Cosmic-ray ionization rate derived from the abundance ratio of HCO⁺ and CO assuming an electron abundance equal to the HCO⁺ abundance (P. Caselli et al. 2002). The ionization rate is calculated only in regions where both tracers are detected at >3σ. Contours indicate the C¹⁸O 2–1 emission, from 3 to 21 times the rms in five equally spaced steps. The C¹⁸O for IRAS4A is shown after correcting for absorption. In each panel, the gray dashed line is perpendicular to the small scale outflow.