New perspective on the multiple population phenomenon in Galactic globular clusters from a wide-field photometric survey

TL;DR

This study uses wide-field photometry to analyze multiple stellar populations in 29 Galactic globular clusters, revealing differences in the radial distribution of first and second generation stars and their relation to cluster parameters.

Contribution

It introduces a wide-field approach with chromosome maps to study the radial distribution of multiple populations, identifying two distinct groups with different dynamical histories.

Findings

All GCs have flat or centrally concentrated 2G star distributions.

A bifurcation in 1G star fractions outside the half-light radius was observed.

Group II GCs are more spatially mixed and have broader galactocentric distributions.

Abstract

Wide-field photometry of Galactic globular clusters (GCs) has been investigated to overcome limitations from the small field of view of the Hubble Space Telescope in the study of multiple populations. In particular, 'chromosome maps' (ChMs) built with ground-based photometry were constructed to identify the first and second generation stars (1G and 2G) over the wide-field of view. The ChMs allow us to derive the fraction of distinct populations in an analyzed field of view. We present here the radial distribution of the 2G fraction in 29 GCs. The distributions show that all the GCs either have a flat distribution or more centrally concentrated 2G stars. Notably, we find that the fraction of 1G stars outside the half-light radius is clearly bifurcated across all mass range. It implies that a group of GCs with lower 1G fractions (hereafter Group II) have efficiently lost their 1G stars in the outermost cluster regions. In fact, in connection with the trends of the radial distribution, most GCs of Group II have spatially mixed populations, while only less massive GCs in Group I (a group with higher 1G fraction) show that feature. Lastly, we investigate links between these two groups and host cluster parameters. We find that most GCs of Group II are distributed along a broader range of galactocentric distances with smaller perigalactic distances < 3.5 kpc. Besides, by using the Gaia data, it is observed that Group II GCs have higher energy on the integrals of motion diagrams than Group I GCs.