Direct Measurement of a Magnetic Field at z=0.692

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Direct Measurement of a Magnetic Field at z0.692
Art Wolfe
Regina Jorgenson IOA Tim Robishaw UCB Carl
HeilesUCB Jason X. ProchaskaUCSC
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Evidence for B fields at z 1
Appleton etal 04

• Far IR vs Radio Correlation
• Dust vs Synchrotron Emission

Correlation Independent of z

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Evidence for B fields at z 1 Statistical
Evidence for Faraday Rotation in Mg II Absorption
Systems at ltzgt?1.3 (Bernet etal. 08)
Control
Mg II
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Redshifted 21 cm Absorption-line Profiles
(Arecibo)
3C 286
AO 023516
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Redshifted 21 cm Absorption-line Profiles
(Arecibo)
1.0 Jy
1.8 Jy
3C 286
AO 023516
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Hyperfine energy states B0
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Hyperfine Energy states B?0
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RCP and LCP exitation
??B
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??B
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(No Transcript)
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Stokes-Parameter Spectra of DLA-3C286 from GBT
DI(n)I(n)-Ic(n)/Ic(n)
DV(n)V(n)/Ic(n)
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Parameters from 21 cm Absorption

• z0.69215260.0000008

• s3.750.20 km s-1

• t00.0950.006

• Blos83.98.8mG
• completely unexpected
• Dynamo theory predicts
• weaker B fields in the past!

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VLBI Continuum maps of 3C 286
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(a)
(b)
Section Cuts Along lines in (a)
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Absorption Geometry
200 pc
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Damped Lya Absorption in DLA-3C286
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Optical Absorption Lines in DLA-3C286
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Optical Absorption Lines in DLA-3C286
Physical Parameters from HIRES spectra

• v21-vopt3.8?0.2 km s-1
• s3.080.13 km s-1
• M/H-1.3
• Dust-to-Gas 1 Galactic

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Optical Absorption Lines in DLA-3C286
Physical Parameters from HIRES spectra

• v21-vopt3.80.2 km s-1
• s3.08?0.13 km s-1
• M/H-1.3
• Dust-to-Gas 1 Galactic

FOS spectrum

• C II 158 mm cooling rate
• lt 1 Galaxy cooling rate
• SSFR lt (1/3)?(SSFR)Milky Way

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Upper Limits on Faraday rotation in 3C 286 at
?1332-1434 MHz (Gaensler Ekers 08)
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Upper Limits on Faraday rotation in 3C 286 at
?1332-1434 MHz (Gaensler Ekers 08)

• RMobs-0.10.1 rad m-2
• RMobsRMDLARMMW
• RMMW1.40.2 rad m-2
• RMDLAlt1.9 rad m-2 (95 c.l.)
• Since
• RMDLA2.6(Ne/1019)Blos(1z)-2
• the electron fraction
• xe1.4?10-4 (95 c.l.)

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Consequences of Strong B Field

• Since (B2plane/8p) gtgt (??2/2), B field
  dominates
• midplane pressure.
• Magnetostatic Equilibrium of Gaseous Disk

Predicted (B2plane/8p)midplanepGS2/2
Observed (B2plane/8p)midplane(715)pGS2/2

• Therefore magnetized H I gas cannot be confined
  by
• its self-gravity
• Minimum l.o.s. gas surface Density ?min 490 M?
  pc-2
• required to confine B field

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• Zeeman Splitting in Molecular Cloud (NGC 2024)
• OH and H I Zeeman Splitting Results
• -Blos gt 100 ?G
• - N(H2)gt1022 cm-2
• But, no H2 absorption in HST spectra

Inferred surface density ?1450 M?pc-2 Maximum
l.o.s B field Blos87 ?G
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• Does B field arise in a molecular cloud ?

• Absence of Lyman and Werner absorption implies
  f(H2)lt7?10-4

• Perhaps radio photons traverse molecular gas,
  while optical
• Photons only go through atomic gas

H II
H I
H2
H I
?21 cm
?1216Å
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• Does B field arise in a molecular cloud ?

• Absence of Lyman and Werner absorption implies
  f(H2)lt7?10-4

• Perhaps radio photons traverse molecular gas,
  while optical
• Photons only go through atomic gas

H II
H I
H2
H I
?21 cm
?1216Å

• But, absence of OH 1612 MHz absorption implies
• ?los lt (1/3)??min

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Interpretation(Transient Configuration)

• B field Enhancement by Merger-induced Shock (F.
  Shu)
• If preshock (B1)? 5 mG in disk of galaxy
• Then postshock (B2)? 100 mG if ushock
  250 km s-1
• Image does not rule out two
  foreground galaxies

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Vint
Two Gaseous Disks Colliding
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Vint
Two Redshifts Predicted but only one observed
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Gravitational impulse imparted by merging
Elliptical Galaxy
Radio beam
E
?
?
3 kpc
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WFPC2 Image of 3C 286 (LeBrun etal 97 Chen 08)

• PSF-Subtracted smoothed (0.2?)
• Diffuse object on top of QSO
• -Asymmetry ?foreground galaxy
• Suggests sightline to QSO passes
• within a few kpc of a galaxy

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WFPC2 Image of 3C 286 (LeBrun etal 97 Chen 08)

• Filament 2.5? SE of QSO
• AB(F702W)23.6 mag
• Is the filament
• (a) Outer spiral arm at zabs ?
• (b) A tidal tail at zabs ?

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Conclusions

• First measurement of galactic B field at z gtgt 0
  results in surprise,
• since BDLA ? 20?ltBISMgt at 6.4 Gyr Look
  BackTime
• -Field is average over neutral gas with (a)
  velocity dispersion
• ?v 3.75 kms-1 and (b) linear scales
  from 50 to 200 pc
• -No evidence for strong SFRs usually
  associated with large fields
• 2. Consequences
• -Magnetic Pressure gtgt self-gravity of H I
  gas
• -Magnetic Pressure may be confined by
  gravity
• of molecular gas
• or
• -B field enhanced by shocks generated by
  galaxy merger
• merger probability pRmerge?tduration0.0
  06 to 0.03
• -Star formation rates in DLAs may be
  suppressed by strong
• B fields

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Stokes I and V spectra of 3C 286 (N. Kanekar 08)

• 2 hr. integration on GBT
• Same S Curve shape as
• Wolfe etal (08)

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Polar Representation of Spectrum in Complex
Visibility Plane