Milestones in the Observations of Cosmic Magnetic Fields

“The first discussion about the need of an interstellar magnetic field to explain the isotropy of the cosmic radiation was given by Alfvén (1937), but Fermi (1949) stressed that the fields filled the vast expanses of interstellar space.”

“Magnetic fields could originate deep in the early phases of the universe (see Grasso & Rubinstein 2001 for a review).”

“We refer to the excellent review by Kronberg (1994) who showed that Lyman-α systems with z = 2.0 ∼ 3.0 possess magnetic fields.”

“From that time onwards practically all large nearby galaxies have been mapped, at ever higher frequencies, first in Effelsberg and later with the VLA (see reviews by: Wielebinski & Krause 1993; Beck et al. 1996; Beck 2000).”

“Both the turbulent fluctuations of electron density (see Armstrong et al. 1995) and random magnetic fields are responsible for the variations (see Minter & Spangler 1996).”

“Zeeman measurements are used mainly to detect the magnetic fields in molecular clouds and provide information about the direction of the field along the line of sight (see Crutcher 1999), which is a key step to understanding the process of star formation in cloud cores (e.g., Li 1998).”

“The most recent review on this topic by Carilli & Taylor (2002) has included a very good summary of recent progress in all respects.”

“This theory could be applied to planets (Steenbeck & Krause 1969b), to magnetic stars , and more recently to spiral galaxies (Ruzmaikin et al. 1988).”

“A large-scale kinetic helicity is probably a necessary ingredient for a large-scale magnetic field (Blackman & Chou 1997) and helical turbulence may provide the key to the generation of large-scale magnetic fields (Blackman 2000; Brandenburg 2001).”

“A result of great significance is the “jump” of polarization vectors (and hence of magnetic field) by 90◦ from the center to the end of jets in some sources (see Bridle & Perley 1984).”

“…with (for FR-II and one-side jets in FR-I sources) or perpendicular to (for two-sided jets of FR-I sources) the elongated jet or bridge component; in the lobes it wraps around the source edges or strong intensity gradients (see reviews by Miley 1980; Bridle & Perley 1984; Saikia & Salter 1988).”

“…Dreher et al. 1987; Taylor et al. 2001; Govoni et al. 2001b; Eilek & Owen 2002) or the background sources (Vallee et al. 1987; Kim et al. 1991; Clarke et al. 2001) have almost reached the following consensus: the random magnetic field in the intracluster gas has a strength of 5µG at a length…”

“Recently, Heiles (2000) has compiled a new catalog of starlight polarizations of 9286 stars, using all previously available data including 1800 stars from Mathewson & Ford (1970a), 126 stars from Appenzeller (1974), 495 stars from Schroeder (1976), 1660 southern OB stars from Klare & Neckel (1977),…”

“Some progress has been made recently in the studies of the evolution of such primordial magnetic fields (e.g., Kulsrud et al. 1997; Howard & Kulsrud 1997).”

“The first observations of the polarization of starlight, made by Hiltner (1949) and Hall (1949), were at first interpreted to be due to the scattering by dust in the Galactic plane.”

“Additional reviews on magnetic fields in galaxies have been made by Zeldovich et al. (1983), Rees (1987), Wielebinski & Krause (1993), Beck et al. (1996), Zweibel & Heiles (1997) and Beck (2001).”

“The first observations of the polarization of starlight, made by Hiltner (1949) and Hall (1949), were at first interpreted to be due to the scattering by dust in the Galactic plane.”

“This theory could be applied to planets (Steenbeck & Krause 1969b), to magnetic stars , and more recently to spiral galaxies (Ruzmaikin et al. 1988).”

“Using recent radio survey data which cover most of the known clusters, a large sample of halo candidates has been found (e.g., Kempner & Sarazin 2001; Giovannini et al. 1999) and some of them have been confirmed already (e.g., Govoni et al. 2001a).”

“As mentioned in the Introduction, the optical Zeeman effect was used by G.E. Hale at the turn of the 20th century to measure the magnetic field of the Sun and by Babcock (1947) to measure the magnetic fields in peculiar magnetic stars.”

“Rand and Kulkarni (1989) noticed the significant effect of the North Polar Spur on pulsar RMs and suggested a concentric-ring model for the reversed fields.”

“This result came both from an equipartition argument for the continuum data (e.g. Deiss et al. 1997) and Faraday rotation studies by Kim et al. (1990).”

“Both the turbulent fluctuations of electron density (see Armstrong et al. 1995) and random magnetic fields are responsible for the variations (see Minter & Spangler 1996).”

“Additional reviews on magnetic fields in galaxies have been made by Zeldovich et al. (1983), Rees (1987), Wielebinski & Krause (1993), Beck et al. (1996), Zweibel & Heiles (1997) and Beck (2001).”

