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Title:
Mass Segregation and the Initial Mass Function of Super Star Cluster M82-F
Authors:
McCrady, Nate; Graham, James R.; Vacca, William D.
Affiliation:
AA(Department of Astronomy, 601 Campbell Hall, University of California, Berkeley, CA 94720-3411 .), AB(Department of Astronomy, 601 Campbell Hall, University of California, Berkeley, CA 94720-3411 .), AC(NASA Ames Research Center, Moffett Field, CA 94035.)
Publication:
The Astrophysical Journal, Volume 621, Issue 1, pp. 278-284. (ApJ Homepage)
Publication Date:
03/2005
Origin:
UCP
ApJ Keywords:
Galaxies: Individual: Messier Number: M82, Galaxies: Star Clusters, Galaxies: Starburst, Infrared: Galaxies
DOI:
10.1086/427487
Bibliographic Code:
2005ApJ...621..278M

Abstract

We investigate the initial mass function and mass segregation in super star cluster M82-F with high-resolution Keck NIRSPEC echelle spectroscopy. Cross-correlation with template supergiant spectra provides the velocity dispersion of the cluster, enabling measurement of the kinematic (virial) mass of the cluster when combined with sizes from NICMOS and Advanced Camera for Surveys (ACS) images. We find a mass of 6.6+/-0.9×105Msolar based on near-IR light and 7.0+/-1.2×105Msolar based on optical light. Using PSF-fitting photometry, we derive the cluster's light-to-mass (L/M) ratio in both near-IR and optical light and compare to population-synthesis models. The ratios are inconsistent with a normal stellar initial mass function for the adopted age of 40-60 Myr, suggesting a deficiency of low-mass stars within the volume sampled. King model light profile fits to new Hubble Space Telescope ACS images of M82-F, in combination with fits to archival near-IR images, indicate mass segregation in the cluster. As a result, the virial mass represents a lower limit on the mass of the cluster.

Based on observations made at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.

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