1. Signposts of massive star formation
How do high mass stars form?
Monolithic collapse
Competitive accretion
Stellar mergers
Implies jets & outflows present to remove excess angular momentum from the system. Therefore most YSO’s undergo periods of extensive mass loss.
Interaction of molecular outflows with ISM. Alter overall structure and chemical composition of regions within the parent molecular cloud. These regions are known to be ideal hosts for maser activity.
IR and radio allow us to view a young protostar
Tui Britton

2. Maser emission Population inversion Stimulated emission like a LASER
Excitation occurs when there is a population inversion and there are more atoms in the excited energy state than the lower energy state
This occurs through various excitation mechanisms:
Collisional with H atoms OR Radiative due to absorption
Masers switch off when the ground state is more densely populated than the excited state.
Population inversion
Stimulated emission like a LASER
Excitation mechanisms

3. Maser surveys Observed: H2O CH3OH OH H2CO SiO HCN NH3
Different molecules give rise to different masers at characteristic frequencies.
Targeted surveys
HOPS – we discovered. 540 masers. 72% new detections. 69% identified with star formation. Interesting water fountain where there is a high velocity spread of masers over 200km/s apart

4. Methanol Maser Surveys
Class I
36 GHz masers in 71 sites
44 GHz % have both types
25 GHz - 1st maser detected!
Class II e.g. 6.7 GHz
Class I: assoc with shocks and outflows, exapnding HII regions. Give us a better understanding of morphology of regions.
Number falls exponentially with linear distance from class II 6.7 GHz
Class I with OH masers more spread out (spatially and in velocity domain)
Class II: assc. With YSO
Roughly 1000 detected therefore pinpointing the locations of young massive stars.

5. Morphology of massive star formation
Water in outflows
class I methanol in shock fronts. Associated with the lobes of outflows where the cold quiescent gas is weak
class II near protostar

6. 25 GHz Methanol Maser Series
8 transitions
Shock environment
0.006 km/s resolution
Test models
1st systematic survey
Class I methanol masers behave differently. 9.9, 104 and 25 GHz are rare and Known to trace higher temperatures and densities of gas in clouds.
25 GHz has not been surveyed.
36,44,84, 95 more widespread. Theory indicates these may appear in different locations due to gradients of physical parameters in shocked gas. Voronkov et al 2006
Awarded telescope time to observe 51 star forming sites in the southern sky. All towards galactic centre so distances are unknown.
Natural signposts for shocks around newly forming massive stars
The sources were selected to have a flux density of this J=5 maser brighter than 1 Jy.
5 Goals – create a catalogue of accurate positions and velocities with resolution down to 0.006km/s
Trace shocks to determine morphology of individual regions.
Use the positions to determine the location in relation to other masers and HII region.
Test the modelling of class I methanol maser.
Possibly add to evolutionary tracking of massive star formation. Class I methanol associated with hII regions, so need to sample different populations to determine evol stage they appear at.
Don’t use in your martini!

7. Results 15 sites 47 masers detected
8 sources exhibit emission in 5 or more transitions
5 sources associated with HII regions
3 sources had only one recognizable transition.
Narrow velocity ranges.

8. G357.96-0.16 H2O maser HII region 6.7 GHz methanol masers H2O maser
6.7 GHz masers from MMB
Water masers from HOPS
Shock morphology
Hot core
Age - evolved region
High velocity outflow
Where are my masers on this picture?
25 GHz methanol maser

9. Compare intensities of transitions
Why is the 25 GHz series different? Which model predicts best?
Taken from Voronkov 2006
Observed relative flux densities of the 25 GHz maser series in G (J=4 transition is taken as a reference),
the best fit model (Model 1) and the typical model (Model 2), which produces 84, 95 and 104 GHz masers. See
Voronkov et al. (2006) for details.
I’m in the process of creating these plots for all my sources in order to determine whether the typical model or the best fit model is more accurate. Given my dataset is the first to systematically survey the 25GHz series, we can gain some insight into the class I methanol maser model as it applies to the 25 GHz series.
1/3 don’t match either model
1/3 match model 1
1/3 match model 2
Explain more on what these models mean.

10. Summary of PhD Results Created data reduction pipeline
1st accurate catalogue of 25 GHz methanol masers
Trace outflows & shocks in 15 sites
Good test of methanol maser modelling
What can we learn from masers?
What can we learn from my survey?
Masers are an important tool for probing the birth environment of newly forming massive stars.
My catalogue will be available online when published.
NRAO want my reduction script to add to their online tutorial.