Publications (44)113.29 Total impact
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Article: The Dependence of Quenching upon the Inner Structure of Galaxies at 0.5<z< 0.8 in the DEEP2/AEGIS Survey
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ABSTRACT: The shutdown of star formation in galaxies is generally termed `quenching'. Although quenching may occur through a variety of processes, the exact mechanism(s) that is in fact responsible for quenching is still in question. This paper addresses quenching by searching for traces of possible quenching processes through their effects on galaxy structural parameters such as surface stellar mass density and Sersic index (n). We analyze the rest-frame U-B color correlations versus these structural parameters using a sample of galaxies in the redshift range 0.5< z<0.8 from the DEEP2/AEGIS survey. We find that Sersic index (n) has the smallest overlap region among all tested parameters and resembles a step-function with a threshold value of n=2.3. There exists, however, a significant population of outliers with blue colors yet high n values that seem to contradict this behavior. We hypothesize that their Sersic values may be distorted by bursts of star formation, AGNs, and/or poor fits, leading us to consider central surface stellar mass density as an alternative to Sersic index. Not only does it correct the outliers, it also forms a tight relationship with color, suggesting that the innermost structure of galaxies is most physically linked with quenching. Furthermore, at z~0.65, the majority of the blue cloud galaxies cannot simply fade onto the red sequence since their GIM2D bulge masses are only half as large on average as the bulge masses of similar red sequence galaxies, thus demonstrating that stellar mass must absolutely increase at the centers of galaxies as they quench. We discuss a two-stage model for quenching in which galaxy star formation rates are controlled by their dark halos while they are still in the blue cloud and a second quenching process sets in later, associated with the central stellar mass build-up.10/2012; -
Article: The DEEP2 Galaxy Redshift Survey: The Voronoi-Delaunay Method catalog of galaxy groups
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ABSTRACT: We present a public catalog of galaxy groups constructed from the spectroscopic sample of galaxies in the fourth data release from the 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<z<1.5 and 1295 groups at z>0.6 in the rest of DEEP2. 25% of EGS galaxies and 14% of high-z DEEP2 galaxies are assigned to galaxy groups. The groups were detected using the Voronoi-Delaunay Method, after it has been optimized on mock DEEP2 catalogs following similar methods to those employed in Gerke et al. (2005). 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). (Abridged)03/2012; -
Article: The DEEP2 Galaxy Redshift Survey: Design, Observations, Data Reduction, and Redshifts
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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]03/2012; -
Article: The Direct Detection of Cool, Metal-Enriched Gas Accretion onto Galaxies at z ~ 0.5
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ABSTRACT: We report on the discovery of cool gas inflow toward six star-forming galaxies with redshifts z ~ 0.35 - 1. Analysis of MgII and FeII resonance-line absorption in Keck/LRIS spectroscopy of this sample reveals velocity shifts of 80 - 200 km/s and equivalent widths for inflowing gas of >~ 0.6 Ang in five of the six objects. The host galaxies exhibit a wide range in star formation rates (SFR ~ 1 - 40 M_sun/yr) and have stellar masses similar to that of the Milky Way (log M_*/M_sun ~ 9.6 - 10.5). Imaging from the Hubble Space Telescope Advanced Camera for Surveys indicates that five of the six galaxies have highly inclined (i > 55 deg), disk-like morphologies. These data represent the first unambiguous detection of inflow into isolated, star-forming galaxies in the distant universe. We suggest that the inflow is due to the infall of enriched material from dwarf satellites and/or a galactic fountain within the galaxies. Assuming that the material has been enriched to 0.1Z_sun and has a physical extent approximately equal to that of the galaxies, we infer mass inflow rates of dM_in/dt >~ 0.2 - 3 M_sun/yr for four of these systems. Finally, from comparison of these absorption lines to the profiles of MgII and FeII absorption in a larger spectroscopic sample of ~100 objects, we measure a covering fraction of cool inflow of at least 6%, but cannot rule out the presence of enriched infall onto as many as ~40 of these galaxies.10/2011; -
