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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 NGC 891 NGC 891 (Krause, priv.comm.) (Krause, priv.comm.) M 51 VLA+Eff 6cm M 51 VLA+Eff 6cm (Fletcher & Beck) (Fletcher & Beck)

Cosmic magnetism ( KSP of the SKA)

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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). - PowerPoint PPT Presentation

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Page 1: 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

NGC 891 NGC 891 (Krause, priv.comm.)(Krause, priv.comm.)

M 51 VLA+Eff 6cm M 51 VLA+Eff 6cm (Fletcher & Beck)(Fletcher & Beck)

Page 2: 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.

RM mapping of nearby galaxies with the SKA

The SKA will detect ~10,000 polarized sources behind M 31

SKA RM SKA RM surveysurvey(simulation (simulation by Bryan by Bryan Gaensler)Gaensler)

Page 3: Cosmic magnetism ( KSP of the SKA)

T.G.Arshakian, R.Beck and M.Krause (MPIfR, Bonn) R.Stepanov and P.Frick (ICMM, Perm) A&A, 2008

Testing the magnetic field models of nearby spiral galaxies with the SKA

SKADS science simulations

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.

Steps1. To simulate the RM maps of a typical spiral galaxy for - the regular and turbulent magnetic field models (disk and halo) - the thermal electron density model

2. To recognize or reconstruct the magnetic field structure from the simulated RM map and assess their reliability.

Page 4: Cosmic magnetism ( KSP of the SKA)

Faraday rotation model for different magnetic fields

model~ RMRMRM turbreg RMreg RMturb RMmodel

BSS model: RMmax = 95 rad m-2, RMmin = -175 rad m-2 for i =100 and RMturb = 30 rad m-2

• Recognition of a magnetic field model by fitting RMreg and RMmodel

• Reconstruction of magnetic field structure from RMmodel map without a priori assumptions about horizontal field

Page 5: Cosmic magnetism ( KSP of the SKA)

Perspectives for the SKA at 1.4 GHz

• 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.

• The RM errors are 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).

Page 6: Cosmic magnetism ( KSP of the SKA)

T.G.Arshakian, R.Beck and M.Krause (MPIfR, Bonn) D. Sokoloff (MSU, Moscow)

A&A, 2008, accepted

Evolution of magnetic fields and observational tests with the SKA

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.

Page 7: Cosmic magnetism ( KSP of the SKA)

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.

Page 8: Cosmic magnetism ( KSP of the SKA)

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

Page 9: Cosmic magnetism ( KSP of the SKA)

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)

Page 10: Cosmic magnetism ( KSP of the SKA)

The radio continuum - FIR correlation of star-forming galaxies

• Holds over a factor ofHolds over a factor of(at least) 10(at least) 1055 in luminosity in luminosity(e.g., Bell 2003)(e.g., Bell 2003)

• Is valid out to (at least) z≈3Is valid out to (at least) z≈3(e.g., Ivison et al. 2005, Seymour et al. 2008)(e.g., Ivison et al. 2005, Seymour et al. 2008)

• Also holds within galaxies,Also holds within galaxies,down to ≈ 50pc scaledown to ≈ 50pc scale(Hughes et al. 2006, Tabatabaei et al. 2007)(Hughes et al. 2006, Tabatabaei et al. 2007)

Page 11: Cosmic magnetism ( KSP of the SKA)

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 !

Page 12: Cosmic magnetism ( KSP of the SKA)

Model for the evolution of magnetic fields

Two main cosmological epochs in the hierarchical formationscenario

Virialization and merging of dark matter halos (z~20)

Formation of the extended large-scale disk (z~10)

Page 13: Cosmic magnetism ( KSP of the SKA)

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)

Page 14: Cosmic magnetism ( KSP of the SKA)

Evolution of magnetic fieldsField amplification in the Milky-Way (MW) type galaxies

Halo merging virialization Turbulent dynamo (t~3x108 yr)

Disk evolution mean-field dynamo (t~1.5x109 yr)

z =10 – disk formation

Page 15: Cosmic magnetism ( KSP of the SKA)

Evolution of magnetic fieldsField amplification in the Milky-Way (MW) type galaxies

Halo merging virialization Turbulent dynamo (t~3x108 yr)

Disk evolution mean-field dynamo (t~1.5x109 yr)

z =10 – disk formation

Mean-field dynamo in tick disk

Mean-field dynamo in thin disk

Page 16: Cosmic magnetism ( KSP of the SKA)

Evolution of magnetic fieldsField amplification in the Milky-Way (MW) type galaxies

Halo merging virialization Turbulent dynamo (t~3x108 yr)

Disk evolution mean-field dynamo (t~1.5x109 yr)

z =10 – disk formation

Major merger

Page 17: Cosmic magnetism ( KSP of the SKA)

Evolution of magnetic fieldsAmplification 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.

Page 18: Cosmic magnetism ( KSP of the SKA)

Evolution of magnetic fieldsField 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

Page 19: Cosmic magnetism ( KSP of the SKA)

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