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Arxiv: JWST NIRSpec High-resolution Spectroscopy of MACS0647-JD at z=10.167: Resolved [OII] Doublet and Electron Density in an Early Galaxy Published: 4/24/2024 11:53:17 PM Updated: 4/24/2024 11:53:17 PM

Paper abstract: We present JWST/NIRSpec high-resolution spectroscopy G395H/F290LP ofMACS0647-JD, a gravitationally lensed galaxy merger at z=10.167. The newspectroscopy, which is acquired for the two lensed images (JD1 and JD2),detects and resolves emission lines in the rest-frame ultraviolet (UV) and blueoptical, including the resolved [OII]3726,3729 doublet, [NeIII]3870, [HeI]3890,H\delta, H\gamma, and [OIII]4363. This is the first observation of theresolved [OII]3726,3729 doublet for a galaxy at z>8. We measure a line fluxratio [OII]3729/3726 = 0.9 \pm 0.3, which corresponds to an estimatedelectron density of \log(n_{e} / \rm{cm}^{-3}) = 2.9 \pm 0.5. This issignificantly higher than the electron densities of local galaxies reported inthe literature. We compile the measurements from the literature and furtheranalyze the redshift evolution of n_{e}. We find that the redshift evolutionfollows the power-law form of n_{e} = A\times (1+z)^{p} withA=54^{+31}_{-23} cm^{-3} and p=1.2^{+0.4}_{-0.4}. This power-law form maybe explained by a combination of metallicity and morphological evolution ofgalaxies, which become, on average, more metal-poor and more compact withincreasing redshift.