D. Herranz

Filtering techniques for the detection of Sunyaev–Zel'dovich clusters in multifrequency maps

The problem of detecting Sunyaev-Zeldovich (SZ) clusters in multifrequency CMB observations is investigated using a number of filtering techniques. A multifilter approach is introduced that optimizes the detection of SZ clusters on microwave maps. An alternative method is also investigated in which maps at different frequencies are combined in an optimal manner so that existing filtering techniques can be applied to the single combined map. The SZ profiles are approximated by the circularly-symmetric template τ(x) = [1 + (x/r c ) 2 ] - θ , with λ ≃ and x ≡ ‖x‖, where the core radius r c and the overall amplitude of the effect are not fixed a priori, but are determined from the data. The background emission is modelled by a homogeneous and isotropic random field, characterized by a cross-power spectrum P v 1 v 2 (q) with q ≡ ‖q‖. The filtering methods are illustrated by application to simulated Planck observations of a 12.8° x 12.8° patch of sky in 10 frequency channels. Our simulations suggest that the Planck instrument should detect 10 000 SZ clusters in 2/3 of the sky. Moreover, we find the catalogue to be complete for fluxes S > 170 mJy at 300 GHz.

Optimal Detection of Sources on a Homogeneous and Isotropic Background

This paper introduces the use of pseudofilters that optimize the detection/extraction of sources on a background. We assume as a first approach that such sources are described by a spherical (central) profile and that the background is represented by a homogeneous and isotropic random field. We make an n-dimensional treatment, placing emphasis on astrophysical applications for spectra, images, and volumes, for the cases of exponential and Gaussian source profiles and scale-free power spectra to represent the background.

SCALE-ADAPTIVE FILTERS FOR THE DETECTION/SEPARATION OF COMPACT SOURCES

This paper presents scale-adaptive filters that optimize the detection/separation of compact sources on a background. We assume that the sources have a multiquadric profile, i.e., τ(x) = [1 + (x/rc)2]-λ,λ ≥ ,x ≡ ||, and a background modeled by a homogeneous and isotropic random field, characterized by a power spectrum P(q) ∝ q-γ,γ ≥ 0,q ≡ ||. We make an n-dimensional treatment but consider two interesting astrophysical applications related to clusters of galaxies (Sunyaev-Zeldovich effect and X-ray emission).

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.

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.

Point source detection and extraction from simulated Planck time-ordered data using optimal adaptive filters

Wavelet-related techniques have proven useful in the processing and analysis of one- and two-dimensional data sets (spectra in the former case, images in the latter). In this work we apply adaptive filters, introduced in a previous work, to optimize the detection and extraction of point sources from a one-dimensional array of time-ordered data such as the one that will be produced by the future 30-GHz LFI28 channel of the ESA Planck mission. At a 4σ detection level, 224 sources over a flux of 0.88 Jy are detected with a mean relative error (in absolute value) of 21 per cent and a systematic bias of −7.7 per cent. The position of the sources in the sky is determined with errors inferior to the size of the pixel. The catalogue of detected sources is complete at fluxes ≥4.3 Jy. The number of spurious detections is less than 10 per cent of the true detections. We compared the results with the ones obtained by filtering with a Gaussian filter and a Mexican Hat Wavelet of width equal to the scale of the sources. The adaptive filter outperforms the other filters in all considered cases. We conclude that optimal adaptive filters are well suited to detect and extract sources with a given profile embedded in a background of known statistical properties. In the Planck case, they could be useful to obtain a real-time preliminary catalogue of extragalactic sources, which would have a great scientific interest, e.g. for follow-up observations.