Top panel: constraints on the sterile neutrino parameter space from Eq. (3). The allowed region is the white area. Taking the abundance φ_obs corresponding to our observed number of galaxies in the target field within 1-σ and 2-σ confidence levels (φ_obs = 19.3 and φ_obs = 14.4, respectively) yields the exclusion regions shown as red shaded areas. Our constraints are compared with upper bounds from X-ray observations of the Milky Way and dwarf galaxies (as reported in Riemer-Sørensen 2014). Grey areas are excluded by current limits on the abundance of DM (Ade et al. 2015). The green line corresponds to the non-resonant DW case with vanishing lepton asymmetry L = 0. We also show the constraints obtained from the abundance of satellites in the Milky Way by Schneider (2016, dashed line) and by Lovell et al. (2016, solid line). The tentative line signal at 3.5 keV corresponding to a sterile neutrino mass m_ν = 7.1 keV (Bulbul et al. 2014; Boyarsky et al. 2014) is shown by the point with errorbars. Bottom panel: the coloured contours correspond to the different values of corresponding to a given combination of sin²(2θ)−m_ν. In both panels we assumed c = 3 and R = 1.6 Mpc as reference values. The sensitivity of the curves to changes in such parameters is the same as the thermal WDM case, shown in Fig. 3.