Quantifying the coexistence of massive black holes and dense nuclear star clusters

Graham, Alister W.; Spitler, Lee R.

doi:10.1111/j.1365-2966.2009.15118.x

Cited by 246 publications

(355 citation statements)

References 232 publications

(345 reference statements)

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“…They are more luminous than globular clusters (Böker et al 2004), have masses of order ∼ 10 6 − 10 7 M⊙ (Walcher et al 2005), have complex star formation histories (Rossa et al 2006;Seth et al 2006), and obey scaling-relations with host galaxy properties as do central supermassive black holes (SMBH; Ferrarese et al 2006;Wehner & Harris 2006); see Böker (2010) for a review. Many host an AGN, i.e., a SMBH ⋆ E-mail: sotiris@mpe.mpg.de, gerhard@mpe.mpg.de (Seth et al 2008), and the ratio of NSC to SMBH mass varies widely (Graham & Spitler 2009;Kormendy & Ho 2013).…”

Section: Introductionmentioning

confidence: 99%

The old nuclear star cluster in the Milky Way: dynamics, mass, statistical parallax, and black hole mass

Chatzopoulos¹,

Fritz²,

Gerhard³

et al. 2014

Monthly Notices of the Royal Astronomical Society

178

216

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We derive new constraints on the mass, rotation, orbit structure and statistical parallax of the Galactic old nuclear star cluster and the mass of the supermassive black hole. We combine star counts and kinematic data from Fritz et al. (2014), including 2'500 line-of-sight velocities and 10'000 proper motions obtained with VLT instruments. We show that the difference between the proper motion dispersions σ l and σ b cannot be explained by rotation, but is a consequence of the flattening of the nuclear cluster. We fit the surface density distribution of stars in the central 1000 ′′ by a superposition of a spheroidal cluster with scale ∼ 100 ′′ and a much larger nuclear disk component. We compute the self-consistent two-integral distribution function f (E, L z ) for this density model, and add rotation self-consistently. We find that: (i) The orbit structure of the f (E, L z ) gives an excellent match to the observed velocity dispersion profiles as well as the proper motion and line-of-sight velocity histograms, including the double-peak in the v l -histograms. (ii) This requires an axial ratio near q 1 = 0.7 consistent with our determination from star counts, q 1 = 0.73 ± 0.04 for r < 70 ′′ . (iii) The nuclear star cluster is approximately described by an isotropic rotator model. (iv) Using the corresponding Jeans equations to fit the proper motion and line-of-sight velocity dispersions, we obtain best estimates for the nuclear star cluster mass, black hole mass, and distance M * (r < 100 ′′ ) = (8.94±0.31| stat ±0.9| syst )×10 6 M ⊙ , M • = (3.86±0.14| stat ±0.4| syst )×10 6 M ⊙ , and R 0 = 8.27±0.09| stat ±0.1| syst kpc, where the estimated systematic errors account for additional uncertainties in the dynamical modeling. (v) The combination of the cluster dynamics with the S-star orbits around Sgr A * strongly reduces the degeneracy between black hole mass and Galactic centre distance present in previous S-star studies. A joint statistical analysis with the results of Gillessen et al. (2009) gives M • = (4.23±0.14)×10 6 M ⊙ and R 0 = 8.33±0.11 kpc.

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Section: Introductionmentioning

confidence: 99%

The old nuclear star cluster in the Milky Way: dynamics, mass, statistical parallax, and black hole mass

Chatzopoulos¹,

Fritz²,

Gerhard³

et al. 2014

Monthly Notices of the Royal Astronomical Society

178

216

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“…Gonzales Delgado et al 2008;Graham & Spitler 2009;Seth et al 2008Seth et al , 2010Graham 2012). For host galaxy masses of 10 10 M and below, BH masses are comparable to or smaller than the mass of the NC.…”

