The Molecule-rich Tail of the Peculiar Galaxy NGC 2782 (Arp 215)

We present the first detection of a large quantity of molecular gas in theextended tail of an interacting galaxy. Using the NRAO 12m telescope, we havedetected CO (1 - 0) at five locations in the eastern tail of the peculiarstarburst galaxy NGC 2782. The CO velocities and narrow (FWHM = 50 km/s) linewidths in these positions agree with those seen in HI, confirming that themolecular gas is indeed associated with the tail rather than the main disk. Asnoted previously, the gas in this tail has an apparent `counter-rotation'compared to gas in the core of the galaxy, probably because the tails do notlie in the same plane as the disk. Assuming the standard Galactic conversionN(H2)/I(CO) factor, these observations indicate a total molecular gas mass of 6X 10**8 M(sun) in this tail. This may be an underestimate of the total H2 massif the gas is metal-poor. This molecular gas mass, and the implied H2/HI massratio of 0.6, are higher than that found in many dwarf irregular galaxies.Comparison with an available H-alpha map of this galaxy, however, shows thatthe rate of star formation in this feature is extremely low relative to theavailable molecular gas, compared to L(H-alpha)/M(H2) values for both spiraland irregular galaxies. Thus the timescale for depletion of the gas in thisfeature is very long.Comment: 19 pages, 6 figures, Latex. To appear in the Astronomical Journa