self-enhanced faraday rotation by extragalactic jets · 2013. 10. 21. · martin krause -...
TRANSCRIPT
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Self-enhanced Faraday rotation by extragalactic jets
Martin Krause (MPE Garching & LMU München)with: Martin Huarte-Espinosa, Paul Alexander, Julia Riley & Christian Kaiser
Annual meeting of the Astronomische Gesellschaft, September 2010, Bonn
Wednesday, September 15, 2010
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Martin Krause - Self-enhanced Faraday rotation by extragalactic jets - AGM, Bonn 2010
Overview
• Introduction: Faraday rotation in clusters (& groups) of galaxies
• FR II jets in magnetised Intra-cluster gas:• enhance rotation measure• change structure function
Wednesday, September 15, 2010
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Martin Krause - Self-enhanced Faraday rotation by extragalactic jets - AGM, Bonn 2010
Magnetic fields in clusters of galaxies: Upcoming surveys ➔ Square Kilometre Array
Semianalytic cosm. model.:
Pred. SKA mid freq. array:
[Krause et al. 2009, MNRAS 400, 646]
Detection statistics:
- pol. background sources measure mag. field in clusters- SKA will measure Faraday rotation in 1000s of gal. clusters w. redshift > 1- SKA: mainly weaker star forming galaxies- currently/ near future: mainly stronger jet sources
Wednesday, September 15, 2010
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Martin Krause - Self-enhanced Faraday rotation by extragalactic jets - AGM, Bonn 2010
Faraday rotation in clusters (and groups) of galaxies: current observations
Intra cluster
(Radians m-2)
A2255 Govoni et al. 2006
3C449, 2231.2+3732 Guidetti et al.
2010
• Faraday rotation is measured against polarised radio emission of typically embedded radio jets.• What is the local effect of the jets on the measured RM?
Wednesday, September 15, 2010
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Martin Krause - Self-enhanced Faraday rotation by extragalactic jets - AGM, Bonn 2010
displaced & compressed magnetised
ICM
Jet-effect on RM:sketch version
y
z
jet beamlobe / cocoon
shocked (compressed)ambient gas
y
x
Magnetic field vectors:1 - radial2 - non-radial
12
O1
O2
• Tangled field• Non-radial component amplified by compression, expansion energy →MF• If observer not ⊥ MF, RM enhanced• RM-Enhancement for observer O1 => edge effect
X-ray cavity1
2
O1 O2
Wednesday, September 15, 2010
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Martin Krause - Self-enhanced Faraday rotation by extragalactic jets - AGM, Bonn 2010
• Flash v3, 3D, MHD, no AMR, constrained transport
• generate turbulent magnetic field cube by the Tribble/ Murgia et al method, Bk∝k-11/3
• multiply with King profile
• let cluster gas relax
• inject bipolar FR II jets in the middle
• vary density & velocity of the jets
• ∀ sim., do sim without jet
• compare RM + statistics: jet-sim. vs. no-jet sim.
Jet ⇔ cluster magnetic fields: simulations
Wednesday, September 15, 2010
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Martin Krause - Self-enhanced Faraday rotation by extragalactic jets - AGM, Bonn 2010
Results [90 deg]: RM ≈ + 20%
Wednesday, September 15, 2010
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Martin Krause - Self-enhanced Faraday rotation by extragalactic jets - AGM, Bonn 2010
Results [45 deg]: RM ≈ +70%
Wednesday, September 15, 2010
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Martin Krause - Self-enhanced Faraday rotation by extragalactic jets - AGM, Bonn 2010
• reproduce observed flattening without intrinsic outer scale of MF
simulations flattening / lobe scale
TefxtfStructure functions
45 degree
Guidetti et al. 2010
Wednesday, September 15, 2010
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Martin Krause - Self-enhanced Faraday rotation by extragalactic jets - AGM, Bonn 2010
Conclusions
• Simulated FR II jets in turbulent cluster mag. fields• RM enhanced @ edges, by about < x 2• ∝cocoon width / inclination• structure function reproduces obs.• FR Is also done, but so far HD, only• expect. similar, maybe weaker effect for FR Is
Wednesday, September 15, 2010