Another Non-segregated Blue Straggler Population in a Globular Cluster: the Case of NGC 2419

TL;DR

This study reveals that NGC 2419 hosts a large, non-segregated Blue Straggler Star population, suggesting the cluster is not yet dynamically relaxed, contrasting with typical globular cluster behavior.

Contribution

It provides the first detailed analysis of BSS distribution in NGC 2419, showing a non-segregated pattern similar to omega Centauri, indicating its dynamical state.

Findings

NGC 2419 has over 230 BSS, one of the largest observed.

BSS distribution is similar to other cluster stars, not centrally concentrated.

NGC 2419 is likely not yet dynamically relaxed.

Abstract

We have used a combination of ACS-HST high-resolution and wide-field SUBARU data in order to study the Blue Straggler Star (BSS) population over the entire extension of the remote Galactic globular cluster NGC 2419. The BSS population presented here is among the largest ever observed in any stellar system, with more than 230 BSS in the brightest portion of the sequence. The radial distribution of the selected BSS is essentially the same as that of the other cluster stars. In this sense the BSS radial distribution is similar to that of omega Centauri and unlike that of all Galactic globular clusters studied to date, which have highly centrally segregated distributions and, in most cases, a pronounced upturn in the external regions. As in the case of omega Centauri, this evidence indicates that NGC 2419 is not yet relaxed even in the central regions. This observational fact is in agreement with estimated half-mass relaxation time, which is of the order of the cluster age.