Masers and the Process of High-mass Star Formation

1. Masers and the Process of High-mass Star Formation Simon Ellingsen University of Tasmania

2. Outline • An overview of masers in high-mass star formation regions. • Useful properties of masers. • Measuring accurate distances. • Masers as probes of the physical conditions and evolutionary state. • Masers as probes of the kinematics Great Barriers in High-Mass Star Formation 13-17 September 2010

3. Star Formation Masers – the current state of play • Masers have been observed from transitions of OH, H2O, CH3OH, SiO, H2CO, NH3, … • There are only a handful of transitions which are both strong and common : • OH at 1665/1667 MHz (hundreds) • Water at 22 GHz (thousands) • Methanol at 6.7, 12.2 GHz (class II) and 44 GHz (class I) (~ 1000 and many hundreds resp.) Great Barriers in High-Mass Star Formation 13-17 September 2010

4. Water and Class I methanol • Water and class I methanol masers are collisionally pumped. • The water masers often occur in high-velocity, collimated outflows, but more generally trace post-shocked gas. • The class I methanol masers are seen at the interface between outflows and ambient molecular gas (see Talk by Maxim) Great Barriers in High-Mass Star Formation 13-17 September 2010

5. IRAS16547-4247/G343.12-0.06 The location of class I methanol masers (yellow contours) compared to the radio continuum (red contours) and H2 emission (false colours) Voronkov et al. (2006) Great Barriers in High-Mass Star Formation 13-17 September 2010

6. OH and Class II methanol • The OH and class II methanol masers are both radiatively pumped. • They are located in the warm (~100 K), dense (~106 cm-3) molecular gas close to the high-mass star. • Some may lie within disks, or jets, but the majority don’t. • There are numerous higher frequency, rarer OH and class II methanol maser transitions. Great Barriers in High-Mass Star Formation 13-17 September 2010

7. + = 6.7 GHz methanol masers + = OH masers + = water masers Green contours = 95 GHz methanol Black contours = 3cm continuum. Blue = 3.6 μm Green = 4.5 μm Red = 8.0 μm Great Barriers in High-Mass Star Formation 13-17 September 2010

8. Relationship to other HMSF tracers • Some masers are associated with UCHII regions (esp. OH and class I methanol). • Most methanol and water masers are associated with objects which show no centimetre radio continuum emission. • Most (perhaps all) methanol masers are associated with MIR sources (24 μm), all are associated with millimetre dust continuum emission. • Many are associated with IRDC and/or EGOs/green fuzzies. Most maser sources are likely at the hot-core, or earlier evolutionary phases. Great Barriers in High-Mass Star Formation 13-17 September 2010

9. Useful properties of masers • Maser emission is very compact, the majority of it originates on scales of a few milliarcseconds. • Maser emission is often intense. Some sources have peak flux densities of more than 1000 Jy, most are > 1 Jy. • Most of the transitions are at wavelengths longer than ~7mm. • The masers are confined to relatively small volumes and trace a specific range of physical conditions. Great Barriers in High-Mass Star Formation 13-17 September 2010

10. Masers and the High-mass star formation process • Accurate distances through trigonometric parallax. • Accurate 3D kinematics through proper motion. • High-resolution information on magnetic fields through maser polarization. • High-resolution information on temperatures and densities through multi-transition studies and modeling. • Estimates of evolutionary phase through statistical studies of maser presence/absence. • Maser variability – is also telling us something, but at the moment we don’t know what. Great Barriers in High-Mass Star Formation 13-17 September 2010

11. Accurate Distances • In the last 3-4 years the VLBA, VERA and more recently the EVN have been able to achieve astrometric accuracy of around 10 μas. • So it is now possible to determine distances accurate at the 10% level using Trigonometric Parallax out to the Galactic Centre. • Measurements have been made towards ~20 Galactic HMSF regions and show kinematic distances often wrong by a factor of 2! Great Barriers in High-Mass Star Formation 13-17 September 2010

12. Reid et al. (2009) combined the results from VLBA and VERA observations of 18 HMSF regions. In this figure blue dots are 12.2 GHz methanol masers (VLBA), green are primarily water masers Great Barriers in High-Mass Star Formation 13-17 September 2010

13. The maser parallax observations also give 3D velocity information. • The interpretation of the implied Galactic Dynamics is still somewhat controversial… • However, they present strong evidence for significant non-circular motions in HMSF regions irrespective of Galactic Dynamics => beware standard kinematic dist. for HMSF! • If you want an accurate distance to your favorite object, talk sweetly to a maser + VLBI person. Great Barriers in High-Mass Star Formation 13-17 September 2010

14. Masers and Evolution? • Any type of maser requires a specific range of physical conditions. • Those transitions which are strong and common are either – not very fussy, or trace conditions which arise commonly and persist. • In many HMSF regions more than one type of maser transition is detected, but there are some which only show one species or transition. • Does the presence/absence of different species trace an evolutionary timeline? Great Barriers in High-Mass Star Formation 13-17 September 2010

