Schrodinger's Galaxy Candidate: Puzzlingly Luminous at $z\approx17$, or Dusty/Quenched at $z\approx5$?

TL;DR

This paper discusses the discovery of a luminous galaxy candidate with ambiguous redshift, challenging early galaxy evolution models, and explores whether it is at $z oughly17$ or $z oughly5$, emphasizing the need for spectroscopic confirmation.

Contribution

It presents a detailed analysis of a galaxy with uncertain redshift, highlighting the implications for galaxy formation models and the importance of follow-up observations.

Findings

The galaxy may be at $z oughly17$ or $z oughly5$, with different implications.

Environmental evidence favors a $z oughly5$ redshift.

Photometric features could be explained by line emission at $z oughly5$.

Abstract

$JWST$'s first glimpse of the $z>10$ Universe has yielded a surprising abundance of luminous galaxy candidates. Here we present the most extreme of these systems: CEERS-1749. Based on $0.6-5\mu$m photometry, this strikingly luminous ($\approx$26 mag) galaxy appears to lie at $z\approx17$. This would make it an $M_{\rm{UV}}\approx-22$, $M_{\rm{\star}}\approx5\times10^{9}M_{\rm{\odot}}$ system that formed a mere $\sim220$ Myrs after the Big Bang. The implied number density of this galaxy and its analogues challenges virtually every early galaxy evolution model that assumes $\Lambda$CDM cosmology. However, there is strong environmental evidence supporting a secondary redshift solution of $z\approx5$: all three of the galaxy's nearest neighbors at $<2.5$" have photometric redshifts of $z\approx5$. Further, we show that CEERS-1749 may lie in a $z\approx5$ protocluster that is $\gtrsim5\times$ overdense compared to the field. Intense line emission at $z\approx5$ from a quiescent galaxy harboring ionized gas, or from a dusty starburst, may provide satisfactory explanations for CEERS-1749's photometry. The emission lines at $z\approx5$ conspire to boost the $>2\mu$m photometry, producing an apparent blue slope as well as a strong break in the SED. Such a perfectly disguised contaminant is possible only in a narrow redshift window ($\Delta z\lesssim0.1$), implying that the permitted volume for such interlopers may not be a major concern for $z>10$ searches, particularly when medium-bands are deployed. If CEERS-1749 is confirmed to lie at $z\approx5$, it will be the highest-redshift quiescent galaxy, or one of the lowest mass dusty galaxies of the early Universe detected to-date. Both redshift solutions of this intriguing galaxy hold the potential to challenge existing models of early galaxy evolution, making spectroscopic follow-up of this source critical.