Gas distribution and starburst activity in the widely separated interacting galaxy pair NGC 6670

We present high-resolution H I 21 cm line, 20 cm radio continuum, and CO (1 -0) line observations of the luminous infrared galaxy pair NGC 6670. NGC 66 70 consists of two edge-on disk galaxies (NGC 6670E and NGC 6670W) with a p rojected nuclear separation of similar to 16 kpc. While there are no optica lly identified tidal features and the molecular disks are not distorted muc h, we have detected a 90 kpc long H I tail, which suggests that the galaxie s are interacting and have already experienced at least one close encounter . The galaxies appear to be gravitationally bound and in a prograde-prograd e orbit, which is the most efficient for producing tidal tails. Our observa tions suggest that the H I at larger galactic radii has been ejected to for m the tails and the remnant H I disks have been perturbed by the interactio n. In particular, we find that the H I disk of NGC 6670E appears to have be en nearly destroyed. We conclude that the previous encounter between the ga laxies had a large impact parameter and that the system is still in an earl y stage of interaction. Even though NGC 6670 is in an early stage of intera ction, we find that there is evidence for nuclear starbursts already presen t. The CO (1-0) observations show large molecular gas reservoirs in the cen tral regions, and the 20 cm radio continuum observations reveal enhanced st ar formation activity in the nuclear regions of both galaxies. The spatial extent of the 20 cm emission and the far-infrared-radio correlation further rule out active galactic nuclei as the source of the IR luminosity from NG C 6670. We estimate the ratio L-IR/M-H2,which is often used as an indicator of star formation efficiency, in the nuclear regions of NGC 6670E and NGC 6670W to be 18 and 11 L-circle dot/M-circle dot, respectively. The nuclear star formation efficiency of these two galaxies has been elevated to the le vel observed in other nearby starburst galaxies (L-IR/M-H2 > 10 L-circle do t/M-circle dot). Other indicators of starburst activity, such as CO brightn ess temperature and infrared surface brightness, are also observed.