A census of new globular clusters in the Galactic bulge

Bica, E.; Ortolani, S.; Barbuy, B.; Oliveira, R. A. P.

doi:10.1051/0004-6361/202346377

A&A

2024

DOI: 10.1051/0004-6361/202346377

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A census of new globular clusters in the Galactic bulge

E. Bica,

S. Ortolani,

B. Barbuy

et al.

Abstract: Context. The number of known globular clusters in the Galactic bulge has been increasing steadily thanks to different new surveys. Aims. The aim of this study is to provide a census of the newly revealed globular clusters in the Galactic bulge, and analyze their characteristics. Methods. In recent years, many globular clusters have been discovered or identified. The stellar populations to which they belong are indicated in their original studies: they are mostly bulge clusters, with some identified as disk or … Show more

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Cited by 7 publications

References 131 publications

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Over 200 globular clusters in the Milky Way and still none with super-Solar metallicity

Garro,

Minniti,

Fernández-Trincado

2024

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A large number of globular clusters in the Milky Way have been studied in recent years, especially in hidden regions such as those of the Galactic bulge. The main goal of this work is to understand what we can learn if we include these new objects into the Milky Way globular cluster (GC) system that we know today. We compiled a catalog of 37 recently discovered globular clusters. Most of them are located in the Galactic bulge, but we also included some of the GCs for comparison. We used a range of distributions for investigating the Galactic GC system based on the metallicity, luminosity function, and age. We considered three samples. We first treated the new GC sample separately from the known and well characterized GCs. Consequently, we merged these two samples, thereby upgrading the Milky Way GC system. Furthermore, we performed a comparison between our clusters sample and the field star population. We found a double-peaked distribution for the luminosity function, which shows an elongated faint end tail. Considering the "merged" sample, the luminosity function peaks at $M_ V up 1.3$ mag and at V up 0.48$ mag. The metallicity distributions also display a bimodality trend. In this case, we compare our new sample compilation with previously published ones, finding that the distributions are in good general agreement. We also constructed the metallicity distribution for the field star sample and, by comparing it with that of the GCs, we learned that a high percentage of field stars show Fe/H $>0$; whereas we did not detect any GCs in the same metallicity range. To understand this inconsistency, we constructed the age-metallicity diagram for both samples, noting that the old and metal-poor population (age $ Gyr and Fe/H -1.0$) is represented by Gcs, while the young and metal-rich population (age $<8$ Gyr and Fe/H $>-1.0$) corresponds to field stars. From the analysis of the GC luminosity function and metallicity distribution, we can conclude that many GCs, probably those that are very faint, have survived strong dynamical processes that are typical of the bulge regions. Moreover, we cannot exclude the possibility that some of them have been accreted during past merging events, especially the metal-poor component, whereas the metal-rich population may be related to the formation of the bulge and/or disk. Finally, the difference that we notice between the cluster and field star samples should be explored in the context of the evolutionary differences among these two stellar populations.

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Over 200 globular clusters in the Milky Way and still none with super-Solar metallicity

Garro,

Minniti,

Fernández-Trincado

2024

A&A

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Combined Gemini-South and HST photometric analysis of the globular cluster NGC 6558

