JADES: Probing interstellar medium conditions at $z\sim5.5-9.5$ with ultra-deep JWST/NIRSpec spectroscopy

Abstract

We present emission line ratios from a sample of 26 Lyman break galaxies from z ∼ 5.5 − 9.5 with −17.0 < M 1500 < −20.4, measured from ultra-deep JWST/NIRSpec MSA spectroscopy from the JWST Advanced Deep Extragalactic Survey (JADES). We use a combination of 28 hour deep PRISM/CLEAR and 7 hour deep G395M/F290LP observations to measure, or place strong constraints on, ratios of widely studied rest-frame optical emission lines including Hα, Hβ,, and [S ii] λλ6716, 6731 in individual z > 5.5 spectra. We find that the emission line ratios exhibited by these z ∼ 5.5 − 9.5 galaxies occupy clearly distinct regions of line-ratio space compared to typical z ∼ 0 − 3 galaxies, instead being more consistent with extreme populations of lower-redshift galaxies. This is best illustrated by the [O iii]/[O ii] ratio, tracing interstellar medium (ISM) ionisation, in which we observe more than half of our sample to have [O iii]/[O ii] > 10. Our high signal-to-noise spectra reveal more than an order of magnitude of scatter in line ratios such as [O ii]/Hβ and [O iii]/[O ii], indicating significant diversity in the ISM conditions within the sample. We find no convincing detections of [N ii] λ6583 in our sample, either in individual galaxies, or a stack of all G395M/F290LP spectra. The emission line ratios observed in our sample are generally consistent with galaxies with extremely high ionisation parameters (log U ∼ −1.5), and a range of metallicities spanning from ∼ 0.1 × Z to higher than ∼ 0.3 × Z , 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.

JADES NIRSpec Spectroscopy of GN-z11: Lyman-$α$ emission and possible enhanced nitrogen abundance in a $z=10.60$ luminous galaxy

“…In summary, the emission line ratios measured for GN-z11 suggest a very high ionization parameter and low oxygen abundance in the vicinity of 10 % solar, broadly in line with findings from galaxies at z ∼ 6 − 10 ( Cameron et al 2023;Sanders et al 2023;Mascia et al 2023;Nakajima et al 2023;Tang et al 2023). However, the detection of strong N iii] emission suggests unexpected abundance patterns, which may have deeper implications for chemical enrichment histories.…”

“…These observations were processed with algorithms developed by the ESA NIRSpec Science Operations Team and the NIRSpec GTO Team. We refer the reader to Cameron et al (2023) for more details of the processing. We note that for the G140M/F070LP grating/filter combination we extended the calibration of the spectrum up to 1.84 µm, taking into account the transmission filter throughput beyond the nominal wavelength range of this configuration (0.70 µm -1.27 µm).…”

“…In Figure 7 we compare our [Ne iii]/[O ii] and ([Ne iii]+ [O ii])/Hδ measurements from GN-z11 with measurements from z > 5.5 galaxies from Cameron et al (2023), z ∼ 0 galaxies from SDSS MPA-JHU catalogs 1 (Aihara et al 2011) and photoionization model grids from Gutkin et al (2016). This line-ratio diagram is analogous to the widely used R23-O32 'ionization vs. (2023), again assuming that the light is dominated by the stellar population rather than an AGN.…”

“…The background grey 2D PDF shows the subset of SDSS galaxies with 0.03 < z < 0.1 for which [Ne iii] λ3869, [O ii] λλ3726, 3729 and Hδ are all detected with S /N > 5. Purple squares show z > 5.5 galaxies fromCameron et al (2023) after adjusting the reported ratios to be in terms of Hδ by assuming a fixed value of Hδ/Hβ = 0.268. Solid lines show model grids fromGutkin et al (2016), plotted for nine different values of metallicity (Z/Z = 0.04, 0.07, 0.15, 0.30, 0.45, 0.60, 0.75, 1.0, 1.5) indicated by the different colours, and seven values of ionization parameter, indicated by marker sizes, in steps of 0.5 from log U = −4.0 (smallest) to log U = −1.0 (largest).…”

JADES: Discovery of extremely high equivalent width Lyman-alpha emission from a faint galaxy within an ionized bubble at z=7.3

“…Although early data from the James Webb Space Telescope (JWST) has already provided unprecedented insights into the interstellar medium (ISM) conditions and ionizing photon production in reionization era galaxies at z > 6 (Curtis-Lake et al 2022; Robertson et al 2022;Endsley et al 2022b;Curti et al 2023;Katz et al 2023a;Arellano-Córdova et al 2022;Trump et al 2022;Tacchella et al 2022;Sun et al 2022;Sanders et al 2023;Fujimoto et al 2023;Cameron et al 2023), placing direct constraints on the escape fraction of LyC photons ( f esc ) is impossible at z > 6 because of the increasing neutrality of the IGM that ab-E-mail: aayush.saxena@physics.ox.ac.uk sorbs virtually all LyC photons along the line of sight (e.g. Inoue et al 2014).…”