Report on a Survey of H$_2$O Masers Towards the Galactic Center

Previous abstract Next abstract

Session 116 -- Galactic Center and Diffuse Galactic Emission
Oral presentation, Saturday, January 15, 10:15-11:45, Salon IV Room (Crystal Gateway)

[116.09] Report on a Survey of H$_2$O Masers Towards the Galactic Center

D.A. Levine (IPAC/UCLA), Mark Morris (UCLA), G. Taylor (Caltech), Eric Schulman (U. Mich)

Galactic H$_2$O masers are associated either with the circumstellar shells of late-type stars or with star-formation regions (SFR). Previous surveys for H$_2$O masers have revealed relatively few near the Galactic Center (GC), which is surprising since the high concentration of molecular gas there would normally be indicative of a high rate of star formation, which, in turn, would be associated with H$_2$O maser activity.

We report on the continuation of a survey using the VLA to make 22.2 GHz observations of IRAS point sources within 2 degrees of the GC, and having 12$\mu$m or 25$\mu$m flux greater than 8 Jy. Taylor, Morris and Schulman (1993, Ap.J., in press) previously observed 97 of 342 candidate sources, detecting H$_2$O maser emission in 30, 7 at the GC. On October 4, 8 and 9 1993 we observed 160 more IRAS candidates at the VLA. Preliminary perusal of the data indicates a similar detection rate. We will present the results of the recent observations.

The resulting H$_2$O maser collection consists of four source flavors: GC circumstellar sources, GC SFRs, line-of-sight circumstellar sources and line-of-sight SFRs. The GC sources are statistically distinguished from foreground sources on the basis of velocity dispersion. We assume that the high velocities of individual sources reflect the high velocity dispersion of stars and gas at the GC, whereas foreground sources should have a velocity dispersion less than a few tens of km/s. We distinguish SFR masers from circumstellar masers using their far-IR colors and H$_2$O spectra.

The primary thrust of this work is to catalog new GC sources in order to gather new information on the galactic mass distribution and on GC star formation, but the line-of-sight sources also provide useful information on Galactic structure.

Saturday program listing