277 research outputs found
Optimized Large-Scale CMB Likelihood And Quadratic Maximum Likelihood Power Spectrum Estimation
We revisit the problem of exact CMB likelihood and power spectrum estimation
with the goal of minimizing computational cost through linear compression. This
idea was originally proposed for CMB purposes by Tegmark et al.\ (1997), and
here we develop it into a fully working computational framework for large-scale
polarization analysis, adopting \WMAP\ as a worked example. We compare five
different linear bases (pixel space, harmonic space, noise covariance
eigenvectors, signal-to-noise covariance eigenvectors and signal-plus-noise
covariance eigenvectors) in terms of compression efficiency, and find that the
computationally most efficient basis is the signal-to-noise eigenvector basis,
which is closely related to the Karhunen-Loeve and Principal Component
transforms, in agreement with previous suggestions. For this basis, the
information in 6836 unmasked \WMAP\ sky map pixels can be compressed into a
smaller set of 3102 modes, with a maximum error increase of any single
multipole of 3.8\% at , and a maximum shift in the mean values of a
joint distribution of an amplitude--tilt model of 0.006. This
compression reduces the computational cost of a single likelihood evaluation by
a factor of 5, from 38 to 7.5 CPU seconds, and it also results in a more robust
likelihood by implicitly regularizing nearly degenerate modes. Finally, we use
the same compression framework to formulate a numerically stable and
computationally efficient variation of the Quadratic Maximum Likelihood
implementation that requires less than 3 GB of memory and 2 CPU minutes per
iteration for , rendering low- QML CMB power spectrum
analysis fully tractable on a standard laptop.Comment: 13 pages, 13 figures, accepted by ApJ
The two-and three-point correlation functions of the polarized five-year WMAP sky maps
We present the two- and three-point real space correlation functions of the
five-year WMAP sky maps, and compare the observed functions to simulated LCDM
concordance model ensembles. In agreement with previously published results, we
find that the temperature correlation functions are consistent with
expectations. However, the pure polarization correlation functions are
acceptable only for the 33GHz band map; the 41, 61, and 94 GHz band correlation
functions all exhibit significant large-scale excess structures. Further, these
excess structures very closely match the correlation functions of the two
(synchrotron and dust) foreground templates used to correct the WMAP data for
galactic contamination, with a cross-correlation statistically significant at
the 2sigma-3sigma confidence level. The correlation is slightly stronger with
respect to the thermal dust template than with the synchrotron template.Comment: 10 pages, 5 figures, published in ApJ. v2: New title, minor changes
to appendix, and fixed some typos. v3: Matches version published in Ap
Constraints on the spectral index of polarized synchrotron emission from WMAP and Faraday-corrected S-PASS data
We constrain the spectral index of polarized synchrotron emission, ,
by correlating the recently released 2.3 GHz S-Band Polarization All Sky Survey
(S-PASS) data with the 23 GHz 9-year Wilkinson Microwave Anisotropy Probe
(WMAP) sky maps. We sub-divide the S-PASS field, which covers the Southern
Ecliptic hemisphere, into regions, and estimate
the spectral index of polarized synchrotron emission within each region using a
simple but robust T-T plot technique. Three different versions of the S-PASS
data are considered, corresponding to either no correction for Faraday
rotation; Faraday correction based on the rotation measure model presented by
the S-PASS team; or Faraday correction based on a rotation measure model
presented by Hutschenreuter and En{\ss}lin. We find that the correlation
between S-PASS and WMAP is strongest when applying the S-PASS model. Adopting
this correction model, we find that the mean spectral index of polarized
synchrotron emission gradually steepens from at low
Galactic latitudes to at high Galactic latitudes, in good
agreement with previously published results. Finally, we consider two special
cases defined by the BICEP2 and SPIDER fields, and obtain mean estimates of
and , respectively.
Adopting the WMAP 23 GHz sky map bandpass filtered to including angular scales
only between and as a spatial template, we constrain
the root-mean-square synchrotron polarization amplitude to be less than
() at 90 GHz (150 GHz) for the BICEP2 field,
corresponding roughly to a tensor-to-scalar ratio of
(), respectively. Very similar constraints are obtained for the
SPIDER field.Comment: 14 pages, 13 Figures, to be submitted to A&
Starlight-polarization-based tomography of the magnetized ISM: Pasiphae's line-of-sight inversion method
We present the first Bayesian method for tomographic decomposition of the
plane-of-sky orientation of the magnetic field with the use of stellar
polarimetry and distance. This standalone tomographic inversion method presents
an important step forward in reconstructing the magnetized interstellar medium
(ISM) in 3D within dusty regions. We develop a model in which the polarization
signal from the magnetized and dusty ISM is described by thin layers at various
distances. Our modeling makes it possible to infer the mean polarization
(amplitude and orientation) induced by individual dusty clouds and to account
for the turbulence-induced scatter in a generic way. We present a likelihood
function that explicitly accounts for uncertainties in polarization and
parallax. We develop a framework for reconstructing the magnetized ISM through
the maximization of the log-likelihood using a nested sampling method. We test
our Bayesian inversion method on mock data taking into account realistic
uncertainties from and as expected for the optical polarization survey
PASIPHAE according to the currently planned observing strategy. We demonstrate
that our method is effective in recovering the cloud properties as soon as the
polarization induced by a cloud to its background stars is higher than , for the adopted survey exposure time and level of systematic
uncertainty. Our method makes it possible to recover not only the mean
polarization properties but also to characterize the intrinsic scatter, thus
opening ways to characterize ISM turbulence and the magnetic field strength.
