Intermediate-mass black holes in globular clusters

17 Apr

[2013MmSAI..84..129L] Lützgendorf, N.; Kissler-Patig, M.; Gebhardt, K.; Baumgardt, H.; Noyola, E.; de Zeeuw, P. T.; Neumayer, N.; Jalali, B.; Feldmeier, A.

Screen Shot 2015-04-17 at 10.11.42For a sample of nine Galactic globular clusters we measured the inner kinematic profiles with integral-field spectroscopy that we combined with existing outer kinematic measurements and HST luminosity profiles. With this information we are able to detect the crucial rise in the velocity-dispersion profile which indicates the presence of a central black hole. In addition, N-body simulations compared to our data will give us a deeper insight in the properties of clusters with black holes and stronger selection criteria for further studies. For the first time, Continue reading

The Central Blue Straggler Population in Four Outer-halo Globular Clusters

17 Apr

[2012ApJ…754..108B] Beccari, Giacomo; Lützgendorf, Nora; Olczak, Christoph; Ferraro, Francesco R.; Lanzoni, Barbara; Carraro, Giovanni; Stetson, Peter B.; Sollima, Antonio; Boffin, Henri M. J.

Screen Shot 2015-04-17 at 10.04.49Using Hubble Space Telescope/Wide Field Planetary Camera 2 data, we have performed a comparative study of the Blue Straggler Star (BSS) populations in the central regions of the globular clusters (GCs) AM 1, Eridanus, Palomar 3, and Palomar 4. Located at distances R GC > 50 kpc from the Galactic center, these are (together with Palomar 14 and NGC 2419) the most distant clusters in the halo. We determine their color-magnitude diagrams and centers of gravity. The four clusters turn out to have similar ages (10.5-11 Gyr), significantly smaller than those Continue reading

High-velocity stars in the cores of globular clusters: the illustrative case of NGC 2808

17 Apr

[2012A&A…543A..82L] Lützgendorf, N.; Gualandris, A.; Kissler-Patig, M.; Gebhardt, K.; Baumgardt, H.; Noyola, E.; Kruijssen, J. M. D.; Jalali, B.; de Zeeuw, P. T.; Neumayer, N.

Screen Shot 2015-04-17 at 09.57.06We report the detection of five high-velocity stars in the core of the globular cluster NGC 2808. The stars lie on the red giant branch and show total velocities between 40 and 45 km s-1. For a core velocity dispersion sigmac = 13.4 km s-1, this corresponds to up to 3.4 sigmac. These velocities are close to the estimated escape velocity (~50 km s-1) and suggest an ejection from the core. Two of these stars have been confirmed in our recent integral field spectroscopy data and we will discuss them in more detail here. Continue reading

Central kinematics of the globular cluster NGC 2808: upper limit on the mass of an intermediate-mass black hole

17 Apr

[2012A&A…542A.129L] Lützgendorf, N.; Kissler-Patig, M.; Gebhardt, K.; Baumgardt, H.; Noyola, E.; Jalali, B.; de Zeeuw, P. T.; Neumayer, N.

Screen Shot 2015-04-17 at 09.38.20Globular clusters are an excellent laboratory for stellar population and dynamical research. Recent studies have shown that these stellar systems are not as simple as previously assumed. With multiple stellar populations as well as outer rotation and mass segregation they turn out to exhibit high complexity. This includes intermediate-mass black holes (IMBHs) which are proposed to sit at the centers of some massive globular clusters. Today’s high angular resolution ground based spectrographs allow velocity-dispersion measurements at a spatial resolution Continue reading

The Search for Intermediate-mass Black Holes in Globular Clusters

16 Apr

[2012Msngr.147…21L] Lützgendorf, N.; Kissler-Patig, M.; de Zeeuw, T.; Baumgardt, H.; Feldmeier, A.; Gebhardt, K.; Jalali, B.; Neumayer, N.; Noyola, E.

Screen Shot 2015-04-16 at 17.06.55Intermediate-mass black holes (IMBHs) fill the gap between supermassive and stellar-mass black holes and they could act as seeds for the rapid growth of supermassive black holes in early galaxy formation. Runaway collisions of massive stars in young and dense stellar clusters could have formed IMBHs that are still present in the centres of globular clusters. We have resolved the central dynamics of a number of globular clusters in our Galaxy using the FLAMES integral-field spectrograph at the VLT. Continue reading

A Dynamical N-body model for the central region of omega Centauri

16 Apr

[2012A&A…538A..19J] Jalali, B.; Baumgardt, H.; Kissler-Patig, M.; Gebhardt, K.; Noyola, E.; Lützgendorf, N.; de Zeeuw, P. T.

Screen Shot 2015-04-16 at 17.00.18Supermassive black holes (SMBHs) are fundamental keys to understand the formation and evolution of their host galaxies. However, the formation and growth of SMBHs are not yet well understood. One of the proposed formation scenarios is the growth of SMBHs from seed intermediate-mass black holes (IMBHs, 102 to 105 Msun;) formed in star clusters. In this context, and also with respect to the low mass end of the M – sigma relation for galaxies, globular clusters are in a mass range that make them ideal systems to look for IMBHs. Continue reading

Kinematic signature of an intermediate-mass black hole in the globular cluster NGC 6388

16 Apr

[2011A&A…533A..36L] Lützgendorf, N.; Kissler-Patig, M.; Noyola, E.; Jalali, B.; de Zeeuw, P. T.; Gebhardt, K.; Baumgardt, H.

Screen Shot 2015-04-16 at 16.00.27 Intermediate-mass black holes (IMBHs) are of interest in a wide range of astrophysical fields. In particular, the possibility of finding them at the centers of globular clusters has recently drawn attention. IMBHs became detectable since the quality of observational data sets, particularly those obtained with HST and with high resolution ground based spectrographs, advanced to the point where it is possible to measure velocity dispersions at a spatial resolution comparable to the size of the gravitational sphere of influence for plausible IMBH masses. Continue reading

Welcome!

16 Apr
Here you find a list of my publications as first and co-author. For an overview of the list (refereed only) please click...
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Very Large Telescope Kinematics for Omega Centauri: Further Support for a Central Black Hole

16 Apr

[2010ApJ…719L..60N] Noyola, Eva; Gebhardt, Karl; Kissler-Patig, Markus; Lützgendorf, Nora; Jalali, Behrang; de Zeeuw, P. Tim; Baumgardt, Holger

Screen Shot 2015-04-16 at 15.07.37The Galactic globular cluster omega Centauri is a prime candidate for hosting an intermediate-mass black hole. Recent measurements lead to contradictory conclusions on this issue. We use VLT-FLAMES to obtain new integrated spectra for the central region of omega Centauri. We combine these data with existing measurements of the radial velocity dispersion profile taking into account a new derived center from kinematics and two different centers from the literature. Continue reading