Rest-frame stacked spectrum, extracted from Cleaned cubes and normalised to the median flux-weighted redshift z = 3.1. The rest-frame frequency resolution is 50 MHz (≈125 km s⁻¹). The stacked spectrum is consistent with a Gaussian profile with a FWHM of 590 ± 70 km s⁻¹; we found no evidence for outflow signatures. The slight positive/negative excess at higher/lower frequencies is likely a weak residual continuum signal and is not associated with the CO(1–0) line.