Planck results challenge dust models and alignment mechanisms - - PowerPoint PPT Presentation

Cosmic Dust & Magnetism - 30 Oct. 2018

• V. Guillet - Planck results challenge dust models and alignment mechanisms

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Collaborators: F. Levrier (ENS/LRA), F. Boulanger (ENS/LRA)

• P. Martin (CITA), L. Fanciullo (ASIAA), A. Jones (IAS),

M.-A. Miville-Deschênes (CEA/SAp), L. Verstraete (IAS),

• G. Green (Stanford University), N. Ysard (IAS), M. Alves (Radboud University)

Planck results challenge dust models and alignment mechanisms

========= Planck 2018 Results XII & others =========

Vincent Guillet (IAS Orsay, LUPM Montpellier)

• n behalf the Planck collaboration

OUTLINE

• 1. Dust polarization at high Galactic latitude
• 2. Magnetic field versus grain alignment

è Origin for the variations of the polarization fraction p ?

• 3. A dust model for translucent lines of sight
• 4. New constraints for high latitude diffuse dust

è Combining Planck and starlight data at high Galactic latitude

• 5. Conclusions & questions

Cosmic Dust & Magnetism - 30 Oct. 2018

• V. Guillet - Planck results challenge dust models and alignment mechanisms

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OUTLINE

• 1. Dust polarization at high Galactic latitude
• 2. Magnetic field versus grain alignment

è Origin for the variations of the polarization fraction p ?

• 3. A dust model for translucent lines of sight
• 4. New constraints for high latitude diffuse dust

è Combining Planck and starlight data at high Galactic latitude

• 5. Conclusions & questions

Cosmic Dust & Magnetism - 30 Oct. 2018

• V. Guillet - Planck results challenge dust models and alignment mechanisms

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Polarization fraction as seen from the Galactic poles

• V. Guillet - Planck results challenge dust models and alignment mechanisms

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0.0 20.0 p [%]

NORTHERN HEMISPHERE SOUTHERN HEMISPHERE p = P/I 353 GHz 80 arcmin What is new since Planck 2015 results ? Polarization at high latitude and low NH (< 1020 cm-2)

Q353 U353

Planck full-sky maps at 353 GHz (850 µm)

• V. Guillet - Planck results challenge dust models and alignment mechanisms

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Planck full-sky maps with reduced systematics

PR3-2018: http://pla.esac.esa.int/pla/

Polarized intensity P353

Smoothing (Planck XIX 2015) Debiasing using full covariance maps (Plaszczynski +2014)

I353 GNILC Intensity map

Generalized Internal Linear Combination (Remazeilles+2011)

Polarization fraction p = P353/I353

CIB : key issue at high latitude Fluctuations removed by GNILC Galactic offset : 0.0181 MJy sr−1 ± 0.0115 MJy sr−1

P = Q2 +U 2

is biased by noise

Low Offset Fidicuial Offset High offset

pmax = 22.4−1.4

+3.5%

(99.9th percentile)

Maximal value for the polarization fraction p = P/I at 353 GHz

• V. Guillet - Planck results challenge dust models and alignment mechanisms

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At FWHM = 80 arcmin of resolution, we have ~ 2.105 pixels

p / E(B-V) < 9% (Serkowski+1975) ?

Systematic drop of the polarization fraction p with NH

Cosmic Dust & Magnetism - 30 Oct. 2018

• V. Guillet - Planck results challenge dust models and alignment mechanisms

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|b| > 5°

95th percentile Running mean (derived from τ353)

A drop long observed and discussed in starlight polarization (optical, NIR):

• Hiltner (1956)
• Serkowski+1975
• Vrba+1981
• Jones (1989)
• Goodman+1992
• Whittet+1994
• Gerakines+1995
• Fosalba+2002
• Andersson+2007
• Whittet+2008
• Alves+2014
• …

Intensity offsets

Planck 2015 results

OUTLINE

• 1. Dust polarization at high Galactic latitude
• 2. Magnetic field versus grain alignment

è Origin for the variations of the polarization fraction p ?

• 3. A dust model for translucent lines of sight
• 4. New constraints for high latitude diffuse dust

è Combining Planck and starlight data at high Galactic latitude

• 5. Conclusions & questions

Cosmic Dust & Magnetism - 30 Oct. 2018

• V. Guillet - Planck results challenge dust models and alignment mechanisms

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How to disentangle between alignment and depolarization ?

