664 research outputs found
Generation of helical magnetic fields from inflation
The generation of helical magnetic fields during single field inflation due
to an axial coupling of the electromagnetic field to the inflaton is discussed.
We find that such a coupling always leads to a blue spectrum of magnetic fields
during slow roll inflation. Though the helical magnetic fields further evolve
during the inverse cascade in the radiation era after inflation, we conclude
that the magnetic fields generated by such an axial coupling can not lead to
observed field strength on cosmologically relevant scales.Comment: 4 pages, 1 figure; Contribution to the proceedings of the
International Conference on Gravitation and Cosmology (ICGC), Goa, India,
December, 201
Detection of microgauss coherent magnetic fields in a galaxy five billion years ago
Magnetic fields play a pivotal role in the physics of interstellar medium in
galaxies, but there are few observational constraints on how they evolve across
cosmic time. Spatially resolved synchrotron polarization maps at radio
wavelengths reveal well-ordered large-scale magnetic fields in nearby galaxies
that are believed to grow from a seed field via a dynamo effect. To directly
test and characterize this theory requires magnetic field strength and geometry
measurements in cosmologically distant galaxies, which are challenging to
obtain due to the limited sensitivity and angular resolution of current radio
telescopes. Here, we report the cleanest measurements yet of magnetic fields in
a galaxy beyond the local volume, free of the systematics traditional
techniques would encounter. By exploiting the scenario where the polarized
radio emission from a background source is gravitationally lensed by a
foreground galaxy at z = 0.439 using broadband radio polarization data, we
detected coherent G magnetic fields in the lensing disk galaxy as seen 4.6
Gyrs ago, with similar strength and geometry to local volume galaxies. This is
the highest redshift galaxy whose observed coherent magnetic field property is
compatible with a mean-field dynamo origin.Comment: 29 pages, 5 figures (including Supplementary Information). Published
in Nature Astronomy on August 28, 201
Cosmic magnetic fields from velocity perturbations in the early Universe
We show, using a covariant and gauge-invariant charged multifluid
perturbation scheme, that velocity perturbations of the matter-dominated dust
Friedmann-Lemaitre-Robertson-Walker (FLRW) model can lead to the generation of
cosmic magnetic fields. Moreover, using cosmic microwave background (CMB)
constraints, it is argued that these fields can reach strengths of between
10^{-28} and 10^{-29} G at the time the dynamo mechanism sets in, making them
plausible seed field candidates.Comment: 11 pages, 1 figure, IOP style, minor changes and typos correcte
A Faraday Rotation Search for Magnetic Fields in Large Scale Structure
Faraday rotation of radio source polarization provides a measure of the
integrated magnetic field along the observational lines of sight. We compare a
new, large sample of Faraday rotation measures (RMs) of polarized extragalactic
sources with galaxy counts in Hercules and Perseus-Pisces, two nearby
superclusters. We find that the average of RMs in these two supercluster areas
are larger than in control areas in the same galactic latitude range. This is
the first RM detection of magnetic fields that pervade a supercluster volume,
in which case the fields are at least partially coherent over several
megaparsecs. Even the most conservative interpretation of our observations,
according to which Milky Way RM variations mimic the background supercluster
galaxy overdensities, puts constraints on the IGM magneto-ionic ``strength'' in
these two superclusters. We obtain an approximate typical upper limit on the
field strength of about 0.3 microGauss l/(500 kpc), when we combine our RM data
with fiducial estimates of electron density from the environments of giant
radio galaxies, and of the warm-hot intergalactic medium (WHIM).Comment: 8 pages, 3 figures, 1 table, to appear in the Astrophysical Journa
The origins of X-ray emission from the hotspots of FRII radio sources
We use new and archival Chandra data to investigate the X-ray emission from a
large sample of compact hotspots of FRII radio galaxies and quasars from the 3C
catalogue. We find that only the most luminous hotspots tend to be in good
agreement with the predictions of a synchrotron self-Compton model with
equipartition magnetic fields. At low hotspot luminosities inverse-Compton
predictions are routinely exceeded by several orders of magnitude, but this is
never seen in more luminous hotspots. We argue that an additional synchrotron
component of the X-ray emission is present in low-luminosity hotspots, and that
the hotspot luminosity controls the ability of a given hotspot to produce
synchrotron X-rays, probably by determining the high-energy cutoff of the
electron energy spectrum. It remains plausible that all hotspots are close to
the equipartition condition.Comment: 49 pages, 16 figures. ApJ accepted. Revised version fixes a typo in
one of the Tables and corrects a statement about 3C27
Wide-field global VLBI and MERLIN combined monitoring of supernova remnants in M82
From a combination of MERLIN (Multi-Element Radio-Linked Interferometer
Network) and global VLBI (Very Long Baseline Interferometry) observations of
the starburst galaxy M82, images of 36 discrete sources at resolutions ranging
from ~3 to ~80 mas at 1.7 GHz are presented. Of these 36 sources, 32 are
identified as supernova remnants, 2 are HII regions, and 3 remain unclassified.
