Ultra-deep GEMINI near-infrared observations of the bulge globular cluster NGC 6624

TL;DR

This study presents the deepest near-infrared color-magnitude diagram of globular cluster NGC 6624, revealing its age, stellar population, and evidence of mass segregation through ultra-deep imaging with adaptive optics.

Contribution

It provides the deepest ground-based near-infrared CMD for NGC 6624, accurately estimates its age, and demonstrates mass segregation in the cluster.

Findings

Deepest near-infrared CMD obtained for NGC 6624.

Estimated cluster age of 12.0 ± 0.5 Gyr.

Detected mass segregation with low-mass stars more concentrated outward.

Abstract

We used ultra-deep $J$ and $K_s$ images secured with the near-infrared GSAOI camera assisted by the multi-conjugate adaptive optics system GeMS at the GEMINI South Telescope in Chile, to obtain a ($K_s$, $J-K_s$) color-magnitude diagram (CMD) for the bulge globular cluster NGC 6624. We obtained the deepest and most accurate near-infrared CMD from the ground for this cluster, by reaching $K_s$ $\sim$ 21.5, approximately 8 magnitudes below the horizontal branch level. The entire extension of the Main Sequence (MS) is nicely sampled and at $K_s$ $\sim$ 20 we detected the so-called MS "knee" in a purely near-infrared CMD. By taking advantage of the exquisite quality of the data, we estimated the absolute age of NGC 6624 ($t_{age}$ = 12.0 $\pm$ 0.5 Gyr), which turns out to be in good agreement with previous studies in the literature. We also analyzed the luminosity and mass functions of MS stars down to M $\sim$ 0.45 M$_{\odot}$ finding evidence of a significant increase of low-mass stars at increasing distances from the cluster center. This is a clear signature of mass segregation, confirming that NGC 6624 is in an advanced stage of dynamical evolution.