On the possible sources of D/H dispersion at high redshift

Recent observations suggest the existence of a white dwarf population in the Galactic halo, while others suggest that deuterium has been astrated in systems at high redshift and low metallicity. We propose that these observations could be signatures of an early population of intermediate-mass stars. Such a population requires a Population III initial mass function different from that of the solar neighborhood, as perhaps also suggested by the observed cosmic infrared background. Also, to avoid over-production of C and N, it is required that the Z = 0 yields of these stars have low (∼10^-3 solar) abundances, as suggested by some recent calculations. Under these assumptions, we present a model that reproduces the observed D versus Si trend and predicts a high cosmic Type Ia supernova rate while producing a white dwarf population that accounts for only ∼1.5% of the dark halo. This scenario can be tested by observations of the cosmic supernova rate and by confirmation and further studies of the putative white dwarf halo population.