Max Voronkov Software Scientist – ASKAP 14th December 2010 Image credit: ALMA Masering ALMA Max Voronkov Software Scientist – ASKAP 14th December 2010

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)

Two classes of methanol masers Class I methanol (CH3OH) masers Collisional excitation (e.g. by shocks) Regions of star formation (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

Masers as evolutionary clocks Image credit: Cormac Purcell Image credit: Simon Ellingsen Ellingsen (2006): class I masers tend to be deeply embedded younger. However recent data show that a significant number of class I masers trace relatively evolved stage of high-mass star-formation Whether class I masers can precede class II masers is unclear

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 I will discuss separately class I and class II methanol masers what we already know from low frequency observations which transitions can be observed with ALMA

My understanding of early ALMA Masers have narrow lines. For methanol we aim at 0.1 km/s resolution ALMA band Frequency Required resolution Correlator mode 3 84-116 GHz 40 kHz 62.5 MHz/2048 channels (mode 18) 6 211-275 GHz 90 kHz 7 275-373 GHz 125 kHz As above, or 500 MHz/4096 channels (mode 9) 9 602-720 GHz 240 kHz 500 MHz/4096 channels (mode 9) The full 2 GHz bandwidth mode is not very useful for masers

G9.62+0.20E: strong class II maser Fine structure at VLBI resolutions (12 GHz maser) 6.7 GHz and 12 GHz masers are the strongest class II methanol masers 107 and 108 GHz transitions are popular weaker masers Image: Goedhart et al. (2005)

ATCA and CABB at 3mm band Frequency below 105 GHz!

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 important for ALMA

Class II methanol maser series J1-(J+1)o A+ Most widespread class II methanol maser series Expect a single cluster of spots at arcsec scale (class II maser) Starts with strongest and most common maser at 6.7 GHz (5000 Jy) But not very impressive for early ALMA except for 107 GHz transition Similar situation is for the second strongest 12.2 GHz transition. Only 108 GHz seems to be useful for early ALMA Transition Approximate frequency 51-60 A+ 6.7 GHz 31-40 A+ 107 GHz 21-30 A+ 157 GHz 11-20 A+ 206 GHz Known masers

Class II methanol maser series J-2-(J+1)-1 E Weak class II methanol maser series (bright in the isotropic case, i.e. no beaming and same optical depth in all directions) Expect a single cluster of spots at arcsec scale (class II maser) Several sources known at 37 GHz (strongest ~ 300 Jy), to be followed up with ATCA in March (PI: S.Ellingsen) Transition Approximate frequency 7-2-8-1 E 37 GHz 6-2-7-1 E 85 GHz 3-2-4-1 E 230 GHz 2-2-3-1 E 279 GHz Known masers

Class II methanol maser series J1-(J+1)2 A- Rare class II methanol maser series (narrow range of density and methanol abundance, quite high densities of 107-108 cm-3) Expect a single cluster of spots at arcsec scale (class II maser) Only two reliable detections: W33(OH) (~10 Jy at 23.1 GHz) and NGC6334-I (~35 Jy at 23.1 GHz) + possible maser in NGC 7538 (0.5 Jy) Transition Approximate frequency 92-101 A+ 23.1 GHz 72-81 A+ 111 GHz 42-51 A+ 247 GHz 32-41 A+ 294 GHz 22-31 A+ 340 GHz Known maser

Class II methanol maser series J2-(J+1)1 A- Rare class II methanol maser series (it is not very clear to me why) Expect a single cluster of spots at arcsec scale (class II maser) Only one known source - W3(OH) Lack of extensive searches (so these masers may be more common than we think they are) Transition Approximate frequency 82-91 A- 28.9 GHz 72-81 A- 81 GHz 42-51 A- 235 GHz 32-41 A- 285 GHz 22-31 A- 335 GHz Known maser

