Megan Gralla

Graduate Student, Department of Astronomy and Astrophysics

Scientific Advisor: Michael Gladders

Contact Information

Phone: 773-834-9845
Location: AAC 124
Email: mgrallaoddjob.uchicago.edu

PhD Thesis

Radio Sources in Galaxy Clusters
Defense Date: July 20, 2011

Ph.D. Committee: John Carlstrom, Dan Hooper, and Don York.

"Dr. Gralla's thesis work has focused on the redshift evolution of the radio source population in galaxy clusters, over a broad swath of both redshift and cluster mass. Understanding the evolution of this active galaxy population is important for models of heating by AGN of the intra-cluster medium, as well as providing input to models addressing the impact of radio sources on Sunyaev-Zeldovich surveys for galaxy clusters."
- Michael Gladders, PhD advisor.

Thesis Abstract:
I present a statistical analysis of the radio source population in galaxy clusters by matching radio sources from two large-area surveys with optically-selected galaxy clusters spanning a wide range of redshift ($sim0.3$ to $sim$ 1) from the Red-Sequence Cluster Surveys (RCS). The first RCS (RCS1) is well-characterized within a cosmological context, with richness measurements calibrated over a wide redshift range. I have focused on the redshift evolution of the radio source population. The richest clusters in the sample have more radio sources than clusters with low or intermediate richness. When divided into bins according to cluster richness, there is no significant difference ($> 1.5sigma$) 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 RCS1 sample can be characterized by the number of (L$_{1.4 GHz} > 4.1 imes 10^{24}$ W Hz$^{-1}$) radio sources per unit (10$^{14}$ M$_{odot}$) mass, which is measured to be 0.031$pm$0.004. I further characterize the population of galaxy cluster-related radio sources through visual inspection of the RCS1 images, finding that although the radio activity of brightest cluster galaxies (BCGs) also does not strongly evolve between the high and low redshift samples, the lower-redshift, richest clusters are more likely to host radio-loud BCGs than the higher-redshift, richest clusters or poorer clusters at the 2-$sigma$ level. The second RCS (RCS2) contains a much larger galaxy cluster sample selected from $>500$ square degrees of imaging data. I have refined and applied an automatic algorithm to identify the BCGs in clusters, and I find some 3$sigma$ evidence that the low redshift clusters have a higher fraction of radio-loud BCGs than the high redshift clusters, further supporting the initial evidence from RCS1. I also investigate the prevalence of extended sources in clusters and the radio activity in non-BCG red sequence galaxies, for which I find no evidence for evolution, in spite of the strong evolution that has been seen in the cluster X-ray AGN population.

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