by Remco C. E. van den Bosch
Remco van den Bosch, Tim de Zeeuw, Karl Gebhardt, Eva Noyola, Glenn van de Ven
We construct orbit-based axisymmetric dynamical models for the globular cluster M15 which fit groundbased line-of-sight velocities and Hubble Space Telescope line-of-sight velocities and proper motions. This allows us to constrain the variation of the mass-to-light ratio M/L as a function of radius in the cluster, and to measure the distance and inclination of the cluster. We obtain a best-fitting inclination of 60±15 degrees, a dynamical distance of 10.3±0.4 kpc and an M/L profile with a central peak. The inferred mass in the central 0.05 parsec is 3400 Msun, implying a central density of at least 7.4•106 Msun pc-3. We cannot distinguish the nature of the central mass concentration. It could be an IMBH or it could be large number of compact objects, or it could be a combination. The central 4 arcsec of M15 appears to contain a rapidly spinning core, and we speculate on its origin.
10 pages, 10 figures, 4 tables. Published in 2006, ApJ, 641, 852
R. C. E. van den Bosch, G. van de Ven, E. K. Verolme, M. Cappellari, P. T. de Zeeuw
We present a flexible and efficient method to construct triaxial dynamical models of galaxies with a central black hole, using Schwarzschild's orbital superposition approach. Our method is general and can deal with realistic luminosity distributions, which project to surface brightness distributions that may show position angle twists and ellipticity variations. The models are fit to measurements of the full line-of-sight velocity distribution (wherever available). We verify that our method is able to reproduce theoretical predictions of a three-integral triaxial Abel model. In the companion paper by van den Ven, de Zeeuw & van den Bosch (2008), we demonstrate that the method recovers the phase-space distribution function. We apply our method to two-dimensional observations of the E3 galaxy NGC 4365, obtained with the integral-field spectrograph sauron, and study its internal structure, showing that the observed kinematically decoupled core is not physically distinct from the main body and the inner region is close to oblate axisymmetric.
21 Pages, 14 (Colour) Figures. Published in 2008, mnras, 385, 647
Remco C. E. van den Bosch & Glenn van de Ven
We investigate how well the intrinsic shape of early-type galaxies can be recovered in the presence of both photometric and two-dimensional stellar kinematic observations. We simulate current state-of-the-art observations for galaxy models that are representative of the full range of observed oblate fast-rotator to triaxial slow-rotator early-type galaxies. By fitting realistic triaxial dynamical models to these simulated observations, we recover the intrinsic shape (and mass-to-light ratio), without making additional (ad-hoc) assumptions on the orientation. For (near) axisymmetric galaxies the dynamical modelling can strongly exclude triaxiality, but the regular kinematics do not further tighten the intrinsic flattening significantly, so that the inclination is nearly unconstrained above the photometric lower limit. Triaxial galaxies can have additional complexity in both the observed photometry and kinematics, such as twists and (central) kinematically decoupled components, which allows the intrinsic shape to be accurately recovered. For galaxies that are very round or show no significant rotation recovery of the shape is degenerate, unless additional constraints such as a thin disk are available.
To be submitted to mnras
Remco C. E. van den Bosch & P. Tim de Zeeuw
Most of the super massive black hole mass (M•) estimates based on stellar kinematics use the assumption that galaxies are axisymmetric oblate spheroids or spherical. Using fully general triaxial orbit based models we explore the effect of relaxing the axisymmetric assumption on the previously studied galaxies M32 and NGC 3379. We find that M32 can only be accurately modeled using an axisymmetric shape viewed nearly edge on and our black hole mass estimate is identical to previous studies. When the observed 5 degree kinematical twist is included in our model of NGC 3379, then the best shape is mildly triaxial and we find that our best-fitting black hole mass estimate doubles, with respect to the axisymmetric model. While this individual result is still consistent with the original estimate and the M•-σ relation, it could have significant impact on the black hole demography as around a third of the most massive galaxies are triaxial.
To be submitted to mnras
Remco C. E. van den Bosch & the sauron team
We use fully general triaxial dynamical models to investigate thirteen nearby galaxies that show a kinematically decoupled core (KDC) in the stellar kinematic maps obtained with sauron. We find that each of these galaxies is fully consistent with triaxial shapes, and we strongly rule out axisymmetry. Their orbital structure is dominated by short axis tube orbits and only contains 20 per cent box orbits. They contain roughly equal parts of prograde and retrograde rotation, indicating that the KDCs are not distinct dynamical structures. These realistic models also show that triaxial galaxies with a super massive black hole can exist.
To be submitted to mnras
The End.
Contact information:
Name: Remco C.E. van den Bosch
McDonald Observatory
The Univesity of Texas at Austin
2511 Speedway
Austin, TX 78712
USA
Email: bosch at astro.as.utexas.edu
WWW: http://www.as.utexas.edu/~bosch
Tel: +1 (512) 471-1499