Spectral properties of the narrow-line region in Seyfert galaxies selected from the SDSS-DR7

Abstract

Although the properties of the narrow-line region (NLR) of active galactic\nnuclei(AGN) have been deeply studied by many authors in the past three decades,\nmany questions are still open. The main goal of this work is to explore the NLR\nof Seyfert galaxies by collecting a large statistical spectroscopic sample of\nSeyfert 2 and Intermediate-type Seyfert galaxies having a high signal-to-noise\nratio in order to take advantage of a high number of emission-lines to be\naccurately measured. 2153 Seyfert 2 and 521 Intermediate-type Seyfert spectra\nwere selected from Sloan Digital Sky Survey - Data Release 7 (SDSS-DR7) with a\ndiagnostic diagram based on the oxygen emission-line ratios. All the\nemission-lines, broad components included, were measured by means of a\nself-developed code, after the subtraction of the stellar component. Physical\nparameters, such as internal reddening, ionization parameter, temperature,\ndensity, gas and stellar velocity dispersion were determined for each object.\nFurthermore, we estimated mass and radius of the NLR, kinetic energy of the\nionized gas, and black-hole accretion rate. From the emission-line analysis and\nthe estimated physical properties, it appears that the NLR is similar in\nSeyfert 2 and Intermediate-Seyfert galaxies. The only differences, lower\nextinction, gas kinematics in general not dominated by the host galaxy\ngravitational potential and higher percentage of [O III]5007 blue asymmetries\nin Intermediate-Seyfert can be ascribed to an effect of inclination of our line\nof sight with respect to the torus axis.\n