Choirs, HI Galaxy Groups: Catalogue and Detection of Star-forming Dwarf
  Group Members
  H{\alpha} observations centred on galaxies selected from the HI Parkes All
Sky Survey (HIPASS, Barnes et al. 2001) typically show one and sometimes two
star-forming galaxies within the approximately 15-arcminute beam of the Parkes
64-m HI detections. In our Survey of Ionization in Neutral Gas Galaxies (SINGG,
Meurer et al. 2006) we found fifteen cases of HIPASS sources containing four or
more emission line galaxies (ELGs). We name these fields Choir groups. In the
most extreme case we found a field with at least nine ELGs. In this paper we
present a catalogue of Choir group members in the context of the wider SINGG
sample. The dwarf galaxies in the Choir groups would not be individually
detectable in HIPASS at the observed distances if they were isolated, but are
detected in SINGG narrow-band imaging due to their membership of groups with
sufficiently large total HI mass. The ELGs in these groups are similar to the
wider SINGG sample in terms of size, H{\alpha} equivalent width, and surface
brightness. Eight of these groups have two large spiral galaxies with several
dwarf galaxies and may be thought of as morphological analogues of the Local
Group. However, on average our groups are not significantly HI-deficient,
suggesting that they are at an early stage of assembly, and more like the M81
group. The Choir groups are very compact at typically only 190 kpc in projected
distance between the two brightest members. They are very similar to SINGG
fields in terms of star formation efficiency (the ratio of star formation rate
to HI mass; SFE), showing an increasing trend in SFE with stellar mass.
