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Class I methanol masers in the regions of high-mass star-formation

Class I methanol masers in the regions of high-mass star-formation. Max Voronkov Software Scientist – ASKAP In collaboration with: Caswell J.L., Ellingsen S.P., Britton T.R., Green J.A., Sobolev A.M. 15 th September 2010. ATCA and CABB.

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Class I methanol masers in the regions of high-mass star-formation

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  1. Class I methanol masers in the regions of high-mass star-formation Max Voronkov Software Scientist – ASKAP In collaboration with: Caswell J.L., Ellingsen S.P., Britton T.R., Green J.A., Sobolev A.M. 15th September 2010

  2. ATCA and CABB All data presented in this talk were obtained with ATCA

  3. 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 YSOs (up to a parsec) • Many maser spots scattered over tens of arcsec • Widespread masers: 36, 44, 84, 95 GHz • Rare/weak: 9.9, 23.4, series at 25, 104.3 GHz • Class II methanol (CH3OH) masers • Radiational excitation (by infrared from YSO) • Regions of high mass star formation only • Located at the nearest vicinity of YSOs • 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 Subject ofthis talk

  4. G343.12-0.06 - outflow association • Some maser spots are associated with an outflow traced by H2 emission • Rare masers are confined to a single spot near the brightest H2 knot

  5. 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) Red contours: peak of the 36 GHz emission in the cube Circles/crosses: maser spots 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)

  6. G357.97-0.16 - new 23.4 GHz maser • First detection of the 23.4 GHz methanol maser in HOPS (PI: Andrew Walsh) towards a single source G357.97-0.16 • HOPS is not sensitive to weak masers (< a few Jy) • There is a water maser nearby with unusually large velocity spread/number of components • Predicted in models (e.g. Cragg et al. 1992) • Followed up with ATCA • Initially observed the new maser transition and 7 lines of the 25 GHz maser series • Position: 17h41m20s.05 -30o45’18’’.1 • Infrared properties are not exciting • 1.3 mJy (12 mm) continuum source ~ 10’’ offset • Test 9.9-GHz observations revealed a very strong maser at this frequency (5th found so far) • There is at least one more 23.4 GHz maser (in G343.12-0.06)

  7. Association with expanding Hii regions? ATCA survey for rare 9.9 GHz masers (need higher temperature and density to form) Class I masers may be associated with ionisation shocks Crosses: 9.9 GHz masers Circle: 6.7 GHz maser (Caswell 2010) Contours: 8.6 GHz continuum Grayscale: NH3(Ho et al. 1986; Garay et al. 1998) G19.61-0.23 W33-Met (G12.80-0.19)

  8. Implications for the evolutionary sequence Image credit: Cormac Purcell Image credit: Simon Ellingsen • 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 • A notable overlap with OH masers which are not associated with the 6.7 GHz methanol masers is expected

  9. 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

  10. 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

  11. 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

  12. Summary Class I methanol masers trace shocks caused by various phenomena Outflows, expanding Hii regions, cloud-cloud collisions Rare class I masers trace more energetic shocks Sometimes class I masers are the only available indication of shocks The evolutionary stage with class I masers 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! We report the detection of a high-velocity spectral feature at 36 GHz in G309.38-0.13 (off by about 30 km s-1 from the peak velocity) This is the largest velocity offset reported so far for a class I methanol maser source associated with a single molecular cloud. There are 23.4 GHz masers in G357.97-0.16 and G343.12-0.06

  13. Contact Us Phone: 1300 363 400 or +61 3 9545 2176 Email: enquiries@csiro.au Web: www.csiro.au Thank you Australia Telescope National Facility Max Voronkov Software Scientist (ASKAP) Phone: 02 9372 4427 Email: maxim.voronkov@csiro.au Web: http://www.narrabri.atnf.csiro.au/~vor010

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