dwarf galaxies and the magnetisation of the igm
DESCRIPTION
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. - PowerPoint PPT PresentationTRANSCRIPT
May 17, 2010 MFPO 2010, Krakow 1
Dwarf galaxies and the Magnetisation of the IGM
Uli Klein
?
May 17, 2010 MFPO 2010, Krakow 2
ICM is magnetized (throughout?)
Galaxy clusters exhibit:
• radio halos
• Faraday rotation
• peripheral radio structures
Clarke et al. (2001)
Coma
Giovannini et al. (1993)
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relativistic electrons have short lifetimes
yr1GHz
1097.821
22
218
21
z
BB
Bt
cmb
B = 1 G, = 1.4 GHz t1/2 = 108 yr @ z = 0
primary electrons require continuous injection, e.g. via
• merger shocks
• galactic wakes
μG)1(25.3 2zBcmb
secondary electrons: hadronic collisions of relativistic protons with thermal gas
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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
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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
B09251420
Fornax A
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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
synαsyn
.ffν νSνSS
,010
,0
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Kepley et al. (2010)
template: NGC 1569
×103 rad m-2
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- 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
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LOF
AR
low
ban
d
LOF
AR
hig
h ba
nd
e.g. spectrum of total radio continuum from the Coma Cluster halo
b = 0.5 1.0 GHz
Thierbach et al. (2003)
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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!
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NB: powerful central radio galaxies cannot do the job: they are pressure-confined!
Per A
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Spiral galaxies: preponderance of synchroton radiation
spiral galaxies:
• continuous SF and SN rate production of CRs
• magnetic fields store CRs containment, (re)acceleration
Sff/Stot < 10% at 1 GHz
(Gioia et al. 1982; Klein 1990)
synαsyn
.ffν νSνSS 10
optically thin case:
Condon (1992)
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1 kpc
Klein et al. (1996)
Mtot = 5·1010 M
D = 3.7 Mpc
nearby template: NGC 4449• (partly) radial B-field structure
• synchrotron halo
Chyźy et al. (2000)
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A2256
Clarke & Enßlin (2006)
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• injection: starburst and radio galaxies
• dispersion: cluster weather
NGC1265
NGC1275 IC1133