Mergers, tidal interactions, and mass exchange in a population of disc globular clusters

Khoperskov, Sergey; Mastrobuono-Battisti, Alessandra; Matteo, P. Di; Haywood, M.

doi:10.1051/0004-6361/201833534

Cited by 35 publications

(23 citation statements)

References 71 publications

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“…We find that the stars in the metal poor regime show a large spread in age, σ age = 0.9 Gyr, and iron content, σ [Fe/H] = 0.24, a higher spread in comparison with the literature (σ [Fe/H] = 0.186, Carretta et al 2010b;Willman & Strader 2012). Large iron spreads in GCs can be explained by a scenario in which two GCs merge (Gavagnin et al 2016;Bekki & Tsujimoto 2016;Khoperskov et al 2018, and references therein). Gavagnin et al (2016) using N-body simulations studied the structural and kinematic signatures in the remnants of GC mergers with a sample of progenitors of different densities and masses.…”

Section: A Possible Merger Remnant As the Seed Of The Sgr Dsph Nscmentioning

confidence: 49%

A Deep View into the Nucleus of the Sagittarius Dwarf Spheroidal Galaxy with MUSE. I. Data and Stellar Population Characterization

Alfaro-Cuello

Kacharov

Neumayer

et al. 2019

ApJ

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The center of the Sagittarius dwarf spheroidal galaxy (Sgr dSph) hosts a nuclear star cluster, M54, which is the only galaxy nucleus that can be resolved into individual stars at optical wavelengths. It is thus a key target for understanding the formation of nuclear star clusters and their relation to globular clusters. We present a large Multi-Unit Spectroscopic Explorer (MUSE) data set that covers M54 out to ∼2.5 half-light radius, from which we extracted the spectra of ∼6 600 cluster member stars. We use these data in combination with HST photometry to derive age and metallicity for each star. The stellar populations show a well defined age-metallicity relation, implying an extended formation history for the central region of Sgr dSph. We classify these populations into three groups, all with the same systemic velocity: young metal rich (YMR; 2.2 Gyr, [Fe/H]= −0.04); intermediate age metal rich (IMR; 4.3 Gyr, [Fe/H]= −0.29); and old metal poor (OMP; 12.2 Gyr, [Fe/H]= − 1.41). The YMR and OMP populations are more centrally concentrated than the IMR population, which are likely stars of the Sgr dSph. We suggest the OMP population is the result of accretion and merging of two or more old and metal poor globular clusters dragged to the center by dynamical friction. The YMR is consistent with being formed by in situ star formation in the nucleus. The ages of the YMR population suggest that it may have been triggered into forming when the Sgr dSph began losing its gas during the most recent interaction with the Milky Way, ∼3 Gyr ago.

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Section: A Possible Merger Remnant As the Seed Of The Sgr Dsph Nscmentioning

confidence: 49%

A Deep View into the Nucleus of the Sagittarius Dwarf Spheroidal Galaxy with MUSE. I. Data and Stellar Population Characterization

Alfaro-Cuello

Kacharov

Neumayer

et al. 2019

ApJ

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“…Lastly, 26 out of 31 N-rich stars appear to behave as halo-like orbits, intriguingly in the prograde sense with respect to the rotation of the bar, suggesting that they were likely formed during the very early stages of the evolution of the Galaxy (e.g., Khoperskov et al 2018), in a similar way as Galactic globular clusters. It is import-ant to note that prograde orbits have been observed before in the inner halo (Bonaca et al 2017;Fernández-Alvar et al 2018;Hayes et al 2018;Lucey et al 2019), as well as for other globular clusters (Moreno et al 2014;Pérez-Villegas et al 2018), however this is not yet well-understood.…”

Section: Orbitsmentioning

confidence: 99%

“…So far, these results demonstrate that those inhomogeneities appear to occur in other star-formation environments. Such stars have received significant attention in recent years, primarily because they are considered as evaporated from stellar clusters, and as such, play an important role in deciphering the early history of the Galactic formation process (Martell & Grebel 2010;Martell et al 2011;Carollo et al 2013;Fernández-Trincado et al 2015a,b, 2016aHelmi et al 2018;Khoperskov et al 2018;Minniti et al 2018a;Ibata et al 2019), as well as providing clues on the mechanism responsible for the ejection from stellar clusters and its relation with chemical peculiarity (e.g., Pereira et al 2017Pereira et al , 2019.…”

Section: Introductionmentioning

confidence: 99%

Chemodynamics of newly identified giants with a globular cluster like abundance patterns in the bulge, disc, and halo of the Milky Way

