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Observational Characterization of Magnetized Turbulence in Molecular Clouds

Observational Characterization of Magnetized Turbulence in Molecular Clouds. Martin Houde The University of Western Ontario. IAU, Beijing - 21 Aug. 2012. Outline. Main Observational Methods and Techniques Polarization Measurements Zeeman Dust mapping *

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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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