“However, these results contradict others (e.g., Blasi et al. 1999).”

“The spectrum of the Coma halo emission has been a subject of numerous studies (e.g., Schlickeiser et al. 1987; Giovannini et al. 1993) which confirmed the non-thermal nature of the halo and hence its magnetic origin.”

“The spectrum of the halos is very steep, often about −1.5 (Deiss et al. 1997; Liang et al. 2000), see the list in Henriksen (1998).”

“…the generation of primordial magnetic fields; Turner andWidrow (1988) proposed an inflation scenario for the creation of primordial magnetic fields; Quashnock et al. (1989) considered the thermoelectric effect in QCD phase transition to generate the magnetic field of 2 × 10−17 G in the early…”

“…in the cluster (e.g., Dreher et al. 1987; Taylor et al. 2001; Govoni et al. 2001b; Eilek & Owen 2002) or the background sources (Vallee et al. 1987; Kim et al. 1991; Clarke et al. 2001) have almost reached the following consensus: the random magnetic field in the intracluster gas has a strength of…”

“Using recent radio survey data which cover most of the known clusters, a large sample of halo candidates has been found (e.g., Kempner & Sarazin 2001; Giovannini et al. 1999) and some of them have been confirmed already (e.g., Govoni et al. 2001a).”

“It was not possible to determine the large-scale magnetic field of the Galaxy in view of the small number of sources, so a survey of a large number of OH masers is needed (see Argon et al. 2000).”

“The Biermann battery in ionization fronts can in principle produce reasonably strong magnetic fields (see Subramanian et al. 1994; Gnedin et al. 2000).”

“These aligned magnetic fields exist between the optical spiral arms or extend independently from optical arms in some galaxies, e.g., NGC 6946 (Beck & Hoernes 1996), NGC 2997 (Han et al. 1999) and IC342 (Krause et al. 1989).”

“…proposed, for example, Harrison (1973) aregued that turbublence in the radiation-dominated era produces the weak seed fields of presently 10−8 G; Hogan (1983) gave a basic argument for considering phase transition as a potential mechanism for the generation of primordial magnetic fields;…”

“Nevertheless, Simard-Normandin & Kronberg (1980) and Sofue & Fujimoto (1983) compared the RM data at low latitudes with model predictions and found that the spiral fields with direction reversals are more suitable for our Galaxy.”

“Analyses of both the distribution and the variance of RMs of extended radio galaxies in the cluster (e.g., Dreher et al. 1987; Taylor et al. 2001; Govoni et al. 2001b; Eilek & Owen 2002) or the background sources (Vallee et al. 1987; Kim et al. 1991; Clarke et al. 2001) have almost reached the…”

“Further halos were found in the A754 (Wielebinski et al. 1977), A1367 (Gavazzi 1978) and other clusters A2255, A2256 and A2319 (e.g., Harris et al. 1980; Bridle et al. 1979; Harris & Miley 1978) though many candidates were reported (see the status presented by Hanisch 1982).”

“The fields, with observed intensities of B ∼ 2 − 10µGauss today must have started at a lower level and become amplified by some mechanism at some cosmological stage (cf. Kulsrud 1999).”

“New RMs of distant pulsars by Rand and Lyne (1994) and Han et al. (1999, 2002) suggested the second and the third field reversals near the Crux-Sctum arm and the Norma arm.”

“However, in our Galaxy, there is a “central molecular zone” at the Galactic center, with a size as large as 400 × 75 pc (Pierce-Price et al. 2000).”

“…dish radio telescopes (Effelsberg 100m, Nobeyama 45m) and large synthesis telescopes (VLA, MOST, ATCA), have revealed many filaments, arcs or loops, threads (e.g., Anantharamaiah et al. 1991; LaRosa et al. 2000, 2001; Lang et al. 1999a, b), plumes (e.g., Duncan et al. 1998) and lobes (Sofue 1985).”

“They are believed to be manifestations of strong vertical field lines (mG strength), i.e., they are illuminated flux tubes in large-scale pervasive fields (Yusef-Zadeh & Morris 1987a; Uchida et al. 1996).”

“…in the vicinity of an accreting disk of the black hole in the galaxy or quasar center (e.g., Contopoulos & Kazanas 1998), and then their outflows can magnetize a large fraction of the entire intergalactic medium (e.g., Daly & Loeb 1990; Furlanetto & Loeb 2001; Kronberg et al. 2001).”

“…measuring pixels, it is now possible to use polarimetry to trace magnetic fields not only in the prestellar cores of bright molecular clouds (e.g., Ward-Thompson et al. 2000), but also in thermal streamers, in the accretion disk around T Tauri stars (e.g., Tamura et al. 1999), in the envelopes of…”

“Diffuse radio continuum emission was found to be present in clusters of galaxies (e.g., Ryle & Windram 1968; Willson 1970; Wielebinski 1978).”

