Rapidly Rotating Circumnuclear Gas Disks in Virgo Disk Galaxies

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Abstract
From a set of 80 Virgo cluster galaxies for which we have obtained high-resolution, long-slit spectra near H alpha, we have identified 14 with interesting circumnuclear (CN) properties. These 14 galaxies exhibit rapidly rotating, discrete gas disks extending of order 500 pc from the nucleus. Peak CN disk velocities match well the outer disk maximum velocity. Masses interior to the outer edge of the CN disk range from some 109 to a few 1010 M., about 3% or 4% of the mass interior to R25. Clear counterrotation is observed in only one galaxy, the previously discussed NGC 4550. While discrete circumnuclear disks are well studied in early-type galaxies, few are known in types Sb or later. Our sample includes types E7/E0 to Sc; half are Sb or later. The frequency of discrete CN components is higher for early-type galaxies. For eight of these galaxies, morphological and kinematic evidence clearly identifies the discrete components as disks. For a few, we have evidence that a stellar disk is corotating with the gas. Many of these galaxies are barred, some weakly; the CN disks exist within the more extended bars. We suggest that gravitational interactions and/or nonaxisymmetric potentials have caused gas to be funneled to the nucleus where it forms the kinematically distinct CN disk. It is likely that we have detected only a fraction of the discrete CN features. Hence, the true frequency may approach 50% for bright galaxies in the Virgo cluster. (C) 1997 American Astronomical Society.

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