Two Remarkably Luminous Galaxy Candidates at $z\approx10-12$ Revealed by JWST

TL;DR

JWST enables exploration of the rest-frame UV/optical light of galaxies during the first few hundred million years, extending beyond the single confirmed GNz11 at $z\approx11$. The authors perform a photometric search for luminous $z>10$ sources using JWST/NIRCam data from the GLASS and CEERS ERS fields, finding two robust candidates with $M_{\rm UV}\approx-21$ and redshifts near $z=12.4^{+0.1}_{-0.3}$ and $z=10.4^{+0.4}_{-0.5}$. SED analyses argue against low-redshift interlopers, with inferred stellar masses of $M_{\ast} \sim 10^9\,M_\odot$ formed within $\lesssim300-400$ Myr after the Big Bang, and GLASS-z10 shows a resolved exponential profile with $r_{50}\approx0.7$ kpc. Together with GNz11, these sources exceed naive Schechter UV LF forecasts, suggesting the bright end of the UV LF was already in place at $z>10$ and implying that future deep JWST surveys could uncover similarly luminous galaxies at even earlier times.

Abstract

The first few hundred Myrs at $z>10$ mark the last major uncharted epoch in the history of the Universe, where only a single galaxy (GNz11 at $z\approx11$) is currently spectroscopically confirmed. Here we present a search for luminous $z>10$ galaxies with $JWST$/NIRCam photometry spanning $\approx1-5μ$m and covering 49 arcmin$^{2}$ from the public Early Release Science programs (CEERS and GLASS). Our most secure candidates are two $M_{\rm{UV}}\approx-21$ systems: GLASS-z12 and GLASS-z10. These galaxies display abrupt $\gtrsim1.8$ mag breaks in their spectral energy distributions, consistent with complete absorption of flux bluewards of Lyman-$α$ that is redshifted to $z=12.4^{+0.1}_{-0.3}$ and $z=10.4^{+0.4}_{-0.5}$. Lower redshift interlopers such as quiescent galaxies with strong Balmer breaks would be comfortably detected at $>5σ$ in multiple bands where instead we find no flux. From SED modeling we infer that these galaxies have already built up $\sim 10^9$ solar masses in stars over the $\lesssim300-400$ Myrs after the Big Bang. The brightness of these sources enable morphological constraints. Tantalizingly, GLASS-z10 shows a clearly extended exponential light profile, potentially consistent with a disk galaxy of $r_{\rm{50}}\approx0.7$ kpc. These sources, if confirmed, join GNz11 in defying number density forecasts for luminous galaxies based on Schechter UV luminosity functions, which require a survey area $>10\times$ larger than we have studied here to find such luminous sources at such high redshifts. They extend evidence from lower redshifts for little or no evolution in the bright end of the UV luminosity function into the cosmic dawn epoch, with implications for just how early these galaxies began forming. This, in turn, suggests that future deep $JWST$ observations may identify relatively bright galaxies to much earlier epochs than might have been anticipated.

Figures (3)

• Figure 1: Summary of photometry and redshift solution for GL-z12. Top: 4.5"$\times$4.5" images spanning $\approx0.9-4.5\mu$m centered on the $z\approx12$ candidate highlighted with white crosshairs. The source is well-detected ($>20\sigma$) in F200W and all redder bands, and abruptly drops out in the bluer filters. Bottom left: Photometry for the source is shown in purple, with upper limits for non-detections plotted at the 1-$\sigma$ level. The best-fit spectral energy distribution (SED) template from EAZY is shown in dark orange -- a Lyman-break galaxy (LBG) at $z=12.2$. The best-fit SED from EAZY constrained to lie at $z<6$ is plotted in silver, which corresponds to a quiescent galaxy at $z\approx3.5$ whose Balmer break produces a drop-off across F200W and F150W. However, such a quiescent galaxy is predicted to be detected ($>5\sigma$) in bluer bands, and is at odds with the dramatic $>1.8$ mag break observed. Bottom right: Probability distributions for the source redshift derived using EAZY (solid orange) and Prospector (dashed orange). We adopt a flat prior across the redshift range depicted ($z=0-20$). The derived distributions are in excellent agreement and suggest a redshift of $z\approx12$, with negligible (EAZY) or no (Prospector) support for solutions at $z<10$
• Figure 2: Summary of photometry and redshift solution for GL-z10, similar to Figure 1. Top: GL-z10 is well-detected in all but the two bluest bands. Bottom left: The best-fit low-$z$ solution (quiescent galaxy at $z\approx2.5$) is disfavored by the F115W image, where a $>5\sigma$ detection is expected. In addition to the JWST data (dark purple), we measure HST photometry (light purple) for this source from data acquired by the BUFFALO program Steinhardt20. The HST data are fully consistent with the JWST data as well as the best-fit SED. Bottom right: The EAZY and Prospector posteriors agree on a $z\approx10$ galaxy.
• Figure 3: Absolute UV magnitude vs. Redshift for a representative sample of known galaxies in the first billion years of the Universe. Galaxies with photometric redshifts, sourced from Bouwens22, are shown as points, and those with spectroscopic redshifts compiled from the literature as squares. The candidates presented in this work are depicted as purple stars, and populate a hitherto unoccupied region of parameter space. The brightness of these sources present a unique opportunity to efficiently extend the spectroscopic frontier to the first few hundred Myrs after the Big Bang.