J/A+A/700/A203 Missing FeII bump in faint JWST AGNs (Trefoloni+, 2025)
The missing Fe II bump in faint JWST active galactic nuclei:
Possible evidence of metal-poor broad-line regions at early cosmic times.
Trefoloni B., Ji X., Maiolino R., D'Eugenio F., Uebler H., Scholtz J.,
Marconi A., Marconcini C., Mazzolari G.
<Astron. Astrophys. 700, A203 (2025)>
=2025A&A...700A.203T 2025A&A...700A.203T (SIMBAD/NED BibCode)
ADC_Keywords: Active gal. nuclei ; QSOs ; Spectroscopy ; Abundances
Keywords: galaxies: active - galaxies: high-redshift - quasars: emission lines -
quasars: general - quasars: supermassive black holes -
galaxies: Seyfert
Abstract:
Recent JWST observations have revealed a large population of
intermediate/low-luminosity active galactic nuclei (AGN) at early
times with peculiar properties, different from local AGN or luminous
quasars. To better understand the physical conditions in the
broad-line regions (BLRs) of these early AGN, we used the optical FeII
(4434-4684Å) and the broad Hbeta emission, and the ratio between
their equivalent widths RFe, as a probe on a purposefully assembled
sample. Specifically, we gathered a sample of 31 high redshift
(=6.5) AGN, observed by JWST, with broad Hbeta detection both in
the high and low luminosity regimes (respectively 14 faint AGN and 17
quasars), to investigate their optical FeII emission properties. In
addition, we carefully selected control samples at lower z. We found
that the population of faint AGN (log(LHb/(erg/s))≲44) exhibits a
significantly lower FeII emission than their local counterparts having
a mean (median) RFe<0.24 (0.12) versus RFe~=0.90 (0.79) in the
control sample. At the same time, the quasars at the epoch of
reionisation observed by JWST present a FeII emission profile that
closely resembles that observed at z<3. We argue that the weakness of
the FeII bump in the faint JWST AGN might be due to the reduced
metallicity of their broad line region (≲0.5Z☉), while luminous
quasars have already reached chemical maturity (∼Z{sun} or higher).
Lastly, we highlight an intriguing similarity between the spectral
properties of the high redshift population of faint AGN with those
harboured in local metal poor dwarf galaxies.
Description:
We assembled a sample of high-redshift AGN observed by JWST spanning a
wide range in terms of luminosity and black hole mass with the aim of
characterising the strength of the RFe. To this end, we performed a
detailed spectroscopic analysis and selected control subsamples at
lower redshift to compare their properties and assess possible
differences. We remark that our control samples are selected to match
the JWST AGN in both Hbeta FWHM and luminosity, which are the direct
emission line observables that best capture the black hole properties
and accretion parameters. Additionally, we also included as a separate
comparison sample three metal-poor dwarf galaxies hosting
low-luminosity AGN as tentative super local counterparts.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
tablea1.dat 115 34 The broad lines spectral properties estimated
from the spectral fits of our sample
tableb1.dat 63 34 Luminosities, black hole mass and Eddington ratio
--------------------------------------------------------------------------------
Byte-by-byte Description of file: tablea1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 19 A19 --- Name Name of the source
21- 29 F9.5 deg RAdeg Right ascension (J2000)
31- 39 F9.5 deg DEdeg Declination (J2000)
41 A1 --- Hbprofile [GL] Hbeta line profile,
G=Gaussian, L=Lorentzian
43- 47 F5.2 [10-7W] logLHb Logarithm of the Hbeta luminosity
49- 52 F4.2 [10-7W] e_logLHb Uncertainty on the logarithm of
the Hbeta luminosity
54- 57 F4.2 --- RFe Ratio of the optical FeII (4434-4684Å)
and the broad Hbeta emission
equivalent widths
59- 62 F4.2 --- e_RFe Uncertainty on the RFe
64- 67 I4 km/s FWHMHb FWHM of the Hbeta line
69- 72 I4 km/s e_FWHMHb Uncertainty on the FWHM of the Hbeta line
74- 77 F4.2 [0.1nm] logEWOIII ?=- Logarithm of the equivalent width
of [OIII]5007
79- 82 F4.2 [0.1nm] e_logEWOIII ?=- Uncertainty on the logarithm of the
equivalent width of [OIII]5007
84- 88 F5.2 --- O3Hb ?=- Ratio between [OIII]5007 and
narrow Hbeta
90- 94 F5.2 --- e_O3Hb ?=- Uncertainty on the ratio between
[OIII]5007 and narrow Hbeta
96-100 F5.2 --- O32 ?=- Ratio between [OIII]5007 and [OII]3728
102-105 F4.2 --- e_O32 ?=- Uncertainty on the ratio between
[OIII]5007 and [OII]3728
107-110 F4.2 --- Oabund ?=- Oxygen abundance, 12+log(O/H)
112-115 F4.2 --- e_Oabund ?=- Uncertainty on the oxygen abundance
--------------------------------------------------------------------------------
Byte-by-byte Description of file: tableb1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 19 A19 --- Name Name of the source
21- 25 F5.2 [10-7W] logL5100 Logarithm of the 5100Å luminosity
27- 30 F4.2 [10-7W] e_logL5100 Uncertainty on the logarithm of the 5100Å
luminosity
32- 36 F5.2 [10-7W] logLbol Logarithm of the bolometric luminosity
38- 41 F4.2 [10-7W] e_logLbol Uncertainty on the logarithm of the
bolometric luminosity
43- 47 F5.2 Msun logMBH Logarithm of the black hole mass
49- 52 F4.2 Msun e_logMBH Uncertainty on the logarithm of the
black hole mass
54- 58 F5.2 --- logEr Logarithm of the Eddington ratio
60- 63 F4.2 --- e_logEr Uncertainty on the logarithm of the
Eddington ratio
--------------------------------------------------------------------------------
Acknowledgements:
Bartolomeo Trefoloni, bartolomeo.trefoloni(at)unifi.it
(End) Patricia Vannier [CDS] 28-Jul-2025