“Furthermore, the superwinds of primeval galaxies can also effectively seed magnetic fields into the intergalactic medium (Kronberg et al. 1999; Birk et al. 2000).”

“…global scale, polarization maps at different wave bands reveal the emission from dust grains orientated by the same magnetic fields, giving roughly consistent results, e.g., the polarization maps of the Orion clouds at 1.3 mm and 3.3 mm by Rao et al. (1998) and 350µm by Hildebrand et al. (2000).”

“The central density-enhanced “cooling flow” regions can have magnetic fields up to ∼40µG with coherence scales up to ∼50kpc (Taylor & Perley 1993).”

“Angular power spectrum analysis of the data may be used to model the Galactic polarized continuum emission at other wavelengths (Fosalba et al. 2002).”

“Radio maps of large areas of the sky at other frequencies are also available now (e.g., 22MHz by Roger et al. 1999; 0.2 to 13.8MHz by Manning & Dulk 2001; 45MHz by Maeda et al. 1999; 2.3GHz by Jonas et al. 1998).”

“All previous detections of the OH lines (and other lines or absorptions) with Zeeman effect have been summarized by Crutcher (1999) and new observations made by, for example, Bourke et al. (2001).”

“…in the vicinity of an accreting disk of the black hole in the galaxy or quasar center (e.g., Contopoulos & Kazanas 1998), and then their outflows can magnetize a large fraction of the entire intergalactic medium (e.g., Daly & Loeb 1990; Furlanetto & Loeb 2001; Kronberg et al. 2001).”

“These aligned magnetic fields exist between the optical spiral arms or extend independently from optical arms in some galaxies, e.g., NGC 6946 (Beck & Hoernes 1996), NGC 2997 (Han et al. 1999) and IC342 (Krause et al. 1989).”

“The latter authors confirmed the local field strength and direction found by Manchester (1974) and the reversal near the Carina-Sagittarius arm.”

“However, magnetic fields in high redshift (z ∼ 2.0 – 3.0) objects with Lyman-α damped systems have been found to be as strong as in nearby galaxies and in some clusters of galaxies (e.g., Kronberg et al. 1990, 1992; Athreya et al. 1998).”

“New detections of CN Zeeman effects offer a good chance to measure the magnetic fields in clouds with densities of 105 to 106 cm−3 (Crutcher et al. 1999).”

“They are believed to be manifestations of strong vertical field lines (mG strength), i.e., they are illuminated flux tubes in large-scale pervasive fields (Yusef-Zadeh & Morris 1987a; Uchida et al. 1996).”

“However, recently, there is a renaissance in the polarization measurement (Reich et al. 1990, 1997, 2001; Dickey et al. 1999; McClure-Griffiths et al. 2001).”

“Radio maps of large areas of the sky at other frequencies are also available now (e.g., 22MHz by Roger et al. 1999; 0.2 to 13.8MHz by Manning & Dulk 2001; 45MHz by Maeda et al. 1999; 2.3GHz by Jonas et al. 1998).”

“…global scale, polarization maps at different wave bands reveal the emission from dust grains orientated by the same magnetic fields, giving roughly consistent results, e.g., the polarization maps of the Orion clouds at 1.3 mm and 3.3 mm by Rao et al. (1998) and 350µm by Hildebrand et al. (2000).”

“…have reached the conclusion that the local regular magnetic fields of our Galaxy point to the direction l ∼ 82◦, and seem to follow the spiral pattern very closely (e.g., Heiles 1996; Andreasyan & Makarov 1989), although the local distortions can be clearly seen in the nearby stars (see Fig.”

“Recently, it has been found that X-ray emission is well correlated with the rms value of the cluster rotation measures (Dolag et al. 2001), implying that the the field strength decreases with the radius according to B ∼ N0.”

“…detected from the halo, except for some polarization associated with the halo-‘G’ in A2256 (Bridle et al. 1979), while multifrequency polarization observations revealed the polarization of many cluster objects (e.g., Feretti et al. 1995; Taylor et al. 2001; Govoni et al. 2001; Eilek & Owen 2002).”

“However, recently, there is a renaissance in the polarization measurement (Reich et al. 1990, 1997, 2001; Dickey et al. 1999; McClure-Griffiths et al. 2001).”

“A significant collection of observations of pulsar RMs was presented by Manchester (1972, 1974), who revealed the local uniform magnetic field of about 2.2±0.4 µG, and directed towards about l ∼ 90◦.”

“…with (for FR-II and one-side jets in FR-I sources) or perpendicular to (for two-sided jets of FR-I sources) the elongated jet or bridge component; in the lobes it wraps around the source edges or strong intensity gradients (see reviews by Miley 1980; Bridle & Perley 1984; Saikia & Salter 1988).”

