On the impact of large angle CMB polarization data on cosmological parameters

(abridged) We study the impact of the large-angle CMB polarization datasets publicly released by the WMAP and Planck satellites on the estimation of cosmological parameters of the $\Lambda$CDM model. To complement large-angle polarization, we consider the high-resolution CMB datasets from either WMAP or Planck, as well as CMB lensing as traced by Planck. In the case of WMAP, we compute the large-angle polarization likelihood starting over from low-resolution frequency maps and their covariance matrices, and perform our own foreground mitigation technique, which includes as a possible alternative Planck 353 GHz data to trace polarized dust. We find that the latter choice induces a downward shift in the optical depth $\tau$, of order ~$2\sigma$, robust to the choice of the complementary high-l dataset. When the Planck 353 GHz is consistently used to minimize polarized dust emission, WMAP and Planck 70 GHz large-angle polarization data are in remarkable agreement: by combining them we find $\tau = 0.066 ^{+0.012}_{-0.013}$, again very stable against the particular choice for high-$\ell$ data. We find that the amplitude of primordial fluctuations $A_s$, notoriously degenerate with $\tau$, is the parameter second most affected by the assumptions on polarized dust removal, but the other parameters are also affected, typically between $0.5$ and $1\sigma$. In particular, cleaning dust with \planck's 353 GHz data imposes a $1\sigma$ downward shift in the value of the Hubble constant $H_0$, significantly contributing to the tension reported between CMB based and direct measurements of $H_0$. On the other hand, we find that the appearance of the so-called low $\ell$ anomaly, a well-known tension between the high- and low-resolution CMB anisotropy amplitude, is not significantly affected by the details of large-angle polarization, or by the particular high-$\ell$ dataset employed.Comment: 19 pages, 4 figures, 3 table

Thermal stability in precision cosmology experiments: the Planck LFI case

Abstract After the great success of NASA's satellite missions COBE and WMAP, the Planck mission represents the third generation of mm-wave instruments designed for space observations of CMB anisotropies. Two instruments, the LowFrequency Instrument (LFI) and the High-Frequency Instrument (HFI) will produce CMB maps with unprecedented angular resolution, sensitivity and frequency coverage. This ambitious task will be achieved by using low noise HEMT detectors cryogenically cooled at B20 K for the LFI and bolometric detectors cooled at 0.1 K for the HFI; in particular, the LFI is based on pseudo-correlation receivers in which the sky signal is continuously compared to a cryogenic reference load in thermal contact with the HFI 4 K stage. Such high sensitivity in Planck detectors calls for a strict control of systematic effects, which must be kept at mK level in the final maps; this in turn imposes tight requirements on the thermal and electrical stability of the different stages in the instrument. In this paper we discuss a study of the impact of thermal fluctuations at the level of the 20 K cooler cold-end on the Planck-LFI measurements and present some viable solutions that have been adopted to keep the residual systematic error within the required values for Planck-LFI.

Galactic foreground contribution to the BEAST CMB Anisotropy Maps

We report limits on the Galactic foreground emission contribution to the Background Emission Anisotropy Scanning Telescope (BEAST) Ka- and Q-band CMB anisotropy maps. We estimate the contribution from the cross-correlations between these maps and the foreground emission templates of an H${\alpha}$ map, a de-striped version of the Haslam et al. 408 MHz map, and a combined 100 $\mu$m IRAS/DIRBE map. Our analysis samples the BEAST $\sim10^\circ$ declination band into 24 one-hour (RA) wide sectors with $\sim7900$ pixels each, where we calculate: (a) the linear correlation coefficient between the anisotropy maps and the templates; (b) the coupling constants between the specific intensity units of the templates and the antenna temperature at the BEAST frequencies and (c) the individual foreground contributions to the BEAST anisotropy maps. The peak sector contributions of the contaminants in the Ka-band are of 56.5% free-free with a coupling constant of $8.3\pm0.4$ $\mu$K/R, and 67.4% dust with $45.0\pm2.0$ $\mu$K/(MJy/sr). In the Q-band the corresponding values are of 64.4% free-free with $4.1\pm0.2$ $\mu$K/R and 67.5% dust with $24.0\pm1.0$ $\mu$K/(MJy/sr). Using a lower limit of 10% in the relative uncertainty of the coupling constants, we can constrain the sector contributions of each contaminant in both maps to $< 20$% in 21 (free-free), 19 (dust) and 22 (synchrotron) sectors. At this level, all these sectors are found outside of the $\mid$b$\mid = 14.6^\circ$ region. By performing the same correlation analysis as a function of Galactic scale height, we conclude that the region within $b=\pm17.5^{\circ}$ should be removed from the BEAST maps for CMB studies in order to keep individual Galactic contributions below $\sim 1$% of the map's rms.Comment: 17 pages PostScript file. Better resolution figures can be found in the web page http://www.das.inpe.br/~alex/beast_foregrounds.html. Accepted for publication in the ApJ Suppl. Serie

In-flight calibration and verification of the Planck-LFI instrument

In this paper we discuss the Planck-LFI in-flight calibration campaign. After a brief overview of the ground test campaigns, we describe in detail the calibration and performance verification (CPV) phase, carried out in space during and just after the cool-down of LFI. We discuss in detail the functionality verification, the tuning of the front-end and warm electronics, the preliminary performance assessment and the thermal susceptibility tests. The logic, sequence, goals and results of the in-flight tests are discussed. All the calibration activities were successfully carried out and the instrument response was comparable to the one observed on ground. For some channels the in-flight tuning activity allowed us to improve significantly the noise performance.Comment: Long technical paper on Planck LFI in flight calibration campaign: 109 pages in this (not final) version, 100 page in the final JINST versio

Planck-LFI CPV: stability check before bias tuning

Planck LFI Commissioning and Performance Verification (CPV)This test consists of a 12-hours data acquisition performed with the instrument set with “CRYO” biases, i.e. the biases that have been obtained in CSL after the tuning activities. The objective of this test is to verify the readiness of the instrument for the CPV bias tuning activity from the signal stability point of view. As during this test the 4K temperature was still around 20 K and the stability was not optimized yet the check on knee frequency is meaningful just from the functionality point of view. No comparison is done between the calculated knee frequencies and the LFI scientific requirements