Evidence for Initial Mass Function Variations from the Integrated Light of Sloan Digital Sky Survey Galaxies

摘要

The Ha equivalent width (EW) is the ratio of the Ha flux to the continuum at 6565A. In normal star forming galaxies the Ha flux is dominated by reprocessed photons from stars with masses greater than 10 M_⊙ and the 6565A continuum is predominantly due to 0.7- 3.0 M_⊙ red giant stars. In these galaxies the Ha 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 Hδ_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 M0 stars are important in accounting for the observed Hα EW distribution.