Metagalactic emissivity (proper) at the Lyman edge (in units of 10²⁶ erg s¹ Hz¹ Mpc³), as a function of redshift. The data points (filled circles and upper limit point) are the emissivity values required in a ΛCDM model of the IGM to match the measured values of the transmitted Lyα flux through the IGM. The shaded regions show the 1σ (dark) and 2σ (light) ranges for a power-law fit (solid line) to the evolution in emissivity. The long-dashed line shows the required source emissivity, allowing for a boost in the total emissivity by 50 per cent from diffuse emission by the IGM. The squares show the estimated contribution from QSOs assuming either a PLE model (filled squares) or a PDE model (open squares) for the QSO luminosity function (see Section 3 of Meiksin 2005). The short-dashed and dotted lines show the deficit left by these (respective) QSO models from the required source emissivity (long-dashed line). The deficit must be made up by sources other than the QSOs. (A metagalactic spectral index of α_MG= 1 has been assumed.)