 galaxy redshift survey, we analyze absorption line strengths in stacked Keck/DEIMOS spectra of red field galaxies with weak to no emission lines, at redshifts 0.7 ≤ z ≤ 1. Comparison with models of stellar population synthesis shows that red galaxies at z ∼ 0.9 have mean luminosity-weighted ages of the order of only 1 Gyr and at least solar metallicities. These ages cannot be reconciled with a scenario where all stars evolved passively after forming at very high z. Rather, a significant fraction of stars can be no more than 1 Gyr old, which means that some star formation in the stacked populations continued to at least z ∼ 1.2. Furthermore, a comparison of these distant galaxies with a local SDSS sample, using stellar populations synthesis models, shows that the drop in the equivalent width of Hδ from z ∼ 0.9 to 0.1 is less than predicted by passively evolving models. This admits of two interpretations: either each individual galaxy experiences continuing low-level star formation, or the red-sequence galaxy population from z ∼ 0.9 to 0.1 is continually being added to by new galaxies with younger stars. Subject headings: Galaxies: evolution — Galaxies: stellar content — Galaxies: distances and redshifts 1. INTRODUCTION The formation of early-type galaxies is one of the on- going riddles of modern cosmology. According to the leading models, massive early-type galaxies have been assembled hierarchically from the merging of less mas- sive structures. Because such mergers are seen locally to be accompanied by star formation (e.g., Schweizer & Seitzer 1992), one of the best ways to test the hierarchical formation paradigm is by determining the star formation history of early-type galaxies. This can be achieved by estimating the ages of stars in galaxies from their inte- grated light, through comparison with stellar population synthesis models. Several groups have attempted this from observations of distant massive galaxies (e.g., Le Borgne et al. 2006, Treu et al. 2005, Daddi et al. 2005, Longhetti et al. 2005, and references therein). However, spectroscopic dating of stellar populations older than ∼ 1 Gyr is best achieved by simultaneously matching the strengths of Balmer and metal lines in their integrated spectra, in order to break the age-metallicity degener- acy. So far, observational difficulties have prevented such detailed studies for all but local samples (e.g., Gonz´ lez a 1993, Trager et al. 2000, Kuntschner 2000, Caldwell et al. 2003, Eisenstein et al. 2003, Thomas et al. 2005, Schiavon 2006, and references therein). In this Letter we present the analysis of absorption line strengths measured in stacked integrated Keck/DEIMOS spectra of red galaxies with redshifts between 0.7 and 1, as part of the DEEP2 survey (Davis et al. 2003). We find that these galaxies have mean light-weighted single stellar population (SSP) ages of order only 1 Gyr and metallicities at least solar. Since these objects are ob- served several billion years after the big bang, this result suggests that stars populating these galaxies were formed during an extended period of time. 2. SAMPLE AND DATA The data used in this Letter consist of k-corrected U and B absolute magnitudes in the Vega system and 1- hour exposure Keck/DEIMOS (Faber et al. 2003) spec- tra from DEEP2 (Davis et al. 2003). Redshift deter- minations are described in Davis et al. (2003), and rest- frame M B magnitudes and U–B colors were derived from CFHT BRI photometry and redshifts by Willmer et al. (2006). The S/N of each 1-hour exposure spectrum is not high enough for accurate measurement of absorption line indices, so we stack spectra of hundreds of galaxies, selected in bins of color, luminosity, and redshift. 2.1. Sample Selection Based on observations taken at the W. M. Keck Observatory Our goal is to study the evolution of red-sequence galaxies, so we first select galaxies by color, as illustrated in left panel of Figure 1, where data for 17,745 DEEP2 galaxies with 0.7 ≤ z ≤ 1.05 were used to produce a contour plot in restframe color-magnitude space. Red- sequence galaxies (RSGs) are chosen to be those with U–B ≥ 0.25, making up a total of 1941 objects. Ideally, we would also like to select galaxies on the basis of mor- phology, but we lack that information for this sample. In order to minimize contamination by reddened late-

Keck-I MOSFIRE Spectroscopy of Compact Star- Forming Galaxies at z≳ 2: High Velocity Dispersions in Progenitors of Compact Quiescent Galaxies

We present Keck-I MOSFIRE near-infrared spectroscopy for a sample of 13 compact star-forming galaxies (SFGs) at redshift 2 ≤ z ≤ 2.5 with star formation rates of SFR ~ 100 M_☉ yr^(–1) and masses of log(M/M_☉) ~10.8. Their high integrated gas velocity dispersions of σ_(int_ =230^(+40)_(-30) km s^(–1), as measured from emission lines of Hα and [O III], and the resultant M_* -σ_(int) relation and M_*-M_(dyn) all match well to those of compact quiescent galaxies at z ~ 2, as measured from stellar absorption lines. Since log(M*/M_(dyn)) =–0.06 ± 0.2 dex, these compact SFGs appear to be dynamically relaxed and evolved, i.e., depleted in gas and dark matter (<13^(+17)_(-13)%), and present larger σ_(int) than their non-compact SFG counterparts at the same epoch. Without infusion of external gas, depletion timescales are short, less than ~300 Myr. This discovery adds another link to our new dynamical chain of evidence that compact SFGs at z ≳ 2 are already losing gas to become the immediate progenitors of compact quiescent galaxies by z ~ 2.

