386 research outputs found
Planck 2015 results:X. Diffuse component separation: Foreground maps
Planck has mapped the microwave sky in temperature over nine frequency bands between 30 and 857 GHz and in polarization over seven frequency bands between 30 and 353 GHz in polarization. In this paper we consider the problem of diffuse astrophysical component separation, and process these maps within a Bayesian framework to derive an internally consistent set of full-sky astrophysical component maps. Component separation dedicated to cosmic microwave background (CMB) reconstruction is described in a companion paper. For the temperature analysis, we combine the Planck observations with the 9-yr Wilkinson Microwave Anisotropy Probe (WMAP) sky maps and the Haslam et al. 408 MHz map, to derive a joint model of CMB, synchrotron, free-free, spinning dust, CO, line emission in the 94 and 100 GHz channels, and thermal dust emission. Full-sky maps are provided for each component, with an angular resolution varying between 7.́5 and 1deg. Global parameters (monopoles, dipoles, relative calibration, and bandpass errors) are fitted jointly with the sky model, and best-fit values are tabulated. For polarization, the model includes CMB, synchrotron, and thermal dust emission. These models provide excellent fits to the observed data, with rms temperature residuals smaller than 4μK over 93% of the sky for all Planck frequencies up to 353 GHz, and fractional errors smaller than 1% in the remaining 7% of the sky. The main limitations of the temperature model at the lower frequencies are internal degeneracies among the spinning dust, free-free, and synchrotron components; additional observations from external low-frequency experiments will be essential to break these degeneracies. The main limitations of the temperature model at the higher frequencies are uncertainties in the 545 and 857 GHz calibration and zero-points. For polarization, the main outstanding issues are instrumental systematics in the 100–353 GHz bands on large angular scales in the form of temperature-to-polarization leakage, uncertainties in the analogue-to-digital conversion, and corrections for the very long time constant of the bolometer detectors, all of which are expected to improve in the near future
Planck 2018 results. III. High Frequency Instrument data processing and frequency maps
This paper presents the High Frequency Instrument (HFI) data processing procedures for the Planck 2018 release. Major improvements in mapmaking have been achieved since the previous Planck 2015 release, many of which were used and described already in an intermediate paper dedicated to the Planck polarized data at low multipoles. These improvements enabled the first significant measurement of the reionization optical depth parameter using Planck-HFI data. This paper presents an extensive analysis of systematic effects, including the use of end-to-end simulations to facilitate their removal and characterize the residuals. The polarized data, which presented a number of known problems in the 2015 Planck release, are very significantly improved, especially the leakage from intensity to polarization. Calibration, based on the cosmic microwave background (CMB) dipole, is now extremely accurate and in the frequency range 100–353 GHz reduces intensity-to-polarization leakage caused by calibration mismatch. The Solar dipole direction has been determined in the three lowest HFI frequency channels to within one arc minute, and its amplitude has an absolute uncertainty smaller than 0.35 μK, an accuracy of order 10−4. This is a major legacy from the Planck HFI for future CMB experiments. The removal of bandpass leakage has been improved for the main high-frequency foregrounds by extracting the bandpass-mismatch coefficients for each detector as part of the mapmaking process; these values in turn improve the intensity maps. This is a major change in the philosophy of “frequency maps”, which are now computed from single detector data, all adjusted to the same average bandpass response for the main foregrounds. End-to-end simulations have been shown to reproduce very well the relative gain calibration of detectors, as well as drifts within a frequency induced by the residuals of the main systematic effect (analogue-to-digital convertor non-linearity residuals). Using these simulations, we have been able to measure and correct the small frequency calibration bias induced by this systematic effect at the 10⁻⁴ level. There is no detectable sign of a residual calibration bias between the first and second acoustic peaks in the CMB channels, at the 10⁻³ level
A LEKID-based CMB instrument design for large-scale observations in Greenland
We present the results of a feasibility study, which examined deployment of a
ground-based millimeter-wave polarimeter, tailored for observing the cosmic
microwave background (CMB), to Isi Station in Greenland. The instrument for
this study is based on lumped-element kinetic inductance detectors (LEKIDs) and
an F/2.4 catoptric, crossed-Dragone telescope with a 500 mm aperture. The
telescope is mounted inside the receiver and cooled to K by a
closed-cycle He refrigerator to reduce background loading on the detectors.
