2020A&A...642L..19G

Context. Milky Way globular clusters (GCs) are difficult to identify at low Galactic latitudes because of high differential extinction and heavy star crowding. The new deep near-infrared (IR) images and photometry from the VISTA Variables in the Via Lactea Extended Survey (VVVX) allow us to chart previously unexplored regions.
Aims. Our long term aim is to complete the census of Milky Way GCs. The immediate goals are to estimate the astrophysical parameters for the newly discovered GC candidates, measuring their reddenings, extinctions, distances, total luminosities, proper motions, sizes, metallicities, and ages.
Methods. We used the near-IR VVVX survey database, in combination with the optical photometry and proper motions (PMs) from Gaia Data Release 2 (DR2), and with the Two Micron All Sky Survey photometry to search for and characterise new GCs within the southern Galactic plane (|b|<5°).
Results. We report the detection of a heretofore unknown Galactic GC at RA=14:09:00.0; Dec=-65:37:12 (J2000) corresponding to l=310.828deg; and b=-3.944deg in galactic coordinates. We calculate a reddening of E(J-K_s)=(0.3±0.03) mag and an extinction of A_Ks=(0.15±0.01)mag for this new GC. Its distance modulus and corresponding distance were measured as (m-M)=(15.93±0.03) mag and D=(15.5±1.0)kpc, respectively. We also estimate the metallicity and age by comparison with known GCs and by fitting PARSEC and Dartmouth isochrones, finding [Fe/H]=(-0.70±0.2)dex and t=(11.0±1.0)Gyr. The mean GC PMs from Gaia DR2 are µ_α^*=(-4.68±0.47)mas/yr and µ_δ=(-1.34±0.45)mas/yr. The total luminosity of our cluster is estimated to be M_Ks=(-7.76±0.5)mag. The core and tidal radii from the radial density profile are r_c∼2.1' (4.6pc) and r_t=6.5' (14.6pc) at the cluster distance.
Conclusions. We have found a new low luminosity, old and metal-rich GC, situated in the far side of the Galactic disk at R_G=11.2kpc from the Galactic centre and at z=1.0kpc below the plane. Interestingly, the location, metallicity, and age of this GC are coincident with the Monoceros ring structure.