Spectral nuclear properties of NLS1 galaxies

Abstract

Context. It is not yet well known whether narrow line Seyfert 1 (NLS1) galaxies follow the MBH-σast; 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 MBH-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 (MBH/M⊙) = 5.4-7.5 for our sample. We found that, in general, most of the galaxies lie below the MBH-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.