Local Analogs of Potential Ionizers of the Intergalactic Medium: Compact Star-forming Galaxies with Intense C IV λ1550 Emission
We performed spectroscopic analyses of five local compact star-forming galaxies (CSFGs) with extremely high [O iii ]/[O ii ] (O _32 ) ratios (>20). These targets remarkably share similar properties with high-redshift C iv emitters at z > 6: high H β equivalent widths (EWs > 200Å), extreme...
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| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
IOP Publishing
2025-01-01
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| Series: | The Astrophysical Journal |
| Subjects: | |
| Online Access: | https://doi.org/10.3847/1538-4357/adde49 |
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| Summary: | We performed spectroscopic analyses of five local compact star-forming galaxies (CSFGs) with extremely high [O iii ]/[O ii ] (O _32 ) ratios (>20). These targets remarkably share similar properties with high-redshift C iv emitters at z > 6: high H β equivalent widths (EWs > 200Å), extreme O _32 ratios, low metallicities (12+log(O/H) ≲ 7.8), low C/O abundances (log(C/O) < −0.7), and high ionization conditions (log U > −2). The ultraviolet (UV) spectra were acquired using the Hubble Space Telescope’s (HST) Cosmic Origins Spectrograph and Space Telescope Imaging Spectrograph. We have identified a wealth of rest-frame UV emission lines (C iv , He ii , O iii ], C iii ]) in the HST spectra. Notably, all our targets show intense C iv emission lines with rest-frame EWs > 10 Å, indicative of hard ionizing radiation. The rest-frame UV emission line diagnostics disfavor an active galactic nucelus and could be consistent with significant shock contributions to the source of ionizing radiation. Four of our targets show high C iv /C iii ] ratios (≥1.4), suggestive of strong Lyman-continuum leakage (LyC escape fraction, f _esc,LyC > 10%) from these sources. This is consistent with their Ly α -inferred LyC escape fractions ( f _esc,LyC = 9%–31%). We derive relative C/O abundances from our sources, showing log(C/O) values from −1.28 to −0.77, comparable to those of reionization-era galaxies at z ≳ 6. The properties of the CSFGs, particularly their intense C iv emission and high O _32 ratios, which suggest significant LyC escape fractions, are similar to those of the reionization-era C iv emitters. These similarities reinforce the hypothesis that these CSFGs are the closest analogs of significant contributors to the reionization of the intergalactic medium. |
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| ISSN: | 1538-4357 |