Sloshing and spiral structures breeding a putative radio mini-halo in the environment of a cool-core cluster Abell 795

TL;DR

This study reports the discovery of a diffuse, ultra-steep radio mini-halo associated with spiral structures and cold fronts in the cool-core galaxy cluster Abell 795, linking radio, X-ray, and optical observations to cluster dynamics.

Contribution

It presents the first detailed analysis connecting spiral X-ray structures, cold fronts, and a radio mini-halo in Abell 795, highlighting the role of sloshing turbulence in mini-halo formation.

Findings

Detection of a 180 kpc ultra-steep radio mini-halo in A795.

Identification of spiral X-ray structures and cold fronts.

Low star formation rate and metallicity distribution consistent with gas mixing.

Abstract

Spiral structures and cold fronts in X-rays are frequently observed in cool core galaxy clusters. However, studies on radio mini-haloes associated with such spirals and their physical connections are rare. Here, we present the detection of an extended diffuse radio emission entrained in the X-ray spiral structure in a known cool core cluster Abell 795 (A795). Though the cool core is a sign of the relaxed nature of the clusters, our re-analysed 30 ks Chandra X-ray data of cluster A795 confirms the presence of an interesting log spiral structure of X-ray deficit region complemented by an X-ray excess counter spiral in the residual map, exposing its dynamical activity. Our new analysis of 150 $\&$ 325 MHz GMRT archival data of the cluster confirms the detection of a $\sim180$ kpc ultra-steep ($\alpha\sim-2.7$) diffuse radio structure which was previously reported as a candidate radio mini halo from low sensitive survey maps. This radio emission spans the entire spiral structure ($\sim186$ kpc), enclosed by two previously reported cold fronts. Furthermore, SDSS DR13 optical spectra, as well as GALEX's FUV data, show a considerably low total star formation rate of 2.52 M$_{\odot}$ yr$^{-1}$ and having no significant variation in metallicity distribution. We argued that the two-phase (hot and cold) plasma at the cluster core with differential velocity has probably caused the spiral formation and has redistributed the secondary electrons from the central BCG or the pre-accelerated electrons which have been (re-)accelerated by the sloshing turbulence to form the observed candidate radio mini-halo structure. This has been supported by a few previous studies that indicate spiral formation and sloshing turbulence may quench star formation and facilitate smooth metallicity distribution by mixing the gas in the core.