AMUSE-Antlia. II. Intracluster X-Ray Population in the Antlia Cluster

Abstract

We conduct a systematic survey of X-ray sources in the inner (r ∼ 200 kpc) region of the Antlia cluster based on Chandra observations, down to a source detection limit of L(0.5–8 keV) ∼ 4.2 × 10−7 ph cm−2 s−1 (2 × 1038 erg s−1). We present an X-ray source catalog with 202 sources and provide their coordinates, multiband flux information, and hardness ratios. We find a statistically significant excess at a significance level of 4.2σ with 37.6 excess sources beyond 3 times the mean effective radius of the two brightest central galaxies (BCGs). This implies that these excess sources could be a genuine intracluster X-ray population that is not associated with the bulk stellar component. Also, the increased number of excess sources in the fields containing a BCG implies a potential connection between the excess sources and BCGs. The discovery of these sources in the Antlia cluster, together with previous research of similar findings in the other two nearby clusters, Virgo and Fornax, indicates that the intracluster X-ray population could be universal in nearby galaxy clusters. Furthermore, we discuss the candidate origins of the excess sources, including low-mass X-ray binaries (LMXBs) associated with intracluster light (ICL-LMXBs), LMXBs in globular clusters (GC-LMXBs), and supernova-kicked LMXBs (SN-kicked LMXBs). We estimate that the contribution of ICL-LMXBs, which should include the LMXBs related to the stellar halo surrounding BCGs, is unlikely to dominate the intracluster X-ray population in Antlia. Meanwhile, GC-LMXBs and SN-kicked LMXBs, each component could contribute ∼30% to the total excess sources.