Early Results from GLASS-JWST. XXV. Electron Density in the Interstellar Medium at $0.7\lesssim z\lesssim 9.3$ with NIRSpec High-resolution Spectroscopy

Abstract

The electron density ($n_{\mathrm{e}}$) of the interstellar medium (ISM) in star-forming galaxies is intimately linked to star formation and ionization condition. Using the high-resolution spectra obtained from the JWST NIRSpec micro shutter assembly (MSA) as part of the GLASS-JWST program, we have assembled the largest sample to date (34 galaxies) with individual $n_{\mathrm{e}}$ measurements derived from the [OII] $\lambda \lambda$3726,29 and/or [SII] $\lambda \lambda$6718,32 doublets at $0.7\lesssim z\lesssim 9.3$. The gravitational lensing magnification by the foreground Abell~2744 cluster allows us to probe $n_{\mathrm{e}}$ in galaxies with stellar masses ($M_{\ast }$) down to $\simeq 10^{7.5}{M}_{\odot }$ across the entire redshift range. Our analysis reveals that the [OII] flux ratios are marginally anti-correlated with specific star formation rate (sSFR) within a 1-$\sigma$ confidence interval, whereas the [SII] flux ratios show no significant correlation with sSFR. Despite clear correlation between sSFR and redshift within our sample, we find no apparent redshift evolution of $n_{\mathrm{e}}$ at $z\simeq 1-9$. Our dataset also includes 13 galaxies where $n_{\mathrm{e}}$ can be measured from both [OII] and [SII]. Contrary to findings at lower redshifts, we observe considerable scatter in $n_{\mathrm{e}}$ measurements from [OII] and [SII], indicating a complex gaseous environment with significant variations in $n_{\mathrm{e}}$ in high-redshift galaxies. This work highlights the unique capability of JWST NIRSpec/MSA high-resolution spectroscopy to characterize the detailed physical properties of the ISM in individual high-redshift galaxies.

15 pages, 7 figures, 2 tables; Accepted for publication in ApJL

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