We describe the optical design and optimisation of the Low Frequency Instrument (LFI), one of two instruments onboard the Planck satellite, which will survey the cosmic microwave background with ...unprecedented accuracy. The LFI covers the 30–70 GHz frequency range with an array of cryogenic radiometers. Stringent optical requirements on angular resolution, sidelobes, main beam symmetry, polarization purity, and feed orientation have been achieved. The optimisation process was carried out by assuming an ideal telescope according to the Planck design and by using both physical optics and multi-reflector geometrical theory of diffraction. This extensive study led to the flight design of the feed horns, their characteristics, arrangement, and orientation, while taking into account the opto-mechanical constraints imposed by complex interfaces in the Planck focal surface.
The Planck satellite, successfully launched on 2009 May 14 to measure with unprecedented accuracy the primary cosmic microwave background (CMB) anisotropies, is operating as expected. The Standard ...Model of the Universe ('concordance' model) provides the current realistic context to analyze the CMB and other cosmological/astrophysical data, inflation in the early universe being part of it. The Planck performance for the crucial primordial parameter r, the tensor-to-scalar ratio related to primordial B-mode polarization, will depend on the quality of data analysis and interpretation. The Ginzburg-Landau (G-L) approach to inflation allows us to take high benefit of the CMB data. The fourth-degree double-well inflaton potential gives an excellent fit to the current CMB+LSS data. We evaluate the Planck precision to the recovery of cosmological parameters, taking into account a reasonable toy model for residuals of systematic effects of instrumental and astrophysical origin based on publicly available information. We use and test two relevant models: the Delta *LCDMr model, i.e., the standard Delta *LCDM model augmented by r, and the Delta *LCDMrT model, where the scalar spectral index, ns , and r are related through the theoretical 'banana-shaped' curve r = r(ns ) coming from the G-L theory with a double-well inflaton potential. In the latter case, the analytical expressions for ns and r are imposed as a hard constraint in a Monte Carlo Markov Chain (MCMC) data analysis. We consider two C l-likelihoods (with and without B modes) and take into account the white noise sensitivity of Planck (LFI and HFI) in the 70, 100, and 143 GHz channels as well as the residuals from systematic errors and foregrounds. We also consider a cumulative channel of the three mentioned. We produce the sky (mock data) for the CMB multipoles CTT l , CTE l , CEE l , and CBB l from the Delta *LCDMr and Delta *LCDMrT models and obtain the cosmological parameter marginalized likelihood distributions for the two models. Foreground residuals affect only the cosmological parameters sensitive to the B modes. As expected, the likelihood r distribution is more clearly peaked near the fiducial value (r = 0.0427) in the Delta *LCDMrT model than in the Delta *LCDMr model. The best value for r in the presence of residuals turns out to be about r 0.04 for both the Delta *LCDMr and the Delta *LCDMrT models. The Delta *LCDMrT model is very stable; its distributions do not change by including residuals and the B modes. For r we find 0.028 < r < 0.116 at a 95% confidence level (CL) with the best value r = 0.04. We also compute the B mode detection probability by the most sensitive HFI-143 channel. At the level of foreground residual equal to 30% of our toy model, only a 68% CL (1 Delta *s) detection is very likely. For a 95% CL detection (2 Delta *s), the level of foreground residual should be reduced to 10% or lower of the adopted toy model. The lower bounds (and most probable value) we infer for r support the searching of CMB B-mode polarization in the current data as well as the planned CMB missions oriented toward B polarization.
Abstract
We present a new, fast, algorithm for the separation of astrophysical components superposed in maps of the sky. The algorithm, based on the Independent Component Analysis (ICA) technique, is ...aimed at recovering both the spatial pattern and the frequency scalings of the emissions from statistically independent astrophysical processes, present along the line-of-sight, from multi-frequency observations, without any a priori assumption on properties of the components to be separated, except that all of them, except possibly one, must have non-Gaussian distributions.
The analysis starts from very simple toy-models of the sky emission in order to assess the quality of the reconstruction when inputs are well known and controlled. In particular, we study the dependence of the results of separation conducted on and off the Galactic plane independently, showing that optimal separation is achieved for sky regions where components are smoothly distributed.
