The heavy solid line shows the number of ionizing photons emitted per second per solar mass (without the factors f_esc and f_star; see § 2.3) for the composite emissivity shown in Fig. 3 and a Scalo IMF. The heavy dashed line shows the rate for a tilted Scalo IMF, where most of the stars have low masses. The dotted lines show the separate contributions from stars with masses (from top to bottom) 120, 85, 60, 40, 25, 20, 15, 12, 9, 7, 5, 4, 3, 2.5, 2, 1.7, 1.5, and 1.25 M_☉, in units of photons s⁻¹.