arXiv subjects

S. M. Faber

Publications and source records attributed to S. M. Faber.

At least 199 records · Page 11Linked to original sources

arXiv2006

All-wavelength Extended Groth strip International Survey: the environment of X-ray sources at z~1

We explore the environment of z~1 AGN using a sample of 53 spectroscopically identified X-ray sources in the All-wavelength Extended Groth strip International Survey. We quantify the local density in the vicinity of an X-ray source by measuring the projected surface density of spectroscopically identified optical galaxies within a radius defined by the 3rd nearest neighbour. Our main result is that X-ray selected AGN at z~1 avoid underdense regions at the 99.89% confidence level. Moreover, although we find that the overall population shares the same (rich) environment with optical galaxies of similar U-B and M_B, there is also tentative evidence (96%) that AGN with blue colors (U-B<1) reside in denser environments compared to optical galaxies. We argue that the results above are a consequence of the whereabouts of massive galaxies, capable of hosting supermassive black holes at their centers, with available cold gas reservoirs, the fuel for AGN activity. At z~1 an increasing fraction of such systems are found in dense regions.

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arXiv2006

AEGIS: The color-magnitude relation for X-ray selected AGN

We discuss the relationship between rest-frame color and optical luminosity for X-ray sources in the range 0.6<z<1.4 selected from the Chandra survey of the Extended Groth Strip (EGS). These objects are almost exclusively active galactic nuclei (AGN). While there are a few luminous QSOs, most are relatively weak or obscured AGN whose optical colors should be dominated by host galaxy light. The vast majority of AGN hosts at z~1 are luminous and red, with very few objects fainter than M_{B}=-20.5 or bluer than U-B=0.6. This places the AGN in a distinct region of color-magnitude space, on the ``red sequence'' or at the top of the ``blue cloud'', with many in between these two modes in galaxy color. A key stage in the evolution of massive galaxies is when star formation is quenched, resulting in a migration from the blue cloud to the red sequence. Our results are consistent with scenarios in which AGN either cause or maintain this quenching. The large numbers of red sequence AGN imply that strong, ongoing star formation is not a necessary ingredient for AGN activity, as black hole accretion appears often to persist after star formation has been terminated.

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arXiv2006

Evolution in the Halo Masses of Isolated Galaxies between z~1 and z~0: From DEEP2 to SDSS

We measure the evolution in the virial mass-to-light ratio (M_{200}/L_B) and virial-to-stellar mass ratio (M_{200}/M_\ast) for isolated ~ L* galaxies between z~1 and z~0 by combining data from the DEEP2 Galaxy Redshift Survey and the Sloan Digital Sky Survey. Utilizing the motions of satellite galaxies around isolated galaxies, we measure line-of-sight velocity dispersions and derive dark matter halo virial masses for these host galaxies. At both epochs the velocity dispersion of satellites correlates with host galaxy stellar mass, σ\propto M_\ast^{0.4+/-0.1}, while the relation between satellite velocity dispersion and host galaxy B-band luminosity may grow somewhat shallower from σ\propto L_B^{0.6+/-0.1} at z~1 to σ\propto L_B^{0.4+/-0.1} at z~0. The evolution in M_200/M_\ast from z~1 to z~0 displays a bimodality insofar as host galaxies with stellar mass below M_\ast ~10^{11} M_Sun/h maintain a constant ratio (the intrinsic increase is constrained to a factor of 1.1+/-0.7) while host galaxies above M_\ast ~10^{11} M_Sun/h experience a factor of 4+/-3 increase in their virial-to-stellar mass ratio. This result can be easily understood if galaxies below this stellar mass scale continue to form stars while star formation in galaxies above this scale is quenched and the dark matter halos of galaxies both above and below this scale grow in accordance with LCDM cosmological simulations. Host galaxies that are red in U-B color have larger satellite dispersions and hence reside on average in more massive halos than blue galaxies at both z~1 and z~0. The redshift and host galaxy stellar mass dependence of M_200/M_\ast agrees qualitatively with the Millennium Run semi-analytic model of galaxy formation. (ABRIDGED)

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arXiv2006

On the Origin of [OII] Emission in Red Sequence and Post-starburst Galaxies

We investigate the emission-line properties of galaxies with red rest-frame colors 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: Ha 6563 and [OII] 3727. There is a strong bimodality in [OII]/Ha ratio in the full SDSS sample which 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 AGN -- 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 [OII]-Ha equivalent width plane 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. [OII] EWs in LINER- and AGN-like galaxies can be as large as in star-forming galaxies. Thus, unless objects with AGN/LINER-like line ratios are excluded, [OII] emission cannot be used directly as a proxy for star formation rate. Lack of [OII] emission is generally used to indicate lack of star formation when post-starburst 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 post-starburst galaxies. Furthermore, post-starburst galaxies identifed in SDSS by requiring minimal Ha EW generally exhibit weak but nonzero line emission with ratios typical of AGNs; few of them show residual star formation. This suggests that most post-starbursts may harbor AGNs/LINERs.