Souza,

Libralato,

Nardiello

et al. 2024

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NGC 6558 is a low-galactic-latitude globular cluster projected in the direction of the Galactic bulge. Due to high reddening, this region presents challenges in deriving accurate parameters, which require meticulous photometric analysis. We present a combined analysis of near-infrared and optical photometry from multi-epoch high-resolution images collected with Gemini-South/GSAOI+GeMS (in the $J$ and $K_S$ filters) and HST /ACS (in the F606W and F814W filters). We aim to refine the fundamental parameters of NGC 6558, utilising high-quality Gemini-South/GSAOI and HST /ACS photometries. Additionally, we intend to investigate its role in the formation of the Galactic bulge. We performed a meticulous differential reddening correction to investigate the effect of contamination from Galactic bulge field stars. To derive the fundamental parameters — age, distance, reddening, and the total-to-selective coefficient — we employed a Bayesian isochrone fitting. The results from high-resolution spectroscopy and RR Lyrae stars were implemented as priors. For the orbital parameters, we employed a barred Galactic mass model. Furthermore, we analysed the age-metallicity relation to contextualise NGC 6558 within the Galactic bulge's history. We studied the impact of two differential reddening corrections on the age derivation. When removing as much as possible of the Galactic bulge field star contamination, the isochrone fitting combined with synthetic colour-magnitude diagrams gives a distance of $8.41^ $ kpc, an age of $13.0 0.9$ Gyr, and a reddening of E($B-V$)$\,\,=0.34 We derived a total-to-selective coefficient of R$_V = 3.2 thanks to the simultaneous near-infrared$-$optical synthetic colour-magnitude diagram fitting, which, aside from errors, agrees with the commonly used value. The orbital parameters showed that NGC 6558 is confined within the inner Galaxy and it is not compatible with a bar-shape orbit, indicating that it is a bulge member. Assembling the old and moderately metal-poor Fe/H clusters in the Galactic bulge, we derived their age-metallicity relation with star formation starting at $13.6 Gyr and effective yields of $ Z_ odot$. The old age derived for NGC 6558 is compatible with other clusters with similar metallicity and a blue horizontal branch in the Galactic bulge, which constitute the moderately metal-poor globular clusters. The age-metallicity relation shows that the starting age of star formation is compatible with the age of NGC 6558, and the chemical enrichment is ten times faster than the ex situ globular cluster branch.

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VVVX survey dusts off a new intermediate-age star cluster in the Milky Way disk

Garro,

Minniti,

Alonso-García

et al. 2024

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In the last decade, many new star clusters have been discovered in heavily obscured regions of the Milky Way bulge and disk. Our primary long-term objective is to seek out additional star clusters in the poorly studied regions of the Milky Way, where detections pose significant challenges. The aim of this pursuit is to finalize the Milky Way's globular and open cluster system census and to gain a comprehensive understanding of both the formation and evolution of these systems and our Galaxy as a whole. We report the discovery of a new star cluster, named Garro 03. We investigated this new target using a combination of near-infrared and optical databases. We employed the VISTA Variables in the Via Láctea Survey and Two Micron All Sky Survey data in the near-infrared, and the Gaia Data Release 3 and the DECam Plane Survey datasets in the optical passband. We constructed density maps and vector proper motion diagrams in order to highlight our target. We performed a photometrical analysis in order to derive its main physical parameters. Garro 03 is located at equatorial coordinates RA = 14:01:29.3 and Dec = $-$65:30:57.0. From our photometric analysis we find that this cluster is not heavily affected by extinction with $A_ Ks 0.04$ mag and $A_G = 1.54 0.02$ mag. It is located at heliocentric distance of $14.1 kpc, which places Garro 03 at $10.6$ kpc from the Galactic centre and Z = $-0.89$ kpc below the Galactic plane. We also calculated the mean cluster proper motion of ($ alpha ast delta 0.27$) mas $. We derived an age of 3 Gyr and metallicity Fe/H 0.2$ by the isochrone-fitting method, employing the PARSEC models. The total luminosity was derived in the $K_s$ and V bands, finding Ks 1.10$ mag and $M_V =-4.06$ mag. Finally, the core and tidal radii were measured constructing the Garro 03 radial density profile and fitting the King model. We obtained $r_c = 3.07 0.98$ pc and $r_t = 19.36 15.96$ pc, respectively. We photometrically confirm the cluster nature for Garro 03, located in the Galactic disk. It is a distant, low-luminosity, metal-rich star cluster of intermediate age. We also searched for possible signatures (streams or bridges) between Garro 03 and Garro 01, but we exclude a companionship with the present analysis. We need spectroscopic data to classify it as an old open cluster or a young globular cluster, and to understand its origin

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A census of new globular clusters in the Galactic bulge

Cited by 7 publications

References 131 publications

Over 200 globular clusters in the Milky Way and still none with super-Solar metallicity

Over 200 globular clusters in the Milky Way and still none with super-Solar metallicity

Combined Gemini-South and HST photometric analysis of the globular cluster NGC 6558

VVVX survey dusts off a new intermediate-age star cluster in the Milky Way disk

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