PoS(MRU)067 1

http://pos.sissa.it tic fields are generated and y be much more magnetically magnetically more y be much tic magnetic fields, including tic magnetic tional techniques. A forward look to what tional techniques. A forward look me exciting new discoveries that further exciting new discoveries that me ould achieve, as indicated by these current these current indicated by ould achieve, as eative Commons Attribution-NonCommercial-ShareAlike Licence. Licence. Commons Attribution-NonCommercial-ShareAlike eative

our knowledge of intergalac explain how intergalactic magne intergalactic space. The IGM ma 1 previously thought. [email protected] [email protected] P. Kronberg Philipp Speaker:

1 Copyright ownedCopyright by the author(s) under the terms of the Cr

© University of Manchester, Manchester, UK UK Manchester, Manchester, of University 2007 October, 1-5 universe radio modern the energy: dark to planets From Address, Canada/ USA USA Canada/ Address, E-mail: I describe the latest state of Philipp Kronberg Affiliation, of University Toronto/ Los Alamos NationalLaboratory Magnetic fields in the Universe and fields in the Universe Magnetic for future probesprospects and observa of the experimental brief mention c the next generation of radio instruments so suggests state-of-the-art measurements, spread from galaxies into energized that we exploration of the extragalactic radio universe will produce. I also discuss some discuss some I also will produce. universe radio the extragalactic of exploration physical principles that can

PoS(MRU)067

± that B i.s. G, and Kronberg B μ , beginning with B i.s B ound to arrive at the e international radio radio e international believed to originate in to originate believed where in this conference. where in this began with attempts by G. began with attempts disk – whose thickness was B i.s Bank in the 1960’s to achieve B lues in the range 1 – 2 magnetic field strength of 5.2 magnetic interstellar magnetic field, field, magnetic interstellar field strength began in the 1940’s, field strength began in the 1940’s, l astronomical instrument (i.e. radio instrument l astronomical arguments to arrive at essentially the arguments remnants is was remarkable that their is was remarkable remnants notably Carl Heiles at U.C. Berkeley. ght was detected by W.A. Hiltner from from Hiltner W.A. by ght was detected due to magnetic field fluctuations along due to magnetic observations. The only confinement observations. The only confinement ray nuclei had been f and analysis not of cosmic radio emission, radioand analysis not of cosmic emission, forced the conclusion that the CR’s were that the CR’s forced the conclusion starlight, and subsequently of the Galactic Shakeshaft & Pauliny-Toth (1962). These Shakeshaft & Pauliny-Toth B i.s lights of the measurements, or deduction of or deduction of lights of the measurements,

