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Astron. Astrophys. 324, 485-489 (1997)

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3. Results

The observed gas kinematics extends out to [FORMULA] ([FORMULA]  kpc) in the receding NW side and about up to [FORMULA] ([FORMULA]  kpc) in the SE approaching side respectively.

For [FORMULA] ([FORMULA] kpc) we are able to disentangle (Fig. 1 and Fig. 2) three kinematically distinct gaseous components, named as fast-rotating (i), slow-rotating (ii) and third (iii).

The fast-rotating gas component (i) shows a velocity curve with a very steep gradient, reaching an observed maximum rotation of 240  [FORMULA] at [FORMULA] ([FORMULA]  kpc) from the center and remaining almost constant for [FORMULA]. Its velocity dispersion has a central peak of about 90  [FORMULA] and it shows a sharp decrease to values lower than 25  [FORMULA] outwards. The radial velocity of the slow-rotating gas component (ii) increases linearly with the distance from the galaxy center reaching 240  [FORMULA] at [FORMULA] ([FORMULA]  kpc). The velocity dispersion remains between 40  [FORMULA] and 50  [FORMULA]. This range is larger in the [N II] line, which however is characterized by a lower signal-to-noise ratio. In the radial range between [FORMULA] and [FORMULA] along the SE side of the major axis the H [FORMULA] and [N II] emissions have triple-peaked lines. Indeed in this region the component (iii) is observed. It has a radial velocity increasing linearly from [FORMULA]   [FORMULA] to [FORMULA]   [FORMULA] and equal to the systemic velocity at [FORMULA] ([FORMULA] kpc). It has a quite low velocity dispersion of [FORMULA] [FORMULA].

For [FORMULA] a single-valued velocity curve is measured, showing the tendency to flatten out. The velocity dispersions in this radial range are lower than 30  [FORMULA].

Adopting the center of symmetry of velocities for [FORMULA] as the systemic heliocentric velocity, we derived [FORMULA]   [FORMULA] in agreement with [FORMULA]   [FORMULA] found by Rubin et al. (1985).

Studying the ionized gas velocity curves of a sample of Sa spirals, also Rubin et al. (1985) noticed along the SE side of the UGC 10205 major axis "a curious three-velocity system" within 10 kpc of the center. It can not be reconciled with our component (i), (ii), and (iii). The reciprocal dispersion (25 [FORMULA]) and the spatial scale ([FORMULA] mm-1) of their image-tube spectrum were respectively 3 and 2 times lower than those of our CCD spectrum. So they did not disentangle the component (i) from the (ii), detecting them as a unique one. They observed a second velocity system, corresponding to velocity curve of component (iii). Finally, for two distinct radii at [FORMULA] they measured intermediate velocities between those of the first and the second system and considered them as related to a third velocity component.

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© European Southern Observatory (ESO) 1997

Online publication: May 26, 1998