Student Science

Intel ISEF 2013 Finalist Profile

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Cool Core Bias in Sunyaev-Zel'dovich Galaxy Cluster Surveys

Henry Lin

Caddo Parish Magnet High School, Shreveport, LA

Sunyaev-Zel'dovich (SZ) surveys search for patches of blue-shifted cosmic microwave background due to the presence of massive clusters of galaxies. In an effort to quantify possible biases in these new surveys, we model thousands of relaxed galaxy clusters via extensive Monte Carlo simulations. "Cool core" density perturbations were added to the centers of each cluster and hydrostatic equilibrium was assumed to calculate the response of the cluster profiles to this addition. Further simulations were employed to perform mock SZ observations of both the perturbed (cool core) and unperturbed (non-cool core) clusters. We find that SZ surveys are slightly biased towards detecting cool core clusters: the median change in the signal-to-noise ratio is 1.3%, though in 10% of these systems, the bias is greater than 8%. Consequently, both the mass of cool core clusters and the cool core fraction may be overestimated by ~5% and ~1%, respectively. Since most cool cores contain active galactic nuclei, we calculate the effect of these radio-loud sources on the SZ signal by adding point sources to the mock clusters. We find that the presence of radio-loud active galactic nuclei generally reduces the cool core bias, sometimes to the sub-percent level. These results support the claim that SZ-selected samples are ideal for cosmological or astrophysical analysis.

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