A re-evaluation of the central velocity-dispersion profile in NGC 6388

21 Aug

[2015arXiv150702813L] Lützgendorf, Nora; Gebhardt, Karl; Baumgardt, Holger; Noyola, Eva; Neumayer, Nadine; Kissler-Patig, Markus; de Zeeuw, Tim

Screen Shot 2015-08-21 at 11.29.20 Recently, two independent groups found very different results when measuring the central velocity dispersion of the galactic globular cluster NGC 6388 with different methods. While L\”utzgendorf et al. (2011) found a rising profile and a high central velocity dispersion (23.3 km/s), measurements obtained by Lanzoni et al. (2013) showed a value 40% lower. The value of the central velocity dispersion has a serious impact on the mass and possible presence of an intermediate-mass black hole at the center of NGC 6388. Continue reading

Intermediate-mass black holes in globular clusters: observations and simulations

17 Apr

[2015arXiv150107441L] Lützgendorf, Nora; Kissler-Patig, Markus; Gebhardt, Karl; Baumgardt, Holger; Kruijssen, Diederik; Noyola, Eva; Neumayer, Nadine; de Zeeuw, Tim; Feldmeier, Anja; van der Helm, Edwin; Pelupessy, Inti; Portegies Zwart, Simon

iau_wbThe study of intermediate-mass black holes (IMBHs) is a young and promising field of research. Formed by runaway collisions of massive stars in young and dense stellar clusters, intermediate-mass black holes could still be present in the centers of globular clusters, today. Our group investigated the presence of intermediate-mass black holes for a sample of 10 Galactic globular clusters. We measured the inner kinematic profiles with integral-field spectroscopy and determined masses or upper limits of central black holes in each cluster. Continue reading

On the coexistence of stellar-mass and intermediate-mass black holes in globular clusters

17 Apr

[2014MNRAS.444…29L] Leigh, Nathan W. C.; Lützgendorf, Nora; Geller, Aaron M.; Maccarone, Thomas J.; Heinke, Craig; Sesana, Alberto

Screen Shot 2015-04-17 at 13.53.31In this paper, we address the question: what is the probability of stellar-mass black hole (BH) binaries co-existing in a globular cluster with an intermediate-mass black hole (IMBH)? Our results suggest that the detection of one or more BH binaries can strongly constrain the presence of an IMBH in most Galactic globular clusters. More specifically, the detection of one or more BH binaries could strongly indicate against the presence of an IMBH more massive than ≳103 Msun in roughly 80 per cent of the clusters in our sample. Continue reading

Large scale kinematics and dynamical modelling of the Milky Way nuclear star cluster

17 Apr

[2014A&A…570A…2F] Feldmeier, A.; Neumayer, N.; Seth, A.; Schödel, R.; Lützgendorf, N.; de Zeeuw, P. T.; Kissler-Patig, M.; Nishiyama, S.; Walcher, C. J.

Screen Shot 2015-04-17 at 13.29.27Within the central 10 pc of our Galaxy lies a dense cluster of stars. This nuclear star cluster forms a distinct component of the Galaxy, and similar nuclear star clusters are found in most nearby spiral and elliptical galaxies. Studying the structure and kinematics of nuclear star clusters reveals the history of mass accretion and growth of galaxy nuclei and central massive black holes. Because the Milky Way nuclear star cluster is at a distance of only 8 kpc, we can spatially resolve the cluster on sub-parsec scales. Continue reading

The Milky Way nuclear star cluster beyond 1 pc

17 Apr

[2014IAUS..303..223F] Feldmeier, A.; Neumayer, N.; Seth, A.; de Zeeuw, P. T.; Schödel, R.; Lützgendorf, N.; Kissler-Patig, M.; Nishiyama, S.; Walcher, C. J.

iau_wbWithin the central 10 pc of our Galaxy lies a dense cluster of stars, the nuclear star cluster, forming a distinct component of our Galaxy. Nuclear star clusters are common objects and are detected in ˜75% of nearby galaxies. It is, however, not fully understood how nuclear clusters form. Because the Milky Way nuclear star cluster is at a distance of only 8 kpc, we can spatially resolve its stellar populations and kinematics much better than in external galaxies. This makes the Milky Way nuclear star cluster a reference object for understanding the structure and assembly history of all nuclear star clusters.

