Seeing sharper and deeper: JWST's first glimpse of the photometric and spectroscopic properties of galaxies in the epoch of reionisation

Understand

We analyse the photometric and spectroscopic properties of four galaxies in the epoch of reionisation (EoR) within the SMACS 0723 JWST Early Release Observations field.

• Given the known spectroscopic redshifts of these sources, we investigated the accuracy with which photometric redshifts can be derived using NIRCam photometry alone, finding that F115W imaging is essential to distinguish between z~8 galaxies with high equivalent width (EW) [O III] {\lambda}5007 emission and z~10 Balmer break galaxies.
• We find that all four sources exhibit strong (\geq 0.6 mag) F356W-F444W colours, which sit at the extreme end of theoretical predictions from numerical simulations.
• We find that these galaxies deviate (by roughly 0.5 dex) from the local correlation between [O III] {\lambda}5007/H\beta and [Ne III] {\lambda}3869/[O II], which is consistent with the predictions from simulations of high-redshift galaxies having elevated line excitation ratios.