1. The University of Western Ontario
Observational Characterization of Magnetized Turbulence in Molecular Clouds
Martin Houde
The University of Western Ontario
IAU, Beijing - 21 Aug. 2012

2. Outline Main Observational Methods and Techniques
Polarization Measurements
Zeeman
Dust mapping *
Goldreich-Kylafis Effect (linear polarization)
Non-polarimetric
Ion-Neutral line widths *
New (and newish) Methods
Principal Component Analysis (M. Heyer et al.) *
Polarization of Atomic Lines (H. Yan)
Turbulent Reconnection (A. Lazarian) *
Polarization Intensity Gradients (P. M. Koch et al.)
Non-Zeeman Circular Polarization Measurements
* Explicitly treats turbulence and Magnetic Fields together
IAU, Beijing - 21 Aug. 2012

3. Polarization Maps - what are they good for?
OMC-1 - SHARP, 350 and 450 µm
E field
B field
Vaillancourt et al., 2008, ApJ, 679, L25
IAU, Beijing - 21 Aug. 2012

4. Polarization Maps - the CF Equation
turbulent
ordered field
IAU, Beijing - 21 Aug. 2012

5. Structure Function beam Dotson 1996 Houde et al. 2009, ApJ, 706, 1504
IAU, Beijing - 21 Aug. 2012
Falceta-Conçalves, Lazarian, and Kowal 2008

6. OMC-1 / SHARP - Results IAU, Beijing - 21 Aug. 2012
Houde et al. 2009, ApJ, 706, 1504

7. Simulation “Data” IAU, Beijing - 21 Aug. 2012
Hennebelle et al. 2011, A&A, 528, 72

8. Ambipolar Diffusion Cut-off
Orion KL (SMA)
IAU, Beijing - 21 Aug. 2012
Houde et al. 2011

9. Magnetized Turbulence
Autocorrelation function
M51 - Effelsberg (100m) + VLA
Fletcher et al (MNRAS)
Houde et al. 2012
Cho, Lazarian, and Vishniac 2002
IAU, Beijing - 21 Aug. 2012

10. Goldreich-Kylafis Effect (1981)
IAU, Beijing - 21 Aug. 2012

11. Goldreich-Kylafis Effect
Girart et al. 2004; Crutcher 2012
IAU, Beijing - 21 Aug. 2012

12. Goldreich-Kylafis Effect
Hezareh et al. 2012
IAU, Beijing - 21 Aug. 2012

13. Goldreich-Kylafis Effect - A Generalization to Circular Polarization?
Is it possible to have imbalance between the population of the sub-levels leading to the two ?
Short answer → no in the ISM...
Then, is there another way of generating circular polarization in molecular lines?
The answer → very difficult ...
⇒ We should not really expect CP in molecular lines ⇐
IAU, Beijing - 21 Aug. 2012

14. Non-Zeeman Circular Polarization
Cotton et al. 2011, ApJ, 736, 96: SiO masers in AGB star IK Tau
IAU, Beijing - 21 Aug. 2012

15. Non-Zeeman Circular Polarization
Circular polarization measurements in Orion KL of the rotational line at GHz with FSPPol at the CSO
Is it an instrumental artifact?
Measured twice: Nov and Feb. 2012
and...
Houde et al. 2012
IAU, Beijing - 21 Aug. 2012

16. Non-Zeeman Circular Polarization
Circular polarization measurements in Orion KL of the rotational line at GHz with FSPPol
Result: no CP down to less than approximately 0.1%
But the weaker HNCO line has CP at approximately - 2%!
Houde et al. 2012
IAU, Beijing - 21 Aug. 2012

17. Model: Photon Scattering
We expect that and will scatter differently off a CO molecule aligned with the B field
along B →
perp. to B →
IAU, Beijing - 21 Aug. 2012

18. Model: Resonant Scattering
We start with an initial condition, e.g., for the parallel state
For one scattering the final state becomes
After N scatterings
IAU, Beijing - 21 Aug. 2012

19. Model: Resonant Scattering
The Zeeman splitting for CO is small (e.g., with )
Remember that the frequency of radiation is GHz and the line width is on the order of 10 MHz...
The large number of scattering N is the key.
IAU, Beijing - 21 Aug. 2012

20. Model: Resonant Scattering
Effect is proportional to
IAU, Beijing - 21 Aug. 2012
Houde et al. 2012

21. Summary Zeeman effect still provides the only direct measurement on B
Several “new” techniques have developed to help characterize magnetized turbulence
e.g., Angular dispersion technique
New effects have been and are being discovered
Goldreich-Kylafis
ion-neutral line width comparisons
Atomic line polarization
turbulent reconnection
Circ. pol. through resonant scattering
I’m confident there is more to come...
IAU, Beijing - 21 Aug. 2012

22. Merci!
Western- 24 May 2012