Masers Surveys with Mopra: Which is best 7 or 3 mm? Simon Ellingsen, Maxim Voronkov & Shari Breen

1. Masers Surveys with Mopra: Which is best 7 or 3 mm?Simon Ellingsen, Maxim Voronkov & Shari Breen 3 November 2008

2. Overview • What maser transitions lie in the 7 and 3 mm frequency bands? • What science could be done with large-scale surveys in these transitions? • The optimal maser configuration. • What sensitivity is required? Maser Surveys with Mopra: Which is best 7 or 3 mm?

3. Masers at millimetre wavelengths • Most of the strong, well studied maser transitions are at centimetre wavelengths - why? • At higher frequencies the number of maser transitions increases, but they are typically less intense and less common than those at centimetre wavelengths. • In both the 7 and 3 mm bands the dominant maser transitions are SiO from late-type stars and class I methanol masers. • The class I methanol masers trace outflows and are quite distinct from the better studied 6.7 GHz (class II) masers. Maser Surveys with Mopra: Which is best 7 or 3 mm?

4. Masers in the 7 mm band Maser Surveys with Mopra: Which is best 7 or 3 mm?

5. Masers in the 3 mm band Maser Surveys with Mopra: Which is best 7 or 3 mm?

6. Class I methanol masers - poor cousins • Methanol maser transitions are empirically divided into two classes on the basis of where they arise. • Class II methanol masers are associated with high-mass star formation regions. They are typically found close to IR sources, OH and water masers (e.g. 6.7, 12.2 GHz). • Class I methanol masers are associated with interactions between outflows and molecular gas, they are offset from IR sources and other types of masers (e.g. 36, 44, 95 GHz). • Theoretically the empirical difference arises from different pumping schemes - collisional for class I, radiative for class II. Maser Surveys with Mopra: Which is best 7 or 3 mm?

7. Maser Surveys with Mopra: Which is best 7 or 3 mm?

8. Class I methanol masers - poor cousins • Methanol maser transitions are empirically divided into two classes on the basis of where they arise. • Class II methanol masers are associated with high-mass star formation regions. They are typically found close to IR sources, OH and water masers (e.g. 6.7, 12.2 GHz). • Class I methanol masers are associated with interactions between outflows and molecular gas, they are offset from IR sources and other types of masers (e.g. 36, 44, 95 GHz). • Theoretically the empirical difference arises from different pumping schemes - collisional for class I, radiative for class II. Maser Surveys with Mopra: Which is best 7 or 3 mm?

9. Science with Class I masers • The association of class I methanol masers with outflows has led to the suggestion that they may trace a very early stage of high-mass star formation. • There are no substantial, sensitive unbiased searches for class I masers. The best targeting strategy is to search towards known class II methanol masers (Ellingsen 2005). • It appears that some class I masers are associated with lower-mass star formation (Kalenskii et al. 2006). • They are potentially powerful probes of the physical conditions at multiple locations in the star forming region. Maser Surveys with Mopra: Which is best 7 or 3 mm?

10. Class I in IRAS16547-4247 Red contours = 25 GHz continuum Yellow contours = 95 GHz class I Colour image = Shock-excited H2 (Voronkov et al. 2006) Maser Surveys with Mopra: Which is best 7 or 3 mm?

11. SiO - Probing Galactic dynamics • Searches for OH/IR stars at 1612 MHz have previously been used to study Galactic structure (Sevenster, Chapman, Habing et al.) • More than 2000 SiO masers are now known, primarily in the Northern hemisphere and from targeted searches (Deguchi et al. 2004) • In addition to Galactic structure SiO masers can be used to investigate stellar evolution, stellar mergers, open star and globular clusters. Maser Surveys with Mopra: Which is best 7 or 3 mm?

12. Galactic Distribution of SiO Masers(Deguchi et al. 2007) Maser Surveys with Mopra: Which is best 7 or 3 mm?

13. SiO - Probing Galactic dynamics • Searches for OH/IR stars at 1612 MHz have previously been used to study Galactic structure (Sevenster, Chapman, Habing et al.) • More than 2000 SiO masers are now known, primarily in the Northern hemisphere and from targeted searches (Deguchi et al. 2004) • In addition to Galactic structure SiO masers can be used to investigate stellar evolution, stellar mergers, open star and globular clusters. Maser Surveys with Mopra: Which is best 7 or 3 mm?

14. 95 GHz Class I Methanol in the DQS • The DQS CS observations included the 95 GHz class I methanol maser transition in the band. • The DQS observations (zoom mode) had TRMS ~ 0.2-0.3 K at the maser frequency. • There are two previously known masers in the region covered, one of which was detected. • This suggests that there would be around 3 detections per sq. degree at this sensitivity. Maser Surveys with Mopra: Which is best 7 or 3 mm?

