Context. The origins of S0 galaxies remain obscure, with various mechanisms proposed for their formation, likely depending on environment. These mechanisms would imprint different signatures in... Show moreContext. The origins of S0 galaxies remain obscure, with various mechanisms proposed for their formation, likely depending on environment. These mechanisms would imprint different signatures in the galaxies' stellar kinematics out to large radii, offering a method for distinguishing between them. Aims: We aim to study a sample of six S0 galaxies from a range of environments, and use planetary nebulae (PNe) as tracers of their stellar populations out to very large radii, to determine their kinematics in order to understand their origins. Methods: Using a special-purpose instrument, the Planetary Nebula Spectrograph, we observe and extract PNe catalogues for these six systems. Results: We show that the PNe have the same spatial distribution as the starlight, that the numbers of them are consistent with what would be expected in a comparable old stellar population in elliptical galaxies, and that their kinematics join smoothly onto those derived at smaller radii from conventional spectroscopy. Conclusions: The high-quality kinematic observations presented here form an excellent set for studying the detailed kinematics of S0 galaxies, in order to unravel their formation histories. We find that PNe are good tracers of stellar kinematics in these systems. We show that the recovered kinematics are largely dominated by rotational motion, although with significant random velocities in most cases. Full Tables 3-7 are available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/549/A115Show less
The central parsec around the supermassive black hole in the Galactic center (GC) hosts more than 100 young and massive stars. Outside the central cusp (R ~ 1'') the majority of these O and Wolf... Show moreThe central parsec around the supermassive black hole in the Galactic center (GC) hosts more than 100 young and massive stars. Outside the central cusp (R ~ 1'') the majority of these O and Wolf-Rayet (W-R) stars reside in a main clockwise system, plus a second, less prominent disk or streamer system at large angles with respect to the main system. Here we present the results from new observations of the GC with the AO-assisted near-infrared imager NACO and the integral field spectrograph SINFONI on the ESO/VLT. These include the detection of 27 new reliably measured W-R/O stars in the central 12'' and improved measurements of 63 previously detected stars, with proper motion uncertainties reduced by a factor of 4 compared to our earlier work. Based on the sample of 90 well measured W-R/O stars, we develop a detailed statistical analysis of their orbital properties and orientations. We show that half of the W-R/O stars are compatible with being members of a clockwise rotating system. The rotation axis of this system shows a strong transition from the inner to the outer regions as a function of the projected distance from Sgr A*. The main clockwise system either is either a strongly warped single disk with a thickness of about 10°, or consists of a series of streamers with significant radial variation in their orbital planes. Eleven out of 61 clockwise moving stars have an angular separation of more than 30° from the local angular momentum direction of the clockwise system. The mean eccentricity of the clockwise system is 0.36 ± 0.06. The distribution of the counterclockwise W-R/O star is not isotropic at the 98% confidence level. It is compatible with a coherent structure such as stellar filaments, streams, small clusters or possibly a disk in a dissolving state: 10 out of 29 counterclockwise moving W-R/O stars have an angular separation of more than 30° from the local angular momentum direction of the counterclockwise system. The observed disk warp and the steep surface density distribution favor in situ star formation in gaseous accretion disks as the origin of the young massive stars. Show less
