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Published online by Cambridge University Press: 03 August 2017
Because of their mutual gravitational interactions, galaxies do not live forever. In extreme collisional events, galaxy pairs can merge into single spheroidal systems. Numerical simulations (Barnes 1988) indeed support the suggestion that the formation of some ellipticals does result from the merging of two disk galaxies (Toomre and Toomre 1972). However, one must then explain the very low molecular-gas content of ellipticals compared to that of spiral galaxies. Could the burst of star formation triggered during the merging exhaust the molecular material of the disk progenitors ? In order to test this hypothesis, data must be collected on the gas content of mergers at various stages of evolution and of “genuine” ellipticals as well. We here report on multi-line 12CO and 13CO observations of a sample of such objects. Our aims were (i) to contribute to a better knowledge of the molecular content of elliptical galaxies, and (ii) to help understand when and how the molecular gas of a merging system is consumed on its way towards an elliptical. The detailed presentation and discussion of the results are to be found in Casoli et al (1988 : Paper I; 1990 : Paper III), Dupraz et al. (1990 : Paper II), and Dupraz and Casoli (1990).