Emission corrections for hydrogen features of the graves et al. Sloan digital sky survey averages of early-type, non-liner galaxies

Abstract

For purposes of recovering correct absorption line strengths for stellar population analysis, emission corrections for Balmer series indices on the Lick index system in Sloan Digital Sky Survey (SDSS) stacked quiescent galaxy spectra are derived as a function of the Mg b index strength. These corrections are obtained by comparing the observed Lick index measurements of the SDSS composite spectra with new observed measurements of 13 Virgo Cluster galaxies, and checked with model grids. From the Hα-Mg b diagram, a linear correction for the observed measurement is constructed using best-fit trend lines. Corrections for Hβ, Hγ, and Hδ are constructed using stellar population models to predict continuum shape changes as a function of Mg b plus Balmer series emission intensities typical of H II regions. The corrections themselves are fairly secure, but the interpretation for Hδ and Hγ indices is complicated by the fact that the Hδ and Hγ indices are sensitive to elemental abundances other than hydrogen. © 2010. The American Astronomical Society. All rights reserved.