A deep Chandra observation of the poor cluster AWM 4 - I. Properties of the central radio galaxy and its effects on the intracluster medium

TL;DR

This study uses Chandra and GMRT observations to analyze the interaction between the central radio galaxy and intracluster medium in the poor cluster AWM 4, revealing insights into feedback processes and jet dynamics.

Contribution

It provides detailed analysis of the central radio galaxy's properties, jet composition, and its limited impact on the intracluster medium in AWM 4, highlighting the complexity of feedback mechanisms.

Findings

The cool core is capable of fueling the active nucleus but is inefficiently heated.

X-ray cavities are not clearly detected, indicating partial filling by relativistic plasma.

Including low Lorentz factor electrons or thermal gas entrainment can reconcile pressure estimates.

Abstract

Using observations from the Chandra X-ray Observatory and Giant Metrewave Radio Telescope, we examine the interaction between the intracluster medium and central radio source in the poor cluster AWM 4. In the Chandra observation a small cool core or galactic corona is resolved coincident with the radio core. This corona is capable of fuelling the active nucleus, but must be inefficiently heated by jet interactions or conduction, possibly precluding a feedback relationship between the radio source and cluster. A lack of clearly detected X-ray cavities suggests that the radio lobes are only partially filled by relativistic plasma. We estimate a filling factor of phi=0.21 (3 sigma upper limit phi<0.42) for the better constrained east lobe. We consider the particle population in the jets and lobes, and find that the standard equipartition assumptions predict pressures and ages which agree poorly with X-ray estimates. Including an electron population extending to low Lorentz factors either reduces (gamma_min=100) or removes (gamma_min=10) the pressure imbalance between the lobes and their environment. Pressure balance can also be achieved by entrainment of thermal gas, probably in the first few kiloparsecs of the radio jets. We estimate the mechanical power output of the radio galaxy, and find it to be marginally capable of balancing radiative cooling.