Planetary nebulae as mass tracers of their parent galaxies: Biases in the estimate of the kinematical quantities

Multi-object and multi-fiber spectrographs on 4 and 8 m telescopes make it possible to use extragalactic planetary nebulae (PNe) in the outer halos of early-type galaxies as kinematical tracers, where classical techniques bas ed on integrated stellar light fail. Until now, published PNe radial veloci ty samples are small, with only a few tens of radial velocity measurements (except for a few cases like NGC 5128 or M 31), causing uncertainties in th e mass and angular momentum estimates based on these data. To quantify thes e uncertainties, we have made equilibrium models for spherical galaxies, wi th and without dark matter, and via Montecarlo simulations we produce radia l velocity samples with different sizes. We then apply, to these discrete r adial velocity fields, the same standard kinematical analysis as it is comm only done with small samples of observed PNe radial velocities. By comparis on of the inferred quantities with those computed from the analytical model , we test for systematic biases and establish a robust procedure to infer t he angular momentum distribution and radial velocity dispersion profiles fr om such samples.