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 * • 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

Polarization Maps - what are they good for? OMC-1 - SHARP, 350 and 450 µm E field B field Vaillancourt et al. , 2008, Ap. J, 679, L 25 IAU, Beijing - 21 Aug. 2012

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

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

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

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

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

Magnetized Turbulence Autocorrelation function M 51 - Effelsberg (100 m) + VLA Fletcher et al. 2011 (MNRAS) Houde et al. 2012 IAU, Beijing - 21 Aug. 2012 Cho, Lazarian, and Vishniac 2002

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

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

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

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 ⇐ 13 IAU, Beijing - 21 Aug. 2012

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

Non-Zeeman Circular Polarization Houde et al. 2012 • 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. . . 15 IAU, Beijing - 21 Aug. 2012

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 16 IAU, Beijing - 21 Aug. 2012

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

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 18 IAU, Beijing - 21 Aug. 2012

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. 19 IAU, Beijing - 21 Aug. 2012

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

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. . . 21 IAU, Beijing - 21 Aug. 2012

Merci! Western- 24 May 2012