Galaxy Cluster Project Research Articles

The Gemini/HST Galaxy Cluster Project: Environment Effects on the Stellar Populations in the Lynx Clusters at z = 1.27

Few detailed investigations of stellar populations in passive galaxies beyond z~1 are based on deep spectroscopic observations, due to the difficulty in obtaining such data. We present a study of stellar populations, structure, and mass-to-light ratios of a large sample of bulge-dominated galaxies in the two z=1.27 clusters Lynx E and Lynx W, based on deep ground-based optical spectroscopy combined with imaging from Hubble Space Telescope. We find that Lynx E has a well-defined core of red passive galaxies, while Lynx W lacks such a core. If all the sample galaxies evolve similarly in size from z=1.27 to the present, the data allow only 0.1 dex size-growth at a fixed dynamical mass. However, to link the Lynx central galaxies to brightest cluster galaxies similar to those of low redshift clusters, the Lynx galaxies would have to grow by at least a factor five, possibly through major merging. The mass-to-light ratios and the Balmer absorption lines of the Lynx galaxies are consistent with passive evolution of the stellar populations from z=1.27 to the present and support ages of 1--3 Gyr. The galaxies in the outskirts of the clusters contain younger stellar populations than found in the cluster cores. However, when evolved passively to z~0 both populations are consistent with the observed populations in the Coma cluster galaxies. The bulge-dominated emission line galaxies in the clusters are dominated by stellar populations with sub-solar metallicities. Thus, additional enrichment of these is required to produce Coma-like stellar populations by z~0.

The Gemini/Hubble Space Telescope Galaxy Cluster Project: Stellar Populations in the Low-redshift Reference Cluster Galaxies

Abstract In order to study stellar populations and galaxy structures at intermediate and high redshift (z = 0.2–2.0) and link these properties to those of low-redshift galaxies, there is a need for well-defined local reference samples. Especially for galaxies in massive clusters, such samples are often limited to the Coma cluster galaxies. We present consistently calibrated velocity dispersions and absorption-line indices for galaxies in the central 2 R 500 × 2 R 500 of four massive clusters at z < 0.1: Abell 426/Perseus, Abell 1656/Coma, Abell 2029, and Abell 2142. The measurements are based on data from the Gemini Observatory, McDonald Observatory, and Sloan Digital Sky Survey. For bulge-dominated galaxies, the samples are 95% complete in Perseus and Coma and 74% complete in A2029 and A2142, to a limit of M B,abs ≤ −18.5 mag. The data serve as the local reference for our studies of galaxy populations in the higher-redshift clusters that are part of the Gemini/HST Galaxy Cluster Project (GCP). We establish the scaling relations between line indices and velocity dispersions as a reference for the GCP. We derive stellar population parameters, ages, metallicities [M/H], and abundance ratios from line indices, both averaged in bins of velocity dispersion and from individual measurements for galaxies in Perseus and Coma. The zero points of relations between the stellar population parameters and the velocity dispersions limit the allowed cluster-to-cluster variation of the four clusters to ±0.08 dex in age, ±0.06 dex in [M/H], ±0.07 dex in [CN/Fe], and ±0.03 dex in [Mg/Fe].

The Gemini/HST Galaxy Cluster Project: Redshift 0.2–1.0 Cluster Sample, X-Ray Data, and Optical Photometry Catalog

Abstract The Gemini/HST Galaxy Cluster Project (GCP) covers 14 z = 0.2–1.0 clusters with X-ray luminosity of in the 0.1–2.4 keV band. In this paper, we provide homogeneously calibrated X-ray luminosities, masses, and radii, and we present the complete catalog of the ground-based photometry for the GCP clusters. The clusters were observed with either Gemini North or South in three or four of the optical passbands g′, r′, i′, and z′. The photometric catalog includes consistently calibrated total magnitudes, colors, and geometrical parameters. The photometry reaches ≈25 mag in the passband closest to the rest-frame B band. We summarize comparisons of our photometry with data from the Sloan Digital Sky Survey. We describe the sample selection for our spectroscopic observations, and establish the calibrations to obtain rest-frame magnitudes and colors. Finally, we derive the color–magnitude relations for the clusters, and briefly discuss these in the context of evolution with redshift. Consistent with our results based on spectroscopic data, the color–magnitude relations support passive evolution of the red sequence galaxies. The absence of change in the slope with redshift constrains the allowable age variation along the red sequence to <0.05 dex between the brightest cluster galaxies and those four magnitudes fainter. This paper serves as the main reference for the GCP cluster and galaxy selection, X-ray data, and ground-based photometry.

