CO line ratio comparison to literature values. We compare the average R₂₁ and R_13/12 values estimated from the distribution of the M101 data points to literature values. Errorbars indicate the 1σ distribution of sample values. If the literature value corresponds to the value for a specific galaxy, the source’s name is provided. Measurement for M101 indicated by the cross. The square symbol indicates the result from M51. Left: collection of R₂₁ distributions. Right: the R_13/12 distribution is shown. Our measurement agrees well with results for M51 and the Milky Way.