A matched filter approach for blind joint detection of galaxy clusters
  in X-ray and SZ surveys
  The combination of X-ray and SZ observations can potentially improve the
cluster detection efficiency when compared to using only one of these probes,
since both probe the same medium: the hot ionized gas of the intra-cluster
medium. We present a method based on matched multifrequency filters (MMF) for
detecting galaxy clusters from SZ and X-ray surveys. This method builds on a
previously proposed joint X-ray-SZ extraction method (Tarr\'io et al. 2016) and
allows to blindly detect clusters, that is finding new clusters without knowing
their position, size or redshift, by searching on SZ and X-ray maps
simultaneously. The proposed method is tested using data from the ROSAT all-sky
survey and from the Planck survey. The evaluation is done by comparison with
existing cluster catalogues in the area of the sky covered by the deep SPT
survey. Thanks to the addition of the X-ray information, the joint detection
method is able to achieve simultaneously better purity, better detection
efficiency and better position accuracy than its predecessor Planck MMF, which
is based on SZ maps only. For a purity of 85%, the X-ray-SZ method detects 141
confirmed clusters in the SPT region, whereas to detect the same number of
confirmed clusters with Planck MMF, we would need to decrease its purity to
70%. We provide a catalogue of 225 sources selected by the proposed method in
the SPT footprint, with masses ranging between 0.7 and 14.5 $\cdot 10^{14}$
Msun and redshifts between 0.01 and 1.2.