they argued, because if the CR’s were really were really they argued, because if the CR’s A.G. Lyne and F.G. Smith. Pulsar RM/DM A.G. Lyne and F.G. Smith. ng locally with the Milky Way disk, and the Milky Way ng locally with B little attention from th from little attention e plane of the Milky Way. Indeed,e plane of the Milky up to the Way. 2 order to produce the observed degree of CR order to produce the observed ting of the 1420.4 MHz hyperfine transition of ting of the 1420.4 MHz hyperfine transition plied by their isotropy, the energy content of on gives particular emphasis to work done by emphasis on gives particular ter and Ludwig Biermann (1950), who pointed űter and Ludwig Biermann l measurements of l measurements has also produced estimates of has also produced estimates interstellar magnetic field strength. interstellar magnetic es et al. (1968) at Jodrell eV. Since the CR sources were eV. Since the CR the test of nearly 60 years, and it is remarkably similar similar remarkably it is and 60 years, nearly test of the ttered within the Galactic within the ttered 16 n. These gave, initially, va val directions were found to be isotropic! val directions were found to be isotropic! eV, they estimated an interstellar an eV, they estimated 16 10 ≈ Philipp Interstellar linear polarization of starli of linear polarization Interstellar Some of the first astronomica the first of Some This result, which involved no conventiona This fact was noted by A.Schl Measurement of the Milky Way’s magnetic of the Milky Way’s Measurement Introduction Introduction G. Enrico Fermi (1949) applied similar (1949) applied similar G. Enrico Fermi 0.3 μ conclusion. same or optical telescope), has stood consensus value of the to the current years, were later extended by others over many The ratio of pulsar RM/DM’s isotropy up to of the optical polarization of measurements by Wielebinski, radio emission continuum myself, and occasionally I call attention to I call attention and occasionally and myself, other colleagues, postdocs, my students, have received rather that earlier results astronomy. In disk. the Milky Way must permeate Davi Verschuur (1968) and R.D. split the difficult detection of the Zeeman Hydroge neutral interstellar at Jodrell Bank by such estimates the first of sight average give a line measurements detail else in more treated the sightline. Pulsar observations are rs, and beyond, up to the largest identifiable to the largest identifiable beyond, up galaxy clusters, and halos, to galaxy proceeding Universe. My descripti structures in the Strange, result. an intriguing out that it was 2. A very brief field in the Milky Way. magnetic story of the 1. high I review some In this brief contribution beginni diffuse media, fields in magnetic investigations from and the first results came cosmic but of cosmic rays. By the late 1940’s and supernova the Galaxy, e.g. in supernovae with th correlate did not directions arrival highest energies, the arri as im of universal (extragalactic) origin large. This intergalactic space is implausibly confined to, and sca somehow Magnetic Fields Magnetic Earth with energies up to ~ 10 visual from known, and even deducible argued, was an Schlűter and Biermann mechanism, PoS(MRU)067

9 G μ – 10 6 . Kronberg e. n aine et al. 2002). synchrotron halo. It tic medium (IGM). (IGM). tic medium component of the component strengths of order 2 ordered laxy. Most recently, work by laxy. Most recently, gnetic field strength was first gnetic field strength was first ve central black holes (BH) of large calculated from estimates of central calculated from estimates d structure using extragalactic radio radio extragalactic using d structure intergalactic medium. At his point we intergalactic medium. ed, is how the cluster magnetic field ed, is how the cluster magnetic et al (1990) analysed the Coma cluster cluster et al (1990) analysed the Coma well established that the ICM of galaxy galaxy that the ICM of well established be the efficiency with which the BH with which the efficiency be the dispersions (e.g. Trem . He produced estimates in the range 2 – in the range . He produced estimates η much lower than those in galaxy disks much lower than those in galaxy field reflects an approximate energy energy an approximate field reflects se, cluster – associated se, cluster G, and the field strength does not appear G, and the field strength does

that Coma had fieldthat Coma e surrounding intergalac 3 cal scale, galaxy filaments, is discussed next. is discussed cal scale, galaxy filaments, galaxies bearing BH’s in the range 10 T of the hot ICM thermal gas rather than just than gas rather the hot ICM thermal T of : k scale field models of the Ga of scale field models e evidence for a significant a significant for evidence MMpc aged searches for galaxy cluster magnetic fields, the the fields, for galaxy cluster magnetic searches aged n 53 t into the surrounding | and component over the Galactic disk. over the component 2 10 / (1) B B | in the next hierarchi B BH ρ <>≈× Philipp = 75). Now, with better data, it is = 75). Now, with better data, it 0 First the “smoothed-out” BH density can be The enormous energy release from the massi energy release from The enormous A current question, not yet well answer A current question, not yet well The question of the ICM physics and ma The question of the ICM physics It was perhaps the relatively much lower density of the intracluster medium medium intracluster the of lower density much relatively the perhaps It was The larger scale Milky Way fiel scale magnetic The larger G for the intracluster medium. Later, Kim Later, Kim G for the intracluster medium. gives a space-averaged BH mass density of BH mass gives a space-averaged μ : 4. Expectations for central Black Hole-produced intergalactic fields magnetic Attempts to detect | to detect Attempts affected by the presence or absence of a diffu a of or absence affected by the presence magnetic that the intracluster is apparent equipartition between | th field in to the magnetic ``matches’’ this with the space density of Combining M

