Journal Article

Quantifying the universality of the stellar initial mass function in old star clusters

Nathan Leigh, Stefan Umbreit, Alison Sills, Christian Knigge, Guido de Marchi, Evert Glebbeek and Ata Sarajedini

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 422, issue 2, pages 1592-1600
Published in print May 2012 | ISSN: 0035-8711
Published online April 2012 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2012.20735.x
Quantifying the universality of the stellar initial mass function in old star clusters

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We present a new technique to quantify cluster-to-cluster variations in the observed present-day stellar mass functions of a large sample of star clusters. Our method quantifies these differences as a function of both the stellar mass and the total cluster mass, and offers the advantage that it is insensitive to the precise functional form of the mass function. We applied our technique to data taken from the Advanced Camera for Surveys (ACS) Survey for Globular Clusters, from which we obtained completeness-corrected stellar mass functions in the mass range 0.25–0.75 M for a sample of 27 clusters. The results of our observational analysis were then compared to Monte Carlo simulations for globular cluster evolution spanning a range of initial mass functions, total number of stars, concentrations and virial radii.

We show that the present-day mass functions of the clusters in our sample can be reproduced by assuming a universal initial mass function for all clusters, and that the cluster-to-cluster differences are consistent with what is expected from two-body relaxation. A more complete exploration of the initial cluster conditions will be needed in future studies to better constrain the precise functional form of the initial mass function. This study is a first step towards using our technique to constrain the dynamical histories of a large sample of old Galactic star clusters and, by extension, star formation in the early Universe.

Keywords: methods: statistical; stars: formation; stars: low-mass; stars: statistics; globular clusters: general

Journal Article.  7337 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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