Class I methanol masers and evolutionary stage of star-formation

Max VoronkovSoftware Scientist – ASKAP

In collaboration with: Caswell J.L., Ellingsen S.P., Britton T.R., Green J.A., Sobolev A.M.

10 December 2009

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 protostars (up to a parsec)

• Many maser spots scattered over tens of arcsec

• Widespread masers: 36, 44, 84, 95 GHz

• Rare/weak: 9.9, series at 25, 104.3 GHz

• Class II methanol (CH3OH) masers

• Regions of high mass star formation only

• Excited by infrared, located at the nearest vicinity of protostars

• 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

Class I methanol masers in outflows

Evolutionary stages of star-formation

• Different maser species may be good tracers of evolution!• OH masers trace late stage (e.g Forster & Caswell 1989)

• Methanol masers at 6.7 GHz trace earlier stages (little overlap with HII regions)

• Class I methanol masers ?

Image credit: Cormac Purcell

Evolution of HMSF as traced by masers

• Infrared data: sources with class I masers are more red (more embedded and therefore younger)

• Class I masers are associated with outflows: trace earlier stages

Diagram suggested by Ellingsen et al. (2007)

GLIMPSE colours for 6.7 GHz masers sources with and without class I maser (Ellingsen 2006)

Search for 9.9 GHz methanol masers

• 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

• Needs higher temperatures and densities to form

• 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

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Circles: 6.7 GHz masers (Phillips et al. 1998; Caswell, unpublished observations)

Contours: 8.6 GHz continuum (from Phillips et al. 1998 for G331.13)

Ellipse: Extended Green Object (EGO)

Implications for the sequence

Image credit: Cormac Purcell

Image credit: Simon Ellingsen

• 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

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

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

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 G307.808-0.456

Summary

• 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!

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Thank you

Australia Telescope National FacilityMax VoronkovSoftware Scientist (ASKAP)

Phone: 02 9372 4427Email: maxim.voronkov@csiro.auWeb: http://www.narrabri.atnf.csiro.au/~vor010