The Disk and Extraplanar Regions of NGC 2403

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) along the major axis. The star formation rate (SFR) in the disk of NGC 2403 during the past 10 Myr has been 1 solar masses per year 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 time scales 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.
Comment: 49 pages, including 17 figures. To appear in ApJ