Magnetic field in the distant galaxy

1. Magnetic field in the distant galaxy Cluster Macs J0717+3745 Annalisa Bonafede PhD student at IRA Radio Astronomy Institute Bologna (Italy) With: L. Feretti, G. Giovannini, M. Murgia, F. Govoni, G. B .Taylor , H. Ebeling, S. Allen, G. Gentile, Y. Philstrom Cosmologicalmagnetic field Ascona, 1/06/2009

2. OUTLINE • Magnetic Field in Galaxy Clusters • The interesting case of MACS J0717+3745 • Radio observations: discovery of the most distant radio halo • Polarization properties • Constrain on the magnetic field strength and structure from polarization and under equipartition assumption • conclusions

3. Galaxy Clusters: Intra Cluster Medium : Non thermal component  magnetic field +relativistic particles Polarization properties of radio sources Radio Diffuse Emission Abell 1240 Abell 2163 Bonafede et al (2009) Feretti et al. (2001), Govoni et al. (2004)

4. 30” 46’00” 30” 45’00” 30” 44’23” 37°43’30” 35s 30s 07h17m25s 40s The cluster Macs J0717+3745 Z=0.55 1 arsec  6.394 kpc “A prime example of a complex major cluster merger” (Ma + 2009) Chandra 60 ksec ACIS-I HST F814w filter Optical emission: Ma et al (2008) Edge et al (2003) X-ray emission: Ma et al (2008) L =2.74±0.03 1045 erg/s [0.1 – 2.4]keV <T> =11 kev T going from 5 to 20 keV

5. The cluster Macs J0717+3745 Z=0.55 1 arsec  6.394 kpc Joint Optical – X-ray analysis 4 distinct sub-clusters ongoing triple merger + 6 Mpc long filament, source of continuous and discrete accretion of matter by the cluster What happens to the non-thermal component of the ICM? Edge et al. 2003

6. The radio side of a triple ongoing merger... Radio observations: VLA – B-array obs 4 freq in the 20 cm band tos ~ 2h per freq. C-array obs 2 freq in the 6 cm band tos ~ 2h per freq θ~ 5’’ x 5” VLA – C-array obs 1.4 GHz, tos~ 2h θ~ 18’’ x15” In full polarization mode θ~ 2’’ x 2” + VLA Archive obs at 8.5 GHz C array obs at 4.8 GHz D-array θ~ 18’’ x15”

7. Observing the compact features HST + VLA 8.5 GHZ A Chandra + VLA 1.4 GHZ 260 kpc B C θ~ 5’’ x 5” θ~ 2’’ x 2” Filamentary structure

8. Observing the extended emission Discovery of themost distant & most powerful radio halo P1.4 GHz~1.6 1026 W/Hz ; also emitting at 4.9 GHz Chandra [0.5-7keV] + VLA 1.4 GHZ θ~ 18’’ x20” 1.5 Mpc 1.5 Mpc

9. Polarized emission from the radio halo 2nd case after Abell 2255 (Govoni e al. 2005) Upper limits 4% con beam 45% quidi non è ‘’strano’’ 1.4 GHZ 5% mean Pol Max ~ 24% θ~ 18’’ x20” Min ~ 0.6%

10. What are we seeing at high resolution? 4.9 GHZ 17% mean Pol 8% mean Pol 1.4 GHZ 20% pol flux 0.4 % pol flux 16% pol flux 9% pol flux

11. Faraday rotation: IF the cluster acts like an external screen: E q H E RM λ d

12. RM But... Faraday rotation internal to the emiting source Strong beam depolarization ...we can verify the fit of Ψ versus λ2 Foreground structure RM due to our galaxy λ2 law RM due to the cluster λ2 law Background structure Within the cluster icm structure Internal rotation NO λ2 law

13. RM fit with PACERMAN algorithm (Polarization Angle CorrRecting Rotation Measure ANalisys ) Dolag et al. (2005) Filamentary part of the radio halo

14. The magnetic field power spectrum Vectorial form Numerical Simulations by murgia et al. 2004 • % Polarization: • Increases with increasing n • Decreases toward the cluster center n ≥3 Λmax 100s kpc

15. Under the equipartition assumption: L computed in a fixed energy range:Emin Emax if Emin is constat with r Using the deprojected brightness profile Factor 2.5 Beta-model from x-ray analysis (Ma et al. 2008)

16. Under the equipartition assumption: L computed in a fixed energy range:Emin Emax Emin =100 and Emax >> Emin

17. Conclusions Discovery of a giant radio haloemitting from 74 MHZ – 4.9 GHz z=0.55  the most distant one P1.4 GHz~1.6 1026 W/Hz  the most powerful one Polarized emission from the radio halo0.6 % – 24% second case after A2255 (Govoni et al. 2005) Magnetic field power spectrum n> 3, Λmax≥ 100skpc Beq~ 1.2 µG, B0 ~3 µG, B decreases as the gas density Under equipartition assumption Bonafede et al, arXiv:0905.3552.