The evolution of HCG 31 : Optical and high-resolution HI study

Abstract

Here we present the results of our new optical imaging and spectroscopic study and the analysis of new high-resolution HI images of the Hickson Compact Group HCG 31. Taking advantage of the improved sensitivity and angular resolution of the new optical and HI images, we have identified an extensive complex of stellar and HI tidal features and their kinematics. Our HI study show that H31A and C are not an advanced merger since their velocity fields can be still separated and have almost orthogonal orientations. All of the current sites of ongoing active star formation are shown to be associated with the highest column density peaks traced in HI. A new companion A0500-0434 located 240 kpc south of the group center is also discovered in HI. A detailed scenario for the tidal interactions involved and the origins of the individual tidal features are constructed using the morphology and kinematics of the tidal features. The derived dynamical mass for the entire group is ihout 2 × 1011 M⊙, which is a few times larger than the sum of the masses of the individual group galaxies. The ultimate fate of the group is that HCG 31 is probably on its way to form a single HI cloud group containing all galaxies.