The X-ray View of Abell 3120

TL;DR

This study analyzes Chandra X-ray data of Abell 3120, confirming it as a poor galaxy cluster with complex thermal and non-thermal emission components, and explores its structure and environment.

Contribution

The paper provides a detailed X-ray analysis of Abell 3120, clarifying its nature and emission characteristics, and evaluates competing hypotheses about its origin.

Findings

X-ray emission extends beyond the central galaxy by 158 kpc

Spectrum modeling excludes purely non-thermal emission

Evidence suggests a thermal plus possibly non-thermal emission component

Abstract

Identification of Abell 3120 as a galaxy cluster has recently been questioned with alternative suggestions including: a fossil remnant of a group merger, non-thermal emission from a radio galaxy, and projected emission from of a filamentary string of galaxies. We report on our analysis of the Chandra observation and evaluate these hypotheses based on our results. Abell 3120 shows X-ray emission extending 158 kpc, well beyond the central galaxy. The spatial distribution of X-rays in the core more closely follows the radio emission showing a jet-like structure extending to the north that is misaligned with the stellar light distribution of the central galaxy. At larger radii the X-ray emission is aligned with the SE-NW running axis of the galaxy distribution in the cluster core. Modeling the X-ray spectrum excludes purely non-thermal emission. The emission weighted temperature is 1.93 - 2.19 keV and the 0.3 - 10 keV luminosity is 1.23$\times10^{43}$ ergs s$^{-1}$. Abell 3120 appears to be a poor cluster with Virgo and MKW 4 as peers. The best fitting model consists of a thermal component and a second component that may be either thermal or non-thermal, with luminosity 25% of the total X-ray luminosity. While, a more detailed spatial-spectral search failed to detect a central AGN, there is some evidence for an extended hard X-ray component. Cooler gas, 1.28 - 1.80 was detected in the central 20 kpc. The second thermal component marginally requires a higher redshift, >0.12, which may be due to a second cluster in the rich surrounding environment consisting of nearly a thousand catalogued galaxies.