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Understanding Tests of Brightest Cluster Galaxy Specialness

Presentation #139.12 in the session Galaxy Clusters/Large Scale Structure, Cosmic Distance — iPoster Session.

Published onJun 29, 2022
Understanding Tests of Brightest Cluster Galaxy Specialness

A longstanding question when studying Brightest Cluster Galaxies (BCGs) and their evolution is whether their luminosities are statistical extremes of the luminosity distribution of other cluster member galaxies, or whether their luminosities follow a different “special” distribution. To explore this question, we use the two statistics proposed by Tremaine & Richstone (1977). Dalal et al. (2021) and Lin et al. (2010) have found that the two Tremaine-Richstone statistics sometimes lead to different conclusions about BCG specialness. To better understand this, we run Monte Carlo simulations of galaxy clusters in which we adjust BCG properties. From these simulations, we compute the Tremaine-Richstone statistics to explore the sensitivity of each statistic to the adjusted BCG specialness. We identify cases in which the statistics lead to different conclusions and apply an independent test to determine which statistic is more reliable. We conclude that the first of the Tremaine-Richstone statistics, which relies on the spread of BCG masses, is more reliable than the second, which utilizes the spread in the mass gap between the BCG and second ranked galaxy.

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