The Two $z\sim 13$ Galaxy Candidates HD1 and HD2 Are Likely Not Lensed

TL;DR

This study assesses whether the high-redshift galaxy candidates HD1 and HD2 are gravitationally lensed, concluding that lensing is unlikely to explain their luminosity, thus supporting their intrinsic brightness at early cosmic times.

Contribution

The paper provides a probabilistic analysis showing that gravitational lensing is an unlikely explanation for the luminosity of $z extasciitilde 13$ galaxy candidates HD1 and HD2, strengthening their case as intrinsically bright early galaxies.

Findings

Low probability (7.39%) of strong lensing at current imaging limits.

Theoretical lensing probability drops below 0.1% with HST and JWST limits.

Unlikely that a single lensing event accounts for both sources' luminosity.

Abstract

The discovery of two UV-bright galaxy candidates at $z\sim 13$, HD1 and HD2, laid the foundation for a new race to study the early Universe. Previous investigations suggested that they are either powered by a supermassive black hole or by an extreme, transient burst of star formation. Given their uncertain nature, we investigate whether these sources could be lensed by a hitherto undetected, faint foreground galaxy. We find that at the current limiting magnitude with which HD1 and HD2 were imaged, there is only a $7.39\%$ probability they are strongly lensed by spherical deflectors and that the hypothetical lensing galaxy was too faint to be detected. Meanwhile, with the limiting magnitudes of the Hubble Space Telescope (HST) and James Webb Space Telescope (JWST), the theoretical probability would drop precipitously to $0.058\%$ and $0.0012\%$, respectively. We further find it unlikely that the luminosities of both sources can be accounted for by lensing that produces a single, resolved image with sufficiently high magnification. Alternatively, in the unlikely event that their brightness results from lensing by an elliptical isothermal galaxy, there is a $30.9 \%$ probability that the lensing galaxy is too faint to be observable at the current limiting magnitude. Future HST (JWST) imaging will drop this probability to $0.245 \%$ ($0.0025 \%$). In summary, while deep imaging with HST and JWST is required to discard the lensing hypothesis entirely, it is unlikely that the exceptional luminosity of the two $z \sim 13$ sources can be accounted for by gravitational lensing.