Pointlike Sources among z > 11 Galaxy Candidates: Contaminants due to Supernovae at High Redshifts?

Abstract

The recent searches for z > 11 galaxies using the James Webb Space Telescope have resulted in an unexpectedly high number of candidate objects, which imply at least 1 order of magnitude higher number density of z > 11 galaxies than the previously favored predictions. A question has risen whether there are some new types of contaminants among these candidates. The candidate sample of Yan et al., totaling 87 dropouts, is the largest one, and we notice that a number of these candidates are pointlike. We hypothesize that the point-source dropouts could be supernovae at high redshifts. Further investigation shows that most of their spectral energy distributions indeed can be explained by supernovae at various redshifts from z ∼ 1 to 15, which lends support to this hypothesis. Attributing such point-source dropouts to supernova contamination cannot eliminate the tension, however, because they only account for ∼10% of the Yan et al. sample. On the other hand, the discovery of “contaminant” supernovae at z > 3 will have a series of important implications. Ironically, the existence of supernovae at z > 10 would still imply that the previously favored picture of early galaxy formation severely underestimates the global star formation rate density such redshifts. Multiple-epoch JWST imaging will be the simplest and yet the most efficient way to further test this hypothesis.