Chandra observations of the interacting galaxies NGC 3395/3396 (Arp 270)

Abstract

In this paper we present the results of a 20-ks high-resolution Chandra X-ray observation of the peculiar galaxy pair NGC 3395/3396, a system at a very early stage of merging, and less evolved than the famous Antennae and Mice merging systems. Previously unpublished ROSAT High-Resolution Imager data are also presented. The point-source population and the hot diffuse gas in this system are investigated and compared with other merging galaxy pairs. 16 X-ray point sources are detected in Arp 270, seven of which are classified as ultraluminous X-ray sources (ULXs, LX>= 1039 erg s-1). From spectral fits and the age of the system it seems likely that these are predominantly high-mass X-ray binaries. The diffuse gas emits at a global temperature of ~0.5 keV, consistent with temperatures observed in other interacting systems, and we see no evidence of the starburst-driven hot gaseous outflows seen in more evolved systems such as The Mice and The Antennae. It is likely that these features are absent from Arp 270 as the gas has had insufficient time to break out of the galaxy discs. 32 per cent of the luminosity of Arp 270 arises from the diffuse gas in the system, this is low when compared with later stage merging systems and gives further credence that this is an early-stage merger. Comparing the ULX population of Arp 270 to other merging systems, we derive a relationship between the star formation rate of the system, indicated by LFIR, and the number [N(ULX)] and luminosity (LULX) of its ULX population. We find N(ULX) ~L0.18FIR and LULX~L0.54FIR. These relationships, coupled with the relation of the point-source X-ray luminosity (LXP) to LK and LFIR+UV (Colbert et al. 2003), indicate that the ULX sources in an interacting system have contributions from both the old and young stellar populations.