arXiv subjects

Anthony H. Gonzalez

Publications and source records attributed to Anthony H. Gonzalez.

142 records · Page 8Linked to original sources

arXiv2002

A Test of Photometric Redshifts for X-ray Selected Sources

We test the effectiveness of photometric redshifts based upon galaxy spectral template fitting for X-ray luminous objects, using a sample of 65 sources detected by Chandra in the field of the Caltech Faint Galaxy Redshift Survey (CFGRS). We find that sources with quasar-dominated spectra (for which galaxy spectral templates are not appropriate) are easily identified, and that photometric redshifts are robust for the rest of the sources in our sample. Specifically, for the 59 sources that are not quasar-dominated at optical wavelengths, we find that the photometric redshift estimates have scatter comparable to the field galaxy population in this region. There is no evidence for a trend of increasing dispersion with X-ray luminosity over the range L_X = 10^39 - 5x10^43 erg/s, nor is there a trend with the ratio of X-ray to optical flux, f_X/f_R. The practical implication of this work is that photometric redshifts should be robust for the majority (~90%) of the X-ray sources down to f_X ~ 10^-16 erg/s/cm^2 that have optical counterparts brighter than R ~ 24. Furthermore, the same photometry can be easily used to identify the sources for which the photometric redshifts are likely to fail. Photometric redshift estimation can thus be utilized as an efficient tool in analyzing the statistical properties of upcoming large Chandra and XMM-Newton data sets and identifying interesting subsamples for further study.

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arXiv2002

Tests of the Las Campanas Distant Cluster Survey from Confirmation Observations for the ESO Distant Cluster Survey

The ESO Distant Cluster Survey (EDisCS) is a photometric and spectroscopic study of the galaxy cluster population at two epochs, z~0.5 and z~0.8, drawn from the Las Campanas Distant Cluster Survey (LCDCS). We report results from the initial candidate confirmation stage of the program and use these results to probe the properties of the LCDCS. Of the 30 candidates targeted, we find statistically significant overdensities of red galaxies near 28. Of the ten additional candidates serendipitously observed within the fields of the targeted 30, we detect red galaxy overdensities near six. We test the robustness of the published LCDCS estimated redshifts to misidentification of the brighest cluster galaxy (BCG) in the survey data, and measure the spatial alignment of the published cluster coordinates, the peak red galaxy overdensity, and the brightest cluster galaxy. We conclude that for LCDCS clusters out to z~0.8, 1) the LCDCS coordinates agree with the centroid of the red galaxy overdensity to within 25'' (~150 h^{-1} kpc) for 34 out of 37 candidates with 3σgalaxy overdensities, 2) BCGs are typically coincident with the centroid of the red galaxy population to within a projected separation of 200 h^{-1} kpc (32 out of 34 confirmed candidates), 3) the red galaxy population is strongly concentrated, and 4) the misidentification of the BCG in the LCDCS causes a redshift error >0.1 in 15-20% of the LCDCS candidates. These findings together help explain the success of the surface brightness fluctuations detection method.

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arXiv2002

The Las Campanas Distant Cluster Survey -- The Correlation Function

We present the first non-local (z>0.2) measurement of the cluster-cluster spatial correlation length, using data from the Las Campanas Distant Cluster Survey (LCDCS). We measure the angular correlation function for velocity-dispersion limited subsamples of the catalog at estimated redshifts of 0.35<z_{est}<0.575, and derive spatial correlation lengths for these clusters via the cosmological Limber equation. The correlation lengths that we measure for clusters in the LCDCS are consistent both with local results for the APM cluster catalog and with theoretical expectations based upon the Virgo Consortium Hubble Volume simulations and the analytic predictions. Despite samples containing over 100 clusters, our ability to discriminate between cosmological models is limited because of statistical uncertainty.