Linearly polarized signals from the sky are modulated with a metal-mesh
half-wave plate that is rotated at the aperture stop of the telescope with a
hollow-shaft motor based on a superconducting magnetic bearing. The modular
detector array design includes at least 2300 LEKIDs, and it can be configured
for spectral bands centered on 150~GHz or greater. Our study considered
configurations for observing in spectral bands centered on 150, 210 and
267~GHz. The entire polarimeter is mounted on a commercial precision rotary air
bearing, which allows fast azimuth scan speeds with negligible vibration and
mechanical wear over time. A slip ring provides power to the instrument,
enabling circular scans (360 degrees of continuous rotation). This mount, when
combined with sky rotation and the latitude of the observation site, produces a
hypotrochoid scan pattern, which yields excellent cross-linking and enables
34\% of the sky to be observed using a range of constant elevation scans. This
scan pattern and sky coverage combined with the beam size (15~arcmin at
150~GHz) makes the instrument sensitive to in the angular
power spectra
Planck 2015 results:X. Diffuse component separation: Foreground maps
Planck has mapped the microwave sky in temperature over nine frequency bands between 30 and 857 GHz and in polarization over seven frequency bands between 30 and 353 GHz in polarization. In this paper we consider the problem of diffuse astrophysical component separation, and process these maps within a Bayesian framework to derive an internally consistent set of full-sky astrophysical component maps. Component separation dedicated to cosmic microwave background (CMB) reconstruction is described in a companion paper. For the temperature analysis, we combine the Planck observations with the 9-yr Wilkinson Microwave Anisotropy Probe (WMAP) sky maps and the Haslam et al. 408 MHz map, to derive a joint model of CMB, synchrotron, free-free, spinning dust, CO, line emission in the 94 and 100 GHz channels, and thermal dust emission. Full-sky maps are provided for each component, with an angular resolution varying between 7.́5 and 1deg. Global parameters (monopoles, dipoles, relative calibration, and bandpass errors) are fitted jointly with the sky model, and best-fit values are tabulated. For polarization, the model includes CMB, synchrotron, and thermal dust emission. These models provide excellent fits to the observed data, with rms temperature residuals smaller than 4μK over 93% of the sky for all Planck frequencies up to 353 GHz, and fractional errors smaller than 1% in the remaining 7% of the sky. The main limitations of the temperature model at the lower frequencies are internal degeneracies among the spinning dust, free-free, and synchrotron components; additional observations from external low-frequency experiments will be essential to break these degeneracies. The main limitations of the temperature model at the higher frequencies are uncertainties in the 545 and 857 GHz calibration and zero-points. For polarization, the main outstanding issues are instrumental systematics in the 100–353 GHz bands on large angular scales in the form of temperature-to-polarization leakage, uncertainties in the analogue-to-digital conversion, and corrections for the very long time constant of the bolometer detectors, all of which are expected to improve in the near future
The Detector System for the Stratospheric Kinetic Inductance Polarimeter (SKIP)
The Stratospheric Kinetic Inductance Polarimeter (SKIP) is a proposed
balloon-borne experiment designed to study the cosmic microwave background, the
cosmic infrared background and Galactic dust emission by observing 1133 square
degrees of sky in the Northern Hemisphere with launches from Kiruna, Sweden.
