ABSTRACT. We present deep, wide-field g and r photometry of the transition-type dwarf galaxy Leo T, obtained with the blue arm of the Large Binocular Telescope. The data confirm the presence of both very young (<1 Gyr) and much older (>5 Gyr) stars. We study the structural properties of the old and young stellar populations by preferentially selecting either population on the basis of their color and magnitude. The young population is significantly more concentrated than the old population, with half-light radii of 104 ± 8 and 148 ± 16 pc, respectively, and their centers are slightly offset. Approximately 10% of the total stellar mass is estimated to be represented by the young stellar population. Comparison of the color-magnitude diagram (CMD) with theoretical isochrones, as well as numerical CMD fitting, suggests that star formation began over 10 Gyr ago and continued in recent times until at least a few hundred Myr ago. The CMD-fitting results are indicative of two distinct star formation bursts, with a quiescent period around 3 Gyr ago, albeit at low significance. The results are consistent with no metallicity evolution and a value of [ Fe/H ] ~ − 1.5 over the entire age of the system. Finally, the data show little, if any, sign of tidal distortion of Leo T.

Subject headings: galaxies: individual (Leo T dSph); galaxies: stellar content; Local Group

^* Based on data acquired using the Large Binocular Telescope (LBT). The LBT is an international collaboration among institutions in the United States, Italy, and Germany. The LBT Corporation partners are the University of Arizona, on behalf of the Arizona university system; Istituto Nazionale di Astrofisica, Italy; LBT Beteiligungsgesellschaft, Germany, representing the Max Planck Society, the Astrophysical Institute Potsdam, and Heidelberg University; The Ohio State University; and The Research Corporation, on behalf of the University of Notre Dame, the University of Minnesota, and the University of Virginia.

Print publication: Issue 2 (2008 June 20)
Received 2007 November 19, accepted for publication 2008 February 26