clusters is magnetized at levels of a few μ a few at levels of clusters is magnetized calculation. we can do a simple energy into the IGM, releases magnetic galaxy bulge velocity derived from BH masses

interstellar magnetic field. field. magnetic interstellar galaxies is directed via a je be retained for a radio galaxies, whose energy release may ignore cluster-embedded in the host cluster ICM. Letting long time (ICM) that initially discour (ICM) that initially should be being that ICM fields assumption gas densities. lower based on their 10 – 100 times 3. fields in clusters of galaxies Magnetic Han and colleagues (this meeting) and Brown colleagues have further refined and (this meeting) Han and colleagues models of the ordered (1980) detail by Dennison investigated in some 10 to deduce RM measurements with targeted (scaled to H Magnetic Fields Magnetic early provided observations (1967) and colleagues in Australia. This investigated by R.D. Davies (1967) and colleagues sources was first and Kronberg (1980), who compared the work of Simard-Normandin was followed by against large RM observations PoS(MRU)067

G BH -7 IG

B Kronberg

is to proceed from from is to proceed IG

of the infall energy of the infall a to at have been a jet-lobe B -3 , . Then η S laxy discs to (comparable) laxy discs to (comparable) model galaxy filaments. For galaxy filaments. model erg cm erg , (3) alactic space occupied by galaxy by galaxy alactic space occupied : H B M tation measures on the Galactic sky is tation measures 8 hifts, can nonetheless define a galaxy t at a Faraday rotation detection of t at a Faraday rotation detection to be the filaments rather than the voids of the rather than to be the filaments to ask if the next level of cosmic system cosmic of level the next ask if to the first investigation of this kind, Xu et Xu et this kind, of investigation the first ⎛⎞ ⎝⎠ ⎜⎟ e magnetic energy density central BH’s that in the galaxy filament zones of LSS. They in the galaxy filament ional to magnetic energy, here adopted as ional to magnetic mbined with sensitive deep galaxy surveys a 3-D model. The 2MASS survey which, a 3-D model.

actor of a few in each of the adopted the adopted actor of a few in each of , partly with the purpose of giving a “feel’’ 1 ss a magnetized environment that that scales that that environment a magnetized ss galaxy filaments in cosmological large scale galaxy filaments in cosmological ous section presented one such calculation of − 4 L I : 7 − VOL BH M fM 8 galaxies over a Hubble time th galaxies over a Hubble time M ⎛⎞ ⎝⎠ ⎜⎟ whether some local Universe galaxy filaments add an local Universe galaxy filaments whether some 10 field strengths from the ga observational detection, either by Faraday rotation or either by Faraday rotation observational detection, 2 as the BH’s Schwarzschildas the radius, R RG f B is the fraction of all interg ⎛⎞ ⎜⎟ ⎝⎠ πε FIL 1.8 10 ergs (2) 8 1.8 10 G. (4) =× BF VOL 26 ==× 0.1 0.1 0.1 10 η f ⎛⎞ ⎝⎠ ⎜⎟ BH BH IG 15 − B Philipp Mc is the fraction of large These numbers suggest that magnetic fields at the level of a few times 10 of a few times at the level fields that magnetic suggest These numbers The angular density of accurate Faraday ro I now briefly describe a first attemp I now briefly describe a first A related way of posing the question of expectations for A related way RG f 1.36 10 =× × × × is the efficiency of conversion of gravitat is the efficiency of conversion of B B ε might be detectable over scales of a few Mpc might within reach of are potentially perhaps by faint synchrotron radiation. “expectation”. “expectation”. in some physically sensible way. The previ in some the progression of magnetic the progression of magnetic leads us ICM’s. This naturally values in cluster or chains of galaxies, posse scale, filaments normalization factors in (3) will, in combination, not likely have a large effect on effect a large have likely not will, in combination, in (3) factors normalization filaments and sheets. Variations by a f filaments radio source and

