Astronomy and Astrophysics – Astronomy
Scientific paper
Nov 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997arep...41..734z&link_type=abstract
Astronomy Reports, Volume 41, Issue 6, November 1997, pp.734-745
Astronomy and Astrophysics
Astronomy
6
Scientific paper
The gas velocities and brightness distribution in the inner region of NGC 7217 are analyzed. This galaxy has a regular axially symmetric shape with flocullent spiral arms that have a system of three distinct rings (outer, inner, and nuclear) - a structure that is rarely observed in the absence of a bar. Observations on the 6-m telescope of the Special Astrophysical Observatory using a scanning Fabry-Perot interferometer reveal a sharp increase in the radial velocity gradient of the gas near R < 2", suggesting that there is a dynamically distinct nucleus with a mass ~ 6 x 10^7 M. The dynamical rotation axis of the gas, like the direction of extension of the HST isophotes within 2" of the center, is nearly perpendicular to the major axis defined by the isophotes further from the center. This indicates that this galaxy has a central gaseous disk with radius ~ 100 pc, whose plane is apparently inclined to the plane of the main galactic disk. Photometric HST measurements show the galactic disk within the nuclear ring (within 1 kpc of the center) to be in the shape of segments of rings or tightly-wound spirals, possibly associated with hydrodynamical instabilities. Analysis of the rotation curve determined from the [NII] 6583 and H_alpha emission lines shows a less steep radial velocity gradient to R ~ 1_2 kpc than obtained in earlier studies, which calls for a reestimation of the masses of the galaxy components. The question of the locations of resonances in the galaxy and their relation to the ring radii is discussed.
Sil'chenko Olga K.
Zasov Anatoli V.
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