H ii Region Population in a Sample of Nearby Galaxies with Nuclear Activity. I. Data and General Results

Abstract

This paper presents the distribution of ionized gas in the disk and circumnuclear region of a sample of 55 galaxies with active nuclei, Seyfert galaxies of type 1 and 2, and low-ionization nuclear emission line regions (LINERs). We use CCD narrow-band H alpha + [N II] images to map the distribution of H II regions and the morphology of the circumnuclear extended emission associated with the active nucleus. We also present [O III] images for a few of the galaxies. An analysis of the presence of extended emission and of H II regions is carried out twofold, as a function of the level of nuclear activity and of the Hubble type. In this sample, the extended emission is more common in Seyfert type 1 than in type 2; however, disk star formation is more common in Seyfert type 2. One-third of the galaxies have circumnuclear H II regions, but only 8% of these are Seyfert 1. The number surface density of H II regions and the location of the brightest H II region indicate that in Seyfert 2 the star formation is more important in the inner disk, as defined by the radius that contains half the total blue luminosity. In Seyfert 1 the distribution of H II regions is more uniform with distance, and the H II regions are farther away from the nucleus than in Seyfert 2. We discuss the possible connection between the dynamical properties of the galaxy, particularly in the inner parts, and the differences found in Seyfert types 1 and 2.