A deep Large Binocular Telescope view of the Canes Venatici I dwarf galaxy

Martin, Nicolas F.
Coleman, Matthew G.
De Jong, Jelte T. A.
Rix, Hans-Walter
Bell, Eric F.
Sand, David J.
Hill, John M.
Thompson, David
Burwitz, Vadim
Giallongo, Emanuele
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We present the first deep color-magnitude diagram of the Canes Venatici I (CVnI) dwarf galaxy from observations with the wide field Large Binocular Camera on the Large Binocular Telescope. Reaching down to the main-sequence turnoff of the oldest stars, it reveals a dichotomy in the stellar populations of CVnI: it harbors an old (> 10 Gyr), metal-poor ([Fe/H] ~ -2.0) and spatially extended population along with a much younger (~ 1.4-2.0 Gyr), 0.5 dex more metal-rich, and spatially more concentrated population. These young stars are also offset by 64_{-20}^{+40} pc to the East of the galaxy center. The data suggest that this young population, which represent ~ 3-5 % of the stellar mass of the galaxy within its half-light radius, should be identified with the kinematically cold stellar component found by Ibata et al. (2006). CVnI therefore follows the behavior of the other remote MW dwarf spheroidals which all contain intermediate age and/or young populations: a complex star formation history is possible in extremely low-mass galaxies.
Comment: 4 pages, 3 figures, accepted for publication in ApJL. Minor changes, conclusions unchanged