2005PASJ...57..917N

We made an unbiased search for molecular clouds in the Galactic Warp. This survey, covering an area of 56 square degrees at l = 252° to 266° and b = -5° to -1°, revealed 70 molecular clouds, while only 6 clouds were previously known in this sector at R ≫ 14.5 kpc. The mass of the clouds is in a range from 7.8 x 10²M_☉ to 8.4 x 10⁴M_☉, significantly less than the most massive giant molecular clouds in the inner disk, ∼ 10⁶M_☉, while the cloud mass spectrum characterized by a power law is basically similar to other parts of the Galaxy. The X factor, N(H²)/[?]T(¹²CO)dV, derived from the molecular clouds in the Warp, is estimated to be 3.5(±1.8)-times larger than that in the inner disk. The total molecular mass in the Warp is estimated to be 7.3 x 10⁵M_☉, and the total mass in the far-outer Galaxy (R ≫ 14.5 kpc) can be estimated to be 2 x 10⁷M_☉. The spatial correlation between the CO and HI distribution appears to be fairly good, and the mass of the molecular gas is about 1% of that of the atomic gas in the far-outer Galaxy. This ratio is similar to that in the interarm, but is ten-times smaller than those of the spiral arms. Only 6 of the 70 Warp clouds show signs of star formation at the IRAS sensitivity, and the star-formation efficiency for high-mass stars in the Warp is found to be smaller than those in other molecular clouds in the Galaxy.