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Exploring Faraday Rotation Measure due to the Intergalactic Magnetic Field with the Square Kilometer Array. Takuya Akahori Chungnam National University. Contents. Introduction Faraday Rotation Measure (RM) due to the Intergalactic Magnetic Field (IGMF) Part 1. present-day local universe - PowerPoint PPT Presentation
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2010.11.4-5 SKA-JP Workshop 2010@NAOJ Akahori 1/14
Exploring Faraday Rotation Measure due to the Intergalactic Magnetic Field w
ith the Square Kilometer Array
Takuya AkahoriChungnam National University
2010.11.4-5 SKA-JP Workshop 2010@NAOJ Akahori 2/14
Contents
• Introduction
• Faraday Rotation Measure (RM) due to the Intergalactic Magnetic Field (IGMF)– Part 1. present-day local universe– Part 2. cosmological effect– Part 3. galactic foreground
• Summary and Future
References:Akahori, Ryu (2010), ApJ, 723, 476ー (2010) to be submittedAkahori, SKA-Japan sub-SWG “Cosmic Magnetism”, Chap. 4
References:Akahori, Ryu (2010), ApJ, 723, 476ー (2010) to be submittedAkahori, SKA-Japan sub-SWG “Cosmic Magnetism”, Chap. 4
2010.11.4-5 SKA-JP Workshop 2010@NAOJ Akahori 3/14
Introduction: Baryon in our Universe
Baryon PhaseBaryon Phase
• ICM (>10ICM (>1077K)K)
• WHIM (10WHIM (105-75-7K)K)
• OthersOthersBaryon Phase Diagram from cosmo. simulation (Piro+ 07)
Intra-Cluster Medium
Warm-Hot Intergalactic Medium
Ionized MediumICM/WHIM
Magnetized?Inter-Galactic Magnetic Field
IGMF
2010.11.4-5 SKA-JP Workshop 2010@NAOJ Akahori 4/14
Introduction: IGMF and RM
Evidences of MagnetizationEvidences of Magnetization• ICM: ICM: RM ~100 [rad mRM ~100 [rad m-2-2] ] IGMF ~1-10 [μG]IGMF ~1-10 [μG]
– Kolmogorov? (Vogt & Ensslin 05; Guidetti+ 08; Bonafede+ 10)
• WHIM: WHIM: RM < 10 [rad mRM < 10 [rad m-2-2] ?] ? IGMF ~ ? IGMF ~ ?
RM through the ICMGovoni+ (10) All sky RM map
Taylor, Stil, Sunstrum (09)
IGMF remains largely unknown
Where is the large-scale structure?
2010.11.4-5 SKA-JP Workshop 2010@NAOJ Akahori 5/14
Model: Our Model for the IGMF
• Goal: Predict RM of WHIMPredict RM of WHIM & test it by future obs. • Method: Simulation of the cosmological structure fo
rmation + turbulence dynamo model (Ryu+ 08)turbulence dynamo model (Ryu+ 08)– MHD…still hard to treat evolution of turbulence and amplification of the IGMF correctly
time [teddy]
En
erg
y d
en
sity
WHIM
ICM Ryu+ (08)10-4μG |B| 10μG
100 h-1 Mpc
Ryu+ (08)
Cho & Ryu (09)
turbulence dynturbulence dynamo modelamo model
1. vorticity energy εw
2. regard εw as εturb
3. εεBB/ε/εturbturb==f(t/tf(t/teddyeddy)) 4. B=(8πεB)1/2
2010.11.4-5 SKA-JP Workshop 2010@NAOJ Akahori 6/14
1 Present-day Local universe: Profiles
• RM: ~100 (GCs), ~10 (Groups), ~0.01-1 (filaments)• RM: a random walk process, peaked at the center
Log10 |RM| [rad m-2]
