The Number and Observability of Population III Supernovae at High Redshifts

We consider the feasibility of detecting Population III pair-instability supernovae (PISNe) at very high redshifts with the James Webb Space Telescope (JWST). Four published estimates for the PISN rate show a rather wide dispersion, between 50 and 2200 deg-2 yr-1. Correcting problems with several of these, we conclude that even a fairly optimistic estimate is probably a further order of magnitude lower than this range, at a rate of the order of 4 deg-2 yr-1 at z ~ 15 and 0.2 deg-2 yr-1 at z ~ 25, both with substantial uncertainty. Although such supernovae (SNe) would be bright enough to be readily detectable with the JWST at any relevant redshift, the lower number densities derived here would likely require either a dedicated wide-angle search strategy or a serendipitous search. We expect that typically about 1 deg2 (or 500 JWST NIRCam images) at 4.5 μm must be imaged to detect one PISN at z ~ 15 and about 35 deg2 to detect one at z ~ 25. If some Population III star formation persists to lower redshifts at z ~ 5, then PISNe may also be detectable in wide-angle ground-based Z-band imaging surveys at ZAB ~ 23, at a density of the order of 1 deg-2 of surveyed area. In the Appendix we consider the possible effects of intergalactic dust in obscuring high-redshift SNe or other high-redshift sources. We show that the obscuration at a given rest wavelength will peak at some maximum redshift and thereafter decline. While it may be a significant effect in observations of the very high redshift universe, it is unlikely, even under rather pessimistic assumptions, to completely obscure primordial objects.