Axion decay represents a viable explanation for several astrophysical phenomena. Specifically, dark matter particles can annihilate, converting mass into gamma rays in galactic halos of massive galaxies via 2 photon decay. Observations in gamma-rays of galactic center halos do not provide significant constraints regarding an axion population with decay constant within \(10^{-2} {\rm keV}-10^{-1} {\rm keV}\). In comparison, constraints provided by observations of X-ray lines originating from regions at redshifts \(z \sim 0.8 - 1.2 \) and cosmic near-infrared background are very significant in this decay constant range.