Stellar Metallicity Gradients in SDSS galaxies
  We infer stellar metallicity and abundance ratio gradients for a sample of
red galaxies in the Sloan Digital Sky Survey (SDSS) Main galaxy sample. Because
this sample does not have multiple spectra at various radii in a single galaxy,
we measure these gradients statistically. We separate galaxies into stellar
mass bins, stack their spectra in redshift bins, and calculate the measured
absorption line indices in projected annuli by differencing spectra in
neighboring redshift bins. After determining the line indices, we use stellar
population modeling from the EZ\_Ages software to calculate ages,
metallicities, and abundance ratios within each annulus. Our data covers the
central regions of these galaxies, out to slightly higher than $1 R_{e}$. We
find detectable gradients in metallicity and relatively shallow gradients in
abundance ratios, similar to results found for direct measurements of
individual galaxies. The gradients are only weakly dependent on stellar mass,
and this dependence is well-correlated with the change of $R_e$ with mass.
Based on this data, we report mean equivalent widths, metallicities, and
abundance ratios as a function of mass and velocity dispersion for SDSS
early-type galaxies, for fixed apertures of 2.5 kpc and of 0.5 $R_e$.
