CO distribution of PGC 66551. (a) and (b) The integrated intensity in Jy beam^–1 km s⁻¹ and velocity of CO, using a threshold of 2.7 mJy (∼5σ_rms). The beam size is shown at the bottom-left corner. (c) Spatial distribution of SFE. The black dashed lines in panels (a) and (b) are the same as Figure 1. The black ellipse in panel (c) presents the new beam size after the convolution.