Near-Infrared Coronal Lines in Seyfert Galaxies

Astronomy and Astrophysics – Astronomy

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Scientific paper

Seyfert galaxies show in their spectra coronal lines (CLs). Researchers have proposed a physical region responsible of the emission of CLs named Coronal Line Region (CLR). Some authors have suggested that CLR is well extended to the NLR; others propose its location between the BLR and NLR while others suggest that CLR is situated in the inner face of the obscuring torus. The goal of this work is contribute to the discussion about the location of the CLR. Our hypothesis is that they are emitted in the inner walls of the torus. Spectral analysis of a sample of Seyfert 1 (Sy1) and Seyfert 2 (Sy2) galaxies can give insights about the location of the CLR. We took NIR spectra of the five Sy1 and five Sy2 galaxies. Those spectra were taken in at the NASA 3-m IRTF using the SpeX spectrome-ter. CLs are observed in all the objects of the sample. [Si VI] λ1.963 μm, is present in all of them; [S VIII] λ0.991 μm, is also present (except in H1143-182 and Mrk 1066); it is frequent to observe too [S IX] λ1.252 μm, and [Si X] λ1.430 μm. [Si VI] λ1.963 μm is observed in both types of galaxies. Values for FWHM, assuming Gaussian profiles, for the [Si VI] λ1.963 μm range from 250 to 530 km/s whilst those for S [IX] λ1.252 μm and [Si X] λ1.43 μm tend to be higher: 300 to 1150 and 260 to 1320 km/s, respectively. This seems to suggest that, for CL, those species with higher ionization potential present higher bulk velocity of the emitting clouds and therefore are situated nearer to the central mass concentration. The apparent fact that CL from species of higher ionization potential (χ) are preferentially observed in Sy1 rather than Sy2 seems to be coherent with the existence of a obscuring torus required by unified models for an active galactic nucleus (AGN): the Sy1 type shows internal regions of the AGN, including the BLR and internal parts of the torus. It is feasible then, that some of the high-χ coronal emission (i.e. [Si X]) are produced in the inner wall of the torus.

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