H-II REGION POPULATION IN A SAMPLE OF NEARBY GALAXIES WITH NUCLEAR ACTIVITY .1. DATA AND GENERAL RESULTS

This paper presents the distribution of ionized gas in the disk and ci rcumnuclear region of a sample of 55 galaxies with active nuclei, Seyf ert 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 m ap the distribution of H II regions and the morphology of the circumnu clear extended emission associated with the active nucleus. We also pr esent [O III] images for a few of the galaxies. An analysis of the pre sence 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 Seyf ert 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 I I 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, a s defined by the radius that contains half the total blue luminosity. In Seyfert 1 the distribution of H II regions is more uniform with dis tance, and the H II regions are farther away from the nucleus than in Seyfert 2. We discuss the possible connection between the dynamical pr operties of the galaxy, particularly in the inner parts, and the diffe rences found in Seyfert types 1 and 2.