The Resolved Stellar Population in 50 Regions of M83 from HST/WFC3 Early
  Release Science Observations
  We present a multi-wavelength photometric study of ~15,000 resolved stars in
the nearby spiral galaxy M83 (NGC5236, D=4.61Mpc) based on Hubble Space
Telescope Wide Field Camera 3 observations using four filters: F336W, F438W,
F555W, and F814W. We select 50 regions (an average size of 260 pc by 280 pc) in
the spiral arm and inter-arm areas of M83, and determine the age distribution
of the luminous stellar populations in each region. This is accomplished by
correcting for extinction towards each individual star by comparing its colors
with predictions from stellar isochrones. We compare the resulting luminosity
weighted mean ages of the luminous stars in the 50 regions with those
determined from several independent methods, including the number ratio of
red-to-blue supergiants, morphological appearance of the regions, surface
brightness fluctuations, and the ages of clusters in the regions. We find
reasonably good agreement between these methods. We also find that young stars
are much more likely to be found in concentrated aggregates along spiral arms,
while older stars are more dispersed. These results are consistent with the
scenario that star formation is associated with the spiral arms, and stars form
primarily in star clusters and then disperse on short timescales to form the
field population. The locations of Wolf-Rayet stars are found to correlate with
the positions of many of the youngest regions, providing additional support for
our ability to accurately estimate ages. We address the effects of spatial
resolution on the measured colors, magnitudes, and age estimates. While
individual stars can occasionally show measurable differences in the colors and
magnitudes, the age estimates for entire regions are only slightly affected.
