LOFAR Observations of Galaxy Clusters

Transcription

1 LOFAR Observations of Galaxy Clusters The Toothbrush Radio Relic Reinout van Weeren Harvard-Smithsonian Center for Astrophysics M. Brüggen, G. Brunetti, H. Röttgering F. de Gasperin, A. Bonafede, W. Forman, G. Ogrean, C. Jones, F. Andrade-Santos, Galaxy Clusters Surveys KSP

2 OUTLINE Introduction LOFAR observations Toothbrush Other clusters Summary

3 RADIO RELICS Reviews: Brunetti & Jones 2014; Feretti Radio (WSRT) + X-rays (XMM) Radio Relics Radio Luminosity (1.4 GHz): W Hz -1 Radio spectral index (F ν α ): -0.8 to -1.5 Polarization: % Size: Distance to cluster center: Mpc ~1-2 Mpc 1 Mpc Morphology: usually elongated MACS J (van Weeren+ 2012; Bonafede+ 2012)

4 QUESTIONS Physics of shocks Origin of Cosmic Rays and magnetic fields in the ICM Particle acceleration mechanisms Acceleration efficiency of shocks Magnetic field amplification Contribution of CRs and B-fields to the ICM pressure budget

5 Origin of the radiating electrons Radiative lifetime of electrons is 10 7 yr << diffusion timescale (Jaffe 1977) electrons are accelerated in-situ Guo+ 2014ab Bonafede Shock acceleration Particles accelerated by multiple crossings of a shock front (diffusive shock acceleration) Problem: low acceleration efficiency PIC simulations show efficient electron acceleration (shock drift acceleration) for low-mach shocks Re-acceleration Guo+ 2014; Caprioli & Spitkovsky 2014 XMM GMRT 325 MHz Relativistic particles accumulated over the lifetime of a cluster Morphological connection between some relics and radio galaxies Efficient re-acceleration for low- Mach shocks Markevitch+ 2005; Giacintucci+ 2008; Kang & Ryu 2011; Kang+ 2012; Shimwell+ 2015

6 MACS J Radio Xray SZ Radio/X-ray: van Weeren+. SZ: Mroczkowski Optical: HST FF images

7 LOFAR HBA LBA

8 Low and High band Antennas : MHz LBA MHz HBA MHz

9 quiet ionosphere wild ionosphere Note: these images have 3 arcmin resolution... Ger de Bruyn & LOFAR EoR team

10 TOOTHBRUSH RX J

11 Non-thermal component of the ICM (cosmic rays) Radio Relic ( Toothbrush ) Radio Halo RX J (z=0.225) Found by inspecting 1.4 GHz NVSS & 325 MHz WENSS survey images XMM X-ray image (+radio contours) Thermal component of the ICM 1 Mpc GMRT radio image (325 MHz) XMM observations by Ogrean+2013: LX ~10 45 erg s -1, T = 8 kev main merger event in the NS direction evidence for shocks (M~1.5) via surface brightness jumps Puzzle: no shock at the Toothbrush relic Ogrean+2013; van Weeren+2012

12 LOFAR MHz One pointing full FOV 4 x 4 degr

13 LOFAR HBA 93 microjy/beam, 6 arcsec resolution GMRT 1.1 mjy/beam, 22 arcsec resolution

14 45 arcsec 22 arcsec 4 arcsec

15 shock: particle injection Spectral index energy losses GMRT 610 MHz LOFAR 150 MHz energy losses energy losses GMRT 610 MHz image

16 Temperature map Chandra kev (243 ks) 5000 counts per bin Chandra + LOFAR

17 northern kink cold front radio relic emission M ~ 1.2? southern shock radio halo emission M = 1.4±0.06 M = 1.7±0.4 (temperature jump)

18 Shock at the northern Toothbrush relic? M = 1.2 M = 1.5 M = 2.8 Chandra: Mach number < 1.6 DSA αinj < -1.8 (!) Measured LOFAR/GMRT/JVLA spectral index: αinj Conclusion: radio spectral index strongly overestimates the Mach number!

19 Radio spectral index for re-acceleration Markevitch+ 2005; Giacintucci+ 2008; Kang & Ryu 2011; Kang Re-acceleration case I Fossil particle population has a steeper spectrum than what would be produced by DSA Spectral index follows DSA spectral index of fossil population erased Re-acceleration case II Fossil particle population has a flatter spectrum than produced by DSA Spectral index of fossil population maintained The case for weak shocks shock shock αfossil αfossil αfossil

20 Relic - Halo connection Spectral index: JVLA 1.5 GHz LOFAR 150 MHz Re-acceleration of pre-accelerated shock electrons due to turbulence??

21 ABELL 2256, VIR-A (M87)

22 LBA 60 MHz,; van Weeren ABELL 2256 HBA MHz (to do: MHz) 1 arcmin resolution 25 arcsec resolution 7 arcsec resolution

23 VIR-A / M87 Work by Francesco de Gasperin 46 MHz (22-70 MHz) dynamic range ~ x16 arcsec resolution

24 SUMMARY First ultra-deep LOFAR cluster image (factor of 10 deeper than anything done before in this frequency band) Toothbrush relic is not associated with a strong shock: Mach 1.6 Toothbrush relic spectrum can be explained by re-acceleration of a flat spectrum fossil population? Toothbrush halo: CR electrons from shocks re-accelerated by merger induced turbulence? LBA 60 MHz observations: see poster Kimberly Emig