308,984 research outputs found
Joint signal extraction from galaxy clusters in X-ray and SZ surveys: A matched-filter approach
The hot ionized gas of the intra-cluster medium emits thermal radiation in
the X-ray band and also distorts the cosmic microwave radiation through the
Sunyaev-Zel'dovich (SZ) effect. Combining these two complementary sources of
information through innovative techniques can therefore potentially improve the
cluster detection rate when compared to using only one of the probes. Our aim
is to build such a joint X-ray-SZ analysis tool, which will allow us to detect
fainter or more distant clusters while maintaining high catalogue purity. We
present a method based on matched multifrequency filters (MMF) for extracting
cluster catalogues from SZ and X-ray surveys. We first designed an X-ray
matched-filter method, analogous to the classical MMF developed for SZ
observations. Then, we built our joint X-ray-SZ algorithm by combining our
X-ray matched filter with the classical SZ-MMF, for which we used the physical
relation between SZ and X-ray observations. We show that the proposed X-ray
matched filter provides correct photometry results, and that the joint matched
filter also provides correct photometry when the relation
of the clusters is known. Moreover, the proposed joint algorithm provides a
better signal-to-noise ratio than single-map extractions, which improves the
detection rate even if we do not exactly know the relation.
The proposed methods were tested using data from the ROSAT all-sky survey and
from the Planck survey.Comment: 22 pages (before appendices), 19 figures, 3 tables, 5 appendices.
Accepted for publication in A&
CARMA observations of massive Planck-discovered cluster candidates at z>0.5 associated with WISE overdensities: strategy, observations and validation
We present 1-2 arcmin spatial resolution CARMA-8 31-GHz observations towards
19 unconfirmed Planck cluster candidates, selected to have significant galaxy
overdensities from the WISE early data release and thought to be at z>1 from
the WISE colors of the putative brightest cluster galaxy (BCG). We find a
Sunyaev-Zeldovich (SZ) detection in the CARMA-8 data towards 9 candidate
clusters, where one detection is considered tentative. For each cluster
candidate we present CARMA-8 maps, a study of their radio-source environment
and we assess the reliability of the SZ detection. The CARMA SZ detections
appear to be SZ-bright, with the mean, primary-beam-corrected peak flux density
of the decrement being -2.9mJy/beam with a standard deviation of 0.8, and are
typically offset from the Planck position by approximately 80 arcsec. Using
archival imaging data in the vicinity of the CARMA SZ centroids, we present
evidence that one cluster matches Abell 586-a known z~0.2 cluster; four
candidate clusters are likely to have 0.3<z<0.7; and, for the remaining 4, the
redshift information is inconclusive. We also argue that the sensitivity limits
resulting from the cross-correlation between Planck and WISE makes it
challenging to use our selection criterion to identify clusters at z > 1.Comment: 29 pages, MNRAS, in pres
X-ray Properties of the First SZE-selected Galaxy Cluster Sample from the South Pole Telescope
We present results of X-ray observations of a sample of 15 clusters selected
via their imprint on the cosmic microwave background (CMB) from the thermal
Sunyaev-Zel'dovich (SZ) effect. These clusters are a subset of the first
SZ-selected cluster catalog, obtained from observations of 178 deg^2 of sky
surveyed by the South Pole Telescope. Using X-ray observations with Chandra and
XMM-Newton, we estimate the temperature, T_X, and mass, M_g, of the
intracluster medium (ICM) within r_500 for each cluster. From these, we
calculate Y_X=M_g T_X and estimate the total cluster mass using a M_500-Y_X
scaling relation measured from previous X-ray studies. The integrated
Comptonization, Y_SZ, is derived from the SZ measurements, using additional
information from the X-ray measured gas density profiles and a universal
temperature profile. We calculate scaling relations between the X-ray and SZ
observables, and find results generally consistent with other measurements and
the expectations from simple self-similar behavior. Specifically, we fit a
Y_SZ-Y_X relation and find a normalization of 0.82 +- 0.07, marginally
consistent with the predicted ratio of Y_SZ/Y_X=0.91+-0.01 that would be
expected from the density and temperature models used in this work. Using the
Y_X derived mass estimates, we fit a Y_SZ-M_500 relation and find a slope