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arXiv2001

Constraints On the Size Evolution of Brightest Cluster Galaxies

We measure the luminosity profiles of 16 brightest cluster galaxies (BCGs) at $0.4 < z < 0.8$ using high resolution F160W NICMOS and F814W WFPC2 HST imaging. The heterogeneous sample is drawn from a variety of surveys: seven from clusters in the Einstein Medium Sensitivity Survey, five from the Las Campanas Distant Cluster Survey and its northern hemisphere precursor, and the remaining four from traditional optical surveys. We find that the surface brightness profiles of all but three of these BCGs are well described by a standard de Vaucouleurs ($r^{1/4}$) profile out to at least $\sim2r_{e}$ and that the biweight-estimated NICMOS effective radius of our high redshift BCGs ($r_{e} = 8.3\pm 1.4$ kpc for $H_{0} = 80$ km s$^{-1}$ Mpc$^{-1}$, $Ω_{m} = 0.2, Ω_Λ= 0.0$) is $\sim 2$ times smaller than that measured for a local BCG sample. If high redshift BCGs are in dynamical equilibrium and satisfy the same scaling relations as low redshift ones, this change in size would correspond to a mass growth of a factor of 2 since $z \sim 0.5$. However, the biweight-estimated WFPC2 effective radius of our sample is 18 $\pm $ 5.1 kpc, which is fully consistent with the local sample. While we can rule out mass accretion rates higher than a factor of 2 in our sample, the discrepancy between our NICMOS and WFPC2 results, which after various tests we describe appears to be physical, does not yet allow us to place strong constraints on accretion rates below that level.

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arXiv2001

Clustering in the Las Campanas Distant Cluster Survey

We utilize a sample of galaxy clusters at 0.35<z<0.6 drawn from the Las Campanas Distant Cluster Survey (LCDCS) to provide the first non-local constraint on the cluster-cluster spatial correlation function. The LCDCS catalog, which covers an effective area of 69 square degrees, contains over 1000 cluster candidates. Estimates of the redshift and velocity dispersion exist for all candidates, which enables construction of statistically completed, volume-limited subsamples. In this analysis we measure the angular correlation function for four such subsamples at z~0.5. After correcting for contamination, we then derive spatial correlation lengths via Limber inversion. We find that the resulting correlation lengths depend upon mass, as parameterized by the mean cluster separation, in a manner that is consistent with both local observations and CDM predictions for the clustering strength at z=0.5.

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arXiv2001

Revisiting Brightest Cluster Galaxy Evolution with the Las Campanas Distant Cluster Survey

We investigate the influence of environment on brightest cluster galaxy (BCG) evolution using a sample of 63 clusters at 0.3 < z < 0.9 drawn primarily from the Las Campanas Distant Cluster Survey and follow-up V, I, and K' photometry. The luminosity evolution of the entire BCG sample is not adequately described by a single evolutionary model. Using the integrated light from the cluster detection as a proxy for cluster Lx and the suggestion by Burke, Collins, & Mann, we set Lx = 2 x 10^{44} ergs/s to be the division between high and low luminosity clusters. At high redshift (z>0.6) BCGs from low-Lx clusters are fainter, on average, than those from high-Lx clusters and are best modeled as having constant luminosity with redshift. The BCGs from high-Lx cluster are best modeled as having a stellar population that formed at large redshift (z_form > 5) and is passively evolving. However, for the entire BCG population, the observed V-I and I-K' colors are well described by a single evolutionary model in which the stellar populations have z_form > 5 and subsequently passively evolve. We conclude that accretion is proportionally more significant for BCGs in lower mass clusters at these redshifts (factor of 2 to 4 increase in mass since z ~ 1 for the low Lx systems) and that the accreted matter is in the form of systems with evolved stellar populations.

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arXiv2001

Tracing Cosmic Evolution with the Las Campanas Distant Cluster Survey

The Las Campanas Distant Cluster Survey (LCDCS), which contains over 1000 cluster candidates at z>0.3, is a unique sample with which to probe the evolution of both cluster galaxies and the properties of the cluster population. Programs are now underway to utilize the LCDCS for both purposes. We provide a brief overview of these programs, and also present new results for the LCDCS cluster correlation function. Utilizing well-defined, approximately dispersion-limited subsamples, we measure the angular correlation function for clusters at z~0.5. Spatial correlation lengths are then derived via Limber inversion. We find that the correlation length depends upon mass, as parameterized by the mean cluster separation, in a manner that is consistent with both local observations and CDM predictions for the clustering strength at z=0.5.

