Bj. Smith et C. Struck, New observations of extra-disk molecular gas in interacting galaxy systems, including a two-component system in Stephanis Quintet, ASTRONOM J, 121(2), 2001, pp. 710-726
We present new CO (1-0) observations of 11 extragalactic tails and bridges
in nine interacting galaxy systems, almost doubling the number of such feat
ures with sensitive CO measurements. Eight of these 11 features were undete
cted in CO to very low CO/H I limits, with the most extreme case being the
NGC 7714/5 bridge. This bridge contains luminous H II regions and has a ver
y high H I column density (1.6 x 10(21) cm(-2) in the 55" CO beam), yet was
undetected in CO to rms T-R(*) = 2.4 mK. The H I column density is higher
than standard and CO self-shielding limits for solar-metallicity gas, sugge
sting that the gas in this bridge is metal-poor and has an enhanced N-H2/I-
CO ratio compared with the Galactic value. Only one of the 11 features in o
ur sample was unambiguously detected in CO, a luminous H I-rich star format
ion region near an optical tail in the compact group Stephan's Quintet. We
detect CO at two widely separated velocities in this feature, at similar to
6000 and similar to 6700 km s(-1). Both of these components have H I and H
a counterparts. These velocities correspond to those of galaxies in the gro
up, suggesting that this gas is material that has been removed from two gal
axies in the group. The CO/H I/H alpha ratios for both components are simil
ar to global values for spiral galaxies.