The age-redshift relation for Luminous Red Galaxies in the Sloan Digital
  Sky Survey
  We present a detailed analysis of 17,852 quiescent, Luminous Red Galaxies
(LRGs) selected from Sloan Digital Sky Survey (SDSS) Data Release Seven (DR7)
spanning a redshift range of 0.0 < z < 0.4. These galaxies are co-added into
four equal bins of velocity dispersion and luminosity to produce high
signal-to-noise spectra (>100A^{-1}), thus facilitating accurate measurements
of the standard Lick absorption-line indices. In particular, we have carefully
corrected and calibrated these indices onto the commonly used Lick/IDS system,
thus allowing us to compare these data with other measurements in the
literature, and derive realistic ages, metallicities ([Z/H]) and alpha-element
abundance ratios ([alpha/Fe]) for these galaxies using Simple Stellar
Population (SSP) models. We use these data to study the relationship of these
galaxy parameters with redshift, and find little evidence for evolution in
metallicity or alpha-elements (especially for our intermediate mass samples).
This demonstrates that our subsamples are consistent with pure passive evolving
(i.e. no chemical evolution) and represent a homogeneous population over this
redshift range. We also present the age-redshift relation for these LRGs and
clearly see a decrease in their age with redshift (5 Gyrs over the redshift
range studied here) which is fully consistent with the cosmological lookback
times in a concordance Lambda CDM universe. We also see that our most massive
sample of LRGs is the youngest compared to the lower mass galaxies. We provide
these data now to help future cosmological and galaxy evolution studies of
LRGs, and provide in the appendices of this paper the required methodology and
information to calibrate SDSS spectra onto the Lick/IDS system.
