Radio halos and relics in galaxy clusters with MWA: projections for SKA Lijo Thomas George, K. S. Dwarakanath Raman Research Institute, Bangalore SKA 2016, Goa, India

Intra-Cluster Medium (ICM) Introduction Galaxy Clusters Dark Matter 80% Intra-Cluster Medium (ICM) 15-17% Luminous Matter (stars etc.) 3-5%

Intra-Cluster Medium (ICM) Introduction Galaxy Clusters Dark Matter 80% Intra-Cluster Medium (ICM) 15-17% Luminous Matter (stars etc.) 3-5% Radio emission Non-thermal, synchrotron B ~ μG, E ~ GeV Radio halos Radio relics X-ray emission T~107-108 K, ρ~10-3–10-4 cm-3 Thermal bremsstrahlung

Radio halos Cluster wide emission (~Mpc) Diffuse (~mJy/arcmin2 at 1.4 GHz) Central regions of the cluster Very little polarization (few %) Rare (~5% of all, ~35% of high Lx) Radio relics Elongated, arc-shaped Peripheries of the cluster Significant polarization (~30%)

HALO RELIC A521 ; z = 0.253 ; 610 MHz (Brunetti et al. 2008)

Kale et al. (2013) A3376 ; z = 0.0456 ; 325 MHz

The issues Diffusion problem (L ~ 1 Mpc, tdiff ~ 10 * tsync) in-situ acceleration Models of halo formation Primary model : turbulence – reacceleration – halos preferentially found in merging clusters Secondary model : p-p collision – radio, gamma – expected radio emission is weak, gamma ray flux not yet detected LX-P1.4 empirical relation

(Kale et al. 2015)

The issues The low detection rate of halos could be due to: Low radio luminosity in low LX clusters (LX < 1044 erg/s) clusters

(Bohringer et al. 2013)

The issues The low detection rate of halos could be due to: Low radio luminosity in low LX clusters (LX < 1044 erg/s) clusters Exponential cut-off of radio spectrum at higher frequencies

A521 (Dallacasa et al. 2009)

The issues The low detection rate of halos could be due to: Low radio luminosity in low LX clusters (LX < 1044 erg/s) clusters Exponential cut-off of radio spectrum at higher frequencies Large angular extents of halos (≥10´ for 1 Mpc at z<0.1) which could get resolved out at higher frequencies (>1.4 GHz) Hence, Low frequency (<1 GHz) observations High quality short spacing data

Murchison Widefield Array (MWA) Low Frequency telescope (80-230 MHz) located in a radio-quiet zone in Western Australia Collaborative effort by institutes in USA, Australia, New Zealand and India (RRI) Telescope Configuration – 128 tiles over 3 km Each tile has 16 dipoles in a 4x4 grid Filled array but poor resolution. At 200 MHz, Θb~2´, RMS~6 mJy/b Source: www.mwatelescope.org

Contours start at 3σ and increase by √2 after, Θb ~ 2´, σ = 5.6 mJy/b PLCK G287.0+32.9, z = 0.39, MWA 200 MHz, Contours start at 3σ and increase by √2 after, Θb ~ 2´, σ = 5.6 mJy/b UNRELATED SOURCES NW RELIC HALO SE RELIC George et al. (submitted)

George et al. (submitted)

LX-P1.4 relation George et al. (submitted)

Current Limitations and Unanswered Questions GMRT (RFI especially in short spacing data) MWA (Resolution, rms (confusion limited), not as sensitive as NVSS) Emission from all merging clusters? (weak turbulence) Radio emission in non-merging clusters due to p-p collisions?

Future Prospects with SKA Better sensitivity and resolution compared to current telescopes Better detection limit for radio halos Telescope Resolution(´´) RMS (μJy/beam) SKA1-Low (120 MHz) 10 20 SKA1-SUR (1.4 GHz) 15 MWA (200 MHz) 120 6000 GMRT (150 MHz) 25 2000

SKA Detection Limits (Kale et al. 2016)

Future Prospects with SKA νb = 1.4 GHz α = -1 νb = 0.6 GHz Avg. halo surf. brightness (25 μJy/100 arcsec2) Confusion Limit at 0.15, 0.6, 1.4 and 5 GHz (Kale et al. 2016)

Future Prospects with SKA Magnetic field measurements in the ICM from FRMs. This along with radio observations of halos will help constrain the secondary model Polarization measurements of relics and halos (SKA-Low and SKA-Mid) Expect to see ~1000s of halos Thank You!