N-body simulations of globular clusters in tidal fields: Effects of intermediate-mass black holes

17 Apr

[2013A&A…558A.117L] Lützgendorf, N.; Baumgardt, H.; Kruijssen, J. M. D.

Screen Shot 2015-04-17 at 11.52.13Intermediate-mass black holes (IMBHs) may provide the missing link to understanding the growth of supermassive black holes in the early Universe. Some formation scenarios predict that IMBHs could have formed by runaway collisions in globular clusters (GCs). However, it is challenging to set observational constraints on the mass of a black hole in a largely gas-free (and hence accretion-free) stellar system such as a GC. Understanding the influence of an IMBH in the center of a GC on its environment might provide indirect detection methods. Continue reading

On central black holes in ultra-compact dwarf galaxies

17 Apr

[2013A&A…558A..14M] Mieske, S.; Frank, M. J.; Baumgardt, H.; Lützgendorf, N.; Neumayer, N.; Hilker, M.

Screen Shot 2015-04-17 at 11.45.03The dynamical mass-to-light (M/L) ratios of massive ultra-compact dwarf galaxies (UCDs) are about 50% higher than predicted by stellar population models.mHere 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. To be self-consistent in our BH mass estimates, Continue reading

Did massive black holes in globular clusters initially satisfy galactic scaling relations?

17 Apr

[2013MNRAS.434L..41K] Kruijssen, J. M. Diederik; Lützgendorf, Nora

Screen Shot 2015-04-17 at 11.38.00The masses of supermassive black holes (SMBHs, MBH = 106-1011 Msun) in the centres of galaxies are related to the host stellar spheroid mass and velocity dispersion. A key question is how these relations originate, and over which range of black hole masses they hold. It has been speculated that intermediate-mass black holes (IMBHs, MBH = 102-105 Msun) could play a fundamental role in the growth of SMBHs. A handful of IMBHs have recently been detected in Galactic globular clusters (GCs), but their masses are inconsistent with the galactic scaling relations of SMBHs. Continue reading

M• – sigma relation for intermediate-mass black holes in globular clusters

17 Apr

[2013A&A…555A..26L] Lützgendorf, N.; Kissler-Patig, M.; Neumayer, N.; Baumgardt, H.; Noyola, E.; de Zeeuw, P. T.; Gebhardt, K.; Jalali, B.; Feldmeier, A.

Screen Shot 2015-04-17 at 11.02.08For galaxies hosting supermassive black holes (SMBHs), it has been observed that the mass of the central black hole (M) tightly correlates with the effective or central velocity dispersion (sigma) of the host galaxy. The origin of this M – sigma scaling relation is assumed to lie in the merging history of the galaxies, but many open questions about its origin and the behavior in different mass ranges still need to be addressed. The goal of this work is to study the black-hole scaling relations for low black-hole masses, Continue reading

Indication for an intermediate-mass black hole in the globular cluster NGC 5286 from kinematics

17 Apr

[2013A&A…554A..63F] Feldmeier, A.; Lützgendorf, N.; Neumayer, N.; Kissler-Patig, M.; Gebhardt, K.; Baumgardt, H.; Noyola, E.; de Zeeuw, P. T.; Jalali, B.

Screen Shot 2015-04-17 at 10.48.23Intermediate-mass black holes (IMBHs) fill the gap between stellar-mass black holes and supermassive black holes (SMBHs). The existence of the latter is widely accepted, but there are only few detections of intermediate-mass black holes (102 – 105Msun) so far. Simulations have shown that intermediate-mass black holes may form in dense star clusters, and therefore may still be present in these smaller stellar systems. Also, extrapolating the M-sigma scaling relation to lower masses predicts intermediate-mass black holes in systems with sigma ~ 10 – 20 km s-1 Continue reading