Non-Zeeman Circular Polarization of Rotational Molecular Spectral Lines Martin Houde The University of Western Ontario non-Zeeman CP - TagKASI 2018
Non-Zeeman Circular Polarization of Rotational Molecular Spectral and velocity gradients Lines Martin Houde The University of Western Ontario non-Zeeman CP - TagKASI 2018
Non-Zeeman Circular Polarization of Rotational Molecular Spectral Lines Martin Houde The University of Western Ontario non-Zeeman CP - TagKASI 2018
The Message… • We are underutilizing molecular lines for polarimetry • But if you use them, then be careful because there is an issue… – … however, that may not be a bad thing. non-Zeeman CP - TagKASI 2018
Outline • Magnetic Fields and Molecules (before) • Zeeman Effect (not in this presentation…) • Goldreich-Kylafis Effect (linear polarization) • Circular Polarization Measurements of Molecular Spectral Lines • Orion KL (FSPPol/CSO) • Physical Model • SNR IC 443(G) (IRAM 30m) • more evidence non-Zeeman CP - TagKASI 2018
B Fields and Molecular Lines - Goldreich-Kylafis Effect from R. M. Crutcher non-Zeeman CP - TagKASI 2018
B Fields and Molecular Lines - Goldreich-Kylafis Effect • Linear polarization measurements in Orion KL of ( ) 12 C 16 O J = 2 → 1 the rotational line at 230.5 GHz obtained at the CSO with FSPPol • Zeeman splitting ~ 0.2 mHz/ µ G – 4 orders of magnitude less than CN Houde+ 2013, ApJ, 764, 24 non-Zeeman CP - TagKASI 2018
Goldreich-Kylafis (CO Linear Polarization) • Complementary to dust DR21(OH) polarization • E.g., can be use to trace outflows • GK effect has a 90 deg ambiguity… • We understand molecules better than dust • but there’s a complication (opportunity)… Lai+ 2003, ApJ 598, 392 non-Zeeman CP - TagKASI 2018
Goldreich-Kylafis Effect- A Generalization to Circular Polarization? • Is it possible to have imbalance between the population σ -lines 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 ... • ⇒ Should not expect significant CP in molecular spectral lines weakly sensitive to the Zeeman effect ⇐ � 7 non-Zeeman CP - TagKASI 2018
CSO / FSPPol - CP Measurements • Circular polarization measurements in Orion KL of ( ) 12 C 16 O J = 2 → 1 the rotational line at 230.5 GHz with FSPPol • Zeeman splitting ~ 0.2 mHz/ µ G – 4 orders of magnitude less than CN Houde+ 2013, ApJ, 764, 24 non-Zeeman CP - TagKASI 2018
How Can We Get CP? - (Faraday) Conversion of LP to CP Circular Polarization Linear Polarization phase shift non-Zeeman CP - TagKASI 2018
Model: Photon Scattering Radiation State of LP at angle θ θ = α ! + β ⊥ ! ⊥ • It may be that and will scatter differently off a molecule aligned with the B field � 10 non-Zeeman CP - TagKASI 2018
Model: Anisotropic Resonant Scattering absorption emission ψ 0 = a → ! " − 1 ! → " " 1 b a ! ! ! ! j lower radiation excited minus lower radiation state state photon state a ′ For one scattering the final state becomes ( ) ! " e i φ ! ! ! 1 " 1 + i φ ! b time ⊥ 1 = ⊥ After N scatterings a iN φ ! ! , ⊥ N = ⊥ ! N " e � 11 non-Zeeman CP - TagKASI 2018
ARS: what do we need � 12
Anisotropic Resonant Scattering Radiation State of LP at angle θ θ = α ! + β ⊥ ( ) , β = sin θ ( ) with α = cos θ ! α e − i φ " + β ⊥ ′ θ j Q ∝ α 2 − β 2 a ′ - ( ) U ∝ 2 αβ cos φ - ( ) - V ∝ 2 αβ sin φ b time ⎛ ⎞ χ = 1 2arctan U ⎜ ⎟ ⎝ Q ⎠ a ( ) + V sin φ ( ) U 0 = U cos φ non-Zeeman CP - TagKASI 2018
IRAM 30m/APEX - SR IC 443 (G) CO Hezareh+ 2013, A&A, 558, 45 non-Zeeman CP - TagKASI 2018
IRAM 30m/APEX - SR IC 443 (G) CO Dust Hezareh+ 2013, A&A, 558, 45 non-Zeeman CP - TagKASI 2018
IRAM 30m/APEX - SR IC 443 (G) CO Dust Hezareh+ 2013, A&A, 558, 45 non-Zeeman CP - TagKASI 2018
IRAM 30m/APEX - SR IC 443 (G) CO Dust Hezareh+ 2013, A&A, 558, 45 non-Zeeman CP - TagKASI 2018
IRAM 30m/APEX - SR IC 443 (G) CO Dust Hezareh+ 2013, A&A, 558, 45 non-Zeeman CP - TagKASI 2018
Line Polarization / Dispersion - SNR IC 443 � 16 non-Zeeman CP - TagKASI 2018
Line Polarization / Dispersion - SNR IC 443 � 16 non-Zeeman CP - TagKASI 2018
More evidence… with the SMA Chamma+ 2018, MNRAS, 480, 1323 Chamma+ 2018, MNRAS, 480, 1323 non-Zeeman CP - TagKASI 2018
More evidence… with the SMA Chamma+ 2018, MNRAS, 480, 1323 Chamma+ 2018, MNRAS, 480, 1323 non-Zeeman CP - TagKASI 2018
Preliminary - OMC-2 FIR 4 (FSPPol/CSO) non-Zeeman CP - TagKASI 2018
CSO / FSPPol - LP SO 2 H 2 CO measurements CH 3 OH C I • CO is not the only species to exhibit polarization • Different species/lines will trace different density regimes -> tomography • Much better suited for the DCF technique non-Zeeman CP - TagKASI 2018
Summary • Detection of non-Zeeman circular polarization in CO and other spectral lines. • Appears to be widespread. • We can account for the levels of CP through anisotropic resonant scattering (Orion KL, SNR IC 443(G), and IK Tau). • Analysis from linear polarization of spectral lines (e.g., for Davis-Chandrasekhar-Fermi analysis) CANNOT be performed without considering CP. ( ) l 4 n CO 3 π c 2 A ba ( ) ′ ( ) I ω ( ) 2 sin 2 ι φ ! − ω Z u ω u ω 4 ! ω 0 3 ω 2 ⇒ Effect proportional to ⇐ 2 B pos non-Zeeman CP - TagKASI 2018
Merci ! non-Zeeman CP - TagKASI 2018
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