SCYON Abstract

Received on November 22 2010

Top-heavy integrated galactic stellar initial mass functions (IGIMFs) in starbursts

AuthorsCarsten Weidner (1), Pavel Kroupa (2), and Jan Pflamm-Altenburg (2)
Affiliation(1) Scottish Universities Physics Alliance (SUPA), School of Physics and Astronomy, University of St Andrews, North Haugh, St Andrews, Fife KY16 9SS, UK
(2) Argelander-Institut für Astronomie (Sternwarte), Auf dem Hügel 71, D-53121 Bonn, Germany
To appear inhttp://arxiv.org/abs/1011.3814
Contactcw60@st-andrews.ac.uk
URLhttp://www-star.st-and.ac.uk/~cw60/
Links

Abstract

Star formation rates (SFR) larger than 1000 M(sun) yr-1 are observed in extreme star bursts. This leads to the formation of star clusters with masses > 106 M(sun) in which crowding of the pre-stellar cores may lead to a change of the stellar initial mass function (IMF). Indeed, the large mass-to-light ratios of ultra-compact dwarf galaxies and recent results on globular clusters suggest the IMF to become top-heavy with increasing star-forming density. We explore the implications of top-heavy IMFs in these very massive and compact systems for the integrated galactic initial mass function (IGIMF), which is the galaxy-wide IMF, in dependence of the star-formation rate of galaxies. The resulting IGIMFs can have slopes, α3, for stars more massive than about 1 M(sun) between 1.5 and the Salpeter slope of 2.3 for an embedded cluster mass function (ECMF) slope (β) of 2.0, but only if the ECMF has no low-mass clusters in galaxies with major starbursts. Alternatively, β would have to decrease with increasing SFR > 10 M(sun) yr-1 such that galaxies with major starbursts have a top-heavy ECMF. The resulting IGIMFs are within the range of observationally deduced IMF variations with redshift.