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The Astrophysical Journal Supplement Series


We present H I and CO (1-0) interferometric observations of 10 comparable-mass interacting systems obtained at the Very Large Array (VLA) and the Owens Valley Radio Observatory (OVRO) millimeter array. The primary intent of this study is to investigate the response of cold gas during the early stages of collision of massive disk galaxies. The sample sources are selected based on their luminosity (MB ≤ -19), projected separation (5-40 kpc), and single-dish CO (1-0) content (SCO ≥ 20 Jy km s-1). These selection criteria result in a sample that primarily consists of systems in the early stages of an interaction or a merger. Despite this sample selection, 50% of the systems show long H I tidal tails indicative of a tidal disruption in a prograde orbit. In addition, all (4/4) of the infrared luminous pairs (LIRGs) in the sample show long H I tails, suggesting that the presence of a long H I tail can be a possible signature of enhanced star formation activity in a collision of gas-rich galaxies. More than half of the groups show a displacement of H I peaks from the stellar disks. The CO (1-0) distribution is generally clumpy and widely distributed, unlike in most IR-selected late stage mergers—in fact, CO peaks are displaced from the stellar nucleus in 20% (4/18) of the galaxies with robust CO detection.

H I and CO (1-0) position-velocity diagrams (PVDs) and rotation curves are also presented, and their comparison with the numerical simulation analyzed in Paper I show evidence for radial inflow and wide occurrences of nuclear molecular rings. These results are further quantified by examining physical and structural parameters derived in comparison with isolated systems in the BIMA SONG sample in our forthcoming paper.


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