Issue |
A&A
Volume 456, Number 1, September II 2006
|
|
---|---|---|
Page(s) | 23 - 36 | |
Section | Cosmology (including clusters of galaxies) | |
DOI | https://doi.org/10.1051/0004-6361:20064918 | |
Published online | 23 August 2006 |
On the efficiency and reliability of cluster mass estimates based on member galaxies
1
INAF/Osservatorio Astronomico di Trieste, via Tiepolo 11, 34131 Trieste, Italy e-mail: biviano@oats.inaf.it
2
INAF/Osservatorio Astronomico di Torino, Strada Osservatorio 20, 10025 Pino Torinese, Italy
3
Dipartimento di Astronomia dell'Università di Trieste, via Tiepolo 11, 34131 Trieste, Italy
4
INFN - National Institute for Nuclear Physics, Trieste, Italy
5
Dipartimento di Fisica Generale “Amedeo Avogadro”, Universitá degli Studi di Torino, Torino, Italy
6
Max-Planck-Institut für Astrophysik, Karl-Schwarzschild Strasse 1, Garching bei München, Germany
Received:
26
January
2006
Accepted:
5
May
2006
Aims.We study the efficiency and reliability of cluster mass estimators that are based on the projected phase-space distribution of galaxies in a cluster region.
Methods.We analyse a data-set of 62 clusters extracted from a concordance ΛCDM cosmological hydrodynamical simulation. We consider both dark matter (DM) particles and simulated
galaxies as tracers of the clusters gravitational potential. Two cluster mass estimators are considered: the virial mass estimator,
corrected for the surface-pressure term, and a mass estimator (that we
call ) based entirely on the velocity dispersion estimate
of the cluster. In order to simulate observations,
galaxies (or DM particles) are first selected in cylinders of given radius (from 0.5
to 1.5h-1 Mpc) and
Mpc length. Cluster
members are then identified by applying a suitable interloper removal
algorithm.
Results.The virial mass estimator overestimates the true mass
by 10% on average, for sample sizes of
60 cluster
members. For similar sample sizes,
underestimates the
true mass by
15%, on average. For smaller sample sizes, the
bias of the virial mass estimator substantially increases, while the
estimator becomes essentially unbiased. The dispersion of
both mass estimates increases by a factor ~2 as the number of
cluster members decreases from ~400 to ~20.
It is possible to reduce the bias in the virial mass estimates either
by removing clusters with significant evidence for subclustering or by
selecting early-type galaxies, which substantially reduces the
interloper contamination. Early-type galaxies cannot however be used
to improve the
estimates since their intrinsic velocity
distribution is slightly biased relative to that of the DM particles.
Radially-dependent incompleteness can drastically affect the virial
mass estimates, but leaves the
estimates almost
unaffected. Other observational effects, like centering and velocity
errors and different observational apertures, have little effect on
the mass estimates.
Key words: galaxies: clusters: general / galaxies: kinematics and dynamics / cosmology: observations / methods: N-body simulations
© ESO, 2006
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