We present new CO ( 1 - 0 ) observations of eleven extragalactic tails and bridges in nine interacting galaxy systems , almost doubling the number of such features with sensitive CO measurements .
Eight of these eleven features were undetected in CO to very low CO/HI limits , with the most extreme case being the NGC 7714/5 bridge .
This bridge contains luminous H II regions and has a very high HI column density ( 1.6 \times 10 ^ { 21 } cm ^ { -2 } in the 55 ^ { \prime \prime } CO beam ) , yet was undetected in CO to rms T _ { R } ^ { * } = 2.4 mK .
The HI column density is higher than standard H _ { 2 } and CO self-shielding limits for solar-metallicity gas , suggesting that the gas in this bridge is metal-poor and has an enhanced N _ { H _ { 2 } } /I _ { CO } ratio compared to the Galactic value .
Only one of the eleven features in our sample was unambiguously detected in CO , a luminous HI-rich star formation region near an optical tail in the compact group Stephan ’ s Quintet .
We detect CO at two widely separated velocities in this feature , at \sim 6000 km s ^ { -1 } and \sim 6700 km s ^ { -1 } .
Both of these components have HI and H \alpha counterparts .
These velocities correspond to those of galaxies in the group , suggesting that this gas is material that has been removed from two galaxies in the group .
The CO/HI/H \alpha ratios for both components are similar to global values for spiral galaxies .