SIO MASER SURVEY OF THE GALACTIC BULGE IRAS SOURCES .3. KINEMATICS OFTHE BULGE STARS

We have surveyed IRAS sources toward the Galactic bulge in the SiO J = 1-0, v = 1 and 2 transitions. The sources were selected from the IRAS Point Source Catalog on the basis of the IRAS 25/12 mu m flux density ratio, extracting dust-enshrouded objects at distances of similar to 8 kpc. SiO masers were detected in 79 of the 129 sources we surveyed i n the region of \l\ < 15 degrees and 3 degrees < \b\ < 15 degrees (exc luding the strips of 4 degrees < \b\ < 5 degrees and 7 < \b\ < 8 degre es). The sources are divided into disk and bulge members based on the observed infrared luminosity. The SiO maser properties of the present samples are quite similar to the maser properties of the SiO sources t hat were found in the strips of \b\ = 4 degrees-5 degrees and 7 degree s-8 degrees in previous studies. A full discussion of the radial veloc ities of the entire bulge SiO maser sources is given. Rotation curve a nalysis shows that the radial velocities of the northern sources are s ystematically shifted from the radial velocities of the southern sourc es. If this shift is interpreted as being the result of a tilt of the rotation axis of the bulge, the tilt angle is derived to be about 7 de grees from the Galactic longitudinal circle. After correcting the effe ct of the tilt on the radial velocities, we obtain an average shift of the radial velocity of -17.7 +/- 7.6 km s(-1) at zero Galactic longit ude for the bulge sources. For the disk sources, in contrast, we get a n average shift of the radial velocity nearly equal to zero, This fact indicates that (1) the local standard of rest is moving toward the Ga lactic center direction, and/or (2) a streaming motion of stars in the Galactic bulge is observed. The velocity dispersion of the bulge sour ces in the rectangular area of \l\ < 4 degrees and \b\ < 5 degrees is found to be about 110 km s(-1). The dispersion of the bulge sources in the remaining area is about 70 km s(-1), which is close to the disper sion of 60-70 km s(-1) of disk stars. Several forbidden regions (holes ) are recognizable in the l - v map of sampled stars; for particular r anges of radial velocities, no star can be found at some Galactic long itudes. The positions of such holes in the l - v map correspond to the contour dips in the H I l - v map taken at low Galactic latitude (\b\ < 3 degrees). This may be evidence for complex streaming motion of st ars resulting from a bar structure in the Galactic bulge.