A search for water masers associated with class II methanol masers - I. Longitude range 6 to 20 degrees

TL;DR

This study used the Australia Telescope Compact Array to detect water masers associated with 6.7-GHz methanol masers in the 6-20 degree Galactic longitude range, revealing correlations with luminosity, infrared objects, and dust properties.

Contribution

First comprehensive survey linking water and methanol masers in this longitude range, highlighting their associations with infrared objects and dust characteristics, and discussing evolutionary implications.

Findings

Water masers are associated with 46% of methanol masers.

Sources with both masers have higher luminosities and more compact dust clumps.

Presence of Extended Green Objects correlates with both masers.

Abstract

The Australia Telescope Compact Array has been used to search for 22-GHz water masers towards the 119 6.7-GHz methanol masers detected in the Methanol Multi-Beam survey between Galactic longitudes 6 and 20 degrees; we find water masers associated with 55 (~46 per cent). Methanol masers with associated water masers have a higher mean integrated luminosity than those without and there is a general trend for sources with more luminous 6.7-GHz methanol masers to be associated with more luminous water maser emission. 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. Analysis of the 1.1-mm dust emission shows dust clumps associated with masers that have greater 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. We conclude 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.