THE DEEP2 GALAXY REDSHIFT SURVEY: THE VORONOI-DELAUNAY METHOD CATALOG OF GALAXY GROUPS

We present a public catalog of galaxy groups constructed from the spectroscopic sample of galaxies in the fourth data release from the Deep Extragalactic Evolutionary Probe 2 (DEEP2) Galaxy Redshift Survey, including the Extended Groth Strip (EGS). The catalog contains 1165 groups with two or more members in the EGS over the redshift range 0 0.6 in the rest of DEEP2. Twenty-five percent of EGS galaxies and fourteen percent of high-z DEEP2 galaxies are assigned to galaxy groups. The groups were detected using the Voronoi-Delaunay method (VDM) after it has been optimized on mock DEEP2 catalogs following similar methods to those employed in Gerke et al. In the optimization effort, we have taken particular care to ensure that the mock catalogs resemble the data as closely as possible, and we have fine-tuned our methods separately on mocks constructed for the EGS and the rest of DEEP2. We have also probed the effect of the assumed cosmology on our inferred group-finding efficiency by performing our optimization on three different mock catalogs with different background cosmologies, finding large differences in the group-finding success we can achieve for these different mocks. Using the mock catalog whose background cosmology is most consistent with current data, we estimate that the DEEP2 group catalog is 72% complete and 61% pure (74% and 67% for the EGS) and that the group finder correctly classifies 70% of galaxies that truly belong to groups, with an additional 46% of interloper galaxies contaminating the catalog (66% and 43% for the EGS). We also confirm that the VDM catalog reconstructs the abundance of galaxy groups with velocity dispersions above ~300 km s^(–1) to an accuracy better than the sample variance, and this successful reconstruction is not strongly dependent on cosmology. This makes the DEEP2 group catalog a promising probe of the growth of cosmic structure that can potentially be used for cosmological tests.

The DEEP2 Redshift Survey: Lyα Emitters in the Spectroscopic Database*

We present the first results of a search for Lyα emitters (LAEs) in the DEEP2 spectroscopic database that uses a search technique that is different from but complementary to traditional narrowband imaging surveys. We have visually inspected ~20% of the available DEEP2 spectroscopic data and have found nine high-quality LAEs with clearly asymmetric line profiles and an additional 10 objects of lower quality, some of which may also be LAEs. Our survey is most sensitive to LAEs at z = 4.4–4.9 and that is indeed where all but one of our high-quality objects are found. We find the number density of our spectroscopically discovered LAEs to be consistent with those found in narrowband imaging searches. The combined, averaged spectrum of our nine high-quality objects is well fit by a two-component model, with a second, lower amplitude component redshifted by ~420 km s−1 with respect to the primary Lyα line, consistent with large-scale outflows from these objects. We conclude by discussing the advantages and future prospects of blank-sky spectroscopic surveys for high-z LAEs.

Far-Infrared Characterization of an Ultraluminous Starburst Associated with a Massively Accreting Black Hole at z = 1.15

As part of the All-Wavelength Extended Groth Strip International Survey (AEGIS), we describe the panchromatic characterization of an X-ray–luminous active galactic nucleus (AGN) in a merging galaxy at z = 1.15. This object is detected at infrared (8, 24, 70, and 160 μm), submillimeter (850 μm), and radio wavelengths, from which we derive a bolometric luminosity Lbol ∼ 9 x 10^12 L☉. We find that the AGN clearly dominates the hot dust emission below 40 μm but its total energetic power inferred from the hard X-rays is substantially less than the bolometric output of the system. About 50% of the infrared luminosity is indeed produced by a cold dust component that probably originates from enshrouded star formation in the host galaxy. In the context of a coeval growth of stellar bulges and massive black holes, this source might represent a “transition” object, sharing properties with both quasars and luminous starbursts. Study of such composite galaxies will help address how the star formation and disk-accretion phenomena may have regulated each other at high redshift and how this coordination may have participated in the buildup of the relationship observed locally between the masses of black holes and stellar spheroids.