v 1 2 0 N ov 1 99 6 Arp 302 : Non - starburst Luminous Infrared Galaxies

Arp 302, a luminous infrared source (LIR = 4.2× 10 11 L⊙), consisting of two spiral galaxies (VV340A and VV340B) with nuclear separation of ∼ 40, has the highest CO luminosity known. Observations with the BIMA array at 5 ×7 resolution reveal that the CO emission is extended over 23.0 kpc in the edge-on spiral galaxy, VV340A, corresponding to 6.7× 10 M⊙ of H2. In the companion face-on galaxy, VV340B, the CO emission is extended over ∼ 10.0 kpc, with 1.1 × 10 M⊙ of H2. The large CO extent is in strong contrast to starburst systems, such as Arp 220, in which the CO extent is typically ≤ 1 kpc. Furthermore, LIR/M(H2) is found to be < ∼ 6.0 L⊙/M⊙ throughout both galaxies. Thus the high IR luminosity of Arp 302 is apparently not due to starbursts in the nuclear regions, but is due to its unusually large amount of molecular gas forming stars at a rate similar to giant molecular clouds in the Milky Way disk. Arp 302 consists of a pair of very gas-rich spiral galaxies that may be interacting and in a phase before a likely onset of starbursts. Subject headings: galaxies: individual (Arp 302, VV340, UGC 09618) – galaxies: interactions – galaxies: spiral – galaxies: starburst – infrared: galaxies – ISM: molecules