Direct Measurement of a Direct Measurement of a Magnetic Field at z=0.692Magnetic Field at z=0.692

Art WolfeArt Wolfe

Regina Jorgenson: IOATim Robishaw: UCBCarl Heiles:UCBJason X. Prochaska:UCSC

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Evidence for B fields at z ≈ 1

Far IR vs Radio Correlation

Dust vs Synchrotron Emission

Correlation Independent of z

Appleton etal ’04

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Evidence for B fields at z ≈ 1:Statistical Evidence for Faraday Rotation in Mg IIAbsorption Systems at <z>1.3 (Bernet etal. ‘08)

Mg II

Control

Redshifted 21 cm Absorption-line Profiles (Arecibo)

AO 0235+16 3C 286

Redshifted 21 cm Absorption-line Profiles (Arecibo)

AO 0235+16 3C 286

1.8 Jy1.0 Jy

Hyperfine energy states: B=0

Hyperfine Energy states: B≠0

B

RCP and LCP exitation

B

Stokes-Parameter Spectra of DLA-3C286 from GBT

DI()=[I()-Ic(c()

DV()=V()/Ic()

Parameters from 21 cm Absorption

• z=0.6921526±0.0000008

• =3.75±0.20 km s-1

• 0=0.095±0.006

•|Blos|=83.9±8.8G

completely unexpected:

Dynamo theory predicts

weaker B fields in the past!

VLBI Continuum maps of 3C 286

Section Cuts

Along lines in (a)

(a)

(b)

Absorption Geometry

200 pc

Damped Ly Absorption in DLA-3C286

Optical AbsorptionLines in DLA-3C286

Optical AbsorptionLines in DLA-3C286

Physical Parameters fromHIRES spectra

• v21-vopt=3.80.2 km s-1

• =3.08±0.13 km s-1

•[M/H]=-1.3

•Dust-to-Gas = 1% Galactic

Optical AbsorptionLines in DLA-3C286

Physical Parameters fromHIRES spectra

• v21-vopt=3.8±0.2 km s-1

• =3.080.13 km s-1

•[M/H]=-1.3

•Dust-to-Gas = 1% Galactic

FOS spectrum

• [C II] 158 m cooling rate < 1% Galaxy cooling rate

• SFR < (1/3)(SFR)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=-0.1±0.1 rad m-2

• RMobs=RMDLA+RMMW

• RMMW=1.4±0.2 rad m-2

• RMDLA<1.9 rad m-2 (95% c.l.)

Since

RMDLA=2.6(Ne/1019)Blos(1+z)-2

the electron fraction

xe≤1.410-4 (95% c.l.)

Consequences of Strong B Field

• Since (B2plane/8π) >> (2/2), B field dominates

midplane pressure.

• Magnetostatic Equilibrium of Gaseous Disk

Predicted: (B2plane/8midplane=G/2

Observed: (B2plane/8midplane≥(715)G2/2

•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

Zeeman Splitting in Molecular Cloud (NGC 2024)

•OH and H I Zeeman Splitting Results-Blos > 100 G

- N(H2)>1022 cm-2

•But, no H2 absorption in HST spectraQuickTime™ and a

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Inferred surface density: =1450 Mpc-2

Maximum l.o.s B field: Blos=87 G

Does B field arise in a molecular cloud ?

•Absence of Lyman and Werner absorption implies f(H2)<710-4

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

H II

H I

H2

H I

=21 cm=1216Å

Does B field arise in a molecular cloud ?

•Absence of Lyman and Werner absorption implies f(H2)<710-4

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

•But, absence of OH 1612 MHz absorption implieslos < (1/3)min

H II

H I

H2

H I

=21 cm=1216Å

Interpretation(Transient Configuration)

•B field Enhancement by Merger-induced Shock (F. Shu) If preshock (B1)= 5 G in disk of galaxy

Then postshock (B2) = 100 G if ushock = 250 km s-1

Image does not rule out two foreground galaxies

Vint

Two Gaseous Disks Colliding

Vint

Two Redshifts Predicted

but only one observed

E

Gravitational impulse imparted by merging Elliptical Galaxy

Radio beam

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 ?

Conclusions1. First measurement of galactic B field at z >> 0 results in surprise, since BDLA 20<BISM> 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 >> 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 p=Rmergetduration=0.006 to 0.03 -Star formation rates in DLAs may be suppressed by strong B fields

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