1 / 26

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., Walsh A.J., Goedhart S., van der Walt D.J., Gaylard M. 13 June 2011. ATCA and CABB.

julietorres
Télécharger la présentation

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

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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., Walsh A.J., Goedhart S., van der Walt D.J., Gaylard M. 13 June 2011

  2. ATCA and CABB Frequencies from 1 GHz to 105 GHz

  3. Present cm capabilities CABB wide band mode New 16cm receivers replaced the old 20 and 13cm receivers We now have a single 2 GHz-wide band from 1.1 to 3.1 GHz

  4. Present mm capabilities CABB wide band mode

  5. CABB - Zoom modes (example: 1 MHz zoom)

  6. CABB - Zoom modes • The width of a filter bank channel is the width of each zoom window • Coarse resolution of the wide band = bandwidth of 1 zoom window • Stitching of adjacent zoom windows is automatic • Up to 16 zoom windows per each 2 GHz sub-band • Individual 2 GHz bands (and associated zooms) can be setup separately (i.e. can have different resolution)

  7. Zoom modes - current experience 1 MHz zoom mode works now 64 MHz zoom mode currently gives only 1 zoom window and no wide-band continuum window • No major issues with the data reduction • Observe calibrators with the same setup! • Master/slave frequency configurations are supported by the online scheduler • Projects with large number of sources & lines are tricky • Not all zoom arrangements work well (hard to know in advance) • Flagging of some baselines/polarisation products is often needed • Velocity coverage is narrow - hard to group sources

  8. Introduction: what is a maser? • A spectral line formed under special conditions (population inversion) • Narrow lines and high brightness temperature (for strong masers, i.e. <-1) • Possible in a limited number of transitions • Sensitive to physical conditions • It is harder to create high-frequency maser Bright masers are often used as tools: to locate targets, to measure parallax, etc Pumping process involves a delicate balance between radiative and collisional transitions. It is not understood well for some masers

  9. Where do we find them? • Star-forming regions in our Galaxy • High-mass: OH, H2O, CH3OH (both classes), a few SiO, NH3 and formaldehyde • Low- and intermediate-mass: OH, H2O, CH3OH (class I) • Supernova remnants: OH • Late-type stars and circumstellar environment • OH, H2O, SiO, SiS, possibly HCN and HC3N • Extragalactic masers (also known as kilomasers, megamasers, etc) • Star-forming regions in LMC and nearby galaxies (OH, H2O, class II CH3OH) • Late-type stars in LMC (SiO, OH) • galactic nuclei (H2O)

  10. I  methanol From now on, I will concentrate on (Galactic) methanol masers (mainly class I methanol masers) For a good review of (submillimetre) masers on other molecules see E.M.L. Humphreys, 2007, IAUS 242, 471

  11. Introduction: two classes of methanol masers • Class I methanol (CH3OH) masers • Usually offset from YSOs (up to a parsec) • Many maser spots scattered over tens of arcsec • Collisional excitation (e.g. by shocks) • Regions of star formation (low-mass ones as well) • Widespread masers: 36, 44, 84, 95 GHz • Rare/weak: 9.9, 23.4, series at 25, 104.3 GHz • Class II methanol (CH3OH) masers • Located at 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, 85/86, 37/38, 107, 108 GHz Subject ofthis talk

  12. 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

  13. Masers as evolutionary clocks Image credit: Cormac Purcell Image credit: Simon Ellingsen • Ellingsen (2006): class I masers tend to be deeply embedded younger. • Outflows are expected at very early stages and class I masers are likely to trace outflows

  14. G343.12-0.06 (outflow association) Voronkov et al. (2006) • 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

  15. 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) Voronkov et al. (2010)

  16. 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) Crosses: 9.9 GHz masers Open boxes: 6.7 GHz maser (Caswell 2010) Contours: 8.6 GHz continuum Grayscale: NH3(Ho et al. 1986; Garay et al. 1998) Grayscale: Spitzer 4.5µm G19.61-0.23 G331.13-0.24 W33-Met (G12.80-0.19)

  17. 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

  18. 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

  19. 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

  20. 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

  21. G357.97-0.16 - new 23.4 GHz maser • First detection of the 23.4 GHz methanol maser • 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 G343.12-0.06 - the jet/outflow source shown before)

  22. G357.97-0.16 - new 23.4 GHz maser Red contour shows 12mm continuum (50% of the peak) Squares are class II methanol masers at 6.7 GHz Crosses are water masers Circle shows position of rare class I masers Background is 8.0µm Spitzer IRAC image Northern source has an OH maser, the associated H2O maser has a large velocity spread with almost continuous emission across 180 km/s

  23. Periodically variable masers Light curve of the class II maser at 6.7 GHz in G331.13-0.24 (Hartebeesthoek data; Goedhart et al.) • There are 9 known periodically variable class II masers • Colliding wind binaries (van der Walt et al.) modulating the flux of HII region or accretion disc inhomogeneities/shadows (Sobolev et al.) • Little is known about variability of class I masers • Pumping of the class I and class II masers are in a direct conflict Can distinguish a flare of the continuum from the pumping boost

  24. Monitoring of class I maser in G331.13-0.24 Currently covered about 60% of the period • There is a dip in the light curve for both class I and class II masers Class I maser Class II maser • Class I maser may have a monotonic fall near the end of the curve when the flux of class II maser rises

  25. Summary 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. 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 with bad spectral resolution! There is a 23.4 GHz maser in G357.97-0.16 (new methanol maser!)

  26. 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

More Related