University of Chicago 2007 July 30 SOFIA-POL 2007 The Infrared - Millimeter Polarization Spectrum John Vaillancourt California Institute of Technology

SOFIA-POL 20072007 July 30University of Chicago

The Infrared - Millimeter Polarization Spectrum

John Vaillancourt

California Institute of Technology


Observing Goals for FIR Polarization Spectra

• Characterize spectrum of different environments– Dense cloud cores– Cloud envelopes– Isolated cores / protostars

• T-tauri stars, Bok globules, other Class I - IV objects– Diffuse clouds - Different morphologies of IR Cirrus clouds

• Test models of alignment efficiency– Radiative torques increase alignment efficiency :

correlation between percent polarization and1. location of embedded stars (direct)2. location of dense clumpy material (inverse)3. dust temperature and/or spectral index (in p.o.s & along l.o.s.)

spectrum falls with (direct) spectrum rises with (inverse)

•B-field orientation changes with depth into cloud, or is unresolved

University of Chicago 2007 July 30 SOFIA-POL 2007

Magnetic field vs. Wavelength

60 m, 100 m, 350 m, 850 m

W3W51

Schleuning et al. 2000(350 m grayscale/contours)

Dotson et al. 2000Dotson et al. 2007Chrysostomou 2002


OMC-1: 450/350 m polarization spectrum

E-vectors

Orion Molecular Cloud: 3polarization vectors from SHARP/SHARC-IIRed = 350 m, Blue = 450 m, Purple = 850 (SCUBA)

10 arcsec beam

B-vectors


OMC-1: 450/350 m position angle variation

• Diamonds mark positions of BNKL, Trapezium, and KHW (north to south)

• Median angle difference (450) - (350) ~ -8 degrees (i.e. CW rotation with )

P > 3










Measured Polarization Spectra

Cloud EnvelopesVaillancourt 2002, 2007

Matthews et al. 2002

• P drops with increasing opacity in cores P ~ [1 - (0/]

• In cloud envelopes, polarization minimum ~ 350 m

Cloud CoresSchleuning 1998

Orion - KHW

Orion - KL

No

rma

lize

d P

ola

riza

tion






correlation between percent polarization and location of embedded stars (direct) location of dense clumpy material (inverse) dust temperature and/or spectral index (in p.o.s & along l.o.s.)




The Diffuse ISM: Infrared Cirrus Clouds- All grains exposed to same radiation field

• Finkbeiner, Davis, & Schlegel (FDS99) -- high latitude dust– T = 9.5 K, = 1.7 (silicate) – T = 16 K, = 2.7 (graphite)

• If silicate is polarized and

graphite unpolarized: TC > TSi, pC < pSi

Polarization rises with wavelength

IRAS 100m N. Gal. Pole (FDS99)

TA > TB, pA < pB


Improving the Polarization Spectrum:Wavelength

• SHARP @ CSO

• 350 & 450 m, 620 m

• SCUBA-2 @ JCMT

• 450 & 850 m

• Bolocam @ CSO - 1100 m

• HAWC @ SOFIA

• 53, 88, 155, 215 m


Improving the Polarization Spectrum: Sensitivity

p ~ 1% in 5 hrs

Improved sensitivity allows observations of more diffuse clouds

Instrument Wavelength

(m)

Beam size

(arcsec)

Sensitivity

(MJy/sr)

No. of IR

filaments

HAWC 88 9 400 2

155 15 100 49

215 21 60 53

SHARP 450 10 300 3

SCUBA-2* 850 15 2* 60*

BOLOCAM 1100 30 0.2 75

*Photometry only

• Consider filaments from Jackson, Werner, & Gautier 2003






correlation between percent polarization and location of embedded stars (direct) location of dense clumpy material (inverse) dust temperature and/or spectral index (in p.o.s & along l.o.s.)




A) Near embedded stars - warm dust, “aligned” via radiative torquesB) Cooler dust away from stars; optically opaque clumpsC) Cold surface layers exposed to the interstellar radiation field (ISRF)

TA > TB > TC

pA pC > pB

Model of Molecular Clouds

ISRF

Falling P-spectrum

TA>TB, pA>pB, A ~ B

Rising P-spectrum

TB>TC, pB<pC, B ~ C

or

TB~TC, pB<pC, B> C










Embedded Stars









TA > TB, pA > pB

Expected Polarization Spectra(Hildebrand et al. 1999)

Dust emission from

• a single grain species at

• a single temperature yields

a flat spectrum in the FIR/SMM

Dust emission from

• multiple grain species at

• multiple temperatures

TA > TB, pA < pB

€

P(ν ) = piFi(ν )

Ftot (ν )i

∑

Fi(ν ) = ν β iBν (Ti)

dP

dλ≠ 0 only if p1 ≠ p2 AND

€

T1 ≠ T2

or

β1 ≠ β 2


Polarization (%), Flux

(Jy/beam)

Temperature (K)

T2, Warm Component

28 K

52 K

Testing the Mixture ModelSpectralEnergyDistributions

T1, Cold Component

OMC-1

BNKL

M42

KHW

(Vaillancourt 2002)



E-vectors

Orion A Molecular Cloud (OMC-1): 3polarization vectors from SHARP/SHARC-II

Red = 350 m, Blue = 450 m

B-vectors

10 arcsec beam



• Diamonds mark positions of BNKL, Trapezium, and KHW (north to south)

• flip in ratio around BNKL also observed at P(100)/P(350) [Vaillancourt 2002]

• Median P(450) / P(350) ratio ~ 1.4

P > 3










Microwave PolarizationWMAP 3-year polarization results

(Page et al. 2006)

K-band: 23 GHz ~ 13 mm

W-band: 94 GHz ~ 3.2 mm

Infer CMB based on spectral dependence of known components

want to know dust pol’n at long wavelengths

3mm10mm

Bennett et al. 2003


Cloud CoresSchleuning 1998

Orion - KHW

Orion - KL

No

rma

lize

d P

ola

riza

tion

Polarization (%), Flux

(Jy/beam)

28 K

52 K

Testing the Mixture ModelOMC-1

BNKLM42

Trapezium

KHW

pcold/phot

€

P(ν ) = piFi(ν )

Ftot (ν )i

∑

Fi(ν ) = ν β iBν (Ti)

dP

dλ≠ 0 only if p1 ≠ p2 AND

For 2 components:PtotFtot = p1F1 + p2F2


Documents

University of Chicago 2007 July 30 SOFIA-POL 2007 The Infrared - Millimeter Polarization Spectrum John Vaillancourt California Institute of Technology