107/108 GHz methanol masers with ALMA
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Transcript of 107/108 GHz methanol masers with ALMA
107/108 GHz methanol masers with ALMA
Simon EllingsenUniversity of Tasmania
Methanol masers – what and where
• Methanol masers are empirically divided into two groups:– Class I masers are associated with outflows and low velocity
shocks, they are collisionally pumped. Strong transitions at 36, 44, 95, 229 GHz.
– Class II masers are exclusively associated with the environment close to very young high-mass stars, they are radiatively pumped. Strong transitions at 6, 12, 107 GHz.
• You frequently find class I and II methanol masers associated with the same object, but not coincident.
• Often multiple class II (or class I) methanol transitions are observed to be coincident spatially and in velocity.
107 GHz methanol masers with ALMA
Great Barriers in High-Mass Star Formation 13-17 September 2010
+ = 6.7 GHz methanol masers
+ = OH masers
+ = water masers
Green contours = 95 GHz methanol
Black contours = 3cm continuum.
Blue = 3.6 μm
Green = 4.5 μm
Red = 8.0 μm
Methanol masers - Science
• What can you do with multiple coincident maser transitions?– Determine the physical conditions at very high
resolution, by modeling the observed ratio of the different transitions.
– Utilize the presence/absence of different transitions as an evolutionary clock.
107 GHz methanol masers with ALMA
Great Barriers in High-Mass Star Formation 13-17 September 2010
Methanol Maser pumping models
Cragg et al. (2005)
Methanol masers - Science
• What can you do with multiple coincident maser transitions?– Determine the physical conditions at very high
resolution, by modeling the observed ratio of the different transitions.
– Utilize the presence/absence of different transitions as an evolutionary clock.
107 GHz methanol masers with ALMA
water
class I methanol
class II methanol
UCHII
OH
10 2 3 4 5Relative lifetime (x 104 years)
6.7 GHz12.2 GHz
EGOs
Methanol masers in A+ rotational subspecies :Class IClass II
Figure courtesy of Maxim Voronkov.
107 GHz methanol masers with ALMA
Low-hanging fruit• The 107 GHz (31-40 A+) methanol
masers are direct analogues of the 6.7 GHz (51-60 A+).
• Approximately 25 107 GHz masers have been detected in previous single-dish searches (e.g. Caswell et al. 2000).
• These look like ideal targets for cycle 0 science :– Intense– Compact– Low frequency
107 GHz methanol masers with ALMA
Caswell et al. (2000)
Class I masers
• There are a number of relatively strong and common class I transitions in band 3 (84 GHz and 95 GHz).
• Also the 229 GHz transition falls within band 6.
• These are more spatially distributed and may be better targets for later cycles.
107 GHz methanol masers with ALMA
Conclusions
• ALMA observations of 107 GHz methanol will allow us to– Constrain the physical conditions in the masing
regions.– Constrain evolutionary maser-based clocks.
107 GHz methanol masers with ALMA
- “close the loop” on the class II methanol masers.