Polarization 101 Polarization 101 Background Star emits Unpolarized Continuum Result: Observed -vector is parallel to plane-of-the-sky component of . E B B Most Likely Orientation Least Likely Orientation E B (Partial) Polarization Observed Result: Observed -vector is perpendicular to plane-of-the-sky component of . E B B Most Likely Orientation Least Likely Orientation E B (Partial) Polarization Observed Result: Observed polarization is perpendi to ray from illuminating source to scatte Absorption Emission Scattering
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Polarization 101 Absorption Emission Scattering. PolarizationPolarization of Background Starlight.
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Polarization 101Polarization 101Background Star emits
Unpolarized Continuum
Result: Observed -vector is parallel to plane-of-the-sky component of .
EB
B
Most LikelyOrientation
Least Likely Orientation
Polarization of Background Starlightby Magnetically Aligned Grains
E
B
(Partial) Polarization Observed
Result: Observed -vector is perpendicular to plane-of-the-sky component of .
EB
B
Most LikelyOrientation
Least Likely Orientation
E
B
(Partial) Polarization Observed
Result: Observed polarization is perpendicular to ray from illuminating source to scatterer.
Ab
sorp
tion
Em
issio
n
Scatt
eri
ng
Background Star emitsUnpolarized Continuum
Result: Observed -vector is parallel to plane-of-the-sky component of .
EB
B
Most LikelyOrientation
Least Likely Orientation
Polarization of Background Starlightby Magnetically Aligned Grains
E
B
(Partial) Polarization Observed
Polarization of Background Starlight
Result: Observed -vector is perpendicular to plane-of-the-sky component of .
EB
B
Most LikelyOrientation
Least Likely Orientation
E
B
(Partial) Polarization Observed
Polarization of Thermal Radiation
Result: Observed polarization is perpendicular to ray from illuminating source to scatterer.
Polarization of Scattered Starlight
WARNING: This illustration is for single scattering, and a single source of illumination.
Circumstellar Nebulae
Will the true source please stand up?
Minchin et al. 1991
AFGL 2146 “The
Juggler” “fake” stars (scatteredlight peaks only)
“real” star (centerof scattered-lightpolarization pattern)
Note: This kind of map also gives disk orientation and information on outflowcavity.
The Future
Large Molecular
Clouds
Jets and Disks
"Cores" and Outflows
Solar System Formation
What’s good where (now)?
Background Starlight
nothing yet...
Thermal Emission
Thermal Emission& Scattered Light
but not inside cold, dark clouds
Magnetic Fields
The GalaxyThe GalaxySerkowski, Mathewson & Ford, et al.
Magnetic Fields
Naïveté:Naïveté:The waywe once thoughtthings might be...
(or)
Disk + Star
Core
Dark Cloud, Theory #2
Dark Cloud, Theory #1
A Truly Theoretical Set of Polarization Maps
Magnetic Fields
Dark C
loud Com
plexes: 1-10 pc scales
B216-217
Magnetic Fields
Pola
riza
tion [
%]
Cold Dark Clouds: (Not) Looking Inside
3
2
1
0
1086420
Extinction [mag]
B216-217 (Goodman et al. 1992)
L1755 (Goodman et al. 1995)
Galaxy (Jones, Klebe & Dickey 1992)
Fit to these dark clouds
Elongated Large Coagulate Grain
Round Grainw/Ice Mantle
Very Small Grain
"Not All Grains are Created Equal"
High-Porosity (Fluffy) Grain
Magnetic Fields
Dark C
loud Com
plexes: 1-10 pc scales
Magnetic Fields
“Go no further than AV~1.3 mag.”
3.0
2.5
2.0
1.5
1.0
0.5
0.0
P R
[%]
43210
43210AV [mag]
Background to Cold Dark Cloud
Arce et al. 1998
Background to General ISM
Magnetic Fields
Dark Cloud Complexes: 1-10 pc scales3D MHD simulation of Gammie, Stone & Ostriker (in prep.)
Field lines“look” straight-ish,even thoughB is significant.