Suzaku Xray Observations of the Nearest NonCool Core Cluster, Antlia: Dynamically Young but with Remarkably Relaxed Outskirts
Abstract
We present the results of seven Suzaku mosaic observations (>200 ks in total) of the nearest noncool core cluster, the Antlia Cluster (or Group), beyond its degreescale virial radius in its eastern direction. The temperature is consistent with the scaled profiles of many other clusters. Its pressure follows the universal profile. The density slope in its outskirts is significantly steeper than that of the nearest cool core cluster (Virgo) with a similar temperature as Antlia, but shallower than those of the massive clusters. The entropy increases all the way out to R _{200}, which is consistent in value with the baseline model predicted by a gravity heatingonly mechanism in the outskirts. Antlia is quite relaxed in this direction. However, the entropy inside ∼R _{500} is significantly higher than the baseline model, which is similar to many other nearby low mass clusters or groups. The enclosed gasmass fraction does not exceed the cosmic value out to 1.3{R}_{200}. Thus, there is no evidence of significant gas clumping, electronion nonequipartition, or departure from the hydrostatic equilibrium approximation that are suggested to explain the entropy and gas fraction anomalies found in the outskirts of some massive clusters. We also present scaling relations for the gas fraction ({f}_{{{gas,200}}}), entropy (K _{200}), and temperature (T _{500}) using 22 groups and clusters with published data in the literature. The enclosed baryon fraction at R _{200} is broadly consistent with the cosmic value. The power law slope of the K _{200}T _{500} relation is 0.638 ± 0.205. The entropy deficit at R _{200} cannot be fully accounted for by the bias or deviation in the gas fraction.
 Publication:

The Astrophysical Journal
 Pub Date:
 September 2016
 DOI:
 10.3847/0004637X/829/1/49
 arXiv:
 arXiv:1602.06950
 Bibcode:
 2016ApJ...829...49W
 Keywords:

 galaxies: clusters: intracluster medium;
 galaxies: groups: individual: the Antlia Cluster;
 intergalactic medium;
 largescale structure of universe;
 Xrays: galaxies: clusters;
 Astrophysics  High Energy Astrophysical Phenomena;
 Astrophysics  Cosmology and Nongalactic Astrophysics
 EPrint:
 24 pages, 16 figures, minor modifications to match the published version in ApJ