Then we consider simulated observations of the microwave sky with angular resolution and instrumental noise, supposed to be white and stationary, at the mean nominal levels for the Planck satellite. The angular response function is assumed to be identical at each frequency since this is, up to now, one of the Fast Independent Component Analysis (FastICA) limitations. We consider several Planck observation channels containing the most important known diffuse signals: the cosmic microwave background (CMB), Galactic synchrotron, dust and free-free emissions. A method for calibrating the reconstructed maps of each component at each frequency has been devised. The spatial patterns of all the components have been recovered on all scales probed by the instrument. In particular, the CMB angular power spectra is recovered at the per cent level up to ℓmax≃2000.
Frequency scalings and normalization have been recovered with better than 1 per cent precision for all the components at frequencies and in sky regions where their signal-to-noise ratio ≳1.5; the error increases at ∼10 per cent level for signal-to-noise ratios ≃1.
Runs have been performed on a Pentium III 600-MHz computer; although the computing time slightly depends on the number of channels and components to be recovered, FastICA typically took about 10 min for all-sky simulations with 3.5-arcmin pixel size.
Although the quoted results have been obtained under a number of simplifying assumptions, we conclude that FastICA is an extremely promising technique for analysing the maps that will be obtained by the forthcoming high-resolution CMB experiments.
Abstract
In this work we have compared the absolute temperature data of the cosmic microwave background (CMB) spectrum with models of CMB spectra distorted by a single or two heating processes at ...different cosmic times. The constraints on the fractional energy injected in the radiation field, Δε/εi, are mainly provided by the precise measures of the FIRAS instrument on board the COBE satellite, while long-wavelength measures are crucial to set constraints on free-free distortions. We find that the baryon density does not influence the limits on Δε/εi derived from current data for cosmic epochs corresponding to the same dimensionless time y
h of dissipation epoch, although the redshift corresponding to the same y
h decreases with the baryon density. Under the hypothesis that two heating processes have occurred at different epochs, the former at any y
h in the range 5 ≥y
h≥ 0.01 (this joint analysis is meaningful for y
h≳ 0.1) and the latter at y
h≪ 1, the limits on Δε/εi are relaxed by a factor ∼2 for both the earlier and the later process with respect to the case in which a single energy injection in the thermal history of the Universe is considered. In general, the constraints on Δε/εi are weaker for early processes (5 ≳y
h≳ 1) than for relatively late processes (y
h≲ 0.1), because of the subcentimetric wavelength coverage of FIRAS data, relatively more sensitive to Comptonization than to Bose-Einstein like distortions.
While from a widely conservative point of view the FIRAS calibration as revised recently by Battistelli et al. only implies a significant relaxation of the constraints on the Planckian shape of the CMB spectrum, the favoured calibrator emissivity law proposed by the authors, quite different from a constant emissivity, implies significant deviations from a Planckian spectrum. An astrophysical explanation of this, although intriguing, seems difficult. We find that an interpretation in terms of CMB spectral distortions should require a proper balance between the energy exchanges at two very different cosmic times or a delicate fine tuning of the parameters characterizing a dissipation process at intermediate epochs, while an interpretation in terms of a relevant millimetric foreground, produced by cold dust, should imply a too large involved mass and/or an increase of the fluctuations at subdegree angular scales. Future precise measurements at longer wavelengths as well as current and future CMB anisotropy space missions will provide independent, direct or indirect, cross-checks.
This work is related to Planck-LFI activities.
Planck 2018 results Aghanim, N.; Akrami, Y.; Aumont, J. ...
Astronomy and astrophysics (Berlin),
09/2020, Letnik:
641
Journal Article
Recenzirano
Odprti dostop
We present measurements of the cosmic microwave background (CMB) lensing potential using the final
Planck
2018 temperature and polarization data. Using polarization maps filtered to account for the ...noise anisotropy, we increase the significance of the detection of lensing in the polarization maps from 5
σ
to 9
σ
. Combined with temperature, lensing is detected at 40
σ
. We present an extensive set of tests of the robustness of the lensing-potential power spectrum, and construct a minimum-variance estimator likelihood over lensing multipoles 8 ≤
L
≤ 400 (extending the range to lower
L
compared to 2015), which we use to constrain cosmological parameters. We find good consistency between lensing constraints and the results from the
Planck
CMB power spectra within the ΛCDM model. Combined with baryon density and other weak priors, the lensing analysis alone constrains
σ
8
Ω
m
0.25
= 0.589 ± 0.020 (1
σ
errors). Also combining with baryon acoustic oscillation data, we find tight individual parameter constraints,
σ
8
= 0.811 ± 0.019,
H
0
= 67.9
−1.3
+1.2
km s
−1
Mpc
−1
, and Ω
m
= 0.303
−0.018
+0.016
. Combining with
Planck
CMB power spectrum data, we measure
σ
8
to better than 1% precision, finding
σ
8
= 0.811 ± 0.006. CMB lensing reconstruction data are complementary to galaxy lensing data at lower redshift, having a different degeneracy direction in
σ
8
− Ω
m
space; we find consistency with the lensing results from the Dark Energy Survey, and give combined lensing-only parameter constraints that are tighter than joint results using galaxy clustering. Using the
Planck
cosmic infrared background (CIB) maps as an additional tracer of high-redshift matter, we make a combined
Planck
-only estimate of the lensing potential over 60% of the sky with considerably more small-scale signal. We additionally demonstrate delensing of the
Planck
power spectra using the joint and individual lensing potential estimates, detecting a maximum removal of 40% of the lensing-induced power in all spectra. The improvement in the sharpening of the acoustic peaks by including both CIB and the quadratic lensing reconstruction is detected at high significance.
