Origin of Galactic and Extragalactic Magnetic Fields

A variety of observations suggest that magnetic fields are present in all galaxies and galaxy clusters. These fields are characterized by a modest strength (10^{-7}-10^{-5} G) and huge spatial scale (~Mpc). It is generally assumed that magnetic fields in spiral galaxies arise from the combined action of differential rotation and helical turbulence, a process known as the alpha-omega dynamo. However fundamental questions concerning the nature of the dynamo as well as the origin of the seed fields necessary to prime it remain unclear. Moreover, the standard alpha-omega dynamo does not explain the existence of magnetic fields in elliptical galaxies and clusters. The author summarizes what is known observationally about magnetic fields in galaxies, clusters, superclusters, and beyond. He then reviews the standard dynamo paradigm, the challenges that have been leveled against it, and several alternative scenarios. He concludes with a discussion of astrophysical and early Universe candidates for seed fields.Comment: 67 pages, 17 figures, accepted for publication in Reviews of Modern Physic

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We present observations of the 12CO(J=1-0) line at 2.6 mm of 65 galaxies located in the Coma supercluster region: 33 actually belong to the Coma supercluster while 32 are either foreground or background objects. These data have been obtained using the NRAO 12 m telescope at Kitt Peak (United States), and for four galaxies, using the IRAM 30 m telescope at Pico Veleta (Spain). Out of these 65 galaxies, 54 had never been observed in the CO(1-0) line; 49 have been detected by us, of which 37 are new detections. We give molecular gas masses deduced from the CO line integrated intensities, and upper limits for the 16 undetected objects, computed with a Galactic conversion factor N(${\rm H}_2$) = 2.3 1020 I(CO) and H0 = 75 km/s/Mpc

<SUP>12</SUP>CO(1-0) observation of isolated late-type galaxies

International audienceWe present 12CO(J=1-0) line observations of 99 galaxies obtained with the SEST 15 m, the Kitt Peak 12 m and the IRAM 30 m telescopes. The target galaxies were selected from the catalogue of isolated galaxies of Karachentseva (\cite{Karachentseva73}). These data are thus representative of the CO properties of isolated late-type galaxies. All objects were observed in their central position, those with large angular sizes were mapped. These new measurements are used to estimate the molecular gas mass of the target galaxies. The molecular gas is on average ~ 18% of the atomic gas mass. Tables 1 and 2 are also available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/411/381 Based on observations made with the 12-m National Radio Astronomical Observatory, Kitt Peak, Arizona, with the Swedish-ESO Submillimetre telescope SEST, La Silla, Chile, with the IRAM 30 m radiotelescope, Pico Veleta, Granada, Spain