Planetary nebulae as kinematic tracers of galaxy halos

Abstract

AbstractThe kinematics and dynamical properties of galaxy stellar halos are difficult to measure, given the faint surface brightness that characterizes these regions. Gas-rich systems such as spiral galaxies can be probed using the radio Hi emission. Early-type galaxies contain less gas, therefore alternative kinematic tracers need to be used. Planetary Nebulae (PNe) can be easily detected far out in the halo thanks to their bright [O iii] emission at 5007 Å. It is therefore possible to map the halo kinematics also in early-type galaxies, typically out to 5 effective radii or beyond. Thanks to the recent spectroscopic surveys targeting extra-galactic PNe, we can now rely on few tens of galaxies where the kinematics of the stellar halos are measured. I will discuss the most important results: (a) the relation of the stellar surface brightness and the PNe number density; (b) the velocity and velocity dispersion two-dimensional fields; (c) the radial profiles of angular momentum; and (d) the relation between the derived kinematics physical properties of the host galaxies.