Chandra Observation of a Group of Galaxies HCG 80: Does the Spiral-Only Group Have Hot Intragroup Gas?

We present an analysis of Chandra X-ray observations of a compact group ofgalaxies, HCG 80 (z=0.03). The system is a spiral-only group composed of fourlate-type galaxies, and has a high-velocity dispersion of 309 km/s. Withhigh-sensitivity Chandra observations, we searched for diffuse X-ray emissionfrom the intragroup medium (IGM); however, no significant emission wasdetected. We place a severe upper limit on the luminosity of the diffuse gas asLX < 6e40 erg/s. On the other hand, significant emission from three of the fourmembers were detected. In particular, we discovered huge halo emission from HCG80a 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 ~4e40erg/s in the 0.5-2 keV band, respectively. It is most likely to be an outflowpowered by intense starburst activity. Based on the results, we discusspossible 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 possiblyat an early stage of IGM evolution.Comment: 12 pages, 6 figures; minor corrections. To appear in PASJ, Vol 56 No.