Detection of CO from SMM J16359+6612, the multiply imaged submillimeter galaxy behind A2218

We report the detection of CO J=3-->2 line emission from all three multiple images (A, B, and C) of the intrinsically faint (similar or equal to0.8 mJy) submillimeter-selected galaxy SMM J16359+6612. The brightest source of the submillimeter continuum emission (B) also corresponds to the brightest CO emission, which is centered at z=2.5168, consistent with the preexisting redshift derived from Halpha. The observed CO flux in the A, B, and C images is 1.2, 3.5, and 1.6 Jy km s(-1), respectively, with a line width of 500+/-100 km s(-1). After correcting for the lensing amplification, the CO flux corresponds to a molecular gas mass of similar to2x10(10) h(71)(-2) M-circle dot, while the extent of the CO emission indicates that the dynamical mass of the system is similar to9x10(10) M-circle dot. Two velocity components are seen in the CO spectra; these could arise either from a rotating compact ring or disk of gas or from merging substructure. The star formation rate in this galaxy was previously derived to be similar to100-500 M-circle dot yr(-1). If all the CO emission arises from the inner few kiloparsecs of the galaxy and if the Galactic CO-to-H-2 conversion factor holds, then the gas consumption timescale is a relatively short 40 Myr, and so the submillimeter emission from SMM J16359+6612 may be produced by a powerful but short-lived circumnuclear starburst event in an otherwise normal and representative high-redshift galaxy.