Magnetism in galaxy sytems at higher z

Philipp Kronberg

Los Alamos National Laboratory

15 min version for NRAO NM Symposium

24 October 2008

RM probes of magnetic fields to high z

• Faraday RM + electron column densities from absorption spectroscopy lines, thermal X-rays …

gives

• <B> in galaxy systems to large z. Spectral resolution & sensitivity must be sufficient to estimate Weq.

Need a large optical telescope to explore faint spectra to large z!

• Magnetic fields now detected to z 3 and beyond

5 22 2

0

rad8.12 10 (1 ) ( ) ( ) ( )

m

s

e

z

RM z Bn z z zdl

Faraday rotation at a distant EGRS, and at an intervenor

B in Gauss, ne in cm-3, l in pc

χ0

χ0 + Δχ (= RM × λ2)

host galaxysystemat ze

interveninggalaxy system at za

Alternatively:since what we measure is a column

density integral, Ne ,

re-write the RM expression as:13 22.63 10 (1 ) ,

/

a e

e e

RM z N B

B n B dl n dl

Kronberg P.P. , & Perry, J.J. ApJ 1982

For mathematical formalisms for probing high – z magnetic fieldssee

Welter, G.L., Perry, J.J. & Kronberg, P.P. ApJ 1984

1.Early thinking and attempts

M.J. Rees & M. Reinhardt A&A 1972A.H. Nelson PASJ 1973

P.P. Kronberg & M. Simard-Normandin Nature 1976P.P. Kronberg, M. Reinhardt & M. Simard-Normandin A&A 1977

RM growth for a widespread, magnetized IGM magnetized IGM

P. Kronberg, M. Reinhardt, & M. Simard-Normandin A&A 61, 771, 1977

P. Kronberg, & M. Simard-Normandin

Nature, 263, 653-656, 1976

Histograms of RRM (Galaxy-corrected)For 5 z - bins

The observed increase of RRM(z)was interpreted here to come from a widespread IGM!

P.P.Kronberg & J.J. Perry, ApJ 263, 518, 1982(37 RM + Abs. spectrum QSO’s)

G.L. Welter, J.J. Perry, & P.P. KronbergApJ 279, 19, 1984(119 RM sample, 40 had abs. spectra)

Earlier attempts to compare quasar RRM and absorption lines

Early magnetic field estimates from [RM]-[optical absorption] comparison

Kronberg & Perry, ApJ 263, 518, 1982

Absorption lines were Mg II, N I, Lα, β, γ, Si II, Si IV, C II - V, Fe II, O VI

13 22.63 10 (1 ) , /a e e eRM z N B B n B dl n dl

*

*

3C191 a quasar jet (z = 1.95) with an ``associated’’ intervenor with rich absorption lines

P.P Kronberg, J.J.Perry & E.L.H. ZukowskiApJL 355, L31, 1990

Note: RM’s are up to ~ 2000 rad m-2 at zs

PKS 1229-021 a jet quasar at z = 1.03 behind a spiral galaxy at z = 0.4

Kronberg, Perry & Zukowski ApJ 387, 528-535, 1992

2. RM(z) Analysis of a Galaxy-corrected,

850/260 source RM sampleP.P. Kronberg, M. Bernet, S.J. Lilly, F. Miniati, Short, M.B., Higdon, D.M.

ApJ. March 2008 • New, off-plane RM dataset from measurements and

compilations of Kronberg and others. Mostly have a wide 2 coverage;

Considerable VLA & Effelsberg pol’n data • Sources had known z, luminosity, spectrum, etc. • Weeded of z-dependent sytematics• New, Bayesian methods developed to remove

Galactic foreground RM (M.B. Short, D.M. Higdon & P.P. Kronberg Bayesian Analysis. 2008)

5 22 2

0

rad8.12 10 (1 ) ( ) ( ) ( )

m

s

e

z

RM z Bn z z zdl

Faraday rotation at a distant EGRS, and at an intervenor

B in Gauss, ne in cm-3, l in pc

χ0

χ0 + Δχ (= RM × λ2)

host galaxysystemat ze

interveninggalaxy system at za

Number – z range – Galaxy-corrected RM

27

-2 21 -2

15.5 10

3.5

20 rad m 1.7 10 cm

C

eRRM

zB G

N

For a typical intervening ``galaxy system’’ at z = 2.5:

