CHANDRAOBSERVATIONS OF THE GALAXY GROUP AWM 5: COOL CORE REHEATING AND THERMAL CONDUCTION SUPPRESSION

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Abstract
We present an analysis of a 40 ks 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 β models, with β = 0.72+0.16 –0.11 and rc = 5.7+1.8 –1.5 kpc, for the inner part, and β = 0.34 ± 0.01 and rc = 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 reheated. In particular, thermal conduction could have been a significant source of reheating. In order for heating due to conduction to balance cooling due to emission of X-rays, conductivity must be suppressed by a large factor (at least ~100). Past active galactic nuclei activity (still visible as a radio source in the center of the group) is, however, the most likely source that reheated 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 × 109 M ☉.

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