Megan B. Gralla — Page 2

arXiv2010

Sunyaev Zel'dovich Effect Observations of Strong Lensing Galaxy Clusters: Probing the Over-Concentration Problem

We have measured the Sunyaev Zel'dovich (SZ) effect for a sample of ten strong lensing selected galaxy clusters using the Sunyaev Zel'dovich Array (SZA). The SZA is sensitive to structures on spatial scales of a few arcminutes, while the strong lensing mass modeling constrains the mass at small scales (typically < 30"). Combining the two provides information about the projected concentrations of the strong lensing clusters. The Einstein radii we measure are twice as large as expected given the masses inferred from SZ scaling relations. A Monte Carlo simulation indicates that a sample randomly drawn from the expected distribution would have a larger median Einstein radius than the observed clusters about 3% of the time. The implied overconcentration has been noted in previous studies with smaller samples of lensing clusters. It persists for this sample, with the caveat that this could result from a systematic effect such as if the gas fractions of the strong lensing clusters are substantially below what is expected.

astro-ph.CO↗

arXiv2010

Constraining the Redshift Evolution of FIRST Radio Sources in RCS1 Galaxy Clusters

We conduct a statistical analysis of the radio source population in galaxy clusters as a function of redshift by matching radio sources from the Faint Images of the Radio Sky at Twenty-Centimeters (FIRST) catalog with 618 optically-selected galaxy clusters from the first Red-Sequence Cluster Survey (RCS1). The number of excess radio sources (above the background level) per cluster is 0.14 +/- 0.02 for clusters with 0.35 < z < 0.65 and is 0.10 +/- 0.02 for clusters with 0.65 < z < 0.95. The richest clusters in the sample have more radio sources than clusters with low or intermediate richness. When we divide our sample into bins according to cluster richness, we do not observe any significant difference (> 1.5 sigma) in the number of radio sources per unit of cluster mass for the galaxy clusters with 0.35 < z < 0.65 as compared to the galaxy clusters with 0.65 < z < 0.95. Thus the entire sample can be characterized by the number of (L(1.4 GHz) > 4.1 X 10^(24) W/Hz) radio sources per unit (10^14 solar masses) mass, which we measure to be 0.031 +/- 0.004. We further characterize the population of galaxy cluster-related radio sources through visual inspection of the RCS1 images, finding that although the radio activity of brightest cluster galaxies (BCGs) also does not strongly evolve between our high and low redshift samples, the lower-redshift, richest clusters are more likely to host radio-loud BCGs than the higher-redshift, richest clusters or poorer clusters at the 2-sigma level.

astro-ph.CO↗