Globular cluster candidates in the Galactic bulge: <i>Gaia</i> and VVV view of the latest discoveries

Gran, F.; Zoccali, M.; Ramos, R. Contreras; Valenti, E.; Rojas-Arriagada, Á.; Carballo‐Bello, J. A.; Alonso-García, J.; Minniti, D.; Rejkuba, M.; Surot, F.

doi:10.1051/0004-6361/201834986

Cited by 41 publications

(46 citation statements)

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“…However, not all over-densities are true clusters; they may simply be groups of stars or statistical fluctuations of the projected stellar density in the plane of the sky (Gran et al 2019;Palma et al 2019;Minniti et al 2021b). Therefore, one of the most reliable methods capable of confirming or discarding the existence of a cluster is the kinematic analysis.…”

Section: Introductionmentioning

confidence: 99%

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

Garro

Minniti

Gómez

et al. 2022

A&A

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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.

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Section: Introductionmentioning

confidence: 99%

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

Garro

Minniti

Gómez

et al. 2022

A&A

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“…The VVV has already enabled the discovery and characterisation of numerous new clusters (e.g. Minniti et al 2011Minniti et al , 2017Borissova et al 2011;Moni Bidin et al 2011;Ivanov et al 2017;Gran et al 2019;Camargo & Minniti 2019), and its extension VVVX is delivering on the promise to find even more in the extended area (e.g. Borissova et al 2018).…”

Section: Introductionmentioning

confidence: 99%

VVVX-Gaia discovery of a low luminosity globular cluster in the Milky Way disk

Garro

Minniti

Gómez

et al. 2020

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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 Láctea 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 = 310.828 deg; and b = −3.944 deg in galactic coordinates. We calculate a reddening of E(J − Ks) = (0.3 ± 0.03) mag and an extinction of AKs = (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 μα* = ( − 4.68 ± 0.47) mas yr−1 and μδ = ( − 1.34 ± 0.45) mas yr−1. The total luminosity of our cluster is estimated to be MKs = ( − 7.76 ± 0.5) mag. The core and tidal radii from the radial density profile are rc ∼ 2.1′ (4.6 pc) and rt = 6.5′ (14.6 pc) 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 RG = 11.2 kpc from the Galactic centre and at z = 1.0 kpc below the plane. Interestingly, the location, metallicity, and age of this GC are coincident with the Monoceros ring structure.

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“…We note that our CAPOS observations find no convincing evidence for the reality of Minni 51, i.e. there is no clustering in metallicity:radial velocity space for the 9 targets, supporting the null finding by Gran et al (2019), and we will not discuss this object further here.…”

Section: Cluster Selectionmentioning

confidence: 49%

CAPOS: The bulge Cluster APOgee Survey

Geisler

Villanova

O’Connell

et al. 2021

A&A

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Context. Bulge globular clusters (BGCs) are exceptional tracers of the formation and chemodynamical evolution of this oldest Galactic component. However, until now, observational difficulties have prevented us from taking full advantage of these powerful Galactic archeological tools. Aims. CAPOS, the bulge Cluster APOgee Survey, addresses this key topic by observing a large number of BGCs, most of which have only been poorly studied previously. Even their most basic parameters, such as metallicity, [α/Fe], and radial velocity, are generally very uncertain. We aim to obtain accurate mean values for these parameters, as well as abundances for a number of other elements, and explore multiple populations. In this first paper, we describe the CAPOS project and present initial results for seven BGCs. Methods. CAPOS uses the APOGEE-2S spectrograph observing in the H band to penetrate obscuring dust toward the bulge. For this initial paper, we use abundances derived from ASPCAP, the APOGEE pipeline. Results. We derive mean [Fe/H] values of −0.85 ± 0.04 (Terzan 2), −1.40 ± 0.05 (Terzan 4), −1.20 ± 0.10 (HP 1), −1.40 ± 0.07 (Terzan 9), −1.07 ± 0.09 (Djorg 2), −1.06 ± 0.06 (NGC 6540), and −1.11 ± 0.04 (NGC 6642) from three to ten stars per cluster. We determine mean abundances for eleven other elements plus the mean [α/Fe] and radial velocity. CAPOS clusters significantly increase the sample of well-studied Main Bulge globular clusters (GCs) and also extend them to lower metallicity. We reinforce the finding that Main Bulge and Main Disk GCs, formed in situ, have [Si/Fe] abundances slightly higher than their accreted counterparts at the same metallicity. We investigate multiple populations and find our clusters generally follow the light-element (anti)correlation trends of previous studies of GCs of similar metallicity. We finally explore the abundances of the iron-peak elements Mn and Ni and compare their trends with field populations. Conclusions. CAPOS is proving to be an unprecedented resource for greatly improving our knowledge of the formation and evolution of BGCs and the bulge itself.

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Globular cluster candidates in the Galactic bulge: Gaia and VVV view of the latest discoveries

Cited by 41 publications

References 50 publications

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

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

VVVX-Gaia discovery of a low luminosity globular cluster in the Milky Way disk

CAPOS: The bulge Cluster APOgee Survey

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