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Diffuse polarizationimaging (and the case forAAsformid-frequencies !)

Diffuse polarizationimaging (and the case forAAsformid-frequencies !). Ger de Bruyn ASTRON, Dwingeloo & Kapteyn Institute , Groningen. Outline. - (Linear) Polarization – science - Some recent resultson diffuse polarization (150-1400 MHz)

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Diffuse polarizationimaging (and the case forAAsformid-frequencies !)

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  1. Diffuse polarizationimaging(and the case forAAsformid-frequencies !) Ger de Bruyn ASTRON, Dwingeloo& Kapteyn Institute, Groningen AAVP-Meeting, Cambridge, UK

  2. Outline - (Linear) Polarization – science - Some recent resultson diffuse polarization (150-1400 MHz) - Optimalfrequency range: 300 – 1400 MHz using RM synthesis - RelevanceforAA’s, and (what) do we need to prove (it) ? - Conclusions AAVP-Meeting, Cambridge, UK

  3. Polarization = Magnetismscience • CosmicMagnetism: one of SKA sciencedrivers (Gaensler et al, 2004) • (butunderpresssurefor SKA1 !? ) • Magnetism is alsoone of 6 KeyScienceProjectsfor LOFAR • (seewww.mpifr-bonn.mpg.de/staff/rbeck/MKSP/mksp.html) • Somescience goals: • all-sky RM grid (> 107sources) • magneticfields in normalgalaxies • - cluster and cosmic-webmagneticfields • magneticfields in pulsars, stars • AGN , giant radio galaxies • - ourGalaxy (foregroundfor CMB and EoR !) Taylor, Stil &Sunstrum, 2009 37,453 sources AAVP-Meeting, Cambridge, UK

  4. Someresultsondiffusepolarization 22 GHzAll-sky (WMAP) 1400 MHz All-skyvery low resolution (0.5-1o) 1400 MHz selectedregions at 0.5-1’ 350 MHz large-sky 4’ resolution 150 MHz FAN region (l=137o, b=+8o) Bottomline: Veryrichpolarizationscience in diffuse (mostlyGalactic) structures. Complex Faraday spectra (Faraday-thin and Faraday-thickcomponents) These need to beunderstoodif we want to properlyinterpret RM grid of discrete sources ! AAVP-Meeting, Cambridge, UK

  5. Full-sky polarization (high freq) images of our Galaxy 22.8 GHz WMAP image (no depolarization ) 1.4 GHz Reich, Wolleben et al (depolarization effects already visible in the Galactic plane) AAVP-Meeting, Cambridge, UK

  6. Arcminpolarizationstructure in inner Galaxy Gaensler et al (2001) ATCA, 1400 MHz Veryrichpolarizationstructure in inner Galaxy No orverylittlecorrelationbetween Q,U and I AAVP-Meeting, Cambridge, UK

  7. WSRT 1400 MHz observations Perseus cluster 21cm pointings (1300-1460 MHz) 92cm background North East West Central de Bruyn & Brentjens, 2011)

  8. Perseus - EAST • Peak in I ~ 5 Jy (3C84) • Pol-noise ~ 5-7 Jy/PSF • DR ~ 106 : 1 • (Relative to an off-axis source !!) • All polarized emission probably • from Galactic foreground • Note ‘embedded’ discrete sources • ! 30”x45” smoothedpolarised intensity

  9. WSRT 325 MHz polarization in our Galaxy’s 2d quadrant Schnitzeler et al (2007) Haverkorn et al (2004) AAVP-Meeting, Cambridge, UK

  10. Galactic location of FAN and Abell 2255 • Haslam et al (1981) • 408 MHz • All-sky (0.85o PSF) Galactic coordinates FAN Abell 2255 Equatorial coordinates AAVP-Meeting, Cambridge, UK

  11. Polarization at 150 MHz (!) in FAN region: ‘the ring’ RM = - 5 rad/m2 RM = - 2 rad/m2 Bernardi et al, 2009 AAVP-Meeting, Cambridge, UK

  12. Stokes Q and U images at RM = - 2 rad/m2 AAVP-Meeting, Cambridge, UK

  13. WSRT 350 MHz Cluster of galaxiesAbell 2255 Pizzo et al, 2010 AAVP-Meeting, Cambridge, UK

  14. Linearpolarizationtowards A2255: a different picture ! Integratedpolarizedintensity at variousFaradaydepths: -4 to +12 rad/m2 +16 to +36 rad/m2 de Bruyn &Pizzo, 2010 AAVP-Meeting, Cambridge, UK

  15. Sum of Faradaydepth frames +16 to +36 rad/m2 PolarisedIntensityStokes Q (U lookssimilar) Note the veryrichangularstructure in pol angle ! AAVP-Meeting, Cambridge, UK

  16. Double-valuedFaraday spectra Diffuse emission Φ = +15 and + 42 rad/m2 (noise bias ~ 60 μJy/beam ) Discrete source: Φ = 0 rad/m2  instrumental Φ = +42 rad/m2  intrinsic AAVP-Meeting, Cambridge, UK

  17. Polarimetry and the case forAA’s • 1) The wholesky is filledwith diffuse polarization (Galaxy is all aroundus !) • needlargesurvey speed ! • 2) Goodresolutionneeded in RM space ( = Faradaydepth) • widefrequency range down to ~ 300 MHz and possibly up to 1400 MHz • Thiswillgive excellent resolution in RM (orFaradaydepth) spacethrough RM synthesis (Brentjens & de Bruyn, 2005) • RMSF ~ 3.5 /Δ(λ2)e.g. 300 - 1000 MHz  4 rad/m2 • 3) A compact array (< 500m ) couldalready prove the science case AND demonstratetechnical performance (cal, imaging, DR, wide FOV, polar) AAVP-Meeting, Cambridge, UK

  18. Conclusions • - Studyingcosmicmagnetismrequiresunderstandingforegroundemission • - Optimalfrequency range: ~ 300 - 1000 MHz • - Minimum resolutionrequiredabout 5’  300 - 500m arraycan do it ! • - Fastsurvey speed needed  ApertureArray • We need to demonstratethisby 2015 (preaching to the converted?) • (Seriousdoubtsthat a 70 - 450 MHz AA-arraywouldbeinterestingor even possible) AAVP-Meeting, Cambridge, UK

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