Near‐Infrared Coronal Lines in Narrow‐Line Seyfert 1 Galaxies

Abstract

We report spectroscopic observations in the wavelength region 0.8-2.4 lm aimed at detecting near-infrared coronal lines in a sample of five narrow-line and one broad-line Seyfert 1 galaxies. Our measurements show that [Si vi] 1.963 lm, [S ix] 1.252 lm, and [S viii] 0.991 lm are present in most of the objects and are useful tracers of nuclear activity. Line ratios between coronal and low-ionization forbidden lines are larger in narrow-line Seyfert 1 galaxies. A positive correlation between FHWM and ionization potential of the forbidden lines is observed. Some coronal lines have widths similar to those of lines emitted in the broad-line region (BLR), indicating that part of their flux originates in gas close to the outer portions of the BLR. Most coronal lines are blueshifted relative to the systemic velocity of the galaxy, and this shift increases with the increase in line width. Asymmetries toward the blue are observed in the profiles of high-ionization Fe lines, suggesting that the emitting gas is related to winds or outflows, most probably originating in material that is being evaporated from the torus. This scenario is supported by models that combine the effects of shock ionization and photoionization by a central continuum source in the gas clouds. The agreement between the coronal line emission predicted by the models and the observations is satisfactory; the models reproduced the whole range of coronal line intensities observed. We also report the detection of [Fe xiii] 1.074, 1.079 lm in three of our objects and the first detection of [P ii] 1.188 lm and [Ni ii] 1.191 lm in a Seyfert 1 galaxy, Ark 564. Using the ratio [P ii]/[Fe ii], we deduced that most Fe present in the outer narrow-line region of Ark 564 is locked up in grains and that the influence of shocks is negligible.

Powerful outflows in the central parsecs of the low-luminosity active galactic nucleus NGC 1386

“…This result contrasts to previous long-slit, seeing-limited observations of AGNs, where a central unresolved coronal gas emission was usually detected, leading to the picture where the these lines were formed between the NLR and the BLR (Erkens et al 1997;Rodríguez-Ardila et al 2002). , respectively.…”

Multi-wavelength properties of the high-energy bright Seyfert 1 galaxy IGR J18027-1455

“…It is interesting to note that the permitted O i λ11287 line is a feature completely associated with the BLR of Seyfert galaxies. In our case this line is marginally detected, as in NGC 863 (Rodríguez-Ardila et al 2002). The non-detection of the Brγ line seems to suggest that thermal UV heating is not important, as it also happens in the case of NGC 1097 (Reunanen et al 2002).…”

Anatomy of the AGN in NGC 5548

“…In some cases the high ionisation emission lines from AGN (of which the X-ray narrow lines would be part) are referred to as originating from the "coronal line region", distinct from the "standard" optical NLR (characterised by [O III]) by the higher ionisation species and larger line widths (see e.g., Erkens et al 1997;Rodríguez-Ardila et al 2002). On the other hand, the spatial extent and morphology of the optical and the X-ray NLRs have been found to be remarkably similar in some sources (Bianchi et al 2006).…”