Spectral nuclear properties of NLS1 galaxies^⋆

¹ Instituto de Astronomía Teórica y Experimental (IATE), Universidad Nacional de Córdoba, CONICET, Observatorio Astronómico de Córdoba, Laprida 854, Córdoba, Argentina
e-mail: eduschmidt@oac.unc.edu.ar
² Observatorio Astronómico, Universidad Nacional de Córdoba, Laprida 854, 5000 Córdoba, Argentina

Received: 19 July 2016
Accepted: 4 August 2016

Abstract

Context. It is not yet well known whether narrow line Seyfert 1 (NLS1) galaxies follow the M_BH − σ_⋆ relation found for normal galaxies. Emission lines, such as [SII] or [OIII]λ5007, have been used as a surrogate of the stellar velocity dispersion and various results have been obtained. On the other hand, some active galactic nuclei (AGNs) have shown Balmer emission with an additional intermediate component (IC) besides the well-known narrow and broad lines. The properties of this IC have not yet been fully studied.

Aims. In order to re-examine the location of NLS1 in the M_BH − σ_⋆ relation, we test some emission lines, such as the narrow component (NC) of Hα and the forbidden [NII]λλ6548,6584 and [SII]λλ6716,6731 lines, as replacements for σ_⋆. On the other hand, we study the properties of the IC of Hα found in 14 galaxies of the sample to find a link between this component, the central engine, and the remaining lines. We also compare the emission among the broad component (BC) of Hα and those emitted at the narrow line region (NLR) to detect differences in the ionizing source in each emitting region.

Methods. We have obtained and studied medium-resolution spectra (170 km s^-1 FWHM at Hα) of 36 NLS1 galaxies in the optical range ~5800−6800 Å. We performed a Gaussian decomposition of the Hα +[NII]λλ6548,6584 profile to study the distinct components of Hα and [NII] lines. We also measured the [SII] lines.

Results. We obtained black hole (BH) masses in the range log  (M_BH/M_⊙) = 5.4−7.5 for our sample. We found that, in general, most of the galaxies lie below the M_BH − σ_⋆ relation when the NC of Hα and [NII] lines are used as a surrogate of σ_⋆. The objects are closer to the relation when [SII] lines are used. Nevertheless, the galaxies are still below this relation and we do not see a clear correlation between the BH masses and FWHM_[SII]. Besides this, we found that 13 galaxies show an IC, most of which are in the velocity range ~700−1500 km s^-1. This is same range as in AGN types and is well correlated with the FWHM of BC and, therefore, with the BH mass. On the other hand, we found that there is a correlation between the luminosity of the BC of Hα and NC, IC, [NII]λ6584, and [SII] lines.