245 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
Explaining Cosmological Anisotropy: Evidence for Causal Horizons from CMB data
The origin of power asymmetry and other measures of statistical anisotropy on
the largest scales of the universe, as manifested in Cosmic Microwave
Background (CMB) and large-scale structure data, is a long-standing open
question in cosmology. In this paper we analyze the Planck Legacy temperature
anisotropy data and find strong evidence for a violation of the Cosmological
principle of isotropy, with a probability of being a statistical fluctuation of
order ~ 10^-9. The detected anisotropy is related to large-scale directional
LCDM cosmological parameter variations across the CMB sky, that are sourced by
three distinct patches in the maps with circularly-averaged sizes between 40 to
70 degrees in radius. We discuss the robustness of our findings to different
foreground separation methods and analysis choices, and find consistent results
from WMAP data when limiting the analysis to the same scales. We argue that
these well-defined regions within the cosmological parameter maps may reflect
finite and casually disjoint horizons across the observable universe. In
particular we show that the observed relation between horizon size and mean
dark energy density within a given horizon is in good agreement with
expectations from a recently proposed model of the universe that explains
cosmic acceleration and cosmological parameter tensions between the high and
low redshift universe from the existence of casual horizons within our
universe.Comment: Revised version in response to referee's comments (submitted to
MNRAS). New section (3.7) on Simulations analysis, including detailed
discussion of Planck simulations. Conclusions unchange
Detection of the ISW and SZ effects from the CMB-Galaxy correlation
We present a cross-correlation analysis of the WMAP cosmic microwave
background (CMB) temperature anisotropies and the SDSS galaxy density
fluctuations. We find significant detections of the angular CMB-galaxy
correlation for both the flux limited galaxy sample (z~0.3) and the high
redshift (z ~ 0.5) color selected sample. The signal is compatible with that
expected from the integrated Sachs-Wolfe (ISW) effect at large angles (\theta >
3deg) and the Sunyaev-Zeldovich (SZ) effect at small scales (\theta < 1 deg).
The detected correlation at low-z is in good agreement with a previous analysis
using the APM survey (z~0.15). The combined analysis of all 3 samples yields a
total significance better than 3 sigma for ISW and about 2.7 \sigma for SZ,
with a Compton parameter y~10^(-6). For a given flat LCDM model, the ISW effect
depends both on the value of \Omega_\Lambda and the galaxy bias b. To break
this degeneracy, we estimate the bias using the ratio between the galaxy and
mass auto-correlation functions in each sample. With our bias estimation, all
samples consistently favor a best fit dark-energy dominated model:
\Omega_\Lambda ~ 0.8, with a 2 \sigma error \Omega_\Lambda=0.69-0.86.Comment: Accepted by ApJL. New figure and further discussion about error
estimate
Measuring the growth of matter fluctuations with third-order galaxy correlations
Measurements of the linear growth factor at different redshifts are
key to distinguish among cosmological models. One can estimate the derivative
from redshift space measurements of the 3D anisotropic galaxy
two-point correlation , but the degeneracy of its transverse (or
projected) component with galaxy bias , i.e. , introduces large errors in the growth measurement. Here we present a
comparison between two methods which break this degeneracy by combining second-
and third-order statistics. One uses the shape of the reduced three-point
correlation and the other a combination of third-order one- and two-point
cumulants. These methods use the fact that, for Gaussian initial conditions and
scales larger than Mpc, the reduced third-order matter
correlations are independent of redshift (and therefore of the growth factor)
while the third-order galaxy correlations depend on . We use matter and halo
catalogs from the MICE-GC simulation to test how well we can recover and
therefore with these methods in 3D real space. We also present a new
approach, which enables us to measure directly from the redshift evolution
of second- and third-order galaxy correlations without the need of modelling
matter correlations. For haloes with masses lower than
M, we find deviations between the different estimates of
, which are comparable to current observational errors. At higher masses we
find larger differences that can probably be attributed to the breakdown of the
