Improved Fe II emission line models for AGN using new atomic datasets

Abstract

Understanding the Fe II emission from Active Galactic Nuclei (AGN) has been a grand challenge for many decades. The rewards from understanding the AGN spectra would be immense, involving both quasar classification schemes such as "Eigenvector 1" and tracing the chemical evolution of the cosmos. Recently, three large Fe II atomic datasets with radiative and electron collisional rates have become available. We have incorporated these into the spectral synthesis code Cloudy and examine predictions using a new generation of AGN Spectral Energy Distribution (SED), which indicates that the UV emission can be quite different depending on the dataset utilized. The Smyth et al dataset better reproduces the observed Fe II template of the I ZW 1 Seyfert galaxy in the UV and optical regions, and we adopt these data. We consider both thermal and microturbulent clouds and show that a microturbulence of $\approx$ 100 km/s reproduces the observed shape and strength of the so-called Fe II "UV bump". Comparing our predictions with the observed Fe II template, we derive a typical cloud density of $10^{11}$ cm${}^{-3}$ and photon flux of $10^{20}$ cm${}^{-2}$ s${}^{-1}$, and show that these largely reproduce the observed Fe II emission in the UV and optical. We calculate the $I$(Fe II)/$I$(Mg II) emission-line intensity ratio using our best-fitting model and obtain log($I$(Fe II)/$I$(Mg II)) $\sim$ 0.7, suggesting many AGNs have a roughly solar Fe/Mg abundance ratio. Finally, we vary the Eddington ratio and SED shape as a step in understanding the Eigenvector 1 correlation.

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• Chemical abundances in the outskirts of nearby galaxy groups measured with joint Suzaku and Chandra observations
• Fe II emission in active galactic nuclei
• Optical and JWST Mid-IR Emission Line Diagnostics for Simultaneous IMBH and Stellar Excitation in z~0 Dwarf Galaxies
• Atomic Data Assessment with PyNeb: Radiative and Electron Impact Excitation Rates for [Fe II] and [Fe III]
• Fantastic Fits with fantasy of Active Galactic Nuclei Spectra -- Exploring the Fe II emission near the H$\alpha$ line
• The warm outer layer of a Little Red Dot as the source of [Fe II] and collisional Balmer lines with scattering wings
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• A Practical Guide to the Partition Function of Atoms and Ions
• JADES -- The small blue bump in GN-z11: insights into the nuclear region of a galaxy at z=10.6
• Spectropolarimetry and spectral decomposition of high-accreting Narrow Line Seyfert 1 galaxies
• Taming the derivative: diagnostics of the continuum and H$\beta$ emission in a prototypical Population B active galaxy
• Unveiling the quasar main sequence: illuminating the complexity of active galactic nuclei and their evolution
• Accretion disc reverberation mapping in a high-redshift quasar
• The relation between quasars' optical spectra and variability
• Searching for signatures of Fe II atomic processes in spectra of active galactic nuclei
• Emission Line Diagnostics for IMBHs in Dwarf Galaxies: Accounting for BH Seeding and ULX Excitation
• The CaFe Project: Optical FeII and Near-Infrared Ca II triplet emission in active galaxies. II. The driver(s) of the Ca II and Fe II and its potential use as a chemical clock
• Mid-infrared extinction curve for protostellar envelopes from JWST-detected embedded jet emission: the case of TMC1A
• Strong correlation between FeII/MgII ratio and Eddington ratio of type 1 Active galactic nuclei