The Central Gas Systems of Early-Type Galaxies Traced by Dust Features, Based on the Hubble Space Telescope WFPC2 Archival Images

Abstract

We investigated the central gas systems of E/S0 galaxies by making use of the WFPC2 images in the Hubble Space Telescope archive. We searched for gas systems that were traced by the dust with a new method of making color excess images in F555W-F814W (V-I). Of 25 sample galaxies, we detected gas systems in 14 galaxies. The dust was newly detected in two galaxies that were thought to contain no dust based on single-band, prerefurbishment data. The full extents of the gas systems are 0.1-3.5 kpc, and the masses of the gas, log M_gas [M_solar], are 4.2-7.2. The active galactic nucleus (AGN) activity is well correlated with the existence of the gas systems. None of galaxies without the gas systems show AGN activity. On the other hand, some galaxies with gas systems show AGN activity; optical AGN activities are shown in five of 11 galaxies in which AGNs are optically studied, and radio activities are shown in six of 14 galaxies. This shows that the AGN activity is driven with the gas system. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the data archive at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.