1. New Class I methanol masers
Max Voronkov
Software Scientist – ASKAP
In collaboration with: Caswell J.L., Ellingsen S.P., Breen S.L., Britton T.R., Green J.A., Sobolev A.M., Walsh A.J. + some data from Zinchenko I.I. and Salii S.V.
3 February 2012

2. Data taken with ATCA, ATCA+CABB, Mopra

3. Introduction: two classes of methanol masers
Class I methanol (CH3OH) masers
Scattered around YSOs (up to a parsec or so)
Many maser spots at arcsec resolution
Collisional excitation (e.g. by shocks)
Regions of star formation
low-mass: Kalenskii et al., 2011, MNRAS, 405, 613
Widespread masers: 36, 44, 84, 95 GHz, …
Rare/weak: 9.9, 23.4, series at 25, GHz
Class II methanol (CH3OH) masers
Located in the nearest vicinity of YSOs
Usually just one maser spot at the arcsec scale
Radiational excitation (by infrared from YSO)
Regions of high mass star formation only
Widespread masers: 6.7, 12 GHz
Rare/weak: 19.9, 23, 28, 85/86, 37/38, 107, 108 GHz
Subject of this talk

4. Methanol maser series Red is class I Green is class II
Interestingly, all but one class II maser series go downwards and eventually terminate at the lowest possible level for that particular series
Class I masers are more interesting for ALMA

5. Widespread class I masers
J0-(J-1)1 A+: 44/95 GHz series
Major published interferometric surveys: Kurtz et al. (2004, ApJS, 155, 149); Cyganowski et al. (2009, ApJ, 702, 1615)
Lots of single dish work: e.g. Haschick et al. (1990, ApJ, 354, 556); Slysh et al. (1994, MNRAS, 268, 464); Val’tts et al. (2000, MNRAS, 317, 315); Ellingsen (2005, MNRAS, 359, 1498); Fontani et al. (2010, A&A, 2010, 517A, 56); Chen et al. (2011, ApJS, 196, 9) + heaps of unpublished data from Breen, Ellingsen and myself
J-1-(J-1)0 E: 36/84 GHz series
Single source interferometric papers, e.g. Fish et al. (2011, ApJ, 729, 14); Voronkov et al. (2010, MNRAS, 408, 133)
Single dish work, e.g. Haschick et al. (1989, ApJ, 339, 949); Kalenskii et al. (2001, ARep, 45, 26)
+ Talk by Stan Kurtz
We’ve completed an ATCA survey at 36 and 44 GHz of all (deeply) southern class I masers known at the time of observations
- some results are shown later in this presentation

6. G343.12-0.06 (outflow association)
See Voronkov et al. (2006, MNRAS, 373, 411)
for more info on the source
G (outflow association)
These are new results from the 36/44 GHz ATCA survey
Some maser spots are associated with the outflow traced by H2 emission
Rare masers are confined to a single spot near the brightest H2 knot
+ 44 GHz masers
x 36 GHz masers

7. ATCA 36/44 GHz survey: G
Red: 8.0 µm, green: 4.5 µm, blue: 3.6 µm
Positions of masers overlaid on the 3-colour Spitzer IRAC image
Extended infrared sources with emission excess at 4.5 µm (EGOs) may trace shocked gas
Association with EGOs -a similar result to that of Cyganowski et al. (2009, ApJ, 702, 1615)
+ 44 GHz masers
 6.7 GHz maser

8. ATCA 36/44 GHz survey: G
Red: 8.0 µm, green: 4.5 µm, blue: 3.6 µm
Positions of masers overlaid on the 3-colour Spitzer IRAC image
Different transitions are highly complementary and are often crucial for the interpretation of morphology.
+ 44 GHz masers
x 36 GHz masers
 6.7 GHz maser

9. What does the theory say about this?
Sobolev et al. (2005, IAUS, 227, 174)
There are different pumping regimes, each favours a separate transition series.
The orientation of maser region w.r.t. the observer has a great influence on the 36/44 GHz flux density ratio (the same is true for the 84/95 GHz flux density ratio)
Maser region elongated along the line of sight is stronger at 44 GHz
Maser region elongated in the plane of the sky is stronger at 36 GHz
We still need to accurately test these predictions on a large sample of sources.
Models show quite clearly that rare/weak masers require more restricted range of physical conditions (mainly they need a higher temperature and density)

10. 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)
This is not the only such source. So far only blue-shifted high-velocity features were found and only at 36 GHz
+ 44 GHz masers
x 36 GHz masers
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)
Voronkov et al. (2010, MNRAS,408, 133)

11. J2-J1 E (25 GHz) methanol masers
Historically, the first methanol maser found in space (Barrett et al., 1971, ApJ, 168, 101)
Believed to be rare
ATCA survey of known class I maser sites brought up 66 detections out of 102 targets observed (Voronkov et al. 2007, IAUS, 242, 182); the majority are weaker than 1 Jy
Now reobserved with CABB - see the poster by Tui Britton
There are other detections, e.g. Brogan et al. (2011, ApJ, 739, 16)
+ talk at this meeting
Example of simultaneous 25 GHz spectra with CABB (Wilson et al., 2011, MNRAS, 416, 832)

