Fraction Of Cluster Galaxies Research Articles

The Massive and Distant Clusters of WISE Survey. VIII. Radio Activity in Massive Galaxy Clusters

Abstract We present a study of the central radio activity of galaxy clusters at high redshift. Using a large sample of galaxy clusters at 0.7 < z < 1.5 from the Massive and Distant Clusters of Wide-field Infrared Survey Explorer Survey and the Faint Images of the Radio Sky at Twenty-Centimeters 1.4 GHz catalog, we measure the fraction of clusters containing a radio source within the central 500 kpc, which we term the cluster radio-active fraction, and the fraction of cluster galaxies within the central 500 kpc exhibiting radio emission. We find tentative (2.25σ) evidence that the cluster radio-active fraction increases with cluster richness, while the fraction of cluster galaxies that are radioluminous ( W Hz−1) does not correlate with richness at a statistically significant level. Compared to that calculated at 0 < z < 0.6, the cluster radio-active fraction at 0 < z < 1.5 increases by a factor of 10. This fraction is also dependent on the radio luminosity. Clusters at higher redshift are much more likely to host a radio source of luminosity W Hz−1 than are lower-redshift clusters. We compare the fraction of radioluminous cluster galaxies to the fraction measured in a field environment. For 0.7 < z < 1.5, we find that both the cluster and field radioluminous galaxy fraction increases with stellar mass, regardless of environment, though at fixed stellar mass, cluster galaxies are roughly 2 times more likely to be radioluminous than field galaxies.

THE CLUSTER AND FIELD GALAXY ACTIVE GALACTIC NUCLEUS FRACTION ATz= 1-1.5: EVIDENCE FOR A REVERSAL OF THE LOCAL ANTICORRELATION BETWEEN ENVIRONMENT AND AGN FRACTION

The fraction of cluster galaxies that host luminous AGN is an important probe of AGN fueling processes, the cold ISM at the centers of galaxies, and how tightly black holes and galaxies co-evolve. We present a new measurement of the AGN fraction in a sample of 13 clusters of galaxies (M >= 10^{14} Msun) at 1<z<1.5 selected from the Spitzer/IRAC Shallow Cluster Survey, as well as the field fraction in the immediate vicinity of these clusters, and combine these data with measurements from the literature to quantify the relative evolution of cluster and field AGN from the present to z~3. We estimate that the cluster AGN fraction at 1<z<1.5 is f_A = 3.0^{+2.4}_{-1.4}% for AGN with a rest-frame, hard X-ray luminosity greater than L_{X,H} >= 10^{44} erg/s. This fraction is measured relative to all cluster galaxies more luminous than M*_{3.6}(z)+1, where M*_{3.6}(z) is the absolute magnitude of the break in the galaxy luminosity function at the cluster redshift in the IRAC 3.6um bandpass. The cluster AGN fraction is 30 times greater than the 3sigma upper limit on the value for AGN of similar luminosity at z~0.25, as well as more than an order of magnitude greater than the AGN fraction at z~0.75. AGN with L_{X,H} >= 10^{43} erg/s exhibit similarly pronounced evolution with redshift. In contrast with the local universe, where the luminous AGN fraction is higher in the field than in clusters, the X-ray and MIR-selected AGN fractions in the field and clusters are consistent at 1<z<1.5. This is evidence that the cluster AGN population has evolved more rapidly than the field population from z~1.5 to the present. This environment-dependent AGN evolution mimics the more rapid evolution of star-forming galaxies in clusters relative to the field.

Spitzer /MIPS 24 μm Observations of Galaxy Clusters: An Increasing Fraction of Obscured Star-forming Members from z = 0.02 to z = 0.83

We study the mid-infrared properties of 1315 spectroscopically confirmed members in eight massive ( -->Mvir 5 × 1014 -->M☉) galaxy clusters covering the redshift range from 0.02 to 0.83. The selected clusters all have deep Spitzer/MIPS 24 μm observations, Hubble and ground-based photometry, and extensive redshift catalogs. We observe for the first time an increase in the fraction of cluster galaxies with mid-infrared star formation rates higher than 5 -->M☉ yr−1 from 3% at -->z = 0.02 to 13% at -->z = 0.83 ( -->RP ≤ 1 Mpc). This increase is reproduced even when considering only the most massive members ( -->M* ≥ 4 × 1010 -->M☉). The 24 μm observations reveal stronger evolution in the fraction of blue/star-forming cluster galaxies than in color-selected samples: the number of dusty, strongly star-forming cluster galaxies increases with redshift, and combining these with the optically defined Butcher-Oemler members [ -->Δ (B − V) z = 0.83. These results, the first of our Spitzer/MIPS Infra-Red Cluster Survey (SMIRCS), support earlier studies indicating that the increase in star-forming members is driven by cluster assembly and galaxy infall, as is expected in the framework of hierarchical formation.

The Butcher-Oemler Effect at Moderate Redshift

We present the results of Butcher-Oemler–style analysis of three moderate-redshift (0.1 < z < 0.2) clusters that have bimodal X-ray surface brightness profiles. We find that at least two of these clusters exhibit unusually high fractions of blue galaxies (fb's) as compared with clusters at comparable redshifts studied by Butcher & Oemler. This implies that star formation is occurring in a high fraction of the galaxies in the two clusters. Our results are consistent with hierarchical clustering models in which subcluster-subcluster mergers create shocks in the intracluster medium. The shocks, in turn, induce simultaneous starbursts in a large fraction of cluster galaxies. Our study therefore lends weight to the hypothesis that the Butcher-Oemler effect is an environmental, as well as evolutionary, phenomenon.

Optical properties of Morgan's poor clusters

The galaxy density, spiral content, and richness of the 23 poor clusters of galaxies cataloged by Morgan and co-workers are determined and compared with those of Abell clusters. It is found that Morgan's clusters generally represent a smooth continuation of the galaxy clustering spectrum from the rich Abell clusters. This continuity in optical properties implies a corresponding continuity in X-ray properties. The extended X-ray emission recently detected from several of Morgan's clusters is consistent with the amount of thermal bremsstrahlung emission expected on the basis of the present optical observations and previous correlations of X-ray-optical cluster properties. The fraction of cluster galaxies that are spirals is a sensitive function of the galaxy surface density, N(-)0.