Astrophysics, abstract
astro-ph/0606633

From: Daniel Zucker [view email]

Date: Mon, 26 Jun 2006 19:34:56 GMT (276kb)

A Curious New Milky Way Satellite in Ursa Major

Authors: D.B. Zucker (1), V. Belokurov (1), N.W. Evans (1), M.J. Irwin (1), J.T. Kleyna (2), M.I. Wilkinson (1), M. Fellhauer (1), D.M. Bramich (1), G. Gilmore (1), H.J. Newberg (3), B. Yanny (4), J.A. Smith (5,6), P.C. Hewett (1), E.F. Bell (7), H.-W. Rix (7), O.Y. Gnedin (8), S. Vidrih (1), R.F.G. Wyse (9), B. Willman (10), E.K. Grebel (11), D.P. Schneider (12), T.C. Beers (13), A.Y. Kniazev (7,14), J.C. Barentine (15), H. Brewington (15), J. Brinkmann (15), M. Harvanek (15), S.J. Kleinman (16), J. Krzesinski (15,17) D. Long (15), A. Nitta (18), S.A. Snedden (15) ((1) Cambridge, (2) Hawaii, (3) RPI, (4) FNAL, (5) LANL, (6) Austin Peay State University, (7) MPIA, (8) OSU, (9) JHU, (10) NYU, (11) Basel, (12) Penn State University, (13) Michigan State University, (14) SAAO, (15) Apache Point, (16) Subaru Telescope, (17) Cracow, (18) Gemini Observatory)

Comments: 4 pages, 4 figures, submitted to ApJ Letters

In this Letter, we study a localized stellar overdensity in the constellation of Ursa Major, first identified in the Sloan Digital Sky Survey (SDSS) data and subsequently followed up with Subaru imaging. Its color-magnitude diagram shows a well-defined sub-giant branch, main sequence and turn-off, from which we estimate a distance of about 30 kpc and a projected size of about 250 pc. Based on its extent and its stellar population, we argue that this is a previously unknown satellite galaxy of the Milky Way, hereby named after its constellation as Ursa Major II (UMa II). 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 may be in the process of disruption.

http://arxiv.org/abs/astro-ph/0606633