May 17, 2010MFPO 2010, Krakow1 Dwarf galaxies and the Magnetisation of the IGM Uli Klein ?

May 17, 2010MFPO 2010, Krakow2 ICM is magnetized (throughout?) Galaxy clusters exhibit: radio halos Faraday rotation peripheral radio structures Clarke et al. (2001) Coma Giovannini et al. (1993)

May 17, 2010MFPO 2010, Krakow3 relativistic electrons have short lifetimes B = 1  G, = 1.4 GHz  t 1/2 = 10 8 z = 0  primary electrons require continuous injection, e.g. via merger shocks galactic wakes secondary electrons: hadronic collisions of relativistic protons with thermal gas

May 17, 2010MFPO 2010, Krakow4 two alternatives: primordial magnetic fields; requires extremely efficient amplification galactic evolution with injection by early starbursts (Kronberg et al. 1999; Bertone et al. 2006) in both cases: particle pools required how did the relativistic plasma get there? AGN

May 17, 2010MFPO 2010, Krakow5 FR I/FR II radio galaxies: P 1.4GHz (FRI/II)  W Hz -1 starburst dwarf galaxies: P 1.4GHz (dwg)  W Hz -1  P 1.4GHz (FRI/II)  · P 1.4GHz (dwg) ΛCDM helps … lifetime of radio galaxy (Bird et al. 2008):  life  1.5·10 7 yr duty cycle:  duty  8·10 8 yr B Fornax A

May 17, 2010MFPO 2010, Krakow6 Dwarf galaxies: deficiency of synchrotron radiation (at GHz frequencies) weak synchrotron emission at low-mass end lack of CR containment Skillman & Klein (1988) Klein, Weiland, Brinks (1991) II Zw 70

May 17, 2010MFPO 2010, Krakow7 Kepley et al. (2010) template: NGC 1569 ×10 3 rad m -2

May 17, 2010MFPO 2010, Krakow8 - break in synchrotron spectrum: cease of SF burst several Myr ago - radio halo - radial magnetic field -B  40 μG (central region) Israel & de Bruyn (1988) Lisenfeld et al. (2004) synchrotron and IC aging (fast in BCDGs!) low-frequency halos will be detectable with LOFAR! 10  90, 110  240 MHz log log S time -  b

May 17, 2010MFPO 2010, Krakow9 LOFAR low band LOFAR high band e.g. spectrum of total radio continuum from the Coma Cluster halo b = 0.5  1.0 GHz Thierbach et al. (2003)

May 17, 2010MFPO 2010, Krakow10 numerous dwarf galaxies should be surrounded by low-frequency halos of synchrotron radiation should be detectable with LOFAR; for B = 3 μG = 50 MHz  t 1/2 = 3.6 · 10 8 yr (centre of low band) = 175 MHz  t 1/2 = 1.9 · 10 8 yr (centre of high band) = 20 MHz  t 1/2 = 5.6 · 10 8 yr should also find lots of ‘idle’ dwarf galaxies!

May 17, 2010MFPO 2010, Krakow11

May 17, 2010MFPO 2010, Krakow12 NB: powerful central radio galaxies cannot do the job: they are pressure-confined! Per A

May 17, 2010MFPO 2010, Krakow13 Spiral galaxies: preponderance of synchroton radiation spiral galaxies: continuous SF and SN rate  production of CRs magnetic fields store CRs  containment, (re)acceleration S ff /S tot < 10% at 1 GHz (Gioia et al. 1982; Klein 1990) optically thin case: Condon (1992)

May 17, 2010MFPO 2010, Krakow14 1 kpc Klein et al. (1996) M tot = 5·10 10 M  D = 3.7 Mpc nearby template: NGC 4449 (partly) radial B-field structure synchrotron halo Chyźy et al. (2000)

May 17, 2010MFPO 2010, Krakow15 A2256 Clarke & Enßlin (2006)

May 17, 2010MFPO 2010, Krakow16 injection: starburst and radio galaxies dispersion: cluster weather NGC1265 NGC1275 IC1133