SUZAKU X-RAY OBSERVATIONS OF THE NEAREST NON-COOL 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 non-cool core cluster, the Antlia Cluster (or Group), beyond its degree-scale 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 heating-only mechanism in the outskirts. Antlia is quite relaxed in this direction. However, the entropy inside similar to R-500 is significantly higher than the baseline model, which is similar to many other nearby low mass clusters or groups. The enclosed gas-mass fraction does not exceed the cosmic value out to 1.3R(200). Thus, there is no evidence of significant gas clumping, electron-ion non-equipartition, 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.

Description
Keywords
galaxies: clusters: intracluster medium, galaxies: groups: individual (the Antlia Cluster), intergalactic medium, large-scale structure of universe, X-rays: galaxies: clusters, VIRIAL RADIUS, GALAXY CLUSTERS, INTRACLUSTER MEDIUM, REPRESENTATIVE SAMPLE, NON-EQUIPARTITION, GAS PROPERTIES, PKS 0745-191, XMM-NEWTON, HOT GAS, ENTROPY, Astronomy & Astrophysics
Citation
Wong, K.et al. (2016): Suzaku X-ray Observations of the Nearest Non-Cool Core Cluster, Antlia: Dynamically Young but with Remarkably Relaxed Outskirts. The Astrophysical Journal, 829(1). DOI: 10.3847/0004-637X/829/1/49