Chandra observations of the galaxy group AWM 5: cool core re-heating and thermal conduction suppression

Abstract

We present an analysis of a 40 ksec Chandra observation of the galaxy group AWM 5. It has a small ($\sim 8$ kpc) dense cool core with a temperature of $\sim 1.2$ keV and the temperature profile decreases at larger radii, from $\sim 3.5$ keV just outside the core to $\sim 2$ keV at $\sim 300$ kpc from the center. The abundance distribution shows a "hole" in the central $\sim 10$ kpc, where the temperature declines sharply. An abundance of at least a few times solar is observed $\sim 15-20$ kpc from the center. The deprojected electron density profile shows a break in slope at $\sim 13$ kpc and can be fit by two ${\hat{I}}^2$-models, with ${\hat{I}}^2=0.72_{-0.11}^{+0.16}$ and $r_c=5.7_{-1.5}^{+1.8}$ kpc, for the inner part, and ${\hat{I}}^2=0.34\pm 0.01$ and $r_c=31.3_{-5.5}^{+5.8}$ kpc, for the outer part. The mass fraction of hot gas is fairly flat in the center and increases for $r>30$ kpc up to a maximum of $\sim 6.5$ at $r\sim 380$ kpc. The gas cooling time within the central 30 kpc is smaller than a Hubble time, although the temperature only declines in the central $\sim 8$ kpc region. This discrepancy suggests that an existing cooling core has been partially re-heated. In particular, thermal conduction could have been a significant source of re-heating. In order for heating due to conduction to balance cooling due to emission of X-rays, the conductivity must be suppressed by a large factor (at least $\sim 100$). Past AGN activity (still visible as a radio source in the center of the group) is however the most likely source that re-heated the central regions of AWM 5.

24 pages, 17 figures, Accepted for publication in the Astrophysical Journal