AGN in the ULIRG HE 0435−5304

Abstract

Context. HE 0435−5304 from Hamburg European Southern Observatory survey is a quasar that appears in the literature with two conflicting redshift values: ∼1.2 and ∼0.4. It was used in the studies of the intergalactic medium through fitting of the narrow absorption lines in its ultraviolet (UV) spectrum. This source is also known historically as a luminous infrared galaxy. Aims. We present optical spectra of HE 0435−5304, aiming to precisely measure its redshift and to study its physical properties. In particular, properties of its active nucleus, which is studied in the context of the source being identified here as an ultra-luminous infrared galaxy (ULIRG), allow us to place this quasar in the context of the general population. Methods. We analyzed optical spectra of the quasar HE 0435−5304. Fitting the spectra, we focused on modeling Hβ and [O III] lines. Based on these, we derived the virial black hole mass, bolometric luminosity, and Eddington ratio of the active galactic nucleus (AGN). Additionally, we performed broad band photometry fitting which allows us to quantify host galaxy parameters. Based on available mixed IR/optical/UV data spanning over a decade, we discuss the possible evolution of physical properties of the source and the influence of the observing conditions on our results. Results. The improved redshift value of HE 0435−5304 is estimated to 0.42788 ± 0.00027 based on the [O II] line – the narrowest line in the spectra – which is mostly consistent with the narrowest components of the other emission lines. The source was found to be a relatively massive and luminous AGN whose host galaxy is actively forming stars. Although its stellar population seems to be heavily obscured, we did not find evidence for significant obscuration of the nucleus. We conclude that the AGN HE 0435−5304 is a rather prominent iron emitter from the extreme type-A population very close to the narrow-line Seyfert 1 group. The fact that the width of the Hβ line appears to be systematically growing in its broadest component with time may suggest that this AGN is changing its broad line region. However, because of the influence of atmospheric effects contaminating spectral profiles, this finding is uncertain.