Galaxy-corrected ``residual’’ RM (RRM) for ~ 800 RM sources to z 3.5

1. smallest RRM’s decline sharply beyond z 1.5

2. strongest RRM perturbations areat 20 – 100 rad m-2

3. Need: precise RM’s and GRM removal

Principal new result: The Universe becomes “Faraday RM – opaque”

at ~1.4 GHz to sources beyond z ~ 1.8

P.P. Kronberg 2007

Cumulative RRM counts compared at z > 1 and z < 1

From Kronberg, Bernet, Miniati, Lilly, Short, & Higdon “ApJ 676, 70, March 2008 “A Global Probe of Cosmic Magnetic Fields to Large Redshifts”

for 0 z 3red & blue curves differ at > 3σ level

Cumulatice plot method:, with. error treatment, etc., in Welter, Perry & Kronberg ApJ 1984

3.New comparison of accurately determined

quasar RM subset with new MgII absorption data

M. Bernet, F. Miniati, S. Lilly, P. Kronberg, M. Dessauges-ZavadskyNature, 15 July, 2008

• 76-Quasar subset at 0.6 z 2, and |b| 30°

• Require radio - optical L.o.S. < 50 kpc at za, and mv<19

• RM’s by PPK (VLA, Effelsberg, ++) + literature RM’s• Typical RM measurement error ~ 2 rad m-2 (

• Spectra from 8m VLT, UVES (echelle) spectrograph

• Intrinsic (rest frame) Lorentzian width of RM = 7+6-2 rad m-2

(determined from larger RM sample study in Kronberg et al. ApJ Mar08)

Ionization potentials of interstellar species:

MgII (singly ionized Mg): 15.035 eV 0 = 2796.35, 2803.53Å

-- excitation level close to that of hydrogen - 13.598 eV

-- compare: e.g. MgI (neutral) 7.646 eV

-- we measured on 0 = 2796.35Å

Ne = column density (cm-2) in the Faraday rotating absorption system

za = redshift of the Faraday rotating absorber

<B> = the ne-weighted magnetic field strength along the column defined by Ne

Effect of MgII absorption (λλ2796.35, 2803.53 Å) on the RM’s of quasars

2.0 z 0.6 mV < 19, and |b| > 30°M.L. Bernet, F. Miniati, S.J. Lilly, P.P. Kronberg, M. Dessauges-Zavadsky

Nature 454, 302-4, 2008 Jul18

All sources

1 or 2 MgII systems

2 systems only

From new VLTObservations of MgIIabsorption linesin 2006-7. UVES spectrograph

Cumulative plot versions RM for the same 3 different MgII absorption line groups

M.L. Bernet, F. Miniati, S.J. Lilly, P.P. Kronberg, M. Dessauges-Zavadsky Nature 454, 302-4, 2008

Method: G.L. Welter, J.J. Perry & P.P. Kronberg ApJ 279, 19, 1984

All sources

1 or 2 MgII systems

2 MgII systems only

Cumulative RM counts

Summary of results (part 3)• Weq 0.3 – 0.6 is typical of galaxy with Ne 9.1019 cm-2 (Rao, S.M., Turnshek, D.A., Nestor, D.B. ApJ 636, 610, 2006)

• σMgII absorbers at restframe za 140+80-50 rad m-2

• σNo absorption 20+10-4 rad m-2 (“noise” level)

• A few source-associated (e.g. 3C191-like) systems are not ruled out

• Magnetic fields (without internal reversals) in intervenor galaxies over 0.6 z 2:

1

2 19 210 G

140rad m 9 10 cmMgII eN

B

Principle conclusions from parts (2) and (3)

• (Part 3) Magnetic field strengths in galaxy systems (Ne 1020

cm-2) up to 60% of Hubble ago are at least comparable to <|B|> at z = 0 .

• Part (2) results indicate same, but 80% of Hubble ago

• i.e. confirms no evidence for a slow galactic dynamo field amplification over cosmic time

* * *

Conclusion

• Late type galaxies contain, and expel magnetic fields of several G out to the largest z’s we can measure.

• The global RRM(z) development is concordant with latest detailed measurements on individual galaxies

• There are probably additions to the story