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Astron. Astrophys. 346, 45-57 (1999)

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The discovery of a gas-rich bar in UGC 2855: a galaxy in a pre-starburst phase?

S. Hüttemeister 1,2, S. Aalto 3,4 and W.F. Wall 5

1 Radioastronomisches Institut der Universität Bonn, Auf dem Hügel 71, D-53121 Bonn, Germany
2 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
3 Onsala Space Observatory, S-43992 Onsala, Sweden
4 California Institute of Technology, Pasadena, CA 91125, USA
5 INAOE, 72000 Puebla, Mexico

Received 15 December 1998 / Accepted 9 March 1999


We present the first interferometric CO observations of the barred late-type galaxy UGC 2855 and its companion UGC 2866. UGC 2855 is shown to belong to the rare class of galaxies with a long ([FORMULA] kpc) continuous molecular bar. The velocity field along the bar is dominated by solid-body rotation and shows few perturbations. This, together with an almost constant and low 12CO/13CO line intensity ratio along the bar and in the center as well as only weak H[FORMULA] emission, indicate that the gas in the bar is not subjected to strong shocks, but surprisingly quiescent. In the central [FORMULA], a high velocity feature consisting of a number of Giant Molecular Associations, is identified. We discuss possible scenarios of the nature of this structure in connection with the question of the presence of an Inner Lindblad Resonance (ILR) in the bar. We suggest that the bar of UGC 2855 is a young object, possibly has no ILR, and that the mass concentration toward the center of the galaxy is just beginning. In contrast, the companion UGC 2866 experiences a strong starburst. We compare the properties of the gas in the bar of UGC 2855 to those we find in NGC 7479. Despite superficial parallels, the two bars are very dissimilar objects in terms of 12CO/13CO line ratio, velocity field and H[FORMULA] activity. NGC 7479 exhibits starburst characteristics, while we argue that UGC 2855 is in a pre-burst stage.

Key words: galaxies: evolution – galaxies: individual: UGC 2855 – galaxies: individual: UGC 2866 – galaxies: ISM – galaxies: starburst – radio lines: galaxies

Send offprint requests to: S. Hüttemeister, RAIUB (huette@astro.uni-bonn.de)

© European Southern Observatory (ESO) 1999

Online publication: May 6, 1999