A Curious New 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 sub-giant branch, main sequence and turn-off, from which we estimate a distance of ~30 kpc and a projected size of ~250 x 125 pc. 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 M_V \~ -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.
Keywords
Cite
@article{arxiv.astro-ph/0606633,
title = {A Curious New Milky Way Satellite in Ursa Major},
author = {D. B. Zucker and V. Belokurov and N. W. Evans and J. T. Kleyna and M. J. Irwin and M. I. Wilkinson and M. Fellhauer and D. M. Bramich and G. Gilmore and H. J. Newberg and B. Yanny and J. A. Smith and P. C. Hewett and E. F. Bell and H. -W. Rix and O. Y. Gnedin and S. Vidrih and R. F. G. Wyse and B. Willman and E. K. Grebel and D. P. Schneider and T. C. Beers and A. Y. Kniazev and J. C. Barentine and H. Brewington and J. Brinkmann and M. Harvanek and S. J. Kleinman and J. Krzesinski and D. Long and A. Nitta and S. A. Snedden},
journal= {arXiv preprint arXiv:astro-ph/0606633},
year = {2010}
}
Comments
4 pages, 4 figures, submitted to ApJ Letters