Gaseous tidal debris found in the NGC 3783 group

Abstract

We have conducted wide-field H i mapping of a ∼5.5 × 5.5-deg2 region surrounding the NGC 3783 galaxy group, to an H i mass limit of ∼4 × 108 M⊙. The observations were made using the multibeam system on the Parkes 64-m radiotelescope, as part of the Galaxy Evolution Multiwavelength Study. We find twelve H i detections in our Parkes data, four more than catalogued in H i Parkes All Sky Survey (HIPASS). We find two new group members, and discover an isolated region of H i gas with an H i mass of ∼4 × 108 M⊙, without a visible corresponding optical counterpart. We discuss the likelihood of this H i region being a low surface brightness galaxy, primordial gas, or a remnant of tidal debris. For the NGC 3783 group we derive a mean recession velocity of 2903 ± 26 km s−1, and a velocity dispersion of 190 ± 24 km s−1. The galaxy NGC 3783 is the nearest galaxy to the luminosity-weighted centre of the group, and is at the group mean velocity. From the X-ray and dynamical state of this galaxy group, this group appears to be in the early stages of its evolution.