372 research outputs found
On the Presence of Thermal SZ Induced Signal in the First Year WMAP Temperature Maps
Using available optical and X-ray catalogues of clusters and superclusters of
galaxies, we build templates of tSZ emission as they should be detected by the
WMAP experiment. We compute the cross-correlation of our templates with WMAP
temperature maps, and interpret our results separately for clusters and for
superclusters of galaxies. For clusters of galaxies, we claim 2-5
detections in our templates built from BCS Ebeling et al. (1998), NORAS
(Boehringer et al. 2000) and de Grandi et al. (1999) catalogues. In these
templates, the typical cluster temperature decrements in WMAP maps are around
15-35 K in the RJ range (no beam deconvolution applied). Several tests
probing the possible influence of foregrounds in our analyses demonstrate that
our results are robust against galactic contamination. On supercluster scales,
we detect a diffuse component in the V & W WMAP bands which cannot be generated
by superclusters in our catalogues (Einasto et al. 1994, 1997), and which is
not present in the clean map of Tegmark, de Oliveira-Costa & Hamilton (2003).
Using this clean map, our analyses yield, for Einasto's supercluster
catalogues, the following upper limit for the comptonization parameter
associated to supercluster scales: y_{SC} < 2.18 \time s 10^{-8} at the 95%
confidence limit.Comment: MNRAS accepted. New section and minor changes include
Limits on Hot Intracluster Gas Contributions to the Tenerife Temperature Anisotropy Map
We limit the contribution of the hot intracluster gas, by means of the
Sunyaev-Zel'dovich effect, to the temperature anisotropies measured by the
Tenerife experiment. The data is cross-correlated with maps generated from the
ACO cluster catalogue, the ROSAT PSPC catalogue of clusters of galaxies, a
catalogue of superclusters and the HEAO 1 A-1 map of X-ray sources. There is no
evidence of contamination by such sources at an rms level of K at
99% confidence level at angular resolution. We place an upper limit on
the mean Comptonization parameter of at the same
level of confidence. These limits are slightly more restrictive than those
previously found by a similar analysis on the COBE/DMR data and indicate that
most of the signal measured by Tenerife is cosmological.Comment: To be published in ApJ (main journal
A linear filter to reconstruct the ISW effect from CMB and LSS observations
The extraction of a signal from some observational data sets that contain
different contaminant emissions, often at a greater level than the signal
itself, is a common problem in Astrophysics and Cosmology. The signal can be
recovered, for instance, using a simple Wiener filter. However, in certain
cases, additional information may also be available, such as a second
observation which correlates to a certain level with the sought signal. In
order to improve the quality of the reconstruction, it would be useful to
include as well this additional information. Under these circumstances, we have
constructed a linear filter, the linear covariance-based filter, that extracts
the signal from the data but takes also into account the correlation with the
second observation. To illustrate the performance of the method, we present a
simple application to reconstruct the so-called Integrated Sachs-Wolfe effect
from simulated observations of the Cosmic Microwave Background and of
catalogues of galaxies.Comment: 8 pages, 6 figures, accepted for publication in the IEEE Journal of
Selected Topics in Signal Processin
Using peak distribution of the cosmic microwave background for MAP and Planck data analysis: formalism and simulations
We implement and further refine the recently proposed method (Kashlinsky,
Hern\'andez-Monteagudo & Atrio-Barandela, 2001 - KHA) for a time efficient
extraction of the power spectrum from future cosmic microwave background (CMB)
maps. The method is based on the clustering properties of peaks and troughs of
the Gaussian CMB sky. The procedure takes only steps where
is the fraction of pixels with standard deviations
in the map of pixels. We use the new statistic introduced in KHA,
, which characterizes spatial clustering of the CMB sky peaks of
progressively increasing thresholds. The tiny fraction of the remaining pixels
(peaks and troughs) contains the required information on the CMB power spectrum
of the entire map. The threshold is the only parameter that determines
the accuracy of the final spectrum. We performed detailed numerical simulations
for parameters of the two-year WMAP and Planck CMB sky data including
cosmological signal, inhomogeneous noise and foreground residuals. In all cases
we find that the method can recover the power spectrum out to the Nyquist scale
of the experiment channel. We discuss how the error bars scale with
allowing to decide between accuracy and speed. The method can determine with
significant accuracy the CMB power spectrum from the upcoming CMB maps in only
operations.Comment: 11 pages, 14 figures. Minor changes, updated references, matches
accepted version in A&
Correlation properties of the kinematic Sunyaev-Zel'dovich effect and implications for Dark Energy
In the context of a cosmological study of the bulk flows in the Universe, we
present a detailed study of the statistical properties of the kinematic
Sunyaev-Zel'dovich (kSZ) effect. We first compute analytically the correlation
function and the power spectrum of the projected peculiar velocities of galaxy
clusters. By taking into account the spatial clustering properties of these
sources, we perform a line-of-sight computation of the {\em all-sky} kSZ power
spectrum and find that at large angular scales (), the local bulk flow
should leave a visible signature above the Poisson-like fluctuations dominant
at smaller scales, while the coupling of density and velocity fluctuations
should give much smaller contribution. We conduct an analysis of the prospects
of future high resolution CMB experiments (such as ACT and SPT) to detect the
kSZ signal and to extract cosmological information and dark energy constraints
from it. We present two complementary methods, one suitable for ``deep and
narrow'' surveys such as ACT and one suitable for ``wide and shallow'' surveys
such as SPT. Both methods can constraint the equation of state of dark energy
to about 5-10% when applied to forthcoming and future surveys, and probe
in complementary redshift ranges, which could shed some light on its time
evolution. These determinations of do not rely on the knowledge of cluster
masses, although they make minimal assumptions on cluster physics.Comment: 17 pages, 11 figures, submitted to ApJ, comments welcome. See
parallel work of S.DeDeo, D.N.Spergel and H.Trak (ApJ, to be submitted
Hydrodynamical simulations of the Sunyaev--Zel'dovich effect
We use a hydrodynamical N-body code to generate simulated maps, of size one
square degree, of the thermal SZ effect. We study three different cosmologies;
the currently-favoured low-density model with a cosmological constant, a
critical-density model and a low-density open model. We stack simulation boxes
corresponding to different redshifts in order to include contributions to the
Compton y-parameter out to the highest necessary redshifts. Our main results
are:
1. The mean y-distortion is around for low-density
cosmologies, and for critical density. These are below
current limits, but not by a wide margin in the former case.
