arXiv subjects
Publications and source records attributed to Tim de Zeeuw.
The SAURON project will deliver two-dimensional spectroscopic data of a sample of nearby early-type galaxies with unprecedented quality. In this paper, we focus on the mapping of their stellar populations using the SAURON data, and present some preliminary results on a few prototypical cases.
In this paper we analyze the relation between radio, optical continuum and Halpha+[NII] emission from the cores of a sample of 21 nearby Fanaroff & Riley type I galaxies as observed with the VLBA and HST. The emission arises inside the inner tens of parsec of the galaxies. Core radio emission is observed in 19/20 galaxies, optical core continuum emission is detected in 12/21 galaxies and Halpha+[NII] core emission is detected in 20/21 galaxies. We confirm the recently detected linear correlation between radio and optical core emission in FR I galaxies and show that both core emissions also correlate with central Halpha+[NII] emission. The tight correlations between radio, optical and Halpha+[NII] core emission constrain the bulk Lorentz factor to gamma ~ 2-5 and gamma =< 2 for a continuous jet and a jet consisting of discrete blobs, respectively, assuming jet viewing angles in the range [30deg,90deg]. Radio and optical core emissions are likely to be synchrotron radiation from the inner jet, possibly with a significant contribution from emission by an accretion disk and/or flow. Elliptical galaxies with LINER nuclei without large-scale radio jets seem to follow the core emission correlations found in FR I galaxies. This suggests that the central engines could be very similar for the two classes of AGNs.
Masses of black holes in nearby galactic nuclei can be measured in a variety of ways, using stellar and gaseous kinematics. Reliable black hole masses are known for several dozen objects, so that demographic questions can start to be addressed with some confidence. Prospects for the near future are discussed briefly.
Milli-arcsecond astrometry provided by Hipparcos and by radio observations makes it possible to retrace the orbits of nearby runaway stars and pulsars with sufficient accuracy to identify their parent stellar cluster or association. For two cases it is even possible to deduce the specific formation scenario. The runaway star zeta Oph and PSR J1932+1059 are the result of a supernova explosion which took place 1 Myr ago in a massive binary in the Upper Scorpius association. The pulsar received a kick velocity of about 350 km/s in this event. The runaway stars mu Col and AE Aur and the isolated eccentric massive binary iota Ori result from a binary-binary encounter, most likely inside the Trapezium cluster, 2.5 Myr ago. Future astrometric missions such as DIVA, FAME and in particular GAIA will allow extension of these studies to a significant fraction of the Galactic disk, and will provide new constraints on the formation and evolution of massive stars.
We present direct observational constraints on the orbital distribution of the stars in the giant elliptical NGC 2320. Long-slit spectra along multiple position angles are used to derive the stellar line-of-sight velocity distribution within one effective radius. In addition, the rotation curve and dispersion profile of an ionized gas disk are measured from the [OIII] emission lines. After correcting for the asymmetric drift, we derive the circular velocity of the gas, which provides an independent constraint on the gravitational potential. To interpret the stellar motions, we build axisymmetric three-integral dynamical models based on an extension of the Schwarzschild orbit- superposition technique. We consider two families of gravitational potential, one in which the mass follows the light (i.e. no dark matter) and one with a logarithmic gravitational potential. Using chi^2-statistics, we compare our models to both the stellar and gas data to constrain the value of the V-band mass-to-light ratio Upsilon-V. We find Upsilon-V = 15.0 \pm 0.6 h75 for the mass-follows-light models and Upsilon-V = 17.0 \pm 0.7 h75 for the logarithmic models. For the latter, Upsilon-V is defined within a sphere of 15'' radius. Models with radially constant Upsilon-V and logarithmic models with dark matter provide comparably good fits to the data and possess similar dynamical structure. Across the full range of Upsilon-V permitted by the observational constraints, the models are radially anisotropic in the equatorial plane over the radial range of our kinematical data (1'' < r < 40''). Along the true minor axis, they are more nearly isotropic. (abridged)
The shape of a cusped galactic nucleus is constrained by the range of shapes of orbits in its gravitational potential. It is shown for scale-free non-axisymmetric discs that while a plausible elongated density model requires at least some orbits to spend more time near the major axis than anywhere else, both regular boxlets and tube orbits generally cross the major axis too fast for self-consistency. If galaxies host inner nuclear discs or flat bars with a cuspy surface light profile ($γ=|{d \log μ/ d \log r}|>0$), their ellipticity $1-{b / a}$ cannot be greater than about ${γ/ 2}$. Discs or bars with a shallow central profile ($γ\le 0.3$) should not be strongly elliptical.
This summary discribes the highlights of the Third Stromlo Symposium, on the nature of the stellar, gaseous, and dark components of the Galactic Halo.
This summary discusses new results on the stellar and gaseous luminous halo, and on the dark halo. It concludes with a look towards the future, with emphasis on the role of space astrometry missions.
A variety of observational approaches have provided evidence for extended halos of dark matter surrounding elliptical galaxies, and for massive dark objects in (some of) their nuclei. What are the properties of the dark halos? How do they relate to the parameters of the luminous matter? What is the demographics of massive central black holes, and what is their dynamical role in shaping the host galaxy? Recent work in this area is described, with special attention to the construction of state-of-the-art dynamical models that incorporate all available observational constraints.
We describe a powerful technique to model and interpret the stellar line-of-sight velocity profiles of galaxies. Following Schwarzschild's modeling approach, a representative library of orbits is calculated in a given potential; then the non-negative superposition of these orbits is determined to fit best a given set of observational constraints. Our implementation incorporates several new features: (i) we calculate velocity profiles and represent them by a Gauss-Hermite series. This allows us to constrain the orbital anisotropy in the fit. (ii) we take into account the error on each observational constraint to obtain an objective chi2 measure for the quality-of-fit. Only projected, observable quantities are included in the fit, and aperture binning and seeing convolution of the data are properly taken into account. This scheme is valid for any geometry, but here we focus on spherical geometry and the issue of dark halos around elliptical galaxies. We model radially extended velocity profiles of the E0 galaxy NGC 2434, and find that constant M/L models are clearly ruled out, regardless of the orbital anisotropy. To study how much dark matter is needed, we considered a sequence of cosmologically motivated `star+halo' potentials, which are specified by the stellar mass-to-light ratio Gamma and the characteristic halo velocity, V_200 (from Navarro et al. 1996). The star+halo models provide an excellent fit to the data, with Gamma=3.35+-0.25 (in B-band solar units) and V_200=450+-100km/s. The best-fitting potential has a circular velocity Vc that is constant (at ~300km/s) to within 10% between 0.2--3 effective radii. In NGC 2434 roughly half of the mass within an effective radius appears to be dark.