5. Search for a detectable magnetic 5. Search for a detectable magnetic field in structure (LSS) so that η reference radiusreference we adopt which Magnetic Fields Magnetic be released “available” the energy We can express as a fraction, to

energy we can calculate the is magnetic, averag Now with some necessary normalisations, and assuming half the relativistic that gas inject into intergalactic space – which we assume spaceinject into intergalactic – which large scale structure (LSS). column density for the supercluster filaments. Three local universe superclusters were universe superclusters Three local filaments. the supercluster density for column now just good enough to test In “RM signal” to radio sources behind them. al. (2006) used both the CfA and 2MASS galaxy surveys to tessilate the CfA survey, it was possible to unlike the CfA did not have spectroscopic reds intergalactic magnetic fields at these levels at these fields magnetic intergalactic for what could be done with a future SKA co redshifts. with spectroscopic 10%, PoS(MRU)067 Source: Source: Kronberg , 19, 2006.) 637 e RM’s to better detect an detect better to e RM’s interesting, and tantalizing testbed for for interesting, and tantalizing testbed densely covered southern sky, compared compared sky, southern covered densely a foreground large scale Galactic feature a foreground large

alactic RM’s for sources of known redshift redshift alactic RM’s for sources of known ment-associated, IGM field strength of order IGM field strength of order ment-associated, galaxy supercluster filament. Looking to the Looking to the filament. galaxy supercluster 5 ). (Xu, Kronberg, Habib & Dufton, ApJ & Dufton, Habib ). (Xu, Kronberg, the best-delineated chain of galaxies, showed an an of galaxies, chain best-delineated the “cleaned” of anomalously larg of anomalously “cleaned” Philipp Comparison of a portion of the smoothed RM sky compared with a comparably smoothed, smoothed, a comparably with compared sky RM smoothed of the a portion of Comparison It is always possible, of course, that It is always possible, ection 4. Figure 1 illustrates the RM sky section 4. Figure expect from might G -- just what we μ The Astrophysical Journal magnitude-limited galaxy distribution from the 2MASS survey.The false colours represent RM (upper) (upper) RM represent colours false survey.The 2MASS the from distribution galaxy magnitude-limited (lower density surface galaxy and relative

0.1 er filaments. Of the three superclusters, superclusters, the three Of filaments. er the superclust from weak RM signal expected which has only Perseus-Pisces, fila with a RM signal consistent interesting Magnetic Fields Magnetic intergalactic an by comparing s-Pisces, Perseu and Virgo, Hercules investigated; with extragalactic (2MASS) density column or galaxy (CfA) length path weighted were The latter source RM’s. Figure 1:

could (perversely) mimic the effect of a mimic could (perversely) more densely cover the sky. that much future however these observations provide an future however these observations in future with extrag possible what will be map. Further details can be found in Xu, details can be found in Xu, Further density map. galaxy column with the a smoothed & Dufton (2006). Kronberg, Habib omitting the galactic plane zone and the less and zone plane galactic the omitting PoS(MRU)067 Kronberg

central black hole. hole. black central , to compare the energy the energy , to compare : M 8 energies represents an energy level Figure 2, adapted from this paper, the from Figure 2, adapted nst overall source size for two classes of nst overall source the formation energy (Equation (2)) of a the formation

radio sources with each other and with the each other with sources radio 6 own by Kronberg et al. (2001) own by Kronberg e of a galaxy cluster. the X-ray centre of a galaxy ithin 150 kpc of rgest dimensions, cut off at a lower bound of ~ 6.5 Mpc in cut off at a lower bound rgest dimensions, and withand the approximate infall energyof a 10 Philipp The total energies of (1) giant (blue diamonds), and (2) cluster-embedded radio sources sources radio cluster-embedded (2) and diamonds), (blue giant of (1) energies total The The upper envelope of the giant sources The upper envelope of It is illuminating, as sh It is illuminating, (green boxes) compared, compared, (green boxes) (Adapted from Kronberg, Dufton, Li, & Colgate ApJ 2001). 2001). ApJ & Colgate Li, Dufton, Kronberg, from (Adapted

