Giant cosmic tsunamis:

Transcription

1 Giant cosmic tsunamis: reconciling observations and models of cluster radio relics Andra Stroe ESO Fellow From Oct Clay Fellow T. Shimwell, C. Rumsey, J. Donnert, R. van Weeren, J. Harwood, M. Brüggen, H. Röttgering, C. Rumsey, H. Intema, R. Saunders, M. Hoeft, M. Hardcastle, T. Jones, M. Kierdorf, H. Akamatsu, R. Beck, C. Rodriguez-Gonzalvez SnowCluster, Mar 2018

2 2 Shocks in merging galaxy clusters Study particle acceleration at low Mach number Study magnetic fields What to learn: How particles are injected? How do they lose energy, i.e. which ageing mechanism? The LHC is not impressed with radio relics! Maybe it's just jealous! Large Hadron Collider

3 3 Ageing mechanism Kardashev-Pacholczyk (KP, Kardashev 1962, Pacholczyk 1970) Jaffe-Perola (JP, Jaffe & Perola 1973) Ageing mechanisms

4 4 Shocks in merging galaxy clusters State of the art in 2014: most relic spectra covered 150 MHz to 2 GHz Highest frequency detection at 5 GHz We looked only here! LOFAR, MWA, LWA (Giacintucci et al. 2008) ATCA, JVLA, AMI, NOEMA, ALMA

5 5 Clusters at low frequencies Steep spectrum sources New types of sources Hoang et al. (2017) Shimwell et al. (2016) de Gasperin et al. (2017) Sausage Abell 2034 GReET

6 6 High frequencies Beyond 2-4 GHz Differentiate between particle acceleration models Why haven t we look here before? e.g. LOFAR, MHz e.g. VLA, ATCA, ALMA Single dish instrument > 2-4 GHz Injection spectrum Differentiate between models

7 7 The 'Toothbrush' and 'Sausage' clusters z~0.2 X-ray luminous, disturbed morphology Merger in the plane of the sky twin, outward traveling shock waves 2.0 Mpc 1.4 Mpc X-ray intensity, radio overlays (van Weeren et al 2010, 2012, Akamatsu & Kawahara 2013, Ogrean et al. 2013)

8 8 16 GHz detection! We were looking for the Sunyaev-Zeldovich signal of the cluster Radio maps with contours drawn at [4, 8, 16, 32] σ RMS Recover northern relic at high S/N 16 GHz 3' resolution 16 GHz 40'' resolution Stroe et al. (2014b)

9 9 16 and 30 GHz detections! For both the 'Sausage' and the 'Toothbrush', AMI and CARMA Stroe et al. (2016)

10 10 More high frequency detections! Single dish instruments! Detection with SRT at 7 GHz: Sausage (Loi et al. 2017) Detections with Effelsberg at 5, 8 and 10 GHz: A2256 (Trasatti et al. 2015), Sausage, Toothbrush, ZwCl, A1612 (Kierdorf et al. 2017) Kierdorf et al. (2017) Loi et al. (2017)

11 11 Integrated spectra at high frequency All the radio, X-ray data and simulations consistent with simple DSA But, steepening after 2 GHz? Also seen in A2256 (Trasatti et al. 2015) Stroe et al. (2014, 2016)

12 12 Steepening at high frequency Inhomogeneous medium - density, temperature gradient across the relic not enough Sunyaev-Zeldovich maybe not enough e.g. Basu et al. (2016) Turbulent reacceleration of cosmic rays possible e.g. Fujita et al. (2016) Pre-accelerated electron population AGN activity - possible e.g. Kang & Ryu (2016) Evolving magnetic field - possible e.g. Donnert et al. (2016)

13 13 Magnetic field evolution Evolving magnetic field: Behind brightness peak, magnetic field declines exponentially alongside adiabatic expansion of the gas Donnert, Stroe et al. (2016)

14 14 Can we constrain models? AMI data 40 GMRT 610 MHz-like resolution

15 15 VLA observations! X Ku K Frequency 8-12 GHz GHz GHz Resolution 7 21 kpc kpc kpc FOV

16 16 The future is bright for radio relics? High frequency data: Single dish GBT VLA ATCA up to 100 GHz ALMA/ACA low band ~30 GHz SKA up to 14 GHz Very large, low-frequency single dish More realistic models ABOUT SKA

17 17 Take away message More data and more modelling needed for radio relics!

18 Back up slides

19 Caveats at high frequency Interferometers lose some of the diffuse flux Stroe et al. 2014, 2016 we can see up to ~3 arcmin scales Stroe et al. (2016)

20 Caveats at high frequency Issues with flux scale Stroe et al checked with point sources does not seem to be a systematic problem Stroe et al. (2016)

21 Caveats at high frequency Difficulty to recover flux at low S/N Stroe et al modelled and did not appear to be an issue Stroe et al. (2016)

22 Caveat at high frequency Single dish instruments poor resolution SRT: 2.9 at 7 GHz Effelsberg: 2.7 at 5 GHz, 1.5 at 8 GHz Stroe et al. (2016)