Non-Zeeman Circular Polarization of Rotational Molecular Spectral - - PowerPoint PPT Presentation

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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

SLIDE 1

Non-Zeeman Circular Polarization

f Rotational Molecular Spectral

Lines

Martin Houde The University of Western Ontario

non-Zeeman CP - TagKASI 2018

SLIDE 2

Non-Zeeman Circular Polarization

f Rotational Molecular Spectral

Lines

Martin Houde The University of Western Ontario

non-Zeeman CP - TagKASI 2018

and velocity gradients

SLIDE 3

Non-Zeeman Circular Polarization

f Rotational Molecular Spectral

Lines

Martin Houde The University of Western Ontario

non-Zeeman CP - TagKASI 2018

SLIDE 4

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

SLIDE 5

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

SLIDE 6

B Fields and Molecular Lines - Goldreich-Kylafis Effect

non-Zeeman CP - TagKASI 2018

from R. M. Crutcher

SLIDE 7

B Fields and Molecular Lines - Goldreich-Kylafis Effect

Linear polarization

measurements in Orion KL of the rotational line at 230.5 GHz

btained at the CSO with

FSPPol

Zeeman splitting ~ 0.2 mHz/µG

– 4 orders of magnitude less than CN

12C16O J = 2 → 1

( )

Houde+ 2013, ApJ, 764, 24

non-Zeeman CP - TagKASI 2018

SLIDE 8

Goldreich-Kylafis (CO Linear Polarization)

Complementary to dust

polarization

E.g., can be use to trace
utflows
GK effect has a 90 deg

ambiguity…

We understand

molecules better than dust

but there’s a complication

(opportunity)… Lai+ 2003, ApJ 598, 392

DR21(OH)

non-Zeeman CP - TagKASI 2018

SLIDE 9

Goldreich-Kylafis Effect- A Generalization to Circular Polarization?

Is it possible to have imbalance between the population
f 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 ⇐

σ -lines

non-Zeeman CP - TagKASI 2018

SLIDE 10

CSO / FSPPol - CP Measurements

Circular polarization

measurements in Orion KL of the rotational line at 230.5 GHz with FSPPol

Zeeman splitting ~ 0.2 mHz/µG

– 4 orders of magnitude less than CN

12C16O J = 2 → 1

( )

Houde+ 2013, ApJ, 764, 24

non-Zeeman CP - TagKASI 2018

SLIDE 11

How Can We Get CP? - (Faraday) Conversion of LP to CP

Linear Polarization Circular Polarization phase shift

non-Zeeman CP - TagKASI 2018

SLIDE 12

Model: Photon Scattering

It may be that and will scatter differently off a

molecule aligned with the B field

Radiation State of LP at angle θ θ = α ! + β ⊥ ! ⊥

non-Zeeman CP - TagKASI 2018

SLIDE 13

Model: Anisotropic Resonant Scattering

!1 " 1+ iφ!

( ) ! " e

iφ! !

⊥1 = ⊥ ψ 0 = a

lower state

!

"

radiation

!

→

absorption

b

excited state

! " −1

minus photon

! →

emission

a

lower state

!

"1

radiation

!

j time a′ a b

For one scattering the final state becomes After N scatterings !N " e

iNφ! ! ,

⊥ N = ⊥

non-Zeeman CP - TagKASI 2018

SLIDE 14

ARS: what do we need

SLIDE 15

Anisotropic Resonant Scattering

Radiation State of LP at angle θ θ = α ! + β ⊥ with α = cos θ

( ), β = sin θ ( )

j time a′ a b

′ θ ! αe−iφ " + β ⊥ Q ∝α 2 − β 2 U ∝2αβcos φ

( )

V ∝2αβsin φ

( )

χ = 1 2arctan U Q ⎛ ⎝ ⎜ ⎞ ⎠ ⎟ U0 =Ucos φ

( )+V sin φ ( )

non-Zeeman CP - TagKASI 2018

SLIDE 16

IRAM 30m/APEX - SR IC 443 (G)

CO

Hezareh+ 2013, A&A, 558, 45

non-Zeeman CP - TagKASI 2018

SLIDE 17

IRAM 30m/APEX - SR IC 443 (G)

CO Dust

Hezareh+ 2013, A&A, 558, 45

non-Zeeman CP - TagKASI 2018

SLIDE 18

IRAM 30m/APEX - SR IC 443 (G)

CO Dust

Hezareh+ 2013, A&A, 558, 45

non-Zeeman CP - TagKASI 2018

SLIDE 19

IRAM 30m/APEX - SR IC 443 (G)

Hezareh+ 2013, A&A, 558, 45

Dust CO

non-Zeeman CP - TagKASI 2018

SLIDE 20

IRAM 30m/APEX - SR IC 443 (G)

Hezareh+ 2013, A&A, 558, 45

Dust CO

non-Zeeman CP - TagKASI 2018

SLIDE 21

Line Polarization / Dispersion - SNR IC 443

non-Zeeman CP - TagKASI 2018

SLIDE 22

Line Polarization / Dispersion - SNR IC 443

non-Zeeman CP - TagKASI 2018

SLIDE 23

Chamma+ 2018, MNRAS, 480, 1323

More evidence… with the SMA

non-Zeeman CP - TagKASI 2018

Chamma+ 2018, MNRAS, 480, 1323

SLIDE 24

Chamma+ 2018, MNRAS, 480, 1323

More evidence… with the SMA

non-Zeeman CP - TagKASI 2018

Chamma+ 2018, MNRAS, 480, 1323

SLIDE 25

Preliminary - OMC-2 FIR 4 (FSPPol/CSO)

non-Zeeman CP - TagKASI 2018

SLIDE 26

CH3OH CI H2CO SO2

CSO / FSPPol - LP measurements

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

SLIDE 27

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.

Bpos

⇒ Effect proportional to ⇐

φ ! −ω Z

2 sin2 ι

( )l4 nCO3πc2Aba

4!ω0

3ω 2

u ω

( ) ′

u ω

( ) I ω ( )

non-Zeeman CP - TagKASI 2018

SLIDE 28

Merci !

non-Zeeman CP - TagKASI 2018