Intrinsic scatter of caustic masses and hydrostatic bias: An observational study
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Date
2017
Journal Title
Journal ISSN
Volume Title
Publisher
EDP Sciences
Abstract
All estimates of cluster mass have some intrinsic scatter and perhaps some bias with true mass even in the absence of measurement
errors for example caused by cluster triaxiality and large scale structure. Knowledge of the bias and scatter values is fundamental
for both cluster cosmology and astrophysics. In this paper we show that the intrinsic scatter of a mass proxy can be constrained
by measurements of the gas fraction because masses with higher values of intrinsic scatter with true mass produce more scattered
gas fractions. Moreover, the relative bias of two mass estimates can be constrained by comparing the mean gas fraction at the same
(nominal) cluster mass. Our observational study addresses the scatter between caustic (i.e., dynamically estimated) and true masses,
and the relative bias of caustic and hydrostatic masses. For these purposes, we used the X-ray Unbiased Cluster Sample, a cluster
sample selected independently from the intracluster medium content with reliable masses: 34 galaxy clusters in the nearby (0.050 <
z < 0.135) Universe, mostly with 14 < log M500/M . 14.5, and with caustic masses. We found a 35% scatter between caustic and
true masses. Furthermore, we found that the relative bias between caustic and hydrostatic masses is small, 0.06 ± 0.05 dex, improving
upon past measurements. The small scatter found confirms our previous measurements of a highly variable amount of feedback from
cluster to cluster, which is the cause of the observed large variety of core-excised X-ray luminosities and gas masses.
Description
Keywords
Astronomy, Statistics studies, Galaxies formation, Cosmology, Physics
Citation
Andreon, S. et al. (2017). Intrinsic scatter of caustic masses and hydrostatic bias: An observational study. Astronomy & Astrophysics, A 606, A25. 10.1051/0004-6361/201730920