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

TL;DR

This study analyzes the outer density profiles of 19 Galactic globular clusters using deep wide-field imaging, revealing two distinct groups influenced differently by tidal forces and highlighting the link between density profiles and cluster dynamics.

Contribution

It provides the first detailed comparison of outer density profiles of globular clusters in the inner Milky Way, identifying two dynamical groups based on mass and tidal interaction signatures.

Findings

Massive clusters have flatter outer profiles ($2.5<3<4$).

Low-mass clusters show steep profiles ($3>4$) indicating tidal effects.

Outer density slopes correlate with half-mass density.

Abstract

Using deep photometric data from WFC@INT and WFI@ESO2.2m 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 10-30 kpc) 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 $-\gamma$ in the outer region, we find that the clusters in our sample can be divided in two groups: a group of massive clusters ($ \ge 10^5 $ M_sun) that has relatively flat profiles with $2.5 < \gamma < 4$ and a group of low-mass clusters ($ \le 10^5 $ M_sun), with steep profiles ($\gamma > 4$) 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.