Chandra X-ray Observatory study of the X-ray emission of PKS 0023-26 and comparison with recent ALMA results

TL;DR

This study uses Chandra X-ray data to analyze the hot gas environment of the quasar PKS 0023-26, revealing a low-temperature galaxy group, a thermal component near the nucleus, and jet-ISM interactions that produce shock-heated gas and excite CO emission.

Contribution

First high-resolution X-ray imaging of PKS 0023-26 showing detailed hot gas distribution and jet-ISM interactions, with comparison to recent ALMA molecular line results.

Findings

No large-scale hot gas detected, indicating a poor galaxy group.

Thermal emission with kT ≈ 0.9 keV near the nucleus.

Jet-driven shocks with Mach number 1.75-2 influence the ISM.

Abstract

We present a deep high-resolution Chandra X-ray Observatory image data of a powerful compact radio source PKS 0023-26 associated with a quasar at redshift 0.322. The earlier studies of the optical environment suggested that the source could be located in a galaxy cluster or a group. However, we report a non-detection of hot gas on large scales (out to $\sim 60$ kpc radius) and place an upper limit on the X-ray luminosity of $<3\times10^{42}$ erg s$^{-1}$, consistent only with the presence of a poor, low-temperature ($\rm kT < 0.5$ keV) galaxy group. X-ray spectral analysis of the central circular region, $r<7$ kpc shows, in addition to the mildly absorbed AGN, a thermal emission component with a temperature of $\rm kT=0.9^{+0.19}_{-0.37}$ keV. We discuss the origin of this hot component as a result of interaction between the evolving radio source and the interstellar medium. Our high angular resolution X-ray image traces the distribution of hot gas which is closely aligned with and extends beyond the radio source, and also in the direction perpendicular to the radio source axis. The X-rays are enhanced at the northern radio lobe and the location of the peak of the CO(3-2)/CO(2-1) line emission, suggesting that the interactions between the jet and cold medium result in the X-ray radiation which excites CO. The shock driven by the jet into the ISM is supersonic with the Mach number of $\mathcal{M} \sim 1.75-2$, creating the cocoon of hot X-rays surrounding the radio source. This result agrees with observations of shocks in other radio galaxies pointing to a prevalent impact of jets on ISM.