Cosmic Dust & Magnetism - 30 Oct. 2018

• V. Guillet - Planck results challenge dust models and alignment mechanisms

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p = pmaxRF cos2γ

In emission (Rayleigh approximation when a << λ) : Grain shape & composition Grain alignment (Rayleigh reduction factor) Magnetic field disorder (line of sight, beam) Magnetic field inclination Angle structure function S

Polarization fraction in Ophiuchus (Planck Int. Results 2015 XX) (Planck Int. Results 2015 XIX) (Planck Int. Results 2015 XIX)

Anticorrelation of S with p also observed at high latitude

Cosmic Dust & Magnetism - 30 Oct. 2018

• V. Guillet - Planck results challenge dust models and alignment mechanisms

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NORTHERN HEMISPHERE SOUTHERN HEMISPHERE 160 arcmin

Inverse correlation of S with p

• V. Guillet - Planck results challenge dust models and alignment mechanisms

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Heiles (1996) Hatano+2013 Planck Int. Results 2015 XIX BlastPOL : Fissel+2016 S and p are anticorrelated Planck 2018 Results XII

S × p

p = C te

Planck 2018 Results. XII 160 arcmin <S x p> shows less variations with

• the column density
• the latitude
• the longitude

than <p> alone.

Model of magnetic field in the high latitude diffuse ISM

Cosmic Dust & Magnetism - 30 Oct. 2018

• V. Guillet - Planck results challenge dust models and alignment mechanisms

12 B B0 Bt

B

Bt

B0

Model (Planck Intermediate Results XLIV 2016)

• Inspired by Jones+1992 model
• fM = Bt / B0 is the ratio of turbulent to ordered B
• pmax is the maximal polarization fraction
• Each of the N layers has the same column density
• αM is the slope of the turbulence power spectrum

Best fit : fM = 0.9, αM = -2.5±0.1, pmax = 0.26, N=7 We demonstrate (Planck 2018 result XII)

with ω the resolution (in arcmin)

Applied to Planck data :

αM = -2.38 (measured on Q and U maps)

S × p = 0.164 fM pmax N ⎛ ⎝ ⎜ ⎞ ⎠ ⎟ ω 160' ⎛ ⎝ ⎜ ⎞ ⎠ ⎟

−1−αM /2

S × p = 0°.31 ω 160' ⎛ ⎝ ⎜ ⎞ ⎠ ⎟

0.18

! B = ! B0 + ! Bt

Ordered (uniform) Turbulent (random)

Planck XLIV model with uniform B0

No dependence of P/I with the dust temperature

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Study at 80’ of resolution Study at 40’ of resolution Check : Tdust does trace the radiation field intensity

Goult Belt clouds: relation between p and S

Cosmic Dust & Magnetism - 30 Oct. 2018

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Study at 40’ of resolution

All regions fall on the same line. Equipartition everywhere ? Well reproduced by the model: not related to the large-scale field.

Multi-resolution analysis from the HLDISM to dense cores

Cosmic Dust & Magnetism - 30 Oct. 2018

• V. Guillet - Planck results challenge dust models and alignment mechanisms

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normalize

• We provide an upper limit of
• n the systematic drop of p with NH that is NOT

explained by the magnetic field structure.

• The drop of S x p seems to be more related to the latitude than to the column density.

By merging results with increasing resolution (from 160’ down to 10’), we probe the polarization properties of all environments observed by Planck

OUTLINE

• 1. Dust polarization at high Galactic latitude
• 2. Magnetic field versus grain alignment

è Origin for the variations of the polarization fraction p ?

• 3. A dust model for translucent lines of sight
• 4. New constraints for high latitude diffuse dust

è Combining Planck and starlight data at high Galactic latitude

• 5. Conclusions & questions

Cosmic Dust & Magnetism - 30 Oct. 2018

• V. Guillet - Planck results challenge dust models and alignment mechanisms

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Dust model for translucent lines of sight (Guillet+2018)

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Why « translucent lines of sight » ?

