Searching for the Synchrotron Cosmic Web with the Murchison Widefield Array Bryan Gaensler Centre for All-sky Astrophysics / The University of Sydney Natasha Hurley-Walker Planelles & Quillis (2013)

The Synchrotron Cosmic Web ›Intergalactic shocks accelerate electrons and amplify magnetic fields (Keshet et al. 2004; Hoeft & Brüggen 2007; Battaglia et al. 2009; Araya-Melo et al. 2012) -faint synchrotron radiation should trace large-scale structure and cosmic filaments → direct image of large-scale structure of the Universe → laboratory for studying particle acceleration in low-density shocks → magnetic field strength of the IGM → direct discriminant on competing models for origin of cosmic magnetism ›Signal should dominate other radio signals on scales ~ 10′ to 1 o at frequencies ~100 MHz Injected fields vs primordial fields (Donnert, Dolag et al. 2008) MHD simulation of magnetised large-scale structure (Brüggen et al. 2005)

Wide-Field Radio Astronomy © Top-Foto, Assen MWA Consortium MWALOFAR ›New generation of interferometers -low frequencies ( MHz) -no moving parts -dedicated supercomputers -enormous fields of view SKA-low Swinburne / LFAA consortium MWA Hubble Space Telescope

The Murchison Widefield Array (MWA) ›Designated SKA precursor in outback Western Australia (Tingay et al. 2012) MHz, including FM band -128 tiles over 3 km → ~1’ resolution » 1000 deg 2 field of view! « -fully operational -proposal call every 6 months MWA Consortium

›Direct detection (Bagchi et al. 2002; Wilcots 2004) -faint emission -Galactic foregrounds -confusion from extragalactic point sources ›Polarisation (Rudnick & Brown 2008) -higher sensitivity, reduced confusion -fainter signals, complex Galactic foregrounds ›Statistical detection (Brown et al. 2010, 2011) -stacking -cross-corr. with tracers of large-scale structure Detecting the Synchrotron Cosmic Web Coma field at 400 MHz (Kronberg et al. 2007) 3C 31 and NGC 315: total intensity and diffuse polarisation (Rudnick & Brown 2008) 2MASS galaxy distribution vs 1.4 GHz radio emission (Brown 2011)

Radio Probes of the Thermal Cosmic Web Xu et al. (2006) Thornton et al. (2013) Braun et al. (2004) ›Faraday rotation from background AGN (Xu et al. 2006; Akahori & Ryu 2010; Stasyzsyn et al. 2010) -need to correct for foreground Galactic Faraday rotation ›21cm emission from the WHIM (Braun 2004; Popping & Braun 2007) -requires sensitivity to N HI < cm -2 ›Dispersion of “fast radio bursts” (Lorimer et al. 2007; Thornton et al. 2013) -need localisations & redshifts

H II regions supernova remnants radio galaxies/AGN Southern Galactic Plane Survey, ATCA 1.4 GHz (Gaensler et al. 2001, 2011) Linearly polarised emission, |P| ≣ (Q 2 + U 2 ) 1/2 from same region (Gaensler et al. 2001, 2011) Visualising ISM Turbulence Polarisation gradient, | ∇ P| = [(∂Q/∂x) 2 +(∂Q/∂y) 2 +(∂U/∂x) 2 +(∂U/∂y) 2 ] 1/2 (Gaensler et al. 2011)

Observed data Visualising ISM Turbulence Gaensler et al. (2011)

›Radio synchrotron: a key diagnostic of the cosmic web ›New generation of wide-field low-frequency interferometers can now search for this signal -MWA and LOFAR fully operational -SKA-low in pre-construction phase ›Web-finding tools may have broader applicability ›Theorists, we need you! -radio surface-brightness simulations & calculations -predictions for polarised synchrotron, Faraday rotation -mock skies & data challenges Summary Brüggen et al. (2005) Gaensler et al. (2011) MWA / Hurley-Walker