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Using masers as evolutionary probes in the G333 GMC (as well as some follow up work)

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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 ... – PowerPoint PPT presentation

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Title: Using masers as evolutionary probes in the G333 GMC (as well as some follow up work)


1
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

2
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

3
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

4
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)

5
Observations
  • Mt 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

6
Observations
  • ATCA
  • Two sessions of ATCA Directors 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

7
Water masers - circles Methanol masers - squares
(Ellingsen 2005) OH masers - crosses (Caswell
1998)
8
4
  • Red 8 µm, green 5.8 µm, blue 3.6 µm. Water
    masers (circles), methanol
  • masers (squares) (Ellingsen 2005) and OH masers
    (crosses) (Caswell 1998).

9
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

10
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

11
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

12
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

13
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
14
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

15
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

16
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

17
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

18
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

19
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20
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

21
8
22
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

12 GHz methanol maser associated with a later
evolutionary phase of massive star formation than
the 6.7 GHz only sources
23
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

24
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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