University of Oulu

Mihos, J., Carr, C., Watkins, A., Oosterloo, T., Harding, P. (2018) BST1047+1156: An Extremely Diffuse and Gas-rich Object in the Leo I Group. Astrophysical Journal Letters, 863 (1), L7. doi:10.3847/2041-8213/aad62e

BST1047+1156 : an extremely diffuse and gas-rich object in the Leo I group

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Author: Mihos, J. Christopher1; Carr, Christopher T.1; Watkins, Aaron E.2;
Organizations: 1Department of Astronomy, Case Western Reserve University
2Astronomy Research Unit, University of Oulu
3Netherlands Institute for Radio Astronomy (ASTRON)
4Kapteyn Astronomical Institute, University of Groningen
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 1.3 MB)
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Language: English
Published: IOP Publishing, 2018
Publish Date: 2018-09-20


We report the detection of diffuse starlight in an extragalactic H ɪ 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 μB = 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 fg = 0.99, its peak H ɪ 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 BV = 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 ɪ 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.

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Series: Astrophysical journal letters
ISSN: 2041-8205
ISSN-E: 2041-8213
ISSN-L: 2041-8205
Volume: 863
Issue: 1
Article number: L7
DOI: 10.3847/2041-8213/aad62e
Type of Publication: A1 Journal article – refereed
Field of Science: 115 Astronomy and space science
Funding: This work was supported in part through NSF grant 1108964 to J.C.M.
Copyright information: © 2018. The American Astronomical Society. All rights reserved. Published in this repository with the kind permission of the publisher.