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JADES: Probing interstellar medium conditions at z ∼ 5.5-9.5 with ultra-deep JWST/NIRSpec spectroscopy

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Saxena, A 
Bunker, AJ 
D'eugenio, F 
Carniani, S 


jats:pWe present emission-line ratios from a sample of 27 Lyman-break galaxies from jats:italicz</jats:italic> ∼ 5.5 − 9.5 with −17.0 < jats:italicM</jats:italic>jats:sub1500</jats:sub> < −20.4, measured from ultra-deep JWST/NIRSpec multi-object spectroscopy from the JWST Advanced Deep Extragalactic Survey (JADES). We used a combination of 28 h deep PRISM/CLEAR and 7 h deep jats:italicG</jats:italic>395jats:italicM</jats:italic>/jats:italicF</jats:italic>290jats:italicLP</jats:italic> observations to measure, or place strong constraints on, ratios of widely studied rest-frame optical emission lines including Hjats:italicα</jats:italic>, Hjats:italicβ</jats:italic>, [O jats:scII</jats:sc>] jats:italicλλ</jats:italic>3726, 3729, [Ne jats:scIII</jats:sc>] jats:italicλ</jats:italic>3869, [O jats:scIII</jats:sc>] jats:italicλ</jats:italic>4959, [O jats:scIII</jats:sc>] jats:italicλ</jats:italic>5007, [O jats:scI</jats:sc>] jats:italicλ</jats:italic>6300, [N jats:scII</jats:sc>] jats:italicλ</jats:italic>6583, and [S jats:scII</jats:sc>] jats:italicλλ</jats:italic>6716, 6731 in individual jats:italicz</jats:italic> > 5.5 spectra. We find that the emission-line ratios exhibited by these jats:italicz</jats:italic> ∼ 5.5 − 9.5 galaxies occupy clearly distinct regions of line-ratio space compared to typical jats:italicz</jats:italic> ∼ 0 − 3 galaxies, instead being more consistent with extreme populations of lower-redshift galaxies. This is best illustrated by the [O jats:scIII</jats:sc>]/[O jats:scII</jats:sc>] ratio, tracing interstellar medium (ISM) ionisation, in which we observe more than half of our sample to have [O jats:scIII</jats:sc>]/[O jats:scII</jats:sc>] > 10. Our high signal-to-noise spectra reveal more than an order of magnitude of scatter in line ratios such as [O jats:scII</jats:sc>]/Hjats:italicβ</jats:italic> and [O jats:scIII</jats:sc>]/[O jats:scII</jats:sc>], indicating significant diversity in the ISM conditions within the sample. We find no convincing detections of [N jats:scII</jats:sc>] jats:italicλ</jats:italic>6583 in our sample, either in individual galaxies, or a stack of all jats:italicG</jats:italic>395jats:italicM</jats:italic>/jats:italicF</jats:italic>290jats:italicLP</jats:italic> spectra. The emission-line ratios observed in our sample are generally consistent with galaxies with extremely high ionisation parameters (log jats:italicU</jats:italic> ∼ −1.5), and a range of metallicities spanning from ∼0.1 × jats:italicZ</jats:italic>jats:sub⊙</jats:sub> to higher than ∼0.3 × jats:italicZ</jats:italic>jats:sub⊙</jats:sub>, suggesting we are probing low-metallicity systems undergoing periods of rapid star formation, driving strong radiation fields. These results highlight the value of deep observations in constraining the properties of individual galaxies, and hence probing diversity within galaxy population.</jats:p>



galaxies: evolution, galaxies: high-redshift, galaxies: ISM

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Astronomy and Astrophysics

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EDP Sciences
European Research Council (695671)
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