A Chandra study of Abell 795 – a sloshing cluster with an FR0 radio galaxy at its centre

Abstract

We present the first X-ray dedicated study of the galaxy cluster A795 and of the Fanaroff-Riley Type 0 hosted in its brightest cluster galaxy. Using an archival 30 ks Chandra observation we study the dynamical state and cooling properties of the intracluster medium, and we investigate whether the growth of the radio galaxy is prevented by the surrounding environment. We discover that A795 is a weakly cool core cluster, with an observed mass deposition rate ⪅14 M⊙yr−1 in the cooling region (central ∼66 kpc). In the inner ∼ 30 kpc we identify two putative X-ray cavities, and we unveil the presence of two prominent cold fronts at ∼60 kpc and ∼178 kpc from the center, located along a cold ICM spiral feature. The central galaxy, which is offset by 17.7 kpc from the X-ray peak, is surrounded by a multi-temperature gas with an average density of ne = 2.14 × 10−2 cm−3. We find extended radio emission at 74-227 MHz centered on the cluster, exceeding the expected flux from the radio galaxy extrapolated at low frequency. We propose that sloshing is responsible for the spiral morphology of the gas and the formation of the cold fronts, and that the environment alone cannot explain the compactness of the radio galaxy. We argue that the power of the two cavities and the sloshing kinetic energy can reduce and offset cooling. Considering the spectral and morphological properties of the extended radio emission, we classify it as a candidate radio mini-halo.

The eMERLIN and EVN View of FR 0 Radio Galaxies

“…At the extreme high energies, a few FR 0s (and candidates) have been detected in the γ-ray band by the Fermi Telescope [74][75][76][77] and have been proposed as possible sources of cosmic neutrinos and high-energy cosmic rays [78][79][80]. All these results foster the idea that the putative jets of FR 0s are possibly characterized by a relativistic bulk speed and that FR 0s may play a crucial role in galaxy evolution via a continuous low-regime jet feedback [81], as supported by numerical simulations of low-power jets (e.g., [82][83][84]).…”

Investigating the spectra and physical nature of galaxy scale jets

“…Tadhunter 2016b; Bicknell et al 2018;O'Dea & Saikia 2021). In addition, there is a growing interest in the population of FR0 galaxies (Baldi et al 2015(Baldi et al , 2018 and their potential role in feedback (Ubertosi et al 2021).…”

The eMERLIN and EVN view of FR0 radio galaxies

“…At the extreme high energies, a few FR 0s (and candidates) have been detected in γ-ray band by the Fermi Telescope [54,60,113,130] and have been proposed as possible sources of cosmic neutrinos and high energy cosmic rays [70,92,133]. All these results foster the idea that the putative jets of FR 0s are possibly characterised by a relativistic bulk speed and that FR 0s may play a crucial role in galaxy evolution via a continuous low-regime jet feedback [137], as supported by numerical simulations of low-power jets (e.g. [87,98,99]).…”