a) CMB-nulled map at 28.4 GHz, constructed using the ILC method (see text), where in this map, β = −3 emission is unchanged by construction; b) 408 MHz map (Remazeilles et al. 2015), strongly dominated by synchrotron emission; c) 545 GHz Planck map, strongly dominated by thermal dust emission; and d) Hα map (Dickinson et al. 2003). An asinh(I) colour scale is used for all images, where I is the intensity in the units indicated. The coordinate along the colour bar is linear in I near zero and becomes logarithmic (ln(2I)) at high intensity. All maps are at 1deg resolution.