1,372 research outputs found
The Angular Power Spectrum of the First-Year WMAP Data Reanalysed
We measure the angular power spectrum of the WMAP first-year temperature
anisotropy maps. We use SpICE (Spatially Inhomogeneous Correlation Estimator)
to estimate Cl's for multipoles l=2-900 from all possible cross-correlation
channels. Except for the map-making stage, our measurements provide an
independent analysis of that by Hinshaw etal (2003). Despite the different
methods used, there is virtually no difference between the two measurements for
l < 700 ; the highest l's are still compatible within 1-sigma errors. We use a
novel intra-bin variance method to constrain Cl errors in a model independent
way. When applied to WMAP data, the intra-bin variance estimator yields
diagonal errors 10% larger than those reported by the WMAP team for 100 < l <
450. This translates into a 2.4 sigma detection of systematics since no
difference is expected between the SpICE and the WMAP team estimator window
functions in this multipole range. With our measurement of the Cl's and errors,
we get chi^2/d.o.f. = 1.042 for a best-fit LCDM model, which has a 14%
probability, whereas the WMAP team obtained chi^2/d.o.f. = 1.066, which has a
5% probability. We assess the impact of our results on cosmological parameters
using Markov Chain Monte Carlo simulations. From WMAP data alone, assuming
spatially flat power law LCDM models, we obtain the reionization optical depth
tau = 0.145 +/- 0.067, spectral index n_s = 0.99 +/- 0.04, Hubble constant h =
0.67 +/- 0.05, baryon density Omega_b h^2 = 0.0218 +/- 0.0014, cold dark matter
density Omega_{cdm} h^2 = 0.122 +/- 0.018, and sigma_8 = 0.92 +/- 0.12,
consistent with a reionization redshift z_{re} = 16 +/- 5 (68% CL).Comment: Matches version accepted by ApJ Letters. Main changes: emphasizes
chi2 value for best-fit model given our estimate of Cls and errors vs. WMAP
team's. Potential detection of systematics in WMAP data quantified. Power
spectrum and other data files available at
http://www.ifa.hawaii.edu/cosmowave/wmap.htm
Cross-correlating the Microwave Sky with Galaxy Surveys
We present results for the cross-correlation between the WMAP 1st-year cosmic
microwave background (CMB) anisotropy data and optical galaxy surveys: the APM
and SDSS DR1 catalogs. Our measurement of a positive CMB-galaxy correlation on
large angles (\theta > 4 deg) yields significant detections of the Integrated
Sachs-Wolfe (ISW) effect and provides a new estimate of dark-energy in the
universe, \Omega_\Lambda=0.69-0.86 (2 \sigma range). In addition, the
correlated signal on small angles (\theta<1 deg) reveals the imprint left by
hot intra-cluster gas in the CMB photons: the thermal Sunyaev-Zeldovich (SZ)
effectComment: 7 pages. Invited talk at XVth Rencontres de Blois (France): "Physical
Cosmology", June 2003. References adde
Error analysis in cross-correlation of sky maps: application to the ISW detection
Constraining cosmological parameters from measurements of the Integrated
Sachs-Wolfe effect requires developing robust and accurate methods for
computing statistical errors in the cross-correlation between maps. This paper
presents a detailed comparison of such error estimation applied to the case of
cross-correlation of Cosmic Microwave Background (CMB) and large-scale
structure data. We compare theoretical models for error estimation with
montecarlo simulations where both the galaxy and the CMB maps vary around a
fiducial auto-correlation and cross-correlation model which agrees well with
the current concordance LCDM cosmology. Our analysis compares estimators both
in harmonic and configuration (or real) space, quantifies the accuracy of the
error analysis and discuss the impact of partial sky survey area and the choice
of input fiducial model on dark-energy constraints. We show that purely
analytic approaches yield accurate errors even in surveys that cover only 10%
of the sky and that parameter constraints strongly depend on the fiducial model
employed. Alternatively, we discuss the advantages and limitations of error
estimators that can be directly applied to data. In particular, we show that
errors and covariances from the Jack-Knife method agree well with the
theoretical approaches and simulations. We also introduce a novel method in
real space that is computationally efficient and can be applied to real data
and realistic survey geometries. Finally, we present a number of new findings
and prescriptions that can be useful for analysis of real data and forecasts,
and present a critical summary of the analyses done to date.Comment: submitted to MNRAS, 26 page
Polarimetry in the Visible and Infrared: Application to CMB Polarimetry
Interstellar polarization from aligned dust grains can be measured both in
transmission at visible and near-infrared wavelengths and in emission at
far-infrared and sub-mm wavelengths. These observations can help predict the
behavior of foreground contamination of CMB polarimetry by dust in the Milky
Way. Fractional polarization in emission from aligned dust grains will be at
the higher range of currently observed values of 4-10%. Away from the galactic
plane, fluctuations in Q and U will be dominated by fluctuations in intensity,
and less influenced by fluctuations in fractional polarization and position
angle.Comment: To be published in the proceedings of "The Cosmic Microwave
Background and its Polarization", New Astronomy Reviews, (eds. S. Hanany and
K.A. Olive
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