2010.08.20ska-kr workshop 2010, kasi, daejeon, korea akahori 1/20 study of faraday rotation due to...
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2010.08.20 SKA-KR Workshop 2010, KASI, Daejeon, Korea Akahori 1/20
Study of Faraday Rotation due to the Intergalactic Magnetic Field~Preparing the Era of the Square Kilometer Array~
Takuya Akahori, Dongsu Ryu
Chungnam National University
2.0
1.0
0.0
-
1.0
-
2.0
Log10 |RM| [rad m-2]
-50 -25 0 25 50[h-1Mpc]
2010.08.20 SKA-KR Workshop 2010, KASI, Daejeon, Korea Akahori 2/20
Contents
• Introduction– State-of-the-Art/Unresolved Problems
• Faraday Rotation Measure (RM) due to the Intergalactic Magnetic Field (IGMF)– Part 1. present-day local universe
• Coherence length, rms value, PDF, power spectrum
– Part 2. cosmological effects• LSS evolution, radio source distribution, X-ray emission
– Part 3. galactic foreground• Scale difference, FFT/FWT filtering analyses
• Summary• Status of SKA in Japan
2010.08.20 SKA-KR Workshop 2010, KASI, Daejeon, Korea Akahori 3/20
Introduction
• RM & synchrotron observations– Simard-Normandin, Kronberg, Button (81), Kim+ (89; 90; 91), Clarke, Kronberg, Bo
hringer (01), Taylor, Fabian, Allen (02), Govoni+ (04), Xu+ (06), Pizzo+ (08), Taylor+ (09), Govoni+ (10)
• Cross correlation & structure function of RM– Brown, Farnsworth, Rudnick (09), Lee+ (09), Stasyszyu+ (10), Mao+ (10)
• Spectral analyses, tomography– Frick+ (01), Brentjens, Bruyn (05), Schnitzeler, Katgert, Bruyn (09)
• Modeling of magnetic field and its power spectrum– Feretti+ (95), Felton (96), Krause+ (09)– Vogt, Ensslin (03; 05), Murgia+ (04), Guidetti+ (08), Bonafede+ (10)
• Simulations and estimation of RM in the LSS– Kulsrud+ (97), Ryu , Kang, Biermann (98), Dolag+ (99; 05), Dubios. Teyssier (08),
Ryu+ (08), Dolag, Stasyszyu (09), Akahori, Ryu (10)
• Relation with metal enrichment, effects of AGN & galaxies
State-of-the-Art / Unresolved Problems
2010.08.20 SKA-KR Workshop 2010, KASI, Daejeon, Korea Akahori 4/20
Observations of RM in Galaxy Clusters
Now) profile of RM, correlation with the X-ray morphologySKA) what’s the origin? when developed? how important?
Radial RM profilesClarke, Kronberg, Bohringer (01)Govoni+ arXiv:1007.5207
Galaxy cluster
RM~ 100 [rad mRM~ 100 [rad m-2-2]]IGMF ~1-10 [μG]IGMF ~1-10 [μG]
2010.08.20 SKA-KR Workshop 2010, KASI, Daejeon, Korea Akahori 5/20
Estimations of RM in Galaxy Clusters
Now) constrains of IGMF structure by fitting with modelsSKA) statistical argument using large samples
n=11/3 (Kolmogorov)?n=11/3 (Kolmogorov)? (e.g. Vogt, Ensslin 05; Guidetti+08; Bonafede+10)
→ existence of Kolmogorov turbulence and turbulence amplification of the IGMF?
- Power-law Gaussian random IGMF model e.g., Murgia+ (2004)
Govoni+ arXiv:1007.5207Guidetti+ (08)
2010.08.20 SKA-KR Workshop 2010, KASI, Daejeon, Korea Akahori 6/20
Observations of RM in the LSS
Now) RM<10 rad m-2, or it has too complicate structures to distinguish them from noise
SKA) 1 source /arcmin2 with ~1 rad m-2 error
Orion ArmRegion ALoop II
Loop I
Coma
Virgo
Perseus
North Polar Spar
Hercules supercluster
All sky RM map, Taylor, Stil, Sunstrum (09)
Xu+ (06)
RM < 10 [rad mRM < 10 [rad m-2-2] ?] ?IGMF < 1 [μG] ?IGMF < 1 [μG] ?
