G. van de Ven

Triaxial orbit based galaxy models with an application to the (apparent) decoupled core galaxy NGC 4365

We present a flexible and efficient method to construct triaxial dynamical models of galaxies with a central black hole, using Schwarzschilds 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 a companion paper by Ven, de Zeeuw & van den Bosch, 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.

The SAURON project – XIX. Optical and near-infrared scaling relations of nearby elliptical, lenticular and Sa galaxies

We present ground-based MDM Observatory V-band and Spitzer/InfraRed Array Camera 3.6-mu m-band photometric observations of the 72 representative galaxies of the SAURON survey. Galaxies in our sample probe the elliptical E, lenticular S0 and spiral Sa populations in the nearby Universe, both in field and cluster environments. We perform aperture photometry to derive homogeneous structural quantities. In combination with the SAURON stellar velocity dispersion measured within an effective radius (sigma(e)), this allows us to explore the location of our galaxies in the colour-magnitude, colour-sigma(e), Kormendy, Faber-Jackson and Fundamental Plane scaling relations. We investigate the dependence of these relations on our recent kinematical classification of early-type galaxies (i.e. slow/fast rotators) and the stellar populations. Slow rotator and fast rotator E/S0 galaxies do not populate distinct locations in the scaling relations, although slow rotators display a smaller intrinsic scatter. We find that Sa galaxies deviate from the colour-magnitude and colour-sigma(e) relations due to the presence of dust, while the E/S0 galaxies define tight relations. Surprisingly, extremely young objects do not display the bluest (V - [3.6]) colours in our sample, as is usually the case in optical colours. This can be understood in the context of the large contribution of thermally pulsing asymptotic giant branch stars to the infrared, even for young populations, resulting in a very tight (V - [3.6])-sigma(e) relation that in turn allows us to define a strong correlation between metallicity and se. Many Sa galaxies appear to follow the Fundamental Plane defined by E/S0 galaxies. Galaxies that appear offset from the relations correspond mostly to objects with extremely young populations, with signs of ongoing, extended star formation. We correct for this effect in the Fundamental Plane, by replacing luminosity with stellar mass using an estimate of the stellar mass-to-light ratio, so that all galaxies are part of a tight, single relation. The new estimated coefficients are consistent in both photometric bands and suggest that differences in stellar populations account for about half of the observed tilt with respect to the virial prediction. After these corrections, the slow rotator family shows almost no intrinsic scatter around the best-fitting Fundamental Plane. The use of a velocity dispersion within a small aperture (e. g. R-e/8) in the Fundamental Plane results in an increase of around 15 per cent in the intrinsic scatter and an average 10 per cent decrease in the tilt away from the virial relation.

Recovery of the internal orbital structure of galaxies

We construct axisymmetric and triaxial galaxy models with a phase-space distribution function that depends on linear combinations of the three exact integrals of motion for a separable potential. These Abel models, first introduced by Dejonghe & Laurent and subsequently extended by Mathieu & Dejonghe, are the axisymmetric and triaxial generalizations of the well-known spherical Osipkov-Merritt models. We show that the density and higher order velocity moments, as well as the line-of-sight velocity distribution of these models can be calculated efficiently and that they capture much of the rich internal dynamics of early-type galaxies. We build a triaxial and oblate axisymmetric galaxy model with projected kinematics that mimic the two-dimensional kinematic observations that are obtained with integral-field spectrographs such as SAURON. We fit the simulated observations with axisymmetric and triaxial dynamical models constructed with our numerical implementation of Schwarzschild orbit-superposition method. We find that Schwarzschild method is able to recover the internal dynamics and three-integral distribution function of realistic models of early-type galaxies.

Scaling relations in early-type galaxies from integral-field stellar kinematics

Early-type galaxies (ETGs) satisfy a now classic scaling relation Re ∝ σ1.2eI-0.8e, the Fundamental Plane (FP; Djorgovski & Davis 1987; Dressler et al. 1987), between their size, stellar velocity dispersion and mean surface brightness. A significant effort has been devoted in the past twenty years to try to understand why the coefficients of the relation are not the ones predicted by the virial theorem Re ∝ σ2eI-1e.

The stellar structure of early-type galaxies: a wide-field Mitchell Spectrograph view

N. F. Boardman1†, A. Weijmans1, R. C. E. van den Bosch2, L. Zhu2, A. Yildirim2, G. van de Ven2, M. Cappellari3, P. T. de Zeeuw4,5, E. Emsellem4, D. Krajnović6 and T. Naab7 School of Physics and Astronomy, University of St Andrews, KY16 9SS UK Max Planck Institute for Astronomy, Königstuhl 17, D-69117 Heidelberg, Germany Sub-department of Astrophysics, Department of Physics, University of Oxford, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany Sterrewacht Leiden, Leiden University, Postbus 9513, 2300 RA, Leiden, The Netherlands Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, D-14482 Potsdam, Germany Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Str. 1, 85741 Garching, Germany

Stellar populations of early-type galaxies in the ATLAS3D sample

ATLAS3D is a multi‐wavelength, volume‐limited survey of 263 morphologically‐selected early‐type galaxies within a distance of 42 Mpc and complete to MK⩽−21.5. Here we present the ATLAS3D project and our first results on the stellar populations of galaxies in the ATLAS3D sample based on SAURON integral‐field spectroscopy. We show relations between integrated line‐strength indices and stellar velocity dispersion σ in the range 55⩽σ(km/s)⩽350. We derive simple‐stellar‐population‐equivalent age, metallicity and α/Fe abundance ratio and discuss their relation to stellar velocity dispersion, environment and galaxy internal kinematics. These preliminary results indicate that slow rotators tend to be older and have less variation in age than fast rotators. We also find that galaxies in lower density environments are on average younger than those in denser environments, as found by other authors.