A Survey of 22 Gigahertz Water Masers Within 2.25 Degrees of the Galactic Center

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Star Formation

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I present the results of a survey of 22-GHz H _2O masers near the Galactic center during which 99 masers were discovered, increasing the number of known H_2O masers in this region by a factor of _sp{~ }>5. For most of this survey, the VLA was used to observe candidate IRAS sources in the inner +/-2.25^circ of the Galaxy. The results demonstrate that the use of 22-GHz masers to study Galactic center kinematics is feasible. Furthermore, the detection rate of 22.3% obtained during the 44 hours of observing time shows that the observational approach taken is efficient. Compilations of the infrared and 22-GHz properties of the masers, as well as the infrared properties of all the observed candidate sources are included. The detected masers were associated with stars (28.3%) and star-formation regions (66.7%) on the basis of IRAS colors and previous identifications in the literature with better than 90% confidence in most cases. The kinematic results include the velocity dispersion as a function of latitude and of longitude. Current models of the Galactic Bulge available in the literature predict different signatures for the velocity dispersion as a function of latitude. These results indicate that the bar models may over-estimate the velocity dispersion at moderate distances from the Galactic center, and may therefore need to be modified. The 14 masers which can be associated with star -formation regions at the Galactic center suggest that active star formation may be fairly common in the inner Galaxy, and that it may occur along large-scale shocks provoked by the bar. We serendipitously discovered an evolved star which probably formed in the Circumnuclear Molecular Disk at the Galactic center, implying that star formation can occur in highly disturbed media. More statistics are needed to confirm the suggested results of the survey. With less than 100 more hours of VLA time, we could increase the number of detected masers by a factor of ~3, potentially making marginal results in the current database statistically significant.

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