Emission Corrections for Hydrogen Features of the Graves et. al 2007 Sloan Digital Sky Survey Averages of Early Type, Non-liner Galaxies

TL;DR

This paper derives emission corrections for Balmer line indices in SDSS galaxy spectra to improve stellar population analysis, using observations and models to account for emission and stellar content effects.

Contribution

It introduces new emission correction methods for Balmer indices in SDSS galaxy spectra based on observed data and stellar population models, enhancing analysis accuracy.

Findings

Derived linear correction for Hα based on Virgo galaxies

Constructed corrections for Hβ, Hγ, Hδ using stellar models

Corrections are robust but interpretation of Hδ and Hγ is complex

Abstract

For purposes of 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, along with corrections for continuum shape and gross stellar content, as a function of the Mg $b$ Lick index strength. These corrections are obtained by comparing the observed Lick index measurements of the SDSS with new observed measurements of 13 Virgo Cluster galaxies, and checked with model grids. From the H$\alpha$ Mg $b$ diagram a linear correction for the observed measurement is constructed using best fit trend lines. Corrections for H$\beta$, H$\gamma$ and H$\delta$ are constructed using stellar population models to predict continuum shape changes as a function of Mg $b$ and Balmer series emission intensities typical of H{\sc II} regions. The corrections themselves are fairly secure, but the interpretation for H$\delta$ and H$\gamma$ indices is complicated by the fact that the H$\delta$ and H$\gamma$ indices are sensitive to elemental abundances other than hydrogen.