1,583 research outputs found
Inverse Compton scattering in mildly relativistic plasma
We investigated the effect of inverse Compton scattering in mildly
relativistic static and moving plasmas with low optical depth using Monte Carlo
simulations, and calculated the Sunyaev-Zel'dovich effect in the cosmic
background radiation. Our semi-analytic method is based on a separation of
photon diffusion in frequency and real space. We use Monte Carlo simulation to
derive the intensity and frequency of the scattered photons for a monochromatic
incoming radiation. The outgoing spectrum is determined by integrating over the
spectrum of the incoming radiation using the intensity to determine the correct
weight. This method makes it possible to study the emerging radiation as a
function of frequency and direction. As a first application we have studied the
effects of finite optical depth and gas infall on the Sunyaev-Zel'dovich effect
(not possible with the extended Kompaneets equation) and discuss the parameter
range in which the Boltzmann equation and its expansions can be used. For high
temperature clusters ( keV) relativistic corrections based
on a fifth order expansion of the extended Kompaneets equation seriously
underestimate the Sunyaev-Zel'dovich effect at high frequencies. The
contribution from plasma infall is less important for reasonable velocities. We
give a convenient analytical expression for the dependence of the cross-over
frequency on temperature, optical depth, and gas infall speed. Optical depth
effects are often more important than relativistic corrections, and should be
taken into account for high-precision work, but are smaller than the typical
kinematic effect from cluster radial velocities.Comment: LateX, 30 pages and 11 figures. Accepted for publication in the
Astrophysical Journa
The gas distribution in the high-redshift cluster MS 1054-0321
We investigate the gas mass distribution in the high redshift cluster MS
1054-0321 using Chandra X-ray and OCRA SZ effect data. We use a superposition
of offset -type models to describe the composite structure of MS
1054-0321. We find gas mass fractions f_{gas}^\rm{X\mbox{-}ray} =
0.087_{-0.001}^{+0.005} and f_{gas}^\rm{SZ} = 0.094_{-0.001}^{+0.003} for
the (main) eastern component of MS 1054-0321 using X-ray or SZ data, but
f_{gas}^\rm{X\mbox{-}ray} = 0.030 _{-0.014}^{+0.010} for the western
component. The gas mass fraction for the eastern component is in agreement with
some results reported in the literature, but inconsistent with the cosmic
baryon fraction. The low gas mass fraction for the western component is likely
to be a consequence of gas stripping during the ongoing merger. The gas mass
fraction of the integrated system is : we suggest that
the missing baryons from the western component are present as hot diffuse gas
which is poorly represented in existing X-ray images. The missing gas could
appear in sensitive SZ maps.Comment: 12 pages, 4 figures, and 5 table
Determination of cosmological parameters: an introduction for non-specialists
I start by defining the cosmological parameters and
. Then I show how the age of the universe depends on them,
followed by the evolution of the scale parameter of the universe for various
values of the density parameters. Then I define strategies for measuring them,
and show the results for the recent determination of these parameters from
measurements on supernovas of type 1a. Implications for particle physics is
briefly discussed at the end.Comment: 12 pages, Latex with epsf.sty. Invited talk at the ``Discussion
meeting on Recent Developments in Neutrino Physics'', held at the Physical
Research Laboratory, Ahmedabad, February 2--4, 199
Unmasking the Active Galactic Nucleus in PKS J2310-437
PKS J2310-437 is an AGN with bright X-ray emission relative to its weak radio
emission and optical continuum. It is believed that its jet lies far enough
from the line of sight that it is not highly relativistically beamed. It thus
provides an extreme test of AGN models. We present new observations aimed at
refining the measurement of the source's properties. In optical photometry with
the NTT we measure a central excess with relatively steep spectrum lying above
the bright elliptical galaxy emission, and we associate the excess wholly or in
part with the AGN. A new full-track radio observation with the ATCA finds that
the core 8.64GHz emission has varied by about 20 per cent over 38 months, and
improves the mapping of the weak jet. With Chandra we measure a
