Transcript 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.,

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)
Resolution
Wide Zoom
Velocity resolution
3mm
7mm
12mm
Velocity coverage
3mm
m/s
7mm
12mm
MHz
kHz
km/s
1
0.5
1.6
3.8
7.1
3.1
7.5
14.3
4
2
6.3
15
29
12.6
30
57
16
8
25
60
114
51
120
229
64
32
101
240
457
202
480
914
Zoom modes - current experience
1 MHz zoom mode works now
64 MHz zoom mode currently gives
only 1 zoom window and no wideband 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
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, 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)
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
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
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
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
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)
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)
Grayscale: Spitzer 4.5µm
G331.13-0.24
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)
W33-Met (G12.80-0.19)
G19.61-0.23
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
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)
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
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
Monitoring of class I maser in G331.13-0.24
Currently covered about
60% of the period
Class I maser
Class II maser
• There is a dip in the
light curve for both
class I and class II
masers
• Class I maser may
have a monotonic fall
near the end of the
curve when the flux of
class II maser rises
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!)
Australia Telescope National Facility
Max Voronkov
Software Scientist (ASKAP)
Phone: 02 9372 4427
Email: [email protected]
Web: http://www.narrabri.atnf.csiro.au/~vor010
Thank you
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