James Webb Space Telescope Feed Post

JWST NIRSpec High-resolution Spectroscopy of MACS0647-JD at z=10.167: Resolved [OII] Doublet and Electron Density in an Early Galaxy

Abstract: We present JWST/NIRSpec high-resolution spectroscopy G395H/F290LP of MACS0647-JD, a gravitationally lensed galaxy merger at z=10.167. The new spectroscopy, which is acquired for the two lensed images (JD1 and JD2), detects and resolves emission lines in the rest-frame ultraviolet (UV) and blue optical, including the resolved [OII]3726,3729 doublet, [NeIII]3870, [HeI]3890, Hd, H?, and [OIII]4363. This is the first observation of the resolved [OII]3726,3729 doublet for a galaxy at z>8. We measure a line flux ratio [OII]3729/3726 =0.9±0.3, which corresponds to an estimated electron density of log(ne/cm-3)=2.9±0.5. This is significantly higher than the electron densities of local galaxies reported in the literature. We compile the measurements from the literature and further analyze the redshift evolution of ne. We find that the redshift evolution follows the power-law form of ne=A×(1+z)p with A=54+31-23 cm-3 and p=1.2+0.4-0.4. This power-law form may be explained by a combination of metallicity and morphological evolution of galaxies, which become, on average, more metal-poor and more compact with increasing redshift.