5,800 research outputs found
Joint Bayesian component separation and CMB power spectrum estimation
We describe and implement an exact, flexible, and computationally efficient
algorithm for joint component separation and CMB power spectrum estimation,
building on a Gibbs sampling framework. Two essential new features are 1)
conditional sampling of foreground spectral parameters, and 2) joint sampling
of all amplitude-type degrees of freedom (e.g., CMB, foreground pixel
amplitudes, and global template amplitudes) given spectral parameters. Given a
parametric model of the foreground signals, we estimate efficiently and
accurately the exact joint foreground-CMB posterior distribution, and therefore
all marginal distributions such as the CMB power spectrum or foreground
spectral index posteriors. The main limitation of the current implementation is
the requirement of identical beam responses at all frequencies, which restricts
the analysis to the lowest resolution of a given experiment. We outline a
future generalization to multi-resolution observations. To verify the method,
we analyse simple models and compare the results to analytical predictions. We
then analyze a realistic simulation with properties similar to the 3-yr WMAP
data, downgraded to a common resolution of 3 degree FWHM. The results from the
actual 3-yr WMAP temperature analysis are presented in a companion Letter.Comment: 23 pages, 16 figures; version accepted for publication in ApJ -- only
minor changes, all clarifications. More information about the WMAP3 analysis
available at http://www.astro.uio.no/~hke under the Research ta
Pattern selection in a lattice of pulse-coupled oscillators
We study spatio-temporal pattern formation in a ring of N oscillators with
inhibitory unidirectional pulselike interactions. The attractors of the
dynamics are limit cycles where each oscillator fires once and only once. Since
some of these limit cycles lead to the same pattern, we introduce the concept
of pattern degeneracy to take it into account. Moreover, we give a qualitative
estimation of the volume of the basin of attraction of each pattern by means of
some probabilistic arguments and pattern degeneracy, and show how are they
modified as we change the value of the coupling strength. In the limit of small
coupling, our estimative formula gives a perfect agreement with numerical
simulations.Comment: 7 pages, 8 figures. To be published in Physical Review
Cosmology with the largest galaxy cluster surveys: Going beyond Fisher matrix forecasts
We make the first detailed MCMC likelihood study of cosmological constraints
that are expected from some of the largest, ongoing and proposed, cluster
surveys in different wave-bands and compare the estimates to the prevalent
Fisher matrix forecasts. Mock catalogs of cluster counts expected from the
surveys -- eROSITA, WFXT, RCS2, DES and Planck, along with a mock dataset of
follow-up mass calibrations are analyzed for this purpose. A fair agreement
between MCMC and Fisher results is found only in the case of minimal models.
However, for many cases, the marginalized constraints obtained from Fisher and
MCMC methods can differ by factors of 30-100%. The discrepancy can be
alarmingly large for a time dependent dark energy equation of state, w(a); the
Fisher methods are seen to under-estimate the constraints by as much as a
factor of 4--5. Typically, Fisher estimates become more and more inappropriate
as we move away from LCDM, to a constant-w dark energy to varying-w dark energy
cosmologies. Fisher analysis, also, predicts incorrect parameter degeneracies.
From the point of mass-calibration uncertainties, a high value of unknown
scatter about the mean mass-observable relation, and its redshift dependence,
is seen to have large degeneracies with the cosmological parameters sigma_8 and
w(a) and can degrade the cosmological constraints considerably. We find that
the addition of mass-calibrated cluster datasets can improve dark energy and
sigma_8 constraints by factors of 2--3 from what can be obtained compared to
CMB+SNe+BAO only. Since, details of future cluster surveys are still being
planned, we emphasize that optimal survey design must be done using MCMC
analysis rather than Fisher forecasting. [abridged]Comment: 26 pages, 13 figures, 7 tables, accepted for publication in JCA
Cosmic Shear from Galaxy Spins
We discuss the origin of galactic angular momentum, and the statistics of the
present day spin distribution. It is expected that the galaxy spin axes are
correlated with the intermediate principal axis of the gravitational shear
tensor. This allows one to reconstruct the shear field and thereby the full
gravitational potential from the observed galaxy spin fields. We use the
direction of the angular momentum vector without any information of its
magnitude, which requires a measurement of the position angle and inclination
on the sky of each disk galaxy. We present the maximum likelihood shear
inversion procedure, which involves a constrained linear minimization. The
theory is tested against numerical simulations. We find the correlation
strength of nonlinear structures with the initial shear field, and show that
accurate large scale density reconstructions are possible at the expected noise
level.Comment: Accepted by the ApJL, revised discussion, minor changes, LaTex file,
8 pages, 1 ps figur
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