Abstract
We utilize medium-resolution JWST/NIRSpec observations of 164 galaxies at z = 2.0-9.3 from the Cosmic Evolution Early Release Science (CEERS) survey to investigate the evolution of the excitation and ionization properties of galaxies at high redshifts. Our results represent the first statistical constraints on the evolution of the [O III]/Hβ versus [N II]/Hα, [S II]/Hα, and [O I]/Hα “BPT” diagrams at z > 2.7, and the first analysis of the O32 versus R23 diagram at z > 4 with a large sample. We divide the sample into five redshift bins containing 30-40 galaxies each. The subsamples at z ∼ 2.3, z ∼ 3.3, and z ∼ 4.5 are representative of the main-sequence star-forming galaxy population at these redshifts, while the z ∼ 5.6 and z ∼ 7.5 samples are likely biased toward high specific star formation rate, due to selection effects. Using composite spectra, we find that each subsample at z = 2.0-6.5 falls on the same excitation sequence in the [N II] and [S II] BPT diagrams and the O32-R23 diagram on average, and is offset from the sequences followed by z = 0 H II regions in the same diagrams. The direction of these offsets are consistent with high-redshift star-forming galaxies uniformly having harder ionizing spectra than typical local galaxies at fixed nebular metallicity. The similarity of the average line ratios suggests that the ionization conditions of the interstellar medium do not strongly evolve between z ∼ 2 and z ∼ 6. Overall, the rest-optical line ratios suggest the z = 2.7-9.3 CEERS/NIRSpec galaxies at log(M */M ⊙) ∼ 7.5-10 have high degrees of ionization and moderately low oxygen abundances (∼0.1-0.3 Z ⊙), but are not extremely metal-poor (<0.1 Z ⊙) even at z > 6.5.
| Original language | English |
|---|---|
| Article number | 54 |
| Journal | Astrophysical Journal |
| Volume | 955 |
| Issue number | 1 |
| DOIs | |
| State | Published - Sep 1 2023 |
Bibliographical note
Publisher Copyright:© 2023. The Author(s). Published by the American Astronomical Society.
Funding
We wish to acknowledge and thank the CEERS team for their work planning and executing the CEERS survey, in particular for their effort designing the NIRSpec MSA observations that feature in this work. This work is based on observations made with the NASA/ESA/CSA James Webb Space Telescope. The data were obtained from the Mikulski Archive for Space Telescopes at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-03127 for JWST. Support for this work was provided through the NASA Hubble Fellowship grant #HST-HF2-51469.001-A awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Incorporated, under NASA contract NAS5-26555. We also acknowledge support from NASA grant JWST-GO-01914. The Cosmic Dawn Center is funded by the Danish National Research Foundation (DNRF) under grant #140. Cloud-based data processing and file storage for this work are provided by the AWS Cloud Credits for Research program. We wish to acknowledge and thank the CEERS team for their work planning and executing the CEERS survey, in particular for their effort designing the NIRSpec MSA observations that feature in this work. This work is based on observations made with the NASA/ESA/CSA James Webb Space Telescope. The data were obtained from the Mikulski Archive for Space Telescopes at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-03127 for JWST. Support for this work was provided through the NASA Hubble Fellowship grant #HST-HF2-51469.001-A awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Incorporated, under NASA contract NAS5-26555. We also acknowledge support from NASA grant JWST-GO-01914. The Cosmic Dawn Center is funded by the Danish National Research Foundation (DNRF) under grant #140. Cloud-based data processing and file storage for this work are provided by the AWS Cloud Credits for Research program.
| Funders | Funder number |
|---|---|
| NIRSpec MSA | |
| National Aeronautics and Space Administration | #HST-HF2-51469.001-A |
| National Aeronautics and Space Administration | |
| Entomological Society of America | |
| Space Telescope Science Institute | NAS5-26555, JWST-GO-01914 |
| Space Telescope Science Institute | |
| Center for Scholarship Administration | NAS5-03127 |
| Center for Scholarship Administration | |
| Danmarks Grundforskningsfond | 140 |
| Danmarks Grundforskningsfond |
ASJC Scopus subject areas
- Astronomy and Astrophysics
- Space and Planetary Science