Average Spectra of Massive Galaxies in the Sloan Digital Sky Survey


Eisenstein DJ, Hogg DW, Fukugita M, Nakamura O, Bernardi M, Finkbeiner DP, Schlegel DJ, Brinkmann J, Connolly AJ, Csabai I, et al. Average Spectra of Massive Galaxies in the Sloan Digital Sky Survey. The Astrophysical Journal. 2003;585 :694-713.

Date Published:

March 1, 2003


We combine Sloan Digital Sky Survey spectra of 22,000 luminous, red,bulge-dominated galaxies to get high signal-to-noise ratio averagespectra in the rest-frame optical and ultraviolet (2600-7000 Å).The average spectra of these massive, quiescent galaxies are early typewith weak emission lines and with absorption lines indicating anapparent excess of α-elements over solar abundance ratios. We makeaverage spectra of subsamples selected by luminosity, environment, andredshift. The average spectra are remarkable in their similarity. Whatvariations do exist in the average spectra as a function of luminosityand environment are found to form a nearly one-parameter family inspectrum space. We present a high signal-to-noise ratio spectrum of thevariation. We measure the properties of the variation with a modifiedversion of the Lick index system and compare to model spectra fromstellar population syntheses. The variation may be a combination of ageand chemical abundance differences, but the conservative conclusion isthat the quality of the data considerably exceeds the current state ofthe models.