The unusual emission line spectrum of I Zw 1

Abstract

Abstract. Most Seyfert 1 galaxies show strong Fe II lines in their spectrum having the velocity and width of the broad emission lines. To remove the Fe II contribution in these objects, an accurate template is necessary. We used very high signal-to-noise, medium resolution archive optical spectra of I Zw 1 to build such a template. I Zw 1 is a bright narrow-line Seyfert 1 galaxy. As such it is well suited for a detailed analysis of its emission line spectrum. Furthermore it is known to have a very peculiar spectrum with, in addition to the usual broad and narrow line regions, two emission regions emitting broad and blue shifted [O III] lines making it a peculiarly interesting object. While analysing the spectra, we found that the narrow-line region is, unlike the NLR of most Seyfert 1 galaxies, a very low excitation region dominated by both permitted and forbidden Fe II lines. It is very similar to the emission spectrum of a blob in η Carinae which is a low temperature (T e ∼ 6500 K), relatively high density (N e = 10 6 cm −3 ) cloud. The Fe II lines in this cloud are mainly due to pumping via the stellar continuum radiation field (Verner et al. 2002). We did not succeed in modelling the spectrum of the broad-line region, and we suggest that a non radiative heating mechanism increases the temperature in the excited H I region, thus providing the necessary additional excitation of the Fe II lines. For the low-excitation narrow-line region, we are able to apply boundaries to the physical conditions accounting for the forbidden and permitted Fe II lines (10 6 < N e < 10 7 cm −3 ; 10 −6 < U < 10 −5 ).

Reaching the peak of the quasar spectral energy distribution – II. Exploring the accretion disc, dusty torus and host galaxy

“…These templates come from Véron-Cetty, Joly & Véron (2004) for the (rest frame) optical range and Vestergaard & Wilkes (2001) in the UV. We use the theoretical Fe II emission template of Verner et al (2009) for the 3100-3500 Å gap between these.…”

Reaching the peak of the quasar spectral energy distribution – I. Observations and models

“…Modelling of these features is often accomplished by making use of an empirical template derived from spectral analysis of the Type I AGN I Zwicky 1. We use that of Véron-Cetty, Joly & Véron (2004). There are two free parameters; the width of the convolving Gaussian, and the normalization.…”

Multi-wavelength study of the gravitational lens system RXS J1131-1231

“…Wills et al 1985;Laor et al 1997;Dietrich et al 2003;Tsuzuki et al 2006), we used template spectra of Fe ii emission instead of theoretical emission models. Namely, we fitted the Fe ii emission in our spectra by using an UV Fe ii template (Vestergaard & Wilkes 2001) and an optical Fe ii template (Véron-Cetty et al 2004). We also tested the optical template of Boroson & Green (1992) but this did not modify significantly our results.…”