4,646 research outputs found
Sunyaev-Zel'dovich Effects from Quasars in Galaxies and Groups
The energy fed by active galactic nuclei to the surrounding diffuse baryons
changes their amount, temperature, and distribution; so in groups and in member
galaxies it affects the X-ray luminosity and also the Sunyaev-Zel'dovich
effect. Here we compute how the latter is enhanced by the transient blastwave
driven by an active quasar, and is depressed when the equilibrium is recovered
with a depleted density. We constrain such depressions and enhancements with
the masses of relic black holes in galaxies and the X-ray luminosities in
groups. We discuss how all these linked observables can tell the quasar
contribution to the thermal history of the baryons pervading galaxies and
groups.Comment: 4 pages, 3 figures, uses REVTeX4 and emulateapj.cls. Accepted by ApJ
Galaxy Cluster Shapes and Systematic Errors in H0 Measured by the Sunyaev-Zel'dovich Effect
Imaging of the Sunyaev-Zel'dovich (SZ) effect in galaxy clusters combined
with cluster plasma x-ray diagnostics can measure the cosmic distance scale to
high redshift. Projecting the inverse-Compton scattering and x-ray emission
along the cluster line-of-sight introduces systematic errors in the Hubble
constant, H0, because the true shape of the cluster is not known. I present a
study of the systematic errors in the value of H0, as determined by the x-ray
and SZ properties of theoretical samples of triaxial isothermal ``beta'' model
clusters, caused by projection effects and observer orientation. I calculate
estimates for H0 for each cluster based on their large and small apparent
angular core radii and their arithmetic mean. I demonstrate that the estimates
for H0 for a sample of 25 clusters have 99.7% confidence intervals for the mean
estimated H0 analyzing the clusters using either their large or mean angular
core radius are within 14% of the ``true'' (assumed) value of H0 (and enclose
it), for a triaxial beta model cluster sample possessing a distribution of
apparent x-ray cluster ellipticities consistent with that of observed x-ray
clusters. This limit on the systematic error in H0 caused by cluster shape
assumes that each sample beta model cluster has fixed shape; deviations from
constant shape within the clusters may introduce additional uncertainty or bias
into this result.Comment: Accepted for publication in the Astrophysical Journal, 24 March 1998;
4 pages, 2 figure
Markov Chain Monte Carlo joint analysis of Chandra X-ray imaging spectroscopy and Sunyaev-Zeldovich Effect data
X-ray and Sunyaev-Zeldovich Effect data can be combined to determine the
distance to galaxy clusters. High-resolution X-ray data are now available from
the Chandra Observatory, which provides both spatial and spectral information,
and Sunyaev-Zeldovich Effect data were obtained from the BIMA and OVRO arrays.
We introduce a Markov chain Monte Carlo procedure for the joint analysis of
X-ray and Sunyaev-Zeldovich Effect data. The advantages of this method are the
high computational efficiency and the ability to measure simultaneously the
probability distribution of all parameters of interest, such as the spatial and
spectral properties of the cluster gas and also for derivative quantities such
as the distance to the cluster. We demonstrate this technique by applying it to
the Chandra X-ray data and the OVRO radio data for the galaxy cluster Abell
611. Comparisons with traditional likelihood-ratio methods reveal the
robustness of the method. This method will be used in follow-up papers to
determine the distances to a large sample of galaxy clusters.Comment: ApJ accepted, scheduled for ApJ 10 October 2004, v614 issue. Title
changed, added more convergence diagnostic tests, Figure 7 converted to lower
resolution for easier download, other minor change
The Variation of Gas Mass Distribution in Galaxy Clusters: Effects of Preheating and Shocks
We investigate the origin of the variation of the gas mass fraction in the
core of galaxy clusters, which was indicated by our work on the X-ray
fundamental plane. The adopted model supposes that the gas distribution
characterized by the slope parameter is related to the preheated temperature.