Class II methanol maser series J2-(J-1)3 A± Rare class II methanol maser series (seem to require rather low densities about 104 cm-3) Pair of maser transitions for A+ and A- methanol at close frequencies Expect a single cluster of spots at arcsec scale (class II maser) Several sources known at 38/87 GHz The only class II series which does not terminate Transition Approximate frequency 62-53 A± 38 GHz 72-63 A± 87 GHz 102-93 A± 233 GHz 112-103 A± 281 GHz 122-113 A± 330 GHz 182-173 A± 624 GHz 192-183 A± 673 GHz Known masers

G357.97-0.16 (good maser target for ALMA) 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

G343.12-0.06 (outflow association) 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 Red contours: peak of the 36 GHz emission across the velocity cube Circles/crosses: maser spots (36/44 GHz) 36 GHz is one of the widespread Class I maser transitions

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: Spitzer 4.5µm Grayscale: NH3 (Ho et al. 1986; Garay et al. 1998) G331.13-0.24 W33-Met (G12.80-0.19) G19.61-0.23

Class I methanol maser series J0-(J-1)1 A+ The most widespread and strong class I methanol maser series Strongest known is ~ 500 Jy at 44 GHz Spots (sub-arcsec size) scattered over a large area of 1 arcmin or more Low contamination from thermal emission Transition Approximate frequency 70-61 A+ 44 GHz 80-71 A+ 95 GHz 110-101 A+ 251 GHz 120-111 A+ 303 GHz 130-121 A+ 356 GHz 180-171 A+ 623 GHz 190-181 A+ 677 GHz Known masers

Class I methanol maser series J-1-(J-1)0 E Second strongest class I methanol maser series, widespread Spots (sub-arcsec size) scattered over a large area of 1 arcmin or more Lower excitation energy than for J0-(J-1)1 A+, so thermal emission is more common (at least at 36 GHz) Transition Approximate frequency 4-1-30 E 36 GHz 5-1-40 E 84 GHz 6-1-70 E 133 GHz 8-1-70 E 229 GHz 9-1-80 E 279 GHz 10-1-90 E 327 GHz 16-1-150 E 623 GHz 17-1-160 E 673 GHz Known masers

Class I methanol maser series J-1-(J-1)-2 E Rare class I methanol maser series, traces strongest shocks Usually just a single maser spot (sub-arcsec size) Only few sources are known Strongest maser in G357.97-0.16 (~70 Jy at 9.9 GHz) Transition Approximate frequency 9-1-8-2 E 9.9 GHz 11-1-10-2 E 104.3 GHz 14-1-13-2 E 243 GHz 15-1-14-2 E 287 GHz 16-1-15-2 E 331 GHz 23-1-22-2 E 608 GHz 24-1-23-2 E 642 GHz 25-1-24-2 E 675 GHz 26-1-25-2 E 706 GHz Known masers

Class I methanol maser series J1-(J-1)2 A- Rare class I methanol maser series, traces strongest shocks Very new maser series, properties are not well understood yet Expect a single maser spot (sub-arcsec size) Only two sources known: G357.97-0.16 (~20 Jy at 23.4 GHz) and G343.12-0.06 (~7 Jy at 23.4 GHz) Transition Approximate frequency 101-92 A- 23.4 GHz 111-102 A- 76.3 GHz 141-132 A- 237 GHz 151-142 A- 291 GHz 161-152 A- 346 GHz 211-202 A- 625 GHz 221-212 A- 681 GHz Known maser

What would I do with ALMA? Look for various high-frequency class I methanol masers There are several good targets studied in detail with ATCA Tracing kinematics and morphology of shocks (outflows, expanding HII regions) at high resolution using widespread masers (e.g. 229 GHz) Start with known widespread maser transition, e.g. 229 GHz Constraining maser models Many new transitions are very important, currently number of transitions ~ number of unknowns in the model What is the highest frequency methanol maser? Applicable to both class I and class II, but more important for class I Follow up of the southern class II targets at 107/108 GHz Accurate positions, high-resolution maps to compare with 6.7-GHz Easy project with guaranteed success In addition, masers are good test targets

Thank you Australia Telescope National Facility Max Voronkov Contact Us Phone: 1300 363 400 or +61 3 9545 2176 Email: enquiries@csiro.au Web: www.csiro.au 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 Thank you