1. 107/108 GHz methanol masers with ALMA
Simon Ellingsen
University of Tasmania
My own very personal ranking of telescopes is based largely on how many methanol maser transitions it can observe. Using this metric the ATCA scores very well, what I’d like to talk about today is how ALMA rates using my personal criteria.

2. 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

3. 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
Class II methanol masers peak at km/s, velocity range km/s
Water maser (blue) at -46 km/s, 4.4 Jy peak at 15:55: :43:05.2 from Breen et al. 2010
OH masers (pink) at 15:55: :43:05.6 Caswell, Haynes & Goss (1980), cover velocity range -50 – 35 km/s, peak -43 km/s.
Class I methanol masers peak at -43 km/s, velocity range km/s
Great Barriers in High-Mass Star Formation September 2010

4. 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.
I’m focusing here only on the science which comes from looking at the multiple methanol transitions.
107 GHz methanol masers with ALMA

5. Great Barriers in High-Mass Star Formation 13-17 September 2010
Methanol Maser pumping models
Cragg et al. (2005)
Conversely those transitions which are rare must require a more narrow range of conditions, or conditions which arise less often. The presence of a rare maser is therefore useful for pinning down the physical conditions in at least a small part of the gas in a star forming region.
This figure shows why the presence/absence of the different maser transitions is potentially very useful. It is clear from these plots of maser brightness temperature for a range of class II methanol maser transitions that the 6.6 and 12.2 GHz masers are both excited over a wide range of parameter space, which overlaps to a very large degree. Therefore sources which show 6.7 GHz methanol masers without 12.2 GHz methanol masers must lie in the relatively small range of parameter space where the two do not overlap. Which also means that most maser sources are close to the region where the maser emission switches on/off, hence small changes in physical conditions can produce large changes in maser brightness.
Great Barriers in High-Mass Star Formation September 2010

6. Methanol masers - Science
water
class I methanol
class II methanol
UCHII OH 1 2 3 4 5
Relative lifetime (x 104 years)
6.7 GHz
12.2 GHz
EGOs
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.
I’m focusing here only on the science which comes from looking at the multiple methanol transitions.
107 GHz methanol masers with ALMA

7. 107 GHz methanol masers with ALMA
Methanol masers in A+ rotational subspecies : Class I Class II Figure courtesy of Maxim Voronkov.
Notice that for the class II masers the J quantum number of final state usually is one greater than J of the initial state. For the class I masers it is the opposite.
Broadly speaking the strongest maser transitions are those at lower frequencies (e.g. the 6.7 GHz class II masers, the 36 and 44 GHz class I masers). The higher frequency transmissions from both classes are typically significantly weaker than the strength of the lower frequency transitions in both cases.
However, it seems that this effect is stronger for the class II masers than the class I.
From where we sit at the moment, it seems that the main class II methanol masers which might be observed with ALMA are the 107 and 156 GHz methanol masers which are in ALMA band 3 and the (as yet) unfunded band 4
107 GHz methanol masers with ALMA

8. 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 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
Emphasise that they can’t be observed with the ATCA. Only a couple of northern sources have been observed with BIMA.
Caswell et al. (2000)
107 GHz methanol masers with ALMA

9. 107 GHz methanol masers with ALMA
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

10. 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.
- “close the loop” on the class II methanol masers.
107 GHz methanol masers with ALMA