-50 -25 0 25 50[h-1Mpc]
2.0
1.0
0.0
-
1.0
-2.0
2010.11.4-5 SKA-JP Workshop 2010@NAOJ Akahori 7/14
1 Present-day Local Universe: Statistics
・ Lognormal profile of PDF・ rms ~ 1.4 [rad m-2] for WHIM
PDF of |RM| for WHIM (105 K<Tx<107 K)Tx: emissivity weighted temperature. Black: 3×16 runs, Red: average, Blue: best-fit
・ Peaked at ~Mpc scale・ PRM(k) traces PB||,proj(k)
2D power spectra of RM and the projected IGMFBlack: 3×16 runs, Red: average
100 h-1 10 h-1 1 h-1Mpc 10 h-1 1 h-1Mpc
2010.11.4-5 SKA-JP Workshop 2010@NAOJ Akahori 8/14
2 Cosmological Effects: RM Stacking
• |RM| increases with integrating RM along LOS
Simulation boxes are stacked up to z=5Redshift distribution of radio sources are considered
Willman+ (08)
z=0.1 0.3 0.5 1.0 3.0 5.0
Log |RM|[rad m-2]
2010.11.4-5 SKA-JP Workshop 2010@NAOJ Akahori 9/14
2 Cosmological Effecs: rms Value
[rad m-2]
RM of WHIM (in) 7-10RM of WHIM (after) 6-7
Subtl. of ICM after the integration
temperature
107K
Subtl. of ICM in the integration
Tx=4keVTx=1.5keV
ALL
CLS1Mpc
TM7
TS8ALLMap
Pixcels w Tx>107K& Sx>10-8 e/s/cm2/sr
TS0ALLMap
Pixcels w Tx>107K& Sx>10-10e/s/cm2/sr
Line of sight
Average of 200 runs
2010.11.4-5 SKA-JP Workshop 2010@NAOJ Akahori 10/14
2 Cosmological Effects: Statistics
• PDF of |RM| follows the log-normal distribution
• Power spectrum peaks at ~0.2º scale
1.4º 0.14º
~0.2º
z<0.05
z<0.3
z<5TM7Average of 200 runs
2010.11.4-5 SKA-JP Workshop 2010@NAOJ Akahori 11/14
2nd order SF (Mao+ 10)
2 Cosmological Effect: Structure Function
• Flat SF profile in ~0.1º-10º
2nd order SFALLTS8TS0
Galactic
10º-100º10º-100º
Intergalactic?
0.2º0.2º
0.1º 1º 10º
Average of 200 runs
2010.11.4-5 SKA-JP Workshop 2010@NAOJ Akahori 12/14
• Galactic foreground RM of order ~10 [rad m-2] is a serious contamination
3 Galactic Foreground: Concept of Analysis
Intrinsic + Galactic
Intrinsic RM
Galactic RM
High-pass filter
GalacticContamination?
10º-100º10º-100º0.2º0.2º
Remove the large scale componentRemove the large scale component
Filtered RM
FFT FWTFFT FWT
2010.11.4-5 SKA-JP Workshop 2010@NAOJ Akahori 13/14
Summary
RM in filaments is discussed using a model IGMF• Present-day local universe
– rms ~ 1 [rad m-2], lognormal, peak at ~Mpc • Cosmological effects
– rms ~ several [rad m-2], lognormal, peak at ~0.2º
• Galactic Foreground– High-pass filters (FFT/FWT) may work well
A concept design for SKA Phase 1 (Garrett+ 10)
Our estimated RM could be tested with the SKAOur estimated RM could be tested with the SKA
2010.11.4-5 SKA-JP Workshop 2010@NAOJ Akahori 14/14
Future
• Wide-band observation– RM ranges from ~0.1 to ~100 rad m-2
• Collaboration with galaxy community– Modeling of galactic foreground– Development of RM analysis
• Participation in projects – ASKAP/POSSUM– Japan SKA consortium SWG– Korea SKA consortium? Sofue, Machida, Kudo (10)