1,256 research outputs found
Tracing the mass profiles of galaxy clusters with member galaxies
The mass distribution of galaxy clusters can be determined from the study of
the projected phase-space distribution of cluster galaxies. The main advantage
of this method as compared to others, is that it allows determination of
cluster mass profiles out to very large radii. Here I review recent analyses
and results on this topic. In particular, I briefly describe the Jeans and
Caustic methods, and the problems one has to face in applying these methods to
galaxy systems. Then, I summarize the most recent and important results on the
mass distributions of galaxy groups, clusters, and superclusters. Additional
covered topics are the relative distributions of the dark and baryonic
components, and the orbits of galaxies in clusters.Comment: 8 pages, 1 figure, invited review at the XXIst IAP Colloquium "Mass
Profiles and Shapes of Cosmological Structures", Paris 4-9 July 2005,
Editors: G. Mamon, F. Combes, C. Deffayet, B. Fort, EDP Sciences, in pres
Galaxies in Present-day Clusters: Evolutionary Constraints from Their Distributions and Kinematics
We discuss evidence in local, present-day clusters of galaxies (from the
ENACS survey) about the way in which those clusters have evolved and about the
evolutionary relationships between the galaxies of different morphological
types in them. This evidence is complementary to that obtained from the study
of clusters at intermediate and high redshifts. We argue that the spatial
distribution and the kinematics of the various types of galaxies in and outside
substructures support the following picture.
The ELLIPTICAL AND S0 GALAXIES have been around for a long time and have
obtained an isotropic velocity distribution. The spatial distribution and
kinematics of the EARLY SPIRALS are consistent with the idea that many of their
kind have transformed into an S0, but that they have survived, most likely
because of their velocities. The distribution and kinematics of the LATE
SPIRALS are consistent with a picture in which they have been accreted fairly
recently. They have mildly radial orbits and hardly populate the central
regions, most likely because they suffer tidal disruption. Finally, the
distribution and kinematics of the GALAXIES IN SUBSTRUCTURES, when taken at
face value, imply tangential velocity anisotropy for these galaxies, but this
result may be (partly) due to the procedure by which these galaxies are
selected. A first attempt to take the effects of selection into account shows
that isotropic (or even mildly radial) orbits of subcluster galaxies cannot be
excluded.Comment: 7 pages, 3 figures. To appear in the proceedings of the IAU
colloquium No. 195: "Outskirts of Galaxy Clusters: intense life in the
suburbs", A. Diaferio ed. (invited contribution
Mass, velocity anisotropy, and pseudo phase-space density profiles of Abell 2142
Aim: We aim to compute the mass and velocity anisotropy profiles of Abell
2142 and, from there, the pseudo phase--space density profile and the
density slope - velocity anisotropy relation, and then to
compare them with theoretical expectations. Methods: The mass profiles were
obtained by using three techniques based on member galaxy kinematics, namely
the caustic method, the method of Dispersion - Kurtosis, and MAMPOSSt. Through
the inversion of the Jeans equation, it was possible to compute the velocity
anisotropy profiles. Results: The mass profiles, as well as the virial values
of mass and radius, computed with the different techniques agree with one
another and with the estimates coming from X-ray and weak lensing studies. A
concordance mass profile is obtained by averaging the lensing, X-ray, and
kinematics determinations. The cluster mass profile is well fitted by an NFW
profile with . The population of red and blue galaxies appear to
have a different velocity anisotropy configuration, since red galaxies are
almost isotropic, while blue galaxies are radially anisotropic, with a weak
dependence on radius. The profile for the red galaxy population agrees
with the theoretical results found in cosmological simulations, suggesting that
any bias, relative to the dark matter particles, in velocity dispersion of the
red component is independent of radius. The relation for red
galaxies matches the theoretical relation only in the inner region. The
deviations might be due to the use of galaxies as tracers of the gravitational
potential, unlike the non--collisional tracer used in the theoretical relation.Comment: 14 pages, 14 figures. Consolidated version including the Corrigendum
published on A&
The ESO Nearby Abell Cluster Survey. XIII. The orbits of the different types of galaxies in rich clusters
We study the orbits of the various types of galaxies observed in the ESO
Nearby Abell Cluster Survey. Galaxies within and outside substructures are
considered separately. We use the mass profile we determined from the
distribution and kinematics of the early-type galaxies (i.e. ellipticals,
excluding the brightest ones, and S0s) outside substructures; the latter were
assumed to be on isotropic orbits, which is supported by the shape of their
velocity distribution. The projected distribution and kinematics of the
galaxies of other types are used to search for equilibrium solutions in the
gravitational potential derived from the early-type galaxies, using the method
described by Binney and Mamon as implemented by Solanes and Salvador-Sole'. For
the brightest ellipticals we are not able to construct equilibrium solutions.
