Chandra Observations of the Galaxy Group Awm 5: Cool Core Re-heating and Thermal Conduction Suppression

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 β-models, with β = 0.72 −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 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 −0.6 (v ∼ 2300 km s ) through the hot group gas. The physical length of the tail is ∼ 42 kpc and its mass is 2.1± 0.2× 10 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