2. In low-density cosmologies, the mean y-distortion comes from a broad range
of redshifts, the bulk coming from and a tail out to . For
critical-density models, most of the contribution comes from .
3. The number of SZ sources above a given depends strongly on instrument
resolution. For a one arcminute beam, there is around 0.1 sources per square
degree with in a critical-density Universe, and around 8 such
sources per square degree in low-density models. Low-density models with and
without a cosmological constant give very similar results.
4. We estimate that the {\sc Planck} satellite will be able to see of order
25000 SZ sources if the Universe has a low density, or around 10000 if it has
critical density.Comment: 9 pages LaTeX file with eleven figures (including four in colour)
incorporated (uses mn.sty and epsf). Further colour images and animations at
http://star-www.cpes.susx.ac.uk/~andrewl/sz/sz.html Updated to match
published versio
Looking the void in the eyes - the kSZ effect in LTB models
As an alternative explanation of the dimming of distant supernovae it has
recently been advocated that we live in a special place in the Universe near
the centre of a large void described by a Lemaitre-Tolman-Bondi (LTB) metric.
The Universe is no longer homogeneous and isotropic and the apparent late time
acceleration is actually a consequence of spatial gradients in the metric. If
we did not live close to the centre of the void, we would have observed a
Cosmic Microwave Background (CMB) dipole much larger than that allowed by
observations. Hence, until now it has been argued, for the model to be
consistent with observations, that by coincidence we happen to live very close
to the centre of the void or we are moving towards it. However, even if we are
at the centre of the void, we can observe distant galaxy clusters, which are
off-centre. In their frame of reference there should be a large CMB dipole,
which manifests itself observationally for us as a kinematic Sunyaev-Zeldovich
(kSZ) effect. kSZ observations give far stronger constraints on the LTB model
compared to other observational probes such as Type Ia Supernovae, the CMB, and
baryon acoustic oscillations. We show that current observations of only 9
clusters with large error bars already rule out LTB models with void sizes
greater than approximately 1.5 Gpc and a significant underdensity, and that
near future kSZ surveys like the Atacama Cosmology Telescope, South Pole
Telescope, APEX telescope, or the Planck satellite will be able to strongly
rule out or confirm LTB models with giga parsec sized voids. On the other hand,
if the LTB model is confirmed by observations, a kSZ survey gives a unique
possibility of directly reconstructing the expansion rate and underdensity
profile of the void.Comment: 20 pages, 9 figures, submitted to JCA
Impact of Systematic Errors in Sunyaev-Zel'dovich Surveys of Galaxy Clusters
Future high-resolution microwave background measurements hold the promise of
detecting galaxy clusters throughout our Hubble volume through their
Sunyaev-Zel'dovich (SZ) signature, down to a given limiting flux. The number
density of galaxy clusters is highly sensitive to cluster mass through
fluctuations in the matter power spectrum, as well as redshift through the
comoving volume and the growth factor. This sensitivity in principle allows
tight constraints on such quantities as the equation of state of dark energy
and the neutrino mass. We evaluate the ability of future cluster surveys to
measure these quantities simultaneously when combined with PLANCK-like CMB
data. Using a simple effective model for uncertainties in the cluster mass-SZ
flux relation, we evaluate systematic shifts in cosmological constraints from
cluster SZ surveys. We find that a systematic bias of 10% in cluster mass
measurements can give rise to shifts in cosmological parameter estimates at
levels larger than the statistical errors. Systematic errors are
unlikely to be detected from the mass and redshift dependence of cluster number
counts alone; increasing survey size has only a marginal effect. Implications
for upcoming experiments are discussed.Comment: 12 pages, 6 figures; accepted to JCAP; revised to match submitted
versio
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