Examples of optical spectra of two [CII] nondetections with robust (top) and less precise (bottom) rest-frame UV spectroscopic redshift. The typical redshift uncertainty due to the spectral resolution (i.e., R ∼ 2700 from Hasinger et al. 2018) of the observations is also shown. Both panels report UV emission and absorption features, such as the Lyα line or the ISM Si II, C IV and He II absorption lines. The spectra (in blue) and the noise (in gray) are smoothed with a Gaussian filter with size of 2 Å for a better visualization of the emission and absorption features.