Image credit ALMA Masering ALMA Max Voronkov Software

Image credit: ALMA Masering ALMA Max Voronkov Software Scientist – ASKAP 14 th 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, H 2 O, CH 3 OH (both classes), a few Si. O, 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, Si. S, 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 (Si. O, OH) • Galactic nuclei (H 2 O)

Two classes of methanol masers • Class I methanol (CH 3 OH) 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 (CH 3 OH) 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 k. Hz 62. 5 MHz/2048 channels (mode 18) 6 211 -275 GHz 90 k. Hz 62. 5 MHz/2048 channels (mode 18) 7 275 -373 GHz 125 k. Hz As above, or 500 MHz/4096 channels (mode 9) 9 602 -720 GHz 240 k. Hz 500 MHz/4096 channels (mode 9) The full 2 GHz bandwidth mode is not very useful for masers

G 9. 62+0. 20 E: 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 3 mm 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 J 1 -(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 J 1 -(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: W 33(OH) (~10 Jy at 23. 1 GHz) and NGC 6334 -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 J 2 -(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 - W 3(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 J 2 -(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 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 72 -63 Known masers

G 357. 97 -0. 16 (good maser target for ALMA) Red contour shows 12 mm 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

G 343. 12 -0. 06 (outflow association) • 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 309. 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) Grayscale: Spitzer 4. 5µm G 331. 13 -0. 24 Crosses: 9. 9 GHz masers Open boxes: 6. 7 GHz maser (Caswell 2010) Contours: 8. 6 GHz continuum Grayscale: NH 3 (Ho et al. 1986; Garay et al. 1998) W 33 -Met (G 12. 80 -0. 19) G 19. 61 -0. 23

Class I methanol maser series J 0 -(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 A+ 95 GHz 80 -71 110 -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 J 0 -(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 G 357. 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 J 1 -(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: G 357. 97 -0. 16 (~20 Jy at 23. 4 GHz) and G 343. 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

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/~vor 010 Thank you Contact Us Phone: 1300 363 400 or +61 3 9545 2176 Email: enquiries@csiro. au Web: www. csiro. au