“Verification of OH maser sources came from VLBI observations (Reid et al. 1980; Zheng et al. 2000) which showed some pairs to come from the same position within the size of a maser spot.”

“Within the scope of the Canadian Galactic Plane Survey (Landecker et al. 2000), the RMs of some 380 sources were determined (Brown & Taylor 2001).”

“A review of very recent developments in the magnetic dynamo theory, most impressively on the magnetic helicity and the evolution of kinetic and magnetic energy spectra, can be found in Blackman (2002).”

“This giant polarized radio arc is very striking, extending more than 1◦ on each side of the Galactic plane (Seiradakis et al. 1985; Tsuboi et al. 1986; Haynes et al. 1992).”

“The intrinsic magnetic field in the filaments or threads is predominantly aligned parallel to the filament (e.g., Lang et al. 1999a, b; Sofue et al. 1987).”

“The Biermann battery in ionization fronts can in principle produce reasonably strong magnetic fields (see Subramanian et al. 1994; Gnedin et al. 2000).”

“Diffuse radio continuum emission was found to be present in clusters of galaxies (e.g., Ryle & Windram 1968; Willson 1970; Wielebinski 1978).”

“However, recently, there is a renaissance in the polarization measurement (Reich et al. 1990, 1997, 2001; Dickey et al. 1999; McClure-Griffiths et al. 2001).”

“The most recent analysis by Frick et al. (2001) using wavelet method basically confirmed the previous conclusions on field reversals and the antisymmetry.”

“For most directions the δRM is less than 10 rad m−2 in a few arcminutes for background sources, but the RM difference can be up to a few tens of rad m−2 near the Galactic plane, and small anomalous regions are possibly associated with some local Galactic features (e.g., Clegg et al. 1992).”

“…dish radio telescopes (Effelsberg 100m, Nobeyama 45m) and large synthesis telescopes (VLA, MOST, ATCA), have revealed many filaments, arcs or loops, threads (e.g., Anantharamaiah et al. 1991; LaRosa et al. 2000, 2001; Lang et al. 1999a, b), plumes (e.g., Duncan et al. 1998) and lobes (Sofue 1985).”

“Most recently detailed discussion on kinematic dynamo and small-scale field were made by Schekochihin et al. (2002).”

“Recently, the detection of circular polarization in AGN cores and nearby galaxy nuclei by the VLBA and ATCA (Homan et al. 2001; Rayner et al. 2000; Bower et al. 1999; Brunthaler et al. 2001) re-opened a window on the physical conditions and magnetic fields in the core regions.”

“This was pointed out first by Lyne & Smith (1968).”

“The studies on the variance of residual RM (observed RM minus foreground Galactic RM) versus source redshift z (e.g., Oren & Wolfe 1995; Perry et al. 1993), mainly due to data quality, have produced controversial results on the cosmological evolution of the magnetic field (in the intervening…”

“Nevertheless, Simard-Normandin & Kronberg (1980) and Sofue & Fujimoto (1983) compared the RM data at low latitudes with model predictions and found that the spiral fields with direction reversals are more suitable for our Galaxy.”

“54+0.18 (Yusef-Zadeh et al. 1997).”

“7; NGC 1097: Beck et al. 1999; M51: Neininger & Horellou 1996) revealed that the polarized emission is strongest in the inner edge of the optical spiral arms or along the dust lanes, clearly associated with local compression effects by shock.”

“The magnetic field could be stronger towards the cluster center (e.g., Govoni et al. 2001b) and very high RMs (of radio galaxies) have been found near the center of the cooling flow clusters (e.g., Ge & Owen 1993).”

“Within the scope of the Canadian Galactic Plane Survey (Landecker et al. 2000), the RMs of some 380 sources were determined (Brown & Taylor 2001).”

“A polarization survey of the southern Galaxy was made at 2.4GHz by Duncan et al. (1995, 1997) using the Parkes radio telescope.”

“…detected from the halo, except for some polarization associated with the halo-‘G’ in A2256 (Bridle et al. 1979), while multifrequency polarization observations revealed the polarization of many cluster objects (e.g., Feretti et al. 1995; Taylor et al. 2001; Govoni et al. 2001; Eilek & Owen 2002).”

“The first attempt to use the Zeeman data to derive the large-scale magnetic field of the Milky Way was made by Reid & Silverstein (1990), and later extended by Caswell & Vaile (1995).”

“…polarization observations of more distant galaxies (e.g., Tadhunter et al. 1992; Scarrott et al. 1990) or active galaxies (Draper et al. 1993; Cimatti et al. 1993) have been used to investigate some interesting issues, such as the “unified” scheme of AGNs, emission mechanisms (Breeveld &…”

“A consensus reached now is that these must be the consequence of a substantial poloidal magnetic field which pervades the central ∼100pc of our Galaxy (Yusef-Zadeh & Morris 1987a; Morris & Yusef-Zadeh 1989).”

