On the variation of the initial mass function

Abstract

(shortened) In this contribution an average or Galactic-field IMF is defined,\nstressing that there is evidence for a change in the power-law index at only\ntwo masses: near 0.5 Msun and 0.08 Msun. Using this supposed universal IMF, the\nuncertainty inherent to any observational estimate of the IMF is investigated,\nby studying the scatter introduced by Poisson noise and the dynamical evolution\nof star clusters. It is found that this apparent scatter reproduces quite well\nthe observed scatter in power-law index determinations, thus defining the\nfundamental limit within which any true variation becomes undetectable.\nDeterminations of the power-law indices alpha are subject to systematic errors\narising mostly from unresolved binaries. The systematic bias is quantified\nhere, with the result that the single-star IMFs for young star-clusters are\nsystematically steeper by d_alpha=0.5 between 0.1 and 1 Msun than the\nGalactic-field IMF, which is populated by, on average, about 5 Gyr old stars.\nThe MFs in globular clusters appear to be, on average, systematically flatter\nthan the Galactic-field IMF, and the recent detection of ancient white-dwarf\ncandidates in the Galactic halo and absence of associated low-mass stars\nsuggests a radically different IMF for this ancient population. Star-formation\nin higher-metallicity environments thus appears to produce relatively more\nlow-mass stars.\n

Keywords

Affiliated Institutions

• Christian-Albrechts-Universität zu Kiel DE

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