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arXiv2006

The Deep Chandra Survey of the Groth Strip - II. optical identification of the X-ray sources

We discuss the optical and X-ray spectral properties of the sources detected in a single 200ks Chandra pointing in the Groth-Westphal Strip region. Optical identifications and spectroscopic redshifts are primarily from the DEEP2 survey. This is complemented with deeper (r~26mag) multi-waveband data (ugriz) from the Canada France Hawaii Legacy Survey to estimate photometric redshifts and to optically identify sources fainter than the DEEP2 magnitude limit (R(AB)~24.5mag). We focus our study on the 2-10keV selected sample comprising 97 sources to the limit ~8e-16erg/s/cm2, this being the most complete in terms of optical identification rate (86%) and redshift determination fraction (63%; both spectroscopic and photometric). We first construct the redshift distribution of the sample which shows a peak at z~1. This is in broad agreement with models where less luminous AGNs evolve out to z~1 with powerful QSOs peaking at higher redshift, z~2. Evolution similar to that of broad-line QSOs applied to the entire AGN population (both type-I and II) does not fit the data. We also explore the observed N_H distribution of the sample and estimate a fraction of obscured AGN (N_H>1e22) of ~48%. This is found to be consistent with both a luminosity dependent intrinsic N_H distribution, where less luminous systems comprise a higher fraction of type-II AGNs, and models with a fixed ratio 2:1 between type-I and II AGNs. We further compare our results with those obtained in deeper and shallower surveys. We argue that a luminosity dependent parametrisation of the intrinsic N_H distribution is required to account for the fraction of obscured AGN observed in different samples over a wide range of fluxes.

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arXiv2006

The DEEP2 Galaxy Redshift Survey: The Relationship Between Galaxy Properties and Environment at z ~ 1

We study the mean environment of galaxies in the DEEP2 Galaxy Redshift Survey as a function of rest-frame color, luminosity, and [OII] equivalent width. The local galaxy overdensity for >14,000 galaxies at 0.75 < z < 1.35 is estimated using the projected 3rd-nearest-neighbor surface density. Of the galaxy properties studied, mean environment is found to depend most strongly on galaxy color; all major features of the correlation between mean overdensity and rest-frame color 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 z ~ 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.

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arXiv2006

The DEEP2 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 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.

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arXiv2006

The DEEP2 Galaxy Redshift Survey: Clustering of Galaxies as a Function of Luminosity at z=1

We measure the clustering of DEEP2 galaxies at z=1 as a function of luminosity on scales 0.1 Mpc/h to 20 Mpc/h. Drawing from a parent catalog of 25,000 galaxies at 0.7 L^*, have a steeper slope. The clustering scale-length, r_0, varies from 3.69 +/-0.14 for the faintest sample to 4.43 +/-0.14 for the brightest sample. The relative bias of galaxies as a function of L/L^* is steeper than the relation found locally for SDSS galaxies (Zehavi et al. 2005) over the luminosity range that we sample. The absolute bias of galaxies at z=1 is scale-dependent on scales r_p<1 Mpc/h, and rises most significantly on small scales for the brightest samples. For a concordance cosmology, the large-scale bias varies from 1.26 +/-0.04 to 1.54 +/-0.05 as a function of luminosity and implies that DEEP2 galaxies reside in dark matter halos with a minimum mass of ~1-3 10^12 h^-1 M_sun.

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arXiv2006

The DEEP2 Galaxy Redshift Survey: Mean Ages and Metallicities of Red Field Galaxies at z ~ 0.9 from Stacked Keck/DEIMOS Spectra

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. This result 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 star formation 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 Hdelta 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.

