2 research outputs found
Multimodality in galaxy clusters from SDSS DR8: substructure and velocity distribution
We search for the presence of substructure, a non-Gaussian, asymmetrical
velocity distribution of galaxies, and large peculiar velocities of the main
galaxies in galaxy clusters with at least 50 member galaxies, drawn from the
SDSS DR8. We employ a number of 3D, 2D, and 1D tests to analyse the
distribution of galaxies in clusters: 3D normal mixture modelling, the
Dressler-Shectman test, the Anderson-Darling and Shapiro-Wilk tests and others.
We find the peculiar velocities of the main galaxies, and use principal
component analysis to characterise our results. More than 80% of the clusters
in our sample have substructure according to 3D normal mixture modelling, the
Dressler-Shectman (DS) test shows substructure in about 70% of the clusters.
The median value of the peculiar velocities of the main galaxies in clusters is
206 km/s (41% of the rms velocity). The velocities of galaxies in more than 20%
of the clusters show significant non-Gaussianity. While multidimensional normal
mixture modelling is more sensitive than the DS test in resolving substructure
in the sky distribution of cluster galaxies, the DS test determines better
substructure expressed as tails in the velocity distribution of galaxies.
Richer, larger, and more luminous clusters have larger amount of substructure
and larger (compared to the rms velocity) peculiar velocities of the main
galaxies. Principal component analysis of both the substructure indicators and
the physical parameters of clusters shows that galaxy clusters are complicated
objects, the properties of which cannot be explained with a small number of
parameters or delimited by one single test. The presence of substructure, the
non-Gaussian velocity distributions, as well as the large peculiar velocities
of the main galaxies, shows that most of the clusters in our sample are
dynamically young.Comment: 15 pages, 11 figures, 2 online tables, accepted for publication in
Astronomy and Astrophysic
Multimodality of rich clusters from the SDSS DR8 within the supercluster-void network
We study the relations between the multimodality of galaxy clusters drawn
from the SDSS DR8 and the environment where they reside. As cluster environment
we consider the global luminosity density field, supercluster membership, and
supercluster morphology. We use 3D normal mixture modelling, the
Dressler-Shectman test, and the peculiar velocity of cluster main galaxies as
signatures of multimodality of clusters. We calculate the luminosity density
field to study the environmental densities around clusters, and to find
superclusters where clusters reside. We determine the morphology of
superclusters with the Minkowski functionals and compare the properties of
clusters in superclusters of different morphology. We apply principal component
analysis to study the relations between the multimodality parametres of
clusters and their environment simultaneously. We find that multimodal clusters
reside in higher density environment than unimodal clusters. Clusters in
superclusters have higher probability to have substructure than isolated
clusters. The superclusters can be divided into two main morphological types,
spiders and filaments. Clusters in superclusters of spider morphology have
higher probabilities to have substructure and larger peculiar velocities of
their main galaxies than clusters in superclusters of filament morphology. The
most luminous clusters are located in the high-density cores of rich
superclusters. Five of seven most luminous clusters, and five of seven most
multimodal clusters reside in spider-type superclusters; four of seven most
unimodal clusters reside in filament-type superclusters. Our study shows the
importance of the role of superclusters as high density environment which
affects the properties of galaxy systems in them.Comment: 16 pages, 12 figures, 2 online tables, accepted for publication in
Astronomy and Astrophysic