  We analyze a scenario in which the lightest heavy neutrino $N_1$ is a dark
matter candidate and the second- heaviest neutrino $N_2$ decays producing a
lepton number. If $N_1$ were in thermal equilibrium, its energy density today
would be much larger than that of the observed dark matter, so we consider
energy injection by the decay of $N_2$. In this paper, we show the parameters
of this scenario that give the correct abundances of dark matter and baryonic
matter and also induce the observed neutrino masses. This model can explain a
possible sterile neutrino dark matter signal of $M_1$=7 keV in the x-ray
observation of x-ray multi-mirror mission.
