Michele Cappellari

Abstract:

We present Galaxy Evolution Explorer far-ultraviolet (FUV) and near-ultraviolet (NUV) imaging of 34 nearby early-type galaxies from the SAURON representative sample of 48 E/S0 galaxies, all of which have ground-based optical imaging from the MDM Observatory. The surface brightness profiles of nine galaxies (≈26 per cent) show regions with blue UV-optical colours suggesting RSF. Five of these (≈15 per cent) show blue integrated UV-optical colours that set them aside in the NUV integrated colour-magnitude relation. These are objects with either exceptionally intense and localized NUV fluxes or blue UV-optical colours throughout. They also have other properties confirming they have had RSF, in particular Hβ absorption higher than expected for a quiescent population and a higher CO detection rate. This suggests that residual star formation is more common in early-type galaxies than we are used to believe. NUV blue galaxies are generally drawn from the lower stellar velocity dispersion (σe < 200 km s-1) and thus lower dynamical mass part of the sample. We have also constructed the first UV Fundamental Planes and show that NUV blue galaxies bias the slopes and increase the scatters. If they are eliminated, the fits get closer to expectations from the virial theorem. Although our analysis is based on a limited sample, it seems that a dominant fraction of the tilt and scatter of the UV Fundamental Planes is due to the presence of young stars in preferentially low-mass early-type galaxies. Interestingly, the UV-optical radial colour profiles reveal a variety of behaviours, with many galaxies showing signs of RSF, a central UV-upturn phenomenon, smooth but large-scale age and metallicity gradients and in many cases a combination of these. In addition, FUV-NUV and FUV-V colours even bluer than those normally associated with UV-upturn galaxies are observed at the centre of some quiescent galaxies. Four out of the five UV-upturn galaxies are slow rotators. These objects should thus pose interesting challenges to stellar evolutionary models of the UV upturn. © 2009 RAS.

Abstract:

We present a determination of the mass of the supermassive black hole (BH) and the nuclear stellar orbital distribution of the elliptical galaxy Centaurus A (Cen A) (NGC 5128) using high-resolution integral-field observations of the stellar kinematics. The observations were obtained with SINFONI (Spectrograph for INtegral Field Observations in the Near Infrared) at the European Southern Observatory Very Large Telescope in the near-infrared (IR) (K band), using adaptive optics (AO) to correct for the blurring effect of the Earth's atmosphere. The data have a spatial resolution of 0.17 arcsec full width at half-maximum and high signal-to-noise ratios (S/N) ≳ 80 per spectral pixel so that the shape of the stellar line-of-sight velocity distribution can be reliably extracted. We detect clear low-level stellar rotation, which is counter-rotating with respect to the gas. We fit axisymmetric three-integral dynamical models to the data to determine the best-fitting values for the BH mass MBH = (5.5 ± 3.0) × 107 M ⊙ (3σ errors) and (M/L)K = (0.65 ± 0.15) in solar units. These values are in excellent agreement with previous determinations from the gas kinematics, and in particular with our own published value, extracted from the same data. This provides one of the cleanest gas versus stars comparisons of MBH determination, due to the use of integral-field data for both dynamical tracers and due to a very well-resolved BH sphere of influence RBH ≈ 0.70 arcsec. We derive an accurate profile of the orbital anisotropy, and carefully test its reliability using spherical Jeans models with radially varying anisotropy. We find an increase in the tangential anisotropy close to the BH, but the spatial extent of this effect seems restricted to the size of RBH instead of that of Rb ≈ 3.9 arcsec of the core in the surface brightness profile, contrary to detailed predictions of current simulations of the binary BH scouring mechanism. More realistic simulations would be required to draw conclusions from this observation. © 2009 RAS.