NEW 2MASS NEAR-INFRARED PHOTOMETRY FOR GLOBULAR CLUSTERS IN M31

Abstract

We present Two Micron All Sky Survey JHKs photometry for 913 star clusters and candidates in the field of M31, which are selected from the latest Revised Bologna Catalog of M31 globular clusters (GCs) and candidates. The photometric measurements in this paper supplement this catalog, and provide the most comprehensive and homogeneous photometric catalog for M31 GCs in the JHKs bandpasses. In general, our photometry is consistent withpreviousmeasurements.Theglobularclusterluminosityfunction(GCLF)peaksfortheconfirmedGCsderived by fitting a t5 distribution using the maximum likelihood method are J0 = 15.348 +0.206 −0.208 , H0 = 14.703 +0.176 −0.180 , and Ks0 = 14.534 +0.142 −0.146 , all of which agree well with previous studies. The GCLFs are different between metal-rich (MR) and metal-poor (MP), and between inner and outer subpopulations, as MP clusters are fainter than their MR counterparts and the inner clusters are brighter than the outer ones, which confirm previous results. The NIR colors of the GC candidates are on average redder than those of the confirmed GCs, which leads to an obscure bimodal distribution of color indices. The relation of (V − Ks)0 and metallicity shows a notable departure from linearity, with a shallower slope toward the redder end. The color‐magnitude diagram (CMD) and color‐color diagram show that many GC candidates are located out of the evolutionary tracks, suggesting that some of them may be false M31 GC candidates. The CMD also shows that the initial mass function of M31 GCs covers a large range, and the majority of the clusters have initial masses between 10 3 and 10 6 M� .