Left panel: the constraints on the parameter space of SD production model for sterile neutrinos. The colored regions represent the allowed region (﹩\overline{\phi }\geqslant {\phi }_{\mathrm{obs}}﹩) in the ﹩\mathrm{log}\,\lambda ﹩–﹩\mathrm{log}y﹩ plane for each value of the scalar mass m_S (shown by different colors according to the labels on the right). For each scalar mass (and hence for each color) lighter and darker tonalities represent the 1-σ and 2-σ confidence levels, respectively. Right panel: for the case ﹩{m}_{S}=100\,\mathrm{GeV}﹩, we compare our bounds from HFF galaxies derived in the present work (green thick lines) with a version of Lyα bounds derived by König et al. (2016): the latter are represented as red (forbidden cases), blue (allowed cases), and purple (constrained cases) segments in the lines of constant ﹩{m}_{\nu }﹩ values in the log λ–log y plane.