P. Vielva

Isotropic wavelets: a powerful tool to extract point sources from cosmic microwave background maps

It is the aim of this paper to introduce the use of isotropic wavelets to detect and determine the flux of point sources appearing in cosmic microwave background (CMB) maps. The most suitable wavelet to detect point sources filtered with a Gaussian beam is the ‘Mexican Hat’. An analytical expression of the wavelet coefficient obtained in the presence of a point source is provided and used in the detection and flux estimation methods presented. For illustration the method is applied to two simulations (assuming Planck mission characteristics) dominated by CMB (100xa0GHz) and dust (857xa0GHz), as these will be the two signals dominating at low and high frequencies respectively in the Planck channels. We are able to detect bright sources above 1.58xa0Jy at 857xa0GHz (82xa0per cent of all sources) and above 0.36xa0Jy at 100xa0GHz (100xa0per cent of all), with errors in the flux estimation below 25xa0per cent. The main advantage of this method is that nothing has to be assumed about the underlying field, i.e. about the nature and properties of the signal plus noise present in the maps. This is not the case in the detection method presented by Tegmark & Oliveira-Costa. Both methods are compared, producing similar results.

Point source detection using the Spherical Mexican Hat Wavelet on simulated all‐sky Planck maps

We present an estimation of the point source (PS) catalogue that could be extracted from the forthcoming ESA Planck mission data. We have applied the Spherical Mexican Hat Wavelet (SMHW) to simulated all-sky maps that include CMB, Galactic emission (thermal dust, free-free and synchrotron), thermal Sunyaev-Zel’dovich effect and PS emission, as well as instrumental white noise . This work is an extension of the one presented in Vielva et al. (2001a). We have developed an algorithm focused on a fast local optimal scale determination, that is crucial to achieve a PS catalogue with a large number of detections and a low flux limit. An important effort has been also done to reduce the CPU time processor for spherical harmonic transformation, in order to perform the PS detection in a reasonable time. The presented algorithm is able to provide a PS catalogue above fluxes: 0.48 Jy (857 GHz), 0.49 Jy (545 GHz), 0.18 Jy (353 GHz), 0.12 Jy (217 GHz), 0.13 Jy (143 GHz), 0.16 Jy (100 GHz HFI), 0.19 Jy (100 GHz LFI), 0.24 Jy (70 GHz), 0.25 Jy (44 GHz) and 0.23 Jy (30 GHz). We detect around 27700 PS at the highest frequency Planck channel and 2900 at the 30 GHz one. The completeness level are: 70% (857 GHz), 75% (545 GHz), 70% (353 GHz), 80% (217 GHz), 90% (143 GHz), 85% (100 GHz HFI), 80% (100 GHz LFI), 80% (70 GHz), 85% (44 GHz) and 80% (30 GHz). In addition, we can find several PS at different channels, allowing the study of the spectral behaviour and the physical processes acting on them. We also present the basic procedure to apply the method in maps convolved with asymmetric beams. The algorithm takes � 72 hours for the most CPU time demanding channel (857 GHz) in a Compaq HPC320 (Alpha EV68 1 GHz processor) and requires 4 GB of RAM memory; the CPU time goes as O(NRoNpix 3/2 log(Npix)), where Npix is the number of pixels in the map and NRo is the number of optimal scales needed.

Combining maximum‐entropy and the Mexican hat wavelet to reconstruct the microwave sky

We present a maximum–entropy method (MEM) and ‘Mexican Hat’ wavelet (MHW) joint analysis to recover the different components of the microwave sky from simulated observations by the ESA Planck satellite in a small patch of the sky (12.8×12.8 deg 2 ). This combined method allows one to improve the CMB, Sunyaev– Zel’dovich and Galactic foregrounds separation achieved by the MEM technique alone. In particular, the reconstructed CMB map is free from any bright point source contamination. The joint analysis also produces point source catalogues at each Planck frequency which are more complete and accurate than those obtained by each method on its own. The results are especially improved at high frequencies where infrared galaxies dominate the point source contribution. Although this joint technique has been performed on simulated Planck data, it could be easily applied to other multifrequency CMB experiments, such as the forthcoming NASA MAP satellite or the recently performed Boomerang and MAXIMA experiments.

