Total, “intrinsically” emitted Lyα (black dots), and the contributions from star formation (; red circles) and cooling radiation (; blue circles). The secondary y axis on the right shows the corresponding flux that would be measured at Earth, in the unrealistic case that Lyα photons escape isotropically, and were not absorbed by dust or scattered out of the LOS by neutral hydrogen. As seen in Fig. 9, the actual measured values are quite a lot smaller.