Journal Article

Top-heavy integrated galactic stellar initial mass functions in starbursts

C. Weidner, P. Kroupa and J. Pflamm-Altenburg

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 412, issue 2, pages 979-986
Published in print April 2011 | ISSN: 0035-8711
Published online March 2011 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2010.17959.x
Top-heavy integrated galactic stellar initial mass functions in starbursts

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Star formation rates (SFRs) larger than 1000 M yr−1 are observed in extreme starbursts. This leads to the formation of star clusters with masses >106 M 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 ultracompact 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 SFR of galaxies. The resulting IGIMFs can have slopes, α3, for stars more massive than about 1 M 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 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.

Keywords: stars: formation; stars: luminosity function, mass function; galaxies: evolution; galaxies: starburst; galaxies: star clusters: general; galaxies: stellar content

Journal Article.  6711 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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