consistent with the self-similar expectation of Y_SZ ~ M^5/3 with a
normalization consistent with predictions from other X-ray studies. We compare
the X-ray mass estimates to previously published SZ mass estimates derived from
cosmological simulations of the SPT survey. We find that the SZ mass estimates
are lower by a factor of 0.89+-0.06, which is within the ~15% systematic
uncertainty quoted for the simulation-based SZ masses.Comment: 28 pages, 19 figures, submitted to Ap
First measurement of cluster temperature using the thermal Sunyaev-Zeldovich effect
We discuss a new method of finding the cluster temperatures which is
independent of distance and therefore very useful for distant clusters. The hot
gas of electrons in clusters of galaxies scatters and distorts the cosmic
microwave background radiation in a well determined way. This
Sunyaev-Zel'dovich (SZ) effect is a useful tool for extracting information
about clusters such as their peculiar radial velocity and optical depth. Here
we show how the temperature of the cluster can be inferred from the SZ effect,
in principle without use of X-ray data. We use recent millimetre observation of
Abell 2163 to determine for the first time a cluster temperature using SZ
observations only. The result T_e = 26^+34_-19 keV at 68% confidence level (at
95% c.l. we find T>1.5 keV) is in reasonable agreement with the X-ray results,
T_e =12.4^+2.8_-1.9 keV.Comment: 7 pages, 2 figure
Is the Sunyaev-Zeldovich effect responsible for the observed steepening in the spectrum of the Coma radio halo ?
The spectrum of the radio halo in the Coma cluster is measured over almost
two decades in frequency. The current radio data show a steepening of the
spectrum at higher frequencies, which has implications for models of the radio
halo origin. There is an on-going debate on the possibility that the observed
steepening is not intrinsic to the emitted radiation, but is instead caused by
the SZ effect. Recently, the Planck satellite measured the SZ signal and its
spatial distribution in the Coma cluster allowing to test this hypothesis.
Using the Planck results, we calculated the modification of the radio halo
spectrum by the SZ effect in three different ways. With the first two methods
we measured the SZ-decrement within the aperture radii used for flux
measurements of the halo at the different frequencies. First we adopted the
global compilation of data from Thierbach et al. and a reference aperture
radius consistent with those used by the various authors. Second we used the
available brightness profiles of the halo at different frequencies to derive
the spectrum within two fixed apertures, and derived the SZ-decrement using
these apertures. As a third method we used the quasi-linear correlation between
the y and the radio-halo brightness at 330 MHz discovered by Planck to derive
the modification of the radio spectrum by the SZ-decrement in a way that is
almost independent of the adopted aperture radius. We found that the spectral
modification induced by the SZ-decrement is 4-5 times smaller than that
necessary to explain the observed steepening. Consequently a break or cut-off
in the spectrum of the emitting electrons is necessary to explain current data.
We also show that, if a steepening is absent from the emitted spectrum, future
deep observations at 5 GHz with single dishes are expected to measure a halo
flux in a 40 arcmin radius that would be 7-8 times higher than currently seen.Comment: 8 pages, 6 figures, accepted in Astronomy and Astrophysics (date of
acceptance 19/08/2013
Foreground separation methods for satellite observations of the cosmic microwave background
A maximum entropy method (MEM) is presented for separating the emission due
to different foreground components from simulated satellite observations of the
cosmic microwave background radiation (CMBR). In particular, the method is
applied to simulated observations by the proposed Planck Surveyor satellite.
The simulations, performed by Bouchet and Gispert (1998), include emission from
the CMBR, the kinetic and thermal Sunyaev-Zel'dovich (SZ) effects from galaxy
clusters, as well as Galactic dust, free-free and synchrotron emission. We find
that the MEM technique performs well and produces faithful reconstructions of
the main input components. The method is also compared with traditional Wiener
filtering and is shown to produce consistently better results, particularly in
the recovery of the thermal SZ effect.Comment: 31 pages, 19 figures (bitmapped), accpeted for publication in MNRA
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