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Observations of Magnetic Fields in Regular and Irregular Clusters

Collaborators present a summary of their research on diffuse synchrotron emissions and rotation measures of radio galaxies in regular and irregular clusters, discussing magnetic field strength, power spectrum, and the relationship with gas density. Results from observations and simulations are presented.

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Observations of Magnetic Fields in Regular and Irregular Clusters

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  1. Observations of Magnetic Fields in Regular and Irregular Clusters Collaborators: Matteo Murgia INAF - Istituto di Radioastronomia Cagliari, Italy Luigina Feretti INAF - Istituto di Radioastronomia Bologna, Italy Gabriele Giovannini Dip. di Astronomia, Univ. di Bologna, Italy Emanuela Orru’ Dip. di Fisica, Univ. di Cagliari, Italy Federica Govoni INAF – Osservatorio Astronomico di Cagliari , Italy

  2. A2029 COMA Regular Cluster Irregular Cluster

  3. Summary of the Talk • DIFFUSE SYNCHROTRON RADIO EMISSIONS Halos, Relics (Irregular Clusters) Mini-Halos (Regular Clusters) • ROTATION MEASURE OF RADIO GALAXIES IN CLUSTERS CLUSTER MAGNETIC FIELDS STRENGTH POWER SPECTRUM GAS DENSITY RELATION

  4. Diffuse Synchrotron Emission in Irregular Clusters: HALOS and RELICS X-RAY – RADIOGovoni et al. (2004) A665 A754 A520 Bacchi et al. (2003) Giovannini & Feretti (2000) Govoni et al. (2001) A1914 A2163 A2256 Clarke TALK Eilek et al.POSTER Delain & RudnickPOSTER A2744 ...Orru’ et al.POSTER A209 ... Giovannini et al. POSTER Feretti et al. (2001) Bacchi et al. (2003)

  5. Diffuse Synchrotron Emission in Regular Clusters: MINI-HALOS NEW MINI-HALO DETECTIONSGovoni et al., in prep. VLA observations at 1400 MHz Beam~ 45” A2029 A1835 Sign of a diffuse, extended emission in A2029 ( VLA observation, 74MHz) Markovic’ et al. (2003) Eilek et al. POSTER

  6. Diffuse Synchrotron Emission in Regular Clusters: MINI-HALOS PKS0745-191Baum & O’Dea (1991) VIRGOOwen et al. (2000) A2390 Bacchi et al. (2003) A2626Rizza et al. (2000), Gitti et al. (2003) Brentjens & de Bruyn TALK PERSEUS CLUSTER Fabian et al. (2000) Burns et al. (1992), Sijbring (1993)

  7. Diffuse Synchrotron Emission 2/7 Beq∝(L k/ФV) SYNCHROTRON EMISSIONMAGNETIC FIELD STRENGTH Magnetic field strength averaged over the entire source volume CLASSICAL EQUIPARTITION ASSUMPTION • ФMagnetic field filling factor • kratio of the energy in relativistic protons to that in electrons • V=Volume • L=Synchrotron Luminosity HALOS Beq ~ 0.1-1μG e.g. Giovannini & Feretti (2002) MINI-HALOS Beq ~ 0.5μG (A2029, A1835) RELICS Beq ~ 0.5-2μG e.g.Ensslin et al. (1998) Magnetic field values consistent with those suggested from the few detection of Inverse Compton hard X-ray emission in clusters with radio halos e.g. Rephaeli & Gruber (2002), Fusco Femiano et al. (2004)

  8. Rotation Measure of Radio Galaxies in Clusters NGC326 Murgia et al. (2001) Kronberg , Physics Today (2002) 20 cm 6 cm

  9. Rotation Measure of Radio Galaxies in Clusters NGC326 Murgia et al., in prep.

  10. Rotation Measures in Regular Clusters Hydra A Taylor & Perley (1993) Lane et al. (2004) -12000 Rad/m/m +5000 Rad/m/m

  11. Rotation Measures in Irregular Clusters A400 (3C75) Eilek & Owen (2002) +170 Rad/m/m -170 Rad/m/m

  12. Rotation Measure of Radio Galaxies in Clusters A2255 RM images obtained by using the PACERMAN (Polarization Angle CorrEcting Rotation Measure Analysis) Algorithm Dolag et al. (2005) A119 Feretti et al. (1999) 3 sources 3C129Taylor et al. (2001) 2 sources A514Govoni et al. (2001) 5 sources

  13. Statistical Studies of Rotation Measures THE ROTATION MEASURE OF RADIO GALAXIES IS REPRESENTATIVE OF THE CLUSTER MAGNETIC FIELD SAMPLE OF IRREGULAR CLUSTERS Clarke (2004) • EMBEDDED GALAXIES • BACKGROUND GALAXIES • CONTROL SAMPLE Lawler & Dennison (1982) Valle’e et al. (1986) Kim et al. (1991) Clarke et al. (2001) Johnston-Hollitt & Ekers (2004)

  14. The Case of A2065 THE ROTATION MEASURE OF RADIO GALAXIES IS REPRESENTATIVE OF THE CLUSTER MAGNETIC FIELD z=0.073 In collaboration with K. Dolag: RM of radio sources in hot galaxy clusters