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arXiv2001

Cluster Galaxy Evolution from a New Sample of Galaxy Clusters at 0.3 < z < 0.9

(Abridged) We analyze photometry and spectroscopy of a sample of 63 clusters at 0.3 ~ 5) and in which many of these galaxies, if not all, accrete mass either in the form of evolved stellar populations or gas that causes only a short term episode of star formation at lower redshifts (1.5 < z < 2). Our data are too crude to reach conclusions regarding the evolutionary state of any particular cluster or to investigate whether the morphological evolution of galaxies matches the simple scenario we discuss, but the statistical nature of this study suggests that the observed evolutionary trends are universal in massive clusters.

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arXiv2001

Brightest Cluster Galaxies and the Las Campanas Distant Cluster Survey

We present our study of the evolution of brightest cluster galaxies based on data from the Las Campanas Distant Cluster Survey (Gonzalez et al. 2001) and HST optical and IR imaging. We briefly discuss the technique that enabled us to use short (~ 3 min) exposures and a small (1m) telescope to efficiently survey about 130 sq. deg. of sky for high-z galaxy clusters. Follow-up imaging is used to construct a sample of several tens of BCGs at 0.3 < z < 0.9 with which to explore their evolution. In particular, we examine the luminosity and color evolution of these galaxies. We confirm the previous results that 1) BCGs in different environments evolve differently (eg. Burke et al 2000), 2) BCGs, particularly those in low-mass clusters, must be accreting significantly since z ~ 1 (Aragon-Salamanca et al. 1998). From measurments of the colors vs. redshift, we conclude that this accretion must consist of old stellar populations. Using HST NICMOS and WFPC2 images, we find preliminary evidence for evolution in the sizes of BCGs that is consistent with the accretion model presented in standard hierarchical models (Aragon-Salamanca et al. 1998), but puzzling differences between NICMOS and WFPC2 scale lengths precludes a definitive conclusion.

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arXiv2001

An Overview of the Las Campanas Distant Cluster Survey

We present the Las Campanas Distant Cluster Survey, which has produced over a thousand galaxy cluster candidates at 0.35 < z < 1.1 (see Gonzalez et al. 2001 for the full catalog). We discuss the technique that enabled us to use short (~ 3 min) exposures and a small (1m) telescope to efficiently survey ~ 130 sq. deg. of sky. Follow-up imaging and spectroscopy using a wide array of telescopes including the Keck and VLT suggest that the bona-fide cluster fraction is ~70%. We construct methods to estimate both the redshift and cluster mass from the survey data themselves and discuss our first result on large-scale structure, the dependence of the cluster correlation length with mean cluster separation at z ~ 0.5 (Gonzalez, Zaritsky, & Wechsler 2001).

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arXiv2001

The Las Campanas Distant Cluster Survey - The Catalog

We present an optically-selected catalog of 1073 galaxy cluster and group candidates at 0.3 0.3, with a false-detection rate of 30%. At z=0.3 we probe down to the level of poor groups while by z=0.8 we detect only the most massive systems (sigma>1000 km/s). We also present a supplemental catalog of 112 candidates that fail one or more of the automated selection criteria, but appear from visual inspection to be bona fide clusters.

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arXiv2000

Measuring the Diffuse Optical Light in Abell 1651

Using drift scan data, a new approach to determining surface brightness profiles, and techniques for detecting low surface brightness signals, we fit the light profile of the brightest cluster galaxy (BCG) in the rich cluster Abell 1651 out to 670 h^{-1} kpc. This radius is a significant fraction of the virial radius of the cluster (2 h^{-1} Mpc; Girardi et al. 1998), indicating that the sizes of the BCG and the cluster are comparable. We find that the profile is consistent with a de Vaucouleurs profile over the radial range probed. We also find that the integrated light profile of the BCG in Abell 1651 contributes 36% of the total cluster light within 500 h^{-1} kpc. Including all luminous components, we obtain M/L_I~160 h for the cluster, which would be overestimated by ~20% without the BCG halo. Furthermore, the relatively red color of the BCG at large radii suggests that recent disruption and tidal stripping of spirals and dwarf ellipticals do not contribute significantly to the halo luminosity. The color and the form of the profile are consistent with a scenario in which the BCG forms from filamentary collapse during the epoch of cluster formation, with relatively little evolution in the past 5 Gyrs (Dubinski 1998). We remove the BCG and other detected galaxies from the image and construct a two dimensional surface brightness map of the cluster core. Several knots of excess emission are found, but the total diffuse component is constrained to contribute less than 5% of the cluster light.