Comparison with observations of relatively hot (~> 3 keV) and low redshift
clusters suggests that the preheated temperature is about 0.5-2 keV, which is
higher than expected from the conventional galactic wind model and possibly
suggests the need for additional heating such as quasars or gravitational
heating on the largest scales at high redshift. The dispersion of the preheated
temperature may be attributed to the gravitational heating in subclusters. We
calculate the central gas fraction of a cluster from the gas distribution,
assuming that the global gas mass fraction is constant within a virial radius
at the time of the cluster collapse. We find that the central gas density thus
calculated is in good agreement with the observed one, which suggests that the
variation of gas mass fraction in cluster cores appears to be explained by
breaking the self-similarity in clusters due to preheated gas. We also find
that this model does not change major conclusions on the fundamental plane and
its cosmological implications obtained in previous papers, which strongly
suggests that not only for the dark halo but also for the intracluster gas the
core structure preserves information about the cluster formation.Comment: 17 pages, to be published in Ap
Measurements of Sunyaev-Zel'dovich Effect Scaling Relations for Clusters of Galaxies
We present new measurements of the Sunyaev-Zel'dovich (SZ) effect from
clusters of galaxies using the Sunyaev-Zel'dovich Infrared Experiment (SuZIE
II). We combine these new measurements with previous cluster observations with
the SuZIE instrument to form a sample of 15 clusters of galaxies. For this
sample we calculate the central Comptonization, y, and the integrated SZ flux
decrement, S, for each of our clusters. We find that the integrated SZ flux is
a more robust observable derived from our measurements than the central
Comptonization due to inadequacies in the spatial modelling of the
intra-cluster gas with a standard Beta model. This is highlighted by comparing
our central Comptonization results with values calculated from measurements
using the BIMA and OVRO interferometers. On average, the SuZIE calculated
central Comptonizations are approximately 60% higher in the cooling flow
clusters than the interferometric values, compared to only approximately 12%
higher in the non-cooling flow clusters. We believe this discrepancy to be in
large part due to the spatial modelling of the intra-cluster gas. From our
cluster sample we construct y-T and S-T scaling relations. The y-T scaling
relation is inconsistent with what we would expect for self-similar clusters;
however this result is questionable because of the large systematic uncertainty
in the central Comptonization. The S-T scaling relation has a slope and
redshift evolution consistent with what we expect for self-similar clusters
with a characteristic density that scales with the mean density of the
universe. We rule out zero redshift evolution of the S-T relation at 90%
confidence.Comment: Accepted to Astrophysical Journal. 52 pages, 14 tables, 7 figures
;replaced to match ApJ accepted versio
Dark matter halo creation in moving barrier models
In hierarchical models, the time derivative of the halo mass function may be
thought of as the difference of two terms - a creation term, which describes
the increase in the number of haloes of mass m from mergers of less massive
objects, and a destruction term, which describes the decrease in the number of
m-haloes as these merge with other haloes, creating more massive haloes as a
result. In models where haloes form from a spherical collapse, the distribution
of halo creation times can be estimated from the same formalism which is used
to estimate halo abundances: the constant-barrier excursion-set approach. In
the excursion set approach, moving, rather than constant-barriers, are
necessary for estimating halo abundances when the collapse is triaxial. We show
how the corresponding estimates are modified by providing analytic estimates of
the creation rate for a wide range of halo masses. We then show that these
moving-barrier based predictions are in better agreement with measurements in
numerical simulations than are the corresponding predictions of the spherical
collapse model. These results should be useful for studies of merger-driven
star-formation rates and AGN activity. We also present a similar study of
creation of haloes conditioned on belonging to an object of a certain mass
today, and reach similar conclusions - the moving barrier based estimates are
in substantially better agreement with the simulations. This part of the study
may be useful for understanding the tendency for the oldest stars to exist in
the most massive objects.Comment: MNRAS accepted, 17 pages, 10 figure
Coherent properties of nano-electromechanical systems
We study the properties of a nano-electromechanical system in the coherent
regime, where the electronic and vibrational time scales are of the same order.
Employing a master equation approach, we obtain the stationary reduced density
matrix retaining the coherences between vibrational states. Depending on the
system parameters, two regimes are identified, characterized by either () an
{\em effective} thermal state with a temperature {\em lower} than that of the
environment or () strong coherent effects. A marked cooling of the
vibrational degree of freedom is observed with a suppression of the vibron Fano
factor down to sub-Poissonian values and a reduction of the position and
momentum quadratures.Comment: 12 pages, 11 figure
Kinetic Sunyaev-Zeldovich effect from galaxy cluster rotation
We show how the temperature and the polarisation of the cosmic microwave
background are affected by bulk rotation of clusters of galaxies owing to the
kinetic Sunyaev-Zeldovich effect. The main effects of rotation are (i) a shift
of the position of the peak of the temperature fluctuation relative to the
center of the cluster by a few percent of the core radius and (ii) a tilt of
the direction of the plane of linear polarisation by several degrees.Comment: 9 pages, 4 figures, submitted A&
A Deep Chandra Observation of the Distant Galaxy Cluster MS1137.5+6625
We present results from a deep Chandra observation of MS1137.5+66, a distant
(z=0.783) and massive cluster of galaxies. Only a few similarly massive
clusters are currently known at such high redshifts; accordingly, this
observation provides much-needed information on the dynamical state of these
rare systems. The cluster appears both regular and symmetric in the X-ray
image. However, our analysis of the spectral and spatial X-ray data in
conjunction with interferometric Sunyaev-Zel'dovich effect data and published
deep optical imaging suggests the cluster has a fairly complex structure. The
angular diameter distance we calculate from the Chandra and Sunyaev-Zel'dovich
effect data assuming an isothermal, spherically symmetric cluster implies a low
value for the Hubble constant for which we explore possible explanations.Comment: 16 pages, 6 figures, submitted to Ap
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