Statistical modelling of dust polarization as a CMB foreground - - PowerPoint PPT Presentation

Statistical modelling of dust polarization as a CMB foreground

François Boulanger Ecole Normale Supérieure

Polarized Galactic and CMB skies

• The successes of ever more powerful experiments have transformed
• bservational cosmology into a high precision science.
• Foremost questions about our Universe do no anymore depend only on

getting new data with higher sensitivity, because the cosmological signals to be discovered are small compared to the foreground emission from our Galaxy.

• Signature of primordial gravitational waves in the polarization of the

CMB (primordial B-modes)

• CMB spectral distortions (departure from black body spectrum)
• 21cm line emission of neutral hydrogen from the epoch of reionization
• f the Universe
• Today, on these topics, observational cosmology is tied to the challenge
• f characterizing statistically the complexity arising from non-linear

interstellar physics (cosmic dust & magnetism).

Take home message

François Boulanger Cosmic Dust and Magnetism Daejeon, Nov. 2, 2018

Observational cosmology

François Boulanger Cosmic Dust and Magnetism Daejeon, Nov. 2, 2018

Much is still to be learned from CMB and mainly from polarization

credit: Josquin Errad

Planck CMB polarization map

4

François Boulanger Cosmic Dust and Magnetism Daejeon, Nov. 2, 2018

CMB Power spectra

Credit E. Calabrese

• E-mode (gradient-like)

polarization validates the acoustic interpretation of temperature peaks and enhances the precision of cosmological parameters.

• B-mode (curl-like) polarization

from gravitational lensing is also detected

• No detection (yet) of the

weaker B-mode signal expected from primordial gravitational waves

Density fluctuations Lensing

François Boulanger Cosmic Dust and Magnetism Daejeon, Nov. 2, 2018

BICEP Collaboration 2014 Primordial B- modes?

BICEP B-modes

L e n s i n g

• The BICEP collaboration published the

deepest polarization observation ever achieved at micro-wave frequencies

• Initial claim: discovery of primordial

B-modes

• The Planck data analysis, followed by

a joint analysis of the Planck and BICEP data, have shown that their signal is dominated by dust polarization.

François Boulanger Cosmic Dust and Magnetism Daejeon, Nov. 2, 2018

The foreground screen from the magnetized ISM

• The power spectra of dust

polarization was characterized over the whole sky using Planck data

• There is no sky area where

the Galactic signal may be neglected

• Any claim for a detection

will face a critical assessment against alternative interpretations involving foregrounds

BICEP/Keck field on Planck image

60°

François Boulanger Cosmic Dust and Magnetism Daejeon, Nov. 2, 2018

2 10 100 500 Multipole, ` 10−4 10−2 100 102 DBB

`

[µK2]

r = 0.1 r = 0.01 r = 0.001 Ddust

`

at 150 GHz Ddust

`

at 95 GHz Dsync

`

at 95 GHz

primordial B modes lensing B modes

50 100 150 200 250 300 350 Frequency [GHz] 10−6 10−4 10−2 100 102 104 BB power in ` ∼ 7.5 [µK2]

r = 0.1 r = 0.01 r = 0.001 lensed-ΛCDM Dust Synchrotron

50 100 150 200 250 300 350 Frequency [GHz] 10−6 10−4 10−2 100 102 104 BB power in ` ∼ 69.5 [µK2]

r = 0.1 r = 0.01 r = 0.001 lensed-ΛCDM Dust Synchrotron

Polarized foregrounds power

➡ Planck data quantify the challenge of the component-separation procedure required for detecting the reionization and recombination peaks of primordial CMB B-modes

François Boulanger Cosmic Dust and Magnetism Daejeon, Nov. 2, 2018 CMB B-mode reionization bump CMB B-mode recombination bump

Planck collaboration XI (2018)

Moving forward with foregrounds

Extending to foregrounds the statistical approach of CMB simulations Data analysis of polarization data Statistical modelling of dust polarization Astrophysics of dust and synchrotron polarization: Cosmic dust & Magnetism

François Boulanger Cosmic Dust and Magnetism Daejeon, Nov. 2, 2018

Modelling motivations

• Statistical modeling of foregrounds is required to

confidently identify primordial CMB B-modes (or set upper limits)

• Propagate instrumental effects in end-to-end simulations
• f data pipeline
• Optimize component separation for CMB polarization

and assess statistically uncertainties

• Astrophysical interpretation of data

François Boulanger Cosmic Dust and Magnetism Daejeon, Nov. 2, 2018

Modelling approach

• Stokes I from 353 GHz dust-only sky map (CMB and

cosmic infrared background subtracted)

• Magnetic field model required to compute noise-free

Stokes Q and U maps

• Ordered magnetic field + statistical model of turbulent

component

• Dust spectral energy distribution for polarization

François Boulanger Cosmic Dust and Magnetism Daejeon, Nov. 2, 2018

Magnetic fields model Solar Neighborhood

Windell Oskay

Solar Neighborhood magnetic field

• Imprint from an ordered magnetic field is clearly apparent on the map of

polarization angles

• We may be seeing a local deformation of the Galactic magnetic field

associated with the Local Bubble (Alves et al. 2018)

• Dust, unlike synchrotron, polarization is sensitive to this because the extension
• f the Bubble towards the pole is comparable to the dust scale-height

Local Bubble

Alves+ 2018 Polarization angle ψ

François Boulanger Cosmic Dust and Magnetism Daejeon, Nov. 2, 2018

polarization fraction

Variable degree of depolarization from the superposition of a small number of ISM clouds, and magnetic coherence lengths along the line of sight, with distinct polarization

