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Multi-line assessment of narrow-line regions in $z \sim$ 3 radio galaxies
Astrophysics of Galaxies · Submitted 7 Mar 2022
abstract compiled · 2026-09-23 · no language-model review
The authors' main claim We confirm that the metallicity of NLRs in AGNs at $z \sim$ 3 is solar or super-solar, without assuming the gas density and ionization parameter thanks to the constrains from the faint emission lines.
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In this paper, we utilize high-quality rest-UV spectra of three radio galaxies at $z \sim$ 3 observed with VLT/FORS2 to measure the flux of several emission lines including relatively faint ones, such as NIV]$\lambda$1486, OIII]$\lambda$1663, and [NeIV]$\lambda$2424. Additionally, we collect fluxes of faint rest-UV emission lines in 12 $z \sim$ 3 radio galaxies from the literature. Previously, physical and chemical properties of narrow-line regions (NLRs) in high-$z$ active galactic nuclei (AGNs) have been investigated mostly by using only strong rest-UV emission-lines (e.g., NV$\lambda$1240, CIV$\lambda$1549, HeII$\lambda$1640, and CIII]$\lambda$1909). Such strong-line diagnostics are based on various assumptions due to the limitation in the number of available emission-line constraints. In this work, both physical and chemical properties of NLR clouds in each object are estimated by fitting detailed photoionization models to the measured emission-line fluxes. We confirm that the metallicity of NLRs in AGNs at $z \sim$ 3 is solar or super-solar, without assuming the gas density and ionization parameter thanks to the constrains from the faint emission lines. This result suggests that high-$z$ radio galaxies are already chemically matured at $z \sim$ 3.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | In this paper, we utilize high-quality rest-UV spectra of three radio galaxies at $z \sim$ 3 observed with VLT/FORS2 to measure the flux of several emission lines including relatively faint ones, such as NIV]$\lambda$1486, OIII]$\lambda$1663, and [NeIV]$\lambda$2424. | method 0.81 | 0.98 | 0.03 | asserted 0.99 |
| s1 | Additionally, we collect fluxes of faint rest-UV emission lines in 12 $z \sim$ 3 radio galaxies from the literature. | method 0.71 | 0.89 | 0.02 | asserted 0.99 |
| s2 | Previously, physical and chemical properties of narrow-line regions (NLRs) in high-$z$ active galactic nuclei (AGNs) have been investigated mostly by using only strong rest-UV emission-lines (e.g., NV$\lambda$1240, CIV$\lambda$1549, HeII$\lambda$1640, and CIII]$\lambda$1909). | background 0.90 | 0.03 | 0.02 | asserted 0.99 |
| s3 | Such strong-line diagnostics are based on various assumptions due to the limitation in the number of available emission-line constraints. | gap 0.49 | 0.06 | 0.02 | asserted 1.00 |
| s4 | In this work, both physical and chemical properties of NLR clouds in each object are estimated by fitting detailed photoionization models to the measured emission-line fluxes. | method 0.98 | 0.97 | 0.05 | asserted 0.99 |
| s5 | We confirm that the metallicity of NLRs in AGNs at $z \sim$ 3 is solar or super-solar, without assuming the gas density and ionization parameter thanks to the constrains from the faint emission lines. | result 1.00 | 0.96 | 0.76 | asserted 1.00 |
| s6 | This result suggests that high-$z$ radio galaxies are already chemically matured at $z \sim$ 3. | interpretation 1.00 | 0.63 | 0.60 | hedged possibility 1.00 |
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Original abstract
In this paper, we utilize high-quality rest-UV spectra of three radio galaxies at $z \sim$ 3 observed with VLT/FORS2 to measure the flux of several emission lines including relatively faint ones, such as NIV]$\lambda$1486, OIII]$\lambda$1663, and [NeIV]$\lambda$2424. Additionally, we collect fluxes of faint rest-UV emission lines in 12 $z \sim$ 3 radio galaxies from the literature. Previously, physical and chemical properties of narrow-line regions (NLRs) in high-$z$ active galactic nuclei (AGNs) have been investigated mostly by using only strong rest-UV emission-lines (e.g., NV$\lambda$1240, CIV$\lambda$1549, HeII$\lambda$1640, and CIII]$\lambda$1909). Such strong-line diagnostics are based on various assumptions due to the limitation in the number of available emission-line constraints. In this work, both physical and chemical properties of NLR clouds in each object are estimated by fitting detailed photoionization models to the measured emission-line fluxes. We confirm that the metallicity of NLRs in AGNs at $z \sim$ 3 is solar or super-solar, without assuming the gas density and ionization parameter thanks to the constrains from the faint emission lines. This result suggests that high-$z$ radio galaxies are already chemically matured at $z \sim$ 3.
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As NeIV requires photons with energies higher than 63.5 eV, this line is an unambiguous AGN tracer [ref] , indeed it is commonly seen in AGN [ref] and not seen in star forming galaxies, not even those hosting the most extreme Wolf-Rayet stars [ref] .
A small and vigorous black hole in the early Universe · Introduction · 0.97
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