Article: Low-ionization Line Emission from Starburst Galaxies: A New Probe of Galactic-Scale Outflows
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ABSTRACT: We study the kinematically narrow, low-ionization line emission from a bright, starburst galaxy at z = 0.69 using slit spectroscopy obtained with Keck/LRIS. The spectrum reveals strong absorption in MgII and FeII resonance transitions with Doppler shifts of -200 to -300 km/s, indicating a cool gas outflow. Emission in MgII near and redward of systemic velocity, in concert with the observed absorption, yields a P Cygni-like line profile similar to those observed in the Ly alpha transition in Lyman Break Galaxies. Further, the MgII emission is spatially resolved, and extends significantly beyond the emission from stars and HII regions within the galaxy. Assuming the emission has a simple, symmetric surface brightness profile, we find that the gas extends to distances > ~7 kpc. We also detect several narrow FeII* fine-structure lines in emission near the systemic velocity, arising from energy levels which are radiatively excited directly from the ground state. We suggest that the MgII and FeII* emission is generated by photon scattering in the observed outflow, and emphasize that this emission is a generic prediction of outflows. These observations provide the first direct constraints on the minimum spatial extent and morphology of the wind from a distant galaxy. Estimates of these parameters are crucial for understanding the impact of outflows in driving galaxy evolution. Comment: Submitted to ApJL. 6 pages, 4 figures. Uses emulateapj format08/2010; -
Article: The Infrared Imaging Spectrograph (IRIS) for TMT: the atmospheric dispersion corrector
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ABSTRACT: We present a conceptual design for the atmospheric dispersion corrector (ADC) for TMT's Infrared Imaging Spectrograph (IRIS). The severe requirements of this ADC are reviewed, as are limitations to observing caused by uncorrectable atmospheric effects. The requirement of residual dispersion less than 1 milliarcsecond can be met with certain glass combinations. The design decisions are discussed and the performance of the design ADC is described. Alternative options and their performance tradeoffs are also presented. Comment: SPIE Astronomical Instrumentation 201007/2010; -
Article: The Infrared Imaging Spectrograph (IRIS) for TMT: Instrument Overview
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ABSTRACT: We present an overview of the design of IRIS, an infrared (0.85 - 2.5 micron) integral field spectrograph and imaging camera for the Thirty Meter Telescope (TMT). With extremely low wavefront error (<30 nm) and on-board wavefront sensors, IRIS will take advantage of the high angular resolution of the narrow field infrared adaptive optics system (NFIRAOS) to dissect the sky at the diffraction limit of the 30-meter aperture. With a primary spectral resolution of 4000 and spatial sampling starting at 4 milliarcseconds, the instrument will create an unparalleled ability to explore high redshift galaxies, the Galactic center, star forming regions and virtually any astrophysical object. This paper summarizes the entire design and basic capabilities. Among the design innovations is the combination of lenslet and slicer integral field units, new 4Kx4k detectors, extremely precise atmospheric dispersion correction, infrared wavefront sensors, and a very large vacuum cryogenic system. Comment: 13 pages, SPIE conference07/2010; -
Article: Galaxies probing galaxies: cool halo gas from a z = 0.47 post-starburst galaxy
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ABSTRACT: We study the cool gas around a galaxy at z = 0.4729 using Keck/LRIS spectroscopy of a bright (B = 21.7) background galaxy at z = 0.6942 at a transverse distance of 16.5/h_70 kpc. The background galaxy spectrum reveals strong FeII, MgII, MgI, and CaII absorption at the redshift of the foreground galaxy, with a MgII 2796 rest equivalent width of 3.93 +/- 0.08 Angstroms, indicative of a velocity width exceeding 400 km/s. Because the background galaxy is large (> 4/h_70 kpc), the high covering fraction of the absorbing gas suggests that it arises in a spatially extended complex of cool clouds with large velocity dispersion. Spectroscopy of the massive (log M_*/M_sun = 11.15 +/- 0.08) host galaxy reveals that it experienced a burst of star formation about 1 Gyr ago and that it harbors a weak AGN. We discuss the possible origins of the cool gas in its halo, including multiphase cooling of hot halo gas, cold inflow, tidal interactions, and galactic winds. We conclude the absorbing gas was most likely ejected or tidally stripped from the interstellar medium of the host galaxy or its progenitors during the past starburst event. Adopting the latter interpretation, these results place one of only a few constraints on the radial extent of cool gas driven or stripped from a galaxy in the distant Universe. Future studies with integral field unit spectroscopy of spatially extended background galaxies will provide multiple sightlines through foreground absorbers and permit analysis of the morphology and kinematics of the gas surrounding galaxies with a diverse set of properties and environments.07/2009; -
