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Observational Characterization of Magnetized Turbulence in Molecular Clouds

Explore various observational methods, polarization measurements, Zeeman effect, and new techniques for studying magnetized turbulence in molecular clouds. Discover insights from polarization maps, structure functions, and simulations, alongside discussions on the Goldreich-Kylafis effect. Uncover the complexities of circular polarization, photon scattering models, and resonant scattering effects in molecular lines. This research aims to deepen our understanding of turbulence and magnetic fields in molecular environments.

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Observational Characterization of Magnetized Turbulence in Molecular Clouds

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

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

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

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

  9. Magnetized Turbulence Autocorrelation function M51 - Effelsberg (100m) + VLA Fletcher et al. 2011 (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 230.5 GHz with FSPPol at the CSO • Is it an instrumental artifact? • Measured twice: Nov. 2011 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 265.8 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 230.5 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 Houde et al. 2012 IAU, Beijing - 21 Aug. 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

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