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Astron. Astrophys. 321, 754-764 (1997)

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The ringed, warped and isolated galaxy NGC 6015 *

L. Verdes-Montenegro 1, A. Bosma 2 and E. Athanassoula 2

1 Instituto de Astrofísica de Andalucía, CSIC, Apdo. 3004, E-18080 Granada, Spain
2 Observatoire de Marseille, 2 Place le Verrier, F-13248 Marseille Cedex 4, France

Received 14 August 1996 / Accepted 25 October 1996


We have studied the neutral hydrogen component of the ringed and unbarred Scd galaxy NGC 6015 with the Westerbork telescope at a resolution of [FORMULA] ([FORMULA]) and a velocity resolution of 33 km s-1. These data have been supplemented with CCD-BVRI surface photometry and optical spectroscopy.

The study of the stellar and HI gas component of NGC 6015 shows that its structure changes from small to large radii. In the inner [FORMULA] there is a blue two armed spiral structure, previously measured by Elmegreen and Elmegreen. In the following [FORMULA] the pattern changes to a flocculent one. At [FORMULA] two pseudoarms start, the outer parts winding in a blue pseudoring [FORMULA] in size. About 41% of the HI emission is concentrated in this ring. The extent of the HI gas is about twice that of the optical emission, and an analysis of the HI distribution and velocity field indicates that NGC 6015 is warped at radii larger than [FORMULA]. In the inner parts the velocity field can be modelled well by normal circular rotation in a disk of the same extent as the optical one.

Assuming, as is known to be the case for barred galaxies, that the outer pseudoring is at the outer Lindblad resonance, we derive a value for the pattern speed of 26.5 km s-1 kpc-1. The expected locations for the other resonances then follow from the combined optical/HI rotation curve, and in particular we find that the end of the inner spiral structure is located at the ultraharmonic (4:1) resonance, in agreement with the result found by Patsis et al. for Sb and Sc type galaxies.

Key words: galaxies: spiral; kinematics and dynamics; structure; NGC 6015 – radio lines: galaxies

* Based partially on data collected at the Observatoire de Haute Provence, France

Send offprint requests to: L. Verdes-Montenegro

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© European Southern Observatory (ESO) 1997

Online publication: June 30, 1998