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Water maser follow-up of the methanol multibeam survey

Titmarsh, AM 2015 , 'Water maser follow-up of the methanol multibeam survey', Research Master thesis, University of Tasmania.

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The Australia Telescope Compact Array has been used to search for 22-GHz water masers towards the 323 6.7-GHz methanol masers detected in the Methanol Multibeam survey between Galactic longitudes 341◦ to 20◦, through the Galactic centre, and we find water masers associated with 156 (∼48 %). Methanol masers with associated water masers have a higher mean integrated luminosity than those without. In sources where both maser species are observed, the luminosities of the methanol and water masers are weakly correlated even after accounting for the partial correlation due to distance. We have inspected the GLIMPSE three colour images of the regions surrounding the masers and cross-matched the maser positions with existing catalogues of Extended Green Objects and Infrared Dark Clouds. We find more Extended Green Objects at sites where both methanol and water masers are present than at sites with only methanol masers, but no significant difference in the fraction embedded within Infrared Dark Clouds. Studying the mid-infrared colours from GLIMPSE, we found no differences between the colours of those sources associated with both methanol and water masers and those associated with just methanol. Analysis of the 1.1-mm thermal dust emission shows dust clumps associated with masers have greater 1.1-mm flux densities and higher column densities than those without. Dust clumps associated with both water and 6.7-GHz methanol masers are generally the most compact clumps followed by those associated with only methanol then the clumps without associated maser emission. Comparing the column density and dust mass calculated from the thermal dust emission at 870 μm, we found no differences between those sources associated with both water and methanol masers and those with methanol only. At 870 μm we found dust clumps at the very highest column densities (above ∼ 1025 cm−2) almost all had an associated methanol maser. We conclude that there is some evidence that protostars with both methanol and water masers are often older than those with only methanol, however, we suggest that the evolutionary phase traced by water masers is not as well defined as for 6.7-GHz methanol masers. Since water masers are collisionally pumped and often show emission further away from their accompanying YSO than the radiatively pumped 6.7-GHz methanol masers, it is likely that water maser properties are not as tightly correlated to the evolution of the parent YSO.

Item Type: Thesis - Research Master
Authors/Creators:Titmarsh, AM
Keywords: Radio astronomy, spectral lines, water masers
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Copyright 2015 the Author

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