Astron. Astrophys. 324, 41-50 (1997)

Starbursts in barred spiral galaxies

II. Molecular and optical study of three Wolf-Rayet galaxies ^*

T. Contini ¹, H. Wozniak ², S. Considère ³ and E. Davoust <sup>1

1</sup> Observatoire Midi-Pyrénées, UMR 5572, 14 Avenue E. Belin, F-31400 Toulouse, France
² Observatoire de Marseille, URA CNRS 237, 2 Place Le Verrier, F-13248 Marseille Cedex 4, France
³ Observatoire de Besançon, EP CNRS 123, B.P. 1615, F-25010 Besançon Cedex, France

Received 27 November 1995 / Accepted 22 January 1997

Abstract

We have searched for dense molecular gas in three barred spiral galaxies with young starbursts, NGC 3049, 5430 and 6764, which are known Wolf-Rayet galaxies. We detected HCN in the latter two, and CS was marginally detected in NGC 6764.

The dense molecular gas contents of the three galaxies are compared to those of other galaxies and to other indicators of star formation. The HCN luminosities (relative to the CO and far infrared ones) in these galaxies with very young starbursts are consistent with those observed in galaxies with older starbursts and in normal galaxies, and so are our upper limits to the CS intensities (relative to CO).

The starburst ages evaluated from our spectrophotometric observations are in the range 3.4 to 6.0 Myr. A circum-nuclear ring is apparent on our images of NGC 5430, the galaxy with the oldest central starburst; this galaxy also has the widest molecular lines. The central star formation rates derived from the H luminosity are consistent with those expected from the global FIR luminosities, and are correlated with the HCN luminosities.

Finally, an independent estimate of the H₂ column density is obtained by optical spectrophotometry; it leads to a H₂ column density to CO intensity ratio which is about 2 to 3 times lower than the standard value, because the CO intensities of the three galaxies are higher than average, relative to their far infrared fluxes.

Key words: galaxies: individual : NGC 3049; NGC 5430; NGC 6764 galaxies: ISM galaxies: starburst radio lines: galaxies

* Based on observations obtained at the 2 meter telescope of Observatoire du Pic du Midi, the 1.93 meter telescope of Observatoire de Haute-Provence, both operated by INSU (CNRS), and at the 30 meter radiotelescope on Pico Veleta, operated by IRAM.

Send offprint requests to: T. Contini, contini@wise.tau.ac.il

© European Southern Observatory (ESO) 1997

Online publication: May 26, 1998

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