34 research outputs found
Cosmic opacity to CMB photons and polarization measurements
Anisotropy data analysis leaves a significant degeneracy between primeval
spectral index (n_s) and cosmic opacity to CMB photons (\tau). Low--l
polarization measures, in principle, can remove it. We perform a likelihood
analysis to see how cosmic variance possibly affects such a problem. We find
that, for a sufficiently low noise level (\sigma_{pix}) and if \tau is not
negligibly low, the degeneracy is greatly reduced, while the residual impact of
cosmic variance on n_s and \tau determinations is under control. On the
contrary, if \sigma_{pix} is too high, cosmic variance effects appear to be
magnified. We apply general results to specific experiments and find that, if
favorable conditions occur, it is possible that a 2--\sigma detection of a
lower limit on \tau is provided by the SPOrt experiment. Furthermore, if the
PLANCK experiment will measure polarization with the expected precision, the
error on low--l harmonics is adequate to determine \tau, without significant
magnification of the cosmic variance. This however indicates that high
sensitivity might be more important than high resolution in \tau
determinations. We also outline that a determination of \tau is critical to
perform detailed analyses on the nature of dark energy and/or on the presence
of primeval gravitational waves.Comment: 17 pages, 11 figures, to be published on New Astronom
Dynamical Dark Energy model parameters with or without massive neutrinos
We use WMAP5 and other cosmological data to constrain model parameters in
quintessence cosmologies, focusing also on their shift when we allow for
non-vanishing neutrino masses. The Ratra-Peebles (RP) and SUGRA potentials are
used here, as examples of slowly or fastly varying state parameter w(a). Both
potentials depend on an energy scale \Lambda. Here we confirm the results of
previous analysis with WMAP3 data on the upper limits on \Lambda, which turn
out to be rather small (down to ~10^{-9} in RP cosmologies and ~10^{-5} for
SUGRA). Our constraints on \Lambda are not heavily affected by the inclusion of
neutrino mass as a free parameter. On the contrary, when the neutrino mass
degree of freedom is opened, significant shifts in the best-fit values of other
parameters occur.Comment: 9 pages, 3 figures, submitted to JCA
Nature of Dark Energy and Polarization Measurements
High sensitivity polarization measures, on wide angular scales, together with
data on anisotropy, can be used to fix DE parameters. In this paper, first of
all, we aim to determine the sensitivity needed to provide significant limits.
Our analysis puts in evidence that there is a class of DE models that
polarization measures can possibly exclude soon. This class includes models
with DE due to a Ratra-Peebles (RP) potential. Using a likelihood analysis, we
show that it is possible to distinguish RP models from LCDM and other dynamical
DE models, already with the sensitivity of experiments like SPOrt or WMAP,
thanks to their negative TE correlation at low-l, when the optical depth tau is
sufficiently large. On the contrary, fixing the energy scale Lambda for RP
potentials or distinguishing between LCDM and other DE potentials requires a
much lower pixel noise, that no planned polarization experiment will achieve.
While reviewing this paper after the referee report, the first-year WMAP data
were released. WMAP finds large positive anisotropy-polarization correlations
at low l; this apparently excludes DE models with RP potentials.Comment: 28 pages, 16 figures, to be published in New Astronomy; replaced with
accepted versio
Improved limits on the tensor-to-scalar ratio using BICEP and Planck data
We present constraints on the tensor-to-scalar ratio r using a combination of BICEP/Keck 2018 (BK18) and Planck PR4 data allowing us to fit for r consistently with the six parameters of the ? CDM model. We discuss the sensitivity of constraints on r to uncertainties in the ? CDM parameters as defined by the Planck data. In particular, we are able to derive a constraint on the reionization optical depth ? and thus propagate its uncertainty into the posterior distribution for r . While Planck sensitivity to r is slightly lower than the current ground-based measurements, the combination of Planck with BK18 and baryon-acoustic-oscillation data yields results consistent with r = 0 and tightens the constraint to r < 0.032 at 95% confidence.Planck is a project of the European Space Agency (ESA) with instruments provided by two scientific consortia funded by ESA member states and led by Principal Investigators from France and Italy, telescope reflectors provided through a collaboration between ESA and a scientific consortium led and funded by Denmark, and additional contributions from NASA (USA). We gratefully acknowledge support from the CNRS/IN2P3 Computing Center for providing computing and data-processing resources needed for this work. This research used resources of the National Energy Research Scientific Computing Center, which is supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC02- 05CH11231. Part of the research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration (Grant No. 80NM0018D0004)
Do WMAP data favor neutrino mass and a coupling between Cold Dark Matter and Dark Energy?
