Globular clusters in the Galactic center region: Expected behavior within the infall and merger scenario

Navarro, M. G.; Capuzzo-Dolcetta, R.; Arca-Sedda, M.; Minniti, D.

doi:10.1051/0004-6361/202245449

Cited by 3 publications

(1 citation statement)

References 56 publications

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“…A sig-nificant number of these dynamical processes are stronger in the deep potential well of the inner Galaxy. Numerical simulations have revealed that the supermassive black hole Sagittarius A* (Ghez et al 2008;Genzel et al 2010) can very efficiently grind clusters, and is a place where globular clusters could be rapidly demolished (Arca-Sedda & Capuzzo-Dolcetta 2017; Navarro et al 2023). In order to address the process of globular-cluster disruption, it is crucial to understand not only clusters that have been destroyed but also surviving globular clusters.…”

Section: Introductionmentioning

confidence: 99%

The globular cluster VVV CL002 falling down to the hazardous Galactic centre

Minniti,

Matsunaga,

Fernández-Trincado

et al. 2024

A&A

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The Galactic centre is hazardous for stellar clusters because of the strong tidal force in action there. It is believed that many clusters were destroyed there and contributed stars to the crowded stellar field of the bulge and the nuclear stellar cluster. However, the development of a realistic model to predict the long-term evolution of the complex inner Galaxy has proven difficult, and observations of surviving clusters in the central region would provide crucial insights into destruction processes. $. The nature of this cluster and its impact on Galactic astronomy need to be addressed with spectroscopic follow up. Here we report the first measurements of its radial velocity and chemical abundance based on near-infrared high-resolution spectroscopy. We find that this cluster has a counter-rotating orbit constrained within 1.0\,kpc of the centre, and as close as 0.2\,kpc at the perigalacticon, confirming that the cluster is not a passerby from the halo but a genuine survivor enduring the harsh conditions of the tidal forces of the Galactic mill. In addition, its metallicity and alpha abundance alpha /Fe +0.4$ and Fe/H $=-0.54$) are similar to those of some globular clusters in the bulge. Recent studies suggest that stars with such alpha -enhanced stars were more common at 3--6\,kpc from the centre around 10 Gyr ago. We infer that VVV CL002 was formed outside but is currently falling down to the centre, showcasing a real-time event that must have occurred to many clusters a long time ago.

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Section: Introductionmentioning

confidence: 99%

The globular cluster VVV CL002 falling down to the hazardous Galactic centre

Minniti,

Matsunaga,

Fernández-Trincado

et al. 2024

A&A

Self Cite

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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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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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Analysis of Kozai cycles in equal-mass hierarchical triple supermassive black hole mergers in the presence of a stellar cluster

Hao,

Kouwenhoven,

Spurzem

et al. 2023

Monthly Notices of the Royal Astronomical Society

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Supermassive black holes (SMBHs) play an important role in galaxy evolution. Binary and triple SMBHs can form after galaxy mergers. A third SMBH may accelerate the SMBH merging process, possibly through the Kozai mechanism. We use N-body simulations to analyze oscillations in the orbital elements of hierarchical triple SMBHs with surrounding star clusters in galaxy centers. We find that SMBH triples spend only a small fraction of time in the hierarchical merger phase (i.e., a binary SMBH with a distant third SMBH perturber). Most of the time, the enclosed stellar mass within the orbits of the innermost or the outermost SMBH is comparable to the SMBH masses, indicating that the influence of the surrounding stellar population cannot be ignored. We search for Eccentric Kozai-Lidov (EKL) oscillations for which (i) the eccentricity of the inner binary and inclination are both oscillate and are anti-phase or in-phase and (ii) the oscillation period is consistent with EKL timescale. We find that EKL oscillations are short-lived and rare: the triple SMBH spends around 3 % of its time in this phase over the ensemble of simulations, reaching around 8 % in the best-case scenario. This suggests that the role of the EKL mechanism in accelerating the SMBH merger process may have been overestimated in previous studies. We follow-up with three-body simulations, using initial conditions extracted from the simulation, and the result can to some extent repeat the observed EKL-like oscillations. This comparison provides clues about why those EKL oscillations with perturbing stars are short-lived.

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Globular clusters in the Galactic center region: Expected behavior within the infall and merger scenario

Cited by 3 publications

References 56 publications

The globular cluster VVV CL002 falling down to the hazardous Galactic centre

The globular cluster VVV CL002 falling down to the hazardous Galactic centre

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

Analysis of Kozai cycles in equal-mass hierarchical triple supermassive black hole mergers in the presence of a stellar cluster

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