Upload
bertram-franklin
View
216
Download
0
Tags:
Embed Size (px)
Citation preview
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Circles: 6.7 GHz masers (Phillips et al. 1998; Caswell, unpublished observations)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!
Contact UsPhone: 1300 363 400 or +61 3 9545 2176
Email: [email protected] Web: www.csiro.au
Thank you
Australia Telescope National FacilityMax VoronkovSoftware Scientist (ASKAP)
Phone: 02 9372 4427Email: [email protected]: http://www.narrabri.atnf.csiro.au/~vor010