Étude cinématique de la galaxie barrée NGC 5383

Abstract

We present some observational results derived from plates taken with the nebular spectrograph at the 1.93-m telescope of the Observatoire de Haute Provence. The dispersion is 35 Å mm⁻¹ and the resolution is 85″ per mm.

Radial velocities were measured at different points in the nucleus and in the bar.

The nucleus is composed of two elements, of 5″ and 12″ diameter, inside a ring of radius 2 kpc. Radial velocities around the ring show a well-defined sinusoid with a maximum displaced about 15° from that predicted from the geometry of the outer parts of the galaxy. We can explain this displacement by a contraction velocity of 43 km s⁻¹.

In the bar the kinematics is quite complex. The slit position (roughly aligned with the bar) was slightly different for each of the four plates taken. For those which bisect the nucleus the velocity field is symmetric, with a sharp discontinuity of 50 km s⁻¹ between the nucleus and the bar. The maximum velocity is not reached in our field of observation. Solid body rotation cannot be accepted.

Spectra along the edge of the nucleus provides evidence for transverse motions in the bar of 100 km s⁻¹ at 4 kpc from the center.

The rotation curve is drawn; in the hypothesis of a radial motion in the bar we have calculated the distribution of mass according to the method of Burbidge and Prendergast inside a 14 kpc radius; the mass is 10¹⁰ M _⊙.

The iso-intensity tracings clearly show the presence of the two nuclear components, the absence of [Nii] emission on the north-west side of the bar and the absence of Hα in the south-west side. The ratio Hα/[Nii] between 2 and 5 at several spots indicates that Hii regions are highly excited in the nucleus and at the extreme end of the bar. The region of the bar where the ratio is less than 1 suggests high excitation by collision of energetic particle perhaps coming from the nucleus.