Finally, we apply our method to an existing dataset of starlight polarization
with known line-of-sight decomposition, demonstrating agreement with previous
results and an improved quantification of uncertainties in cloud properties.Comment: 28 pages, including 2 appendices, submitted to A&
Bright-Moon Sky as a Wide-Field Linear Polarimetric Flat Source for Calibration
Next-generation wide-field optical polarimeters like the Wide-Area Linear
Optical Polarimeters (WALOPs) have a field of view (FoV) of tens of arcminutes.
For efficient and accurate calibration of these instruments, wide-field
polarimetric flat sources will be essential. Currently, no established
wide-field polarimetric standard or flat sources exist. This paper tests the
feasibility of using the polarized sky patches of the size of around ten-by-ten
arcminutes, at a distance of up to 20 degrees from the Moon, on bright-Moon
nights as a wide-field linear polarimetric flat source. We observed 19 patches
of the sky adjacent to the bright-Moon with the RoboPol instrument in the
SDSS-r broadband filter. These were observed on five nights within two days of
the full-Moon across two RoboPol observing seasons. We find that for 18 of the
19 patches, the uniformity in the measured normalized Stokes parameters and
is within 0.2 %, with 12 patches exhibiting uniformity within 0.07 % or
better for both and simultaneously, making them reliable and stable
wide-field linear polarization flats. We demonstrate that the sky on
bright-Moon nights is an excellent wide-field linear polarization flat source.
Various combinations of the normalized Stokes parameters and can be
obtained by choosing suitable locations of the sky patch with respect to the
MoonComment: 8 pages including appendix, 6 figures and 3 tables. Submitted to
Astronomy and Astrophysics for review. Comments are welcom
Recommended from our members
Planck 2015 results. XXIII. The thermal Sunyaev-Zeldovich effect--cosmic infrared background correlation
We use Planck data to detect the cross-correlation between the thermal
Sunyaev-Zeldovich (tSZ) effect and the infrared emission from the galaxies that
make up the the cosmic infrared background (CIB). We first perform a stacking
analysis towards Planck-confirmed galaxy clusters. We detect infrared emission
produced by dusty galaxies inside these clusters and demonstrate that the
infrared emission is about 50% more extended than the tSZ effect. Modelling the
emission with a Navarro--Frenk--White profile, we find that the radial profile
concentration parameter is . This indicates
that infrared galaxies in the outskirts of clusters have higher infrared flux
than cluster-core galaxies. We also study the cross-correlation between tSZ and
CIB anisotropies, following three alternative approaches based on power
spectrum analyses: (i) using a catalogue of confirmed clusters detected in
Planck data; (ii) using an all-sky tSZ map built from Planck frequency maps;
and (iii) using cross-spectra between Planck frequency maps. With the three
different methods, we detect the tSZ-CIB cross-power spectrum at significance
levels of (i) 6 , (ii) 3 , and (iii) 4 . We model the
tSZ-CIB cross-correlation signature and compare predictions with the
measurements. The amplitude of the cross-correlation relative to the fiducial
model is . This result is consistent with
predictions for the tSZ-CIB cross-correlation assuming the best-fit
cosmological model from Planck 2015 results along with the tSZ and CIB scaling
relations.Comment: 18 pages, 16 figure
Cosmoglobe DR1. III. First full-sky model of polarized synchrotron emission from all WMAP and Planck LFI data
We present the first model of full-sky polarized synchrotron emission that is
derived from all WMAP and Planck LFI frequency maps. The basis of this analysis
is the set of end-to-end reprocessed Cosmoglobe Data Release 1 sky maps
presented in a companion paper, which have significantly lower instrumental
systematics than the legacy products from each experiment. We find that the
resulting polarized synchrotron amplitude map has an average noise rms of
at 30 GHz and FWHM, which is 30% lower than
the recently released BeyondPlanck model that included only LFI+WMAP Ka-V data,
and 29% lower than the WMAP K-band map alone. The mean -to- power
spectrum ratio is , with amplitudes consistent with those measured
previously by Planck and QUIJOTE. Assuming a power law model for the
synchrotron spectral energy distribution, and using the -- plot method,
we find a full-sky inverse noise-variance weighted mean of
between Cosmoglobe DR1 K-band and 30 GHz, in
good agreement with previous estimates. In summary, the novel Cosmoglobe DR1
synchrotron model is both more sensitive and systematically cleaner than
similar previous models, and it has a more complete error description that is
defined by a set of Monte Carlo posterior samples. We believe that these
products are preferable over previous Planck and WMAP products for all
synchrotron-related scientific applications, including simulation, forecasting
and component separation.Comment: 15 pages, 15 figures, submitted to 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
Cosmoglobe: Towards end-to-end CMB cosmological parameter estimation without likelihood approximations
We implement support for a cosmological parameter estimation algorithm as
proposed by Racine et al. (2016) in Commander, and quantify its computational
efficiency and cost. For a semi-realistic simulation similar to Planck LFI 70
GHz, we find that the computational cost of producing one single sample is
about 60 CPU-hours and that the typical Markov chain correlation length is
100 samples. The net effective cost per independent sample is 6 000
CPU-hours, in comparison with all low-level processing costs of 812 CPU-hours
for Planck LFI and WMAP in Cosmoglobe Data Release 1. Thus, although
technically possible to run already in its current state, future work should
aim to reduce the effective cost per independent sample by at least one order
of magnitude to avoid excessive runtimes, for instance through multi-grid
preconditioners and/or derivative-based Markov chain sampling schemes. This
work demonstrates the computational feasibility of true Bayesian cosmological
parameter estimation with end-to-end error propagation for high-precision CMB
experiments without likelihood approximations, but it also highlights the need
for additional optimizations before it is ready for full production-level
analysis.Comment: 10 pages, 8 figures. Submitted to A&
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