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 Frequencies from 1 GHz to 105 GHz

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

Present mm capabilities CABB wide band mode

CABB - Zoom modes (example: 1 MHz zoom)

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) ResolutionVelocity resolutionVelocity coverage WideZoom3mm7mm12mm3mm7mm12mm MHzkHzm/skm/s

Zoom modes - current experience 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 1 MHz zoom mode works now No major issues with the data reduction Observe calibrators with the same setup! Master/slave frequency configurations are supported by the online scheduler 64 MHz zoom mode currently gives only 1 zoom window and no wide- band continuum window

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

Where do we find them? Star-forming regions in our Galaxy High-mass: OH, H 2 O, CH 3 OH (both classes), a few SiO, NH 3 and formaldehyde Low- and intermediate-mass: OH, H 2 O, CH 3 OH (class I) Supernova remnants: OH Late-type stars and circumstellar environment OH, H 2 O, SiO, SiS, possibly HCN and HC 3 N Extragalactic masers (also known as kilomasers, megamasers, etc) Star-forming regions in LMC and nearby galaxies (OH, H 2 O, class II CH 3 OH) Late-type stars in LMC (SiO, OH) galactic nuclei (H 2 O)

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

Introduction: two classes of methanol masers Class I methanol (CH 3 OH) 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, GHz Class II methanol (CH 3 OH) 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 of this talk

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

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

Some maser spots are associated with an outflow traced by H 2 emission Rare masers are confined to a single spot near the brightest H 2 knot G (outflow association) Voronkov et al. (2006)

G : 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 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 CH 3 OH abundance shocks have to be mild (shock velocities not much more than 10 km/s interaction with moving gas) Voronkov et al. (2010)

Association with expanding Hii regions? Grayscale: NH 3 (Ho et al. 1986; Garay et al. 1998) Crosses: 9.9 GHz masers Open boxes: 6.7 GHz maser (Caswell 2010) Contours: 8.6 GHz continuum W33-Met (G ) G 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 Class I masers may be associated with ionisation shocks driven by an expanding HII region into surrounding molecular cloud G Grayscale: Spitzer 4.5µm Another possible example (but it has an outflow as well)

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 G

G 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 G the jet/outflow source shown before)

G 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 H 2 O maser has a large velocity spread with almost continuous emission across 180 km/s

Periodically variable masers Light curve of the class II maser at 6.7 GHz in G (Hartebeesthoek data; Goedhart et al.) Can distinguish a flare of the continuum from the pumping boost 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

Monitoring of class I maser in G 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 Currently covered about 60% of the period

Summary We report the detection of a high-velocity spectral feature at 36 GHz in G (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 G (new methanol maser!)

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