Emission-Line Ratios and Ionization Conditions of CEERS Star-Forming Galaxies with JWST/NIRSpec

TL;DR

This study uses JWST/NIRSpec to analyze emission-line ratios in 71 star-forming galaxies across a wide redshift range, revealing that specific star formation rate primarily influences ionization conditions over other factors.

Contribution

It provides new insights into the relationship between emission-line ratios and galaxy properties, emphasizing the role of sSFR in ionization conditions across cosmic time.

Findings

Line ratios modestly correlate with sSFR

Weak correlation between line ratios and excess sSFR

sSFR governs ionization conditions more than SFR or main sequence distance

Abstract

Galaxy emission-line fluxes can be analyzed to determine star formation rates (SFR) and ISM ionization. Here, we investigate rest-frame optical emission lines of 71 star-forming galaxies at redshift 0.7 < z < 7 from the Cosmic Evolution Early Release Science (CEERS) survey using JWST/NIRSpec. We use H${\alpha}$ line fluxes to measure SFRs. We combine these with HST CANDELS stellar mass estimates to determine the redshift evolution of specific SFR (sSFR) and compare our sample with the star-forming galaxy main sequence. We create [O III]${\lambda}$5008/H${\beta}$ versus [Ne III]${\lambda}$3870/[O II]${\lambda}$3728 line ratio diagrams and correlate these ratios with sSFR and the distance of each galaxy from the main sequence (excess sSFR). We find a modest correlation between the line ratios and sSFR, which is consistent with previous work analyzing similar samples. However, we find a weak correlation between the line ratios and excess sSFR. Taken together, our results suggest that sSFR is the parameter that governs ionization conditions rather than SFR or a galaxy's distance from the main sequence. These measurements reveal a rich diversity of ISM conditions and physical galaxy properties throughout cosmic time.