L. Moscardini et al., THE CLUSTER DISTRIBUTION AS A TEST OF DARK-MATTER MODELS .3. THE CLUSTER VELOCITY-FIELD, Monthly Notices of the Royal Astronomical Society, 282(2), 1996, pp. 384-400
We study the large-scale velocity fields traced by galaxy clusters in
numerical simulations of a box of side 960 h(-1) h(-1), and compare th
em with available data on real clusters. In order to test the reliabil
ity of the simulations, which are based on an optimized version of the
Zel'dovich approximation, we compare their cluster velocities with th
ose of 'exact' N-body simulations, and find a remarkable agreement bet
ween the two according to a variety of statistical tests. We analyse c
old dark matter (CDM) models with density parameter in the range 0.2 l
ess than or equal to Ohm(0) less than or equal to 1, both with and wit
hout the cosmological constant term to provide a flat geometry. We als
o simulate a cold+hot dark matter (CHDM) model, with 30 per cent provi
ded by the hot component. Comparison with real data is performed by ap
plying tests based on the cumulative velocity frequency distribution (
CVFD) and bulk flow statistics. For the CVFD, we use observational vel
ocity data from different authors, and find that results based on diff
erent data sets are contradictory. In particular, the recent infrared
Tully-Fisher (IRTF) data of Giovanelli yield smaller velocities with s
maller errors than both the IRTF and D-n-sigma data of Hudson. It turn
s out that the Giovanelli data are only only consistent with the open
Ohm(0) = 0.4 and the flat Omega(0) = 0.2 models, while the Hudson data
, though less discriminatory because of their larger errors, appear to
exclude open models with Ohm(0) less than or equal to 0.4 and hat mod
els with Ohm(0) = 0.2. This latter conclusion also holds if one pools
all the data into a single sample regardless of the systematic differe
nces in the two different sources. Furthermore, CVFD and bulk flow ana
lyses of the Branchini et al. reconstructed velocity data again disfav
our precisely those models accepted on the grounds of Giovanelli's sam
ple. Finally, we confirm that the Lauer & Postman reported bulk flow d
etermination would be a rare event in the cosmological models we have
analysed.