Spatial profiles of the envelopes. The black, quasi-vertical lines show the intensity profile of the quasar, while the red line is the intensity profile of the envelope, integrated across the spectral width of the Lyα line (i.e. an arbitrary range of 20 Å for objects with no significant envelope, and a 1    ×    FWHM for the other objects). The blue and green lines show the noise, i.e. the profile integrated across wavelength ranges of the same width, but centred 76 Å bluer, respectively redder than the envelope emission line (except for BR 2237 − 0607, for which the noise was sampled at  ± 29 Å from the emission line).