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• Dust polarization expectations• The PILOT experiment
J.-Ph. Bernard CESR Toulouse
Dust polarization at long wavelengths
J.-Ph. Bernard, Orsay, Bpol meeting 2006, Oct26th 2006
° Measured in absorption in the visible
Matthewson & Ford 1970
° Measured in emission in the FIR/mm(ground, Archeops, Boomerang)
850 m OMC-3 in Orion A
Dust Polarization
J.-Ph. Bernard, Orsay, Bpol meeting 2006, Oct26th 2006
UV extinction UV rise (PAH) is not polarized
Bump (VSG) is not polarized
IR extinction
- Visible extinction (BG) is polarized- 10 m absorption feature is polarized- 3.4 m ice feature is polarized
So, small (Carbonaceous) grain emission is not expected to be polarized while large (Silicate) grains is.
Lessons from extinction
J.-Ph. Bernard, Orsay, Bpol meeting 2006, Oct26th 2006Desert et al 1990
cold dust (silicate ?)cold dust (silicate ?)
warm dust (graphite ?)warm dust (graphite ?)
Model by Finkbeiner, Davis, Schlegel (FDS)mm excess:- FIRAS data show =1.7near the Galactic plane- WMAP data show thatthis extends down to >2-3 mm
Complications ...
T1=9.6 K, 1=1.5T2=16.4 K, 2=2.6
100 m 1 mm 10 mm
J.-Ph. Bernard, Orsay, Bpol meeting 2006, Oct26th 2006
cold dust (silicate ?)cold dust (silicate ?)
warm dust (graphite ?)warm dust (graphite ?)
Model by Finkbeiner, Davis, Schlegel (FDS)mm excess:- FIRAS data show =1.7near the Galactic plane- WMAP data show thatthis extends down to >2-3 mm
Complications ...
T1=9.6 K, 1=1.5T2=16.4 K, 2=2.6
Would imply a polarizationdegree highly variablewith wavelength
X-foreground = magnetic dipoleemission from vibrating dust
X-foreground =spinning small dust
J.-Ph. Bernard, Orsay, Bpol meeting 2006, Oct26th 2006
Alternative ModelsMeny et al. in prep.
Two-Level Systems
In principle, such models predict no large change of polarization with wavelength
J.-Ph. Bernard, Orsay, Bpol meeting 2006, Oct26th 2006
DCD+TLS Model
€
T =17.9 ± 0.22 K
lc = 2.6 ± 0.17 nm
Ahop = 63.8 ±1.3
Ares =1.06 ± 0.4
DCD
TLS: hoping
TLS: resonant
FDSFDS
TLSTLSBest fit:
Alternative Models
J.-Ph. Bernard, Orsay, Bpol meeting 2006, Oct26th 2006
J.-Ph. Bernard, Orsay, Bpol meeting 2006, Oct26th 2006
From Vaillancourt et al.
Dust polarization certainly varies with in some (dense to very dense) objects ...
FIR/submm Observations ?
J.-Ph. Bernard, Orsay, Bpol meeting 2006, Oct26th 2006
... but the observed variations match none of the models.Indeed, they could be entirely due to confusion on line-of-sight, so ..We have no clue if it varies in the diffuse ISM
From Vaillancourt et al.
FIR/submm Observations ?
TLS Hoping
TLS Res.DCD
Planck will be very sensitive to the shape of the dust emissivity and therefore, should allow to select a dust model
Dust Temperature is an important parameter. For B-pol, we may consider measuringit (with B-pol itself, or otherwise) in order to understand dust foreground.
FIR/submm Planck
Predictions of TLS model with dust Temperature
Planck: unpolarized
Planck: polarized
J.-Ph. Bernard, Orsay, Bpol meeting 2006, Oct26th 2006
J.-Ph. Bernard, Orsay, Bpol meeting 2006, Oct26th 2006
From Pelkonen et al.
For a resolution of 15'
0.5 mag
Planck sensitivity to dust polar
FIR/submm Planck
Planck should allow to detect -variations of the dust polarization(at 3- every 1° below Av=0.5 mag).
Detecting more precisely smaller variations toward more diffuse clouds may require using a polarized instrument at higher frequency like PILOT
Planck: unpolarized
Planck: polarized
J.-Ph. Bernard, Orsay, Bpol meeting 2006, Oct26th 2006
Planck: unpolarized
PILOT
Planck: polarized
PILOT vs Planck -coverage
J.-Ph. Bernard, Orsay, Bpol meeting 2006, Oct26th 2006
- Today, we don't really know if dust polarization will vary with in the sub-mm, and if yes, how ...- So, it is difficult to devise how well we will be able to subtract it from CMB channels for B-pol (and even Planck, actually ...).- WMAP has only one dust-dominated channel (90GHz). We could compare it to Archeops polarization at 353 GHz to start constraining variations.- Planck (and PILOT) should answer the question ... but actual life could be significantly more complicated than described here.
° Other open questions: + Is there l-variations appart from dust distribution ? + Is there a contribution from spinning dust ? + Is there a contribution from HVCs ? + Is there a contribution from ZL ?
J.-Ph. Bernard, Orsay, Bpol meeting 2006, Oct26th 2006
Conclusion (Dust polarization)
The END
PILOT is the pilot fishFuture CMB-pol mission ?
PILOT
http://pilot.cesr.fr J.-Ph. Bernard, Orsay, Bpol meeting 2006, Oct26th 2006
• PILOT will attempt at measuring the linear polarization from dust emission in our Galaxy to very high accuracy levels at high frequencies• The goal is to understand the physics of dust polarization, to ultimately help with component separation for B-pol• PILOT is a test-bed for the use of compact multiplexed bolometer arrays for polarization measurements• PILOT is funded by CNES. Detailed definition is ending and realization of the instrument is starting. • First flight expected in end-2008 (Kiruna)