Properties of the Hα emission seen by SOAR in comparison to the ALMA CO(1−0) measurements. Upper: Hα map with contours for the CO(1−0) emission overlaid as red contours (upper panel of Fig. 4). This shows the cold molecular gas seen by ALMA to be extended significantly to the south-west, tracing the Hα emission seen by SOAR. Contours start at 2σ and are incremented in 2σ steps. The synthesised beam for the CO(1−0) observation is depicted in the lower-left corner (hatched ellipse). Lower: ratio of Hα to CO(1−0) emission, where the scaling is arbitrary. The plot shows the flux ratio summed in annular apertures centred on the CO(1−0) peak for pixels where the intensity of the CO(1−0) emission is at least 2σ.