Using the integrated H fluxes, the masses of ionised gas were estimated to lie in the range 107 to 10. This amounts to between less than 1% and more than 50% of the estimated dynamical masses. The two companion galaxies had the lowest fraction of ionised gas mass to dynamical mass, and the galaxies with the most peculiar RCs (ESO 350-IG38, ESO 338-IG04 and ESO 400-G43) apparently have the largest fraction of their mass in the form of ionised gas.
This paper presents the most extensive study of the central dynamics and optical velocity fields of BCGs as yet. In addition, all the observations have been done with the same instrument and the sample selection, reductions and analysis are homogeneous. In a forthcoming paper (Paper II) we will discuss the interpretation of the velocity fields and rotation curves in terms of more detailed mass models. In addition we will discuss what the results presented here tell us about the triggering mechanism for the starburst activity present in these galaxies.
This work was partly supported by the Swedish Natural Science Research Council. We thank Jean-Luc Gach from Marseille Observatory for mounting and dismounting the instrument on the telescope and for assistance during the observations. Eva Örndahl is thanked for useful comments on the manuscript. Anna Westman is thanked for her help in editing the text. We would also like to thank Albert Bosma for stimulating discussions on the interpretation of velocity fields. This research has made use of the NASA/IPAC Extragalactic Database (NED)which is operate by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.
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