THE DETECTION OF MASSIVE MOLECULAR-COMPLEXES IN THE RING GALAXY SYSTEM ARP-143

We have imaged the kiloparsec-scale distribution of (CO)-C-12(J = 1-0) emission in the ring galaxy system Arp 143 (NGC 2444/2445) using the OVRO millimeter array, We find two giant molecular complexes in the ri ng component (NGC 2445) and a bright central source. The ring complexe s represent 20%-60% of the detected M-H2 depending on the relative I-C O-N-H2 for the ring and nucleus, Their individual H-2 masses and surfa ce densities (Sigma(H2)) exceed typical spiral arm giant molecular clo uds and associations regardless of the conversion factor. Both are ass ociated with a 6 kpc ridge of peak Sigma(H I) and massive star formati on activity. Ha imaging shows a patchy ring of H II regions situated a long the outer edge of the H I ring. The kinematics of the H I ring sh ow clear signs of expansion. A simple rotating-expanding ring model (V -exp = 118 + 30 km s(-1)) fits the data reasonably well, which implies a ring age of 60 +/- 15 Myr. NGC 2445's ring is able to form very lar ge molecular complexes promptly in a metal-poor ISM and trigger massiv e star formation. Nearly 80% of the detected (CO)-C-12(1-0) flux origi nates in a resolved central source that is slightly offset from NGC 24 45's starburst nucleus, We find an ordered velocity field in this comp onent. Assuming an inclined disk, we argue that it is dynamically stab le. The central Sigma(H2) (9 x 10 M. pc(-2)) significantly exceeds Sig ma(H2) values commonly found in normal spirals but is much smaller tha n values derived in similar sized regions of IR-luminous galaxies, The nuclear H-2 may be the result of a previous encounter with NGC 2444. (CO)-C-12(1-0) emission in ring galaxies may be dominated by the nucle us, which could bias the interpretation of single-dish measurements.