well-constrained power-law spectral index for the X-ray core, uncontaminated by
extended emission from the cluster environment, with a negligible level of
intrinsic absorption. Weak X-ray emission from the resolved radio jet is also
measured. Our analysis suggests that the optical continuum in this radio galaxy
has varied by at least a factor of four over a timescale of about two years,
something that should be testable with further observations. We conclude that
the most likely explanation for the bright central X-ray emission is
synchrotron radiation from high-energy electrons.Comment: 7 pages, 12 figure
Constraints in Cosmological Parameter Space from the Sunyaev-Zel'dovich Effect and Thermal Bremsstrahlung
We discuss how the space of possible cosmological parameters is constrained by the angular diameter distance function, D_A(z), as measured using the SZ/X-ray method which combines Sunyaev-Zel'dovich (SZ) effect and X-ray brightness data for clusters of galaxies. New X-ray satellites, and ground-based interferometers dedicated to SZ observations, should soon lead to D_A(z) measurements limited by systematic rather than random error. We analyze the systematic and random error budgets to make a realistic estimate of the accuracy achievable in the determination of (Omega_m,Lambda,h), the density parameters of matter and cosmological constant, and the dimensionless Hubble constant, using D_A(z) derived from the SZ/X-ray method, and the position of the first ``Doppler'' peak in the cosmic microwave background fluctuations. We briefly study the effect of systematic errors. We find that Omega_m, Lambda, and w are affected, but h is not by systematic errors which grow with redshift. With as few as 70 clusters, each providing a measurement of D_A(z) with a 7% random and 5% systematic error, Omega_m can be constrained to +/-0.2, Lambda to +/-0.2, and h to +/-0.11 (all at 3 sigma). We also estimate constraints for the alternative three-parameter set (Omega_m,w,h), where w is the equation of state parameter. The measurement of D_A(z) provides constraints complementary to those from the number density of clusters in redshift space. A sample of 70 clusters (D_A measured with the same accuracy as before) combined with cluster evolution results (or a known matter density), can constrain w within +/-0.45 (at 3 sigma). Studies of X-ray and SZ properties of clusters of galaxies promise an independent and powerful test for cosmological parameters
A Merger Scenario for the Dynamics of Abell 665
We present new redshift measurements for 55 galaxies in the vicinity of the
rich galaxy cluster Abell 665. When combined with results from the literature,
we have good velocity measurements for a sample of 77 confirmed cluster members
from which we derive the cluster's redshift z=0.1829 +/- 0.0005 and
line-of-sight velocity dispersion of 1390 +/- 120 km/s. Our analysis of the
kinematical and spatial data for the subset of galaxies located within the
central 750 kpc reveals only subtle evidence for substructure and
non-Gaussianity in the velocity distribution. We find that the brightest
cluster member is not moving significantly relative to the other galaxies near
the center of the cluster. On the other hand, our deep ROSAT high resolution
image of A665 shows strong evidence for isophotal twisting and centroid
variation, thereby confirming previous suggestions of significant substructure
in the hot X-ray--emitting intracluster gas. In light of this evident
substructure, we have compared the optical velocity data with N-body
simulations of head-on cluster mergers. We find that a merger of two similar
mass subclusters (mass ratios of 1:1 or 1:2) seen close to the time of
core-crossing produces velocity distributions that are consistent with that
observed.Comment: 30 pages and 7 figures. Accepted by the Astrophysical Journal Full
resoultion figures 1 and 3 available in postscript at
http://www.physics.rutgers.edu/~percy/A665paper.htm
Numerical simulations of colliding jets in an external wind:application to 3C 75