15. 95 GHz class I methanol masers in the DQS(cube courtesy of Nadia Lo) Known source Possible New Detection Maser Surveys with Mopra: Which is best 7 or 3 mm?

16. 95 GHz Class I Methanol in the DQS • The DQS CS observations included the 95 GHz class I methanol maser transition in the band. • The DQS observations (zoom mode) had TRMS ~ 0.2-0.3 K at the maser frequency. • There are two previously known masers in the region covered, one of which was detected. • This suggests that there would be around 3 detections per sq. degree at this sensitivity. Maser Surveys with Mopra: Which is best 7 or 3 mm?

17. The Best Option for Masers • The best maser science would be achieved from a sensitive search for class I methanol and SiO masers. • The best wavelength range in which to do this is the 7mm band (both system performance and maser intensity are better there). • With 42-50 GHz frequency setup you get multiple SiO transitions, class I methanol, thermal methanol at 48 GHz, CS(1-0) + isotopes, HCCCN, CCS. • Zoom mode gives approximately 900 km/s velocity coverage at 0.21 km/s resolution for up to 16 sub-bands. • Using the ‘strawman’ 7mm survey specifications and CMZ results as a guide we would expect TRMS = 0.12 K (1 pass) Maser Surveys with Mopra: Which is best 7 or 3 mm?

18. Does the Strawman stand up? • Deguchi et al. (2004) surveyed 400 colour-selected IRAS sources and detected 254 SiO masers in the 43 GHz lines (RMS ~0.07 K). • A 1-pass Mopra survey would detect 37% of the Nobeyama sources and a 2-pass survey would detect 51%. • Targeted 44 GHz class I methanol maser (Slysh et al. 1994 & Kurtz et al. 2004) suggest a similar scenario for those. • Assuming the SiO and class I masers show similar flux density distributions, I estimate approximately 20 class I maser detections and a similar number of SiO per sq deg. • A 2-pass strawman survey is 3.1 years of telescope time to cover 90 sq degrees (HOPS) Maser Surveys with Mopra: Which is best 7 or 3 mm?

19. Maser Surveys with Mopra: Which is best 7 or 3 mm?

20. Does the Strawman stand up? • Deguchi et al. (2004) surveyed 400 colour-selected IRAS sources and detected 254 SiO masers in the 43 GHz lines (RMS ~0.07 K). • A 1-pass Mopra survey would detect 37% of the Nobeyama sources and a 2-pass survey would detect 51%. • Targeted 44 GHz class I methanol maser (Slysh et al. 1994 & Kurtz et al. 2004) suggest a similar scenario for those. • Assuming the SiO and class I masers show similar flux density distrubutions, I estimate approximately 20 class I maser detections and a similar number of SiO per sq deg. • A 2-pass strawman survey is 3.1 years of telescope time to cover 90 sq degrees (HOPS) Maser Surveys with Mopra: Which is best 7 or 3 mm?

21. Thermal + Masers = Complementary • Masers are good at signposting interesting regions (e.g. young star formation regions, outflows etc) and can be used to measure kinematics. • The masers trace “special” conditions, but generally it is easier and more reliable to use thermal lines to estimate important physical parameters (temperature, density etc). • Thermal observations at the maser locations are critical to better understanding the star formation and/or outflow physics (as well as how the masers are produced). • Thermal methanol can measure the temperature, CS traces the dense gas, thermal SiO the outflows etc. Maser Surveys with Mopra: Which is best 7 or 3 mm?

22. Kalenskii et al. (2007): Rotation diagrams from 96.7 GHz series of methanol (similar to 48 GHz series). Multiple series gives better constraints. Maser Surveys with Mopra: Which is best 7 or 3 mm?

23. ATCA + CABB better for masers? • To determine associations and make the most of any science from maser surveys requires accurate positions for the masers => ATCA observations of the detections. • The ATCA achieves the same sensitivity as the Mopra Strawman 7mm survey in 10 seconds onsource. • The ATCA could potentially observe 0.1 sq deg per hour (onsource), but a practical implementation with current limitations probably requires a factor of several slower. • With CABB it would be possible to simultaneously observe the SiO, Class I methanol and continuum (hypercompact HII region search). Maser Surveys with Mopra: Which is best 7 or 3 mm?

24. Mopra observations (Maxim Voronkov) of 36 GHz class I methanol masers in the low-mass star forming region BHR71. Maser Surveys with Mopra: Which is best 7 or 3 mm?

25. Conclusions • The requirements of maser and thermal surveys are not particularly compatible: • At 7mm the masers are stronger, but the thermal lines are weaker and less prevalent. • At 3mm the masers are weaker, the system is worse, achieving worthwhile sensitivity very difficult. • A smaller-scale maser survey (with the ATCA) of part of the Mopra survey region may yield the best science. Maser Surveys with Mopra: Which is best 7 or 3 mm?