R. B. Barreiro

Comparison of filters for the detection of point sources in Planck simulations

We study the detection of extragalactic point sources in 2D flat simulations for all the frequencies of the forthcoming ESA’s Planck mission. In this work, we have used the most recent available templates of the microwave sky: as for the diffuse Galactic components and the Sunyaev‐Zel’dovich clusters we have used the ‘Plank Reference Sky Model’; as for the extragalactic point sources, our simulations ‐ which comprise all the source populations relevant in this frequency interval ‐ are based on up-to-date cosmological evolution models for sources. To consistently compare the capabilities of different filters for the compilation of ‐ hopefully ‐ the most complete blind catalogue of point sources, we have obtained three catalogues by filtering the simulated sky maps with: the matched filter (MF), the Mexican Hat Wavelet (MHW1) and the Mexican Hat Wavelet 2 (MHW2), the first two members of the Mexican Hat Wavelet Family. For the nine Planck frequencies we show the number of real and spurious detections and the percentage of spurious detections at different flux detection limits as well as the completeness level of the catalogues and the average errors in the estimation of the flux density of detected sources. Allowing a 5 per cent of spurious detections, we obtain the following number of detections by filtering with the MHW2 an area equivalent to half of the sky: 580 (30 GHz), 342 (44 GHz), 341 (70 GHz), 730 (100 GHz), 1130 (143 GHz), 1233 (217 GHz), 990 (353 GHz), 1025 (545 GHz) and 3183 (857 GHz). Our current results indicate that the MF and the MHW2 yield similar results, whereas the MHW1 performs worse in some cases and especially at very low fluxes. This is a relevant result, because we are able to obtain comparable results with the well-known MF and with this specific wavelet, the MHW2, which is much easier to implement and use.

The effect of point sources on satellite observations of the cosmic microwave background

ABSTRACT We study the effect of extragalactic point sources on satellite observations of the cosmic mi-crowavebackground(CMB). In order to separate the contributionsdue to differentforegroundcomponents, a maximum-entropy method is applied to simulated observations by the PlanckSurveyor satellite. In addition to point sources, the simulations include emission from theCMB and the kinetic and thermal Sunyaev-Zel’dovich (SZ) effects from galaxy clusters, aswell as Galactic dust, free-free and synchrotron emission.We find that the main input com-ponents are faithfully recovered and, in particular, that the quality of the CMB reconstructionis only slightly reduced by the presence of point sources. In addition, we find that it is pos-sible to recover accurate point source catalogues at each of the Planck Surveyor observingfrequencies.Key words: methods: data analysis – techniques: image processing – cos mic microwavebackground. 1 INTRODUCTIONA new generation of cosmic microwave background (CMB) satel-lite missions are currently in the final stages of design. The NASAMAP satellite is expected to be launched by 2000, followed by theESA Planck Surveyor in 2007 (Bersanelli et al. 1996). Both mis-sions will provide detailed all-sky maps of the CMB anisotropies,leading to definitive measurements of the CMB power spectrum .This should allow tight constraints to be placed on fundamentalcosmological parameters and distinguish between competing the-ories of structure formation in the early Universe such as inflationand topological defects.The maps produced by these satellites will, however, containcontributions from various foreground components, most notablyGalactic dust, free-free and synchrotron emission as well as thekinetic and thermal SZ effects from galaxy clusters. In addition,significant contamination from extragalactic point source s is alsoexpected. It is therefore clear that in order to obtain maps of theCMB anisotropies alone, it is necessary to separate the emissiondue to these various components.In a previous paper, Hobson et al. (1998) (hereafter Paper I)use a non-linear maximum-entropy method (MEM) to separate theemission due to the different foreground components from simu-lated Planck Surveyor observations of a 10 ×10 deg

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.

Correlation of excursion sets for non-Gaussian cosmic microwave background temperature distributions

We present a method, based on the correlation function of excursion sets above a given threshold, to test the Gaussianity of the CMB temperature fluctuations in the sky. In particular, this method can be applied to discriminate between standard inflationary scenarios and those producing non-Gaussianity such as topological defects. We have obtained the normalized correlation of excursion sets, including different levels of noise, for 2-point probability density functions constructed from the Gaussian, \chi_n^2 and Laplace 1-point probability density functions in two different ways. Considering subdegree angular scales, we find that this method can distinguish between different distributions even if the corresponding marginal probability density functions and/or the radiation power spectra are the same.

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.

