Direct Measurement of a Magnetic Field at z=0.692 Art Wolfe Regina Jorgenson: IOA Tim Robishaw: UCB Carl Heiles:UCB Jason X. Prochaska:UCSC

Evidence for B fields at z ≈ 1 Far IR vs Radio Correlation Dust vs Synchrotron Emission Correlation Independent of z Appleton etal ’04

Evidence for B fields at z ≈ 1: Statistical Evidence for Faraday Rotation in Mg II Absorption Systems at  1.3 (Bernet etal. ‘08) Mg II Control

Redshifted 21 cm Absorption-line Profiles (Arecibo) AO C 286

Redshifted 21 cm Absorption-line Profiles (Arecibo) AO C Jy 1.0 Jy

Hyperfine energy states: B=0

Hyperfine Energy states: B≠0

BB RCP and LCP exitation

BB

Stokes-Parameter Spectra of DLA-3C286 from GBT D I( ) =[I( )-I c (  c ( ) D V( ) =V( )/I c ( )

Parameters from 21 cm Absorption z= ±  =3.75±0.20 km s -1  0 =0.095±0.006 |B los |=83.9±8.8  G 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 Absorption Lines in DLA-3C286

Optical Absorption Lines in DLA-3C286 Physical Parameters from HIRES spectra v 21 -v opt =3.8  0.2 km s -1  =3.08±0.13 km s -1 [M/H]=-1.3 Dust-to-Gas = 1% Galactic

Optical Absorption Lines in DLA-3C286 Physical Parameters from HIRES spectra v 21 -v opt =3.8±0.2 km s -1  =3.08  0.13 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

Upper Limits on Faraday rotation in 3C 286 at = MHz (Gaensler & Ekers ‘08)

Upper Limits on Faraday rotation in 3C 286 at = MHz (Gaensler & Ekers ‘08) RM obs =-0.1±0.1 rad m -2 RM obs =RM DLA +RM MW RM MW =1.4±0.2 rad m -2 RM DLA <1.9 rad m -2 (95% c.l.) Since RM DLA =2.6(N e /10 19 )B los (1+z) -2 the electron fraction x e ≤1.4  (95% c.l.)

Consequences of Strong B Field Since (B 2 plane /8π) >> (  2 /2), B field dominates midplane pressure. Magnetostatic Equilibrium of Gaseous Disk Predicted: (B 2 plane /8  midplane =  G   /2 Observed: (B 2 plane /8  midplane ≥(715)  G  2 /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 -B los > 100  G - N(H 2 )>10 22 cm -2 But, no H 2 absorption in HST spectra Inferred surface density:  =1450 M  pc -2 Maximum l.o.s B field: B los =87  G

Does B field arise in a molecular cloud ? Absence of Lyman and Werner absorption implies f(H 2 )<7  Perhaps radio photons traverse molecular gas, while optical Photons only go through atomic gas H II H I H2H2 =21 cm =1216Å

Does B field arise in a molecular cloud ? Absence of Lyman and Werner absorption implies f(H 2 )<7  Perhaps radio photons traverse molecular gas, while optical Photons only go through atomic gas But, absence of OH 1612 MHz absorption implies  los < (1/3)  min H II H I H2H2 =21 cm =1216Å

Interpretation(Transient Configuration) B field Enhancement by Merger-induced Shock (F. Shu) If preshock (B 1 )  = 5  G in disk of galaxy Then postshock (B 2 )  = 100  G if u shock = 250 km s -1 Image does not rule out two foreground galaxies

V int Two Gaseous Disks Colliding

V int Two Redshifts Predicted but only one observed

E Gravitational impulse imparted by merging Elliptical Galaxy Radio beam 3 kpc  

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

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 z abs ? (b) A tidal tail at z abs ?

Conclusions 1.First measurement of galactic B field at z >> 0 results in surprise, since B DLA  20  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=R merge  t duration =0.006 to 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)

Polar Representation of Spectrum in Complex Visibility Plane