“Thomson & Nelson (1980) re-analyzed 48 pulsar RMs listed by Manchester & Taylor (1977) and found field reversal near the first inner spiral arm, i.e., the Carina-Sagittarius arm.”

“OH masers have now been detected in the prestellar cores of clouds, L1544 (Crutcher & Troland 2000).”

“A polarization survey of the southern Galaxy was made at 2.4GHz by Duncan et al. (1995, 1997) using the Parkes radio telescope.”

“In fact, magnetic fields can be easily-developed in the vicinity of an accreting disk of the black hole in the galaxy or quasar center (e.g., Contopoulos & Kazanas 1998), and then their outflows can magnetize a large fraction of the entire intergalactic medium (e.g., Daly & Loeb 1990; Furlanetto &…”

“Many objects (or even core components) have been studied using high resolution multifrequency VLBI/VLBA polarization data (e.g., Venturi & Taylor 1999).”

“This was mostly done by Cordes’ group (Simonetti et al. 1984; Simonetti & Cordes 1986; Lazio et al. 1990; Clegg et al. 1992).”

“…in the vicinity of an accreting disk of the black hole in the galaxy or quasar center (e.g., Contopoulos & Kazanas 1998), and then their outflows can magnetize a large fraction of the entire intergalactic medium (e.g., Daly & Loeb 1990; Furlanetto & Loeb 2001; Kronberg et al. 2001).”

“Concentrating on selected Galactic regions, Broten et al. (1988) have confirmed the existence of magnetic field reversals in the Milky Way.”

“The density wave in spiral galaxies can provide a spiral shock wave and the subsequent α-effect which may alter the field configuration of the dynamo (Mestel & Subramanian 1991; Subramanian & Mestel 1993).”

“This giant polarized radio arc is very striking, extending more than 1◦ on each side of the Galactic plane (Seiradakis et al. 1985; Tsuboi et al. 1986; Haynes et al. 1992).”

“Scarrott et al. (1987) showed the perpendicularity between the radio and optical polarization vectors, exactly as expected if magnetic dichroism and the synchrotron process are responsible for the polarization at the shorter and longer wavelengths respectively.”

“The intrinsic magnetic field in the filaments or threads is predominantly aligned parallel to the filament (e.g., Lang et al. 1999a, b; Sofue et al. 1987).”

“A significant step here was made by Hamilton & Lyne (1987), who measured the Faraday rotation of 163 pulsars, so increasing the total number of pulsar RM measured to 185.”

“Recently, the detection of circular polarization in AGN cores and nearby galaxy nuclei by the VLBA and ATCA (Homan et al. 2001; Rayner et al. 2000; Bower et al. 1999; Brunthaler et al. 2001) re-opened a window on the physical conditions and magnetic fields in the core regions.”

“Recently a return to the dust polarization method of measuring magnetic fields has been made possible by the advent of polarization measurements in the infrared, far-infrared, sub-mm and mm (e.g., Cudlip et al. 1982; Dowell et al. 1998; Hildebrand et al. 2000).”

“Combination of results from both polarimetry of dust emission and Zeeman observations can provide a three-dimensional view of the magnetic fields in the clouds (Houde et al. 2002).”

“Recently a return to the dust polarization method of measuring magnetic fields has been made possible by the advent of polarization measurements in the infrared, far-infrared, sub-mm and mm (e.g., Cudlip et al. 1982; Dowell et al. 1998; Hildebrand et al. 2000).”

“…inherently weak effect due to the weak magnetic fields (a few µG along the line of sight) is difficult to pick up against strong instrumental effects (e.g., Verschuur 1995a), and such observations rarely produced consistent results (e.g., Verschuur 1995b; Troland & Heiles 1982; Myers et al. 1995).”

“Optical polarization observations of more distant galaxies (e.g., Tadhunter et al. 1992; Scarrott et al. 1990) or active galaxies (Draper et al. 1993; Cimatti et al. 1993) have been used to investigate some interesting issues, such as the “unified” scheme of AGNs, emission mechanisms (Breeveld &…”

“Within a few arcminutes, the RM value can vary from 500 to −500 rad m−2 in “the Pelican” (Lang et al. 1999a), from 100 to 2300 rad m−2 in the Northern Threads (Lang et al. 1999b), from 2000 to 5500 rad m−2 along “the Snake” (Gray et al. 1995), or from −4200 to −370 rad m−2 in the filament G359.”

“The mapping of a wide strip of the Galactic plane at 1.4GHz, called the “medium latitude survey”, was started in Effelsberg by Uyaniker et al. (1998, 1999, see Fig.”