Effect of component separation on the temperature distribution of the cosmic microwave background

We present a study of the effect of component separation on the recovered cosmic microwave background (CMB) temperature distribution. First, we extract the CMB component from simulated multifrequency Planck data (in small patches of the sky) using the maximum-entropy method (MEM), Wiener filter (WF) and a linear combination of the frequency channels (LCFC). We then apply a wavelet-based method to study the Gaussianity of the recovered CMB and compare it with the same analysis for the input map. When the original CMB map is Gaussian (and assuming that point sources have been removed), we find that neither MEM nor WF introduce non-Gaussianity in the CMB reconstruction. Regarding the LCFC, the Gaussian character is also preserved provided that the appropriate combination of frequency channels is used. On the contrary, if the input CMB map is non-Gaussian, all the studied methods produce a reconstructed CMB with lower detections of non-Gaussianity than the original map. In this case, MEM produces in general the highest non-Gaussian detections in the recovered map and, therefore, provides the best reconstruction from the considered methods to search for non-Gaussianity. We have also studied the effect of point sources in the MEM reconstruction. If no attempt of removing point sources is performed, they clearly contaminate the CMB reconstruction, introducing spurious non-Gaussianity. However, if the brightest point sources are removed from the data using the Mexican Hat Wavelet, the Gaussian character of the CMB is preserved in the reconstruction.

Testing gaussianity on archeops data

Aims. We performed a Gaussianity analysis using a goodness-of-fit test and the Minkowski functionals on the sphere to study the measured Archeops Cosmic Microwave Background (CMB) temperature anisotropy data for a 143 GHz Archeops bolometer. We consider large angular scales, greater than 1.8 degrees, and a large fraction of the North Galactic hemisphere, around 16%, with a galactic latitude b > 15 degrees. Methods. The considered goodness-of-fit test, first proposed by Rayner & Best (1989, Smooth Tests of Goodness of Fit), was applied to the data after a signal-to-noise decomposition. The three Minkowski functionals on the sphere were used to construct a χ 2 statistic using different thresholds. The former method was calibrated using simulations of Archeops data containing the CMB signal and instrumental noise in order to check its asymptotic convergence. Two kind of maps produced with two different map-making techniques (coaddition and Mirage) are analysed. Results. Archeops maps for both Mirage and coaddition map-making, are compatible with Gaussianity. From these results we can exclude a dust and atmospheric contamination larger than 7.8% (90% CL). Also the non-linear coupling parameter fnl can be constrained to be fnl = 200 +1100 −800 at the 95% CL and on angular scales of 1.8 degrees. For comparison, the same method was applied to data from the NASA WMAP satellite in the same region of sky. The 1-year and 3-year releases were used. Results are compatible with those obtained with Archeops, implying in particular an upper limit for fnl on degree angular scales.

Statistical analysis of undetected point sources in cosmic microwave background maps

Cosmic microwave background (CMB) temperature anisotropies follow a Gaussian statistical distribution in the standard inflationary model, but there are non-Gaussian contributions due to astrophysical foregrounds. The detection of the non-Gaussian signal due to extragalactic point sources and its distinction from the possible intrinsic non-Gaussianity is an issue of great importance in CMB analysis. The Mexican Hat Wavelet Family (MHWF), which has been proved very useful for the detection of extragalactic point sources, is applied here to the study of non-Gaussianity due to point sources in CMB maps. We carry out simulations of CMB maps with the characteristics of the forthcoming Planck mission at 70 and 100 GHz and filter them with the MHWF. By comparing the skewness and kurtosis of simulated maps with and without point sources, we are able to detect clearly the non-Gaussian signal due to point sources for flux limits as low as 0.4 Jy (70 GHz) and 0.3 Jy (100 GHz). The second and third members of the MHWF perform better in this respect than the Mexican Hat Wavelet (MHW1) and much better than the Daubechies 4 wavelet. We have also estimated the third order, K 3 , and fourth order, K 4 , cumulants produced by point sources at these Planck channels by means of a fit with the MHWF. The average relative errors with respect to the real values are below 12 per cent for fluxes down to 0.6 Jy (70 GHz) and 0.4 Jy (100 GHz). The values of these cumulants allow us to distinguish between different source counts models. From the estimated cumulants and assuming a power law for the source number counts we are able to obtain the coefficients a and A of the differential number counts, a = 2.19 ± 0.46 (a = 2.26 ± 0.19), A = 24.3 ± 4.3 (A = 21.0 ± 4.2) for 70 (100) GHz, assuming a flux limit of 1 Jy. These results are consistent with the values obtained from simulations containing only point sources, which are: a = 2.32 ± 0.06 (a = 2.35 ± 0.16), A = 22.1 ± 1.5 (A = 20.0 ± 3.7) for 70 (100) GHz.

Scalar quantities as detectors of non-Gaussianity in cosmic microwave background maps

We study the power of several scalar quantities constructed on the sphere (presented in Monteserin et al. 2005) to detect non-Gaussianity on the temperature distribution of the cosmic microwave background (CMB). The test has been performed using non-Gaussian CMB simulations with injected skewness or kurtosis generated through the Edgeworth expansion. We have also taken into account in the analysis the effect of anisotropic noise and the presence of a Galactic mask. We find that the best scalars to detect an excess of skewness in the simulations are the derivative of the gradient, the fractional isotropy, the Laplacian and the shape index. For the kurtosis case, the fractional anisotropy, the Laplacian and the determinant are the quantities that perform better.