NGC 6946. Errors bars correspond to the observations. Solid lines correspond the median results of the best-fit models and thin gray lines to the best-fit models. The values of the secondary parameters for these best-fit models are given in the lower-left corner of the middle panels. (a) Best-fit model including using RADEX. (b) Best-fit model without using RADEX. (c) Best-fit models including . (d) Best-fit models without . (e) Infrared profiles of the best-fit model including . (f) Infrared profiles of the best-fit model without . The cosmic ray ionization rate ζ_CR is given for each model in the upper panels.