Spectra for the AzTEC-3 system. The red line shows the single Gaussian fit to the data, and the blue line shows the double Gaussian fit to the data. For AzTEC-3, the blue wing <  − 500 km s⁻¹ is significantly more prominent than the red wing. We fit LBG-3 and Gal-SW with double Gaussians to account for the additional “bumps” in the spectra (most obvious in LBG-3), which are likely blended flux from the SMG. The atmospheric transmission is shown as a gray line in the top subplot for every source.