Alignment and signed-intensity anomalies in WMAP data

Significant alignment and signed-intensity anomalies of local features of the cosmic microwave background (CMB) are detected on the three-year WMAP data, through a decomposition of the signal with steerable wavelets on the sphere. In addition to identifying local features of a signal at specific scales, steerable wavelets allow one to determine their local orientation and signed-intensity. Firstly, an alignment analysis identifies two mean preferred planes in the sky, both with normal axes close to the CMB dipole axis. The first plane is defined by the directions toward which local CMB features are anomalously aligned. A mean preferred axis is also identified in this plane, located very close to the ecliptic poles axis. The second plane is defined by the directions anomalously avoided by local CMB features. This alignment anomaly provides further insight on recent results (Wiaux et al. 2006a). Secondly, a signed-intensity analysis identifies three mean preferred directions in the southern galactic hemisphere with anomalously high or low temperature of local CMB features: a cold spot essentially identified with a known cold spot (Vielva et al. 2004), a second cold spot lying very close to the southern end of the CMB dipole axis, and a hot spot lying close to the southern end of the ecliptic poles axis. In both analyses, the anomalies are observed at wavelet scales corresponding to angular sizes around 10° on the celestial sphere, with global significance levels around 1%. Further investigation reveals that the alignment and signed-intensity anomalies are only very partially related. Instrumental noise, foreground emissions, as well as some form of other systematics, are strongly rejected as possible origins of the detections. An explanation might still be envisaged in terms of a global violation of the isotropy of the Universe, inducing an intrinsic statistical anisotropy of the CMB.

An ultradeep submillimetre map: beneath the SCUBA confusion limit with lensing and robust source extraction

Extracting sources with low signal-to-noise ratio (S/N) from maps with structured background is a non-trivial task which has become important in studying the faint end of the submillimetre (submm) number counts. In this paper, we study the source extraction from submm jiggle-maps from the Submillimetre Common-User Bolometer Array (SCUBA) using the Mexican hat wavelet (MHW), an isotropic wavelet technique. As a case study, we use a large (11.8-arcmin 2 ) jiggle-map of the galaxy cluster Abell 2218 (A2218), with a 850-μm la rms sensitivity of 0.6-1 mJy. We show via simulations that MHW is a powerful tool for the reliable extraction of low-S/N sources from the SCUBA jiggle-maps and nine sources are detected in the A2218 850-μm image. Three of these sources are identified as images of a single background source with an unlensed flux of 0.8 mJy. Further, two single-imaged sources also have unlensed fluxes <2 mJy, below the blank-field confusion limit. In this ultradeep map, the individual sources detected resolve nearly all of the extragalactic background light at 850 μm, and the deep data allow to put an upper limit of 44 sources arcmin -2 to 0.2 mJy at 850 μm.

A Bayesian non-parametric method to detect clusters in Planck data

We show how one may expect a significant number of Sunyaev–Zeldovich (SZ) detections in future Planck data without any of the typical assumptions needed in present component separation methods, such as concerning the power spectrum or the frequency dependence of any of the components, circular symmetry or a typical scale for the clusters. We reduce the background by subtracting an estimate of the point sources, dust and cosmic microwave background (CMB). The final SZ effect map is estimated in Fourier space. The catalogue of returned clusters is complete above flux ≈200 mJy (353 GHz), while the lowest flux reached by our method is ≈70 mJy (353 GHz). We predict a large number of detections (∼9000) over four-fifths of the sky. This large number of SZ detections will allow a robust and consistent analysis of the evolution of the cluster population with redshift and will have important implications for determining the best cosmological model.

Cosmic microwave background power spectrum estimation and map reconstruction with the expectation-maximization algorithm

We apply the iterative expectation-maximization algorithm (EM) to estimate the power spectrum of the cosmic microwave background (CMB) from multifrequency microwave maps. In addition, we are also able to provide a reconstruction of the CMB map. By assuming that the combined emission of the foregrounds plus the instrumental noise is Gaussian distributed in Fourier space, we have simplified the EM procedure, finding an analytical expression for the maximization step. By using the simplified expression, the CPU time can be greatly reduced. We test the stability of our power spectrum estimator with realistic simulations of Planck data, including point sources and allowing for spatial variation of the frequency dependence of the Galactic emissions. Without prior information about any of the components, our new estimator can recover the CMB power spectrum up to scales l≈ 1500 with less than 10 per cent error. This result is significantly improved if the brightest point sources are removed before applying our estimator. In this way, the CMB power spectrum can be recovered up to l≈ 1700 with 10 per cent error and up to l≈ 2100 with 50 per cent error. This result is very close to the one that would be obtained in the ideal case of only CMB plus white noise, for which all our assumptions are satisfied. Moreover, the EM algorithm also provides a straightforward mechanism for reconstructing the CMB map. The recovered cosmological signal shows a high degree of correlation (r= 0.98) with the input map and low residuals.