“Finally Verschuur (1968) and Devies et al. (1968) gave a definite proof of the Zeeman effect in the Perseus spiral arm by observing HI in absorption against Cassiopea A.”

“Afterwards, Costa et al. (1991), Rand & Lyne (1994), Qiao et al. (1995), van Ommen et al. (1997) and Han et al. (1999) contributed a number of new RMs, providing RM data for some 320 objects.”

“The most recent status in this field, described using much more new data was given by Han et al. (2002) who reported the detection of counterclockwise magnetic field near the Norma arm (see Fig.”

“Their catalog includes polarization measurements by Hiltner (1956), Hall (1958), Behr (1959), Loden (1961), Appenzeller (1968), and Visvanathan (1967).”

“In some cases the halo contribution may be significant (e.g., Soida et al. 2001).”

“Due to limited sensitivity and resolution, it is still too early to observe the dust polarization at these bands in nearby Galaxies, although Greaves et al. (2000) have reported results on M82 and Siebenmorgen et al. (2001) on NGC 1808.”

“…disk (or the so-called dust ring) in a few pc from Sgr A* (Hildebrand et al. 1990, 1993; Novak et al. 2000), the giant molecular cloud Sgr B2 at 100 pc from the center as well as some other clouds near the center (Novak et al. 1997, 2000), and for thermal filaments (Morris et al. 1992).”

“From that time onwards practically all large nearby galaxies have been mapped, at ever higher frequencies, first in Effelsberg and later with the VLA (see reviews by: Wielebinski & Krause 1993; Beck et al. 1996; Beck 2000).”

“The VLA and VLBA have been used to study the Zeeman effect in water masers (Sarma et al. 2001).”

“The first attempt to use the Zeeman data to derive the large-scale magnetic field of the Milky Way was made by Reid & Silverstein (1990), and later extended by Caswell & Vaile (1995).”

“This work was followed up by Segalovitz et al. (1976) who mapped M51 at a second frequency as well as tried to observe M31.”

“Some early papers (e.g., Piddington 1964, 1978) considered that if an intergalactic magnetic field exists with B ∼ 10−8 G, it could be compressed by galactic rotation to B ∼ 10−5 G, intensities that are actually observed in galaxies.”

“A report of a halo in the Perseus cluster of galaxies was made by Ryle & Windram (1968), but the first clear detection was actually made by Large et al. (1959) in the Coma cluster.”

“Such a primordial magnetic field could in principle be detected by the Faraday rotation of microwave background polarization (Kosowsky & Loeb 1996) or by the correlation of the Faraday sky (Kolatt 1998).”

“The fields are most likely to be toroidal in the circumstellar disk (Tamura et al. 1999).”

“Observations by Beck et al. (1978, 1980) of M31 using the 100m Effelsberg dish at λ = 11 cm allowed a definite detection of magnetic field, which showed a surprisingly homogenous distribution.”

“…inherently weak effect due to the weak magnetic fields (a few µG along the line of sight) is difficult to pick up against strong instrumental effects (e.g., Verschuur 1995a), and such observations rarely produced consistent results (e.g., Verschuur 1995b; Troland & Heiles 1982; Myers et al. 1995).”

“Afterwards, more and better data were accumulated for the circumnuclear disk (or the so-called dust ring) in a few pc from Sgr A* (Hildebrand et al. 1990, 1993; Novak et al. 2000), the giant molecular cloud Sgr B2 at 100 pc from the center as well as some other clouds near the center (Novak et al.…”

“Detection of ordered magnetic fields at scale of hundreds to thousand pc in high redshift objects of z > 2 (Udomprasert et al. 1997; Athreya et al. 1998) poses a stiff challenge to the dynamo mechanism for generating magnetic fields, primarily due to the very short time available for amplification…”

“Soon afterwards, it was noticed that the rotation measures were dependant on both Galactic latitudes (Garder & Whiteoak 1963) and longitudes (Morris & Berge 1964).”

“Using the data available at the time, Axon & Ellis (1976) compiled a catalog of 5070 stars with reliable distances.”

“Radio relic sources have been detected in or between clusters of galaxies, for example, the bridge emission between Coma and A1367 (Kim et al. 1989), and the extended source adjacent to three Abell clusters of galaxies of Rood Group #27 (Harris et al. 1993).”

“Surveys of larger areas of linearly polarized radio emission were continued at several frequencies (e.g., Berkhuijsen & Brouw 1963; Wielebinski & Shakeshaft 1964; Mathewson & Milne 1965; Berkhuijsen et al. 1964; Mathewson et al. 1966; Baker & Smith 1971; Wilkinson 1973; Baker & Wilkinson 1974).”

