Dark-matter decay radiation
= Dark-matter decay radiation
If a <dark matter> particle of mass $m_\chi$ radiates power $\epsilon$ independently of its neighbours, optically thin isotropic emission has volume emissivity $j=\epsilon\rho/m_\chi$. Its <surface brightness> is $I=(4\pi)^{-1}\int j\,dz$ and therefore traces the mass column rather than its square.