Astronomy and Astrophysics – Astrophysics
Scientific paper
Dec 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006aas...209.9704h&link_type=abstract
2007 AAS/AAPT Joint Meeting, American Astronomical Society Meeting 209, #97.04; Bulletin of the American Astronomical Society, V
Astronomy and Astrophysics
Astrophysics
Scientific paper
The stellar initial mass function (IMF) is widely treated as universal-independent of factors such as galaxy type, radiation environment, chemical composition and time. While this conclusion seems physically unlikely considering the great diversity of star forming environments across the universe systematic IMF variations are as yet trumped by measurement errors. Systematic IMF variations would impact a wide range of astrophysical disciplines, from theories of star formation to measurements of star formation rates and mass-to-light ratios. We present the results of our study of the IMF in a sample of 130,000 actively star forming galaxies in the Sloan Digital Sky Survey (SDSS). H alpha equivalent widths (EW) are compared to broadband colors to constrain the IMF within the 3" SDSS apertures which contain on average 25% of the total light from the galaxies. The H alpha EW is effectively the ratio of massive O and B stars, via UV photons reprocessed into H alpha flux, to post main sequence stars of around a solar mass, which dominate the light of the red continuum. As a result our method is sensitive to the IMF slope above a solar mass. In this parameter space the effects of the age of the stellar population are largely orthogonal to those of the IMF and the effects of metallicity are small compared to IMF variations. Monte Carlo simulations reveal that for our large data set the random errors in the measured IMF slope are negligible compared to the systematic errors which are dominated by star formation history. We find that for luminous galaxies the agreement with a universal IMF is good. However, low luminosity galaxies appear to exhibit IMF variations above what can be attributed to systematics.
Glazebrook Kark
Hoversten Erik A.
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