GA-NIFS: A massive black hole in a low-metallicity AGN at z ∼ 5.55 revealed by JWST/NIRSpec IFS

Abstract

We present rest-frame optical data of the compact z = 5.55 galaxy GS_3073 obtained using the integral field spectroscopy mode of the Near-InfraRed Spectrograph on board the James Webb Space Telescope. The galaxy’s prominent broad components in several hydrogen and helium lines (though absent in the forbidden lines) and v detection of a large equivalent width of He IIλ4686, EW(He II) ∼20 Å, unambiguously identify it as an active galactic nucleus (AGN). We measured a gas phase metallicity of Zgas/Z⊙∼0.21−0.04+0.08 , which is lower than what has been inferred for both more luminous AGN at a similar redshift and lower redshift AGN. We empirically show that classical emission line ratio diagnostic diagrams cannot be used to distinguish between the primary ionisation source (AGN or star formation) for systems with such low metallicity, though different diagnostic diagrams involving He IIλ4686 prove very useful, independent of metallicity. We measured the central black hole mass to be log(MBH/M⊙)∼8.2 ± 0.4 based on the luminosity and width of the broad line region of the Hα emission. While this places GS_3073 at the lower end of known high-redshift black hole masses, it still appears to be overly massive when compared to its host galaxy’s mass properties. We detected an outflow with a projected velocity ≳700 km s−1 and inferred an ionised gas mass outflow rate of about 100 M⊙ yr−1, suggesting that one billion years after the Big Bang, GS_3073 is able to enrich the intergalactic medium with metals.

A JWST/NIRSpec First Census of Broad-line AGNs at z = 4–7: Detection of 10 Faint AGNs with M BH ∼ 106–108 M ⊙ and Their Host Galaxy Properties

“…Compared to the AGNs at z ∼ 0 (Reines & Volonteri 2015), our AGNs at z ∼ 4-7 have similar black hole masses but systematically lower stellar masses. Similar results are obtained in previous studies with a smaller number of AGNs (Kocevski et al 2023;Übler et al 2023;Kocevski et al 2023), but we confirm this trend of lower M * (higher M BH ) with a sample of 10 AGNs at z = 4-7. Our results at z = 4-7 showing lower M * (higher M BH ) than z ∼ 0 AGNs indicate that the black hole grows faster than its host galaxy at high redshift.…”

The Puzzling Properties of the MACS1149-JD1 Galaxy at z = 9.11

“…The high level of ionization is also hinted at by the very high [O III]λ5007/ Hβ = 10.03 ± 0.31, which would correspond to the AGN-star formation boundary in the Baldwin, Phillips, & Terlevich (Baldwin et al 1981;Lamareille et al 2009;Lamareille 2010) diagram. Indeed, this diagram appears insufficient to separate star formation from AGN photoionization at z 6 (Cameron et al 2023b;Übler et al 2023). However, we do not see any evidence of a broad component in the Balmer lines.…”

Pure Spectroscopic Constraints on UV Luminosity Functions and Cosmic Star Formation History from 25 Galaxies at z spec = 8.61–13.20 Confirmed with JWST/NIRSpec

“…Another possibility is that a part of the observed UV luminosity densities at z > 10 are produced by AGNs, and there are no excessive SFR densities at z > 10 beyond the constant star formation efficiency model. Although the quasar luminosity function shows a very rapid decline at z > 4 compared to that of galaxies (e.g., Harikane et al 2022b), recent spectroscopic studies report faint AGNs in galaxy samples at z > 4 (Harikane et al 2023b;Kocevski et al 2023;Larson et al 2023;Übler et al 2023). Indeed, two bright galaxies in our spectroscopic sample, CEERS_1019 and GN-z11, could have AGNs (Bunker et al 2023;Larson et al 2023), although they are removed from the sample used for the SFR density calculations.…”