On two mass estimators for clusters of galaxies
Abstract
The two most common mass estimators that use velocity dispersions and positions of objects in a stellar system, the virial mass estimator (VME) and the projected mass estimator (PME), are revisited and tested using Nbody experiments. We consider here only spherical, isolated, and isotropic velocity dispersion systems. We have found that the PME can overestimate masses by ~ 20%, for realistic cluster mass profiles, if applied only to regions around the total system's effective radius. The VME can yield a correct mass at different radii provided that the potential energy term is correctly taken into account and the system is completely sampled; otherwise, it may lead to similar errors as the PME. A surface pressure (3PV) term recently alluded to be usually neglected when using the VME and therefore required as a correction term is here found not necessarily required, although it can be used to yield a reasonable correction term. The preferred method here, however, is the virial theorem due to its simplicity and better agreement with Nbody experiments. The possible reasons for the mass discrepancies found when using the PME and the VME in some Nbody simulations are also briefly discussed.
 Publication:

Astronomy and Astrophysics
 Pub Date:
 May 1999
 arXiv:
 arXiv:astroph/9902166
 Bibcode:
 1999A&A...345..439A
 Keywords:

 CELESTIAL MECHANICS;
 STELLAR DYNAMICS;
 GALAXIES: CLUSTERS: GENERAL;
 Astrophysics
 EPrint:
 10 pages &