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Dwarf galaxies and the Magnetisation of the IGM

Dwarf galaxies and the Magnetisation of the IGM. Uli Klein. ?. Coma. Giovannini et al. (1993). Clarke et al. (2001). ICM is magnetized (throughout?) Galaxy clusters exhibit: radio halos Faraday rotation peripheral radio structures. relativistic electrons have short lifetimes.

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Dwarf galaxies and the Magnetisation of the IGM

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  1. Dwarf galaxies and the Magnetisation of the IGM Uli Klein ?

  2. Coma Giovannini et al. (1993) Clarke et al. (2001) ICM is magnetized (throughout?) Galaxy clusters exhibit: • radio halos • Faraday rotation • peripheral radio structures

  3. relativistic electrons have short lifetimes B = 1 G,  = 1.4 GHz  t1/2 = 108 yr @ z = 0 • primary electrons require continuous injection, e.g. via • merger shocks • galactic wakes secondary electrons: hadronic collisions of relativistic protons with thermal gas

  4. early starbursts (Kronberg et al. 1999; Bertone et al. 2006) AGN in both cases: particle pools required how did the relativistic plasma get there? two alternatives: • primordial magnetic fields; requires extremely efficient amplification • galactic evolution with injection by

  5. B09251420 Fornax A FR I/FR II radio galaxies: P1.4GHz(FRI/II)  1024.7 W Hz-1 starburst dwarf galaxies: P1.4GHz(dwg)  1020.5 W Hz-1 • P1.4GHz(FRI/II)  15000 · P1.4GHz(dwg) ΛCDM helps … lifetime of radio galaxy (Bird et al. 2008): life  1.5·107 yr duty cycle: duty  8·108 yr

  6. II Zw 70 Klein, Weiland, Brinks (1991) Skillman & Klein (1988) Dwarf galaxies: deficiency of synchrotron radiation (at GHz frequencies) weak synchrotron emission at low-mass end lack of CR containment

  7. template: NGC 1569 ×103 rad m-2 Kepley et al. (2010)

  8. log S - time b log  Israel & de Bruyn (1988) Lisenfeld et al. (2004) - break in synchrotron spectrum: cease of SF burst several Myr ago - radio halo - radial magnetic field - B  40 μG (central region) synchrotron and IC aging (fast in BCDGs!) low-frequency halos will be detectable with LOFAR! 10  90, 110  240 MHz

  9. LOFAR high band LOFAR low band e.g. spectrum of total radio continuum from the Coma Cluster halo b = 0.5  1.0 GHz Thierbach et al. (2003)

  10. numerous dwarf galaxies should be surrounded by low-frequency halos of synchrotron radiation should be detectable with LOFAR; for B = 3 μG  = 50 MHz  t1/2 = 3.6 · 108 yr (centre of low band) • = 175 MHz  t1/2 = 1.9 · 108 yr (centre of high band) • = 20 MHz  t1/2 = 5.6 · 108 yr should also find lots of ‘idle’ dwarf galaxies!

  11. Per A NB: powerful central radio galaxies cannot do the job: they are pressure-confined!

  12. Spiral galaxies: preponderance of synchroton radiation optically thin case: Condon (1992) Sff/Stot< 10% at 1 GHz (Gioia et al. 1982; Klein 1990) spiral galaxies: • continuous SF and SN rate  production of CRs • magnetic fields store CRs  containment, (re)acceleration

  13. 1 kpc nearby template: NGC 4449 (partly) radial B-field structure synchrotron halo Mtot = 5·1010M D = 3.7 Mpc Klein et al. (1996) Chyźy et al. (2000)

  14. A2256 Clarke & Enßlin (2006)

  15. injection: starburst and radio galaxies dispersion: cluster weather NGC1265 NGC1275 IC1133

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