Stellar Population Properties and Evolution Analysis of NGC 628 with the
  Panchromatic Photometry
  Panchromatic spectral energy distribution (SED) from the ultraviolet (UV),
optical to infrared (IR) photometry of NGC 628, combined with the evolutionary
stellar population synthesis, is used to derive the spatially resolved age,
metallicity and reddening maps. These parameter distributions show that the
bulge of this galaxy is a disk-like pseudobulge, which has the S{\'e}rsic index
close to the exponential law, rich gas, and a young circumnuclear ring
structure. We also discover the disk has two distinct regions with different
radial age and metallicity gradients. The inner region is older and has a much
steeper age gradient than the outer region of the disk. Both these two regions
and the central young structure can be seen in the radial profile of the
optical color. Based on the age and reddening distributions, we consider that
the pseudobulge and disk are likely to have grown via the secular evolution,
which is the redistribution of mass and energy through the angular momentum
transport caused by the non-axisymmetric potential of the spirals. However,
possible gas accretion events could affect the outer region of the disk, due to
abundant H{\sc i} gas accumulating in the outer disk.