Article: Optical Rotation Curves of Distant Field Galaxies: Keck Results at Redshifts to z ~ 1
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ABSTRACT: Spatially resolved velocity profiles are presented for nine faint field galaxies in the redshift range 0.1 z 1, based on moderate-resolution spectroscopy obtained with the Keck 10 m telescope. These data were augmented with high-resolution Hubble Space Telescope images from WFPC2, which provided V and I photometry, galaxy type, orientation, and inclination. The effects of seeing, slit width, and slit misalignment with respect to galaxy major axis were modeled along with inclination for each source, in order to derive a maximum circular velocity from the observed rotation curve. The lowest redshift galaxy, though highly elongated, shows a distorted low-amplitude rotation curve that suggests a merger in progress seen perpendicular to the collision path. The remaining rotation curves appear similar to those of local galaxies in both form and amplitude, implying that some massive disks were in place at z ~ 1. The key result is that the kinematics of these distant galaxies show evidence for only a modest increase in luminosity (ΔMB 0.6) compared to velocity-luminosity (Tully-Fisher) relations for local galaxies.The Astrophysical Journal 01/2009; 465(1):L15. · 6.02 Impact Factor -
Article: The DEEP2 Galaxy Redshift Survey: Clustering of Galaxies in Early Data
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ABSTRACT: We measure the two-point correlation function ξ(rp, π) in a sample of 2219 galaxies between z = 0.7 and 1.35 to a magnitude limit of RAB = 24.1 from the first season of the DEEP2 Galaxy Redshift Survey. From ξ(rp, π) we recover the real-space correlation function, ξ(r), which we find can be approximated within the errors by a power law, ξ(r) = (r/r0)-γ, on scales ~0.1-10 h-1 Mpc. In a sample with an effective redshift of zeff = 0.82, for a ΛCDM cosmology we find r0 = 3.53 ± 0.81 h-1 Mpc (comoving) and γ = 1.66 ± 0.12, while in a higher redshift sample with zeff = 1.14 we find r0 = 3.12 ± 0.72 h-1 Mpc and γ = 1.66 ± 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, r0, 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 ± 0.13 if σ8DM = 1 today or b = 1.19 ± 0.16 if σ8DM = 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.The Astrophysical Journal 12/2008; 609(2):525. · 6.02 Impact Factor -
Article: The DEEP Groth Strip Survey. VII. The Metallicity of Field Galaxies at 0.26
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ABSTRACT: Using spectroscopic data from the Deep Extragalactic Evolutionary Probe Groth Strip Survey (DGSS), we analyze the gas-phase oxygen abundances in the warm ionized medium for 64 emission-line field galaxies in the redshift range 0.26 < z < 0.82. These galaxies comprise a small subset selected from among 693 objects in the DGSS. They are chosen for chemical analysis by virtue of having the strongest emission lines. Oxygen abundances relative to hydrogen are in the range 8.4 < 12 + log(O/H) < 9.0 with typical internal plus systematic measurement uncertainties of 0.17 dex. The 64 DGSS galaxies collectively exhibit an increase in metallicity with B-band luminosity, i.e., an L-Z relation like that seen among local galaxies. Using the DGSS sample and local galaxy samples for comparison, we searched for a "second parameter" that might explain some of the dispersion seen in the L-Z relation. Parameters such as galaxy color, emission-line equivalent width, and effective radius were explored but found to be uncorrelated with residuals from the mean L-Z relation. Subsets of DGSS galaxies binned by redshift also exhibit L-Z correlations with slopes and zero points that evolve smoothly with redshift. DGSS galaxies in the highest redshift bin (z = 0.6-0.82) are brighter, on average, by ~1 mag at fixed metallicity than those in the lowest DGSS redshift bin (z = 0.26-0.40) and by up to ~2.4 mag compared to local (z < 0.1) emission-line field galaxies. Alternatively, DGSS galaxies in the highest redshift bin (z = 0.6-0.82) are, on