bias model and non-Poissonian shot noise.Comment: 24 pages, 20 figures, 2 tables, accepted for publication in MNRA
Full sky Integrated Sachs-Wolfe maps for the MICE Grand Challenge lightcone simulation
We present full-sky maps of the Integrated Sachs-Wolfe effect (ISW) for the
MICE Grand Challenge lightcone simulation up to redshift 1.4. The maps are
constructed in the linear regime using spherical Bessel transforms. We compare
and contrast this procedure against analytical approximations found in the
literature. By computing the ISW in the linear regime we remove the substantial
computing and storage resources required to calculate the non-linear
Rees-Sciama effect. Since the linear ISW is larger in this has a neglegible impact on the maps produced and only becomes
relevant on scales which are dominated by cosmic microwave background (CMB)
anisotropies. The MICE simulation products have been extensively used for
studies involving current and future galaxy surveys. The availability of these
maps will allow MICE to be used for future galaxy and CMB cross-correlation
studies, ISW reconstruction studies and ISW void-stacking studies probed by
galaxy surveys such as DES, DESI, Euclid and Rubin LSST. The pipeline developed
in this study is provided as a public Python package pyGenISW. This could be
used in future studies for constructing the ISW from existing and future
simulation suites probing vast sets of cosmological parameters and models.Comment: 11 pages, 6 figures, to be submitted to Monthly Notices of the Royal
Astronomical Society. The analysis presented in this paper was calculated
using pyGenISW which is available here: https://github.com/knaidoo29/pyGenIS
Dust Polarization From Starlight Data
We present a statistical analysis of the interstellar medium (ISM)
polarization from the largest compilation available of starlight data, which
comprises ~ 5500 stars. The measured correlation between the mean polarization
degree and extinction indicates that ISM dust grains are not fully aligned with
the uniform component of the large-scale Galactic magnetic field. Moreover, we
estimate the ratio of the uniform to the random plane-of-the-sky components of
the magnetic field to be B_u/B_r = 0.8. From the analysis of starlight
polarization degree and position angle we find that the magnetic field broadly
follows Galactic structures on large-scales. On the other hand, the angular
power spectrum C_l of the polarization degree for Galactic plane data is found
to be consistent with a power-law, C_l ~ l^{-1.5} (where l = 180 deg/\theta is
the multipole order), for angular scales \theta > 10 arcmin. We argue that this
data set can be used to estimate diffuse polarized emission at microwave
frequencies.Comment: 7 pages, 7 figures. To appear in proc. of the AIP conf.
``Astrophysical Polarized Backgrounds'', eds. S. Cecchini, S. Cortiglioni, R.
Sault and C. Sbarr
Cosmological Three-Point Function: Testing The Halo Model Against Simulations
We perform detailed comparison of the semi-analytic halo model predictions
with measurements in numerical simulations of the two and three point
correlation functions (3PCF), as well as power spectrum and bispectrum. We
discuss the accuracy and self-consistency of the halo model description of
gravitational clustering in the non-linear regime and constrain halo model
parameters. We exploit the recently proposed multipole expansion of three point
statistics that expresses rotation invariance in the most natural way. This not
only offers technical advantages by reducing the integrals required for the
halo model predictions, but amounts to a convenient way of compressing the
information contained in the 3PCF. We find that, with an appropriate choice of
the halo boundary and mass function cut-off, halo model predictions are in good
agreement with the bispectrum measured in numerical simulations. However, the
halo model predicts less than the observed configuration dependence of the 3PCF
on ~ Mpc scales. This effect is mainly due to quadrupole moment deficit,
possibly related to the assumption of spherical halo geometry. Our analysis
shows that using its harmonic decomposition, the full configuration dependence
of the 3PCF in the non-linear regime can be compressed into just a few numbers,
the lowest multipoles. Moreover, these multipoles are closely related to the
highest signal to noise eigenmodes of the 3PCF. Therefore this estimator may
simplify future analyses aimed at constraining cosmological and halo model
parameters from observational data.Comment: Minor corrections. Accepted for publication by Ap
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