The Hubble Missing Globular Cluster Survey

I. Survey overview and the first precise age estimate for ESO452-11 and 2MASS-GC01

¹ INAF – Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, Via Gobetti 93/3, Bologna, 40129, Italy
² INAF, Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, Padova 35122, Italy
³ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
⁴ Department of Physics and Astronomy, University of Bologna, Via Gobetti 93/2, 40129 Bologna, Italy
⁵ atlanTTic, Universidade de Vigo, Escola de Enxeñaría de Telecomunicación, 36310 Vigo, Spain
⁶ Universidad de La Laguna, Avda. Astrofísico Fco. Sánchez, 38205 La Laguna, Tenerife, Spain
⁷ INAF – Osservatorio Astronomico di Abruzzo, Via M. Maggini, 64100 Teramo, Italy
⁸ INFN – Sezione di Pisa, Universitá di Pisa, Largo Pontecorvo 3, 56127 Pisa, Italy
⁹ Instituto de Astrofísica de Canarias, Calle Vía Láctea s/n, 38206 La Laguna, Tenerife, Spain
¹⁰ INAF – Osservatorio Astronomico di Roma, Via Frascati 33, 00078 Monte Porzio Catone, Roma, Italy
¹¹ INAF – Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
¹² Astrophysics Research Institute, Liverpool John Moores University, 146 Brownlow Hill, Liverpool L3 5RF, UK
¹³ Institute for Computational Cosmology & Centre for Extragalactic Astronomy, Department of Physics, Durham University, South Road, Durham DH1 3LE, UK
¹⁴ ESO – European Southern Observatory, Alonso de Cordova 3107, Vitacura, Santiago, Chile

^★ Corresponding author: davide.massari@inaf.it

Received: 3 February 2025
Accepted: 1 May 2025

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 [M/H]≃−0.80_−0.11^+0.08 and an age of t=13.59_−0.69^+0.48 Gyr. Its location on the agemetallicity 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 t=7.22_−1.11^+0.93Gyr at [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.