Within the frame of cosmologies where Dark Energy (DE) is a self--interacting
scalar field, we allow for a CDM--DE coupling and non--zero neutrino masses,
simultaneously. In their 0--0 version, i.e. in the absence of coupling and
neutrino mass, these cosmologies provide an excellent fit to WMAP, SNIa and
deep galaxy sample spectra, at least as good as \LambdaCDM. When the new
degrees of freedom are open, we find that CDM--DE coupling and significant
neutrino masses (~0.1eV per \nu species) are at least as likely as the 0--0
option and, in some cases, even statistically favoured. Results are obtained by
using a Monte Carlo Markov Chain approach.Comment: 18 pages, 10 figures, submitted to JCA
Planck intermediate results. VIII. Filaments between interacting clusters
About half of the baryons of the Universe are expected to be in the form of
filaments of hot and low density intergalactic medium. Most of these baryons
remain undetected even by the most advanced X-ray observatories which are
limited in sensitivity to the diffuse low density medium. The Planck satellite
has provided hundreds of detections of the hot gas in clusters of galaxies via
the thermal Sunyaev-Zel'dovich (tSZ) effect and is an ideal instrument for
studying extended low density media through the tSZ effect. In this paper we
use the Planck data to search for signatures of a fraction of these missing
baryons between pairs of galaxy clusters. Cluster pairs are good candidates for
searching for the hotter and denser phase of the intergalactic medium (which is
more easily observed through the SZ effect). Using an X-ray catalogue of
clusters and the Planck data, we select physical pairs of clusters as
candidates. Using the Planck data we construct a local map of the tSZ effect
centered on each pair of galaxy clusters. ROSAT data is used to construct X-ray
maps of these pairs. After having modelled and subtracted the tSZ effect and
X-ray emission for each cluster in the pair we study the residuals on both the
SZ and X-ray maps. For the merging cluster pair A399-A401 we observe a
significant tSZ effect signal in the intercluster region beyond the virial
radii of the clusters. A joint X-ray SZ analysis allows us to constrain the
temperature and density of this intercluster medium. We obtain a temperature of
kT = 7.1 +- 0.9, keV (consistent with previous estimates) and a baryon density
of (3.7 +- 0.2)x10^-4, cm^-3. The Planck satellite mission has provided the
first SZ detection of the hot and diffuse intercluster gas.Comment: Accepted by A&
Planck 2015 results. XXVII. The Second Planck Catalogue of Sunyaev-Zeldovich Sources
We present the all-sky Planck catalogue of Sunyaev-Zeldovich (SZ) sources detected from the 29 month full-mission data. The catalogue (PSZ2) is the largest SZ-selected sample of galaxy clusters yet produced and the deepest all-sky catalogue of galaxy clusters. It contains 1653 detections, of which 1203 are confirmed clusters with identified counterparts in external data-sets, and is the first SZ-selected cluster survey containing > confirmed clusters. We present a detailed analysis of the survey selection function in terms of its completeness and statistical reliability, placing a lower limit of 83% on the purity. Using simulations, we find that the Y5R500 estimates are robust to pressure-profile variation and beam systematics, but accurate conversion to Y500 requires. the use of prior information on the cluster extent. We describe the multi-wavelength search for counterparts in ancillary data, which makes use of radio, microwave, infra-red, optical and X-ray data-sets, and which places emphasis on the robustness of the counterpart match. We discuss the physical properties of the new sample and identify a population of low-redshift X-ray under- luminous clusters revealed by SZ selection. These objects appear in optical and SZ surveys with consistent properties for their mass, but are almost absent from ROSAT X-ray selected samples
Planck intermediate results V : Pressure profiles of galaxy clusters from the Sunyaev-Zeldovich effect
This article has an erratum: http://dx.doi.org/10.1051/0004-6361/201220040ePeer reviewe
Planck 2018 results. IV. Diffuse component separation
We present full-sky maps of the cosmic microwave background (CMB) and polarized synchrotron and thermal dust emission, derived from the third set of Planck frequency maps. These products have significantly lower contamination from instrumental systematic effects than previous versions. The methodologies used to derive these maps follow closely those described in earlier papers, adopting four methods (Commander, NILC, SEVEM, and SMICA) to extract the CMB component, as well as three methods (Commander, GNILC, and SMICA) to extract astrophysical components. Our revised CMB temperature maps agree with corresponding products in the Planck 2015 delivery, whereas the polarization maps exhibit significantly lower large-scale power, reflecting the improved data processing described in companion papers; however, the noise properties of the resulting data products are complicated, and the best available end-to-end simulations exhibit relative biases with respect to the data at the few percent level. Using these maps, we are for the first time able to fit the spectral index of thermal dust independently over 3 degree regions. We derive a conservative estimate of the mean spectral index of polarized thermal dust emission of beta_d = 1.55 +/- 0.05, where the uncertainty marginalizes both over all known systematic uncertainties and different estimation techniques. For polarized synchrotron emission, we find a mean spectral index of beta_s = -3.1 +/- 0.1, consistent with previously reported measurements. We note that the current data processing does not allow for construction of unbiased single-bolometer maps, and this limits our ability to extract CO emission and correlated components. The foreground results for intensity derived in this paper therefore do not supersede corresponding Planck 2015 products. For polarization the new results supersede the corresponding 2015 products in all respects