language: en

arXiv:0811.3654v2 [astro-ph] 16 Dec 2008

[submitted to ApJ]

[Preprint typeset using LATEX style emulateapj v. 2/19/04]

CHANDRA OBSERVATIONS OF THE GALAXY GROUP AWM 5: COOL CORE RE-HEATING AND THERMAL CONDUCTION SUPPRESSION

A. Baldi, W. Forman, C. Jones, P. Nulsen, L. David, R. Kraft
Harvard-Smithsonian Center for Astrophysics
and A. Simionescu
Max Planck Institute for Extraterrestrial Physics

[submitted to ApJ]

ABSTRACT We present an analysis of a 40 ksec Chandra observation of the galaxy group AWM 5. It has a small (? 8 kpc) dense cool core with a temperature of ? 1.2 keV and the temperature profile decreases at larger radii, from ? 3.5 keV just outside the core to ? 2 keV at ? 300 kpc from the center. The abundance distribution shows a "hole" in the central ? 10 kpc, where the temperature declines sharply. An abundance of at least a few times solar is observed ? 15 ? 20 kpc from the center. The deprojected electron density profile shows a break in slope at ? 13 kpc and can be fit by two ?-models, with ? = 0.72 +0.16 ?0.11 and r c = 5.7 +1.8 ?1.5 kpc, for the inner part, and ? = 0.34 � 0.01 and r c = 31.3 +5.8 ?5.5 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 ? 6.5% at r ? 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 ? 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 ? 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. We also studied the properties of the ram pressure stripped tail in the group member NGC 6265. This galaxy is moving at M ? 3.4 +0.5 ?0.6 (v ? 2300 km s ?1 ) through the hot group gas. The physical length of the tail is ? 42 kpc and its mass is 2.1 � 0.2 � 10 9 M ? .

Subject headings: conduction ? galaxies: clusters: individual (AWM 5) ? galaxies: individual (NGC 6269, NGC 6265) ? (galaxies:) intergalactic medium ? radio continuum: galaxies ? X-rays: galaxies: clusters

1. INTRODUCTION