Gas Distribution and Starburst Activity in the Widely Separated Interacting Galaxies NGC 6670
Abstract
We present high resolution H I 21 cm line, 20 cm radio continuum, and CO(1-0) line observations of the luminous infrared galaxy NGC 6670. NGC 6670 consists of two edge-on disk galaxies (NGC 6670E and NGC 6670W) with a projected nuclear separation of ~16 kpc. While there are no optically identified tidal features and the molecular disks are not distorted much, we have detected a 90 kpc long H I tail which suggests that the galaxies are interacting and have already experienced at least one close encounter. Our observations suggest that the previous encounter between the galaxies had a large impact parameter and that the system is still in an early stage of interaction. Even though NGC 6670 is in an early stage of interaction, we find evidence of starburst. The CO(1-0) observations show large molecular gas reservoirs in the central regions and the 20 cm radio continuum observations reveal enhanced star formation activity in the nuclear regions of both galaxies. We estimate the ratio LIR/MH2, 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 Lsun/Msun, respectively. The nuclear star formation efficiency of these two galaxies has been elevated to the level observed in other nearby starburst galaxies (LIR/MH2 > 10 Lsun/Msun). Other indicators of starburst activity such as CO brightness temperature and infrared surface brightness are also observed.
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