Magnetic Fields Magnetic 6. as calorimeters Large radio sources of energy BH release Figure 2:

within only ~ 1½ orders of magnitude of within only ~ 1½ orders of magnitude energy of the original BH “reservoir”. In BH “reservoir”. energy of the original energy contents are plotted agai approximate with the la source. (1) those w a sample projection, and (2) contents of different classes of extended contents of different PoS(MRU)067

, ° η Kronberg ource: the ource: the

) . Such a situation a situation . Such the Schwarzschild the Schwarzschild R , S / S R Fig. 2 should also be Fig. 2 should also R A 0.4 GHz image of an 8 0.4 GHz image A 267, 2007.(S : their observed sizes. In their observed sizes. nd the internal volumend the internal , es get upwards-corrected to 659 = 0.1 used in equation (3). B = 0.1 in the above plot, so that = 0.1 in the above < 150 kpc have strikingly lower

Figure 3 diameter field near the North Galactic near the field diameter Pole, showing the radio halo of the image The galaxies. of cluster Coma represents a combination of the DRAO the and telescope Arecibo EllipsesInterferometer. representing sources discrete removed brightest the power half x 6.5’ 2.5’ the show For beam. DRAO of the dimensions text, and see the description further Kothes, Salter, & Perillat Kronberg, ApJ Astrophysical Journal

reduce the gap with the upper η φ cl r ma, whichma, reduce the energy could also r further details the reader is referred to to referred is the reader details further r calculated using the measured thermal the measured calculated using gy calculation requires assumptions about about requires assumptions gy calculation 100 and the Arecibo radio telescope, and the 7- radio telescope, and the the Arecibo counterparts. But when the very substantial when the very substantial But counterparts. =

llness of the gap gives a direct confirmation llness of the gap gives a direct confirmation ales down to 5’ (Kronberg, Kothes, Salter ales down to 5’ (Kronberg, Kothes, BC has produced the deepest radio image of image radio BC has produced the deepest onal– to- relativistic plasma energy ratio, energy ratio, plasma to- relativistic onal– e giant source radio lobes will already havee giant source radio lower in proportion to lower in proportion k ergy estimates somewhat, but not drastically. drastically. but not somewhat, ergy estimates onal-to-magnetic coupling happens at a few onal-to-magnetic at the BH is larger than the at 7 R correction of the points in correction of the om X-ray images, these energi X-ray images, om work done by the time they reach time work done by the PdV tivistic protons, a tivistic protons, invisible rela in the k) in Figure 2 would be in Figure 2 would work, an upwards ) of the synchrotron radiating plas ) of the synchrotron φ Philipp in the BH accretion disk. That would in the BH accretion disk. S Finally, we note that those sources in Fig 2 at Finally, we note that those sources If the effective final infall radius radius infall final the effective If central BH. The sources’ internal ener BH. The sources’ central

R : work of the cluster-embedded sources is work of the cluster-embedded M 8 addition to the PdV and radiation losses. for diffusion made

the energy fraction ( the energy ( factor filling

7. A new, deep search for faint diffuse synchrotron radiation GHz of at 0.4 combination novel A recent, at Penticton DRAO Interferometer element sc yet seen at on resolution diffuse emission Magnetic Fields Magnetic 10 radius, the upper line radius, the upper is plausible, for example if the gravitati for example is plausible, times times i.e. efficiency, is high and it justifies the normalisation the normalisation it justifies high and is i.e. efficiency, be comparable with the giant radio sources! Fo sources! radio the giant with be comparable (2001). Kronberg, Dufton, Li, and Colgate energy contents than their giant radio source energy contents than their giant PdV intracluster hot gas pressure fr lower values of either would reduce the en of either would reduce lower values On the other side of this energy ledger, th On the other side to some lost energy due envelope of the giants in Figure 2. The sma envelope of the giants in Figure the gravitati that radio measurements from estimates in Fig 2. These were adopted as in Fig 2. estimates PoS(MRU)067 Kronberg , 29, 1990 , 158, 1962 1962 , 158, of intergalactic intergalactic of 355 82 ther, there are 6 – 8 ther, 267, 2007