average, 40% (0.15 dex) more metal-poor at fixed luminosity than local (z < 0.1) emission-line field galaxies. For 0.6 < z < 0.8 galaxies, the offset from the local L-Z relation is greatest for objects at the low-luminosity (MB > -19) end of the sample and is vanishingly small for objects at the high-luminosity end of the sample (MB ~ -22). We compare these data to simple single-zone, exponential-infall PÉGASE2 models, which follow the chemical and luminous evolution of galaxies from formation to z = 0. A narrow range of model parameters can qualitatively produce the slope of the L-Z relation and the observed evolution of slope and zero point with redshift when at least two of the following are true: (1) low-mass galaxies have lower effective chemical yields than massive galaxies, (2) low-mass galaxies assemble on longer timescales than massive galaxies, and (3) low-mass galaxies begin the assembly process at a later epoch than massive galaxies. The single-zone models do a reasonable job of reproducing the observed evolution for the low-luminosity galaxies (MB ~ -19) in our sample but fail to predict the relative lack of evolution in the L-Z plane observed for the most luminous galaxies (MB ~ -22). More realistic multizone models will be required to explain the chemoluminous evolution of large galaxies.The Astrophysical Journal 12/2008; 599(2):1006. · 6.02 Impact Factor -
Article: The DEEP Groth Strip Survey. I. The Sample
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ABSTRACT: The Deep Extragalactic Exploratory Probe (DEEP) is a multiphase research program dedicated to the study of the formation and evolution of galaxies and of large-scale structure in the distant universe. This paper describes the first five-year phase, denoted DEEP1. A series of 10 DEEP1 papers will discuss a range of scientific topics (e.g., the study of photometric and spectral properties of a general distant galaxy survey, the evolution observed in galaxy populations of varied morphologies). The observational basis for these studies is the Groth Survey Strip field, a 127 arcmin2 region that has been observed with the Hubble Space Telescope (HST) in both broad I-band and V-band optical filters and with the Low Resolution Imaging Spectrograph on the Keck Telescopes. Catalogs of photometric and structural parameters have been constructed for 11,547 galaxies and stars at magnitudes brighter than 29, and spectroscopy has been conducted for a magnitude-color weighted subsample of 818 objects. We evaluate three independent techniques for constructing an imaging catalog for the field from the HST data and discuss the depth and sampling of the resultant catalogs. The selection of the spectroscopic subsample is discussed, and we describe the multifaceted approach taken to prioritizing objects of interest for a variety of scientific subprograms. A series of Monte Carlo simulations then demonstrates that the spectroscopic subsample can be adequately modeled as a simple function of magnitude and color cuts in the imaging catalog.The Astrophysical Journal Supplement Series 12/2008; 159(1):41. · 13.46 Impact Factor -
Article: The DEEP Groth Strip Galaxy Redshift Survey. III. Redshift Catalog and Properties of Galaxies
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ABSTRACT: The Deep Extragalactic Evolutionary Probe (DEEP) is a series of spectroscopic surveys of faint galaxies, targeted at understanding the properties and clustering of galaxies at redshifts z ~ 1. We present the redshift catalog of the DEEP1 Groth Strip pilot phase of this project, a Keck LRIS survey of faint galaxies in the Groth Survey Strip imaged with HST WFPC2. The redshift catalog and data, including reduced spectra, are made publicly available through a Web-accessible database. The catalog contains 658 secure galaxy redshifts with a median z = 0.65. The distribution of these galaxies shows large-scale structure walls to z ~ 1. We find a bimodal distribution in the galaxy color-magnitude diagram that persists to the same distance. A similar color division has been seen locally by the SDSS and to z ~ 1 by the COMBO-17 survey. The HST imaging allows us to measure structural properties of the galaxies, and we find that the color division corresponds generally to a structural division. Most red galaxies, ~75%, are centrally concentrated, with a red bulge or spheroidal stellar component, while blue galaxies usually have exponential profiles. However, there are two subclasses of red galaxies that are not bulge dominated: edge-on disks and a second category that we term diffuse red galaxies (DIFRGs). Comparison to a local sample drawn from the RC3 suggests that distant edge-on