Confirmation and physical characterization of the new bulge globular cluster Patchick 99 from the VVV and Gaia surveys

Alonso-García

et al. 2021

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Context. The Sagittarius (Sgr) dwarf galaxy is merging with the Milky Way, and the study of its globular clusters (GCs) is important to understand the history and outcome of this ongoing process. Aims. Our main goal is to characterize the GC system of the Sgr dwarf galaxy. This task is hampered by high foreground stellar contamination, mostly from the Galactic bulge. Methods. We performed a GC search specifically tailored to find new GC members within the main body of this dwarf galaxy using the combined data of the VISTA Variables in the Via Lactea Extended Survey near-infrared survey and the Gaia Early Data Release 3 optical database. Results. We applied proper motion cuts to discard foreground bulge and disk stars, and we found a number of GC candidates in the main body of the Sgr dwarf galaxy. We selected the best GCs as those objects that have significant overdensities above the stellar background of the Sgr galaxy and that possess color-magnitude diagrams with well-defined red giant branches consistent with the distance and reddening of this galaxy. Conclusions. We discover eight new GC members of the Sgr galaxy, which adds up to 29 total GCs known in this dwarf galaxy. This total number of GCs shows that the Sgr dwarf galaxy hosts a rather rich GC system. Most of the new GCs appear to be predominantly metal-rich and have low luminosity. In addition, we identify ten other GC candidates that are more uncertain and need more data for proper confirmation.

Section: Discussionmentioning

confidence: 99%

Eight more low luminosity globular clusters in the Sagittarius dwarf galaxy

Alonso-García

et al. 2021

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“…However, the information coming from the analysis of a handful of Milky Way (MW) GCs may still be incomplete, either because some of them are very faint, too small, or widespread, or because they are embedded by dust and thus difficult to find. Indeed, most of the 'missing' GCs are likely located in obscured regions close to the Galactic centre or near the Galactic plane on the far side of the Galaxy Garro et al 2020Garro et al , 2021b.…”

Section: Introductionmentioning

confidence: 99%

“…A step forwards has been possible thanks to the VISTA Variables in the Via Láctea (VVV) survey and its eXtension (VVVX). More than 300 candidate star clusters have been discovered in the Galactic bulge and disk but only a fraction of them have been analysed (Froebrich et al 2007;Borissova et al 2014;Camargo 2018;Palma et al 2019;Camargo & Minniti 2019;Garro et al 2020Garro et al , 2021bMinniti et al 2021a;Obasi et al 2021, just to mention a few).…”

Section: Introductionmentioning

confidence: 99%

“…Furthermore, these latter authors compared the CMD of potential candidates with those of well-characterised Galactic GCs as well as their respective background fields in order to verify that the cluster red giant branch (RGB) appears tighter than that observed in the background. Another method used to discriminate field stars from cluster candidates is statistical decontamination, as done by Palma et al (2016), Minniti et al (2011), and Garro et al (2021b). In this latter method, the stars of the cluster CMD that fall in the same intervals of colour and magnitude as those of the background CMD are removed.…”

Section: Introductionmentioning

confidence: 99%

“…Coherent stellar motions ensure the cluster membership, and allow us to separate the stars belonging to an association from those randomly distributed in the field. Several studies (Zoccali et al 2002;Sariya & Yadav 2015;Baumgardt et al 2018;Garro et al 2020Garro et al , 2021bObasi et al 2021;Minniti et al 2021a, just to mention a few) have incorporated this technique, especially exploiting the high precision of Gaia proper motions (PMs), confirming, in many cases, the GC nature of some objects. Complementary evidence in support of the cluster identification is the presence of RR Lyrae stars, which are good tracers of old stellar populations (e.g.…”

Section: Introductionmentioning

confidence: 99%

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Inspection of 19 globular cluster candidates in the Galactic bulge with the VVV survey

Garro

et al. 2022

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Context. The census of the globular clusters (GCs) in the Milky Way (MW) is still a work in progress. The advent of new deep surveys has made it possible to discover many new star clusters both in the Galactic disk and bulge, but many of these new candidates have not yet been studied in detail, leaving a veil on their true physical nature. Aims. We explore the nature of 19 new GC candidates in the Galactic bulge by analysing their colour-magnitude diagrams (CMDs) in the near-infrared (NIR) using the VISTA Variables in the Via Láctea Survey (VVV) database. We estimate their main astrophysical parameters: reddening and extinction, distance, total luminosity, mean cluster proper motions (PMs), metallicity, and age. Methods. We obtain the cluster catalogues including the likely cluster members by applying a decontamination procedure on the observed CMDs based on the vector PM diagrams from VIRAC2. We adopt NIR reddening maps in order to calculate the reddening and extinction for each cluster, and then estimate the distance moduli and heliocentric distances. Metallicities and ages are evaluated by fitting theoretical stellar isochrones. We also calculate their luminosities in comparison with known Galactic GCs. Results. We estimate a wide reddening range of 0.25 E(J − K s ) 2.0 mag and extinction 0.11 A K s 0.86 mag for the sample clusters, as expected in the bulge regions. The range of heliocentric distances is 6.8 D 11.4 kpc. This allows us to place these clusters between 0.56 and 3.25 kpc from the Galactic centre, assuming R = 8.2 kpc. Also, their PMs are kinematically similar to the typical motion of the Galactic bulge, apart from VVV-CL160, which shows different PMs. We also derive their metallicities and ages, finding −1.40 [Fe/H] 0.0 dex and t ≈ 8 − 13 Gyr respectively. The luminosities are calculated both in K s − and V−bands, recovering −3.4 M V −7.5. We also examine the possible RR Lyrae members found in the cluster fields. Conclusions. Based on their positions, kinematics, metallicities, and ages, and comparing our results with the literature, we conclude that nine candidates are real GCs, seven need more observations to be fully confirmed as GCs, and three candidates are discarded as GCs and appear to be younger open clusters.

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

Garro

et al. 2021

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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.