A 0.8-2.4 μm spectral atlas of active galactic nuclei

Abstract

Aims. We present a near-infrared spectral atlas of 47 active galactic nuclei (AGN) of all degrees of activity in the wavelength interval of 0.8–2.4 μm, including the fluxes of the observed emission lines. We analyze the spectroscopic properties of the continuum and emission line spectra of the sources. Methods. In order to exclude aperture and seeing effects we used near-infrared spectroscopy in the short cross-dispersed mode (SXD, 0.8–2.4 μm), taking the JHK-bands spectra simultaneously. Results. We present the most extensive NIR spectral atlas of AGN to date. This atlas offers a suitable database for studying the continuum and line emission properties of these objects in a region full of interesting features. The shape of the continuum of QSOs and Sy 1’s are similar, being essentially flat in the H and K bands, while a strong variation is found in the J band. In Seyfert 2 galaxies, the continuum in the Fλ × λ space smoothly decreases in flux from 1.2 μm redwards in almost all sources. In J, it smoothly rises bluewards in some sources, while in others a small decrease in flux is observed. The spectra are dominated by strong emission features of Hi, Hei, Heii, [Siii] and by conspicuous forbidden lines of low and high ionization species. Molecular lines of H2 are common features of most objects. The absence of Oi and Fe ii lines in Seyfert 2 galaxies and the smaller FWHM of these lines relative to that of Hi in the Seyfert 1 give observational support to the fact that they are formed in the outermost portion of the broad-line region. The[P ii] and coronal lines are detected for all degrees of activity. The [Fe II] 12570 Å/16436 Å line ratio becomes a reliable reddening indicator for the narrow-line region of Seyfert galaxies.