Properties of the continuum and broad line emission gas in active galactic nuclei with moderate to strong Feii emission

Abstract

We study a sample of 67 active galactic nuclei (AGN) with moderate to strong Feii emission to investigate the relation between the observed AGN continuum and the lines produced by the broad line region (BLR), in particular, Feii. We found that the continuum in the optical/near-infrared can be described in terms of two components: a power-law, characterized by the spectral index α, and hot dust emission, represented by a Plank function of temperature T. These two parameters seem not to be related to the strength of Feii emission. In addition to Feii, we study other low-ionization BLR lines such as Oi and Caii (hereafter CaT). We found that the full-width at half maximum of these three lines are similar, suggesting that they are produced in the same spatial region of the BLR.We measure the Feii strength in the optical and the near-infrared region and found that they are strongly correlated. This result evidences the presence of a common excitation mechanism for the Feii emission in the wavelength interval 4000-24000 Å.