2008ApJ...687.1004P

We present deep imaging of the star-forming dwarf galaxy IC 2574 in the M81 group taken with the Large Binocular Telescope (LBT) in order to study in detail the recent star formation history of this galaxy and to constrain the stellar feedback on its H I gas. We identify the star-forming areas in the galaxy by removing a smooth disk component from the optical images. We construct pixel-by-pixel maps of stellar age and stellar mass surface density in these regions by comparing their observed colors with simple stellar populations synthesized with Starburst99. We find that an older burst occurred about 100 Myr ago within the inner 4 kpc and that a younger burst happened in the last 10 Myr mostly at galactocentric radii between 4 and 8 kpc. We analyze the stellar populations residing in the known H I holes of IC 2574. Our results indicate that, even at the remarkable photometric depth of the LBT data, there is no clear one-to-one association between the observed H I holes and the most recent bursts of star formation in IC 2574. The stellar populations formed during the younger burst are usually located at the periphery of the H I holes and are seen to be younger than the holes' dynamical age. The kinetic energy of hole expansion is found to be, on average, 10% of the total stellar energy released by the stellar winds and supernova explosions of the young stellar populations within the holes. With the help of control apertures distributed across the galaxy we estimate that the kinetic energy stored in the H I gas in the form of its local velocity dispersion is about 35% of the total stellar energy.