Galaxy and Mass Assembly (GAMA): the star formation rate dependence of the stellar initial mass function

Abstract

The stellar initial mass function (IMF) describes the distribution in stellar\nmasses produced from a burst of star formation. For more than fifty years, the\nimplicit assumption underpinning most areas of research involving the IMF has\nbeen that it is universal, regardless of time and environment. We measure the\nhigh-mass IMF slope for a sample of low-to-moderate redshift galaxies from the\nGalaxy And Mass Assembly survey. The large range in luminosities and galaxy\nmasses of the sample permits the exploration of underlying IMF dependencies. A\nstrong IMF-star formation rate dependency is discovered, which shows that\nhighly star forming galaxies form proportionally more massive stars (they have\nIMFs with flatter power-law slopes) than galaxies with low star formation\nrates. This has a significant impact on a wide variety of galaxy evolution\nstudies, all of which rely on assumptions about the slope of the IMF. Our\nresult is supported by, and provides an explanation for, the results of\nnumerous recent explorations suggesting a variation of or evolution in the IMF.\n