Section: Black Holes As a Possible Explanation For Elevated M/lmentioning

confidence: 99%

On central black holes in ultra-compact dwarf galaxies

Mieske

Frank

Baumgardt

et al. 2013

A&A

102

200

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Context. The dynamical mass-to-light (M/L) ratios of massive ultra-compact dwarf galaxies (UCDs) are about 50% higher than predicted by stellar population models. Aims. Here we investigate the possibility that these apparently elevated M/L ratios of UCDs are caused by a central black hole (BH) that heats up the internal motion of stars. We focus on a sample of ∼50 extragalactic UCDs from the literature for which velocity dispersions and structural parameters have been measured. Methods. To be self-consistent in our BH mass estimates, we first redetermine the dynamical masses and M/L ratios of our sample UCDs, using up-to-date distance moduli and a consistent treatment of aperture and seeing effects. On average, the homogeneously redetermined dynamical mass and M/L ratios agree to within 5% with previous literature results. We calculate the ra-pop between the dynamical and the stellar population M/L for an assumed age of 13 Gyr. Ψ > 1 indicates an elevated dynamical M/L ratio, suggesting dark mass on top of a canonical stellar population of old age. For all UCDs with Ψ > 1 we estimate the mass of a hypothetical central black hole needed to reproduce the observed integrated velocity dispersion Results. Massive UCDs (M > 10 7 M ) have an average Ψ = 1.7 ± 0.2, implying notable amounts of dark mass in them. We find that, on average, central BH masses of 10-15% of the UCD mass can explain these elevated dynamical M/L ratios. The implied BH masses in UCDs range from several 10 5 M to several 10 7 M . In the M BH -luminosity plane, UCDs are offset by about two orders of magnitude in luminosity from the relation derived for galaxies. Our findings can be interpreted such that massive UCDs originate from progenitor galaxies with masses around ∼10 9 M , and that those progenitors have SMBH occupation fractions of ∼60-100%. The suggested UCD progenitor masses agree with predictions from the tidal stripping scenario. Also, the typical BH mass fractions of nuclear clusters in such ∼10 9 M galaxy bulges agree with the 10-15% BH fraction estimated for UCDs. Lower-mass UCDs (M < 10 7 M ) exhibit a bimodal distribution in Ψ, suggestive of a coexistence of massive globular clusters and tidally stripped galaxies in this mass regime. Conclusions. Central BHs as relict tracers of tidally stripped progenitor galaxies are a plausible explanation for the elevated dynamical M/L ratios of UCDs. Direct observational tests of this scenario are suggested.

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“…Many nuclear star clusters also contain a supermassive black hole (e.g. Seth et al 2008a;Graham & Spitler 2009). The nuclear regions of galaxies are of special interest for galaxy formation and evolution studies because of the scaling correlations between the mass of the nuclear star cluster and other galaxy properties, such as the galaxy mass (e.g.…”

Section: Introductionmentioning

confidence: 99%

KMOS view of the Galactic centre

Feldmeier-Krause

Neumayer

Schödel

et al. 2015

A&A

106

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Context. The Galactic centre hosts a crowded, dense nuclear star cluster with a half-light radius of 4 pc. Most of the stars in the Galactic centre are cool late-type stars, but there are also > ∼ 100 hot early-type stars in the central parsec of the Milky Way. These stars are only 3−8 Myr old. Aims. Our knowledge of the number and distribution of early-type stars in the Galactic centre is incomplete. Only a few spectroscopic observations have been made beyond a projected distance of 0.5 pc of the Galactic centre. The distribution and kinematics of earlytype stars are essential to understand the formation and growth of the nuclear star cluster. Methods. We cover the central >4 pc 2 (0.75 sq. arcmin) of the Galactic centre using the integral-field spectrograph KMOS (VLT). We extracted more than 1000 spectra from individual stars and identified early-type stars based on their spectra. Results. Our data set contains 114 bright early-type stars: 6 have narrow emission lines, 23 are Wolf-Rayet stars, 9 stars have featureless spectra, and 76 are O/B type stars. Our wide-field spectroscopic data confirm that the distribution of young stars is compact, with 90% of the young stars identified within 0.5 pc of the nucleus. We identify 24 new O/B stars primarily at large radii. We estimate photometric masses of the O/B stars and show that the total mass in the young population is > ∼ 12 000 M . The O/B stars all appear to be bound to the Milky Way nuclear star cluster, while less than 30% belong to the clockwise rotating disk. We add one new star to the sample of stars affiliated with this disk. Conclusions. The central concentration of the early-type stars is a strong argument that they have formed in situ. An alternative scenario, in which the stars formed outside the Galactic centre in a cluster that migrated to the centre, is refuted. A large part of the young O/B stars is not on the disk, which either means that the early-type stars did not all form on the same disk or that the disk is dissolving rapidly.

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Quantifying the coexistence of massive black holes and dense nuclear star clusters

Cited by 246 publications

References 232 publications

The old nuclear star cluster in the Milky Way: dynamics, mass, statistical parallax, and black hole mass

The old nuclear star cluster in the Milky Way: dynamics, mass, statistical parallax, and black hole mass

On central black holes in ultra-compact dwarf galaxies

KMOS view of the Galactic centre

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