Outer density profiles of 19 Galactic globular clusters from deep and wide-field imaging

Abstract

Using deep photometric data from Wide Field Camera at the Isaac Newton Telescope and Wide Field Imager at the ESO 2.2-m telescope we measure the outer number density profiles of 19 stellar clusters located in the inner region of the Milky Way halo (within a Galactocentric distance range of 10-30kpc) in order to assess the impact of internal and external dynamical processes on the spatial distribution of stars. Adopting power-law fitting templates, with index -γ in the outer region, we find that the clusters in our sample can be divided in two groups: a group of massive clusters (≥105M⊙) that has relatively flat profiles with 2.5 < γ < 4, and a group of low-mass clusters (≤105M⊙), with steep profiles (γ > 4) and clear signatures of interaction with the Galactic tidal field. We refer to these two groups as 'tidally unaffected' and 'tidally affected', respectively. Our results also show a clear trend between the slope of the outer parts and the half-mass density of these systems, which suggests that the outer density profiles may retain key information on the dominant processes driving the dynamical evolution of globular clusters. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.