High-Redshift Galaxy Candidates at $z = 9-10$ as Revealed by JWST Observations of WHL0137-08

Abstract

We report the discovery of four galaxy candidates observed 450 - 600 Myr after the Big Bang with photometric redshifts between z ~ 8.3 - 10.2 measured using the JWST NIRCam imaging of the galaxy cluster WHL0137-08 observed in 8 filters spanning 0.8-5.0 micron, plus 9 Hubble filters spanning 0.4-1.7 micron. One candidate is gravitationally lensed with a magnification of ~8, while the other three are located in a nearby NIRCam module with expected magnifications of <~ 1.1. Using SED fitting, we estimate the stellar masses of these galaxies are typically in the range log M*/Msun = 8.3 - 8.7. All appear young with mass-weighted ages < 240 Myr, low dust content A_V < 0.15 mag, and specific star formation rates sSFR ~0.25 - 10 /Gyr for most. One z ~ 9 candidate is consistent with an age < 5 Myr and a sSFR ~10 /Gyr, as inferred from a strong F444W excess, implying [OIII]+H-beta rest-frame equivalent width ~2000 Angstrom, although an older z ~ 10 object is also allowed. Another z ~ 9 candidate is lensed into an arc 2.4 arcsec long with a magnification of ~8. This arc is the most spatially-resolved galaxy at z ~ 9 known to date, revealing structures ~30 pc across. Follow-up spectroscopy of WHL0137-08 with JWST/NIRSpec will be useful to spectroscopically confirm these high-redshift galaxy candidates and to study their physical properties in more detail.