A Curious Milky Way Satellite in Ursa Major
Abstract
In this Letter, we study a localized stellar overdensity in the constellation of Ursa Major, first identified in Sloan Digital Sky Survey (SDSS) data and subsequently followed up with Subaru imaging. Its color-magnitude diagram (CMD) shows a well-defined subgiant branch, main sequence, and turnoff, from which we estimate a distance of ~30 kpc and a projected size of ~250×125 pc2. The CMD suggests a composite population with some range in metallicity and/or age. Based on its extent and stellar population, we argue that this is a previously unknown satellite galaxy of the Milky Way, hereby named Ursa Major II (UMa II) after its constellation. Using SDSS data, we find an absolute magnitude of MV~-3.8, which would make it the faintest known satellite galaxy. UMa II's isophotes are irregular and distorted with evidence for multiple concentrations; this suggests that the satellite is in the process of disruption.
Based in part on data collected at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan.- Publication:
-
The Astrophysical Journal
- Pub Date:
- October 2006
- DOI:
- 10.1086/508628
- arXiv:
- arXiv:astro-ph/0606633
- Bibcode:
- 2006ApJ...650L..41Z
- Keywords:
-
- Galaxies: Dwarf;
- galaxies: individual (Ursa Major II);
- Galaxies: Local Group;
- Astrophysics
- E-Print:
- 4 pages, 4 figures, submitted to ApJ Letters