An approach to detection of point sources in very high-resolution microwave maps

Abstract

This paper deals with the detection problem of extragalactic point sources in multi-frequency, microwave sky maps that will be obtainable in future cosmic microwave background (CMB) radiation experiments with instruments capable of very high spatial resolution. With spatial resolutions that can be 0.1-1.0 arcsec or better, the extragalactic point sources will appear isolated. The same also holds for the compact structures due to the Sunyaev-Zeldovich (SZ) effect (both thermal and kinetic). This situation is different from the maps obtainable with instruments such as WMAP or Planck where, because of the lower spatial resolution (≈5-30 arcmin), the point sources and the compact structures due to the SZ effect form a uniform noisy background (confusion noise). The point source detection techniques developed in the past are therefore based on the assumption that all the emissions that contribute to the microwave background can be modeled with homogeneous and isotropic (often Gaussian) random fields and make use of the corresponding spatial power spectra. In the case of very high-resolution observations, such an assumption cannot be adopted since it still holds only for the CMB. Here, we propose an approach based on the assumption that the diffuse emissions that contribute to the microwave background can be locally approximated by two-dimensional low-order polynomials. In particular, two sets of numerical techniques are presented that contain two different algorithms each. The first set makes use of the a priori information about the spectral properties of CMB and SZ and is suited to detecting an extragalactic point source with a different spectrum for these emissions. In this set, one algorithm is a modification of the internal linear combination method, which is widely used in cosmology to extract the component of interest from a mixture of signals, and it is appropriate for extragalactic point sources with a known spectrum. The other one does not make use of this piece of information. The second set is tailored to detecting of extragalactic point sources with a similar spectrum to that of the CMB or SZ. Also in this set one algorithm is specific for extragalactic point sources with known spectrum whereas the other does not make use of this information. The performance of the algorithms is tested with numerical experiments that mimic the physical scenario expected for high Galactic latitude observations with the Atacama Large Millimeter/Submillimeter Array (ALMA). © ESO, 2013.