We report the discovery of two small intergalactic HII regions in the loose group of galaxies around the field elliptical NGC 1490. The HII regions are located at least 100 kpc from any optical galaxy but are associated with a number of large HI clouds that are lying along an arc 500 kpc in length and that have no optical counterpart on the Digital Sky Survey. The sum of the HI masses of the clouds is almost 1010 M☉ and the largest HI cloud is about 100 kpc in size. Deep optical imaging reveals a very low surface brightness counterpart to this largest HI cloud, making this one of the HI richest optical galaxies known (MHI/LV ∼ 200). Spectroscopy of the HII regions indicates that the abundance in these HII regions is only slightly sub-solar, excluding a primordial origin of the HI clouds. The HI clouds are perhaps remnants resulting from the tidal disruption of a reasonably sized galaxy, probably quite some time ago, by the loose group to which NGC 1490 belongs. Alternatively, they are remnants of the merger that created the field elliptical NGC 1490. The isolated HII regions show that star formation on a very small scale can occur in intergalactic space in gas drawn from galaxies by tidal interactions. Many such intergalactic small star formation regions may exist near tidally interacting galaxies.
Recycling Intergalactic and Interstellar Matter
- Pub Date:
- June 2004
- To appear in the proceedings of the IAU Symposium #217, Recycling Intergalactic and Interstellar Matter, eds. P.-A. Duc, J. Braine, and E. Brinks, 6 pages with low resolution figures. The full paper with high resolution images can be downloaded from http://www.astron.nl/~morganti/Papers/cloud.ps.gz