15. Methanol Maser pumping models Cragg et al. (2005) Great Barriers in High-Mass Star Formation 13-17 September 2010

16. Masers and Evolution? • Any type of maser requires a specific range of physical conditions. • Those transitions which are strong and common are either – not very fussy, or trace conditions which arise commonly and persist. • In many HMSF regions more than one type of maser transition is detected, but there are some which only show one species or transition. • Does the presence/absence of different species trace an evolutionary timeline? Great Barriers in High-Mass Star Formation 13-17 September 2010

17. water • Assuming that each maser species arises only once and that mass plays only a secondary role the following sequence has been inferred : • The relationship between the major class II methanol transitions, OH masers and UCHII regions is reasonably well established. • How water and class I methanol masers may fit into this scheme is a work in progress. OH class II methanol 6.7 GHz 12.2 GHz UCHII class I methanol Relative lifetime (x 104 years) 0 1 2 3 4 5 Great Barriers in High-Mass Star Formation 13-17 September 2010

18. The Enigmatic Class I masers • Class I methanol masers are often associated with outflow-molecular gas interaction. • Hence our naïve expectation might be that they should be one of the youngest/earliest maser transitions to arise. • A recent large survey for class I methanol masers towards EGOs (Chen et al. 2010, submitted) suggests that this is not the case. • This survey for 95 GHz class I methanol masers with Mopra detected 105 from 193 sites searched. Great Barriers in High-Mass Star Formation 13-17 September 2010

19. Class I methanol masers were detected towards 55% of EGOs. • Sensitivity and transition selection is playing a role here and the “true” association rate is definitely higher (see e.g. Cyganowski et al. 2009 who achieved a rate of 89% for sensitive 44 GHz observations). • Detection rates were highest for those EGOs with an associated class II methanol , water or OH masers (80%, 95% & 93% respectively). Great Barriers in High-Mass Star Formation 13-17 September 2010

20. These plots show the MIR colours for the EGO driving sources. Either the GLIMPSE point source within 2’’ of a class II maser, or that closest to catalogued EGO position (non-class II sources). Black squares – associated with both class I and II methanol. Open triangles – class II, no class I. Open circles – class I, no class II. The class I only methanol masers are less red than either class II only or class I+II sources. What does this mean? Great Barriers in High-Mass Star Formation 13-17 September 2010

21. These results suggest that either : • The class I only methanol masers are associated with lower-mass objects or • class I methanol masers can arise at more than one evolutionary phase during the HMSF process. • The first possibility is known to be true (e.g. Kalenskii, et al. 2010), however, EGOs are argued to only be associated with high-mass objects. • Class I masers have also been associated both with outflows, and with shocks associated with expanding HII regions (Voronkov et al. 2010). • Either hypothesis presents some difficulties for including class I masers in an HMSF evolutionary timeline. Great Barriers in High-Mass Star Formation 13-17 September 2010

22. EGOs water OH class II methanol 6.7 GHz 12.2 GHz UCHII class I methanol Relative lifetime (x 104 years) 0 1 2 3 4 5 Great Barriers in High-Mass Star Formation 13-17 September 2010

23. Kinematics from Masers • Perhaps the most important role masers have played in studies of high-mass star formation to date has been as high-resolution tracers of the kinematics. • However, VLBI proper motion observations reveal a bewildering range of morphologies : • Outflows (e.g. Genzel et al. 1981 ; Moscadelli et al. 2010) • Disks/Torus (e.g. Matthews et al. 2010 ; Sanna et al. 2010) • Rings (e.g. Bartkiewicz et al. 2008 ; Torrelles et al. 2001) • Expanding HII regions (e.g. Fish & Reid 2007) Great Barriers in High-Mass Star Formation 13-17 September 2010

24. methanol (green), water (red) and OH masers (blue), H2CO (triangle), 1.3cm continuum emission (dashed contours) towards G23.01-0.41 (Sanna et al. 2010b). H2O proper motions (Sanna et al. 2010b) Methanol proper motions (Sanna et al. 2010b) Great Barriers in High-Mass Star Formation 13-17 September 2010

25. Conclusions • Masers are playing an increasing role as tools for investigating a range of aspects of the process of high-mass star formation. • but they only trace a sub-set of the interesting objects… • Their utility is likely to further increase in the next 5 years, primarily as a result of • parallax/proper motion observations and • improved understanding of their relation to evolution state, magnetic field probes and variability. Great Barriers in High-Mass Star Formation 13-17 September 2010

26. Some maser-related posters P20 – Gallaway et al. MMB IR counterparts P24 – Green et al. MAGMO B fields from OH survey P28 – Hindson et al. G305 Complex P36 – Longmore et al. HOPS water masers P11 – Pandian et al. SEDs of maser YSOs P19 – Sawada-Satoh et al. methanol in S269 P26 – Surcis et al. masers and B fields. P32 – Torres et al. OH masers and B fields Great Barriers in High-Mass Star Formation 13-17 September 2010

27. Great Barriers in High-Mass Star Formation 13-17 September 2010

28. EGOs water OH class II methanol 6.7 GHz 12.2 GHz UCHII class I methanol Relative lifetime (x 104 years) 0 1 2 3 4 5 Great Barriers in High-Mass Star Formation 13-17 September 2010