IAU Symposium Abstract S186-080P

Gas segregation in the interacting system Arp 105

P.-A. Duc1, E. Brinks 2 J. Wink 3, and I.F. Mirabel4
1 European Southern Observatory, Germany < pduc@eso.org >
2 U. de Guanajuato, Mexico < ebrinks@andromeda.cimat.mx >
3 IRAM, France < wink@iram.fr >
4 C.E. Saclay, France < mirabel@discovery.saclay.cea.fr >

Arp 105 is an example of a collision between an infrared luminous spiral and an elliptical galaxy in a cluster of galaxies. This system hosts two star-forming tidal dwarf galaxies at the ends of the tails emanating from the spiral. We have carried out at CFHT long-slit spectroscopy on the different components, and mapped the CO and HI gas with the Very Large Array and the Plateau de Bure interferometers. We found an extreme spatial segregation between the molecular gas, concentrated in the central regions of the spiral, and the atomic gas only distributed along the tidal tails. HI clouds as massive as 6~109 Msun are associated with the tidal dwarf galaxies. Ionized gas is found coincident with the peaks of the HI column density. Thanks to these observations we could study the dynamics of the system. In the northern tail, the HI is made out of two individual components, one following the optical arm, and another one, kinematically decoupled from the tail, which show signs of rotation. Evidence of rotation is also seen in Halpha in the tidal object at the tip of the southern tail. These observations show that some tidal dwarf galaxies might have already acquired a dynamical independence.