THE INTERSTELLAR MEDIUM IN DISTANT STAR-FORMING GALAXIES: TURBULENT PRESSURE, FRAGMENTATION, AND CLOUD SCALING RELATIONS IN A DENSE GAS DISK AT z=2.3

We have used the Institut de Radioastronomie Millimetrique (IRAM) Plateau de Bure Interferometer and the Expanded Very Large Array to obtain a high-resolution map of the CO(6-5) and CO(1-0) emission in the lensed, star-forming galaxy SMM J2135-0102 at z = 2.32. The kinematics of the gas are well described by a model of a rotationally supported disk with an inclination-corrected rotation speed, nu(rot) = 320 +/- 25 km s(-1), a ratio of rotational-to-dispersion support of nu/sigma = 3.5 +/- 0.2, and a dynamical mass of (6.0 +/- 0.5) x 10(10) M-circle dot within a radius of 2.5 kpc. The disk has a Toomre parameter, Q = 0.50 +/- 0.15, suggesting that the gas will rapidly fragment into massive clumps on scales of L-J similar to 400 pc. We identify star-forming regions on these scales and show that they are similar to 10x denser than those in quiescent environments in local galaxies, and significantly offset from the local molecular cloud scaling relations (Larson's relations). The large offset compared to local molecular cloud line-width-size scaling relations implies that supersonic turbulence should remain dominant on scales similar to 100x smaller than in the kinematically quiescent interstellar medium (ISM) of the Milky Way, while the molecular gas in SMM J2135 is expected to be similar to 50x denser than that in the Milky Way on all scales. This is most likely due to the high external hydrostatic pressure we measure for the ISM, P-tot/k(B) similar to (2 +/- 1) x 10(7) K cm(-3). In such highly turbulent ISM, the subsonic regions of gravitational collapse (and star formation) will be characterized by much higher critical densities, n(crit) > = 10(8) cm(-3), a factor greater than or similar to 1000x more than the quiescent ISM of the Milky Way.