218 research outputs found
An Objective and Automatic Cluster Finder: An Improvement of the Matched-Filter Method
We describe an objective and automated method for detecting clusters of
galaxies from optical imaging data. This method is a variant of the so-called
`matched-filter' technique pioneered by Postman et al. (1996). With
simultaneous use of positions and apparent magnitudes of galaxies, this method
can, not only find cluster candidates, but also estimate their redshifts and
richnesses as byproducts of detection. We examine errors in the estimation of
cluster's position, redshift, and richness with a number of Monte Carlo
simulations. No systematic discrepancies between the true and estimated values
are seen for either redshift or richness. Spurious detection rate of the method
is about less than 10% of those of conventional ones which use only surface
density of galaxies. A cluster survey in the North Galactic Pole is executed to
verify the performance characteristics of the method with real data. Two known
real clusters are successfully detected. We expect these methods based on
`matched-filter' technique to be essential tools for compiling large and
homogeneous optically-selected cluster catalogs.Comment: 13 pages, 12 PostScript figures, uses LaTeX L-AA, A&AS accepte
Dependence of the Build-up of the Colour-Magnitude Relation on Cluster Richness at z ~ 0.8
We present environmental dependence of the build-up of the colour-magnitude
relation (CMR) at z ~ 0.8. It is well established that massive early-type
galaxies exhibit a tight CMR in clusters up to at least z ~ 1. The faint end of
the relation, however, has been much less explored especially at high redshifts
primarily due to limited depths of the data. Some recent papers have reported a
deficit of the faint red galaxies on the CMR at 0.8 < z < 1, but this has not
been well confirmed yet and is still controversial. Using a deep, multi-colour,
panoramic imaging data set of the distant cluster RXJ1716.4+6708 at z=0.81,
newly taken with the Prime Focus Camera (Suprime-Cam) on the Subaru Telescope,
we carry out an analysis of faint red galaxies with a care for incompleteness.
We find that there is a sharp decline in the number of red galaxies toward the
faint end of the CMR below M*+2. We compare our result with those for other
clusters at z ~ 0.8 taken from the literature, which show or do not show the
deficit. We suggest that the "deficit" of faint red galaxies is dependent on
the richness or mass of the clusters, in the sense that poorer systems show
stronger deficits. This indicates that the evolutionary stage of less massive
galaxies depends critically on environment.Comment: 11 pages, 10 figures, accepted for publication in MNRA
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