Astronomy and Astrophysics – Astronomy
Scientific paper
Aug 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002aj....124..706a&link_type=abstract
The Astronomical Journal, Volume 124, Issue 2, pp. 706-721.
Astronomy and Astrophysics
Astronomy
10
Galaxies: Evolution, Galaxies: Individual: Ngc Number: Ngc 4550, Galaxies: Individual: Ngc Number: Ngc 4138, Galaxies: Nuclei, Galaxies: Structure
Scientific paper
Two lenticular galaxies with counterrotating stellar components in their disks have been studied with the Multi-Pupil Fiber Spectrograph of the 6 m telescope (at the Special Astrophysical Observatory). In NGC 4138 the nucleus is certainly chemically distinct, with the central concentration of magnesium enhancement marginally exceeding that of iron. The ionized gas within R=4" of the nucleus rotates circularly in an inclined ring, perhaps a kind of a circumnuclear polar ring surrounding a compact stellar minibar. NGC 4550 exhibits complex extended structures in its center that can be identified by enhanced levels of magnesium and iron indices; the stellar population of the unresolved nucleus is younger than that of the circumnuclear region. We conclude that although NGC 4550 does not possess a chemically distinct nucleus in the ordinary sense of the term, there are nevertheless clear signatures of a secondary star formation burst confined perhaps to the counterrotating stellar gaseous disk. We argue that the inclination of the counterrotating disk differs from that of the main stellar disk, implying that the two disks are not coplanar. Both galaxies seem to have possessed bars, either actually present or already dissolved. Partly based on observations collected with the 6 m telescope (BTA) at the Special Astrophysical Observatory of the Russian Academy of Sciences.
Afanasiev Victor L.
Sil'chenko Olga K.
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