Australia Telescope Compact Array H I observations of the NGC 6845 galaxy group

Abstract

We present the results of Australia Telescope Compact Array (ATCA) H I line and 20-cm radio continuum observations of the galaxy quartet NGC 6845. The HI emission extends over all four galaxies but can only be associated clearly with the two spiral galaxies, NGC 6845A and B, which show signs of strong tidal interaction. We derive a total HI mass of at least 1.8 × 1010 M⊙, most of which is associated with NGC 6845A, the largest galaxy of the group. We investigate the tidal interaction between NGC 6845A and B by studying the kinematics of distinct H I components and their relation to the known H II regions. No H I emission is detected from the two lenticular galaxies, NGC 6845C and D. A previously uncatalogued dwarf galaxy, ATCA J2001-4659, was detected 4.4 arcmin NE from NGC 6845B and has an Hi mass of ∼5 × 108 M⊙. No HI bridge is visible between the group and its newly detected companion. Extended 20-cm radio continuum emission is detected in NGC 6845A and B as well as in the tidal bridge between the two galaxies. We derive star formation rates of 15-40 M ⊙ yr-1.