Reddening map of the Perseus cluster field. The colour indicates the reddening value E(B − V) from 0.1 (magenta) to 0.3 mag (red; see colour bar). The positions of the catalogued galaxies are over-plotted by white symbols where the symbol size scales with the brightness in the WISE W1 band. The diagonal white lines are curves of equal Galactic latitude from l = −11° (top left) to −15° (bottom right) in steps of one degree.