On the linear filters for point source extraction of the Planck mission

Abstract

The manifestation of point sources in the upcoming PLANCK maps is a direct reflection of the properties of the pixelized antenna beam shape for each frequency, which is related to the scan strategy, pointing accuracy, noise properties and map-making algorithm. In this paper we firstly compare analytically two filters for the PLANCK point source extraction, namely, the adaptive top-hat filter (ATHF), the theoretically-optimal filter (TOF). Our analyses are based on the premise that the experiment parameters the TOF assume and require are already known: the CMB and noise power spectrum and a circular Gaussian beam shape and size, whereas the ATHF does not need any a priori knowledge. The analyses show that the TOF is optimal in terms of the gain after the parameter inputs. We simulate the PLANCK HFI 100 GHz channel with elliptical beam in rotation to test the efficiency of the TOF and the ATHF. We also apply the ATHF on the WMAP Q-band map and the derived map (the foreground-cleaned map by Tegmark, de Oliveira Costa & Hamilton) from the WMAP 1-year data. The uncertainties on the angular power spectrum will hamper the efficiency of the TOF. To tackle the real situations for the PLANCK point source extraction, most importantly, the elliptical beam shape with slow precession and change of the ellipticity ratio due to possible mirror degradation effect, the ATHF is computationally efficient and well suited for the construction of the PLANCK Early Release Compact Source Catalogue.