A WARPED DISK MODEL FOR M33 AND THE 21 CENTIMETER LINE-WIDTH IN SPIRAL GALAXIES

To determine the actual H I distribution and the velocity field in the outermost disk of the spiral galaxy M33, a tilted-ring model is fitte d to 21 cm line data taken with the Arecibo telescope. Since M33 is on e of the main calibrators for the extragalactic distance scale derived through the Tully-Fisher relation, the outer disk warping is of inter est for a correct determination and deprojection of the galaxy's line width. Even though our best model predicts small effects on the observ ed line width of M33, we show that similar outer disk warping in galax ies oriented differently along our line of sight, could affect the wid ths considerably. Therefore there may be systematic effects in the det ermination of the rotation velocities and dynamic masses of spiral gal axies, whose exact value depends also on which method is used For meas uring the galaxy's total line width.