Predicted Hα fluxes as a function of star formation rate (left), stellar mass (middle), and specific star formation rate (right) for the FIRSTLIGHT simulated galaxies at 6.5 <  z <  10.5. Grey and black horizontal dashed lines mark respectively the 10σ and 5σ limits of medium deep (10 ks) and deep (40 ks) MRS spectroscopic observations. Other known z >  7 galaxies with detected [OIII] 88μm emission lines (Inoue et al. 2016; Laporte et al. 2017; Hashimoto et al. 2019, 2018; Tamura et al. 2019) are also shown with filled symbols (SFR and stellar mass measurements of A2444_YD4 SXFD-NB10006-2 have been corrected for the lower proportion of low-mass stars in the Kroupa IMF relative to the standard Salpeter assumed in Inoue et al. 2016; Laporte et al. 2017, respectively). For these galaxies, ratios of [OIII] 88μm/[OIII] 0.5007 μm = 10 and [OIII] 0.5007 μm/Hα = 1.1 are used to derive the expected Hα fluxes (vertical lines show the minimum and maximum expected Hα fluxes considering different line ratios of R[OIII] and [OIII]0.5007 μm/Hα; see text for details). For the galaxies magnified by gravitational lensing, such as MACS1149-JD1, A2744_YD4, and MACS0416_Y1, the de-magnified expected fluxes are shown as empty symbols (SFR and M_* measurements refer to intrinsic values).