Gas dynamics in barred spiral galaxies – II. NGC 7496 and 289

• Published in: Monthly notices of the Royal Astronomical Society 1984-10, Vol.210 (3), p.547-563
• Main Authors: Pence, W. D., Blackman, C. P.
• Format: Article
• Language: English
• Subjects: Astronomy; Earth, ocean, space; Exact sciences and technology; Interstellar medium (ism) and nebulae in external galaxies; Stellar systems. Galactic and extragalactic objects and systems. The universe
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/210.3.547

The gas velocity fields in the barred spiral galaxies NGC 7496 and 289 have been measured by means of long-slit spectra obtained with the Anglo-Australian telescope. Pronounced deviations from circular motion of the type predicted by recent theoretical models are seen in NGC 7496: the isovelocity contours are distorted into a characteristic S-shaped pattern and there is a large velocity gradient across the bar. The velocity field is virtually identical to that of a previously observed barred spiral, NGC 5383 for which a number of models have been published. The nuclear [O III] emission lines are very asymmetric with a wing extending to about 1000 km s−1 to the blue of the systemic velocity; this wing is only faintly seen in the Balmer lines. NGC 289 has a much smaller bar and consequently the non-circular motions are less pronounced. The most obvious effect is that the kinematic major and minor axes are not perpendicular which is a signature of oval distortions. Both galaxies have a mass (within the outermost velocity measurement) of $8 \times 10^{10} M_\odot$. One significant difference between the galaxies is that the neutral hydrogen contributes about 20 per cent of the mass of NGC 289 but only about 2 per cent of the mass of NGC 7496. As a further test of the models of gas streaming in barred spirals we have collected the results from 11 previously studied galaxies and show that the appearance of the velocity field depends on the orientation of the bar to the line-of-sight, in good agreement with the model predictions.