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arXiv1999

Some Implications of the Anisotropic Distribution of Satellite Galaxies

We examine a possible connection between the anisotropic distribution of satellite galaxies around giant spiral galaxies and the evolution of satellite systems. The observed polar anisotropy (Zaritsky et al.1997) is either imprinted by initial conditions or develops from an initially symmetric distribution. We attempt to discriminate between these two possibilities by exploring the implications of the latter one. From the observed distribution of satellite galaxies relative to the primary galaxy's disk, we derive constrains on the orbital inclinations of the current satellite population. Using this derived inclination limit and assuming that the initial population had no preferred orbital inclination, we estimate the size of the hypothesized original population. We find that our best-fit models imply a population of destroyed (or inhibited) satellites whose combined luminosity (assuming the same M/L as for the observed satellites) is between 18% and 103% of the current disk luminosity.

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arXiv1999

The Velocity Function of Galaxies

We present a galaxy circular velocity function, Psi(log v), derived from existing luminosity functions and luminosity-velocity relations. Such a velocity function is desirable for several reasons. First, it enables an objective comparison of luminosity functions obtained in different bands and for different galaxy morphologies, with a statistical correction for dust extinction. In addition, the velocity function simplifies comparison of observations with predictions from high-resolution cosmological N-body simulations. We derive velocity functions from five different data sets and find rough agreement among them, but about a factor of 2 variation in amplitude. These velocity functions are then compared with N-body simulations of a LCDM model (corrected for baryonic infall) in order to demonstrate both the utility and current limitations of this approach. The number density of dark matter halos and the slope of the velocity function near v_*, the circular velocity corresponding to an ~L_* spiral galaxy, are found to be comparable to that of observed galaxies. The primary sources of uncertainty in construction of Psi(log v) from observations and N-body simulations are discussed and explanations are suggected to account for these discrepancies.

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arXiv1997

Malmquist Bias and the Distance to the Virgo Cluster

This paper investigates the impact of Malmquist bias on the distance to the Virgo cluster determined by the H_0 Key Project using M100, and consequently on the derived value of H_0. Malmquist bias is a volume-induced statistical effect which causes the most probable distance to be different from the raw distance measured. Consideration of the bias in the distance to the Virgo cluster raises this distance and lowers the calculated value of H_0. Monte Carlo simulations of the cluster have been run for several possible distributions of spirals within the cluster and of clusters in the local universe. Simulations consistent with known information regarding the cluster and the errors of measurement result in a bias of about 6.5%-8.5%. This corresponds to an unbiased distance of 17.2-17.4 Mpc and a value of H_0 in the range 80-82 km/s/Mpc. The problem of determining the bias to Virgo illustrates several key points regarding Malmquist bias. Essentially all conventional astronomical distance measurements are subject to this bias. In addition, the bias accumulates when an attempt is made to construct "distance ladders" from measurements which are individually biased. As will be shown in the case of Virgo, the magnitude and direction of the bias are sensitive to the spatial distribution of the parent poputation from which the observed object is drawn - a distribution which is often poorly known. This leads to uncertainty in the magnitude of the bias, and adds to the importance of minimizing the number of steps in "distance ladders".

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arXiv1996

Distant Galaxy Clusters Identified From Optical Background Fluctuations

We present the first high redshift (0.3 < z < 1.1) galaxy clusters found by systematically identifying optical low surface brightness fluctuations in the background sky. Using spectra obtained with the Keck telescope and I-band images from the Palomar 1.5m telescope, we conclude that at least eight of the ten candidates examined are high redshift galaxy clusters. The identification of such clusters from low surface brightness fluctuations provides a complementary alternative to classic selection methods based on overdensities of resolved galaxies, and enables us to search efficiently for rich high redshift clusters over large areas of the sky. The detections described here are the first in a survey that covers a total of nearly 140 sq. degrees of the sky and should yield, if these preliminary results are representative, over 300 such clusters.

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