Probing non-Gaussianities on Large Scales in WMAP5 and WMAP7 Data using Surrogates

Probing Gaussianity represents one of the key questions in modern cosmology, because it allows to discriminate between different models of inflation. We test for large-scale non-Gaussianities in the cosmic microwave background (CMB) in a model-independent way. To this end, so-called first and second order surrogates are generated by first shuffling the Fourier phases belonging to the scales not of interest and then shuffling the remaining phases for the length scales under study. Using scaling indices as test statistics we find highly significant signatures for both non-Gaussianities and asymmetries on large scales for the WMAP data of the CMB. We find remarkably similar results when analyzing different ILC-maps based on the WMAP five and seven year data. Such features being independent from the map-making procedure would disfavor the fundamental principle of isotropy as well as canonical single-field slow-roll inflation - unless there is some undiscovered systematic error in the collection or reduction of the CMB data or yet unknown foreground contributions.Comment: 4 pages, 3 figures, to appear in the Proceedings of Moriond Cosmology 201

The joint large-scale foreground-CMB posteriors of the 3-year WMAP data

Using a Gibbs sampling algorithm for joint CMB estimation and component separation, we compute the large-scale CMB and foreground posteriors of the 3-yr WMAP temperature data. Our parametric data model includes the cosmological CMB signal and instrumental noise, a single power law foreground component with free amplitude and spectral index for each pixel, a thermal dust template with a single free overall amplitude, and free monopoles and dipoles at each frequency. This simple model yields a surprisingly good fit to the data over the full frequency range from 23 to 94 GHz. We obtain a new estimate of the CMB sky signal and power spectrum, and a new foreground model, including a measurement of the effective spectral index over the high-latitude sky. A particularly significant result is the detection of a common spurious offset in all frequency bands of ~ -13muK, as well as a dipole in the V-band data. Correcting for these is essential when determining the effective spectral index of the foregrounds. We find that our new foreground model is in good agreement with template-based model presented by the WMAP team, but not with their MEM reconstruction. We believe the latter may be at least partially compromised by the residual offsets and dipoles in the data. Fortunately, the CMB power spectrum is not significantly affected by these issues, as our new spectrum is in excellent agreement with that published by the WMAP team. The corresponding cosmological parameters are also virtually unchanged.Comment: 5 pages, 4 figures, submitted to ApJL. Background data are available at http://www.astro.uio.no/~hke under the Research ta

Large scale directional anomalies in the WMAP 5yr ILC map

We study the alignments of the low multipoles of CMB anisotropies with specific directions in the sky (i.e. the dipole, the north Ecliptic pole, the north Galactic pole and the north Super Galactic pole). Performing $10^5$ random extractions we have found that: 1) separately quadrupole and octupole are mildly orthogonal to the dipole but when they are considered together, in analogy to \cite{Copi2006}, we find an unlikely orthogonality at the level of 0.8% C.L.; 2) the multipole vectors associated to $\ell=4$ are unlikely aligned with the dipole at $99.1$ C.L.; 3) the multipole vectors associated to $\ell=5$ are mildly orthogonal to the dipole but when we consider only maps that show exactly the same correlation among the multipoles as in the observed WMAP 5yr ILC, these multipole vectors are unlikely orthogonal to the dipole at $99.7$ C.L..Comment: 12 pages, 10 figures, 3 tables. Accepted for publication in JCAP. Few references added and some typos correcte

Analysis of CMB foregrounds using a database for Planck

Within the scope of the Planck IDIS (Integrated Data Information System) project we have started to develop the data model for time-ordered data and full-sky maps. The data model is part of the Data Management Component (DMC), a software system designed according to a three-tier architecture which allows complete separation between data storage and processing. The DMC is already being used for simulation activities and the modeling of some foreground components. We have ingested several Galactic surveys into the database and used the science data-access interface to process the data. The data structure for full-sky maps utilises the HEALPix tessellation of the sphere. We have been able to obtain consistent measures of the angular power spectrum of the Galactic radio continuum emission between 408 MHz and 2417 MHz.Comment: 7 pages, 6 figures. To appear in the Proceedings of the MPA/ESO/MPE Joint Astronomy Conference "Mining The Sky

The Planck-LFI instrument: analysis of the 1/f noise and implications for the scanning strategy

We study the impact of the 1/f noise on the PLANCK Low Frequency Instrument (LFI) osbervations (Mandolesi et al 1998) and describe a simple method for removing striping effects from the maps for a number of different scanning stategies. A configuration with an angle between telescope optical axis and spin-axis just less than 90 degrees (namely 85 degress) shows good destriping efficiency for all receivers in the focal plane, with residual noise degradation < 1-2 %. In this configuration, the full sky coverage can be achieved for each channel separately with a 5 degrees spin-axis precession to maintain a constant solar aspect angle.Comment: submitted to Astronomy and Astrophysics, 12 pages, 15 PostSript figure

Astrophysical components separation of COBE-DMR 4yr data with FastICA

We present an application of the fast Independent Component Analysis method to the COBE-DMR 4yr data. Although the signal-to-noise ratio in the COBE-DMR data is typically $\sim 1$, the approach is able to extract the CMB signal with high confidence when working at high galactic latitudes. The reconstructed CMB map shows the expected frequency scaling of the CMB. We fit the resulting CMB component for the rms quadrupole normalisation Qrms and primordial spectral index n and find results in excellent agreement with those derived from the minimum-noise combination of the 90 and 53 GHz DMR channels without galactic emission correction. Including additional channels (priors) such as the Haslam map of radio emission at 408 MHz and the DIRBE 140um map of galactic infra-red emission, the FastICA algorithm is able to both detect galactic foreground emission and separate it from the dominant CMB signal. Fitting the resulting CMB component for Qrms and n we find good agreement with the results from Gorski et al.(1996) in which the galactic emission has been taken into account by subtracting that part of the DMR signal observed to be correlated with these galactic template maps. We further investigate the ability of FastICA to evaluate the extent of foreground contamination in the COBE-DMR data. We include an all-sky Halpha survey (Dickinson, Davies & Davis 2003) to determine a reliable free-free template. In particular we find that, after subtraction of the thermal dust emission predicted by the Finkbeiner, Davis & Schlegel (1999) model 7, this component is the dominant foreground emission at 31.5 GHz. This indicates the presence of an anomalous dust correlated component which is well fitted by a power law spectral shape $\nu^{-\beta}$ with $\beta \sim 2.5$ in agreement with Banday et al. (2003).Comment: Submitted to MNRA