Oral Presentation
Redshift Evolution of the Electron Density in the ISM at z~0-8 Uncovered with JWST/NIRSpec Spectra and Line-Spread Function Determinations
Presenter: Yuki Isobe (The University of Tokyo)
In this talk, we present electron densities n_e in the inter-stellar medium (ISM) of star-forming galaxies at z=4-8 observed by the JWST/NIRSpec GLASS and ERO programs. We carefully evaluate line-spread functions of the NIRSpec instrument as a function of wavelength with the calibration data of a planetary nebula taken onboard, and obtain secure [OII]3726,3729 doublet fluxes for 4 galaxies at z=4.02-7.67 falling on the star-formation main sequence with the NIRSpec high and medium resolution spectra. We thus derive the electron densities of singly-ionized oxygen nebulae with the standard n_e indicator of [OII] doublet, and find that the electron densities of the z=4-8 galaxies are n_e~800 cm^(-3) significantly higher than those of z=0-3 galaxies at a given stellar mass, star-formation rate (SFR), and specific SFR. Interestingly, typical electron densities of singly ionized nebulae increase from z=0 to z=2-3 and z=4-8, which is approximated by the evolutionary relation of n_e proportional to (1+z)^p for p~2 or ~1-2. These results may suggest that nebula densities of high-z galaxies are generally high due to the compact morphologies of high-z galaxies evolving by r_e approximately proportional to (1+z)^(-1) (r_vir proportional to (1+z)^(-1)) for a given stellar (halo) mass whose inverse square corresponds to the p~2 evolutionary relation, while the p~1-2 evolutionary relation is explained by the reduction of n_e due to the high electron temperature of the high-z metal poor nebulae.
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