335 research outputs found
The APM Galaxy Survey:- V. Catalogues of Galaxy Clusters
We describe the construction of catalogues of galaxy clusters from the APM
Galaxy survey using an automated algorithm based on Abell-like selection
criteria. We investigate the effects of varying several parameters in our
selection algorithm, including the magnitude range, and radius from the cluster
centre used to estimate the cluster richnesses. We quantify the accuracy of the
photometric distance estimates by comparing with measured redshifts, and we
investigate the stability and completeness of the resulting catalogues. We find
that the angular correlation functions for different cluster catalogues are in
good agreement with one another, and are also consistent with the observed
amplitude of the spatial correlation function of rich clusters.Comment: 14 pages, PostScript, including 15 figures, submitted to MNRAS. Also
available from ftp://ftp-astro.physics.ox.ac.uk/pub/gbd/papers/apm5.ps.g
The richness dependence of galaxy cluster correlations: Results from a redshift survey of rich APM clusters
We analyse the spatial clustering properties of a new catalogue of very rich
galaxy clusters selected from the APM Galaxy Survey. These clusters are of
comparable richness and space density to Abell Richness Class
clusters, but selected using an objective algorithm from a catalogue
demonstrably free of artificial inhomogeneities. Evaluation of the two-point
correlation function for the full sample and for richer
subsamples reveals that the correlation amplitude is consistent with that
measured for lower richness APM clusters and X-ray selected clusters. We apply
a maxmimum likelihood estimator to find the best fitting slope and amplitude of
a power law fit to , and to estimate the correlation length
(the value of at which is equal to unity). For
clusters with a mean space density of 1.6\times 10^{-6}\hmpccc (equivalent to
the space density of Abell Richness clusters), we find
r_{0}=21.3^{+11.1}_{-9.3} \hmpc (95% confidence limits). This is consistent
with the weak richness dependence of expected in Gaussian models
of structure formation. In particular, the amplitude of at all
richnesses matches that of for clusters selected in N-Body
simulations of a low density Cold Dark Matter model.Comment: MNRAS submitted, 9 pages, LaTeX (mn), 7 figures. Also available at
http://www-astronomy.mps.ohio-state.edu/~racc
Density and Velocity Fields from the PSCz Survey
We present the results for the predicted density and peculiar velocity fields
and the dipole from the PSCz survey of 15,000 IRAS galaxies over 84% of the
sky. We find a significant component to the dipole arising between 6000 and
15,000 km/s, but no significant component from greater distances. The
misalignment with the CMB is 20 degrees. The most remarkable feature of the
PSCz model velocity field is a coherent large-scale flow along the baseline
connecting Perseus-Pisces, the Local Supercluster, Great Attractor and the
Shapley Concentration. We have measured the parameter beta using the amplitude
of the dipole, bulk flow and point by point comparisons between the individual
velocities of galaxies in the MarkIII and SFI datasets, and the large-scale
clustering distortion in redshift space.All our results are consistent with
beta = 0.6 +- 0.1.Comment: 8 pages, 8 figures. To appear in 'Towards an Understanding of Cosmic
Flows', Victoria, July 1999, eds Courteau,S., Strauss,M., Willick,J. PAS
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