Metal-poor nuclear star clusters in two dwarf galaxies near Centaurus A suggesting formation from the in-spiraling of globular clusters

Fahrion, Katja; Müller, Oliver; Rejkuba, M.; Hilker, M.; Lyubenova, M.; Ven, Glenn van de; Georgiev, Iskren Y.; Lelli, Federico; Pawlowski, Marcel S.; Jerjen, Helmut

doi:10.1051/0004-6361/201937120

Cited by 50 publications

(75 citation statements)

References 164 publications

(237 reference statements)

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“…Their virial masses range from 6×10 5 M in DW3 to 1.2×10 6 M in ESO269-06. We note that KK197-NSC has a dynamical mass-to-light ratios estimate from Fahrion et al (2020). We find a ∼ 3.5× lower M/L V than their published value of M/L V = 5.65 ± 0.5.…”

Section: Nuclear Star Clusterscontrasting

confidence: 52%

A population of luminous globular clusters and stripped nuclei with elevated mass to light ratios around NGC 5128

Dumont,

Seth,

Strader

et al. 2021

Preprint

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The dense central regions of tidally disrupted galaxies can survive as ultra-compact dwarfs (UCDs) that hide among the luminous globular clusters (GCs) in the halo of massive galaxies. An exciting confirmation of this model is the detection of overmassive black holes in the centers of some UCDs, which also lead to elevated dynamical mass-to-light ratios (M/L dyn ). Here we present new high-resolution spectroscopic observations of 321 luminous GC candidates in the massive galaxy NGC 5128/Centaurus A. Using these data we confirm 27 new luminous GCs, and measure velocity dispersions for 57 luminous GCs (with g-band luminosities between 2.5 × 10 5 and 2.5 × 10 7 L ), of which 48 have no previous reliable measurements. Combining these data with size measurements from Gaia, we determine the M/L dyn for all 57 luminous GCs. We see a clear bimodality in the M/L dyn distribution, with a population of normal GCs with mean M/L dyn = 1.51 ± 0.31, and a second population of ∼20 GCs with elevated mean M/L dyn = 2.68 ± 0.22. We show that black holes with masses ∼ 4-18% of the luminous GCs can explain the elevated mass-to-light ratios. Hence, it is plausible that the NGC 5128 sources with elevated M/L dyn are mostly stripped galaxy nuclei that contain massive central black holes, though future high spatial resolution observations are necessary to confirm this hypothesis for individual sources. We also present a detailed discussion of an extreme outlier, VHH81-01, one of the largest and most massive GC in NGC 5128, making it an exceptionally strong candidate to be a tidally stripped nucleus.

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Section: Nuclear Star Clusterscontrasting

confidence: 52%

A population of luminous globular clusters and stripped nuclei with elevated mass to light ratios around NGC 5128

Dumont,

Seth,

Strader

et al. 2021

Preprint

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“…A note on the velocity extraction of KK 197 and KKs 58. In Fahrion et al (2020a) we derived for these two galaxies lineof-sight velocities of 643.2 ± 3.5 km s −1 and 482.6 ± 12.6 km s −1 , respectively. This differs slightly from the values measured here, due to a different set of SSP models used, as well as different ways of extracting the spectra from the cube.…”

Section: Radial Velocity and Stellar Population Measurementsmentioning

confidence: 99%

“…We then inspected all the individual spectra to create a catalog of GCs. Two of our galaxies -KKs 58 and KK 197have already been analyzed in Fahrion et al (2020a). These two dSphs contain a NSC, and KK 197 furthermore hosts two GCs and an extended stellar association.…”

Section: Globular Clusters and Planetary Nebulae Detectionmentioning

confidence: 99%

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The properties of dwarf spheroidal galaxies in the Cen A group

