63 research outputs found
The Metallicity of the Intracluster Medium Over Cosmic Time: Further Evidence for Early Enrichment
We use Chandra X-ray data to measure the metallicity of the intracluster
medium (ICM) in 245 massive galaxy clusters selected from X-ray and
Sunyaev-Zel'dovich (SZ) effect surveys, spanning redshifts .
Metallicities were measured in three different radial ranges, spanning cluster
cores through their outskirts. We explore trends in these measurements as a
function of cluster redshift, temperature, and surface brightness "peakiness"
(a proxy for gas cooling efficiency in cluster centers). The data at large
radii (0.5--1 ) are consistent with a constant metallicity, while at
intermediate radii (0.1-0.5 ) we see a late-time increase in
enrichment, consistent with the expected production and mixing of metals in
cluster cores. In cluster centers, there are strong trends of metallicity with
temperature and peakiness, reflecting enhanced metal production in the
lowest-entropy gas. Within the cool-core/sharply peaked cluster population,
there is a large intrinsic scatter in central metallicity and no overall
evolution, indicating significant astrophysical variations in the efficiency of
enrichment. The central metallicity in clusters with flat surface brightness
profiles is lower, with a smaller intrinsic scatter, but increases towards
lower redshifts. Our results are consistent with other recent measurements of
ICM metallicity as a function of redshift. They reinforce the picture implied
by observations of uniform metal distributions in the outskirts of nearby
clusters, in which most of the enrichment of the ICM takes place before cluster
formation, with significant later enrichment taking place only in cluster
centers, as the stellar populations of the central galaxies evolve.Comment: 13 pages. Accepted version, to appear in MNRA
Cosmology and Astrophysics from Relaxed Galaxy Clusters I: Sample Selection
This is the first in a series of papers studying the astrophysics and
cosmology of massive, dynamically relaxed galaxy clusters. Here we present a
new, automated method for identifying relaxed clusters based on their
morphologies in X-ray imaging data. While broadly similar to others in the
literature, the morphological quantities that we measure are specifically
designed to provide a fair basis for comparison across a range of data quality
and cluster redshifts, to be robust against missing data due to point-source
masks and gaps between detectors, and to avoid strong assumptions about the
cosmological background and cluster masses. Based on three morphological
indicators - Symmetry, Peakiness and Alignment - we develop the SPA criterion
for relaxation. This analysis was applied to a large sample of cluster
observations from the Chandra and ROSAT archives. Of the 361 clusters which
received the SPA treatment, 57 (16 per cent) were subsequently found to be
relaxed according to our criterion. We compare our measurements to similar
estimators in the literature, as well as projected ellipticity and other image
measures, and comment on trends in the relaxed cluster fraction with redshift,
temperature, and survey selection method. Code implementing our morphological
analysis will be made available on the web.Comment: MNRAS, in press. 43 pages in total, of which 17 are tables (please
think twice before printing). 18 figures, 4 tables. Machine-readable tables
will be available from the journal and at the url below; code will be posted
at http://www.slac.stanford.edu/~amantz/work/morph14
Cosmological Parameters from Observations of Galaxy Clusters
Studies of galaxy clusters have proved crucial in helping to establish the
standard model of cosmology, with a universe dominated by dark matter and dark
energy. A theoretical basis that describes clusters as massive,
multi-component, quasi-equilibrium systems is growing in its capability to
interpret multi-wavelength observations of expanding scope and sensitivity. We
review current cosmological results, including contributions to fundamental
physics, obtained from observations of galaxy clusters. These results are
consistent with and complementary to those from other methods. We highlight
several areas of opportunity for the next few years, and emphasize the need for
accurate modeling of survey selection and sources of systematic error.
Capitalizing on these opportunities will require a multi-wavelength approach
and the application of rigorous statistical frameworks, utilizing the combined
strengths of observers, simulators and theorists.Comment: 53 pages, 21 figures. To appear in Annual Review of Astronomy &
Astrophysic
Thermodynamic Profiles of Galaxy Clusters from a Joint X-ray/SZ Analysis
We jointly analyze Bolocam Sunyaev-Zeldovich (SZ) effect and Chandra X-ray
data for a set of 45 clusters to derive gas density and temperature profiles
without using spectroscopic information. The sample spans the mass and redshift
range
and . We define cool-core (CC) and non-cool core (NCC)
subsamples based on the central X-ray luminosity, and 17/45 clusters are
classified as CC. In general, the profiles derived from our analysis are found
to be in good agreement with previous analyses, and profile constraints beyond
are obtained for 34/45 clusters. In approximately 30% of the CC
clusters our analysis shows a central temperature drop with a statistical
significance of ; this modest detection fraction is due mainly to a
combination of coarse angular resolution and modest S/N in the SZ data. Most
clusters are consistent with an isothermal profile at the largest radii near
, although 9/45 show a significant temperature decrease with
increasing radius. The sample mean density profile is in good agreement with
previous studies, and shows a minimum intrinsic scatter of approximately 10%
near . The sample mean temperature profile is consistent
with isothermal, and has an intrinsic scatter of approximately 50% independent
of radius. This scatter is significantly higher compared to earlier X-ray-only
studies, which find intrinsic scatters near 10%, likely due to a combination of
unaccounted for non-idealities in the SZ noise, projection effects, and sample
selection.Comment: 42 pages, 52 figure
A Comparison and Joint Analysis of Sunyaev-Zel'dovich Effect Measurements from Planck and Bolocam for a set of 47 Massive Galaxy Clusters
We measure the SZ signal toward a set of 47 clusters with a median mass of
M and a median redshift of 0.40 using data from
Planck and the ground-based Bolocam receiver. When Planck XMM-like masses are
used to set the scale radius , we find consistency between
the integrated SZ signal, , derived from Bolocam and Planck
based on gNFW model fits using A10 shape parameters, with an average ratio of
(allowing for the % Bolocam flux calibration
uncertainty). We also perform a joint fit to the Bolocam and Planck data using
a modified A10 model with the outer logarithmic slope allowed to vary,
finding (measurement error followed by
intrinsic scatter). In addition, we find that the value of scales with
mass and redshift according to . This mass scaling is in good agreement with recent
simulations. We do not observe the strong trend of with redshift seen
in simulations, though we conclude that this is most likely due to our sample
selection. Finally, we use Bolocam measurements of to test the
accuracy of the Planck completeness estimate. We find consistency, with the
actual number of Planck detections falling approximately below the
expectation from Bolocam. We translate this small difference into a constraint
on the the effective mass bias for the Planck cluster cosmology results, with
.Comment: Updated to include one additional co-author. Also some minor changes
to the text based on initial feedbac
- …