The Dynamical State of the Globular Cluster M10 (NGC 6254)

Studying the radial variation of the stellar mass function (MF) in globular clusters (GCs) has proved a valuable tool to explore the collisional dynamics leading to mass segregation and core collapse. Recently, Pasquato et al. (2009) used the mass segregation profile to investigate the presence of an intermediate-mass black hole (IMBH) in NGC 2298. As a relaxed cluster with a large core, M10 (NGC 6254) is suitable for a similar investigation. In order to study the radial dependence of the luminosity and MF of M10, we used deep high resolution archival images obtained with the Advanced Camera for Survey (ACS) on board the Hubble Space Telescope, reaching out to approximately the cluster's half-mass radius (r hm), combined with deep Wide Field and Planetary Camera 2 (WFPC2) images that extend our radial coverage to more than 2 r hm. From our photometry, we derived a radial mass segregation profile and a global MF that we compared with those of simulated clusters containing different energy sources (namely hard binaries and/or an IMBH) able to halt core collapse and to quench mass segregation. A set of direct N-body simulations of GCs, with and without an IMBH of mass 1% of the total cluster mass, comprising different initial mass functions and primordial binary fractions, was used to predict the observed mass segregation profile and MF. The mass segregation profile of M10 is not compatible with cluster models without either an IMBH or primordial binaries, as a source of energy appears to be moderately quenching mass segregation in the cluster. Unfortunately, the present observational uncertainty on the binary fraction in M10 does not allow us to confirm the presence of an IMBH in the cluster, since an IMBH, a dynamically non-negligible binary fraction (~5%), or both can equally well explain the radial dependence of the cluster MF.