Evidence for IMF Variations from the Integrated Light of SDSS Galaxies

TL;DR

This study uses SDSS galaxy data to investigate how the stellar initial mass function (IMF) varies with galaxy properties, finding evidence for IMF changes with surface brightness and the importance of 120 M_o stars.

Contribution

It provides new evidence that the IMF varies with galaxy surface brightness and highlights the significance of high-mass stars in modeling galaxy spectra.

Findings

IMF varies with galaxy surface brightness

120 M_o stars are crucial for explaining H alpha EW distribution

Spectral synthesis uncertainties affect IMF variation interpretations

Abstract

The H alpha equivalent width (EW) is the ratio of the H alpha flux to the continuum at 6565{\AA}. In normal star forming galaxies the H alpha flux is dominated by reprocessed photons from stars with masses greater than 10 M_o and the 6565{\AA} continuum is predominantly due to 0.7-3.0 M_o red giant stars. In these galaxies the H alpha EW is effectively the ratio of high mass to low mass stars and is thus sensitive to the stellar initial mass function (IMF). In Hoversten & Glazebrook 2008 we used ~131,000 galaxies from the Sloan Digital Sky Survey to show evidence for systematic variations in the IMF with galaxy luminosity. In this proceeding we use that sample, with the addition of H delta_A measurements, to investigate other parameterizations of the IMF. We find evidence for IMF variations with surface brightness, and also show that, modulo uncertainties in spectral synthesis models, that 120 M_o stars are important in accounting for the observed H alpha EW distribution.