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Astron. Astrophys. 345, 439-447 (1999)

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On two mass estimators for clusters of galaxies

Héctor Aceves and Jaime Perea

Instituto de Astrofísica de Andalucía, CSIC, Apdo. Postal 3004, E-Granada 18080, Spain

Received 20 July 1998 / Accepted 4 February 1999


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 N-body experiments. We consider here only spherical, isolated, and isotropic velocity dispersion systems.

We have found that the PME can overestimate masses by [FORMULA]%, 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 ([FORMULA]) 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 N-body experiments. The possible reasons for the mass discrepancies found when using the PME and the VME in some N-body simulations are also briefly discussed.

Key words: celestial mechanics, stellar dynamics – galaxies: clusters: general

Send offprint requests to: H. Aceves (aceves@iaa.es)

© European Southern Observatory (ESO) 1999

Online publication: April 19, 1999