disks are similar in appearance and frequency to those at low redshift, but analogs of DIFRGs are rare among local red galaxies. DIFRGs have significant emission lines, indicating that they are reddened mainly by dust rather than age. The DIFRGs in our sample are all at z > 0.64, suggesting that DIFRGs are more prevalent at high redshifts; they may be related to the dusty or irregular extremely red objects beyond z > 1.2 that have been found in deep K-selected surveys. We measure the color evolution of both red and blue galaxies by comparing our U - B colors to those from the RC3. For red galaxies, we find a reddening of only 0.11 mag from z ~ 0.8 to now, about half the color evolution measured by COMBO-17. Larger, more carefully defined samples with better colors are needed to improve this measurement. Reconciling evolution in color, luminosity, mass, morphology, and star formation rates will be an active topic of future research.The Astrophysical Journal 12/2008; 620(2):595. · 6.02 Impact Factor -
Article: The DEEP2 Galaxy Redshift Survey: First Results on Galaxy Groups
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ABSTRACT: We use the first 25% of the DEEP2 Galaxy Redshift Survey spectroscopic data to identify groups and clusters of galaxies in redshift space. The data set contains 8370 galaxies with confirmed redshifts in the range 0.7 ≤ z ≤ 1.4, over 1 deg2 on the sky. Groups are identified using an algorithm (the Voronoi-Delaunay method) that has been shown to accurately reproduce the statistics of groups in simulated DEEP2-like samples. We optimize this algorithm for the DEEP2 survey by applying it to realistic mock galaxy catalogs and assessing the results using a stringent set of criteria for measuring group-finding success, which we develop and describe in detail here. We find in particular that the group finder can successfully identify ~78% of real groups and that ~79% of the galaxies that are true members of groups can be identified as such. Conversely, we estimate that ~55% of the groups we find can be definitively identified with real groups and that ~46% of the galaxies we place into groups are interloper field galaxies. Most importantly, we find that it is possible to measure the distribution of groups in redshift and velocity dispersion, n(σ, z), to an accuracy limited by cosmic variance, for dispersions greater than 350 km s-1. We anticipate that such measurements will allow strong constraints to be placed on the equation of state of the dark energy in the future. Finally, we present the first DEEP2 group catalog, which assigns 32% of the galaxies to 899 distinct groups with two or more members, 153 of which have velocity dispersions above 350 km s-1. We provide locations, redshifts and properties for this high-dispersion subsample. This catalog represents the largest sample to date of spectroscopically detected groups at z ~ 1.The Astrophysical Journal 12/2008; 625(1):6. · 6.02 Impact Factor -
Article: The DEEP Groth Strip Survey. VI. Spectroscopic, Variability, and X-Ray Detection of Active Galactic Nuclei
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ABSTRACT: We identify active galactic nuclei (AGNs) in the Groth-Westphal Survey Strip (GSS) using the independent and complementary selection techniques of optical spectroscopy and photometric variability. We discuss the X-ray properties of these AGNs using Chandra/XMM-Newton data for this region. From a sample of 576 galaxies with high-quality spectra we identify 31 galaxies with AGN signatures. Seven of these have broad emission lines (Type 1 AGNs). We also identify 26 galaxies displaying nuclear variability in Hubble Space Telescope Wide Field Planetary Camera 2 (HST WFPC2) images of the GSS separated by ~7 yr. The primary overlap of the two selected AGN samples is the set of broad-line AGNs, of which 80% appear as variable. Only a few narrow-line AGNs approach the variability threshold. The broad-line AGNs have an average redshift of z 1.1, while the other spectroscopic AGNs have redshifts closer to the mean of the general galaxy population (z 0.7). Eighty percent of the identified broad-line AGNs are detected in X-rays, and these are among the most luminous X-ray sources in the GSS. Only one narrow-line AGN is X-ray detected. Of the variable nuclei galaxies within the X-ray survey, 27% are X-ray detected. We find that 1.9% ± 0.6% of GSS galaxies to Vgal = 24 are broad-line AGNs, 1.4% ± 0.5% are narrow-line AGNs, and 4.5% ± 1.4% contain variable nuclei. The fraction of spectroscopically identified BLAGNs and NLAGNs at z ~ 1 reveals a marginally significant increase of 1.3% ± 0.9% when compared to the local population.The Astrophysical Journal Supplement Series 12/2008; 166(1):69. · 13.46 Impact Factor -
