2023/01/17 by Yuki Isobe, Masami Ouchi, Isobe, Yuki +13
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysics and Star Formation Studies #Astrophysics of Galaxies (astro-ph.GA) #FOS: Physical sciences #Galaxies: Formation, Evolution, Phenomena
paper · pdf · doi:10.48550/arxiv.2301.06811
openalex publication_date 2023/01/17 · openalex created_date 2023/01/20 · openalex updated_date 2026/07/28
We present electron densities n\rm e in the inter-stellar medium (ISM) of star-forming galaxies at z=4-9 observed by the JWST/NIRSpec GLASS, ERO, and CEERS 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]λλ3726,3729 doublet fluxes for 14 galaxies at z=4.02-8.68 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\rm e indicator of [OII] doublet, and find that the electron densities of the z=4-9 galaxies are n\rm e\gtrsim 300 cm-3 significantly higher than those of low-z 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=1-3 and z=4-9, which is approximated by the evolutionary relation of n\rm e∝(1+z)p with p∼ 1-2. Although it is not obvious that the ISM property of n\rm e is influenced by global galaxy properties, 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\rm e approximately proportional to (1+z)-1 (r\rm vir ∝ (1+z)-1) for a given stellar (halo) mass whose inverse square corresponds to the p∼ 2 evolutionary relation. The p∼ 1-2 evolutionary relation can be explained by a combination of the compact morphology and the reduction of n\rm e due to the high electron temperature of the high-z metal poor nebulae.