Early Polarization Science with ASKAP – Galactic PoleTakuya AkahoriSydney Institute for Astronomy (SIfA), The University of Sydney, AustraliaJSPS Postdoctoral Fellow for Research Abroad, Japan

with B. M. Gaensler, and the POSSUM Collaboration

2013/8/5 @ ATNF, AustraliaASKAP Early Science Workshop

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Continuum Polarization Observation Cosmic Magnetism

Impossible to know our universe without knowing Cosmic Magnetism

CMB PolarizationInflation theory

QUIET, PolarBeaR, LiteBIRD

Key Sciences in Modern CosmologyEpock of Reionization Dark age / First stars

MWA, LOFAR, SKA“Foreground” ・・・

• SFR, IMF• Turbulence

ISM, SNR

• Spiral/Halo• Instabilities

Milky Way

• Cosmology• UHECRs

IGM

• Environment• Feedback

AGN

• Population• Morphology

Galaxies

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Observation toward Galactic Pole Best to study the IGMF

› Galactic RM depends on b, and is smallest toward the poles

NVSS-RM (Schnitzeler 10)

RM

Galactic latitude

Galactic Halo

Mao+ (10) Stil+ (11) TA+ (13) TA, Ryu (10;11)

IGMF

+0.0±0.5 rad/m2

~0.00±0.02 µG

+6.3±0.5 rad/m2

~0.31±0.02 µG MRI

Parker Loop

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The IGMF in the Cosmic Web Big Mystery and New Frontier

› What is the origin and nature of the IGMF?- Practically, radio polarimetry is a unique probe- RM~1-10 rad/m2 through filaments? (TA, Ryu 10;11)

Coma cluster(Kim+ 89)

AMR-MHDinitial uniform

B~10 pG(Dubois & Tessier 08)

(M)HDBiermann battery & turbulence dynamo(Ryu+ 98; Ryu+ 08)

SPH-MHDmagnet-gas injection

(Donnert+ 09;Stasyszyn+ 10)

log B(µG)-1

-2

-3

-4

log ρ/ρ0

0 2 4 6 log ρ/ρ0

0 1 2 3 4 log ρ/ρ0

0 1 2 3 4

log B(µG)-0-1-2-3-4

log B(µG)-0-2

-4

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Progress of Extragalactic RM Studies Intrinsic, Intervening, and the IGMF

› Multiple RMs along LoSs› Which RM component

contributes to the observed RM?

› And how?

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Solid: RM 6cmDashed: RM 21cm

Bernet+ (12) Hammond+ (12)

Intervening galaxies

Large Intrinsic

Small Intrinsic

No intervening galaxies

Large Intrinsic

Small Intrinsic

This talkChallenge to discover RM of the IGMF (1-10 rad/m2)

Bryan Gaensler’s TalkThermal emvironment of active galaxies. Galaxy evolution over cosmic time. Turbulence properties and covering fraction of absorbers

<~50%? [1,2]

σINT~5-12 rad/m2? [2]

[1] Zhu, M’erard 13, [2] TA, Gaensler, Ryu in prep.

Radio Galaxies Quasars

“risk hedge”

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Is the IGMF good for Early Science? Yes. Statistics of RM

› RM of the IGMF could be extracted (D>10)TA, Ryu 10;11; TA et al. 13; TA, Gaensler, Ryu, in prep.

Previous Observation ASKAP-12, 6 hours

FoV = 900 deg2 toward the South GPー Model IGM 　ー Mock Obs. 　ー Residual RM

Galaxy filter

High-z filter

High-pass filter

Mock Obs. Map

Extracted Map

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Is the IGMF good for Early Science? Yes. Synthesis of RM

› Null IGMF could be excluded at 2-3σ signif. (700-1800 MHz)TA+ submitted; Ideguchi, TA+, submitted

ASKAP-12, 1 hour, 1 mJy source, RMIGMF=10 rad/m2

ー 1150-1450 MHz 　ー 700-1000 MHz 　ー (700-1000+1150-1450) MHz 　ー 700-1800 MHz

Mock Obs. Spectrum

Model

RM Synthesis

QU-fitting

1σ1σ

1σ

1σ1σ

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Is the IGMF good for Full Science? Of course, Yes!

› Statistics of RM Structure Function› Synthesis of RM RM~a few rad/m2

TA, Gaensler, Ryu, in prep.; TA+ submitted; Ideguchi, TA+, submitted

ー ASKAP-12ー ASKAP-18ー ASKAP-36

ー ASKAP-363σ 3σ

1σ

ASKAP-12, 6 hours

FoV = 900 deg2 toward the South GPー Model IGM 　ー Mock Obs. 　ー Residual RM

ASKAP-36, 15 hours

1σ 1σ

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Summary: Continuum Polarization Observation toward Galactic Pole

• The IGMF in the cosimc web is a mystery & frontier in cosmology• Practically, radio polarimetry is a unique probe of the IGMF

Scientific Backgrounds

• A survery toward the Galactic pole is the best to study the IGMF• We pay attention to the LoS toward which the RM is predominant

Target with ASKAP-12

• Survery specification: continuum pol. survey (Gaensler et al.)• 6 hours per pointing is required to extract RM due to the IGMF• 700 – 1800 MHz is required to exclude null IGMF at 2-3 σ signif.• Full survery with ASKAP-36 would provide further improvements• Technical requirement: the POSSUM pipeline + QU-fit (installed)

Requirement and Feasibility