Kavli Affiliate: Steven W. Allen
| First 5 Authors: Madeline C. Casas, Ky Putnam, Adam B. Mantz, Steven W. Allen, Taweewat Somboonpanyakul
| Summary:
The most dynamically relaxed clusters of galaxies play a special role in
cosmological studies as well as astrophysical studies of the intracluster
medium (ICM) and active galactic nucleus feedback. While high spatial
resolution imaging of the morphology of the ICM has long been the gold standard
for establishing a cluster’s dynamical state, such data are not available from
current or planned surveys, and thus require separate, pointed follow-up
observations. With optical and/or near-IR photometric imaging, and red-sequence
cluster finding results from those data, expected to be ubiquitously available
for clusters discovered in upcoming optical and mm-wavelength surveys, it is
worth asking how effectively photometric data alone can identify relaxed
cluster candidates, before investing in, e.g., high-resolution X-ray
observations. Here we assess the ability of several simple photometric
measurements, based on the redMaPPer cluster finder run on Sloan Digital Sky
Survey data, to reproduce X-ray classifications of dynamical state for an X-ray
selected sample of massive clusters. We find that two simple metrics
contrasting the Bright Central Galaxy (BCG) to other cluster members can
identify a complete sample of relaxed clusters with a purity of ~40 per cent in
our data set. Including minimal ICM information in the form of a center
position increases the purity to ~60 per cent. However, all three metrics
depend critically on correctly identifying the BCG, which is presently a
challenge for optical red-sequence cluster finders.
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