An Analysis of Soft X-ray Structures at Kiloparsec Distances from the Active Nucleus of Centaurus A Galaxy

TL;DR

This study re-analyzes Chandra X-ray data of Centaurus A, revealing soft X-ray structures at kiloparsec scales associated with radio lobes, and identifies both synchrotron emission and dense gas possibly linked to galaxy outflows.

Contribution

It provides a systematic spectral analysis of soft X-ray features at large distances from the nucleus, highlighting the nature of emission and gas properties in the galaxy's lobes.

Findings

Power-law X-ray emission with photon index ~2 at lobe edges

Detection of dense, cold gas in East and West regions

Evidence of gaseous condensations possibly from galaxy outflows

Abstract

Here we re-analyze the archival {\it Chandra} data for the central parts of the Centaurus\,A radio galaxy, aiming for a systematic investigation of the X-ray emission associated with the inner radio lobes in the system, and their immediate surroundings. In particular, we focus on four distinct features characterized by the soft excess with respect to the adjacent fields. Those include the two regions located at kpc distances from the nucleus to the West and East, the extended bow-shock structure to the South, and a fragment of a thin arc North from the center. The selected North, West, and South features coincide with the edges of the radio lobes, while the East structure is seemingly displaced from the radio-emitting plasma. Our X-ray spectral analysis reveals (i) a power-law emission component with photon index $\Gamma \sim 2$ in the North, East, and South regions, and (ii) a dense (number density $\sim 0.3$\,cm$^{-3}$) and relatively cold (temperature $\sim 0.2$\,keV) gas in the East and West regions. The power-law emission is consistent with the synchrotron continuum generated at the edges of the radio structure, and implies that the efficiency of the electron acceleration at the terminal bow-shock does not vary dramatically over the inner lobes' extension. The presence of gaseous condensations, on the other hand, could possibly be understood in terms of a massive outflow from the central regions of the galaxy.