Predicted Fe ii Emission‐Line Strengths from Active Galactic Nuclei

Abstract

We present theoretical Fe II emission line strengths for physical conditions typical of Active Galactic Nuclei with Broad-Line Regions. The Fe II line strengths were computed with a precise treatment of radiative transfer using extensive and accurate atomic data from the Iron Project. Excitation mechanisms for the Fe II emission included continuum fluorescence, collisional excitation, self-fluorescence amoung the Fe II transitions, and fluorescent excitation by Ly α and Ly β. A large Fe II atomic model consisting of 827 fine structure levels (including states to E ≈ 15 eV) was used to predict fluxes for approximately 23,000 Fe II transitions, covering most of the UV, optical, and IR wavelengths of astrophysical interest. Spectral synthesis for wavelengths from λ 1600Å to 1.2 µm is presented. Applications of present theoretical templates to the analysis of observations are described. In particular, we discuss recent observations of near-IR Fe II lines in the 8500Å-1 µm region which are predicted by the Ly α fluorescence mechanism. We also compare our UV spectral synthesis with an empirical iron template for the prototypical, narrowline Seyfert galaxy I Zw 1. The theoretical Fe II template presented in this work should also applicable to a variety of objects with Fe II spectra formed under similar excitation conditions, such as supernovae and symbiotic stars.

EVIDENCE FOR NON-EVOLVING Fe II/Mg II RATIOS IN RAPIDLY ACCRETINGz∼ 6 QSOs

“…We modified the template following Kurk et al (2007) by adding a constant flux density between 2770 and 2820 Å equal to 20% of the mean flux density of the template between 2930 and 2970 Å. The justification for this operation comes from the theoretical Fe ii emission line strength of Sigut & Pradhan (2003). Since the Fe ii and the Mg ii are not distributed in the same way within the BLR, we decided not to fix the Doppler broadening of the Fe ii template to the one measured for the Mg ii emission line.…”

Contribution of the disk emission to the broad emission lines in AGNs: Two-component model

“…We took the relative strength of these lines from Korista (1992) (Korista 1992;Popović et al 2001Popović et al , 2002Popović et al , 2003. In comparison with the list of Fe II lines given by Sigut & Pradhan (2003), the Fe II template used here gives a better fit to the Fe II lines of the present sample of AGNs. (4) We included the He I λλ4921.93, 5015.68 Å lines (Véron et al 2002), assuming that they originate in the same region, i.e.…”

“…On the other hand, we include the He Iλ6678.15 Å and SiIIλ6371 lines (Véron et al 2002), and each line has been represented by one Gaussian. Also, one can expect a contribution of Fe II lines in the Hα wavelength region, but on the bases of the calculation given by Sigut & Pradhan (2003) In the fitting procedure we included these lines assuming that they originate from the same region, i.e. that they have the same width and redshift.…”

THE CONNECTIONS BETWEEN THE UV AND OPTICAL Fe ii EMISSION LINES IN TYPE 1 AGNs

“…There are some indications that microturbulence may have a significant influence on the Fe II strength (Netzer & Wills 1983;Verner et al 2003;Sigut and Pradhan 2003;Baldwin et al 2004;Bruhweiler & Verner 2008;Sameshima et al 2011). Baldwin et al (2004) showed that a photoionization model may reproduce well the observed shape and the EW of the UV Fe II 2200-2800 bump, but only if a microturbulent gas motion is taken into account.…”