127 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 relation between velocity dispersion and mass in simulated clusters of galaxies: dependence on the tracer and the baryonic physics
[Abridged] We present an analysis of the relation between the masses of
cluster- and group-sized halos, extracted from CDM cosmological N-body
and hydrodynamic simulations, and their velocity dispersions, at different
redshifts from to . The main aim of this analysis is to understand
how the implementation of baryonic physics in simulations affects such
relation, i.e. to what extent the use of the velocity dispersion as a proxy for
cluster mass determination is hampered by the imperfect knowledge of the
baryonic physics. In our analysis we use several sets of simulations with
different physics implemented. Velocity dispersions are determined using three
different tracers, DM particles, subhalos, and galaxies.
We confirm that DM particles trace a relation that is fully consistent with
the theoretical expectations based on the virial theorem and with previous
results presented in the literature. On the other hand, subhalos and galaxies
trace steeper relations, and with larger values of the normalization. Such
relations imply that galaxies and subhalos have a per cent velocity
bias relative to the DM particles, which can be either positive or negative,
depending on halo mass, redshift and physics implemented in the simulation.
We explain these differences as due to dynamical processes, namely dynamical
friction and tidal disruption, acting on substructures and galaxies, but not on
DM particles. These processes appear to be more or less effective, depending on
the halo masses and the importance of baryon cooling, and may create a
non-trivial dependence of the velocity bias and the \soneD--\Mtwo relation
on the tracer, the halo mass and its redshift.
These results are relevant in view of the application of velocity dispersion
as a proxy for cluster masses in ongoing and future large redshift surveys.Comment: 13 pages, 16 figures. Minor modifications to match the version in
press on MNRA
Dependency of halo concentration on mass, redshift and fossilness in Magneticum hydrodynamic simulations
We study the dependency of the concentration on mass and redshift using three
large N-body cosmological hydrodynamic simulations carried out by the
Magneticum project. We constrain the slope of the mass-concentration relation
with an unprecedented mass range for hydrodynamic simulations and find a
negative trend on the mass-concentration plane and a slightly negative redshift
dependency, in agreement with observations and other numerical works. We also
show how the concentration correlates with the fossil parameter, defined as the
stellar mass ratio between the central galaxy and the most massive satellite,
in agreement with observations. We find that haloes with high fossil parameter
have systematically higher concentration and investigate the cause in two
different ways. First we study the evolution of haloes that lives unperturbed
for a long period of time, where we find that the internal region keeps
accreting satellites as the fossil parameter increases and the scale radius
decreases (which increases the concentration). We also study the dependency of
the concentration on the virial ratio and the energy term from the surface
pressure . We conclude that fossil objects have higher concentration
because they are dynamically relaxed, with no in-fall/out-fall material and had
time to accrete their satellites.Comment: 13 pages, 10 figure
Gone after one orbit: How cluster environments quench galaxies
The effect of galactic orbits on a galaxy's internal evolution within a
galaxy cluster environment has been the focus of heated debate in recent years.
To understand this connection, we use both the Gpc) and the
Gpc boxes from the cosmological hydrodynamical simulation set Magneticum
Pathfinder. We investigate the velocity-anisotropy, phase space, and the
orbital evolution of up to resolved satellite galaxies
within our sample of 6776 clusters with at low redshift, which we also trace back in time. In
agreement with observations, we find that star-forming satellite galaxies
inside galaxy clusters are characterised by more radially dominated orbits,
independent of cluster mass. Furthermore, the vast majority of star-forming
satellite galaxies stop forming stars during their first passage. We find a
strong dichotomy both in line-of-sight and radial phase space between
star-forming and quiescent galaxies, in line with observations. The tracking of
individual orbits shows that the star-formation of almost all satellite
galaxies drops to zero within after in-fall. Satellite
galaxies that are able to remain star-forming longer are characterised by
tangential orbits and high stellar mass. All this indicates that in galaxy
clusters the dominant quenching mechanism is ram-pressure stripping.Comment: 22 pages, 16 figures, accepted by MNRA
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