Insights for Early Massive Black Hole Growth from JWST Detection of the [Ne v] <i>λ</i>3427 Emission Line

Abstract We use the narrow [Ne v] λ 3427 emission line detected in the recently published JWST spectra of two galaxies, at z ≃ 6.9 and 5.6, to study the key properties of the active galactic nuclei (AGN) and the supermassive black holes (SMBHs) in their centers. Using a new empirical scaling linking the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mfenced close="]" open="["> <mml:mrow> <mml:mi mathvariant="normal">Ne</mml:mi> <mml:mspace width="0.25em"/> <mml:mi mathsize="small" mathvariant="normal">V</mml:mi> </mml:mrow> </mml:mfenced> </mml:math> line emission with AGN accretion-driven (continuum) emission, derived from a highly complete low-redshift AGN sample, we show that the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mfenced close="]" open="["> <mml:mrow> <mml:mi mathvariant="normal">Ne</mml:mi> <mml:mspace width="0.25em"/> <mml:mi mathsize="small" mathvariant="normal">V</mml:mi> </mml:mrow> </mml:mfenced> </mml:math> emission in the two z &gt; 5 galaxies implies total (bolometric) AGN luminosities of order L bol ≈ (4–8) × 10 45 erg s −1 . Assuming that the radiation emitted from these systems is Eddington limited, the (minimal) black hole (BH) masses are of order M BH ≳ 10 7 M ⊙ . Combined with the published stellar masses of the galaxies, estimated from dedicated fitting of their spectral energy distributions, the implied BH-to-stellar mass ratios are of order M BH / M host ≈ 0.1–1. This is considerably higher than what is found in the local Universe, but is consistent with the general trend seen in some other z ≳ 5 AGN. Given the intrinsic weakness of the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mfenced close="]" open="["> <mml:mrow> <mml:mi mathvariant="normal">Ne</mml:mi> <mml:mspace width="0.25em"/> <mml:mi mathsize="small" mathvariant="normal">V</mml:mi> </mml:mrow> </mml:mfenced> </mml:math> line and the nature of the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mfenced close="]" open="["> <mml:mrow> <mml:mi mathvariant="normal">Ne</mml:mi> <mml:mspace width="0.25em"/> <mml:mi mathsize="small" mathvariant="normal">V</mml:mi> </mml:mrow> </mml:mfenced> </mml:math> –to– L bol scaling, any (rare) detection of the [Ne v] λ 3427 line at z &gt; 5 would translate to similarly high AGN luminosities and SMBH masses, thus providing a unique observational path for studying luminous AGN well into the epoch of reionization, including obscured sources.