This is most likely the result of the formation history and the special
location of these galaxies at the centres of their clusters. The data for the
early spirals allow equilibrium solutions and are consistent with isotropic
orbits, although there is an apparent radial anisotropy at about 0.45 r200. For
the late spirals an equilibrium solution with isotropic orbits is rejected by
the data. The orbits are nearly isotropic within about 0.7 r200, but then
become increasingly radial outwards. Finally, the data for the galaxies in
substructures indicate that isotropic solutions are not acceptable, and
tangential orbits are indicated. We briefly discuss the possible implications
of these velocity-anisotropy profiles for current ideas of the evolution and
transformation of galaxies in clusters. (Abridged)Comment: A&A, accepted. 13 pages, 10 figure
RASS-SDSS Galaxy Cluster Survey. VII. On the Cluster Mass to Light ratio and the Halo Occupation Distribution
We explore the mass-to-light ratio in galaxy clusters and its relation to the
cluster mass. We study the relations among the optical luminosity (),
the cluster mass () and the number of cluster galaxies within
() in a sample of 217 galaxy clusters with confirmed 3D
overdensity. We correct for projection effects, by determining the galaxy
surface number density profile in our cluster sample. This is best fitted by a
cored King profile in low and intermediate mass systems. The core radius
decreases with cluster mass, and, for the highest mass clusters, the profile is
better represented by a generalized King profile or a cuspy Navarro, Frenk &
White profile. We find a very tight proportionality between and
, which, in turn, links the cluster mass-to-light ratio to the Halo
Occupation Distribution vs. . After correcting for
projection effects, the slope of the and
relations is found to be , close, but still significantly less
than unity. We show that the non-linearity of these relations cannot be
explained by variations of the galaxy luminosity distributions and of the
galaxy M/L with the cluster mass. We suggest that the nonlinear relation
between number of galaxies and cluster mass reflects an underlying nonlinear
relation between number of subhaloes and halo mass.Comment: 15 pages, 15 figures, accepted for publication in A&
The AGN fraction - velocity dispersion relation in clusters of galaxies
Some previous investigations have found that the fraction (f_AGN) of active
galactic nuclei (AGNs) is lower in clusters than in the field. This can result
from the suppression of galaxy-galaxy mergers in high-velocity dispersion
(sigma_v) clusters, if the formation and/or fueling of AGNs is directly related
to the merging process. We investigate the existence of a relation between
f_AGN and sigma_v in galaxy clusters in order to shed light on the formation
and evolution processes of AGNs and cluster galaxies. Using data from the Sloan
Digital Sky Survey we determine f_AGN and sigma_v for the clusters in two
samples, extracted from the catalogs of Popesso et al. (2006a) and Miller et
al. (2005), and excluding clusters with significant evidence for substructures.
We find a significant f_AGN-sigma_v anti-correlation. Clusters with sigma_v
lower and, respectively, higher than 500 km/s have AGN fractions of and , on average. The f_AGN-sigma_v relation can be
described by a model that assumes f_AGN is proportional to the galaxies merging
rate, plus a constant. Since f_AGN increases with decreasing sigma_v, AGNs are
likely to have played a significant role in heating the intra-cluster medium
and driving galaxy evolution in cluster precursors and groups.Comment: 4 pages, 3 figures, A&A Letter accepted for publicatio
- âŠ