Theoretical Fei–iiiEmission‐Line Strengths from Active Galactic Nuclei with Broad‐Line Regions

Abstract

We present theoretical iron emission line strengths for physical conditions typical of active galactic nuclei (AGNs) with broad-line regions. The non-local thermodynamic equilibrium (NLTE) models include a new and extensive treatment of radiative transfer in the Fe iii ion, complementing the Fe ii emission line strengths predicted in our earlier works. We also briefly present preliminary results for the Fe i emission from AGNs using a reduced atom model. We can satisfactorily reproduce the empirical UV Fe iii emission line template of Vestergaard & Wilkes for the prototypical narrow-line Seyfert 1 galaxy I Zw 1, both in terms of the general Fe iii flux distribution and the relative strength of the Fe iii and Fe ii emission. However, a number of detailed features are still not matched; the most prominent example is the strongest single Fe iii feature observed in the I Zw 1 spectrum, UV47: it is predicted to be strong only in models suppressing Fe-H charge exchange reactions. We examine the role of variations in cloud turbulent velocity and iron abundance and carry out Monte Carlo simulations to demonstrate the effect of uncertainties in atomic data on the computed spectra.

Extreme quasars at high redshift

“…Fe +2 is 2% of Fe +1 in the partially-ionized zone (PIZ): Fe +1 still remains the dominant ionization stage of iron in the PIZ, as required by the strong optical Feii emission required for these sources. In the spectral range between 1800 and 2100 Å, however, the dominant contribution may be due to Feiii, as predicted by the models of Sigut et al (2004), which assumes log U ∼ −3.…”

“…A significant fraction of Feiii is present at the illuminated face of the cloud within the Hii zone, but only if the ionization parameter is very low (log U −3, Fig. 3 of Sigut et al 2004). Fe +2 is 2% of Fe +1 in the partially-ionized zone (PIZ): Fe +1 still remains the dominant ionization stage of iron in the PIZ, as required by the strong optical Feii emission required for these sources.…”

“…The role of Lyα fluorescence in explaining the UV and IR Feii emission has been known since the late 1980s from photoionization simulations (e.g., Sigut & Pradhan 1998;Verner et al 2004;Sigut et al 2004) as well as from observational evidence (e.g., Penston 1987;Marinello et al 2016;Clowes et al 2016, and references therein). As mentioned, a specific feature that is believed to be enhanced by Lyα fluorescence is the Feii UV #191 multiplet at 1785 Å.…”

VLT/ISAAC spectra of the Hβ region in intermediate-redshift quasars

“…Theoretical calculations of Feii emission, assuming the predominance of photoionization in the broad line region have greatly improved in the past decade (Sigut & Pradhan 2003;Sigut et al 2004;Verner et al 1999) with a 371-level model of the Fe + ion presently included in the photionization code CLOUDY v. 07.01 (Ferland et al 1998). A detailed analysis of the Feii emission in I Zw 1 (Véron-Cetty et al 2004) reveals rich and complex emission from several line systems, each associated with a well-defined redshift and FWHM.…”

Testing the relativistic Doppler boost hypothesis for supermassive binary black holes candidates via broad emission line profiles

“…The numbers of these BBH candidates that have Mg ii, C iii], and C iv lines in their SDSS spectra are among the top three, hence we take them for following analysis. We adopt a model with three components to fit each observed spectrum, i.e., a power-law for continuum, a Gaussian profile for each broad line, and multiple lines from Fe ii templates (Sigut & Pradhan 2003;Sigut et al 2004) described by Gaussian profiles with the same velocity dispersion (which can be different from that for the broad line). Fe ii lines are considered here as they contaminate the above three lines (especially Mg ii) significantly.…”