621 research outputs found
Simulating Astro-H Observations of Sloshing Gas Motions in the Cores of Galaxy Clusters
Astro-H will be the first X-ray observatory to employ a high-resolution
microcalorimeter, capable of measuring the shift and width of individual
spectral lines to the precision necessary for estimating the velocity of the
diffuse plasma in galaxy clusters. This new capability is expected to bring
significant progress in understanding the dynamics, and therefore the physics,
of the intracluster medium. However, because this plasma is optically thin,
projection effects will be an important complicating factor in interpreting
future Astro-H measurements. To study these effects in detail, we performed an
analysis of the velocity field from simulations of a galaxy cluster
experiencing gas sloshing, and generated synthetic X-ray spectra, convolved
with model Astro-H Soft X-ray Spectrometer (SXS) responses. We find that the
sloshing motions produce velocity signatures that will be observable by Astro-H
in nearby clusters: the shifting of the line centroid produced by the
fast-moving cold gas underneath the front surface, and line broadening produced
by the smooth variation of this motion along the line of sight. The line shapes
arising from inviscid or strongly viscous simulations are very similar,
indicating that placing constraints on the gas viscosity from these
measurements will be difficult. Our spectroscopic analysis demonstrates that,
for adequate exposures, Astro-H will be able to recover the first two moments
of the velocity distribution of these motions accurately, and in some cases
multiple velocity components may be discerned. The simulations also confirm the
importance of accurate treatment of PSF scattering in the interpretation of
Astro-H/SXS spectra of cluster plasmas.Comment: 27 pages, 20 figures, submitted to the Astrophysical Journa
The Dark Matter Distribution in Galaxy Cluster Cores
Determining the structure of galaxy clusters is essential for an
understanding of large scale structure in the universe, and may hold important
clues to the identity and nature of dark matter particles. Moreover, the core
dark matter distribution may offer insight into the structure formation
process. Unfortunately, cluster cores also tend to be the site of complicated
astrophysics. X-ray imaging spectroscopy of relaxed clusters, a standard
technique for mapping their dark matter distributions, is often complicated by
the presence of their putative ``cooling flow'' gas, and the dark matter
profile one derives for a cluster is sensitive to assumptions made about the
distribution of this gas. Here we present a statistical analysis of these
assumptions and their effect on our understanding of dark matter in galaxy
clusters.Comment: Poster contribution to the 13th Annual Astrophysics Conference in
Maryland, The Emergence of Cosmic Structure; 4 page
The Outer Limits of Galaxy Clusters: Observations to the Virial Radius with Suzaku, XMM, and Chandra
The outskirts of galaxy clusters, near the virial radius, remain relatively
unexplored territory and yet are vital to our understanding of cluster growth,
structure, and mass. In this presentation, we show the first results from a
program to constrain the state of the outer intracluster medium (ICM) in a
large sample of galaxy clusters, exploiting the strengths of three
complementary X-ray observatories: Suzaku (low, stable background), XMM-Newton
(high sensitivity), and Chandra (good spatial resolution). By carefully
combining observations from the cluster core to beyond r_200, we are able to
identify and reduce systematic uncertainties that would impede our spatial and
spectral analysis using a single telescope. Our sample comprises nine clusters
at z ~ 0.1-0.2 fully covered in azimuth to beyond r_200, and our analysis
indicates that the ICM is not in hydrostatic equilibrium in the cluster
outskirts, where we see clear azimuthal variations in temperature and surface
brightness. In one of the clusters, we are able to measure the diffuse X-ray
emission well beyond r_200, and we find that the entropy profile and the gas
fraction are consistent with expectations from theory and numerical
simulations. These results stand in contrast to recent studies which point to
gas clumping in the outskirts; the extent to which differences of cluster
environment or instrumental effects factor in this difference remains unclear.
From a broader perspective, this project will produce a sizeable fiducial data
set for detailed comparison with high-resolution numerical simulations.Comment: 8 pages, 6 figures. To appear in the proceedings of the Suzaku 2011
Conference, "Exploring the X-ray Universe: Suzaku and Beyond.
Detection of x-rays from galaxy groups associated with the gravitationally lensed systems PG 1115+080 and B1422+231
Gravitational lenses that produce multiple images of background quasars can
be an invaluable cosmological tool. Deriving cosmological parameters, however,
requires modeling the potential of the lens itself. It has been estimated that
up to a quarter of lensing galaxies are associated with a group or cluster
which perturbs the gravitational potential. Detection of X-ray emission from
the group or cluster can be used to better model the lens. We report on the
first detection in X-rays of the group associated with the lensing system PG
1115+080 and the first X-ray image of the group associated with the system
B1422+231. We find a temperature and rest-frame luminosity of 0.8 +/- 0.1 keV
and 7 +/- 2 x 10^{42} ergs/s for PG 1115+080 and 1.0 +infty/-0.3 keV and 8 +/-
3 x 10^{42} ergs/s for B1422+231. We compare the spatial and spectral
characteristics of the X-ray emission to the properties of the group galaxies,
to lens models, and to the general properties of groups at lower redshift.Comment: Accepted for publication in ApJ. 17 pages, 5 figures. Minor changes
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