Chandra observation of a group of galaxies HCG 80: Does the spiral-only group have hot intragroup gas?

Abstract

We present an analysis of Chandra X-ray observations of a compact group of galaxies, HCG 80 (z = 0.03). The system is a spiral-only group composed of four late-type galaxies, and has a high-velocity dispersion of 309 km s -1. With high-sensitivity Chandra observations, we searched for diffuse X-ray emission from the intragroup medium (IGM); however, no significant emission was detected. We place a severe upper limit on the luminosity of the diffuse gas as LX < 6 × 1040 erg s-1. On the other hand, significant emission from three of the four members were detected. In particular, we discovered huge halo emission from HCG 80a that extends on a scale of ̃ 30 kpc perpendicular to the galactic disk, whose X-ray temperature and luminosity were measured to be ̃ 0.6 keV and ̃ 4 × 1040 erg s-1 in the 0.5-2 keV band, respectively. It is most likely to be an outflow powered by intense starburst activity. Based on the results, we discuss possible reasons for the absence of diffuse X-ray emission in the HCG 80 group, suggesting that the system is subject to galaxy interactions, and is possibly at an early stage of IGM evolution.