BST1047+1156: An Extremely Diffuse and Gas-rich Object in the Leo I Group
Abstract
We report the detection of diffuse starlight in an extragalactic H I cloud in the nearby Leo I galaxy group. We detect the source, BST1047+1156, in both broadband optical and the Galaxy Evolution Explorer (GALEX) ultraviolet (UV) light. Spanning ∼2 kpc in radius, it has a peak surface brightness of μ B = 28.8 mag arcsec-2, making it the lowest surface brightness object ever detected via integrated light. Although the object is extremely gas rich, with a gas fraction of f g = 0.99, its peak H I column density is well below levels where star formation is typically observed in galaxies. Nonetheless, BST1047+1156 shows evidence for young stellar populations: along with the detected UV emission, the object is extremely blue, with B - V = 0.14 ± 0.09. The object has two tidal tails and is found embedded within diffuse gas connecting the spiral galaxy M96 to the group’s extended H I Leo Ring. The nature of BST1047+1156 is unclear. It could be a disrupting tidal dwarf, recently spawned from star formation triggered in the Leo I group’s tidal debris. Alternatively, the object may have been a pre-existing galaxy—the most extreme example of a gas-rich field low surface brightness galaxy known to date—which had a recent burst of star formation triggered by encounters in the group environment.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- August 2018
- DOI:
- 10.3847/2041-8213/aad62e
- arXiv:
- arXiv:1807.11544
- Bibcode:
- 2018ApJ...863L...7M
- Keywords:
-
- galaxies: evolution;
- galaxies: groups: individual: Leo I;
- galaxies: interactions;
- galaxies: irregular;
- galaxies: structure;
- Astrophysics - Astrophysics of Galaxies;
- Astrophysics - Cosmology and Nongalactic Astrophysics
- E-Print:
- 8 pages, 4 figures, accepted for publication in ApJ Letters. (Revised version fixes a few typos and missing references caught during the copy-editing stage.)