magnetic and particle and particle magnetic , 178, 2001 2001 , 178, , , 29, 2006, 29, 560 659 equation (3). A second equation (3). 355 , 237, 1950 1950 , 237, 5A , 74, 1980. 242 , 1207, 1968 ions to giant radio sources discussed ions to giant radio 220 radio halo. This zone radio halo. This SERC), the U.S. Department of Energy SERC), the U.S. Department nd to Rob Beswick with the final for help subtraction of all discrete sources imaged sources imaged of all discrete subtraction and co-authors involved in the results and co-authors involved in the the Arecibo resolution is reproduced in is reproduced resolution the Arecibo als two deep “holes” that provide a radio als two deep “holes” that provide galaxy progenitor. Ra galaxy progenitor.

e first indication of global energy input from e first indication e aggregate release of release e aggregate ources were removed are shown by yellow shown by yellow removed are ources were 8 ul for the support of the Natural Sciences and ul for the support of the Natural single , 740, 2002 2002 , 740, uliny-Toth, I. I. K. The Observatory, , & Colgate, S. A. Astrophys. J. xploring small scale CMB fluctuations. xploring small in extent, and although 1.5 Jy in total flux it has not 1.5 Jy in total flux it has in extent, and although 574 nt with the calculation in nt with the calculation , 391, 1967 1967 , 391, 31 , L93, 1980, L93, , 775, 1968, 775, , 1169, 1949, 1169, 239 21 75 Philipp E. Fermi, Phys. Rev. Phys. Rev. Fermi, E. Kronberg, P. P., Dufton, Q. W., Li, H. Li, W., Q. Dufton, P., P. Kronberg, Davies, R.D., IAU Symp. No Symp. IAU R.D., Davies, Xu, Y., Kronberg, P. P., Habib, S., & Dufton, Q. W. Astrophys. J. J. Astrophys. Perillat, P. C. J. and Kothes, R., Salter, P., P. Kronberg, Kim, K.T., Kronberg, P. P., Dewdney, P. E., & Landecker, T. L. Astrophys. J. Astrophys. L. T. Landecker, & E., P. Dewdney, P., P. Kronberg, K.T., Kim, Simard-Normandin, M., & Kronberg, P.P. Astrophys J. Astrophys P.P. Kronberg, & M., Simard-Normandin, A. Schlüter & L. Biermann, Zeitschrift. für Naturforschung. Naturforschung. für Zeitschrift. L. Biermann, & Schlüter A. Wielebinski, R., Shakeshaft, J. R., & Pa & J. R., Shakeshaft, R., Wielebinski, Davies,Booth,D. R. R.S.,Wilson, & A.J.,Nature, L., PRL, G. Verschuur, Tremaine, S. D. et al., Astrophys. J. J. Astrophys. et al., D. S. Tremaine, Dennison, B. Astrophys. B. Dennison,

[5] [7] [1] [2] [6] [3] [4] [9] [8] [12] [11] [13] [10]

References References ellipses. Only diffuse emission remains after remains after Only diffuse emission ellipses. is a 2 – 4 Mpc, wly revealed features ne several Among by the DRAO interferometer. cluster’s Coma the of westward extension Acknowledgements 8. co-workers indebted to the many I am conference review, a in this brief summarized Figure 3. Locations where the brightest s the brightest where Locations Figure 3. feature. The energy content diffuse with this giant associated radio galaxies co-spatially with th consistent this Region A is thus of also gratef of this article. I am formatting Magnetic Fields Magnetic at image combined 2007). The and Perillat Engineering Research Council of Canada (N Engineering Research Council of University at the appointment Scientist Visiting (DOE), and a current Distinguished Sydney and CSIRO. energy from these 6 – 8 galaxies. This is th energy from these nuclei consiste central galaxy feature, B is ~ 1° diffuse prominent e window to the outside universe for previously been seen. The image also reve been seen. The image previously synchrotron emission has comparable dimens comparable has synchrotron emission it does not have a above, except that