2015A&A...584A.114S

Pre-merger tidal interactions between pairs of galaxies are known to induce significant changes in the morphologies and kinematics of the stellar and interstellar medium components. Large amounts of gas and stars are often found to be disturbed or displaced as tidal debris. This debris then evolves, sometimes forming stars and occasionally forming tidal dwarf galaxies. Here we present results from our HI study of Arp 65, an interacting pair hosting extended HI tidal debris. In an effort to understand the evolution of tidal debris produced by interacting pairs of galaxies, including in situ star and tidal dwarf galaxy formation, we are mapping HI in a sample of interacting galaxy pairs. The Arp 65 pair is the latest member of this sample to be mapped. Our resolved HI 21cm line survey is being carried out using the Giant Metrewave Radio Telescope. We used our HI survey data as well as available SDSS optical, Spitzer infra-red and GALEX UV data to study the evolution of the tidal debris and the correlation of HI with the star-forming regions within it. In Arp 65 we see a high impact pre-merger tidal interaction involving a pair of massive galaxies (NGC90 and NGC93) that have a stellar mass ratio of ∼1:3. The interaction, which probably occurred ∼1.0-2.5x10⁸yr ago, appears to have displaced a large fraction of the HI in NGC90 (including the highest column density HI) beyond its optical disk. We also find extended on-going star formation in the outer disk of NGC90. In the major star-forming regions, we find the Hi column densities to be ∼4.7x10²⁰cm^–2 or lower. But no signature of star formation was found in the highest column density HI debris SE of NGC90. This indicates conditions within the highest density HI debris remain hostile to star formation and it reaffirms that high HI column densities may be a necessary but not sufficient criterion for star formation.