Fantastic Fits with fantasy of Active Galactic Nuclei Spectra -- Exploring the Fe II emission near the H$\alpha$ line

Abstract

In this study, a refined approach for multicomponent fitting of active galactic nuclei (AGN) spectra is presented utilizing the newly developed Python code $fantasy$ (fully automated python tool for AGN spectra analysis). AGN spectra are modeled by simultaneously considering the underlying broken power-law continuum, predefined emission line lists, and an Fe II model, which is here extended to cover the wavelength range 3700 - 11000 A. The Fe II model, founded solely on atomic data, effectively describes the extensive emission of the complex iron ion in the vicinity of the H$\gamma$ and H$\beta$ lines, as well as near the H$\alpha$ line, which was previously rarely studied. The proposed spectral fitting approach is tested on a sample of high-quality AGN spectra from the Sloan Digital Sky Survey (SDSS) Data Release 17. The results indicate that when Fe II emission is present near H$\beta$, it is also detected redward from H$\alpha$, potentially contaminating the broad H$\alpha$ line wings and thus affecting the measurements of its flux and width. The production of Fe II emission is found to be strongly correlated with Eddington luminosity and appears to be controlled by the similar mechanism as the hydrogen Balmer lines. The study highlights the benefits of fitting AGN type 1 spectra with the $fantasy$ code, pointing that it may be used as a robust tool for analyzing a large number of AGN spectra in the coming spectral surveys.