32 research outputs found
Numerical simulations of bent, disrupted radio jets
We present preliminary results from three-dimensional hydrodynamical simulations designed to investigate the physics of jet bending and disruption. The specific scenario considered here involves a mildly supersonic jet crossing a contact discontinuity at the interface between the interstellar medium (ISM) and the intercluster medium (ICM) and then encountering a cross-wind in the ICM. The resultant morphologies show many of the features observed in radio sources including jet flaring, bending, and extended tails
A numerical simulation of galaxy subcluster mergers
We present preliminary results of a 3-D numerical simulation of two merging subclusters of galaxies. By self-consistently modelling the intracluster gas and dark matter dynamics, we hope to gain insight as to how the dynamics of both relate to such observables as the cluster x-ray emission, radio source morphology, and velocity dispersions
Weak Gravitational Lensing and Cluster Mass Estimates
Hierarchical theories of structure formation predict that clusters of
galaxies should be embedded in a web like structure, with filaments emanating
from them to large distances. The amount of mass contained within such
filaments near a cluster can be comparable to the collapsed mass of the cluster
itself. Diffuse infalling material also contains a large amount of mass. Both
these components can contribute to the cluster weak lensing signal. This
``projection bias'' is maximized if a filament lies close to the line-of-sight
to a cluster. Using large--scale numerical simulations of structure formation
in a cosmological constant dominated cold dark matter model, we show that the
projected mass typically exceeds the actual mass by several tens of percent.
This effect is significant for attempts to estimate cluster masses through weak
lensing observations, and will affect weak lensing surveys aimed at
constructing the cluster mass function.Comment: 4 pages, 3 figures. LaTeX2e, uses emulateapj.sty and onecolfloat.sty.
To be submitted to the Astrophysical Journal Letter
Numerical models of jet disruption in cluster cooling flows
We present a coherent picture for the formation of the observed diverse radio morphological structures in dominant cluster galaxies based on the jet Mach number. Realistic, supersonic, steady-state cooling flow atmospheres are evolved numerically and then used as the ambient medium through which jets of various properties are propagated. Low Mach number jets effectively stagnate due to the ram pressure of the cooling flow atmosphere while medium Mach number jets become unstable and disrupt in the cooling flow to form amorphous structures. High Mach number jets manage to avoid disruption and are able to propagate through the cooling flow
The Evolution of X-Ray Clusters in a Cold Plus Hot Dark Matter Universe
We present the first self-consistently computed results on the evolution of
X-ray properties of galaxy clusters in a Cold + Hot Dark Matter (CHDM) model.
We have performed a hydrodynamic plus N-body simulation for the COBE-compatible
CHDM model with standard mass components: Omega(hot) = 0.3, Omega(cold) = 0.6
and Omega(baryon) = 0.1 (h = 0.5). In contrast with the CDM model, which fails
to reproduce the observed temperature distribution function dN/dT (Bryan et al.
1994b), the CHDM model fits the observational dN/dT quite well. Our results on
X-ray luminosity are less firm but even more intriguing. We find that the
resulting X-ray luminosity functions at redshifts z = 0.0, 0.2, 0.4, 0.7 are
well fit by observations, where they overlap. The fact that both temperatures
and luminosities provide a reasonable fit to the available observational data
indicates that, unless we are missing some essential physics, there is neither
room nor need for a large fraction of gas in rich clusters: 10% (or less) in
baryons is sufficient to explain their X-ray properties. We also see a tight
correlation between X-ray luminosity and gas temperature.Comment: 11 pages, 3 figures uuencoded postscript file, (92 kb), accepted for
publication in Astrophysical Journal Letters. Also available via anonymous
ftp at zeus.ncsa.uiuc.edu in gc3/publications/gc3005, LCA01
The Observational Consequences of Merging Clusters of Galaxies
We present an observational analysis of numerical simulations of galaxy
cluster mergers. We identify several observational signatures of recent merger
activity, and quantitatively assess the uncertainty introduced into cluster
mass estimates when invoking the commonly held assumptions of hydrostatic
equilibrium, virial equilibrium, spherical symmetry and isothermality. We find
that mergers result in multiple X-ray peaks, long-lived elongation of the X-ray
emission as well as isophotal twisting and centroid shifting to a degree
consistent with recent observations. We also find an enlargement of the X-ray
core relative to the dark matter core. Mergers result in non-isothermal
clusters exhibiting observable inhomogeneities in the emission-weighted X-ray
temperature of several keV on linear scales of less than 0.5 Mpc. The resulting
gas dynamics are extremely complex, and we present an example of what might be
observed by a high resolution X-ray spectrograph. We further speculate that the
gas dynamics, via shocks, bulk flows and turbulence, play an important role in
the evolution of cluster galaxies and associated radio sources, particularly
wide-angle tailed (WAT) sources and radio halos. We find that X-ray based by
cluster mass estimates made under equilibrium assumptions can be uncertain 50\%
or more in the first 2 Gyrs after a merger and by up to 25\% after 2 Gyrs
depending on the details of the analysis and projection effects. Uncertainties
can be considerably larger if the temperature is not well constrained.Comment: 42 pages, Latex, 23 postscript figures, Accepted for publication in
Ap
Redshifts and Optical Properties for a Statistically Complete Sample of Poor Galaxy Clusters
From the poor cluster catalog of White et al. (1996), we define a sample of
71 optically-selected poor galaxy clusters. The surface-density enhance- ment
we require for our clusters falls between that of the loose associations of
Turner and Gott (1976) and the Hickson compact groups (Hickson, 1982). We
review the selection biases and determine the statistical comleteness of the
sample. For this sample, we report new velocity measurements made with the ARC
3.5-m Dual-Imaging spectrograph and the 2.3-m Steward Observatory MX fiber
spectrograph. Combining our own measurements with those from the literature, we
examine the velocity distributions, velocity dispersions, and 1-d velocity
substructure for our poor cluster sample, and compare our results to other poor
cluster samples. We find that approximately half of the sample may have
significant 1-d velocity substructure. The optical morphology, large-scale
environment, and velocity field of many of these clusters is indicative of
young, dynamically evolving systems. In future papers, we will use this sample
to derive the poor cluster X-ray luminosity function and gas mass function (see
astro-ph/9606120), and will examine the optical/X-ray properties of the
clusters in more detail.Comment: 15 pages LaTeX, 3 tables, 5 postscript figures. To appear in the
August 1996 Astronomical Journa
The Effect of the Cosmic Web on Cluster Weak Lensing Mass Estimates
In modern hierarchical theories of structure formation, rich clusters of
galaxies form at the vertices of a weblike distribution of matter, with
filaments emanating from them to large distances and with smaller objects
forming and draining in along these filaments. The amount of mass contained in
structure near the cluster can be comparable to the collapsed mass of the
cluster itself. As the lensing kernel is quite broad along the line of sight
around cluster lenses with typical redshifts near z=0.5, structures many Mpc
away from the cluster are essentially at the same location as the cluster
itself, when considering their effect on the cluster's weak lensing signal. We
use large-scale numerical simulations of structure formation in a
Lambda-dominated cold dark matter model to quantify the effect that large-scale
structure near clusters has upon the cluster masses deduced from weak lensing
analysis. A correction for the scatter in possible observed lensing masses
should be included when interpreting mass functions from weak lensing surveys.Comment: 14 pages, 11 figures. LaTeX2e, uses emulateapj.sty and
onecolfloat.st