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

Max VoronkovSoftware Scientist – ASKAP

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

15th September 2010

ATCA and CABB

All data presented in this talk were obtained with ATCA

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 of

this talk

• 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

G343.12-0.06 - outflow association

G309.38-0.13: high-velocity feature at 36 GHz

Red: 8.0 µm, green: 4.5 µm, blue: 3.6 µm

Background: Spitzer IRAC data

Excess of 4.5 µm may be a signature ofShocks (Extented Green Objects)

Red contours: peak of the 36 GHz emission in the cube

Circles/crosses: maser spots

Garay et al. (2002): to increase CH3OHabundance shocks have to be mild(shock velocities not much more than 10 km/s interaction with moving gas)

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)

Association with expanding Hii regions?

Grayscale: NH3 (Ho et al. 1986; Garay et al. 1998)

Crosses: 9.9 GHz masersCircle: 6.7 GHz maser (Caswell 2010)

Contours: 8.6 GHz continuum

W33-Met (G12.80-0.19) G19.61-0.23

ATCA survey for rare 9.9 GHz masers (need higher temperature and density to form)

Class I masers may be associated with ionisation shocks

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

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 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

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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