QUIJOTE scientific results – I. Measurements of the intensity and polarisation of the anomalous microwave emission in the Perseus molecular complex

In this paper, we present Q-U-I JOint Tenerife Experiment (QUIJOTE) 10-20 GHz observations (194 h in total over ???250 deg2) inintensity and polarisation of G159.6-18.5, one of the most widelystudied regions harbouring anomalous microwave emission (AME). Bycombining with other publicly available intensity data, we achieve themost precise spectrum of the AME measured to date in an individualregion, with 13 independent data points between 10 and 50 GHz beingdominated by this emission. The four QUIJOTE data points provide thefirst independent confirmation of the downturn of the AME spectrum atlow frequencies, initially unveiled by the COSMOlogical Structures OnMedium Angular Scales experiment in this region. Our polarisation maps,which have an angular resolution of ???1?? and a sensitivity of ???25 ??K beam-1, are consistent with zero polarisation. Weobtain upper limits on the polarisation fraction of ?? {textless} 6.3 and{textless}2.8 per cent (95 per cent C.L.), respectively, at 12 and 18 GHz(??AME {textless} 10.1 and {textless}3.4 per cent with respect to theresidual AME intensity), a frequency range where no AME polarisationobservations have been reported to date. The combination of theseconstraints with those from other experiments confirm that all themagnetic dust models based on single-domain grains, and most of thoseconsidering randomly oriented magnetic inclusions, predict higherpolarisation levels than is observed towards regions with AME. Also,neither of the two considered models of electric dipole emission seemsto be compatible with all the observations together. More stringentconstraints of the AME polarisation at 10-40 GHz are necessary todisentangle between different models, to which future QUIJOTE data willcontribute.

An optimal estimator for the CMB–LSS angular power spectrum and its application to WMAP and NVSS data

We use a quadratic maximum likelihood (QML) method to estimate the angular power spectrum of the cross-correlation between cosmic microwave background and large-scale structure maps as well as their individual auto-spectra. We describe our implementation of this method and demonstrate its accuracy on simulated maps. We apply this optimal estimator to Wilkinson Microwave Anisotropy Probe (WMAP) 7-yr and National Radio Astronomical Observatory (NRAO) Very Large Array Sky Survey (NVSS) data and explore the robustness of the angular power spectrum estimates obtained by the QML method. With the correction of the declination systematics in NVSS, we can safely use most of the information contained in this survey. We then make use of the angular power spectrum estimates obtained by the QML method to derive constraints on the dark energy critical density in a flat Λ cold dark matter model by different likelihood prescriptions. When using just the cross-correlation between WMAP 7-yr and NVSS maps with 1°.8 resolution, the best-fitting model has a cosmological constant of approximately 70 per cent of the total energy density, disfavouring an Einstein–de sitter universe at more than 2σ confidence level.

CMB polarization as a probe of the anomalous nature of the Cold Spot

One of the most interesting explanations for the non-Gaussian Cold Spot detected in the WMAP data by Vielva et al. (2004), is that it arises from the interaction of the CMB radiation with a cosmic texture (Cruz et al. 2007b). In this case, a lack of polarization is expected in the region of the spot, as compared to the typical values associated to large uctuations of a Gaussian and isotropic random eld. In addition, other physical processes related to a non-linear evolution of the gravitational eld could lead to a similar scenario. However, some of these alternative scenarios (e.g., a large void in the large scale structure) have been shown to be very unlikely. In this work we characterise the polarization properties of the Cold Spot under both hypotheses: a large Gaussian uctuation and an anomalous feature generated, for instance, by a cosmic texture. We also propose a methodology to distinguish between them, and we discuss its discrimination power as a function of the instrumental noise level. In particular, we address the cases of current experiments, like WMAP and Planck, and others in development as QUIJOTE. We nd that for an ideal experiment with a high polarization sensitivity, the Gaussian hypothesis could be rejected at a signicance level better than 0.8%. While WMAP is far from providing useful information in this respect, we nd that Planck will be able to reach a signicance of around 7%; in addition, we show that the ground-based experiment QUIJOTE could provide a signicance of around 1%, close to the ideal case. If these results are combined with the signicance level found for the Cold Spot in temperature, the capability of QUIJOTE and Planck to reject the alternative hypothesis becomes 0.025% and 0.124%, respectively.