Using masers as evolutionary probes in the G333 GMC (as

well as some follow up work)

Shari Breen, Simon Ellingsen, Ben Lewis, Melanie Johnston-Hollitt,

Simon Wotherspoon, Indra Bains, Michael Burton, Maria Cunningham, Nadia Lo &

Tony Wong

Talk Outline

• 1 - The G333 GMC– The region– Our observations– Analysis and results

• 2 - Follow up observations and analysis with 1.2 mm dust clumps from Hill et al. (2005)– Water masers– 12 GHz methanol masers

Masers and mm mapping data

• Masers pinpoint ‘special’ sources within mm mapping data

• mm mapping data along with maser observations may hold the key to unlocking the evolutionary stages that the different species of masers are tracing

The G333.2-0.6 GMC• Located at 3.6 kpc (Lockman 1979) • Extends ~ 1.2 x 0.6 degrees on the sky• 61 13CO (Bains et al. 2006) clumps• 95 1.2 mm dust continuum clumps (Mookerjea et al. 2004)• Completely searched for 6.7 GHz methanol masers (Ellingsen et al. 1996) and 1665 and 1667 MHz OH masers (Caswell et al. 1980)

ObservationsMt Pleasant

• Two regions completely searched in 2005• Velocity coverage of 431 km s-1 centred on -40 km s-1

– Region 1 ~750 pointings– RMS noise limits below 1 Jy in 78% of data

– Region 2 ~300 pointings– RMS noise limits below 1 Jy in 35% of data

• 9 water maser detections, 5 of which are new discoveries

Observations

ATCA• Two sessions of ATCA Director’s time

• Preliminary observations– 2006 June 19, 1.5D array, 8 masers detected

• Final observations – 8 masers observed on 2006 July 16 &17, 6A array– RMS noise limits ~0.15 Jy in a single spectral channel– RMS noise in continuum images typically 0.02 Jy beam-1

– Positions accurate to about 0.5 arcseconds

Water masers - circles

Methanol masers - squares (Ellingsen 2005)

OH masers - crosses (Caswell 1998)

4Red = 8 µm, green = 5.8 µm, blue = 3.6 µm. Water masers (circles), methanol masers (squares) (Ellingsen 2005) and OH masers (crosses) (Caswell 1998).

Associations between maser species and IR sources

• More water (9) masers than either methanol (4) or OH (3)

• Relatively few associations between species• Water masers lie along the main axis of star

formation, methanol tend to be located near the periphery

• 4 of the 5 new detections have associated GLIMPSE point sources

• 4 previous detections are clearly projected against regions of bright mid-IR emission

Associations between maser species and IR sources

• Comparison of the [3.6]-[4.5] colours of water maser associated GLIMPSE sources with those associated with methanol masers (Ellingsen 2006) shows that the water associated sources are clustered towards the less red end of the range observed in the methanol associated sources

• Methanol masers trace a generally earlier evolutionary phase than water masers

13CO clump analysis: Water Masers

• Increasing probability of maser presence associated with increasing values of all clump properties (confidence 95% or higher)

• Estimated regression relation is

• Misclassification rates are good when probability threshold set to 0.5– 33 clumps in region with no associated

maser - model predicts 31 correctly– 7 clumps with associated masers - model

predicts 5 of these have associated water masers

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logpi

1− pi= −21.2 +1.3xINTEGTRATED + 8.1xRADIUS −1.2xMASS

1.2 mm clump analysis: Water Masers

• Increasing probability of maser presence associated with increasing values of all clump properties (95% confidence for higher)

• Estimated regression relation is

• Misclassification rates are good when probability threshold set to 0.5– 66 clumps in region with no associated

maser - model predicts 65 correctly– 7 clumps with associated masers - model

predicts 4 of these have associated water masers

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logpi

1− pi= −11.5 + 9.2xRADIUS

Physical implications of the dust/water maser model

• Model only uses radius as a predictor

• No more information is offered from any other property

• If set pi to be 0.5 corresponds to a clump radius of ~1.25 pc

Clumps with r ≥ 1.25 pc have a probability of 0.5 or greater of having an associated water maser

13CO clump analysis: Methanol Masers

• Increasing probability of maser presence associated with increasing values of column density and integrated flux

• Estimated regression relation is

• If pi is set to 0.5 the model is good at determining clumps with no associated maser

• If pi is set to 0.12 the model correctly predicts the 5 clumps with associated masers and falsely predicts that 9 of the 56 clumps with no associated maser emission

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logpi

1− pi= −5.56 +1.47xF int −1.53xFpeak

1.2 mm clump analysis: Methanol

Masers• Increasing probability associated

with clump density, radius and mass• Estimated regression relation is

• Good misclassification rates when probability set to 0.5– 90 dust clumps have no associated

maser model predicts correctly for 89– 5 clumps with associated masers

model correctly predicts 3 of these

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logpi

1− pi= −94.5 + 0.0015xFpeak + 78.3xradius −2.2xFv −0.00083xmass +10.66xdensity

Conclusions from the G333 observations

• More water masers than either methanol or OH masers, with few associations between species

• Water masers located close to the main axis of star formation within the GMC

• Water masers associated GLIMPSE point sources are similar to those associated with methanol masers although slightly less red

• Water masers are associated with bigger, brighter, more massive and denser 13CO and 1.2 mm dust clumps

• Present models with low misclassification rate that can be tested on larger scales

Testing the dust/water maser model

• Hill et al. (2005) observed 404 1.2 mm dust clumps

• ~70 clumps have a probability of 0.5 or greater of having an associated water maser

• Preliminary results have shown that more that 75% of the masers that we detect are associated with clumps that we predicted had a high probability of maser presence

• Will complete ATCA observations in 2008 August

22 GHz results

• Majority of water masers lie in the centre of the 1.2 mm dust clumps

• No 22 GHz continuum detected that is not associated with a dust clump that is also associated with a water maser

Methanol masers at 6 & 12 GHz

• Lewis (2007) targeted observations of 12 GHz methanol masers towards 6.7 GHz methanol masers

• 27 target sources overlap with Hill et al. (2005) 1.2 mm dust clump sources– 12 GHz masers detected at 17

• Only clump mass can be used singularly as a predictor

• Implies that 12 GHz methanol masers are associated with less dense clumps than 6.7 GHz methanol only clumps

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Methanol masers at 6 & 12 GHz

• Estimated regression relation is

• Model correctly predicts 16 of the 17 clumps with associated 12 GHz masers and 6 of the 6.7 GHz methanol masers without 12 GHz emission€

logpi

1− pi= −0.77 + 0.12xFv + 5.1xradius −0.00092xmass

12 GHz methanol maser associated with a later evolutionary phase of massive star formation than the 6.7 GHz only sources

Summary of main results

• 6.7 GHz methanol masers trace the earliest stages of massive star formation followed by 12 GHz methanol masers - supported by theory

• water masers present at a later evolutionary stage

13CO and 1.2 mm dust clump analysis: Water Masers

• Fitted a Binomial GLM to maser presence/absence data • Predicts the probability pi of finding a water maser in the

ith clump in terms of clump properties x1i, x2i,….xmi

• Where yi is the maser presence or absence in the ith clump and b terms are the regression coefficients to be estimated

• stepwise model selection used to select the simplest model with the greatest predictive power

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y i ~ Bin(1, pi)

logpi

1− pi= β 0 + β1x1i + β 2x2i + ....+ βmxmi