Size and properties of the narrow-line region in Seyfert-1 galaxies from spatially-resolved optical spectroscopy

Abstract

Context. Spatially resolved emission-line spectroscopy is a powerful tool for determining the physical conditions in the narrow-line region (NLR) of active galactic nuclei (AGNs). We recently used optical long-slit spectroscopy to study the NLRs of a sample of six Seyfert-2 galaxies. We have shown that such an approach, in comparison to the commonly used [O iii] narrow-band imaging alone, allows us to probe the size of the NLR in terms of AGN photoionisation. Moreover, several physical parameters of the NLR can be directly accessed. Aims. We here apply the same methods to study the NLR of six Seyfert-1 galaxies and compare our results to those of Seyfert-2 galaxies. Methods. We employ diagnostically valuable emission-line ratios to determine the physical properties of the NLR, including the core values and radial dependencies of density, ionisation parameter, and reddening. Tracking the radial change of emission-line ratios in diagnostic diagrams allows us to measure the transition between AGN-like and H ii-like line excitation, and thus to measure the size of the NLR.Results. In the diagnostic diagrams, we find a transition between line ratios falling in the AGN regime and those typical of H ii regions in two Seyfert-1 galaxies, thereby determining the size of the NLR. The central electron temperature and ionisation parameter are, in general, higher in type-1 Seyferts than in type 2s. In almost all cases, both electron density and ionisation parameter decrease with radius and the decrease is faster in Seyfert-1 galaxies than in Sy 2s. In several objects, the gaseous velocity distribution is characteristic of rotational motion in an (inclined) emission-line disk in the centre. We give estimates of the black-hole masses and discuss our findings in detail for each object.

X-ray narrow line region variability as a geometry probe

“…From optical studies it is clear that the high-ionization as well as the high critical density lines tend to be stronger in Seyfert 1's, see e.g. Bennert et al (2006). This is consistent with the compact size of the NLR we find in NGC 5548.…”

“…They conclude that constant density models are excluded and that a steep density profile (n ∼ r −2 ) is preferred. Another study of six Seyfert 1 galaxies in the optical show different results however for the density slopes (Bennert et al 2006). Some Seyfert 1 galaxies show a slope ∼r −1 , others a slope ∼r −2 .…”

An X-ray variable absorber within the broad line region in Fairall 51

“…This translates to Eddington ratios λ Edd ≈ 0.03, and λ Edd ≈ 0.02, respectively. We calculated the Eddington luminosity as L Edd = 1.26 × 10 38 (M/M ) erg s −1 , where we used M ≈ 10 8 M for the black hole mass (Bennert et al 2006).…”

“…The black-hole mass of Fairall 51 was estimated as M ≈ 10 8 M by Bennert et al (2006) based on the relation between the luminosity at 5100 Å and the black hole mass (Peterson et al 2004). …”

The dusty heart of nearby active galaxies

“…Type (b) luminosity distance based on CMB reference frame redshifts from NED and H 0 = 73, Ω m = 0.27, and Ω vac = 0.73; (c) L X = absorption-corrected 2−10 keV luminosity from Dadina (2007), except for NGC 3227 (Tueller et al 2008), logarithmic intrinsic Hydrogen column densities N H in units of cm −2 from Tueller et al (2008), except ESO 323-G77 (average of Beckmann et al 2006;Malizia et al 2007); (d) L V ≡ νL ν (5500 Å); from Bentz et al (2009), except NGC 7213 (Winkler 1992), ESO 323-G77 (Schmid et al 2003), and MCG-6-30-15 (Bennert et al 2006). Additional extinction correction applied to IC 4329A and ESO 323-G77 , and NGC 3783 (A V = 1.0 from Hα/Hβ; de Grijp et al 1992); (e) (2006): S: Seyfert, L: LINER, S1i: optical type 2 with broad Hydrogen lines in the infrared; S1h: type 2 with detected polarized optical broad lines; (b) luminosity distance based on CMB reference frame redshifts from NED and H 0 = 73, Ω m = 0.27, and Ω vac = 0.73; (c) L X = absorption-corrected 2−10 keV luminosity from Dadina (2007), except IC 5063 (Tueller et al 2008), MCG-3-34-64 andNGC 4507 (Hönig et al 2008a), NGC 5995 (Horst et al 2008), and NGC 7674 (Bianchi et al 2005); logarithmic intrinsic Hydrogen column densities in units of 10 22 cm −2 from Tueller et al (2008), except ESO 428-G14 (Della Ceca et al 2008, NGC 5643 (Maiolino et al 1998), and NGC 7674 (Bianchi et al 2005, changing- way is a conversion of the size-luminosity relation to 12 μm.…”