Transcript New Class I methanol masers Max Voronkov Software Scientist – ASKAP In collaboration with: Caswell J.L., Ellingsen S.P., Breen S.L., Britton T.R., Green.

New Class I methanol masers
Max Voronkov
Software Scientist – ASKAP
In collaboration with: Caswell J.L., Ellingsen S.P., Breen S.L., Britton T.R., Green J.A., Sobolev A.M.,
Walsh A.J. + some data from Zinchenko I.I. and Salii S.V.
3 February 2012
Data taken with ATCA, ATCA+CABB, Mopra
Introduction: two classes of methanol masers
• Class I methanol (CH3OH) masers
• Scattered around YSOs (up to a parsec or so)
• Many maser spots at arcsec resolution
• Collisional excitation (e.g. by shocks)
• Regions of star formation
• low-mass: Kalenskii et al., 2011, MNRAS, 405, 613
• 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 in 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, 28, 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
Widespread class I masers
• J0-(J-1)1 A+: 44/95 GHz series
• Major published interferometric surveys: Kurtz et al. (2004, ApJS,
155, 149); Cyganowski et al. (2009, ApJ, 702, 1615) + Talk by Stan Kurtz
• Lots of single dish work: e.g. Haschick et al. (1990, ApJ, 354, 556);
Slysh et al. (1994, MNRAS, 268, 464); Val’tts et al. (2000, MNRAS,
317, 315); Ellingsen (2005, MNRAS, 359, 1498); Fontani et al. (2010,
A&A, 2010, 517A, 56); Chen et al. (2011, ApJS, 196, 9) + heaps of
unpublished data from Breen, Ellingsen and myself
• J-1-(J-1)0 E: 36/84 GHz series
• Single source interferometric papers, e.g. Fish et al. (2011, ApJ,
729, 14); Voronkov et al. (2010, MNRAS, 408, 133)
• Single dish work, e.g. Haschick et al. (1989, ApJ, 339, 949);
Kalenskii et al. (2001, ARep, 45, 26)
We’ve completed an ATCA survey at 36 and 44 GHz of all (deeply)
southern class I masers known at the time of observations
- some results are shown later in this presentation
See Voronkov et al.
G343.12-0.06 (outflow association) (2006, MNRAS, 373, 411)
for more info on the source
These are new
results from the
36/44 GHz ATCA
survey
Some maser spots
are associated
with the outflow
traced by H2
emission
Rare masers are
confined to a
single spot near
the brightest H2
knot
+ 44 GHz masers
x 36 GHz masers
ATCA 36/44 GHz survey: G333.466-0.164
Red: 8.0 µm, green: 4.5 µm, blue: 3.6 µm
Positions of masers
overlaid on the 3-colour
Spitzer IRAC image
Extended infrared sources
with emission excess at
4.5 µm (EGOs) may trace
shocked gas
Association with EGOs a similar result to that of
Cyganowski et al. (2009,
ApJ, 702, 1615)
+ 44 GHz masers
 6.7 GHz maser
ATCA 36/44 GHz survey: G333.466-0.164
Red: 8.0 µm, green: 4.5 µm, blue: 3.6 µm
Positions of masers
overlaid on the 3-colour
Spitzer IRAC image
Different transitions are
highly complementary
and are often crucial for
the interpretation of
morphology.
+ 44 GHz masers
x 36 GHz masers
 6.7 GHz maser
What does the theory say about this?
• Sobolev et al. (2005, IAUS, 227, 174)
• There are different pumping regimes, each favours a separate
transition series.
• The orientation of maser region w.r.t. the observer has a great
influence on the 36/44 GHz flux density ratio (the same is true for the
84/95 GHz flux density ratio)
• Maser region elongated along the line of sight is stronger at 44 GHz
• Maser region elongated in the plane of the sky is stronger at 36 GHz
We still need to accurately test these predictions on a large sample of sources.
Models show quite clearly that rare/weak masers require more restricted
range of physical conditions (mainly they need a higher temperature and
density)
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)
This is not the only such source. So far
only blue-shifted high-velocity features
were found and only at 36 GHz
+ 44 GHz masers
x
36 GHz masers
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, MNRAS,408, 133)
J2-J1 E (25 GHz) methanol masers
• Historically, the first methanol
maser found in space (Barrett et
al., 1971, ApJ, 168, 101)
• Believed to be rare
• ATCA survey of known class I
maser sites brought up 66
detections out of 102 targets
observed (Voronkov et al. 2007,
IAUS, 242, 182); the majority are
weaker than 1 Jy
• Now reobserved with CABB - see
the poster by Tui Britton
• There are other detections, e.g.
