We have imaged the kpc scale distribution of ^ { 12 } CO ( 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 ring component ( NGC 2445 ) and a bright central source .
The ring complexes represent 20 - 60 \% of the detected M _ { H _ { 2 } } , depending on the relative I _ { CO } – N _ { H _ { 2 } } for the ring and nucleus .
Their individual H _ { 2 } masses and surface densities ( \Sigma _ { H _ { 2 } } ) exceed typical spiral arm GMAs regardless of the conversion factor .
Both are associated with a 6 kpc ridge of peak \Sigma _ { HI } and massive star formation ( MSF ) activity .
H \alpha imaging shows a patchy ring of HII regions situated along the outer edge of the HI ring .
The kinematics of the HI ring show clear signs of expansion .
A simple rotating-expanding ring model ( V _ { exp } = 118 \pm 30 km s ^ { -1 } ) fits the data reasonably well , implying a ring age of \gtrsim 60 \pm 15 Myrs .
NGC 2445 ’ s ring is able to promptly form very large molecular complexes in a metal poor ISM and trigger MSF .

Nearly eighty per cent of the detected ^ { 12 } CO ( 1-0 ) flux originates in a resolved central source that is slightly offset from NGC 2445 ’ s starburst nucleus .
We find an ordered velocity field in this component .
Assuming an inclined disk , we argue that it is dynamically stable .
The central \Sigma _ { H _ { 2 } } ( 910 M _ { \odot } pc ^ { -2 } ) significantly exceeds \Sigma _ { H _ { 2 } } commonly found in normal spirals , but is much smaller than 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 . ^ { 12 } CO ( 1-0 ) emission in ring galaxies may be dominated by the nucleus , which could bias the interpretation of single-dish measurements .