Kinematic properties of early-type galaxy haloes using planetary nebulae

Abstract

We present new planetary nebulae (PNe) positions, radial velocities and magnitudes for six early-type galaxies obtained with the Planetary Nebulae Spectrograph (PNS), along with derived two-dimensional velocity and velocity dispersion fields, and the _s13_s17945_s19 parameters (i.e. the number of PNe per unit luminosity). We also present new deep absorption-line long-slit kinematics for three galaxies in the sample, obtained with the FOcal Reducer and low dispersion Spectrograph (FORS2) at the Very Large Telescope (VLT). We extend this study to include additional 10 early-type galaxies with PNe radial velocity measurements available from the literature, including previous PNS studies, in order to obtain a broader description of the outer-halo kinematics in early-type galaxies. These data extend the information derived from stellar absorption-line kinematics to typically several and up to 8 effective radii. The combination of photometry, absorption-line and PNe kinematics shows (i) a good agreement between the PNe number density distribution and the stellar surface brightness in the region where the two data sets overlap_s19 (ii) a good agreement between PNe and absorption-line kinematics_s19 (iii) that the mean rms velocity profiles fall into two groups, with part of the galaxies characterized by slowly decreasing profiles and the remainder having steeply falling profiles_s19 (iv) a larger variety of velocity dispersion radial profiles_s19 (v) that twists and misalignments in the velocity fields are more frequent at large radii, including some fast rotator galaxies_s19 (vi) that outer haloes are characterized by more complex radial profiles of the specific angular momentum-related _s13_s17955_s19R parameter than observed within 1 Re_s19 (vii) that many objects are more rotationally dominated at large radii than in their central parts and (viii) that the halo kinematics are correlated with other galaxy properties, such as total B band and X-ray luminosity, isophotal shape, total stellar mass, V/_s13_s17963_s19 and _s13_s17945_s19 parameter, with a clear separation between fast and slow rotators.