Brogan et al. (2011, ApJ, 739, 16)
+ talk at this meeting
Example of simultaneous 25 GHz spectra with
CABB (Wilson et al., 2011, MNRAS, 416, 832)
VLBI observations of the class I masers
• Early attempts were not very successful
• Spots were resolved on long baselines
• Commonly assumed sizes: 10-100 au
Ask Karl Menten for more info
However,
• We did not have accurate positions
• We could not choose the best sources (there were no VLA or ATCA
maps yet for a large number of sources)
• Widespread masers like that at 44 GHz may not be the best targets
• Observed 10 strongest 25 GHz (J=5&6) masers with LBA in July 2011
• Correlated a couple of weeks ago, no results yet
• As far as I know, VLBI was attempted at 44 GHz with KVN ask Kee-Tae Kim
Rare 9.9/104 GHz methanol masers
These masers belong to J-1-(J-1)-2 E series.
• 9-1-8-2 E at 9.9 GHz
• Maser in W33-Met was known from the single dish
work of Slysh et al. (1993, ApJ, 413, L133)
• Sensitive (limits as low as 0.1 Jy) ATCA survey of
Voronkov et al. (2010, MNRAS, 405, 2471): two new
detections out of 46 new targets observed
• Two single source papers: Voronkov et al. (2011,
MNRAS, 413, 2339 and 2006, MNRAS, 373, 411)
• 11-1-10-2 E at 104 GHz
• Single dish surveys: Voronkov et al. (2005, Ap&SS,
295, 217; Voronkov et al. 2007, IAUS, 242, 182)
• The only additional source is G305.21+0.21
• Interferometry - single source G343.12-0.06,
Voronkov et al. (2006, MNRAS, 373, 411)
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
See Voronkov et al. (2010, MNRAS, 405, 2471)
(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
G331.13-0.24
W33-Met (G12.80-0.19)
G19.61-0.23
Implications for the evolutionary sequence
Image credit: Cormac Purcell
Ellingsen et al. (2007, IAUS, 242, 213); Breen et al. (2010)
• 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
• There is a notable overlap with OH masers which are not associated with
the 6.7 GHz methanol masers
Evolutionary stages traced by class I masers
• Comparison of different class I transitions is still immature
• But attempts are made, e.g. Pratap et al. (2008, AJ, 135, 1718)
• Best to understand first how class I masers fit into common picture
based on other maser species (i.e. OH, water, class II methanol)
• The majority of known class I methanol masers have a class II
maser at 6.7 GHz in the vicinity
• Sample is biased towards a particular evolutionary stage
• Need blind surveys! But they are hard to do at high frequency
• Some attempts: MALT45 (Walsh et al.), also ask Gary Fuller
• Follow-up of Methanol Multi-beam (MMB) 6.7-GHz detections
• 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
• CABB delays slowed the project down
• Detected 10 masers out of 19 targets despite a very coarse spectral
resolution (almost 7 km/s)
G357.97-0.16 - new 23.4 GHz maser
• First maser in J1-(J-1)2 A- series (J=10)
• 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)
See Voronkov et al. (2011, MNRAS, 413, 2339) for details
G357.97-0.16 - new 23.4 GHz maser
Also see a poster
by Tui Britton
Yellow contour shows 12mm
continuum (50% of the peak)
Cyan contours show 16cm
continuum (observations by
CASS summer students
A.Dicker, C.-E. Green and
D.Compton )
Red: 8.0 µm, green: 4.5 µm,
blue: 3.6 µm - IRAC images
Squares are class II methanol
masers at 6.7 GHz
Crosses are water masers
Circle shows position of rare
class I masers
Northern source has an OH maser, the associated H2O maser has a large
velocity spread with almost continuous emission across 180 km/s
Class I methanol masers with ALMA
• Prediction for masers in ALMA bands 6 and 7 based on low-frequency data
• 36/84 GHz: 8-1-70E at 229, 9-1-80E at 278 GHz, 10-1-90E at 327 GHz
• e.g., Slysh et al. (2002, ARep, 46, 49); Fish et al. (2011, ApJ, 729, 14)
• Recent SMA observations of S255 by Zinchenko, Salii, Sobolev et al.
• 44/95 GHz: 110-101A+ at 250, 120-111A+ at 303, 130-121A+ at 356 GHz
• 9.9/104 GHz: 14-1-13-2E at 242, 15-1-14-2E at 287, 16-1-15-2E at 331 GHz
• 23.4 GHz: 141-132A- at 237, 151-142A- at 291, 161-152A- at 346 GHz
• 25 GHz J2-J1E is a cm-wavelength series, but J2-(J-1)1E gives some mm masers
• In particular, the 42-31E maser at 218 GHz has been found in S255
These masers correspond to excitation energies of about 300-500 K
Summary
• Studies of different transitions are very complementary
• Filling the dots in morphology, high-velocity features, modelling
• Rare/weak masers (9.9, 23.4, 25 and 104 GHz) trace stronger shocks/
higher temperatures and densities
• Outflow shocks vs. shocks caused by other mechanisms
• Some class I masers may be caused by expanding HII regions
• Implications for maser-based evolutionary sequence
• 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
• Many candidate class I maser transitions can be observed by ALMA
• G343.12-0.06 and G357.97-0.16 are promising targets - we could even
double the number of known maser transitions
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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