Schrodinger's Galaxy Candidate: Puzzlingly Luminous at $z≈17$, or Dusty/Quenched at $z≈5$?


$JWST$’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 $0.6-5μ$m photometry, this strikingly luminous ($≈$26 mag) galaxy appears to lie at $z≈17$. This would make it an $M_m̊UV≈-22$, $M_̊⋆≈5times10^9M_rø̊dot$ system that formed a mere $∼220$ Myrs after the Big Bang. The implied number density of this galaxy and its analogues challenges virtually every early galaxy evolution model that assumes $Łambda$CDM cosmology. However, there is strong environmental evidence supporting a secondary redshift solution of $z≈5$: all three of the galaxy’s nearest neighbors at $<2.5$’’ have photometric redshifts of $z≈5$. Further, we show that CEERS-1749 may lie in a $z≈5$ protocluster that is $rsim5times$ overdense compared to the field. Intense line emission at $z≈5$ 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 $z≈5$ conspire to boost the $>2μ$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 ($Δ złesssim0.1$), 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 $z≈5$, 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.

arXiv e-prints