Müller

Fahrion

Rejkuba

et al. 2021

A&A

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Dwarf spheroidal galaxies (dSphs) have been extensively investigated in the Local Group, but their low luminosity and surface brightness make similar work in more distant galaxy groups challenging. Modern instrumentation unlocks the possibility of scrutinizing these faint systems in other environments, expanding the parameter space of group properties. We use MUSE spectroscopy to study the properties of 14 known or suspected dSph satellites of Cen A. Twelve targets are confirmed to be group members based on their radial velocities. Two targets are background galaxies at ∼50 Mpc: KK 198 is a face-on spiral galaxy, and dw1315-45 is an ultradiffuse galaxy with an effective radius of ∼2300 pc. The 12 confirmed dSph members of the Cen A group have old and metal-poor stellar populations and follow the stellar metallicity-luminosity relation defined by the dwarf galaxies in the Local Group. In the three brightest dwarf galaxies (KK 197, KKs 55, and KKs 58), we identify globular clusters, as well as a planetary nebula in KK 197, although its association with this galaxy and/or the extended halo of Cen A is uncertain. Using four discrete tracers, we measure the velocity dispersion and dynamical mass of KK 197. This dSph appears dark matter dominated and lies on the radial acceleration relation of star-forming galaxies within the uncertainties. It also is consistent with predictions stemming from modified Newtonian dynamics (MOND). Surprisingly, in the dwarf KK 203 we find an extended Hα ring. Careful examination of Hubble Space Telescope photometry reveals a very low level of star formation at ages between 30-300 Myr. The Hα emission is most likely linked to a ∼40 Myr old supernova remnant, although other possibilities for its origin cannot be entirely ruled out.

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“…It is difficult to predict from our present simulations whether a nuclear star cluster would form. Observations of chemical properties of some dwarf galaxies suggest that their nuclear star clusters formed by dynamical sinking of GCs (Fahrion et al 2020); the galaxies had much smaller radii and brightnesses than the UDGs investigated in this work. Future work should address in which galaxies MOND predicts the formation of a nuclear star cluster through the merging of the GC system.…”

Section: Discussionmentioning

confidence: 61%

Evolution of globular-cluster systems of ultra-diffuse galaxies due to dynamical friction in MOND gravity

Bílek

Zhao

Famaey

et al. 2021

A&A

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Context. Dynamical friction can be used to distinguish Newtonian gravity and modified Newtonian dynamics (MOND) because it works differently in these frameworks. This concept, however, has yet to be explored very much with MOND. Previous simulations showed weaker dynamical friction during major mergers for MOND than for Newtonian gravity with dark matter. Analytic arguments suggest the opposite for minor mergers. In this work, we verify the analytic predictions for MOND by high-resolution N-body simulations of globular clusters (GCs) moving in isolated ultra-diffuse galaxies (UDGs). Aims. We test the MOND analog of the Chandrasekhar formula for the dynamical friction proposed by Sánchez-Salcedo on a single GC. We also explore whether MOND allows GC systems of isolated UDGs to survive without sinking into nuclear star clusters. Methods. The simulations are run using the adaptive-mesh-refinement code Phantom of Ramses. The mass resolution is 20 M⊙ and the spatial resolution 50 pc. The GCs are modeled as point masses. Results. Simulations including a single GC reveal that, as long as the apocenter of the GC is over about 0.5 effective radii, the Sánchez-Salcedo formula works excellently, with an effective Coulomb logarithm increasing with orbital circularity. Once the GC reaches the central kiloparsec, its sinking virtually stops, likely because of the core stalling mechanism. In simulations with multiple GCs, many of them sink toward the center, but the core stalling effect seems to prevent them from forming a nuclear star cluster. The GC system ends up with a lower velocity dispersion than the stars of the galaxy. By scaling the simulations, we extend these results to most UDG parameters, as long as these UDGs are not external-field dominated. We verify analytically that approximating the GCs by point masses has little effect if the GCs have the usual properties, but for massive GCs such as those observed in the NGC 1052-DF2 galaxy, further simulations with resolved GCs are desirable.

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Metal-poor nuclear star clusters in two dwarf galaxies near Centaurus A suggesting formation from the in-spiraling of globular clusters

Cited by 50 publications

References 164 publications

A population of luminous globular clusters and stripped nuclei with elevated mass to light ratios around NGC 5128

A population of luminous globular clusters and stripped nuclei with elevated mass to light ratios around NGC 5128

The properties of dwarf spheroidal galaxies in the Cen A group

Evolution of globular-cluster systems of ultra-diffuse galaxies due to dynamical friction in MOND gravity

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