Point-like sources among z>11 galaxy candidates: contaminants due to supernovae at high redshifts?

TL;DR

The paper investigates whether high-redshift galaxy candidates from JWST data are contaminated by supernovae, finding that some point-like sources could indeed be supernovae at z~1-15, affecting galaxy formation models.

Contribution

It proposes that some z>11 galaxy candidates are actually high-redshift supernovae, highlighting a potential contamination source in JWST galaxy surveys.

Findings

Some point-like z>11 candidates are consistent with supernovae spectra.

Supernovae at z~1-15 could mimic high-redshift galaxy signatures.

Supernova contamination accounts for ~10% of the candidate sample.

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 an 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. (2023a), totalling 87 dropouts, is the largest one, and we notice that a number of these candidates are point-like. 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--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.'s 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.