THE DETECTION OF MOLECULAR GAS IN THE RING GALAXY ARP-143

We have used the NRAO 12 m telescope to map the inner 10 kpc of NGC 24 45, the ring galaxy in Arp 143, in CO-12(J = 1-0). Emission is peaked near the ring galaxy nucleus, but we find evidence for an additional a symmetric and extended CO component. This extended CO distribution is consistent with an approximately 8 kpc diameter crescent-shaped ring o f molecular gas, similar to the one seen in H I, accounting for approx imately half of the total CO flux. Assuming this distribution, we deri ve a total H-2 mass for NGC 2445 of 0.4-2.4 x 10(10) M., depending on whether a Galactic or low-metallicity LMC conversion factor is used, a nd an H-2/H I mass ratio between 0.9 and 5. The ring is experiencing l ow rates of massive star formation despite very high gas column densit ies. We find that the gas surface density exceeds the critical thresho ld for star formation throughout the ring, even without a possible con tribution from a significant molecular component. The absence of vigor ous star formation is most simply understood in terms of its youth (ap proximately 30 Myr): massive stars have not had time to form in large numbers. Our results support the interpretation that NGC 2445 is a nas cent ring galaxy, seen prior to its ring starburst phase.