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

NIRSpec G395H/F290LP spectra of MACS0647-JD lensed images JD1 and JD2 (IDs 3593 and 3349, respectively, in the catalog used for preparing the observation). Left panel: Slitlet positions overlaid on 1.6 '' × 1.6 '' NIRCam color images (blue:F115W; green:F150W; red:F200W). Right panel: 2D and 1D NIRSpec high-resolution spectra of JD1 (top) and JD2 (bottom). Several emission lines are detected while the continuum is not. Emission lines are indicated with blue-colored labels and orange vertical dashed lines. The gray shaded area represents the uncertainties obtained from the pipeline. The green lines represent the standard deviations of the spectral fluxes after removing the emission lines. We multiply the flux uncertainties by a factor of two to match the overall level of the standard deviations. This is shown with a red line. These rescaled uncertainties are used for the analysis in this paper. 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.