• Stars from our sample are at low latitude and 0.15 < E(B-V) < 0.8
• Standard extinction and polarization curves also

Constraints from on Planck Int. Results 2015 XXI

• (P/I) 850 µm

= [ 4.2 ± 0.5 ] pV/τV

• P850 µm / pv

= [ 5.4 ± 0.5] MJy/sr

• I850 µm / AV

= [ 1.2 ± 0.1 ] MJy/sr

• New SED per unit extinction derived for this translucent lines of sight

Why use porous grains ?

• A simple way to boosts the dust emissivity

Why choose prolate shape ?

• Emissivity in polarization is more boosted with prolate shapes

Porosity and shape effects are here a convenient way to adapt existing models to Planck constraints without changing the dust

• ptical properties.

Dust model for translucent lines of sight (Guillet+2018)

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• V. Guillet - Planck results challenge dust models and alignment mechanisms

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https://www.ias.u-psud.fr/DUSTEM/ Derived from the Compiegne+2011 dust model 2 populations of large grains

• Porous (porosity=20%) astrosilicate (WD01: βsubmm = 2)
• Amorphous carbon (Zubko+1996: β ~ 1.5)

Prolate grains

• b/a = 1/3
• Same alignment function for carbon and silicate

Candidate models :

• A : silicate aligned, carbon not aligned
• B : same as A, with DL01 astrosilicate (βsubmm = 1.6)
• C : silicate and carbon aligned
• D : composite silicate with 6% carbon inclusions

Fitted size distribution Fitted alignment size-dependence

Dust model for translucent lines of sight (Guillet+2018)

Cosmic Dust & Magnetism - 30 Oct. 2018

• V. Guillet - Planck results challenge dust models and alignment mechanisms

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SOFIA bands

Fitted polarized extinction Fitted polarized emission Models differ much in Wien part of the polarized SED. With SOFIA observations , we could :

à disentangle between dust models à measure the temperature of aligned grains à B-modes à check the alignment of carbon (warm) grains (BLASTPol)

OUTLINE

• 1. Dust polarization at high Galactic latitude
• 2. Magnetic field versus grain alignment

è Origin for the variations of the polarization fraction p ?

• 3. A dust model for translucent lines of sight
• 4. New constraints for high latitude diffuse dust

è Combining Planck and starlight data at high Galactic latitude

• 5. Conclusions & questions

Cosmic Dust & Magnetism - 30 Oct. 2018

• V. Guillet - Planck results challenge dust models and alignment mechanisms

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Comparison of angles with the optical at high latitude

Cosmic Dust & Magnetism - 30 Oct. 2018

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Starlight polarization data from a series of Papers by Berdyugin et al., published between 2001 and 2014.

• North : 2075 stars with b > 30 °
• South : 316 stars with b < - 60°

SOUTH NORTH

• Remarkable agreement (despite no selection)
• Width of histogram explained by noise & dispersion of starlight

polarization angles within the Planck beam

• Unexplained systematic shift of ~ 3° deg.

No variation with NH of the dust polarization ratios

Cosmic Dust & Magnetism - 30 Oct. 2018

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binning in NH binning in NH

Maximal polarization fraction in the optical : pV/E(B-V)

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1) One can not directly compare the maximal polarization fraction in emission and in extiction

Planck 2018 Results XII Serkowski 1975 Maximal polarization fraction P/I = 22% pV /E(B-V) = 9% NH range 5.1019 – 1020 cm-2 > 1021 cm-2 (E(B-V) > 0.15 mag) Percentile 99.9 % 95 %

We find: pV /E(B-V) < 13%

2) Fitting a percentile is difficult with low statistics: here 99th percentile è We use our knowledge of RS/V to estimate the max of pV /E(B-V) at low NH

What a dust model for the HLDISM should at least satisfy

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Planck polarization constraints for a model of High Latitude Diffuse dust (è B-modes)

– RP/p = P850 µm/pV = 5.4 MJy/sr – RS/V = 4.2 – Maximal P/I = 22% Planck 2018 Results XII – Maximal pV/E(B-V) = 13% – βP = 1.53 ± 0.2 with βP–βI = 0.05 ± 0.03 (Planck 2018 Results XI)

Family of dust SEDs (WISE, IRAS, Planck)_________________

– Planck Int. Results 2016 XXIX provides famillies of I(λ) /AV – I850 µm/AV = 0.9 – 1.0 MJy/sr

Extinction per H

– Translucent lines of sight : NH /E(B-V) ~ 5.8 1021 cm-2/mag (Bohlin 1978 & Rachford 2009) – High latitude ISM : NH /E(B-V) ~ 8.3 1021 cm-2/mag (Liszt 2014)

Some observational constraints still missing in extinction :

– Spectral dependence of starlight polarization percentage at low NH (< 1020 cm-2) è Serkowski’s law ? Which mean λmax ? Which mean K ? – Spectral dependence of extinction curve from the UV to the NIR è Rv ~ 3 ? – Depletions measures ?

