Cluster Mass Functions in the Large and Small Magellanic Clouds: Fading and Size-of-Sample Effects
- 1 October 2003
- journal article
- Published by American Astronomical Society in The Astronomical Journal
- Vol. 126 (4), 1836-1848
- https://doi.org/10.1086/378056
Abstract
The properties of 939 star clusters in the Large and Small Magellanic Clouds were determined from ground-based CCD images in UBVR passbands. The areal coverage was extensive, corresponding to 11.0 sq-kpc in the LMC and 8.3 sq-kpc in the SMC. After corrections for reddening, the colors and magnitudes of the clusters were converted to ages and masses, and the resulting mass distributions were searched for the effects of fading, evaporation, and size-of-sample bias. The data show a clear signature of cluster fading below the detection threshold. The initial cluster mass function (ICMF) was determined by fitting the mass and age distributions with cluster population models. These models suggest a new method to determine the ICMF that is nearly independent of fading or disruption and is based on the slope of a correlation between age and the maximum cluster mass in equally spaced intervals of log-age. For a nearly uniform star formation rate, this correlation has a slope equal to 1/(alpha-1) for an ICMF of dn(M)/dM proportional to M^-alpha. We determine that alpha is between 2 and 2.4 for the LMC and SMC using this method plus another method in which models are fit to the mass distribution integrated over age and to the age distribution integrated over mass. The maximum mass method also suggests that the cluster formation rate in the LMC age gap between 3 and 13 Gy is about a factor of ten below that in the period from 0.1 Gy to 1 Gy. The oldest clusters correspond in age and mass to halo globular clusters in the Milky Way. They do not fit the trends for lower-mass clusters but appear to be a separate population that either had a very high star formation rate and became depleted by evaporation or formed with only high masses.Comment: To be published in AJ, October 2003. Available from ftp.lowell.edu, cd pub/dah/papers/mccKeywords
This publication has 42 references indexed in Scilit:
- Dynamical evolution of star clusters in tidal fieldsMonthly Notices of the Royal Astronomical Society, 2003
- Star cluster formation and disruption time-scales - I. An empirical determination of the disruption time of star clusters in four galaxiesMonthly Notices of the Royal Astronomical Society, 2003
- Compact Star Clusters in Nearby Dwarf Irregular GalaxiesThe Astronomical Journal, 2002
- Updating the Census of Star Clusters in the Small Magellanic CloudThe Astronomical Journal, 2000
- Predicted HST FOC and broad band colours for young and intermediate simple stellar populationsAstronomy and Astrophysics Supplement Series, 1999
- A Revised and Extended Catalog of Magellanic System Clusters, Associations, and Emission Nebulae. II. The Large Magellanic CloudThe Astronomical Journal, 1999
- Integrated UBV Photometry of 624 Star Clusters and Associations in the Large Magellanic CloudThe Astrophysical Journal Supplement Series, 1996
- The relationship between infrared, optical, and ultraviolet extinctionThe Astrophysical Journal, 1989
- The young SMC cluster NGC 330The Astronomical Journal, 1985
- UBVRI photometry. II - The Cousins VRI system, its temperature and absolute flux calibration, and relevance for two-dimensional photometryPublications of the Astronomical Society of the Pacific, 1979