The $Hubble$ Missing Globular Cluster Survey. I. Survey overview and the first precise age estimate for ESO452-11 and 2MASS-GC01

TL;DR

The Hubble Missing Globular Cluster Survey (MGCS) used Hubble Space Telescope data to precisely determine the ages of two previously uncharacterized globular clusters, revealing one as old and the other as relatively young, with implications for their origins.

Contribution

This study provides the first precise age estimates for ESO452-11 and 2MASS-GC01, demonstrating the survey's effectiveness in characterizing previously unstudied globular clusters.

Findings

ESO452-11 is an old, metal-intermediate globular cluster (~13.6 Gyr).

2MASS-GC01 is a young, metal-intermediate cluster (~7.2 Gyr).

Results suggest different origins and evolutionary histories for the two clusters.

Abstract

We present the $Hubble$ Missing Globular Cluster Survey (MGCS), a $Hubble$ $Space$ $Telescope$ Treasury Program dedicated to the observation of all kinematically confirmed Milky Way globular clusters that missed previous $Hubble$ imaging. After introducing the aims of the programme and describing its target clusters, we showcase the first results of the survey. These are related to two clusters, one located at the edge of the Milky Way bulge and observed in optical bands, namely ESO452-11, and one located in the Galactic disc observed in the near-IR, namely 2MASS-GC01. For both clusters, the deep colour-magnitude diagrams obtained from the MGCS observations reach several magnitudes below their main-sequence turn-off and thus enable the first precise estimate of their age. By using the methods developed in the Cluster Ages to Reconstruct the Milky Way Assembly (CARMA) project, we find ESO452-11 to be an old metal-intermediate globular cluster, with ${\rm [M/H]}\simeq-0.80^{+0.08}_{-0.11}$ and an age of ${\rm t}=13.59^{+0.48}_{-0.69}$ Gyr. Its location on the age-metallicity relation makes it consistent with an in situ origin, in agreement with its dynamical properties. On the other hand, the results for 2MASS-GC01 highlight it as a young metal-intermediate cluster, with an age of ${\rm t}=7.22^{+0.93}_{-1.11}$ Gyr at ${\rm [M/H]}=-0.73^{+0.06}_{-0.06}$. Despite the large associated uncertainty, our age estimate for this extremely extincted cluster indicates it to be either the youngest globular cluster known to date or a massive and compact open cluster, which is consistent with its almost circular, disc-like orbit