A Strong Correlation between Circumnuclear Dust and Black Hole Accretion in Early‐Type Galaxies

We present a detailed investigation of the incidence of circumnuclear duststructure in a large, well-matched sample of early-type galaxies with andwithout Active Galactic Nuclei (AGN). All 34 early-type AGN hosts in our samplehave circumnuclear dust, while dust is only observed in 26% (nine) of apair-matched sample of 34 early-type, inactive galaxies. This resultdemonstrates a strong correlation between the presence of circumnuclear dustand accretion onto the central, supermassive black hole in elliptical andlenticular galaxies. This correlation is not present at later Hubble types,where a sample of 31 active and 31 inactive galaxies all contain circumnucleardust. These archival, HST observations reveal a wide range of mostly chaoticdust morphologies. Current estimates suggest the dust settling or destructiontime is on order of 10^8 years and therefore the presence of dust in ~ 50% ofearly-type galaxies requires frequent replenishment and similarly frequentfueling of their central, supermassive black holes. The observed dust could beinternally-produced (via stellar winds) or externally-accreted, although thereare observational challenges for both of these scenarios. Our analysis alsoreveals that approximately a third of the early-type galaxies withoutcircumnuclear dust have nuclear stellar disks. These nuclear stellar disks mayprovide a preferred kinematic axis to externally-accreted material and thismaterial may in turn form new stars in these disks. The observed incidence ofnuclear stellar disks and circumnuclear dust suggests that episodicreplenishment of nuclear stellar disks occurs and is approximately concurrentwith the fueling of the central AGN.Comment: ApJ, in press. 35 pages, 8 figures, 2 table