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Water masers within the G333.2–0.6 giant molecular cloudWater masers within the G333.2–0.6 giant molecular cloud
Astrophysical Masers and their Environments Proceedings IAU Symposium No. 242, 2007
Abstract. We report the results of a blind search for 22 GHz water masers in two regions,
covering approximately half a square degree, within the G333.2–0.6 giant molecular cloud. The
complete search of the two regions was carried out with the 26 m Mount Pleasant radio telescope
and resulted in the detection of nine water masers, five of which are new detections. Australia
Telescope Compact Array (ATCA) observations of these detections have allowed us to obtain
positions with arcsecond accuracy, allowing meaningful comparison with infrared and molecular
data for the region.We find that for the regions surveyed there are more water masers than either
6.7 GHz methanol, or main-line OH masers. The water masers are concentrated towards the
central axis of the star formation region, in contrast to the 6.7 GHz methanol masers which tend
to be located near the periphery. The colours of the GLIMPSE point sources associated with
the water masers are slightly less red than those associated with methanol masers. Statistical
investigation of the properties of the 13CO and 1.2 mm dust clumps with and without associated
water masers shows that the water masers are associated with the more massive, denser and
brighter 13CO and 1.2 mm dust clumps. We present statistical models that can predict those
13CO and 1.2 mm dust clumps likely to have associated water masers.
1. Introduction
The G333.2–0.6 giant molecular cloud (GMC) is located at a distance of 3.6 kpc
(Lockman 1979) and extends approximately 1.2 x 0.6 degrees on the sky. The GMC has
been the focus of numerous observations, including 1.2 mm dust continuum observations
by Mookerjea et al. (2004) who identified 95 dust clumps within the region. Observations
of 13CO by Bains et al. (2006) identified 61 13CO clumps within the GMC and showed
that the emission takes the form of a string of knots with the clumps arranged along an
axis aligned NW to SE. Complete surveys of the region have been carried out by Ellingsen
et al. (1996) for 6.7 GHz methanol masers and Caswell et al. (1980) for 1665 and 1667
MHz OH masers. These surveys resulted in the detection of four methanol and three
OH masers within the regions surveyed for water masers. Here we present the results
of an untargeted survey within two distinct regions of the G333.2–0.6 GMC which has
resulted in the detection of nine water masers, five of which are new detections. The two
regions surveyed cover over half a square degree and encompass much of the high density
gas and dust regions of the GMC. For greater detail of the observations and analysis see
Breen et al. (2007).
2. Discussion and conclusions
2.1. Association with other maser species and infrared sources
We find that within the regions surveyed there are more water than either methanol or
OH masers and that there are relatively few associations between the different maser
species. Comparison between the relative locations of the water masers and the 6.7 GHz
methanol masers shows that the water masers lie along the main axis of star formation
within the GMC while the methanol masers tend to be located near the periphery. Four
of the five newly discovered water masers have an associated GLIMPSE point source
and the four previously detected water masers are all projected against regions of bright
mid-infrared emission. Comparison of the (3.6)–(4.5) colours of the water maser associated
GLIMPSE point sources with those associated with methanol masers (Ellingsen 2006)
shows that the sources associated with the water masers are clustered toward the less
red end of the range observed in the methanol associated sources. This coupled with the
relative positions of the water and methanol masers within the GMC lends support to
the idea that methanol masers trace an earlier evolutionary phase than water masers.
2.2. 13CO and 1.2 mm dust clump analysis
We have investigated the properties of the 13CO (Bains et al. 2006) and the dust clumps
(Mookerjea et al. 2004) that are associated with water maser emission by fitting a Binomial
generalised linear model to the maser presence/absence data using the 13CO and
dust clump properties as predictors. This analysis has shown that in general water masers
are associated with bigger, brighter, more massive and denser 13CO and dust clumps.
Stepwise model selection based on the Akaike Information Criteria was used to select the
most parsimonious models with the greatest predictive properties for both the 13CO and
the dust clumps. The estimated regression relations for the 13CO and dust clumps are
(maths equations that can not be copied into here!)
respectively, where pi is the probability of maser presence in the ith clump and xintegrated,
xradius and xmass represent clump properties integrated flux density of the clump peak
(10 K km s?1 ), mass (103 M) and radius (pc). These models have low misclassification
rates and allow the probability of maser presence within a given clump to be calculated,
enabling efficient targeted searches to be carried out where suitable data is available.
References
Bains, I., Wong, T., Cunningham, M., Sparks, P., Brisbin, D., Calisse, P., Dempsey, J. T.,
Deragopian, G., Ellingsen, S., Fulton, B., Herpin, B., Jones, P., Kouba, Y., Kramer, C.,
Ladd, E. F., Longmore, S. N., McEvoy, J., Maller, M., Minier, V., Mookerjea, B., Phillips,
C., Purcell, C. R., Walsh, A., Voronkov, M. A., Burton, M. G. 2006, MNRAS 367, 1609
Breen, S. L., Ellingsen, S. P, Johnston-Hollitt, M., Wotherspoon, S., Bains, I., Burton, M. G.,
Cunningham, M., Lo, N., Senkbeil, C. E., Wong, T. 2007 MNRAS in press
Caswell, J. L., Haynes, R. F., Goss, W.M 1980, Aust. J. Phys., 33, 639
Ellingsen, S. P., von Bibra, M. L., McCulloch, P. M., Norris, R. P., Deshpande, A. A., Phillips,
C. J. 1996, MNRAS 280, 378
Ellingsen, S. P. 2006, ApJ 638, 241
Lockman, F. J. 1979, ApJ 232, 761
Mookerjea, B., Kramer, C., Nielbock, M., Nyman, L. 2004, A & A 426, 119
Water masers within the G333.2–0.6 giant molecular cloud
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