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arXiv2006

On the Correlations of Massive Black Holes with their Host Galaxies

We address the correlations of black hole (BH) mass with four different host-galaxy properties from eleven existing data sets. To guide theoretical understanding, we first try to quantify the tightness of the intrinsic correlations. Given the estimated measurement errors, we evaluate the probability distribution of the residual variance in excess of that expected from the measurement errors. Our central result is that the current data sets do not allow definite conclusions regarding the quality of the true correlations because the obtained probability distributions for the residual variance overlap for most quantities. We then consider which of the relations offer the best inferences of BH mass when there is no direct measurement available. As with the residual variances, we find that the probability distribution of expected uncertainty in inferred BH masses overlaps significantly for most of the relations. Photometric methods would then be preferred because the data are easier to obtain, as long as bulge-disk decomposition or detailed modeling of the photometric profile (as in \citet{graham:01}) do not present problems. Determining which correlation offers the best inferences requires reducing the uncertainty in the expected error in the inferred BH masses (the ``error on the error''). This uncertainty is currently limited by uncertainty in the residual variance for all of the relations.

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arXiv2005

The DEEP2 Galaxy Redshift Survey: Probing the Evolution of Dark Matter Halos around Isolated Galaxies at z ~ 1

Using the first 25% of DEEP2 Redshift Survey data, we probe the line-of-sight velocity dispersion profile for isolated galaxies with absolute B-band magnitude -22<M_B-5log(h)<-21 at z=0.7-1.0, using satellite galaxies as luminous tracers of the underlying velocity distribution. Measuring the velocity dispersion beyond a galactocentric radius of ~200 kpc/h (physical) permits us to determine the total mass, including dark matter, around these bright galaxies. We find a line-of-sight velocity dispersion (sigma_los) of 162^{+44}_{-30} km/s at ~110 kpc/h, 136^{+26}_{-20} km/s at ~230 kpc/h, and 150^{+55}_{-38} km/s at ~320 kpc/h. Assuming an NFW model for the dark matter density profile, this corresponds to a mass within r_{200} of M_200=5.5^{+2.5}_{-2.0} x 10^12 M_Sun/h for our sample of satellite hosts with mean luminosity ~2.5L*. Roughly $~60% of these host galaxies have early-type spectra and are red in restframe (U-B) color, consistent with the overall DEEP2 sample in the same luminosity and redshift range. The halo mass determined for DEEP2 host galaxies is consistent with that measured in the Sloan Digital Sky Survey for host galaxies within a similar luminosity range relative to M*_B. This comparison is insensitive to the assumed halo mass profile, and implies an increase in the dynamical mass-to-light ratio (M_200/L_B) of isolated galaxies which host satellites by a factor of ~2.5 from z ~ 1 to z ~ 0. Our results are consistent with scenarios in which galaxies populate dark matter halos similarly from z ~ 0 to z ~ 1, except for ~1 magnitude of evolution in the luminosity of all galaxies.

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arXiv2005

The DEEP2 Galaxy Redshift Survey: Clustering of Groups and Group Galaxies at z~1

We study the clustering properties of groups and of galaxies in groups in the DEEP2 Galaxy Redshift Survey dataset at z~1. Four clustering measures are presented: 1) the group correlation function for 460 groups with estimated velocity dispersions of sigma>200 km/s, 2) the galaxy correlation for the full galaxy sample, using a flux-limited sample of 9800 objects between 0.7<z<1.0, 3) the galaxy correlation for galaxies in groups, and 4) the group-galaxy cross-correlation function. Using the observed number density and clustering amplitude of the groups, the estimated minimum group dark matter halo mass is M_min~6 10^12 h^-1 M_Sun for a flat LCDM cosmology. Groups are more clustered than galaxies, with a relative bias of b=1.7 +/-0.04 on scales r_p=0.5-15 Mpc/h. Galaxies in groups are also more clustered than the full galaxy sample, with a scale-dependent relative bias which falls from b~2.5 +/-0.3 at r_p=0.1 Mpc/h to b~1 +/-0.5 at r_p=10 Mpc/h. The correlation functions for all galaxies and galaxies in groups can be fit by a power-law on scales r_p=0.05-20 Mpc/h. We empirically measure the contribution to the projected correlation function for galaxies in groups from a `one-halo' term and a `two-halo' term by counting pairs of galaxies in the same or in different groups. The projected cross-correlation between shows that red galaxies are more centrally concentrated in groups than blue galaxies at z~1. DEEP2 galaxies in groups appear to have a shallower radial distribution than that of mock galaxy catalogs made from N-body simulations, which assume a central galaxy surrounded by satellite galaxies with an NFW profile. We show that the clustering of galaxies in groups can be used to place tighter constraints on the halo model than can be gained from using the usual galaxy correlation function alone.