  15. Results from Rotation Measures Lawler & Dennison (1982) Tribble (1991) Felten (1996) Sokoloff et al. (1998) APPROXIMATION: Magnetic field tangled on a single scale Λc. Screen made by cells of uniform size, electron density, and magnetic field strength, with a field orientation at random angles in each cell. ANALYTICAL APPROXIMATION: <RM>=-91 Rad/m2 σRM=78 Rad/m2 RM Structures of 5-10 kpc Magnetic fields in IRREGULAR clusters ~5μG Magnetic fields in REGULAR clusters are higher ~10-30μG

  16. Magnetic Field – Gas Density Relation Correlation between clusters X-ray surface brightness Sx and Faraday rotation measure calculated in the sources locationDolag et al. (2001) IRREGULAR CLUSTERS

  17. Magnetic Field – Gas Density Relation Dolag et al., in prep. Regular Clusters Irregular Clusters

  18. Results from Rotation Measures Lawler & Dennison (1982) Tribble (1991) Felten (1996) Sokoloff et al. (1998) APPROXIMATION: Magnetic field tangled on a single scale Λc. Screen made by cells of uniform size, electron density, and magnetic field strength, with a field orientation at random angles in each cell. ANALYTICAL APPROXIMATION: <RM>=-91 Rad/m2 σRM=78 Rad/m2 • RM IMAGES WITH SMALL SPATIAL SCALES • <RM>≠0 • MAGNETO HYDRODYNAMIC SIMULATIONS Dolag et al. (2002) CLUSTER MAGNETIC FIELDS FLUCTUATE OVER A WIDE RANGE OF SPATIAL SCALES

  19. Magnetic Field Power Spectrum USING A MULTI-SCALE MAGNETIC FIELD MODEL WITH A POWER SPECTRUM WHICH FOLLOW: IT IS POSSIBLE TO STUDY THE BEHAVIOUR OF THE RM FOR DIFFERENT VALUES OF THE SPECTRL INDEX OF THE POWER SPECTRUM. Murgia et al. (2004)

  20. Magnetic Field Power Spectrum Cluster magnetic field strengths can be calculated through their effects on the polarization properties of radio galaxies by using an analytical formulation based on the approximation that the magnetic field is tangled on a single scale : Efforts into extending the analysis of the Faraday maps beyond the the tangled cell model Ennslin & Vogt (2003) Vogt & Ennslin(2003) Vogt & Ennslin (2005) Murgia et al. (2004) • DEVELOPED A NUMERICAL METHOD • TO DETERMINE THE MAGNETIC POWER • SPECTRUM BY SIMULATING THE • FARADAY ROTATION EFFECTS • ON THE POLARIZATION • PROPERTIES OF RADIO • GALAXIES AND RADIO HALOS • DEVELOPED A FOURIER ANALYSIS • OF RM MAPS TO DETERMINE THE • MAGNETIC FIELD POWER • SPECTRUM: • CORRELATION LENGTH • STRENGTH

  21. Magnetic Field Power Spectrum Vogt & Ennslin (2005) A BAYESIAN VIEW ON FARADAY ROTATION MAPS RM map(Vogt et al. 2005)with PACERMAN algorithmDolag et al. (2005)

  22. Magnetic Field Power Spectrum A119 (Irregular Cluster) Cells 10 kpc B=B =5μG Feretti et al. (1999) 0 0.9 B∝n B=B =7.5μG Dolag et al. (2001) n=2 6kpc - 770 kpc B =5μG <B>=1.5μG e 0 0 Murgia et al. (2004)

  23. Magnetic Field Power Spectrum

  24. Magnetic Field Power Spectrum: Simulated halo brigthness and polarization images Murgia et al. (2004) n=2 n=3 n=4

  25. Diffuse Synchrotron Polarized Emission A2255: The first detection of polarized emission in a radio halo Relic Halo Govoni et al. (2005)

  26. SYNTHESIS Magnetic fields are common in regular and irregular clusters and most of what we know comes from the detection of radio waves • DIFFUSE SYNCHROTRON RADIO EMISSIONS Halos, Relics (Irregular Clusters) Mini-Halos (Regular Clusters) • ROTATION MEASURE OF RADIO GALAXIES Analytical Approximation CLUSTER MAGNETIC FIELDS Equipartition Reconciling magnetic fields values GAS DENSITY RELATION POWER SPECTRUM STRENGTH

  27. SYNTHESIS Magnetic fields are common in regular and irregular clusters and most of what we know comes from the detection of radio waves • DIFFUSE SYNCHROTRON RADIO EMISSIONS Halos, Relics (Irregular Clusters) Mini-Halos (Regular Clusters) • ROTATION MEASURE OF RADIO GALAXIES Analytical Approximation CLUSTER MAGNETIC FIELDS Observations suggest that probably both small and large scales structures coexist Equipartition Reconciling magnetic fields values GAS DENSITY RELATION POWER SPECTRUM STRENGTH Regular clusters > Irregular clusters If the magnetic field fluctuates up to scales of some hundred kpc, then steep power spectra may give rise to detectable polarized filaments.

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