The retrograde orbit of the globular cluster FSR1758 revealed with Gaia DR2

Simpson, Jeffrey D.

doi:10.1093/mnras/stz1699

Cited by 13 publications

(21 citation statements)

References 40 publications

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“…2. These include the extended globular cluster FSR1758 [94,95] -from which the arboreal moniker originates--as well as the anomalous ω Centauri, which has for many years been believed to have begun life as the nucleus of a dwarf galaxy [96]. These clusters may have all originally been part of the Sequoia galaxy.…”

Section: B the Shardsmentioning

confidence: 99%

Velocity substructure from Gaia and direct searches for dark matter

et al. 2020

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Data from the Gaia satellite show that the solar neighbourhood of the Milky Way's stellar halo is imprinted with substructure from several accretion events. Evidence of these events is found in "the Shards", stars clustering with high significance in both action space and metallicity. Stars in the Shards share a common origin, likely as ancient satellite galaxies of the Milky Way, so will be embedded in dark matter (DM) counterparts. These "Dark Shards" contain two substantial streams (S1 and S2), as well as several retrograde, prograde and lower energy objects. The retrograde stream S1 has a very high Earth-frame speed of ∼ 550 km s −1 while S2 moves on a prograde, but highly polar orbit and enhances peak of the speed distribution at around 300 km s −1 . The presence of the Dark Shards locally leads to modifications of many to the fundamental properties of experimental DM signals. The S2 stream in particular gives rise to an array of effects in searches for axions and in the time dependence of nuclear recoils: shifting the peak day, inducing non-sinusoidal distortions, and increasing the importance of the gravitational focusing of DM by the Sun. Dark Shards additionally bring new features for directional signals, while also enhancing the DM flux towards Cygnus.

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Section: B the Shardsmentioning

confidence: 99%

Velocity substructure from Gaia and direct searches for dark matter

et al. 2020

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“…Note that the eccentricity of the GC orbits cannot be constrained at present from available observations alone in a model-independent manner. The uncertainties in the observed parameters depend on the inherent assumptions in modeling the underlying potential (Simpson 2019). With better data, when the eccentricity distribution is more constrained, this analysis can be further improved.…”

Section: Discussionmentioning

confidence: 99%

Milky Way globular cluster dynamics: are they preferentially co-rotating?

Das

Roy

2020

Res. Astron. Astrophys.

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The motion of baryonic components of the Milky Way is governed by both luminous and dark matter content of the Galaxy. Thus, the dynamics of Milky Way globular clusters (GCs) can be used as tracers to infer the mass model of the Galaxy up to a large radius. In this work, we apply the directly observable line-of-sight velocities to test if the dynamics of the GC population are consistent with an assumed axisymmetric gravitational potential of the Milky Way. For this, we numerically compute the phase space distribution of the GC population where the orbits are either oriented randomly or co-/counter-rotating with respect to the stellar disk. Then we compare the observed position and line-of-sight velocity distribution of ∼150 GCs with those of the models. We found that, for the adopted mass model, the co-rotating scenario is the favored model based on various statistical tests. We do the analysis with and without the GCs associated with the progenitors of early merger events. This analysis can be extended in the near future to include precise and copious data to better constrain the Galactic potential up to a large radius.

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“…All of this evidence supports the genuine GC nature of FSR 1758, and not the hypothesis that this is the remnant nucleus of a dwarf galaxy. However, the dynamical properties of FSR 1758 reveal that it is not a cluster that originated in the inner Galaxy, and on the contrary is a halo intruder which circulates throughout the bulge in a highly eccentric, radial, and retrograde orbital configuration (see, e.g., Simpson 2019;Villanova et al 2019;Yeh et al 2020).…”

Section: Introductionmentioning

confidence: 99%

“…Regarding its origin, several different scenarios have been proposed for FSR 1758. Simpson (2019), based on its retrograde orbit, claimed that it could be an accreted halo GC; Villanova et al (2019) argued that it is a genuine MW GC based on the above evidence; and Yeh et al (2020) also supports the idea that it is likely a halo GC formed inside the MW, as the highly eccentric and retrograde orbital configuration are not uncommon among in situ halo GCs (Massari et al 2019). On the other hand, Myeong et al (2019) suggested that it belongs to the remnant debris of an early accretion event in the Milky Way, likely associated with a massive dwarf galaxy, similar to accretion events suggested for other GCs (see, e.g., Myeong et al 2019;Kruijssen et al 2019).…”

Section: Introductionmentioning

confidence: 99%

CAPOS: the bulge Cluster APOgee Survey II. The Intriguing "Sequoia" Globular Cluster FSR 1758

Romero-Colmenares,

Fernández-Trincado,

Geisler

et al. 2021

Preprint

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We present results from a study of fifteen red giant members of the intermediate-metallicity globular cluster (GC) FSR 1758 using high-resolution near-infrared spectra collected with the Apache Point Observatory Galactic Evolution Experiment II survey (APOGEE-2), obtained as part of CAPOS (the bulge Cluster APOgee Survey). Since its very recent discovery as a massive GC in the bulge region, evoking the name Sequoia, this has been an intriguing object with a highly debated origin, and initially led to the suggestion of a purported progenitor dwarf galaxy of the same name. In this work, we use new spectroscopic and astrometric data to provide additional clues to the nature of FSR 1758. Our study confirms the GC nature of FSR 1758, and as such we report for the first time the existence of the characteristic N-C anti-correlation and Al-N correlation, revealing the existence of the multiple-population phenomenon, similar to that observed in virtually all GCs. Furthermore, the presence of a population with strongly enriched aluminium makes it unlikely FSR 1758 is the remnant nucleus of a dwarf galaxy, as Al-enhanced stars are uncommon in dwarf galaxies. We find that FSR 1758 is slightly more metal rich than previously reported in the literature, with a mean metallicity [Fe/H] between −1.43 to −1.36 (depending on the adopted atmospheric parameters), and with a scatter within observational error, again pointing to its GC nature. Overall, the α-enrichment ( +0.3 dex), Fe-peak (Fe, Ni), light-(C, N), and odd-Z (Al) elements follow the trend of intermediate-metallicity GCs. Isochrone fitting in the Gaia bands yields an estimated age of ∼ 11.6 Gyr. We use the exquisite kinematic data, including our CAPOS radial velocities and Gaia eDR3 proper motions, to constrain the N-body density profile of FSR 1758, and found that it is as massive (∼2.9±0.6 × 10 5 M ) as NGC 6752. We confirm a retrograde and eccentric orbit for FSR 1758. A new examination of its dynamical properties with the GravPot16 model favors an association with the Gaia-Enceladus-Sausage accretion event. Thus, paradoxically, the cluster that gave rise to the name of the Sequoia dwarf galaxy does not appear to belong to this specific merging event.

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The retrograde orbit of the globular cluster FSR1758 revealed with Gaia DR2

Cited by 13 publications

References 40 publications

Velocity substructure from Gaia and direct searches for dark matter

Velocity substructure from Gaia and direct searches for dark matter

Milky Way globular cluster dynamics: are they preferentially co-rotating?

CAPOS: the bulge Cluster APOgee Survey II. The Intriguing "Sequoia" Globular Cluster FSR 1758

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