Article: A Survey of Galaxy Kinematics to z ~ 1 in the TKRS/GOODS-N Field. II. Evolution in the Tully-Fisher Relation
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ABSTRACT: We use kinematic measurements of a large sample of galaxies from the Team Keck Redshift Survey in the GOODS-N field to measure evolution in the optical and near-IR Tully-Fisher (TF) relations to z = 1.2. We construct TF relations with integrated line-of-sight velocity widths of ~1000 galaxies in B and ~670 in J; these relations have large scatter, and we derive a maximum likelihood least-squares method for fitting in the presence of scatter. The B-band TF relations, from z = 0.4 to 1.2, show evolution of ~1.0-1.5 mag internal to our sample without requiring calibration to a local TF relation. There is evolution in both TF intercept and slope, suggesting differential luminosity evolution. In J band, there is evolution in slope but little evolution in overall luminosity. The slope measurements imply that bright, massive blue galaxies fade more strongly than fainter blue galaxies from z ~ 1.2 to now. This conclusion runs counter to some previous measurements and to our naive expectations, but we present a simple set of star formation histories to show that it arises naturally if massive galaxies have shorter timescales of star formation, forming most of their stars before z ~ 1, while less massive galaxies form stars at more slowly declining rates. This model predicts that the higher global star formation rate at z ~ 1 is mostly due to higher star formation rate in massive galaxies. The amount of fading in B constrains star formation timescale more strongly than redshift of formation. TF and color-magnitude relations can provide global constraints on the luminosity evolution and star formation history of blue galaxies.The Astrophysical Journal 12/2008; 653(2):1049. · 6.02 Impact Factor -
Article: The DEEP Groth Strip Survey. IX. Evolution of the Fundamental Plane of Field Galaxies
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ABSTRACT: Fundamental plane studies provide an excellent means of understanding the evolutionary history of early-type galaxies. Using the Low Resolution Imaging Spectrograph on the Keck Telescope, we obtained internal stellar kinematic information for 36 field galaxies in the Groth Strip, 21 early-type and 15 disk galaxies. Their redshifts range from 0.3 to 1.0, with a median redshift of 0.8. The slope of the relation shows no difference compared with the local slope. However, there is significant evolution in the zero-point offset; an offset due to evolution in magnitude requires a 2.4 mag luminosity brightening at z = 1. We see little differences of the offset with bulge fraction, which is a good surrogate for galaxy type. Correcting for the luminosity evolution reduces the orthogonal scatter in the fundamental plane to 8%, consistent with the local scatter. This scatter is measured for our sample and does not include results from other studies, which may have different selection effects. The difference in the degree of evolution between our field sample and published cluster galaxies suggests a more recent formation epoch, around z = 1.5 for field galaxies compared to z > 2.0 for cluster galaxies. The magnitude difference implies that the field early-type galaxies are about 2 Gyr younger than the cluster ellipticals using standard single-burst models. However, the same models imply a significant change in the rest-frame U-B color from then to the present, which is not seen in our sample. Continuous low-level star formation, however, would serve to explain the constant colors over this large magnitude change. A consistent model has 7% of the stellar mass created after the initial burst, using an exponentially decaying star formation rate with an e-folding time of 5 Gyr.The Astrophysical Journal 12/2008; 597(1):239. · 6.02 Impact Factor -
Article: A Survey of Galaxy Kinematics to z ~ 1 in the TKRS/GOODS-N Field. I. Rotation and Dispersion Properties
