Molecular Gas within the Milky Way's Nuclear Wind

We report the first direct detection of molecular hydrogen associated with the Galactic nuclear wind. The FarUltraviolet Spectroscopic Explorer spectrum of LS 4825, a B1 Ib-II star at 1, b = 1.67 degrees,-6.63 degrees lying d = 9.9(-0.8)(+1.4)kpc from the Sun, similar to 1 kpc below the Galactic plane near the Galactic center, shows two high-velocity H-2 components at v(LSR) = - 79 and -108 km s(-1). In contrast, the FUSE spectrum of the nearby (similar to 0.6 degrees away) foreground star HD 167402 at d = 4.9(-0.7)(+0.8) kpc reveals no H 2 absorption at these velocities. Over 60 lines of H-2 from rotational levels J= 0 to 5 are identified in the high-velocity clouds. For the v(LSR) = - 79 km s(-1) cloud we measure total log N(H-2) >= 16.75 cm(-2), molecular fraction f(H2) >= 0.8%, and T-01 >= 97 and T-25 <= 439 K for the ground- and excited-state rotational excitation temperatures. At v(LSR) = - 108 km s(-1), we measure log N(H-2) = 16.13 +/- 0.10 cm(-2), integral(H2) >= 0.5%, and T-01 = 77(-18)(+34 )and T-25 = 1092(-117)(+149) M K, for which the excited-state ortho- to para-H-2 is 1.0(-0.1)(+0.3), much less than the equilibrium value of 3 expected for gas at this temperature. This nonequilibrium ratio suggests that the -108 km s(-1) cloud has been recently excited and has not yet had time to equilibrate. As the LS 4825 sight line passes close by a tilted section of the Galactic disk, we propose that we are probing a boundary region where the nuclear wind is removing gas from the disk.