Observed CH₂NH spectra toward six CONs, including both nuclei in Arp 220. The horizontal black dashed line shows zero flux, the vertical black dashed line shows the systemic velocity of each galaxy, and the red line indicates the Gaussian best fit. Systemic velocities are adopted from Aalto et al. (2015b) for IC 860 and Zw 049.057, from Martín et al. (2016) for Arp 220, from Sakamoto et al. (2013) for NGC 4418, from García-Burillo et al. (2015) for IRAS 17208−0014, and from Falstad et al. (2021) for IRAS 17578−0400.