The radio galaxy 3C 75 is remarkable because it contains a pair of radio-loud active galaxies, each of which produces a two-sided jet, with the jet beams appearing to collide and merge to the west of the galaxies. Motivated by 3C 75, we have conducted three-dimensional hydrodynamic simulations of jet collisions. We have extended previous studies by modelling the physical properties of the cluster atmosphere, including an external wind, and using realistic jet powers obtained from observational data. We are able to produce a morphology similar to that of 3C 75. The simulations imply that direct contact between the bulk jet flows on the west of the source is required to produce a morphology consistent with 3C 75. We quantify how the merging jets decelerate, how the wind deflects the jets and cocoons, the entrainment of intra-cluster material into the cocoons, the cocoon energetics, and how the jet interactions generate enstrophy. By comparing simulations of pairs of two-sided jets with those of single two-sided sources, we determine how the interaction between two bipolar jets changes their evolution. The unprecedented sensitivity and angular resolution of upcoming observatories will lead to the detection of many more complex sources at high redshift, where interacting jets are expected to be more numerous. The morphology of these complex sources can provide significant insight into the conditions in their environments
The Sunyaev-Zel'dovich effects from a cosmological hydrodynamical simulation: large-scale properties and correlation with the soft X-ray signal
Using the results of a cosmological hydrodynamical simulation of the
concordance LambdaCDM model, we study the global properties of the
Sunyaev-Zel'dovich (SZ) effects, both considering the thermal (tSZ) and the
kinetic (kSZ) component. The simulation follows gravitation and gas dynamics
and includes also several physical processes that affect the baryonic
component, like a simple reionization scenario, radiative cooling, star
formation and supernova feedback. Starting from the outputs of the simulation
we create mock maps of the SZ signals due to the large structures of the
Universe integrated in the range 0 < z < 6. We predict that the Compton
y-parameter has an average value of (1.19 +/- 0.32) 10^-6 and is lognormally
distributed in the sky; half of the whole signal comes from z < 1 and about 10
per cent from z > 2. The Doppler b-parameter shows approximately a normal
distribution with vanishing mean value and a standard deviation of 1.6 10^-6,
with a significant contribution from high-redshift (z > 3) gas. We find that
the tSZ effect is expected to dominate the primary CMB anisotropies for l >~
3000 in the Rayleigh-Jeans limit, while interestingly the kSZ effect dominates
at all frequencies at very high multipoles (l >~ 7 10^4). We also analyse the
cross-correlation between the two SZ effects and the soft (0.5-2 keV) X-ray
emission from the intergalactic medium and we obtain a strong correlation
between the three signals, especially between X-ray emission and tSZ effect
(r_l ~ 0.8-0.9) at all angular scales.Comment: 12 pages, 15 figures. Accepted for publication in MNRAS. Minor
changes, added reference
Constraints on the Energy Content of the Universe from a Combination of Galaxy Cluster Observables
We demonstrate that constraints on cosmological parameters from the
distribution of clusters as a function of redshift (dN/dz) are complementary to
accurate angular diameter distance (D_A) measurements to clusters, and their
combination significantly tightens constraints on the energy density content of
the Universe. The number counts can be obtained from X-ray and/or SZ
(Sunyaev-Zel'dovich effect) surveys, and the angular diameter distances can be
determined from deep observations of the intra-cluster gas using their thermal
bremsstrahlung X-ray emission and the SZ effect. We combine constraints from
simulated cluster number counts expected from a 12 deg^2 SZ cluster survey and
constraints from simulated angular diameter distance measurements based on the
X-ray/SZ method assuming a statistical accuracy of 10% in the angular diameter
distance determination of 100 clusters with redshifts less than 1.5. We find
that Omega_m can be determined within about 25%, Omega_Lambda within 20%, and w
within 16%. We show that combined dN/dz + D_A constraints can be used to
constrain the different energy densities in the Universe even in the presence
of a few percent redshift dependent systematic error in D_A. We also address
the question of how best to select clusters of galaxies for accurate diameter
distance determinations. We show that the joint dN/dz + D_A constraints on
cosmological parameters for a fixed target accuracy in the energy density
parameters are optimized by selecting clusters with redshift upper cut--offs in
the range 0.5 < z < 1.Comment: LateX, 6 pages, 5 figures. Accepted for publication in The
Astrophysical Journa
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