2007ApJ...664..820D

Wide-field images obtained with WIRCam and MegaCam on the Canada-France-Hawaii Telescope are used to probe the spatial distribution of young stars in the Sc galaxy NGC 2403. Bright main-sequence stars and blue supergiants are detected out to projected galactocentric distances of ∼14 kpc (∼7 disk scale lengths), as measured along the major axis. The star formation rate (SFR) in the disk of NGC 2403 during the past 10 Myr has been 1 M_☉/yr based on the number of bright main-sequence stars. The radially averaged number density of red supergiants (RSGs) per unit r-band surface brightness is constant throughout the disk, indicating that (1) RSGs follow the integrated r-band light, and (2) the SFR per unit mass has been constant with radius when averaged over timescales of a few tens of millions of years. The mean color of RSGs varies with galactocentric distance, suggesting that there is a metallicity gradient among recently formed stars. A comparison of the radially averaged number density of bright main-sequence stars also indicates that the SFR per unit stellar mass in NGC 2403 has been ∼3 times higher than in NGC 247 during recent epochs, and this is in rough agreement with what would be predicted from the far-infrared fluxes of these galaxies. Finally, the data are used to investigate the extraplanar regions of NGC 2403. A population of M giants with peak brightness M_K=-8 is detected at projected distances between 12 and 14 kpc above the disk plane, and six new globular cluster candidates are identified.