H I and CO spectra for the Perseus molecular cloud for one coordinate. The blue line shows the H I spectral line obtained from the HI4PI survey in the left panel and the observed ¹²CO 7(1−0) line obtained by Dame et al. (2001) in the right panel. The red line shows a Gaussian fit to each spectrum. The x axis shows the LSR velocity and the y axis shows the main-beam brightness temperature. In this work, we are interested in the peak emission by CO and H I averaged along the entire cloud.