Depolarization from Turbulence

Model with no turbulence

François Boulanger Cosmic Dust and Magnetism Daejeon, Nov. 2, 2018

25%

• Magnetic field
• Power-law spectrum
• Uniform + random
• Distribution of matter from total

intensity Planck map

• Correlation between magnetic

field and matter (=> field anisotropy)

• Summing emission over N

emitting layers (ISM structure along the line of sight)

Ordered field Turbulent field

Planck Collaboration Int. XLIV (2016), Ghosh + 2017, Vansyngel+ 2017, Planck Collaboration XII (2018)

North Galactic Pole South Galactic Pole Galactic Plane Sun L

• c

a l B u b b l e

B0

Bt

B

Phenomelogical Model

François Boulanger Cosmic Dust and Magnetism Daejeon, Nov. 2, 2018

[Planck int. res. XLIV. A&A 596, 105]

Polarization fraction and angles

• High dust polarization

fraction (p0=0.26 ± 0.04)

• Turbulence is sub/

trans-Alvenic (fM = 0.9 ± 0.1)

• Small number of

structures/turbulent cells along the line of sight (N~4-7)

Polarization fraction Polarization angle

fM fM N N p0 (%) p0 (%)

PhD Andrea Bracco, Planck Collaboration Int. XLIV (2016)

Statistics on southern Galactic cap

C François Boulanger Cosmic Dust and Magnetism Daejeon, Nov. 2, 2018

The slopes of power-spectra are matched for a magnetic field power spectrum exponent αM = -2.5

Model/Data

N=4 and 7

Vansyngel+ 2017

Exponents of magnetic field power spectrum Polarization parameter

Magnetic field power spectrum

François Boulanger Cosmic Dust and Magnetism Daejeon, Nov. 2, 2018

Dispersion function of polarization angles

S for our phenomenological model

• Gaussian model of the magnetic field accounts for the anti-correlation

between S and p (Vincent Guillet’s talk) and the filamentary structure of the S map.

• In this model, filaments tend to be present where the ordered field
• rientation is close to the line of sight

Filamentary structure of dust polarization angles

François Boulanger Cosmic Dust and Magnetism Daejeon, Nov. 2, 2018

How to compare statistically simulations and observations ? How to derive a statistical model from simulations ?

Moving forward using MHD simulations

log(NH (cm-2))

• Statistical multi-scale analysis allows us

to build a low dimensional model that captures the image statistics

• This model may be used to build

multiple images with the same statistical characteristics

• These images may used to optimize and

assess uncertainties of Foregrounds/ CMB component separation

Compiegne et al. 2011 Guillet et al. 2018

Large dust grains AME

Draine & Fraisse 2009 Draine & Hensley 2013 Jones et al. 2013

Magnetic grains/inclusions

Dust polarization

Magnetic Dipole Emission

Credit: Lapo Fanciullo

Dust spectral energy distribution

The spectral indices for polarization and total intensity is small (0.05 ± 0.03) and not

• f high statistical significance

The dust SED in polarization is remarkably well fit by a single temperature modified black-body emission law from 353 to 44 GHz SED Total intensity ≈ Polarization Emission from a single grain type dominates the long- wavelength emission in both polarization and total intensity

François Boulanger Cosmic Dust and Magnetism Daejeon, Nov. 2, 2018

10−6 10−5 10−4 SED [µK] 50 100 200 400 Frequency [GHz]

−4 −2 2 4

Res (σ)

Dust SED in polarization

Modified black-body fit

➡ The interplay between magnetic field structure and dust polarization properties (including grain alignment) generates frequency decorrelation

Frequency decorrelation:

François Boulanger Cosmic Dust and Magnetism Daejeon, Nov. 2, 2018

Planck Results L. (2017)

U Q

Different intensity ratios and polarization angles between frequencies among sky pixels

Chluba+17 and Mangilli (Foreground conference, Tenerife) Second order expansion for a greybody SED with fixed T0:

}

Frequency decorrelation

Cross-spectrum:

François Boulanger Cosmic Dust and Magnetism Daejeon, Nov. 2, 2018 François Boulanger Cosmic Dust and Magnetism Daejeon, Nov. 2, 2018

How to model frequency decorrelation?

Method applied fitting Planck total intensity data from 100 to 857 GHz

• Power spectra exponent &

amplitude

• Depolarization
• E/B asymmetry, TE correlation
• Non-Gaussianity

Magnetic fields Ordered component

• Fixed model, currently 2D must become

3D (Gaia) Turbulent component

• Statistical parametric model
• MHD simulations
• Correlation between B fields & matter

Dust properties

• Number of polarized components
• Variations on the sky & along the line of

sight

• Correlation between dust, matter & B

fields

Model-Data Correspondences

Dust polarization maps

• Large scale patterns
• Non-stationarity of dust

polarization power Spectral energy distribution

• Dimensionality of the

component separation

• Frequency decorrelation

François Boulanger Cosmic Dust and Magnetism Daejeon, Nov. 2, 2018

Thanks to Thiem, the LOC & SOC for an exciting conference

CAFE LATTE

1st Conference on

Cosmology with Astrophysics of Interstellar Foreground Emission in LATTEs 11-15 May 2020 - La0es (South of France)

Objec@ves:

• Gather scien@fic from different fields for a beFer understanding and modeling of

interstellar foregrounds which contaminate cosmological data. Program:

• Cosmological goals
• Physics of Interstellar Foregrounds
• Applied Mathema@cs

Contact :

• vincent.guillet@ias.u-psud.fr
• francois.boulanger@ens.fr