SUMMARY

Dust polarization at high Galactic latitude

• Full-sky maps available on the Planck Legacy Archive : (I,Q,U) at 353, 217, 143 and 100GHz, with their covariance

matrices.

• Before debiasing, smooth maps so as to get a median P/σP> 3. Never select pixels on SNR.
• pmax = 21 - 26% (99.9th percentile), depending on the intensity offset (~ 0.02 MJy/sr).

Magnetic field versus grain alignment

• No observed dependence of p with the dust temperature.
• < S x p > is proposed as a tracer of grain alignment.
• From NH = 1020 to 2.1022 cm-2, p drops by a factor 3-4, but <S x p> drops by at most 25%. This means than less than

25% of the drop of p can be attributed to a loss of alignment, the rest being explained by depolarization.

• An important part of the decrease of < S x p > with NH is an effect of latitude.

A dust model for translucent lines of sight

• The DustEM tool was amended for polarization. Download it on https://www.ias.u-psud.fr/DUSTEM/
• Models based on porous elongated (3:1) prolate grains reconcile models using astrosilicates with Planck data.

New constraints for high latitude diffuse dust

• The maximal polarization fraction at very low reddening (E(B-V) << 0.15) is p/E(B-V) = 13%
• Submm-to-optical polarization ratios P850 µm/pv and (P/I)850 µm / (p/tau)V do not show any dependence on NH.
• The spectral index of polarization and intensity are almost identical.
• Spectral information of dust extinction and polarization by extinction at high latitude are missing for future models.

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My questions of interest for this week

1) RATs alignment mechanism (e.g. Hoang & Lazarian 2014)

• RATs alignment also depends on the gas pressure. Can this be tested in the diffuse ISM, or in the transition from

the diffuse ISM to the dense ISM ?

• I have not understood how one computes the Rayleigh Reduction Factor for grains in Low-J attractors.

2) Dust evolution and polarization

• Is the constancy of polarization ratio in contradiction with dust evolution, i.e. with the observed variations of dust
• ptical properties seen in total intensity ?
• We expect grain to coagulate in dense clouds and form aggregates, changing their shape, porosity and

composition : – How will this affect their polarization properties (represented by pmax) ? – Can this effect be disentangled from a loss of alignment ?

3) Contamination of CMB polarization by dust polarized emission

• In a model with silicate and carbon grains aligned, variations in the alignment efficiency of both populations

would create decorrelation between frequencies ? How to handle this ?

4) Polarization by scattering

• Polarization by scattering has been observed in circumstellar discs with ALMA
• It allows to constrain the grain size (Kataoka+2015), better than unpolarized observations of scattering.
• Can polarization by scattering be used to observe grain growth in dense clouds via NIR-MIR (3-50 µm)

polarization observations, and complement coreshine studies ?

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BACKUP SLIDES

Comparing optical and submm polarization data

1) Potential background to the star

• 3D reddening data cube : Pan-STARRS (Green+2017)
• Distances: Gaia parallaxes (Gaia Collaboration+2018)

è By interpolation, we estimate E(B-V)∞ and E(B-V)* è Uncertainties to be reevaluated

2) Beam depolarization

• Acts like a bias on p2:
• High (resp. low) p values are little (resp. strongly) affected
• Uncertainties to be reevaluated

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(demonstration in Planck 2018 Results XII)

Methodology

• Selection of lines of sight with little background: E(B-V)*/ E(B-V)∞ < 0.75
• Reestimate uncertainties (background, beam depolarization)
• Polarization ratios by correlation analysis in Q and U: no noise bias

Limits of this approach

• The effect of grain alignement and magnetic field structure is almost

achromatic in emission, NOT in extinction (e.g. Voshchinnikov 1989)

è But small deviations when γ is small (Guillet+ in preparation)