Date: 7/10/2023
JADES: Probing interstellar medium conditions at z\sim5.5-9.5 with
ultra-deep JWST/NIRSpec spectroscopy
Published: 2/8/2023 9:24:53 PM
Updated: 7/7/2023 5:52:36 PM
Paper abstract: We present emission line ratios from a sample of 26 Lyman break galaxies fromz~5.5-9.5 with -17.05.5 spectra. We find thatthe emission line ratios exhibited by these z~5.5-9.5 galaxies occupyclearly distinct regions of line-ratio space compared to typical z~0-3galaxies, instead being more consistent with extreme populations oflower-redshift galaxies. This is best illustrated by the [OIII]/[OII] ratio,tracing interstellar medium (ISM) ionisation, in which we observe more thanhalf of our sample to have [OIII]/[OII]>10. Our high signal-to-noise spectrareveal more than an order of magnitude of scatter in line ratios such as[OII]/H\beta and [OIII]/[OII], indicating significant diversity in the ISMconditions within the sample. We find no convincing detections of [NII] in oursample, either in individual galaxies, or a stack of all G395M/F290LP spectra.The emission line ratios observed in our sample are generally consistent withgalaxies with extremely high ionisation parameters (log U~-1.5), and arange of metallicities spanning from ~0.1\times Z_\odot to higher than~0.3\times Z_\odot, suggesting we are probing low-metallicity systemsundergoing periods of rapid star-formation, driving strong radiation fields.These results highlight the value of deep observations in constraining theproperties of individual galaxies, and hence probing diversity within galaxypopulation.