Dusty nuclear disks and filaments in early-type galaxies

We examine the dust properties of a nearby distance-limited sample of early -type galaxies using WFPC2 of the Hubble Space Telescope. Dust is detected in 29 out of 67 galaxies (43%), including 12 with small nuclear dusty disks . In a separate sample of 40 galaxies biased for the detection of dust by v irtue of their detection in IRAS 100 mum band, dust is found in similar to 78% of the galaxies, 15 of which contain dusty disks. In those galaxies wit h detectable dust, the apparent mass of the dust correlates with radio and far-infrared luminosity, becoming more significant for systems with filamen tary dust. A majority of IRAS and radio detections are also associated with dusty galaxies rather than dustless galaxies. This indicates that thermal emission from clumpy, filamentary dust is the main source of the far-IR rad iation in early-type galaxies. Dust in small disklike morphology tends to b e well aligned with the major axis of the host galaxies, while filamentary dust appears to be more randomly distributed with no preference for alignme nt with any major galactic structure. This suggests that, if the dusty disk s and filaments have a common origin, the dust originates externally and re quires time to dynamically relax and settle in the galaxy potential in the form of compact disks. More galaxies with visible dust than without dust di splay emission lines, indicative of ionized gas, although such nuclear acti vity does not show a preference for dusty disk over filamentary dust. There appears to be a weak relationship between the mass of the dusty disks and central velocity dispersion of the galaxy, suggesting a connection with a s imilar recently recognized relationship between the latter and the black ho le mass.