The unusual morphology of the intragroup medium in NGC 5171

Abstract

We present the results of a 24 ks XMM-Newton observation of the NGC 5171 group of galaxies. NGC 5171 is unusual in that it is an X-ray bright group (L > 10^42 erg/s), with irregular contours which are not centred on a bright galaxy. The global spectrum is adequately described by a single temperature APEC model with T = 0.96 +/- 0.04 keV, and Z = 0.13 +/- 0.02 Zsol, in good agreement with previous ROSAT data. We find the X-ray contours are centred on a bright ridge of emission stretching from the BGG to a nearby galaxy. Spectral mapping reveals this ridge to be both cool (T ~ 1.1 keV) and metallic (Z ~ 0.4 Zsol) in comparison to its surrounding, suggesting it is the result of a tidal interaction between the two galaxies. Optical data reveals the member galaxies to have a high velocity dispersion (sigma = 494 +/- 99 km/s), and a significantly non-Gaussian velocity distribution, suggesting the group is in the process of merging. A region of hot gas with T = 1.58 +/- 0.36 keV is found to the West of the bright central ridge, and we interpret this as shock-heating resulting from the merging. A further region of emission to the South-East of the bright central ridge, with T = 1.14 +/- 0.13 keV, is probably associated with a background group, four times more distant.

arXiv comment10 pages, 8 figures, to be published in MNRAS

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