2010.08.20 SKA-KR Workshop 2010, KASI, Daejeon, Korea Akahori 7/20
Estimations of RM in the LSS
• Cosmological HD/MHD simulations– MHD…still hard to treat the evolution of
turbulence and amplification of the IGMF correctly
log |B| μG
5 Mpc
Dubios, Teyssier (08)
Now) estimations of RM from HD/MHD simulationsSKA) observational appearance of RM
→ Radio source distribution in space→ Uncertainty of RM at the source, our local group, and our galaxy→ Of course, a reasonable IGMF model
Stasyszyn+ arXiv:1003.5085Akahori, Ryu (10) ApJ submitted
2010.08.20 SKA-KR Workshop 2010, KASI, Daejeon, Korea Akahori 8/20
• Turbulence Dynamo Model① Calculate curl component of flow motion & its energy εw
② Regard εw as the turbulence energy εturb
③ Adopt the growth model εB/εturb=f(t/teddy) & B=(8πεB)1/2
Our Model for the IGMF
time [teddy]
En
erg
y d
en
sity
filaments
GCs
Ryu+ (08)
10-4μG |B| 10μG
100 h-1 Mpc
Ryu+ (08) Cho & Ryu (09)
IGMF ~0.1 [μG]IGMF ~0.1 [μG]RM~ 1 [rad mRM~ 1 [rad m-2-2]]
2010.08.20 SKA-KR Workshop 2010, KASI, Daejeon, Korea Akahori 9/20
1 Present-day local universe: 2D map
• RM ~100 (GCs), ~10 (Groups), ~0.01-1 (filaments)• Mixture of positive and negative RM, that reflects the rand
omness and the coherence scale of IGMFs in the LSS
2.0
1.0
0.0
-1.0
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2.0
Log10 |RM| [rad m-2]
-50 -25 0 25 50[h-1Mpc]
(z=0, L=100 h-1 Mpc)
-10 -5 0 5 10[h-1Mpc]
Log10 |RM| [rad m-2]
10.
5.0
0.0
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5.0
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10.
RM[rad m-2]
2010.08.20 SKA-KR Workshop 2010, KASI, Daejeon, Korea Akahori 10/20
1 Present-day local universe: radial profile
• Inducement of RM is a random walk process with the coherence length < path length, but is dominated by the contribution from the density peak along LOS
2010.08.20 SKA-KR Workshop 2010, KASI, Daejeon, Korea Akahori 11/20
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) is close to PB||,proj
(k): RM traces B well
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↑ in good agreement with Cho, Ryu (09)
2010.08.20 SKA-KR Workshop 2010, KASI, Daejeon, Korea Akahori 12/20
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]
2010.08.20 SKA-KR Workshop 2010, KASI, Daejeon, Korea Akahori 13/20
2 Cosmological effects: statistics
• rms of RM
• PDF– lognormal
[rad m-2]
WHIM+ICM 40WHIM (theoretical) 7-10
WHIM (observational) 6-10
rms of RM integrated up to z. ICM candidates are subtracted in the integration (theoretical) or after the integration (observational) of RM
★ observational
T [K]
107
★ theoreticalTx=4keV
Tx=1.5keV
ALL
CLS
1Mpc
TM7
T57 Map Pixcels w Tx>107K
TS8 MapPixcels w Tx>107K
& Sx>10-8 e/s/cm2/sr
TS0 MapPixcels w Tx>107K
& Sx>10-10e/s/cm2/sr
2010.08.20 SKA-KR Workshop 2010, KASI, Daejeon, Korea Akahori 14/20
2 Cosmological effects: statistics
• P(k): peak scale at ~0.2º• S2(r): characteristic scale at ~0.1-0.2º
2D power spectra P(k) integrated up to z=0.05, 0.3, 5 (thin to thick)
2nd order structure function S2(r)
1.4º 0.14º
~0.2º
2010.08.20 SKA-KR Workshop 2010, KASI, Daejeon, Korea Akahori 15/20
All sky RM (Taylor+ 09)
• Galactic RM is a serious contamination for studying RM in filaments– galactic RM ~10-100 [rad m-2]
3 Galactic foreground: Concept of Analysis
Spectra of observed all-sky RM(Frick+ 01)
Key point: peak scales are different
10-100 degree10-100 degree0.1-1 degree0.1-1 degree
Chop! Use!
