The recent EDGES collaboration detection of an absorption signal at a central frequency of \nu = 78 \pm 1 MHz points to the presence of a significant Lyman- \alpha background by a redshift of z = 18 .
The timing of this signal constrains the dark matter particle mass ( m _ { \chi } ) in the warm dark matter ( WDM ) cosmological model .
WDM delays the formation of small-scale structures , and therefore a stringent lower limit can be placed on m _ { \chi } , based on the presence of a sufficiently strong Ly- \alpha~ { } background due to star formation at z = 18 , Our results show that the coupling the spin temperature to the gas through Ly- \alpha~ { } pumping requires a minimum mass of m _ { \chi } > 3 keV if atomic cooling halos dominate the star formation rate at z = 18 , and m _ { \chi } > 2 keV if { H _ { 2 } } cooling halos also form stars efficiently at this redshift .
These limits match or exceed the most stringent limits cited to date in the literature , even in the face of the many uncertainties regarding star-formation at high redshift .