Spectral imaging of galaxy clusters with Planck
  The Sunyaev-Zeldovich (SZ) effect is a promising tool for detecting the
presence of hot gas out to the galaxy cluster peripheries. We developed a
spectral imaging algorithm dedicated to the SZ observations of nearby galaxy
clusters with Planck, with the aim of revealing gas density anisotropies
related to the filamentary accretion of materials, or pressure discontinuities
induced by the propagation of shock fronts. To optimize an unavoidable
trade-off between angular resolution and precision of the SZ flux measurements,
the algorithm performs a multiscale analysis of the SZ maps as well as of other
extended components, such as the cosmic microwave background (CMB) anisotropies
and the Galactic thermal dust. The demixing of the SZ signal is tackled through
kernel weighted likelihood maximizations. The CMB anisotropies are further
analyzed through a wavelet analysis, while the Galactic foregrounds and SZ maps
are analyzed via a curvelet analysis that best preserves their anisotropic
details. The algorithm performance has been tested against mock observations of
galaxy clusters obtained by simulating the Planck High Frequency Instrument and
by pointing a few characteristic positions in the sky. These tests suggest that
Planck should easily allow us to detect filaments in the cluster peripheries
and detect large-scale shocks in colliding galaxy clusters that feature
favorable geometry.
