1. Class I methanol masers and shocks
Max Voronkov
Software Scientist – ASKAP
In collaboration with: Caswell J.L., Ellingsen S.P., Britton T.R., Green J.A., Sobolev A.M.
8 July 2010

2. Introduction: two classes of methanol masers
Class I methanol (CH3OH) masers
Collisional excitation (e.g. by shocks)
Regions of star formation (possibly low-mass ones as well)
Usually offset from YSOs (up to a parsec)
Many maser spots scattered over tens of arcsec
Widespread masers: 36, 44, 84, 95 GHz
Rare/weak: 9.9, 23.4, series at 25, GHz
Class II methanol (CH3OH) masers
Radiational excitation (by infrared from YSO)
Regions of high mass star formation only
Located at the nearest vicinity of YSOs
Usually just one maser spot at the arcsec scale
Widespread masers: 6.7, 12 GHz
Rare/weak: 19.9, 23, 85/86, 37/38, 107, 108 GHz
Subject of this talk

3. Class I methanol masers in outflows

4. G309.38-0.13: high-velocity feature at 36 GHz
Background: Spitzer IRAC data
Red: 8.0 µm, green: 4.5 µm, blue: 3.6 µm
Excess of 4.5 µm may be a signature of
Shocks (Extented Green Objects)
Red contours: peak of the 36 GHz
emission in the cube
Circles/crosses: maser spots
Garay et al. (2002): to increase CH3OH
abundance shocks have to be mild
(shock velocities not much more than
10 km/s interaction with moving gas)

5. Search for 9.9 GHz methanol masers
These masers need higher than average temperatures
and densities to form
This is one of the rare class I masers
Only two sources were known prior to this work
Two new detections out of 48 targets observed
Detection limits as low as 0.1 Jy
ATCA observations (pre-CABB)
6A and 6C arrays
Continuum at 8.6 GHz as a by-product
Spectral resolution 0.12 km/s
Obtained absolute positions for masers

6. Sources detected at 9.9 GHz
Grayscale: 4.5 µm (above)
and NH3 (below)
(Ho et al. 1986; Garay et al. 1998)
Crosses: 9.9 GHz masers
Circles: 6.7 GHz masers (Phillips et al. 1998; Caswell 2010)
Contours: 8.6 GHz continuum (from Phillips et al for G331.13)
Ellipse: Extended Green Object (EGO)

7. Implications for the evolutionary sequence
Image credit: Cormac Purcell
Image credit: Simon Ellingsen
Ellingsen (2006): class I masers tend to be deeply embedded younger.
More than one phenomenon may be responsible for the class I masers
Stage with class I masers is likely to outlast 6.7 GHz (class II) masers
Whether class I masers can precede class II masers is unclear
A notable overlap with OH masers which are not associated with the 6.7 GHz methanol masers is expected

8. Search for methanol masers towards OH
The majority of class I methanol masers were found towards known class II masers at 6.7 GHz
Biased towards a particular evolutionary stage
Need blind surveys!
Blind surveys are impeded by the lack of a widespread low frequency class I maser (lowest sensible is 36 GHz!)
Search for class I methanol masers in old OH-selected SFR
Search for 44 GHz class I methanol masers towards OH masers not detected at 6.7 GHz in the Parkes Methanol Multibeam survey
Unfortunately delays of CABB zoom mode implementation slowed the project down

9. Search for methanol masers towards OH
The majority of class I methanol masers were found towards known class II masers at 6.7 GHz
Biased towards a particular evolutionary stage
Need blind surveys!
Blind surveys are impeded by the lack of a widespread low frequency class I maser (lowest sensible is 36 GHz!)
Search for class I methanol masers in old OH-selected SFR
Search for 44 GHz class I methanol masers towards OH masers not detected at 6.7 GHz in the Parkes Methanol Multibeam survey
Unfortunately delays of CABB zoom mode implementation slowed the project down

10. Observations without zooms
Coarse spectral resolution of 1 MHz = 6.8 km/s at 44 GHz
Not sensitive to weak masers (weaker than tens of Jy)
Can’t measure flux density and radial velocity accurately
Observed 19 OH masers which didn’t show up in MMB
Detected 10 methanol masers at 44 GHz (even without zooms!)
New 44 GHz maser G

11. Summary
We report the detection of a high-velocity spectral feature at 36 GHz in G (off by about 30 km s-1 from the peak velocity)
This is the largest velocity offset reported so far for a class I methanol maser source associated with a single molecular cloud.
Class I methanol masers may be caused by expanding HII regions
This is in addition to the outflow scenario
Applies to all class I maser transitions, not just to 9.9 GHz
The evolutionary stage with the class I maser activity is likely to
outlast the stage when the 6.7-GHz methanol masers are present
overlap in time with the stage when the OH masers are active
Search for the class I methanol masers at 44 GHz towards OH masers not associated with the 6.7 GHz masers was very successful
The detection rate exceeds 50% even without zoom modes!

12. Thank you Australia Telescope National Facility Max Voronkov
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Australia Telescope National Facility
Max Voronkov
Software Scientist (ASKAP)
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Thank you