A Database of 2MASS Near-Infrared Colors of Magellanic Cloud Star Clusters

The (rest-frame) near-IR domain contains important stellar populationdiagnostics and is often used to estimate masses of galaxies at low as well ashigh redshifts. However, many stellar population models are still relativelypoorly calibrated in this part of the spectrum. To allow an improvement of thiscalibration we present a new database of integrated near-infrared JHKsmagnitudes for 75 star clusters in the Magellanic Clouds, using the 2-MicronAll-Sky Survey (2MASS). The majority of the clusters in our sample have robustage and metallicity estimates from color-magnitude diagrams available in theliterature, and populate a range of ages from 10 Myr to 15 Gyr and a range in[Fe/H] from -2.17 to +0.01 dex. A comparison with matched star clusters in the2MASS Extended Source Catalog (XSC) reveals that the XSC only provides a goodfit to the unresolved component of the cluster stellar population. We alsocompare our results with the often-cited single-channel JHK photometry ofPersson and collaborators, and find significant differences, especially fortheir 30"-diameter apertures up to ~2.5 mag in the K-band, more than 1 mag inJ-K, and up to 0.5 mag in H-K. Using simulations to center apertures based onmaximum light throughput (as performed by Persson et al, we show that thesedifferences can be attributed to near-IR-bright cluster stars (e.g., Carbonstars) located away from the true center of the star clusters. The wide age andmetallicity coverage of our integrated JHKs photometry sample constitutes afundamental dataset for testing population synthesis model predictions, and fordirect comparison with near-IR observations of distant stellar populations.Comment: AJ August 2006 issue, 67 pages, 8 tables, 17 figure