Systematic distortion of the outer regions of the galaxy.

The distribution of hydrogen in the galaxy can be deduced from 21-cm H-line data, using the Oort model. The Leiden and Australian groups have shown in unpublished work that if the Lund pole is shifted, the major concentration of hydrogen remains close to the galactic plane, with small deviations. The 21-cm data of both the Carnegie Institution and Leiden Observatories have been analyzed with respect to the new galactic plane derived by the Leiden and Australian groups, to see if the outermost hydrogen in the galaxy showed deviations which could be attributed to tidal distortion by the Large Magellanic Cloud. A deviation does exist, the center of mass of the outermost hydrogen lying consistently below the plane on the side closest to the LMC, while the outermost hydrogen on the far side lies consistently above the plane. This deviation is as great as 300 pc for principal condensations and even more for the tenuous outer edges. An order-of-magnitude calculation indicates that gravitational forces alone would not cause a deviation of more than about 30 pc even for masses of 7 X 1010 and 4 X io9 solar masses for the galaxy and LMC, respectively. The distortion, while in the proper direction, would thus appear to be considerably greater than one would expect from gravitational forces only. We understand that this same effect has independently been noted by J. F. Kerr and J. V. Hindman in Australia. Department of Terrestrial Magnetism, Carnegie Institution of Washington, Washington, D. C.