Nuclear Gas and Dust Disks in Nearby 3CR Elliptical Galaxies

Abstract

Using WFPC2 V, R, I, and H?+[N II] images, we examine the morphologies, environments, colors, and line emission of dust and gas disks located in the cores of seven low-redshift elliptical galaxies hosting 3C radio sources: NGC 383 (3C 31)/NGC 382, NGC 547 (3C 40), NGC 3862 (3C 264), NGC 4261 (3C 270), NGC 5532 (3C 296), NGC 7720 (3C 465)/NGC 7720A, and UGC 12064 (3C 449). The color maps are generally consistent with absorption by dust in flattened configurations viewed at intermediate inclinations. In most cases the disks are nonuniform in continuum light and are surrounded by arcs, filaments, and diffuse absorbing clumps, suggesting that the dust in the cores of these galaxies is not dynamically settled. Extended, clumpy or smooth H? + [N II] line emission is detected in all four cases (NGC 383, NGC 3862, UGC 12064, and NGC 7720) for which narrowband images are available. Line emission is found at projected locations from the nuclei to the edges of the disks.?????The major axes of the disks and their hosts are preferentially aligned, with the degree of alignment uncorrelated with disk size. As projected on the sky, all the disks are more flattened than their host galaxies. Three of the hosts have boxy isophotes, and the remainder are normal in shape. The two boxiest galaxies, NGC 4261 and NGC 5532, show significant displacements between their nuclear and isophotal centers.?????The mass of the disk in NGC 4261 is estimated using radiative transfer calculations. Scattering into the line of sight is included in the approximation that the dust is isotropically illuminated by surrounding stars. The observed colors and surface brightness are shown to be matched by a thin layer of dust that lies in front of three-quarters (eastern edge) to one-quarter (western edge) of the starlight. When a Galactic opacity curve is used, the mass determined is an order of magnitude larger than that found assuming the dust lies in a foreground screen. The opacity falls more steeply toward the infrared than do those of Galactic and Magellanic Cloud grains, suggesting that the dust is not unprocessed material from a merger with a spiral or irregular galaxy.