An Unbiased Survey for Molecular Clouds in the Southern Galactic Warp

Abstract

We have made an unbiased survey for molecular clouds in the Galactic Warp. This survey, covering an area of 56 square degrees at l = 252 deg to 266 deg and b = -5 deg to -1 deg, has revealed 70 molecular clouds, while only 6 clouds were previously known in the region. The number of molecular clouds is, then, an order of magnitude greater than previously known in this sector at R > 14.5 kpc. The mass of the clouds is in a range from 7.8x10(2) Mo to 8.4x10(4) Mo, significantly less than the most massive giant molecular clouds in the inner disk, ~10(6) Mo, while the cloud mass spectrum characterized by a power law is basically similar to other parts of the Galaxy. The X factor, N(H2)/Wco(12CO), 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 as 7.3x10(5) Mo, and total mass in the far-outer Galaxy (R > 14.5 kpc) can be estimated as 2x10(7) Mo. The spatial correlation between the CO and HI distribution appears 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 star formation efficiency for high-mass stars in the Warp is found to be smaller than those in other molecular clouds in the Galaxy.

arXiv comment29 pages, including 12 (pages of) figures, accepted for PASJ, and will be published in PASJ Vol.57, No.6. Tables and color-figures are available on-line: http://www.a.phys.nagoya-u.ac.jp/~masa/study/nakagawa_etal2005_warp.pdf

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• The spiral structure of our Milky Way Galaxy
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• 3D Distribution of Molecular Gas in the Barred Milky Way
• A large catalogue of molecular clouds with accurate distances within 4 kpc of the Galactic disk
• Mapping the Galactic Metallicity Gradient with Open Clusters: The State-of-the-Art and Future Challenges
• The almost ubiquitous association of 6.7 GHz methanol masers with dust
• Constraints on dark matter annihilations from diffuse gamma-ray emission in the Galaxy
• Molecular clouds in the extreme outer Galaxy between $l=34.75^{\circ }$ to $45.25^{\circ }$
• The Extinction and Distance of the MBM Molecular Clouds at High Galactic Latitude
• First Detection of the Molecular Cloud Population in the Extended Ultraviolet (XUV) Disk of M83
• Star formation activity beyond the outer Arm I: WISE-selected candidate star-forming regions
• A New Search for Star Forming Regions in the Southern Outer Galaxy
• Discovery of a distant molecular cloud in the extreme outer Galaxy with the Nobeyama 45-m telescope