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

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

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

4. Maser Surveys with Mopra: Which is best 7 or 3 mm? Masers in the 7 mm band Frequency (GHz) Molecule/TypeComments 36.17 Methanol (class I) Common, strong 37.70, 38.29, 38.45 Methanol (class II) Rare, weak 42.37 - 43.12 SiO (late-type stars) Common, strong 44.07 Methanol (class I) Common, strong

5. Maser Surveys with Mopra: Which is best 7 or 3 mm? Masers in the 3 mm band Frequency (GHz) Molecule/TypeComments 84.52, 95.17 Methanol (class I) Common, strong 86.14 - 86.85 SiO (late-type stars) Common, strong 89.07 HCN (late-type stars) Weak, rare 86.2, 86.6, 86.9, 107.01, 108.0 Methanol (class II) Weak, rare Intermediate

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

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.

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

10. Maser Surveys with Mopra: Which is best 7 or 3 mm? Class I in IRAS16547-4247 Red contours = 25 GHz continuum Yellow contours = 95 GHz class I Colour image = Shock-excited H 2 (Voronkov et al. 2006)

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

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

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

14. Maser Surveys with Mopra: Which is best 7 or 3 mm? 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 T RMS ~ 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.

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

16. Maser Surveys with Mopra: Which is best 7 or 3 mm? 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 T RMS ~ 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.

17. Maser Surveys with Mopra: Which is best 7 or 3 mm? 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 T RMS = 0.12 K (1 pass)

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

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)

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

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

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

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

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