Upper panel: Planck y map with the 40% galactic mask and point-source mask from the view of the north galactic pole. Lower panel: Planck y map after masking galaxy clusters. The galaxy groups/clusters detected by the Planck tSZ, ROSAT X-ray, and SDSS optical surveys described in Sect. 2.3 are all masked by three times the radius (3 × R₅₀₀) of each galaxy cluster. The region outside of the SDSS DR7 survey is also excluded.