Planck 2018 results Aghanim, N.; Akrami, Y.; Aumont, J. ...
Astronomy and astrophysics (Berlin),
09/2020, Letnik:
641
Journal Article
Recenzirano
Odprti dostop
We describe the legacy
Planck
cosmic microwave background (CMB) likelihoods derived from the 2018 data release. The overall approach is similar in spirit to the one retained for the 2013 and 2015 ...data release, with a hybrid method using different approximations at low (
ℓ
< 30) and high (
ℓ
≥ 30) multipoles, implementing several methodological and data-analysis refinements compared to previous releases. With more realistic simulations, and better correction and modelling of systematic effects, we can now make full use of the CMB polarization observed in the High Frequency Instrument (HFI) channels. The low-multipole
EE
cross-spectra from the 100 GHz and 143 GHz data give a constraint on the ΛCDM reionization optical-depth parameter
τ
to better than 15% (in combination with the
TT
low-
ℓ
data and the high-
ℓ
temperature and polarization data), tightening constraints on all parameters with posterior distributions correlated with
τ
. We also update the weaker constraint on
τ
from the joint TEB likelihood using the Low Frequency Instrument (LFI) channels, which was used in 2015 as part of our baseline analysis. At higher multipoles, the CMB temperature spectrum and likelihood are very similar to previous releases. A better model of the temperature-to-polarization leakage and corrections for the effective calibrations of the polarization channels (i.e., the polarization efficiencies) allow us to make full use of polarization spectra, improving the ΛCDM constraints on the parameters
θ
MC
,
ω
c
,
ω
b
, and
H
0
by more than 30%, and n
s
by more than 20% compared to TT-only constraints. Extensive tests on the robustness of the modelling of the polarization data demonstrate good consistency, with some residual modelling uncertainties. At high multipoles, we are now limited mainly by the accuracy of the polarization efficiency modelling. Using our various tests, simulations, and comparison between different high-multipole likelihood implementations, we estimate the consistency of the results to be better than the 0.5
σ
level on the ΛCDM parameters, as well as classical single-parameter extensions for the joint likelihood (to be compared to the 0.3
σ
levels we achieved in 2015 for the temperature data alone on ΛCDM only). Minor curiosities already present in the previous releases remain, such as the differences between the best-fit ΛCDM parameters for the
ℓ
< 800 and
ℓ
> 800 ranges of the power spectrum, or the preference for more smoothing of the power-spectrum peaks than predicted in ΛCDM fits. These are shown to be driven by the temperature power spectrum and are not significantly modified by the inclusion of the polarization data. Overall, the legacy
Planck
CMB likelihoods provide a robust tool for constraining the cosmological model and represent a reference for future CMB observations.
The destriping technique is a viable tool for removing different kinds of systematic effects in CMB-related experiments. It has already been proven to work for gain instabilities that produce the ...so-called $1/f$ noise and periodic fluctuations due to e.g. thermal instability. Both effects, when coupled to the observing strategy, result in stripes on the observed sky region. Here we present a maximum-likelihood approach to this type of technique and provide also a useful generalization. As a working case we consider a data set similar to what the planck satellite will produce in its Low Frequency Instrument (LFI). We compare our method to those presented in the literature and find some improvement in performance. Our approach is also more general and allows for different base functions to be used when fitting the systematic effect under consideration. We study the effect of increasing the number of these base functions on the quality of signal cleaning and reconstruction. This study is related to planck LFI activities.
