Maps of the contributions of the different layers to the line intensity integrated between 8 and 13.5 km s⁻¹. First column: relative error of the model with respect of the data in percentage. Second to fifth columns: contribution of the foreground, inner, background, and CMB layers to the line integrated intensity in percentage of that measured on the data. Each row corresponds to a given line: from top to bottom, ¹²CO (1 − 0), ¹³CO (1 − 0) and (2 − 1), C¹⁸O (1 − 0) and (2 − 1), HCO⁺ (1 − 0), and H¹³CO⁺ (1 − 0). The percentage on the top center of each panel is the mean±rms value computed over the associated maps. Positive and negative relative errors or contributions are shown in red and blue, respectively.