Deep Chandra observations of edges and bubbles in the NGC5846 galaxy group

Abstract

We use a combined 120ks Chandra exposure to analyze X-ray edges produced by non-hydrostatic gas motions (sloshing) from galaxy collisions, and cavities formed by active galactic nucleus (AGN) activity. Evidence for gas sloshing is seen in the spiral morphology and multiple cold front edges in NGC5846's X-ray surface brightness distribution, while the lack of spiral structure in the temperature map suggests that the perturbing interaction was not in the plane of the sky. Density and spectral modeling across the edges indicate that the relative motion of gas in the cold fronts is at most transonic. Evidence for AGN activity is seen in two inner bubbles at 0.6kpc, filled with 5GHz and 1.5GHz radio plasma and coincident with Hα emission, and in a ghost bubble at 5.2kpc west of NGC5846's nucleus. The outburst energy and ages for the inner (ghost) bubbles are ∼1055erg and ∼2 Myr (∼5 × 1055erg and 12 Myr), respectively, implying an AGN duty cycle of 10 Myr. The inner bubble rims are threaded with nine knots, whose total 0.5-2keV X-ray luminosity is 0.3 × 1040 erg s-1, a factor 2-3 less than that of the surrounding rims, and 0.7keV mean temperature is indistinguishable from that of the rims. We suggest that the knots may be transient clouds heated by the recent passage of a shock from the last AGN outburst. We also observe gas stripping from a cE galaxy, NGC5846A, in a 0.5kpc long (∼105 M⊙) hot gas tail, as it falls toward NGC5846. © 2011 The American Astronomical Society. All rights reserved.