Context.The Planck satellite, scheduled for launch in 2007, will produce a set of all sky maps in nine frequency bands spanning from 30 GHz to 857 GHz, with an unprecedented sensitivity and ...resolution. Planets, minor bodies and diffuse interplanetary dust will contribute to the (sub)mm sky emission observed by Planck, representing a source of foreground contamination to be removed before extracting the cosmological information. Aims.The aim of this paper is to assess the expected level of contamination in the survey of the forthcoming Planck mission. Methods.Starting from existing far-infrared (far-IR) models of the Zodiacal Light Emission (ZLE), we present a new method to simulate the time-dependent level of contamination from ZLE at Planck frequencies. Results.We studied the possibility of Planck to detect and separate the ZLE contribution from the other astrophysical signals. Conclusions.We discuss the conditions in which Planck will be able to increase the existing information on the ZLE and IDP physical properties. This work is done in the framework of the Planck/LFI activities.
Anisotropy and polarization of the CMB are probing cosmological models with unprecedented precision. The WMAP satellite data are largely consistent with concordance ACDM cosmology. However, ...intriguing flukes are known to exist that may pinpoint at physics beyond the standard model. Constraining the violations of discrete symmetries in the CMB pattern is a promising mean to investigate these discrepancies. In this paper we constrain the Parity and symmetries through CMB datasets. We describe the basic formalism, the relevant estimators and the overall analysis strategy. We provide marginal evidence for large scale Parity anomaly in the WMAP data that may be soon confirmed or discarded by the Planck satellite. Planck is currently measuring CMB anisotropies and their polarization with a level of precision that will remain unparalleled for many years to come. We also show how the CMB can be used to constrain fundamental symmetry violations in the photon sector through the so-called cosmological birefringence phenomenon. Finally, we provide forecasts for Planck and we discuss how emission from a specific diffuse foreground component arising within the Solar System needs to be kept under strict control to avoid incurring into false positive detections.
Planck 2018 results Akrami, Y.; Aumont, J.; Baccigalupi, C. ...
Astronomy and astrophysics (Berlin),
09/2020, Letnik:
641
Journal Article
Recenzirano
Odprti dostop
We analyse the
Planck
full-mission cosmic microwave background (CMB) temperature and
E
-mode polarization maps to obtain constraints on primordial non-Gaussianity (NG). We compare estimates obtained ...from separable template-fitting, binned, and optimal modal bispectrum estimators, finding consistent values for the local, equilateral, and orthogonal bispectrum amplitudes. Our combined temperature and polarization analysis produces the following final results:
f
NL
local
= −0.9 ± 5.1;
f
NL
equil
= −26 ± 47; and
f
NL
ortho
= −38 ± 24 (68% CL, statistical). These results include low-multipole (4 ≤
ℓ
< 40) polarization data that are not included in our previous analysis. The results also pass an extensive battery of tests (with additional tests regarding foreground residuals compared to 2015), and they are stable with respect to our 2015 measurements (with small fluctuations, at the level of a fraction of a standard deviation, which is consistent with changes in data processing). Polarization-only bispectra display a significant improvement in robustness; they can now be used independently to set primordial NG constraints with a sensitivity comparable to WMAP temperature-based results and they give excellent agreement. In addition to the analysis of the standard local, equilateral, and orthogonal bispectrum shapes, we consider a large number of additional cases, such as scale-dependent feature and resonance bispectra, isocurvature primordial NG, and parity-breaking models, where we also place tight constraints but do not detect any signal. The non-primordial lensing bispectrum is, however, detected with an improved significance compared to 2015, excluding the null hypothesis at 3.5
σ
. Beyond estimates of individual shape amplitudes, we also present model-independent reconstructions and analyses of the
Planck
CMB bispectrum. Our final constraint on the local primordial trispectrum shape is
g
NL
local
= (−5.8 ± 6.5) × 10
4
(68% CL, statistical), while constraints for other trispectrum shapes are also determined. Exploiting the tight limits on various bispectrum and trispectrum shapes, we constrain the parameter space of different early-Universe scenarios that generate primordial NG, including general single-field models of inflation, multi-field models (e.g. curvaton models), models of inflation with axion fields producing parity-violation bispectra in the tensor sector, and inflationary models involving vector-like fields with directionally-dependent bispectra. Our results provide a high-precision test for structure-formation scenarios, showing complete agreement with the basic picture of the ΛCDM cosmology regarding the statistics of the initial conditions, with cosmic structures arising from adiabatic, passive, Gaussian, and primordial seed perturbations.
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