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Register a new userLimits on Polarized Dust Spectral Index Variations for CMB Foreground Analysis
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Using Planck polarization data, we search for and constrain spatial variations of the polarized dust foreground for cosmic microwave background (CMB) observations, specifically in its spectral index, $beta_d$. Failure to account for such variations will cause errors in the foreground cleaning that propagate into errors on cosmological parameter recovery from the cleaned CMB map. It is unclear how robust prior studies of the Planck data which constrained $beta_d$ variations are due to challenges with noise modeling, residual systematics, and priors. To clarify constraints on $beta_d$ and its variation, we employ two pixel space analyses of the polarized dust foreground at $>3.7^{circ}$ scales on $approx 60%$ of the sky at high Galactic latitudes. A template fitting method, which measures $beta_d$ over three regions of $approx 20%$ of the sky, does not find significant deviations from an uniform $beta_d = 1.55$, consistent with prior Planck determinations. An additional analysis in these regions, based on multifrequency fits to a dust and CMB model per pixel, puts limits on $sigma_{beta_d}$, the Gaussian spatial variation in $beta_d$. At the highest latitudes, the data support $sigma_{beta_d}$ up to $0.45$, $0.30$ at mid-latitudes, and $0.15$ at low-latitudes. We also demonstrate that care must be taken when interpreting the current Planck constraints, $beta_d$ maps, and noise simulations. Due to residual systematics and low dust signal to noise at high latitudes, forecasts for ongoing and future missions should include the possibility of large values of $sigma_{beta_d}$ as estimated in this paper, based on current polarization data.
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Science opportunities and recommendations concerning optical/infrared polarimetry for the upcoming decade in the field of cosmology. Community-based White Paper to Astro2010 in response to the call for such papers.
The characterization of the dust polarization foreground to the Cosmic Microwave Background (CMB) is a necessary step towards the detection of the B-mode signal associated with primordial gravitational waves. We present a method to simulate maps of polarized dust emission on the sphere, similarly to what is done for the CMB anisotropies. This method builds on the understanding of Galactic polarization stemming from the analysis of Planck data. It relates the dust polarization sky to the structure of the Galactic magnetic field and its coupling with interstellar matter and turbulence. The Galactic magnetic field is modelled as a superposition of a mean uniform field and a random component with a power-law power spectrum of exponent $alpha_{rm M}$. The model parameters are constrained to fit the power spectra of dust polarization EE, BB and TE measured using Planck data. We find that the slopes of the E and B power spectra of dust polarization are matched for $alpha_{rm M} = -2.5$. The model allows us to compute multiple realizations of the Stokes Q and U maps for different realizations of the random component of the magnetic field, and to quantify the variance of dust polarization spectra for any given sky area outside of the Galactic plane. The simulations reproduce the scaling relation between the dust polarization power and the mean total dust intensity including the observed dispersion around the mean relation. We also propose a method to carry out multi-frequency simulations including the decorrelation measured recently by Planck, using a given covariance matrix of the polarization maps. These simulations are well suited to optimize component separation methods and to quantify the confidence with which the dust and CMB B-modes can be separated in present and future experiments. We also provide an astrophysical perspective on our modeling of the dust polarization spectra.
The characterization of the Galactic foregrounds has been shown to be the main obstacle in the challenging quest to detect primordial B-modes in the polarized microwave sky. We make use of the Planck-HFI 2015 data release at high frequencies to place new constraints on the properties of the polarized thermal dust emission at high Galactic latitudes. Here, we specifically study the spatial variability of the dust polarized spectral energy distribution, and its potential impact on the determination of the tensor-to-scalar ratio. We use the correlation ratio of the $C_ell^{BB}$ angular power spectra between the 217- and 353-GHz channels as a tracer of these potential variations, computed on different high Galactic latitude regions, ranging from 80% to 20% of the sky. The new insight from Planck data is a departure of the correlation ratio from unity that cannot be attributed to a spurious decorrelation due to the cosmic microwave background, instrumental noise, or instrumental systematics. The effect is marginally detected on each region, but the statistical combination of all the regions gives more than 99% confidence for this variation in polarized dust properties. In addition, we show that the decorrelation increases when there is a decrease in the mean column density of the region of the sky being considered, and we propose a simple power-law empirical model for this dependence, which matches what is seen in the Planck data. We explore the effect that this measured decorrelation has on simulations of the BICEP2-Keck Array/Planck analysis and show that the 2015 constraints from those data still allow a decorrelation between the dust at 150 and 353GHz of the order of the one we measure. Finally we show that either spatial variation of the dust SED or of the dust polarization angle could produce decorrelations between 217- and 353-GHz data similar to those we observe in the data.
The Cosmic Microwave Background anisotropies are difficult to measure at large angular scales. In this paper, we present a new analysis of the Planck High Frequency Instrument data that brings the cosmological part and its major foreground signal close to the detector noise. The solar dipole signal, induced by the motion of the solar system with respect to the CMB, is a very efficient tool to calibrate a detector or a set of detectors with high accuracy. In this work, the solar dipole signal is used to extract corrections of the frequency maps offsets reducing significantly uncertainties. The solar dipole parameters are refined together with the improvement of the high frequency foregrounds, and of the CMB large scales cosmological anisotropies. The stability of the solar dipole parameters is a powerful way to control the galactic foregrounds removal in the component separation process. It is used to build a model for Spectral Energy Distribution spatial variations of the interstellar dust emission. The knowledge of these variations will help future CMB analyses in intensity, and also in polarization to measure faint signal related to the optical reionization depth and the tensor-to-scalar ratio of the primordial anisotropies. The results of this work are: improved solar dipole parameters, a new interstellar dust model, and a large scale cosmological anisotropies map.
We combine the latest datasets obtained with different surveys to study the frequency dependence of polarized emission coming from Extragalactic Radio Sources (ERS). We consider data over a very wide frequency range starting from $1.4$ GHz up to $217$ GHz. This range is particularly interesting since it overlaps the frequencies of the current and forthcoming Cosmic Microwave Background (cmb) experiments. Current data suggest that at high radio frequencies, ($ u geq 20$ GHz) the fractional polarization of ERS does not depend on the total flux density. Conversely, recent datasets indicate a moderate increase of polarization fraction as a function of frequency, physically motivated by the fact that Faraday depolarization is expected to be less relevant at high radio-frequencies. We compute ERS number counts using updated models based on recent data, and we forecast the contribution of unresolved ERS in CMB polarization spectra. Given the expected sensitivities and the observational patch sizes of forthcoming cmb experiments about $sim 200 $ ( up to $sim 2000 $ ) polarized ERS are expected to be detected. Finally, we assess that polarized ERS can contaminate the cosmological B-mode polarization if the tensor-to-scalar ratio is $r< 0.05$ and they have to be robustly controlled to de-lens cmb B-modes at the arcminute angular scales.
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