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Cosmic magnetism ( KSP of the SKA)

Cosmic magnetism ( KSP of the SKA) understand the origin and evolution of magnetism in the Galaxy, extragalactic objects, clusters and inter-galactic/-cluster space. SKADS in the MPI für Radioastronmie (Bonn) the Galaxy and nearby spiral galaxies. M 51 VLA+Eff 6cm (Fletcher & Beck).

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Cosmic magnetism ( KSP of the SKA)

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  1. Cosmic magnetism(KSP of the SKA) understand the origin and evolution of magnetism in the Galaxy, extragalactic objects, clusters and inter-galactic/-cluster space. SKADS in the MPI für Radioastronmie (Bonn) the Galaxy and nearby spiral galaxies M 51 VLA+Eff 6cm (Fletcher & Beck) NGC 891 (Krause, priv.comm.)

  2. Cosmic magnetism(KSP of the SKA) understand the origin and evolution of magnetism in the Galaxy, extragalactic objects, clusters and inter-galactic/-cluster space. RM mapping of nearby galaxies with the SKA The SKA will detect ~10,000 polarized sources behind M 31 SKA RM survey(simulation by Bryan Gaensler)

  3. Testing the magnetic field models of nearby spiral galaxies with the SKA SKADS science simulations T.G.Arshakian, R.Beck and M.Krause (MPIfR, Bonn) R.Stepanov and P.Frick (ICMM, Perm)A&A, 2008 • The aim is to estimate the required number density of polarized sources to be • detected with the SKA for reliable recognition or reconstruction of the magnetic • field structure in nearby spiral galaxies. • Steps • To simulate the RM maps of a typical spiral galaxy for • - the regular and turbulent magnetic field models (disk and halo) • - the thermal electron densitymodel • 2.To recognize or reconstruct the magnetic field structure from the simulated RM map • and assess their reliability.

  4. RMreg RMturb RMmodel BSS model: RMmax = 95 rad m-2, RMmin = -175 rad m-2 for i =100 and RMturb = 30 rad m-2 Faraday rotation model for different magnetic fields • Recognitionof a magnetic field model by fitting RMreg and RMmodel • Reconstructionof magnetic field structure from RMmodel map without a priori • assumptions about horizontal field

  5. Reconstruction of magnetic field structures is possible from a sample of  1000 RM sources: • few galaxies at ~1 Mpc with T < 1 h, and, • ~60 galaxies between 1 to 10 Mpc with tens to hundred hours with the SKA. • Recognition can be reliably performed from a limited sample of  50 RM measurements: • ~600 spiral galaxies (<10 Mpc, p~0.2 µJy) can be recognized within T ~ 15 min SKA observation time, and • ~60.000 galaxies (100 Mpc, p~0.015 µJy) with T ~ 100 h. • TheRM errorsare much smaller at low frequencies: RM data can be used for detection and recognition of weak galactic and intergalactic magnetic fields with LOFAR, ASKAP and SKA-AA if background sources are still polarized at low frequencies (<300 MHz). Perspectives for the SKA at 1.4 GHz

  6. Evolution of magnetic fields and observational tests with the SKA T.G.Arshakian, R.Beck and M.Krause (MPIfR, Bonn) D. Sokoloff (MSU, Moscow)A&A, 2008, accepted • The aim is to model the cosmological evolution of magnetic fields in disk • and puffy galaxies and test it with the planned SKA. • Method. The dynamo theory to derive the timescales of amplification and • ordering of magnetic fields.

  7. Magnetic fields in nearby galaxies: dynamo mechanism Presence of regular large-scale magnetic fields. Dynamo theory: successfully reproduces large-scale for nearby galaxies (Beck 2005; Shukhurov 2005). Dynamo theory: to predict the generation and evolution of magnetic fields at high-z.

  8. Magnetic fields in distant galaxies: perspectives for the SKA Evidence • RM of distant background galaxies • FIR-Radio correlation SKA: high sensitivity and angular resolution • -> huge number of distant galaxies with the same resolution as in nearby galaxies • -> huge number of RM from point sources

  9. RM of distant background sources • The SKA All-sky Survey will provide a large sample of RMs • Expected RMs from a homogeneous regular IGM field : λ (1+z)-2 ; ne  (1+z)3; B  (1+z)2 → RMIGM  (1+z)3 • However: Population of intervening galaxies towards distant quasars with strong regular fields detected (Kronberg et al. 2008; Bernet et al. 2008)

  10. The radio continuum - FIR correlation of star-forming galaxies • Holds over a factor of • (at least) 105 in luminosity • (e.g., Bell 2003) • Is valid out to (at least) z≈3 • (e.g., Ivison et al. 2005, Seymour et al. 2008) • Also holds within galaxies, • down to ≈ 50pc scale • (Hughes et al. 2006, Tabatabaei et al. 2007)

  11. Model for the evolution of magnetic fields Measures of magnetic evolution Angular momentum of the galaxy () Radial and vertical height (R and h) Turbulence velocity of the ionized gas (v) Turbulence length scale of the gas (l) Gas density () Evolution of magnetic fields is coupled with the formation and evolution of galaxies !

  12. Model for the evolution of magnetic fields Two main cosmological epochs in the hierarchical formation scenario Virialization and merging of dark matter halos (z~20) Formation of the extended large-scale disk (z~10)

  13. Evolution of magnetic fields Three phase model • z~40:Generation of seed magnetic fields • Biermann battery mechanism • z~20: Merging of halos and virialization • Turbulent dynamo (small scale) • z~10: Formation of the large-scale disk • Mean-field dynamo (large scale)

  14. Evolution of magnetic fields Field amplification in the Milky-Way (MW) type galaxies z =10 – disk formation Disk evolution mean-field dynamo (t~1.5x109 yr) Halo merging virialization Turbulent dynamo (t~3x108 yr)

  15. Evolution of magnetic fields Field amplification in the Milky-Way (MW) type galaxies z =10 – disk formation Disk evolution mean-field dynamo (t~1.5x109 yr) Halo merging virialization Turbulent dynamo (t~3x108 yr) Mean-field dynamo in thin disk Mean-field dynamo in tick disk

  16. Evolution of magnetic fields Field amplification in the Milky-Way (MW) type galaxies z =10 – disk formation Disk evolution mean-field dynamo (t~1.5x109 yr) Halo merging virialization Turbulent dynamo (t~3x108 yr) Major merger

  17. Evolution of magnetic fields Amplification in dwarf (DW), MW type and giant disk (GD) galaxies Strong magnetic field at z~10  strong radio continuum  SF can be traced to z<10 with the SKA. Polarized radio disks are expected at z<3 in all galaxies.

  18. Evolution of magnetic fields Field ordering in DW, MW type and GD galaxies Faraday rotatation is expected at z<3 in DW, MW and GD galaxies Anticorrelation between galaxy size and coherence scale

  19. Observational tests with the SKA • Recognition of magnetic field structures is possible for • a large number of nearby spiral galaxies • (60,000 galaxies up to 100 Mpc) • Reconstruction of magnetic field structure is possible for • few nearby extended sources • Test of magnetic evolution (dynamo models) is possible • with the polarized syncrotron emission and Faraday rotation • up to z~5

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