Constraining the properties of 1.2-mm dust clumps that contain luminous water masers
Breen, SL and Ellingsen, SP, Constraining the properties of 1.2-mm dust clumps that contain luminous water masers, Monthly Notices of the Royal Astronomical Society, 416, (1) pp. 178-204. ISSN 1365-2966 (2011) [Refereed Article]
We have conducted a sensitive water maser search with the Australia Telescope Compact
Array towards 267 1.2-mm dust clumps presented in the literature. We combine our new
observations with previous water maser observations to extend our sample to 294 1.2-mm
dust clumps, towards which we detect 165 distinct water maser sites towards 128 1.2-mm dust
clumps. Within the fields of our observations, we additionally find four water masers with
no apparent associated 1.2-mm dust continuum emission. Our overall detection rate of 44 per
cent appears to vary as a function of Galactic longitude. We find that there is an excellent
correspondence between the locations of the detected water masers with the peak of the target
1.2-mm dust clump sources. As expected from previous similar studies, the water masers are
chiefly detected towards the bigger, brighter and more massive 1.2-mm dust clumps.
We find further evidence to suggest that the water masers tend to increase in flux density
(and therefore luminosity), as well as velocity range, as the sources evolve.We also show that
the current sample of water maser sources suffers less from evolutionary biases than previous
We have compared the locations of the water masers with dust clumps which have a
previously determined associationwith 6.7-GHz methanol masers and 8-GHz radio continuum.
We find that the fraction of 1.2-mm dust clump sources in our sample that are associated only
with water masers (41) is higher than that of the sources associated only with methanol masers
(13). This suggests that water masers can be present at an even earlier evolutionary stage
than 6.7-GHz methanol masers. Comparison of the water maser detection rates associated
with different combinations of methanol maser and radio continuum, as well as those with
neither tracer, shows that the highest detection rate is towards those sources which also exhibit
methanol maser emission.
We have tested a previously hypothesized model for water maser presence towards 1.2-mm
dust clumps. We not only find water masers towards a high proportion of the clumps that the
model predicts would have associated water masers, but also find a number of water masers
towards sources with a low calculated probability. We propose that this is likely an artefact
of the poorly determined distances to the sources. We suggest refinements and future work
which will further constrain the nature of the driving sources associated with water masers.