Early-Type Galaxy Archeology: Ages, Abundance Ratios, and Effective
  Temperatures from Full-Spectrum Fitting
  The stellar populations of galaxies hold vital clues to their formation
histories. In this paper we present results based on modeling stacked spectra
of early-type galaxies drawn from the Sloan Digital Sky Survey (SDSS) as a
function of velocity dispersion, sigma, from 90 km/s to 300 km/s. The spectra
are of extremely high quality, with typical S/N of 1000/A, and a wavelength
coverage of 4000A-8800A. Our population synthesis model includes variation in
16 elements from C to Ba, the shift in effective temperature, Delta(Teff), of
the stars with respect to a solar metallicity isochrone, amongst other
parameters. In our approach we fit the full optical spectra rather than a
select number of spectral indices and are able to, for the first time, measure
the abundances of the elements V, Cr, Mn, Co, and Ni from the integrated light
of distant galaxies. Our main results are as follows: 1) light-weighted stellar
ages range from 6-12 Gyr from low to high sigma; 2) [Fe/H] varies by less than
0.1 dex across the entire sample; 3) Mg closely tracks O, and both increase
from ~0.0 at low sigma to ~0.25 at high sigma; Si and Ti show a shallower rise
with sigma, and Ca tracks Fe rather than O; 4) the iron peak elements V, Cr,
Mn, and Ni track Fe, while Co tracks O, suggesting that Co forms primarily in
massive stars; 5) C and N track O over the full sample and [C/Fe] and [N/Fe]
exceed 0.2 at high sigma; and 6) the variation in Delta(Teff) with total
metallicity follows theoretical predictions based on stellar evolution theory.
Our derived [Mg/Fe] and [O/Fe] abundance ratios are 0.05-0.1 dex lower than
most previous determinations. Under the conventional interpretation that the
variation in these ratios is due to star formation timescale variations, our
results suggest longer star formation timescales for massive early-type
galaxies than previous studies. (ABRIDGED)