“Several mechanisms to produce the seed fields at different epochs of the universe have been proposed, for example, Harrison (1973) aregued that turbublence in the radiation-dominated era produces the weak seed fields of presently 10−8 G; Hogan (1983) gave a basic argument for considering phase…”

“First polarization of stars, later photoelectric surface photometry in Magellanic Clouds (e.g., Mathewson & Ford 1970b, 1970c; Schmidt 1970) gave us some real insight of the magnetic fields in these nearby galaxies.”

“Radio maps of large areas of the sky at other frequencies are also available now (e.g., 22MHz by Roger et al. 1999; 0.2 to 13.8MHz by Manning & Dulk 2001; 45MHz by Maeda et al. 1999; 2.3GHz by Jonas et al. 1998).”

“Using recent radio survey data which cover most of the known clusters, a large sample of halo candidates has been found (e.g., Kempner & Sarazin 2001; Giovannini et al. 1999) and some of them have been confirmed already (e.g., Govoni et al. 2001a).”

“Some progress has been made recently in the studies of the evolution of such primordial magnetic fields (e.g., Kulsrud et al. 1997; Howard & Kulsrud 1997).”

“Studies of the Faraday rotation across the Galaxy were first made by Gardner & Davies (1966) and later by Gardner et al. (1969).”

“Magnetic fields around protostars (Greaves & Holland 1998) are banded and there is probably a centrally contracted field, which collimates the bipolar outflowing gas (Greaves et al. 2001; Momose et al. 2001).”

“Recently, the detection of circular polarization in AGN cores and nearby galaxy nuclei by the VLBA and ATCA (Homan et al. 2001; Rayner et al. 2000; Bower et al. 1999; Brunthaler et al. 2001) re-opened a window on the physical conditions and magnetic fields in the core regions.”

“This was mostly done by Cordes’ group (Simonetti et al. 1984; Simonetti & Cordes 1986; Lazio et al. 1990; Clegg et al. 1992).”

“The successful polarization observation of radio source led to RM catalogs across the sky (e.g., Ellis & Axon 1978; Simrad-Normandin et al. 1981; Broten et al. 1988).”

“…disk (or the so-called dust ring) in a few pc from Sgr A* (Hildebrand et al. 1990, 1993; Novak et al. 2000), the giant molecular cloud Sgr B2 at 100 pc from the center as well as some other clouds near the center (Novak et al. 1997, 2000), and for thermal filaments (Morris et al. 1992).”

“…into the dynamo and used computer simulations to show possible consequences comparable to observational results, e.g., the bar-effect by Moss et al. (2001) and Otmianowska et al. (2002), the swing-excitation by Rohde et al. (1999), the very detailed considerations of supernova and…”

“The radio Zeeman effect was predicted for the HI line by Bolton and Wild (1957) but it took some time to be detected.”

“…of loop I. Andreasyan (1980) attributed the antisymmetry to the local disk field with reversed directions above and below the plane, as Berge & Seielstad (1967) suggested, while Han et al. (1997) argued that the antisymmetry is the result of the magnetic field in the thick disk or…”

“Many objects have multifrequency polarization data that have been analysed for magnetic fields (e.g., Johnson et al. 1995; Murgia et al. 2001).”

“Zeeman measurements are used mainly to detect the magnetic fields in molecular clouds and provide information about the direction of the field along the line of sight (see Crutcher 1999), which is a key step to understanding the process of star formation in cloud cores (e.g., Li 1998).”

“…dish radio telescopes (Effelsberg 100m, Nobeyama 45m) and large synthesis telescopes (VLA, MOST, ATCA), have revealed many filaments, arcs or loops, threads (e.g., Anantharamaiah et al. 1991; LaRosa et al. 2000, 2001; Lang et al. 1999a, b), plumes (e.g., Duncan et al. 1998) and lobes (Sofue 1985).”

“Werner et al. (1988) first detected the polarization in the far-infrared band, and concluded that the field was predominantly azimuthal.”

“This was mostly done by Cordes’ group (Simonetti et al. 1984; Simonetti & Cordes 1986; Lazio et al. 1990; Clegg et al. 1992).”

“Due to limited sensitivity and resolution, it is still too early to observe the dust polarization at these bands in nearby Galaxies, although Greaves et al. (2000) have reported results on M82 and Siebenmorgen et al. (2001) on NGC 1808.”

“…Heiles 1997; Vallée 1997, 1998; Balbus & Hawley 1998; Kulsrud 1999; Weiss & Tobias 2000; Title 2000; Beck 2000, 2001; Ferrière 2001; Kronberg et al. 2001; Carilli & Taylor 2002; Han & Wielebinski 2002; Widrow 2002; Tobias 2002; Ossendrijver 2003; Han et al. 2004; Brandenburg & Subramanian 2004).”