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ABSTRACT: We present kinematic measurements of a large sample of galaxies from the Team Keck Redshift Survey in the GOODS-N field. We measure line-of-sight velocity dispersions from integrated emission for 1089 galaxies with median redshift 0.637 and spatially resolved kinematics for a subsample of 380 galaxies. This is the largest sample of galaxies to z ~ 1 with kinematics to date and allows us to measure kinematic properties without morphological preselection. Emission-line widths provide a dynamical measurement for the bulk of blue galaxies. To fit the spatially resolved kinematics, we construct models that fit both line-of-sight rotation amplitude and velocity dispersion. Integrated line width correlates well with a combination of the velocity gradient and dispersion and is a robust measure of galaxy kinematics. The spatial extents of emission and continuum are similar, and there is no evidence that line widths are affected by nuclear or clumpy emission. The measured rotation gradient depends strongly on slit position angle alignment with galaxy major axis, but integrated line width does not. Even for galaxies with well-aligned slits, some have kinematics dominated by dispersion (V/σ < 1) rather than rotation. These are probably objects with disordered velocity fields, not dynamically hot stellar systems. About 35% of the spatially resolved sample are dispersion dominated; galaxies that are both dispersion dominated and bright exist at high redshift but appear rare at low redshift. This kinematic morphology may probe galaxies' evolutionary state. It is linked to photometric morphology in HST ACS images: dispersion-dominated galaxies include a higher fraction of irregulars and chain galaxies, while rotation-dominated galaxies are mostly disks and irregulars. Only one-third of chain/hyphen galaxies are dominated by rotation; high-redshift elongated objects cannot be assumed to be inclined disks.The Astrophysical Journal 12/2008; 653(2):1027. · 6.02 Impact Factor -
Article: The Stellar Mass Tully-Fisher Relation to z = 1.2 from AEGIS
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ABSTRACT: We combine newly measured rotation velocities, velocity dispersions, and stellar masses to construct stellar mass Tully-Fisher relations (M*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*TFR using only rotation velocity (Vrot) shows large scatter (~1.5 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*TFR using the kinematic estimator S0.5, which is defined as 1/2 and accounts for disordered or noncircular motions through the gas velocity dispersion (σg). The new M*TFR, termed S0.5/M*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 ~1.2 "magnitudes," assuming a constant mass-to-light ratio. Interestingly, the S0.5/M*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.The Astrophysical Journal 12/2008; 660(1):L35. · 6.02 Impact Factor -
Article: Are There Blue, Massive E/S0 Galaxies at z < 1? Kinematics of Blue Spheroidal Galaxy Candidates
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ABSTRACT: Several recent studies find that 10%–50% of morphologically selected field early-type galaxies at redshifts z 1 have blue colors indicative of recent star formation. Such "blue spheroids" might be massive early-type galaxies with active star formation, perhaps induced by recent merger events. Alternatively, they could be starbursting, low-mass spheroids. To distinguish between these two choices, we have selected 10 "Blue Spheroid Candidates" (BSCs) from a quantitatively selected E/S0 sample to study their properties, including kinematics from Keck spectra obtained as part of the DEEP Groth Strip Survey (GSS). Most BSCs (70%) turn out to belong to two broad categories, while the remaining objects are likely to be misclassified objects. Type 1 BSCs have underlying red stellar components with bluer inner components. Type 2 BSCs do not show an obvious sign of the underlying red stellar component, and their overall colors are quite blue [(U-B)rest < 0]. Both type 1 and type 2 BSCs have internal velocity dispersions measured from emission lines σ 80 km s-1 and estimated dynamical masses of only a few ×1010 M or less. For type 1 BSCs, we estimate σ of the red component using the fundamental plane relation of distant field absorption-line galaxies and find that these σ estimates are similar to the σ measured from emission lines. Overall, we conclude that our type 1 and type 2 BSCs are more likely to be star-forming low-mass spheroids than star-forming, massive, early-type galaxies.The Astronomical Journal 12/2007; 122(2):750. · 4.03 Impact Factor
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1998–2010
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University of California, Santa Cruz
- Department of Astronomy and Astrophysics
Santa Cruz, CA, USA
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2008
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CSU Mentor
Long Beach, CA, USA
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1995
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Johns Hopkins University
- Department of Physics and Astronomy
Baltimore, MD, USA
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