Overlay of the ALMA HCN(1–0) map (contours) on the HST/NICMOS F190N continuum image at 1.9 μm HST (colour scale as shown in Jy). The contour spacing is 3σ, 7σ, 12σ, 24σ, 50σ, and 120σ, where 1σ = 0.028 Jy beam⁻¹ km s⁻¹. The white circle of r = 8″ locates the inner region of the galaxy disk, which was excluded of our analysis. The HST/NICMOS F190N image has been degraded to the spatial resolution of HCN(1–0) (1 pc).