“…polarized thermal emission from dust at mm, sub-mm or infrared wavelengths, of optical starlightpolarization due to anisotropic scattering by magnetically-igned dust grains, of radio synchrotron emission, and of Faraday rotation of polarized radio sources (see Han & Wielebinski 2002, for a review).”

“The Galactic magnetic field has two components: a regular component Br and a random component b, so that the total Galactic magnetic field is given as B = Br + b (for review see Beck et al. 1996; Han & Wielebinski 2002).”

“…or be the central part of the field amplified by a galactic turbulent dynamo process, which is argued bymany authors (for reviews, see Kronberg 1994; Han & Wielebinski 2002 and references therein), or be a field structure carried out from the central engine by a lower velocity magnetized disk wind.”

“Li et al. (2014) present evidence that the B-field in clouds is also aligned with the local large-scale B-field in the diffuse ISM and that the latter is further aligned with the Galactic plane (Han & Wielebinski 2002; Jansson & Farrar 2012).”

“In [28] the authors cite [33] and [19] as reason to model the regular GMF with a bisymmetric spiral arm pattern.”

“Large scale magnetic fields of μGauss strength have been observed in cosmic structures at a great variety of length scales and redshifts: from stars to galaxies to regions around high redshift quasars as well as from clusters and superclusters to the region of low density filaments [1–8].”

“The large-scale field in the Galactic disk has been studied by using RMs of pulsars and extragalactic radio sources (Beck 2001, Han & Wielebinski 2002, Haverkorn 2015 for review), and using total and polarized synchrotron intensities of the Galactic synchrotron emission as well as RMs (Haverkorn,…”

“…galaxies, galaxy clusters and high-redshift protogalactic structures, the presence of magnetic fields has been repeatedly verified (Klein, Wielebinski & Morsi 1988; Kim et al. 1989; Kronberg 1994; Beck et al. 1996; Carilli & Taylor 2002; Han & Wielebinski 2002; Vallee 2004; Beck et al. 2005).”

“Large scale magnetic fields, with strengths 10−7–10−5 G, have been observed in spiral and disc galaxies, galaxy clusters and high redshift condensations [see (Kronberg 1994; Han & Wielebinski 2002) and references therein].”

“…fields play a vital role in many astrophysical systems and in cosmology, and the possible sources for the fields on different scales has been the focus of immense research over the years (Kronberg 1994; Han & Wielebinski 2002; Parker 1979; Zeldovich, Ruzmaikin & Sokoloff 1983; Beck et al. 1996).”

“For example, Han & Wielebinski (2002) and Prouza &̌Smı́da (2003) detected it with maximum strengths at a large height of 1.5 kpc at both sides above and below the plane, being the maximum strengths of 1µG approximately.”

“Magnetic fields (MFs) seem to be omnipresent in the Universe, from the Earth to the huge intergalactic voids (Kronberg 1994; Han & Wielebinski 2002; Govoni & Feretti 2004; Vallée 2004; Ryu et al. 2012), including stars, galaxies, clusters, and perhaps filaments.”

“I point out here only the reviews of Wielebinski and Krause (1993), Beck et al. (1996), Han and Wielebinski (2002), Wiele- binski and Beck (2010), and Beck and Wielebinski (2012).”

“Such magnetic fields are required by observation [7] and although a number of possible formation mechanisms are known — see, for example, ref.”

“Inflationary magnetogenesis has long been recognised as one of the most promising frameworks for the generation of today’s observed cosmological magnetic fields, see [1–5], and [6– 12].”

“The information on the field has been obtained through observations of Zeeman splitting, polarized thermal emission from dust, optical starlight polarization, radio synchrotron emission, and the Faraday rotation of polarized radio sources (see, Han & Wielebinski 2002, for a review).”

“The origin of cosmic magnetism remains an essentially open question despite the efforts and the established widespread presence of magnetic (B) fields in the universe [1–4].”

“The strength of magnetic fields in galaxies and galaxy clusters is of the order of μGauss [1–4], and a lower bound of the order of 10−15 Gauss on coherent magnetic fields in the intergalactic medium has also been reported [5–9].”

“Galactic magnetic fields are toroidal (Han & Wielebinski 2002), so less inclined galaxies should have more of their polarization cancel out from the integration.”

“The galactic magnetic field has a strength of roughly 3µG parallel to the spiral arms, but with large fluctuations (Han and Wielebinski, 2002).”

“On the other hand, since the MF equipartition is derived from radio synchrotron emission, it mainly reflects the field component perpendicular to the line of sight (Han & Wielebinski 2002).”

“The Milky Way and other spiral galaxies have coherent magnetic fields of μG-order magnitude, while galaxy clusters and remote protogalactic clouds also carry fields of similar strength (Han & Wielebinski 2002, Vallée 2011).”

“The magnetic field of the Milky Way has been extensively studied through radio observations and Faraday rotation measures [25].”