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arXiv2005

Measuring the Growth of Structure with Spectroscopically Identified Groups and Clusters

Number counts of galaxy clusters offer a very promising probe of the Dark Energy (DE) equation-of-state parameter, $w$. The basic goal is to measure abundances of these objects as a function of redshift, compare this to a theoretical prediction, and infer the values of cosmological parameters. Various teams have proposed such a measurement, including the South Pole Telescope, the Dark Energy Survey and the Red-Sequence Cluster Survey. The specific study discussed here detects clusters and smaller galaxy groups in the three-dimensional distribution of galaxies inferred from a large spectroscopic redshift survey. This method allows the abundance, $N$, of groups and clusters to be measured as a function of \emph{velocity dispersion}, as well as of redshift, permitting a more sensitive test of cosmology.

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arXiv2005

Galaxy Luminosity Functions to z~1: DEEP2 vs. COMBO-17 and Implications for Red Galaxy Formation

The DEEP2 and COMBO-17 surveys are used to study the evolution of the luminosity function of red and blue galaxies to $z \sim 1$. Schechter function fits show that, since $z = 1$, $M^*_B$ dims by $\sim$ 1.3 mag per unit redshift for both color classes, $ϕ^*$ of blue galaxies shows little change, while $ϕ^*$ for red galaxies has formally nearly quadrupled. At face value, the number density of blue galaxies has remained roughly constant since $ z = 1$, whereas that of red galaxies has been rising. Luminosity densities support both conclusions, but we note that most red-galaxy evolution occurs between our data and local surveys and in our highest redshift bin, where the data are weakest. We discuss the implications of having most red galaxies emerge after $z = 1$ from precursors among the blue population, taking into account the properties of local and distant E/S0s. We suggest a ``mixed'' scenario in which some blue galaxies have their star-formation quenched in gas-rich mergers, migrate to the red sequence with a variety of masses, and merge further on the red sequence in one or more purely stellar mergers. E/S0s of a given mass today will have formed via different routes, in a manner that may help to explain the fundamental plane and other local scaling laws.

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arXiv2005

Hot Stars in Old Stellar Populations: A Continuing Need for Intermediate Ages

We investigate the effect of a small contamination of hot, old, metal-poor starlight on the inferred stellar populations of early-type galaxies in the core of the Coma Cluster. We find that the required correction to the Balmer and metal absorption-line strengths for old, metal-poor stars does not significantly affect the inferred age of the stellar population when the Hbeta strength is large. Intermediate-aged populations are therefore still needed to explain enhanced Balmer-line strengths in early-type galaxies. This gives us increased confidence in our age estimates for these objects. For galaxies with weak Balmer-line strengths corresponding to very old populations (t>10 Gyr), however, a correction for hot stars may indeed alter the inferred age, as previously suggested. Finally, the inferred metallicity [Z/H] will always be higher after any correction for old, metal-poor starlight than without, but the enhancement ratios [E/Fe] will strengthen only slightly.

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arXiv2005

Characterizing the Adaptive Optics Off-Axis Point-Spread Function. II. Methods for Use in Laser Guide Star Observations

Most current astronomical adaptive optics (AO) systems rely on the availability of a bright star to measure the distortion of the incoming wavefront. Replacing the guide star with an artificial laser beacon alleviates this dependency on bright stars and therefore increases sky coverage, but it does not eliminate another serious problem for AO observations. This is the issue of PSF variation with time and field position near the guide star. In fact, because a natural guide star is still necessary for correction of the low-order phase error, characterization of laser guide star (LGS) AO PSF spatial variation is more complicated than for a natural guide star alone. We discuss six methods for characterizing LGS AO PSF variation that can potentially improve the determination of the PSF away from the laser spot, that is, off-axis. Calibration images of dense star fields are used to determine the change in PSF variation with field position. This is augmented by AO system telemetry and simple computer simulations to determine a more accurate off-axis PSF. We report on tests of the methods using the laser AO system on the Lick Observatory Shane Telescope. [Abstract truncated.]

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arXiv2005

The DEEP Groth Strip Survey. I. The Sample

The Deep Extragalactic Exploratory Probe (DEEP) is a multi-phase 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 ten 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 square arcminute region which has been observed with the Hubble Space Telescope 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.

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arXiv2005

The DEEP2 Galaxy Redshift Survey: First results on galaxy groups

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 one square degree 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(sigma,z), to an accuracy limited by cosmic variance, for dispersions greater than 350km/s. 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 350km/s. 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.

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