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.

APOGEE-2S view of the globular cluster Patchick 125 (Gran 3). New metallicity and elemental abundances from high-resolution spectroscopy

“…More recently, the VVV/VVVX survey has revealed that the census of Galactic GCs is still not complete, and more than 300 new low-luminosity GC candidates have been identified in the VVV/VVVX bulge+disc area toward the inner galaxy (see e.g. Minniti et al 2020Minniti et al , 2021b, bulge region (Minniti et al 2017a(Minniti et al ,b, 2018bCamargo & Minniti 2019;Palma et al 2019;Garro et al 2021b;Obasi et al 2021), disc region (Garro et al 2020), the extension of the Hrid halo stream (Minniti et al 2021a), and the Sagittarius system (Minniti et al 2021c;Garro et al 2021a). A few of those candidates have been confirmed as true GCs (Contreras Ramos et al 2018;Gran et al 2019;Barbá et al 2019;Villanova et al 2019;Gran et al 2021a;Romero-Colmenares et al 2021;Dias et al 2021).…”

The Pristine Inner Galaxy Survey (PIGS) IV: A photometric metallicity analysis of the Sagittarius dwarf spheroidal galaxy

“…Many studies (e.g. Keller et al 2010;Hyde et al 2015;Mucciarelli et al 2017;Hayes et al 2020;Garro et al 2021) have shown that a metallicity gradient is present both in the streams and in a small central region of the Sgr remnant, which is connected to the intricate chemo-dynamical evolution of this dwarf galaxy. The PIGS data is an excellent dataset to study the metallicity gradient in the core of the galaxy.…”

Unveiling the nature of 12 new low-luminosity Galactic Globular Cluster Candidates

“…Finally, the total luminosity in K s −band for each cluster is derived following the same approach of Garro et al (2021a). We first derive the absolute magnitude (M K s ) measuring the cluster total flux.…”

“…Although Kharchenko et al (2016) have demonstrated that the larger contribution in luminosity arises from the brightest stars, since the first 10-12 members accumulate more than half of the integrated luminosity of the cluster, we are aware that the resulting M K s are a lower limit, because our photometry does not include fainter and lower mass stars. Therefore, in order to quantify the fraction of luminosity missed we adopt the same procedure of Garro et al (2021a), comparing the luminosity of our sample with those of known Galactic GCs. Once this luminosity fraction is obtained, we add this to the absolute magnitude and convert it into the absolute magnitude in V−band.…”

“…(b) We adopt subscripts NIR and GEDR3 in order to indicate if the distance is derived from the 2MASS and/or VVV/VVVX in NIR or Gaia EDR3 (GEDR3) photometries. (c) The absolute magnitude in V−band is calculated from the comparison with the well-known Galactic GCs following Garro et al (2021a). (d) We highlight the age used in the fit of the isochrones (Fig.…”