2010.08.20 SKA-KR Workshop 2010, KASI, Daejeon, Korea Akahori 16/20
3 Galactic foreground: High-pass filters
High-pass filters have potential to subtract galactic component
Intrinsic+Noise
High-passfilter
• Fast Fourier transformation (FFT)• Fast Wavelet transformation (FWT)• Transform→ low frequency cut at kf → inverse-Transform
• Parameter: kf
Noise RM• Gaussian random fluctuation• Kolmogorov spectrum |Q(k)|2 k∝ -11/3(k>kn), k-1(k<kn)• <RM>=0, <RM>rms= σn
• Parameters: σn & kn
Intrinsic RM Filtered RM(FFT/FWT)
2010.08.20 SKA-KR Workshop 2010, KASI, Daejeon, Korea Akahori 17/20
3 Galactic foreground: What’s the Best kf?
• A high-pass filter with kf ~ degree would effectively reduce the galactic foreground contamination
rms of RM as a function of the filter scales of FFT (left) and FWT (right)Noise model: kn= 5 (2.8º scale), <RM>rms, noise= 20 [rad m-2]
2010.08.20 SKA-KR Workshop 2010, KASI, Daejeon, Korea Akahori 18/20
Summary
RM in filaments is discussed using a model IGMF• Present-day local universe
– rms ~ 1 [rad m-2] for WHIM, lognormal, peak at ~Mpc • Cosmological effects (stcking up to z=5)
– rms ~ several-10 [rad m-2] for WHIM, lognormal, peak at ~0.2º
• Galactic Foreground– Degree-scale high-pass filters (FFT/FWT) works well
• SKA will highlight and reveal origin and nature of the IGMF. Our estimated RM is in detection range on SKA.
• The high-pass filter is quite effective to remove galactic foreground RM, which would improve statistical analyses
– e.g., cross correlation and structure function
2010.08.20 SKA-KR Workshop 2010, KASI, Daejeon, Korea Akahori 19/20
Status of SKA in Japan
• Japanese SKA consortium (SKA-JP)– since 2008.5, ~70 members, ~20 Institute– Science & Engineer Working Groups– Regular meeting (TV, Site) ~1/month
• International Workshops– SKA-JP WS 2004.11, 2008.11– SKA-JP Workshop 2010.11.3-4@NAOJ
• Recommendation of Science Council of Japan– LCGT, TMT, SKA, SPICA, ASTRO-H,..– Japan should bear 10% (~2-300M$?) of co
nstruction and use costs– But, “observer” so far
2010.08.20 SKA-KR Workshop 2010, KASI, Daejeon, Korea Akahori 20/20
Status of SKA in Japan
• Science Working Group– 8 subgroups Cosmic Magnetic Fields / AGN / Pulsars /
Galaxy evolution and high-z universe / Astrometry / Star and Planet Formation / Wide-Band Spectral Line Survey / Antenna
– Summary of unresolved problems To be uploaded on SKA memo http://www.skat
elescope.org/pages/page_memos.htm
• Engineer Working Group – Ultra-wide band polarized wave m
easurement on >~ 10 GHzUltra-wide feed, tapered slot antennaDigital polarized wave measurement system
• Collaboration with East-Asian countries