Spectral nuclear properties of NLS1 galaxies

Abstract

It is not yet well known whether narrow line Seyfert 1 (NLS1) galaxies follow the $M_{BH} - \sigma_{\star}$ relation found for normal galaxies. Emission lines, such as [SII] or [OIII]$\lambda$5007, 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. In order to re-examine the location of NLS1 in the $M_{BH} - \sigma_{\star}$ relation, we test some emission lines, such as the narrow component (NC) of H$\alpha$ and the forbidden [NII]$\lambda \lambda$6548,6584 and [SII]$\lambda \lambda$6716,6731 lines, as replacements for $\sigma_{\star}$. On the other hand, we study the properties of the IC of H$\alpha$ 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 H$\alpha$ and those emitted at the narrow line region (NLR). We have obtained and studied medium-resolution spectra (170 km s$^{-1}$ FWHM at H$\alpha$) of 36 NLS1 galaxies in the optical range $\sim$5800 - 6800\AA. We found that, in general, most of the galaxies lie below the $M_{BH} - \sigma_{\star}$ relation when the NC of H$\alpha$, [SII], and [NII] lines are used as a surrogate of $\sigma_{\star}$. Besides this, we found that 13 galaxies show an IC, most of which are in the velocity range $\sim$ 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 H$\alpha$ and NC, IC, [NII]$\lambda$6584, and [SII] lines.