Excitation and Ionization Properties of Star-forming Galaxies at z = 2.0–9.3 with JWST/NIRSpec
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 con...
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
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IOP Publishing
2023-01-01
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| Series: | The Astrophysical Journal |
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| Online Access: | https://doi.org/10.3847/1538-4357/acedad |
| _version_ | 1797682241239777280 |
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| author | Ryan L. Sanders Alice E. Shapley Michael W. Topping Naveen A. Reddy Gabriel B. Brammer |
| author_facet | Ryan L. Sanders Alice E. Shapley Michael W. Topping Naveen A. Reddy Gabriel B. Brammer |
| author_sort | Ryan L. Sanders |
| collection | DOAJ |
| description | 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 ]/H β versus [N II ]/H α , [S II ]/H α , and [O I ]/H α “BPT” diagrams at z > 2.7, and the first analysis of the O _32 versus R _23 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 O _32 –R _23 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. |
| first_indexed | 2024-03-11T23:56:43Z |
| format | Article |
| id | doaj.art-16ca249b49df4769a22afda71a335b6d |
| institution | Directory Open Access Journal |
| issn | 1538-4357 |
| language | English |
| last_indexed | 2024-03-11T23:56:43Z |
| publishDate | 2023-01-01 |
| publisher | IOP Publishing |
| record_format | Article |
| series | The Astrophysical Journal |
| spelling | doaj.art-16ca249b49df4769a22afda71a335b6d2023-09-18T10:29:36ZengIOP PublishingThe Astrophysical Journal1538-43572023-01-0195515410.3847/1538-4357/acedadExcitation and Ionization Properties of Star-forming Galaxies at z = 2.0–9.3 with JWST/NIRSpecRyan L. Sanders0https://orcid.org/0000-0003-4792-9119Alice E. Shapley1https://orcid.org/0000-0003-3509-4855Michael W. Topping2https://orcid.org/0000-0001-8426-1141Naveen A. Reddy3https://orcid.org/0000-0001-9687-4973Gabriel B. Brammer4https://orcid.org/0000-0003-2680-005XDepartment of Physics and Astronomy, University of California , Davis, One Shields Avenue, Davis, CA 95616, USA; Department of Physics and Astronomy, University of Kentucky , 505 Rose Street, Lexington, KY 40506, USADepartment of Physics & Astronomy, University of California , Los Angeles, 430 Portola Plaza, Los Angeles, CA 90095, USASteward Observatory, University of Arizona , 933 N. Cherry Avenue, Tucson, AZ 85721, USADepartment of Physics & Astronomy, University of California , Riverside, 900 University Avenue, Riverside, CA 92521, USACosmic Dawn Center (DAWN) , Denmark; Niels Bohr Institute, University of Copenhagen , Jagtvej 128, DK-2200 Copenhagen N, DenmarkWe 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 ]/H β versus [N II ]/H α , [S II ]/H α , and [O I ]/H α “BPT” diagrams at z > 2.7, and the first analysis of the O _32 versus R _23 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 O _32 –R _23 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.https://doi.org/10.3847/1538-4357/acedadHigh-redshift galaxiesIonizationEmission-line galaxiesGalaxy evolution |
| spellingShingle | Ryan L. Sanders Alice E. Shapley Michael W. Topping Naveen A. Reddy Gabriel B. Brammer Excitation and Ionization Properties of Star-forming Galaxies at z = 2.0–9.3 with JWST/NIRSpec The Astrophysical Journal High-redshift galaxies Ionization Emission-line galaxies Galaxy evolution |
| title | Excitation and Ionization Properties of Star-forming Galaxies at z = 2.0–9.3 with JWST/NIRSpec |
| title_full | Excitation and Ionization Properties of Star-forming Galaxies at z = 2.0–9.3 with JWST/NIRSpec |
| title_fullStr | Excitation and Ionization Properties of Star-forming Galaxies at z = 2.0–9.3 with JWST/NIRSpec |
| title_full_unstemmed | Excitation and Ionization Properties of Star-forming Galaxies at z = 2.0–9.3 with JWST/NIRSpec |
| title_short | Excitation and Ionization Properties of Star-forming Galaxies at z = 2.0–9.3 with JWST/NIRSpec |
| title_sort | excitation and ionization properties of star forming galaxies at z 2 0 9 3 with jwst nirspec |
| topic | High-redshift galaxies Ionization Emission-line galaxies Galaxy evolution |
| url | https://doi.org/10.3847/1538-4357/acedad |
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