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Paper: Ten Years of Nearby Galaxies Research with the Multi-Pupil Spectrograph of the 6m Telescope
Volume: 282, Galaxies: The Third Dimension
Page: 121
Authors: Sil'Chenko, O. K.
Abstract: We have started our study of central regions of early-type disk galaxies with the Multi-Pupil Field Spectrograph of the 6m telescope of SAO RAS in 1989. During the first year of observations we found chemically distinct stellar nuclei in 7 among 12 observed. The metallicity difference between the nuclei and surrounding bulges, estimated from the Mgb equivalent width radial variations, reached typically almost an order. Since then we have observed more than 50 S0, Sa, and Sb nearby galaxies with 3 different variants of the Multi-Pupil Spectrograph; the sample is biased in favor of galaxies with chemically distinct nuclei. By using these data, we construct 2D maps of such spectral characteristics as: continuum intensity, emission line intensities, line-of-sight velocities of stellar and gaseous components, stellar velocity dispersion, Lick indices Hβ, Mgb, Fe5270, and Fe5335. By confronting isophote characteristics and those of the stellar population, we have found compact circumnuclear stellar disks with typical radii of a few hundred parsecs in the most galaxies under consideration. The disks are always more metal-rich and often significantly younger than the bulges; in more than 50% of all cases they are inclined to the main symmetry planes. During our investigations we have also discovered such spectacular phenomenon as circumnuclear gas polar rings in regular spiral galaxies with chemically distinct nuclei: they are found in NGC 2841, 6340, and 7217. Some features of the global disk structure in the galaxies under consideration which may be related to the origin of chemically distinct nuclei will be discussed.
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