The instrument contains 2317 single-polarization, horn-coupled, aluminum
lumped-element kinetic inductance detectors (LEKID). The LEKIDs will be
maintained at 100 mK with an adiabatic demagnetization refrigerator. The
polarimeter operates in two configurations, one sensitive to a spectral band
centered on 150 GHz and the other sensitive to 260 and 350 GHz bands. The
detector readout system is based on the ROACH-1 board, and the detectors will
be biased below 300 MHz. The detector array is fed by an F/2.4 crossed-Dragone
telescope with a 500 mm aperture yielding a 15 arcmin FWHM beam at 150 GHz. To
minimize detector loading and maximize sensitivity, the entire optical system
will be cooled to 1 K. Linearly polarized sky signals will be modulated with a
metal-mesh half-wave plate that is mounted at the telescope aperture and
rotated by a superconducting magnetic bearing. The observation program consists
of at least two, five-day flights beginning with the 150 GHz observations.Comment: J Low Temp Phys DOI 10.1007/s10909-013-1014-3 The final publication
is available at link.springer.co
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&
A Monte Carlo comparison between template-based and Wiener-filter CMB dipole estimators
We review and compare two different CMB dipole estimators discussed in the
literature, and assess their performances through Monte Carlo simulations. The
first method amounts to simple template regression with partial sky data, while
the second method is an optimal Wiener filter (or Gibbs sampling)
implementation. The main difference between the two methods is that the latter
approach takes into account correlations with higher-order CMB temperature
fluctuations that arise from non-orthogonal spherical harmonics on an
incomplete sky, which for recent CMB data sets (such as Planck) is the dominant
source of uncertainty. For an accepted sky fraction of 81% and an angular CMB
power spectrum corresponding to the best-fit Planck 2018 CDM model, we
find that the uncertainty on the recovered dipole amplitude is about six times
smaller for the Wiener filter approach than for the template approach,
corresponding to 0.5 and 3K, respectively. Similar relative differences
are found for the corresponding directional parameters and other sky fractions.
We note that the Wiener filter algorithm is generally applicable to any dipole
estimation problem on an incomplete sky, as long as a statistical and
computationally tractable model is available for the unmasked higher-order
fluctuations. The methodology described in this paper forms the numerical basis
for the most recent determination of the CMB solar dipole from Planck, as
summarized by arXiv:2007.04997.Comment: 8 pages, 10 figures, submitted to A&
B-mode polarization forecasts for GreenPol
We present tensor-to-scalar ratio forecasts for GreenPol, a hypothetical
ground-based B-mode experiment aiming to survey the cleanest regions of the
Northern Galactic hemisphere at five frequencies between 10 and 44 GHz. Its
primary science goal would be to measure large-scale CMB polarization
fluctuations at multipoles , and thereby constrain the
primordial tensor-to-scalar ratio. The observations for the suggested
experiment would take place at the Summit Station (72deg N, 38deg W) on
Greenland, at an altitude of 3216 meters above sea level. In this paper we
simulate various experimental setups, and derive limits on the tensor-to-scalar
ratio after CMB component separation using a Bayesian component separation
implementation called Commander. When combining the proposed experiment with
Planck HFI observations for constraining polarized thermal dust emission, we
find a projected limit of r<0.02 at 95 % confidence for the baseline
configuration. This limit is very robust with respect to a range of important
experimental parameters, including sky coverage, detector weighting, foreground
priors etc. Overall, GreenPol would have the possibility to provide deep CMB
polarization measurements of the Northern Galactic hemisphere at low
frequencies.Comment: 10 pages, 8 figures. To be submitted to A&
Non-detection of a statistically anisotropic power spectrum in large-scale structure
We search a sample of photometric luminous red galaxies (LRGs) measured by
the Sloan Digital Sky Survey (SDSS) for a quadrupolar anisotropy in the
primordial power spectrum, in which P(\vec{k}) is an isotropic power spectrum
P(k) multiplied by a quadrupolar modulation pattern. We first place limits on
the 5 coefficients of a general quadrupole anisotropy. We also consider
axisymmetric quadrupoles of the form P(\vec{k}) = P(k){1 +
g_*[(\hat{k}\cdot\hat{n})^2-1/3]} where \hat{n} is the axis of the anisotropy.
When we force the symmetry axis \hat{n} to be in the direction (l,b)=(94
degrees,26 degrees) identified in the recent Groeneboom et al. analysis of the
cosmic microwave background, we find g_*=0.006+/-0.036 (1 sigma). With uniform
priors on \hat{n} and g_* we find that -0.41<g_*<+0.38 with 95% probability,
with the wide range due mainly to the large uncertainty of asymmetries aligned
with the Galactic Plane. In none of these three analyses do we detect evidence
for quadrupolar power anisotropy in large scale structure.Comment: 23 pages; 10 figures; 3 tables; replaced with version published in
JCAP (added discussion of scale-varying quadrupolar anisotropy
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