Radial Star Formation Histories in Fifteen Nearby Galaxies
  New deep optical and near-infrared imaging is combined with archival
ultraviolet and infrared data for fifteen nearby galaxies mapped in the Spitzer
Extended Disk Galaxy Exploration Science survey. These images are particularly
deep and thus excellent for studying the low surface brightness outskirts of
these disk-dominated galaxies with stellar masses ranging between 10^8 and
10^11 Msun. The spectral energy distributions derived from this dataset are
modeled to investigate the radial variations in the galaxy colors and star
formation histories. Taken as a whole, the sample shows bluer and younger stars
for larger radii until reversing near the optical radius, whereafter the trend
is for redder and older stars for larger galacto-centric distances. These
results are consistent with an inside-out disk formation scenario coupled with
an old stellar outer disk population formed through radial migration and/or the
cumulative history of minor mergers and accretions of satellite dwarf galaxies.
However, these trends are quite modest and the variation from galaxy to galaxy
is substantial. Additional data for a larger sample of galaxies are needed to
confirm or dismiss these modest sample-wide trends.