12. VLBI observations of the class I masers
Early attempts were not very successful
Spots were resolved on long baselines
Commonly assumed sizes: au
Ask Karl Menten for more info
However,
We did not have accurate positions
We could not choose the best sources (there were no VLA or ATCA maps yet for a large number of sources)
Widespread masers like that at 44 GHz may not be the best targets
Observed 10 strongest 25 GHz (J=5&6) masers with LBA in July 2011
Correlated a couple of weeks ago, no results yet
As far as I know, VLBI was attempted at 44 GHz with KVN -
ask Kee-Tae Kim

13. Rare 9.9/104 GHz methanol masers
These masers belong to J-1-(J-1)-2 E series.
E at 9.9 GHz
Maser in W33-Met was known from the single dish work of Slysh et al. (1993, ApJ, 413, L133)
Sensitive (limits as low as 0.1 Jy) ATCA survey of Voronkov et al. (2010, MNRAS, 405, 2471): two new detections out of 46 new targets observed
Two single source papers: Voronkov et al. (2011, MNRAS, 413, 2339 and 2006, MNRAS, 373, 411)
E at 104 GHz
Single dish surveys: Voronkov et al. (2005, Ap&SS, 295, 217; Voronkov et al. 2007, IAUS, 242, 182)
The only additional source is G
Interferometry - single source G , Voronkov et al. (2006, MNRAS, 373, 411)

14. Association with expanding Hii regions?
Class I masers may be associated with ionisation shocks driven by an expanding HII region into surrounding molecular cloud
This result is currently based on observations of 9.9 GHz masers (need higher temperature and density to form than 36/44 GHz) but should apply to other class I methanol masers as well
Another possible example
(but it has an outflow as well)
See Voronkov et al. (2010, MNRAS, 405, 2471)
Crosses: 9.9 GHz masers
Open boxes: 6.7 GHz maser (Caswell 2010)
Contours: 8.6 GHz continuum
Grayscale: Spitzer 4.5µm
Grayscale: NH3 (Ho et al. 1986; Garay et al. 1998) G
W33-Met (G ) G

15. Implications for the evolutionary sequence
Image credit: Cormac Purcell
Ellingsen et al. (2007, IAUS, 242, 213); Breen et al. (2010)
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
There is a notable overlap with OH masers which are not associated with the 6.7 GHz methanol masers

16. Evolutionary stages traced by class I masers
Comparison of different class I transitions is still immature
But attempts are made, e.g. Pratap et al. (2008, AJ, 135, 1718)
Best to understand first how class I masers fit into common picture based on other maser species (i.e. OH, water, class II methanol)
The majority of known class I methanol masers have a class II maser at 6.7 GHz in the vicinity
Sample is biased towards a particular evolutionary stage
Need blind surveys! But they are hard to do at high frequency
Some attempts: MALT45 (Walsh et al.), also ask Gary Fuller
Follow-up of Methanol Multi-beam (MMB) 6.7-GHz detections
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
CABB delays slowed the project down
Detected 10 masers out of 19 targets despite a very coarse spectral resolution (almost 7 km/s)

17. G new 23.4 GHz maser
First maser in J1-(J-1)2 A- series (J=10)
Found in HOPS (unbiased survey at 12mm; PI: Andrew Walsh) towards only one location
HOPS is not sensitive to weak masers (< 10 Jy)
Predicted in models (e.g. Cragg et al. 1992) as a class I maser
Followed up with ATCA
Observed the new maser transition + 7 lines of the 25 GHz maser series
Also discovered an unusually strong 9.9-GHz maser (and only 5th found so far)
There is at least one more 23.4 GHz maser (in G the jet/outflow source shown before)
See Voronkov et al. (2011, MNRAS, 413, 2339) for details

18. G357.97-0.16 - new 23.4 GHz maser Also see a poster by Tui Britton
Yellow contour shows 12mm continuum (50% of the peak)
Cyan contours show 16cm continuum (observations by CASS summer students A.Dicker, C.-E. Green and D.Compton )
Red: 8.0 µm, green: 4.5 µm, blue: 3.6 µm
- IRAC images
Squares are class II methanol masers at 6.7 GHz
Crosses are water masers
Circle shows position of rare class I masers
Northern source has an OH maser, the associated H2O maser has a large velocity spread with almost continuous emission across 180 km/s

19. Class I methanol masers with ALMA
Prediction for masers in ALMA bands 6 and 7 based on low-frequency data
36/84 GHz: E at 229, E at 278 GHz, E at 327 GHz
e.g., Slysh et al. (2002, ARep, 46, 49); Fish et al. (2011, ApJ, 729, 14)
Recent SMA observations of S255 by Zinchenko, Salii, Sobolev et al.
44/95 GHz: A+ at 250, A+ at 303, A+ at 356 GHz
9.9/104 GHz: E at 242, E at 287, E at 331 GHz
23.4 GHz: A- at 237, A- at 291, A- at 346 GHz
25 GHz J2-J1E is a cm-wavelength series, but J2-(J-1)1E gives some mm masers
In particular, the 42-31E maser at 218 GHz has been found in S255
These masers correspond to excitation energies of about K

20. Summary Studies of different transitions are very complementary
Filling the dots in morphology, high-velocity features, modelling
Rare/weak masers (9.9, 23.4, 25 and 104 GHz) trace stronger shocks/ higher temperatures and densities
Outflow shocks vs. shocks caused by other mechanisms
Some class I masers may be caused by expanding HII regions
Implications for maser-based evolutionary sequence
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
Many candidate class I maser transitions can be observed by ALMA
G and G are promising targets - we could even double the number of known maser transitions

21. Thank you Australia Telescope National Facility Max Voronkov
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Max Voronkov
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