verified.'
author:
- |
    B. M. Schäfer$^{1}$[^1], C. Pfrommer$^{1}$, R. M. Hell$^{1}$and M. Bartelmann$^{2}$\
    $^1$Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Stra[ß]{}e 1, Postfach 1317, 85741 Garching, Germany\
    $^2$Institut für theoretische Astrophysik, Tiergartenstra[ß]{}e 15, 69121 Heidelberg, Germany
bibliography:
- 'bibtex/aamnem.bib'
- 'bibtex/references.bib'
title: |
    Detecting Sunyaev-Zel’dovich clusters with [[*Planck*]{}]{}:\
    II. Foreground components and optimised filtering schemes
---

\[firstpage\]

galaxies: clusters: general, cosmology: cosmic microwave background, methods: numerical, space vehicles: [ *Planck*]{}

Introduction {#sect_intro}
============

The Sunyaev-Zel’dovich (SZ) effect is the most important extragalactic source of secondary anisotropies in the CMB sky. The thermal SZ-effect is explained by the fact that CMB photons are put in thermal contact with electrons of the hot intra-cluster medium (ICM) by Compton-interactions which causes a transfer of energy from the ICM to the CMB. Because of the smallness of the Thompson cross-section and of the diluteness of the ICM this transfer of thermal energy is small. In the direction of a cluster, low-energetic photons with frequencies below $\nu=217$ GHz are removed from the line-of-sight. At frequencies above $\nu=217$ GHz CMB photons are scattered into the line-of-sight, causing a distinct modulation of the CMB surface brightness as a function of observing frequency, which enables the detection of clusters of galaxies 