The Evolution of Bulge-dominated Field Galaxies from z ≈ 1 to the Present

Abstract We analyze the stellar populations and evolutionary history of bulge-dominated field galaxies at redshifts as part of the Gemini/Hubble Space Telescope (HST) Galaxy Cluster Project (GCP). High signal-to-noise optical spectroscopy from the Gemini Observatory and imaging from the HST are used to analyze a total of 43 galaxies, focusing on the 30 passive galaxies in the sample. Using the size–mass and velocity dispersion–mass relations for the passive field galaxies we find no significant evolution of sizes or velocity dispersions at a given dynamical mass between and the present. We establish the Fundamental Plane and study mass-to-light (M/L) ratios. The M/L versus dynamical mass relation shows that the passive field galaxies follow a relation with a steeper slope than the local comparison sample, consistent with cluster galaxies in the GCP at z = 0.86. This steeper slope indicates that the formation redshift is mass dependent, in agreement with “downsizing,” meaning that the low-mass galaxies formed their stars more recently while the high-mass galaxies formed theirs at higher redshift. The zero-point differences of the scaling relations for the M/L ratios imply a formation redshift of for the passive field galaxies. This is consistent with the line index which implies a formation redshift of .

Life in Low Density Environments – Field Galaxies from z=1.0 to the Present

AbstractWe present results on the stellar populations of bulge-dominated field galaxies at redshifts up to ≈1.0. The sample consists of non-cluster galaxies observed as part of the spectroscopic observations for the Gemini/HST Galaxy Cluster Project (GCP). Our preliminary results show that the bulge-dominated field galaxies contain younger stellar populations than cluster galaxies at similar redshifts. Future work will include photometry from Hubble Space Telescope and will be aimed at establishing the evolution of the sizes and the mass-to-light ratios for the field galaxies.

THE GEMINI/ HST CLUSTER PROJECT: STRUCTURAL AND PHOTOMETRIC PROPERTIES OF GALAXIES IN THREE z = 0.28-0.89 CLUSTERS

We present the data processing and analysis techniques we are using to determine structural and photometric properties of galaxies in our Gemini/HST Galaxy Cluster Project sample. The goal of this study is to understand cluster galaxy evolution in terms of scaling relations and structural properties of cluster galaxies at redshifts 0.15 < z < 1.0. To derive parameters such as total magnitude, half-light radius, effective surface brightness, and Sersic n, we fit r^{1/4} law and Sersic function 2-D surface brightness profiles to each of the galaxies in our sample. Using simulated galaxies, we test how the assumed profile affects the derived parameters and how the uncertainties affect our Fundamental Plane results. We find that while fitting galaxies which have Sersic index n < 4 with r^{1/4} law profiles systematically overestimates the galaxy radius and flux, the combination of profile parameters that enter the Fundamental Plane has uncertainties that are small. Average systematic offsets and associated random uncertainties in magnitude and log r_e for n > 2 galaxies fitted with r^{1/4} law profiles are -0.1+-0.3 and 0.1+-0.2 respectively. The combination of effective radius and surface brightness, log r_e - \beta log <I>_e, that enters the Fundamental Plane produces offsets smaller than -0.02+-0.10. This systematic error is insignificant and independent of galaxy magnitude or size. A catalog of photometry and surface brightness profile parameters is presented for three of the clusters in our sample, RX J0142.0+2131, RX J0152.7-1357, and RX J1226.9+3332 at redshifts 0.28, 0.83, and 0.89 respectively.

Mass dependent Evolution of Field Early-Type Galaxies Since z=1

AbstractWe present the Fundamental Plane (FP) of field early-type galaxies at 0.5 &lt; z &lt; 1.0. Our project is a continuation of our efforts to understand the formation and evolution of early-type galaxies in different environments. The target galaxies were selected from the comprehensive and homogeneous data set of the Gemini/HST Galaxy Cluster Project. The distant field early-type galaxies follow a steeper FP relation compared to the local FP. The change in the slope of the FP can be interpreted as a mass-dependent evolution. Similar results have been found for cluster early-type galaxies in high redshift galaxy clusters at 0.8 &lt; z &lt;1. Therefore, the slope change of the FP appears to be independent of the environment of the galaxies.