A matched filter approach for blind joint detection of galaxy clusters in X-ray and SZ surveys

Abstract

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 (Tarrío 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 · 10 14 M and redshifts between 0.01 and 1.2.

ComPRASS: a Combined Planck-RASS catalogue of X-ray-SZ clusters

“…The resolution of the published maps is 1.72 arcmin/pixel. As in Tarrío et al (2016) and Tarrío et al (2018), to make them directly compatible with the all-sky X-ray map mentioned above, we up-sampled them to a resolution of 0.86 arcmin/pixel by zero-padding in the spherical harmonics domain, i.e. by adding new modes with zero power.…”

“…The X-ray-SZ joint detection method can be seen as an evolution of the MMF3 detection method, one of the MMF methods used to detect clusters from Planck observations, that incorporates X-ray observations to improve the detection performance. In Tarrío et al (2018), we evaluated this method in the area of the sky covered by the SPT survey using data from the RASS and Planck surveys. We showed that, thanks to the addition of the X-ray information, the method is able to simultaneously achieve better purity, better detection efficiency, and better position accuracy than its predecessor, the Planck MMF3 detection method.…”

“…Tarrio In this paper, we present ComPRASS, a Combined Planck-RASS catalogue of X-ray-SZ sources. This all-sky catalogue contains 2323 galaxy cluster candidates and was constructed by applying the X-ray-SZ joint detection method proposed in Tarrío et al (2018) on all-sky maps from the Planck and RASS surveys. We present an external validation of the catalogue using existing X-ray, SZ and optical cluster catalogues.…”

The Galaxy Cluster Mass Scale and Its Impact on Cosmological Constraints from the Cluster Population

“…Examples of the multiwavelength studies include Schuecker et al (2004) and Tarrío et al (2018) who combined RASS data in a matched filter approach for joint detection with SDSS and Planck data, respectively. They showed that detection probability, purity, and source identification can be improved in such an approach.…”

Spectral imaging of the thermal Sunyaev–Zel’dovich effect in X-COP galaxy clusters: method and validation

“…For instance, Remazeilles et al (2013) propose a method which implements needlet decomposition, while in the recent work by Aghanim et al (2019) the authors apply suitable matched multi-filters (see e.g. Herranz et al 2002;Melin et al 2006;Tarrío et al 2016Tarrío et al , 2018 to data from Planck and from the Atacama Cosmology Telescope (Swetz et al 2011).…”