Fernández-Trincado

Beers

Tang

et al. 2019

Monthly Notices of the Royal Astronomical Society

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The latest edition of the APOGEE-2/DR14 survey catalogue and the first Payne data release of APOGEE abundance determinations by Ting et al. are examined. We identify 31 previously unremarked metal-poor giant stars with anomalously high levels of nitrogen in the chemical space defined by [Fe/H] and [N/Fe]. The APOGEE chemical abundance patterns of such objects revealed that these are chemically distinct from the Milky Way (MW) in most chemical elements. We have found all these objects have a [N/Fe] > ∼ + 0.5, and are thus identified here as nitrogen-rich stars. An orbital analysis of these objects revealed that a handful of them shares the orbital properties of the bar/bulge, and possibly linked to tidal debris of surviving globular clusters trapped into the bar component. 3 of the 31 stars are actually halo interlopers into the bulge area, which suggests that halo contamination is not insignificant when studying N-rich stars found in the inner Galaxy, whereas the rest of the N-rich stars share orbital properties with the halo population. Most of the newly identified population exhibit chemistry similar to the so-called second-generation globular cluster stars (enriched in aluminum, [Al/Fe] > ∼ + 0.5), whereas a handful of them exhibit lower abundances of aluminum, [Al/Fe]< +0.5, which are thought to be chemically associated with the first-generation of stars, as seen in globular clusters, or compatible with origin from a tidally disrupted dwarf galaxy.

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“…Where detailed measurements of kinematics are possible, rotation seems to be a common dynamical ingredient of NSCs (Feldmeier et al 2014;Nguyen et al 2018) and is also commonly found in a high fraction of GCs (van de Ven et al 2006;Bellazzini et al 2012;Bianchini et al 2013;Kacharov et al 2014;Fabricius et al 2014;Kimmig et al 2015;Bellini et al 2017;Kamann et al 2018;Bianchini et al 2018;Sollima et al 2019). The presence of internal rotation can be an indicator of their formation mechanism (Mastrobuono-Battisti & Perets 2013, 2016Hénault-Brunet et al 2015;Gavagnin et al 2016;Khoperskov et al 2018;Mastrobuono-Battisti et al 2019a) and can give important clues on their long-term dynamical evolution (e.g., Einsel & Spurzem 1999;Tiongco et al 2018). Fabricius et al (2014) and Kamann et al (2018) found that GCs with high internal central rotation are more flattened, showing that internal rotation plays an important role in forming the shape of GCs.…”

Section: Introductionmentioning

confidence: 99%

A Deep View into the Nucleus of the Sagittarius Dwarf Spheroidal Galaxy with MUSE. II. Kinematic Characterization of the Stellar Populations

Alfaro-Cuello

Kacharov

Neumayer

et al. 2020

ApJ

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The Sagittarius dwarf spheroidal galaxy (Sgr dSph) is in an advanced stage of disruption but still hosts its nuclear star cluster (NSC), M54, at its center. In this paper, we present a detailed kinematic characterization of the three stellar populations present in M54: young metal-rich (YMR); intermediate-age metal-rich (IMR); and old metal-poor (OMP), based on the spectra of ∼ 6500 individual M54 member stars extracted from a large MUSE/VLT dataset. We find that the OMP population is slightly flattened with a low amount of rotation (∼ 0.8 km s −1 ) and with a velocity dispersion that follows a Plummer profile. The YMR population displays a high amount of rotation (∼ 5 km s −1 ) and a high degree of flattening, with a lower and flat velocity dispersion profile. The IMR population shows a high but flat velocity dispersion profile, with some degree of rotation (∼ 2 km s −1 ). We complement our MUSE data with information from Gaia DR2 and confirm that the stars from the OMP and YMR populations are comoving in 3D space, suggesting that they are dynamically bound. While dynamical evolutionary effects (e.g. energy equipartition) are able to explain the differences in velocity dispersion between the stellar populations, the strong differences in rotation indicate different formation paths for the populations, as supported by an N-body simulation tailored to emulate the YMR-OMP system. This study provides additional evidence for the M54 formation scenario proposed in our previous work, where this NSC formed via GC accretion (OMP) and in situ formation from gas accretion in a rotationally supported disc (YMR).

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Mergers, tidal interactions, and mass exchange in a population of disc globular clusters

Cited by 35 publications

References 71 publications

A Deep View into the Nucleus of the Sagittarius Dwarf Spheroidal Galaxy with MUSE. I. Data and Stellar Population Characterization

A Deep View into the Nucleus of the Sagittarius Dwarf Spheroidal Galaxy with MUSE. I. Data and Stellar Population Characterization

Chemodynamics of newly identified giants with a globular cluster like abundance patterns in the bulge, disc, and halo of the Milky Way

A Deep View into the Nucleus of the Sagittarius Dwarf Spheroidal Galaxy with MUSE. II. Kinematic Characterization of the Stellar Populations

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