High Resolution Surveys of the Water and Methanol Star Formation Masers in the Central Molecular Zone
We present some of the first high resolution fully interferometric surveys of 6.7 GHz methanol and 22 GHz water masers towards the Central Molecular Zone (CMZ). These masers are good signposts for early (<0.05 Myrs) star formation. Using the Jansky Very Large Array (VLA), we searched the inner 3 x 0.7 deg of the Galactic Center (GC) for methanol masers with resolutions of 0.9” (0.04 pc) and 0.4 km/s (8 kHz) and an average channel sensitivity of ~0.01 Jy/beam. With this high resolution and sensitivity, we have detected ~100 methanol masers, which is over a factor of two more than has previously been detected. We have also conducted two surveys of water masers in this region. As part of the Survey of Water and Ammonia in the Galactic Center (SWAG), the Australia Telescope Compact Array (ATCA) was used to survey a variety of molecular lines, including the 22 GHz water line. With the ATCA, we have detected over 200 water masers using resolutions of 26” (1 pc) and 2 km/s (60 kHz) and an average channel sensitivity of ~0.01 Jy/beam. Afterward, we conducted the first on-the-fly (OTF) VLA survey of water masers with improved resolutions of 0.7” (0.03 pc) and 0.4 km/s (26 kHz) and an average channel sensitivity of ~0.05 Jy/beam. Although the analysis of this OTF survey is not yet complete, we have already identified water masers that were not visible in the SWAG data.The improvement in the number of detected masers allows us to better analyze the distribution of these masers. We show that the SWAG water masers appear uniformly distributed along the Galactic plane, despite the asymmetry of the molecular gas distribution, where ~2/3 of the gas mass is located at positive Galactic longitudes. The methanol masers follow the molecular gas distribution, with a majority of the masers being found at positive longitudes. This could indicate a difference in the star forming history of these two parts of the CMZ and/or that the 22 GHz water masers are contaminated by water masers produced from evolved stars as well as star forming regions, indicating that a larger percentage of 22 GHz water masers are produced by evolved stars than is currently thought. We show a tentative indication supporting the latter case.
American Astronomical Society Meeting Abstracts #229
- Pub Date:
- January 2017