Physical characterization of recently discovered globular clusters in the Sagittarius dwarf spheroidal galaxy

Abstract

Context. Globular clusters (GCs) are important tools for rebuilding the accretion history of a galaxy. In particular, newly discovered GCs in the Sagittarius (Sgr) dwarf galaxy can be used as probes of the accretion event onto the Milky Way (MW). Aims. Our main aim is to characterize the GC system of the Sgr dwarf galaxy by measuring its main physical parameters. Methods. We built the optical and near-infrared color-magnitude diagrams for 21 new Sgr GCs using the VISTA Variables in the Via Lactea Extended Survey near-infrared database combined with the Gaia Early Data Release 3 optical database. We derived metallicities and ages for all targets using the isochrone-fitting method with PARSEC isochrones. We also used the relation between red giant branch slope and metallicity as an independent method to confirm our metallicity estimates. In addition, the total luminosities were calculated in the near-infrared and in the optical. We then constructed the metallicity distribution (MD), the globular cluster luminosity function (GCLF), and the age-metallicity relation for the Sgr GC system. Results. We find that there are 17 metal-rich GCs with −0.9 < [Fe/H]<  − 0.3, plus 4 metal-poor GCs with −2.0 < [Fe/H]<  − 1.1 in the new Sgr GC sample. The metallicity estimates using isochrones and red giant branch slopes agree well. Even though our age estimates are rough, we find that the metal-poor GCs are consistent with an old population with an average age of ∼13 Gyr, while the metal-rich GCs show a wider age range, between 6 − 8 Gyr and 10 − 13 Gyr. Additionally, we compare the MD and the GCLF for the Sgr GC system with those of the MW, M31, and Large Magellanic Cloud galaxies. Conclusions. We conclude that the majority of the metal-rich GCs are located within the main body of the Sgr galaxy. We confirm that the GCLF is not a universal distribution because the Sgr GCLF peaks at fainter luminosities (MV ≈ −5.5 mag) than the GCLFs of the MW, M31, and Large Magellanic Cloud. Moreover, the MD shows a double-peaked distribution, and we note that the metal-rich population looks like the MW bulge GCs. We compared our results with the literature and conclude that the Sgr progenitor could have been a reasonably large galaxy able to retain the supernovae ejecta, thus enriching its interstellar medium.