Sizes, flux densities and radio brightnesses are given for all of the detected
sources. Additionally, global VLBI only data from this project are used to
image four of the most compact radio sources. These data provide a fifth epoch
of VLBI observations of these sources, covering a 19-yr time-line. In
particular, the continued expansion of one of the youngest supernova remnants,
43.31+59.3 is discussed. The deceleration parameter is a power-law index used
to represent the time evolution of the size of a supernova remnant. For the
source 43.31+59.3, a lower limit to the deceleration parameter is calculated to
be 0.53+/-0.06, based on a lower limit of the age of this source.Comment: 31 pages, 12 figures, 7 table
Optimización de la producción de biomasa usando glicerol crudo, de una cepa mutante de Yarrowia lipolytica con actividad incrementada de lipasa
218-225The yeast Yarrowia lipolytica accumulates oils and is able to produce extracellular lipases when growing in different carbon sources including glycerol, the principal by-product of the biodiesel industry. In this study, biomass production of a novel mutant strain of Y. lipolytica was statistically optimized by Response Surface Methodology in media containing biodiesel-derived glycerol as main carbon source. This strain exhibited distinctive morphological and fatty acid profile characteristics, and showed an increased extracellular lipase activity. An organic source of nitrogen and the addition of 1.0 g/l olive oil were necessary for significant lipase production. Plackett-Burman and Central Composite Statistical Designs were employed for screening and optimization of fermentation in shaken flasks cultures, and the maximum values obtained were 16.1 g/l for biomass and 12.2 Units/ml for lipase, respectively. Optimized batch bioprocess was thereafter scaled in aerated bioreactors and the values reached for lipase specific activity after 95 percent of the glycerol had been consumed, were three-fold higher than those obtained in shaken flasks cultures. A sustainable bioprocess to obtain biomass and extracellular lipase activity was attained by maximizing the use of the by-products of biodiesel industry
Field theory of the photon self-energy in a medium with a magnetic field and the Faraday effect
A convenient and general decomposition of the photon self-energy in a
magnetized, but otherwise isotropic, medium is given in terms of the minimal
set of tensors consistent with the transversality condition. As we show, the
self-energy in such a medium is completely parametrized in terms of nine
independent form factors, and they reduce to three in the long wavelength
limit. We consider in detail an electron gas with a background magnetic field,
and using finite temperature field theory methods, we obtain the one-loop
formulas for the form factors, which are exact to all orders in the magnetic
field. Explicit results are derived for a variety of physical conditions. In
the appropriate limits, we recover the well-known semi-classical results for
the photon dispersion relations and the Faraday effect. In more general cases,
where the semi-classical treatment or the linear approximation (weak field
limit) are not applicable, our formulas provide a consistent and systematic way
for computing the self-energy form factors and, from them, the photon
dispersion relations.Comment: Revtex, 27 page
A Global Probe of Cosmic Magnetic Fields to High Redshifts
Faraday rotation (RM) probes of magnetic fields in the universe are sensitive
to cosmological and evolutionary effects as increases beyond 1
because of the scalings of electron density and magnetic fields, and the growth
in the number of expected intersections with galaxy-scale intervenors,
N/. In this new global analysis of an unprecedented large sample of RM's
of high latitude quasars extending out to 3.7 we find that the
distribution of RM broadens with redshift in the 20 80 rad m range
range, despite the (1 +) wavelength dilution expected in the observed
Faraday rotation. Our results indicate that the Universe becomes increasingly
``Faraday-opaque'' to sources beyond 2, that is, as increases
progressively fewer sources are found with a ``small'' RM in the observer's
frame. This is in contrast to sources at z \la1. They suggest that the
environments of galaxies were significantly magnetized at high redshifts, with
magnetic field strengths that were at least as strong within a few Gyr of the
Big Bang as at the current epoch. We separately investigate a simple unevolving
toy model in which the RM is produced by MgII absorber systems, and find that
it can approximately reproduce the observed trend with redshift. An additional
possibility is that the intrinsic RM associated with the radio sources was much
higher in the past, and we show that this is not a trivial consequence of the
higher radio luminosities of the high redshift sources.Comment: 10 pages, 8 figures Astrophysical Jounrnal in press, March 200
Magnetic field generation in Higgs inflation model
We study the generation of magnetic field in Higgs-inflation models where the
Standard Model Higgs boson has a large coupling to the Ricci scalar. We couple
the Higgs field to the Electromagnetic fields via a non- renormalizable
dimension six operator suppressed by the Planck scale in the Jordan frame. We
show that during Higgs inflation magnetic fields with present value
Gauss and comoving coherence length of can be generated in the
Einstein frame. The problem of large back-reaction which is generic in the
usual inflation models of magneto-genesis is avoided as the back-reaction is
suppressed by the large Higgs-curvature coupling.Comment: 10 pages, RevTeX
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