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

Abstract

We report spectroscopic observations in the wavelength region 0.8-2.4 microns aimed at detecting near-infrared coronal lines in a sample of 5 narrow-line and 1 broad-line Seyfert 1 galaxies. Our measurements show that [SiVI] 1.963mu, [SIX] 1.252mu and [SVIII] 0.991mu 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 that 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. Assymetries towards 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 [FeXIII] 1.074,1.079mu in three of our objects and the first detection of [PII] 1.188mu and [NiII] 1.191mu in a Seyfert 1 galaxy, ARK 564. Using the ratio [PII]/[FeII] we deduced that most Fe present in the outer NLR of ARK 564 is locked up in grains, and the influence of shocks is negligible.