54 research outputs found
The large scale magnetic field structure of the spiral galaxy NGC 5775
In order to better determine the large-scale 3D-structure of magnetic fields
in spiral galaxies we present a Faraday rotation analysis of the edge-on spiral
galaxy NGC 5775. Deep radio-continuum observations in total power and linear
polarization were performed at 8.46 GHz with the VLA and the 100-m Effelsberg
telescope. They were analyzed together with archival 4.86 and 1.49 GHz
VLA-data. We thus can derive rotation measures from a comparison of three
frequencies and determine the intrinsic magnetic field structure. A very
extended halo is detected in NGC 5775, with magnetic field lines forming an
X-shaped structure. Close to the galactic disk the magnetic field is
plane-parallel. The scaleheights of the radio emission esimated for NGC 5775
are comaprable with other galaxies. The rotation measure distribution varies
smoothly on both sides along the major axis from positive to negative values.
From the derived distribution of rotation measures and the plane-parallel
intrinsic magnetic field orientation along the galactic midplane we conclude
that NGC 5775 has an 'even axisymmetric' large-scale magnetic field
configuration in the disk as generated by an \alpha \Omega -dynamo which is
accompanied by a quadrupolar poloidal field. The magnetic field lines of the
plane-parallel component are pointing 'outwards'. The observed X-shaped halo
magnetic field, however, cannot be explained by the action of the disk's
mean-field dynamo alone. It is probably due to the influence of the galactic
wind together with the dynamo action.Comment: 11 pages, 13 figures, A&A accepte
APPROACH TO CLUSTERING COSTS AND LOSSES INCURRED AS A RESULT OF WATER NETWORK FAILURE
The availability of the gas supply system safety concerns the crucial issue in gas infrastructure operation and management. In recent years, the observed development of gas supply system does not protect against the failure occurrence of the gas network. Gas network requires proper analysis of its functioning, as it forms a complex system. Gas companies are responsible for supplying gas to consumers in reliable and safe way. In the paper the approach to failure cost and losses assessment with implementation of clustering analysis was presented. Such comparison can be helpful in costs assessment in different distribution gas systems. The analysis, was based on the operational data obtained from the gas companies
A large-scale, regular intergalactic magnetic field associated with Stephan's Quintet?
Regular magnetic fields are frequently found within and in the outskirts of
galaxies, but their presence, properties, and origin has not yet been
established for galaxy groups. On the basis of broadband radio polarimetric
imaging with the Westerbork Synthesis Radio Telescope (WSRT), we made use of
Rotation Measure Synthesis to disentangle contributions from magnetic fields on
various scales for several polarised radio sources inside, behind, or in the
vicinity of the Stephan's Quintet (HCG92, SQ). We recognise the signature of a
large-scale, genuinely regular, magnetised screen, seemingly constrained to the
Quintet itself. Although we cannot exclude a contribution from the Milky Way,
our analysis favours a magnetic structure within the SQ system. If indeed
associated with the galaxy group in question, it would span a volume of at
least and have a strength at least
as high as that previously detected within large spiral galaxies. This field
would then surpass the extent of any other known galactic, regular magnetic
fields, have a considerable strength of a few microgauss, and would be the
first known example of such a structure in a galaxy system other than a galaxy
pair. Several other explanations are also presented and evaluated.Comment: 13 pages, 7 figures, 3 table
Magnetic fields and hot gas in M 101
Context. Studies of nearby spiral galaxies in radio and X-ray wavelengths reveal the structure and energy balance of the magnetic fields and the hot interstellar medium (ISM). In some spiral galaxies, large-scale ordered magnetic fields have been found between the spiral stellar arms (the so-called magnetic arms). One of the considered explanations of their origin is magnetic reconnection, which according to theoretical studies can efficiently heat the low-density ISM.
Aims. We present, for the first time, high-resolution C-band (5 GHz) radio maps of the nearby face-on spiral galaxy M 101 to study the magnetic fields and verify the existence of the magnetic arms. The analysis of the archival XMM-Newton X-ray data is performed to search for signatures of gas heating by magnetic reconnection effects in the disk and the halo of this galaxy.
Methods. We combine the Very Large Array (VLA) and Effelsberg radio maps of M 101 to restore the large-scale emission lost in the interferometric observations. From the obtained maps, we derive magnetic field strengths and energy densities, and compare them with the properties of the hot gas found with the spectral analysis of the X-ray data.
Results. Most of the X-ray emission likely comes from the hot gas in the halo of M 101. Its temperature is highest above the massive stellar arm and an inter-arm region with enhanced polarised radio emission, as well as in the inter-arm area where neither Hα nor H
Hot magnetic halo of NGC 628 (M 74)
Context. In several spiral galaxies that are observed face-on, large-scale ordered magnetic fields (the so-called magnetic arms) were found. One of the explanations was the action of the magnetic reconnection, which leads to a higher ordering of the magnetic fields. Because it simultaneously converts the energy of the magnetic fields into thermal energy of the surroundings, magnetic reconnection has been considered as a heating mechanism of the interstellar medium for many years. Until recently, no clear observational evidence for this phenomenon was found. Aims. We search for possible signatures of gas heating by magnetic reconnection effects in the radio and X-ray data for the face-on spiral galaxy NGC 628 (M 74), which presents pronounced magnetic arms and evidence for vertical magnetic fields. Methods. The strengths and energy densities of the magnetic field in the spiral and magnetic arms were derived, as were the temperatures and thermal energy densities of the hot gas, for the disk and halo emission. Results. In the regions of magnetic arms, higher order and lower energy density of the magnetic field is found than in the stellar spiral arms. The global temperature of the hot gas is roughly constant throughout the disk. Conclusions. The comparison of the findings with those obtained for the starburst galaxy M 83 suggests that magnetic reconnection heating may be present in the halo of NGC 628. The joint analysis of the properties of the magnetic fields and the hot gas in NGC 628 also provided clues for possible tidal interaction with the companion galaxy
Imaging of hypnosis with functional magnetic resonance
Aim. The aim of the study was imaging of the central nervous system activity with the fMRI method during hypnosis as well as confirmation of the observations linking subjective effects of suggested analgesia with the functional changes on the neurophysiological level. Method. At first volunteers (7 female, 7 male) were examined with fMRI in the resting state and then four times during application of painful stimuli such as pricking of the right hand. Four experimental conditions were associated with this stimulation: only nociceptive stimulation, after analgesic suggestion, after hypnotic induction and after consecutive analgesic suggestion in hypnosis. In the fifth condition, concentration of attention was an experimental condition, while the control condition was distraction of attention (e.g. free associations). The contrast differences between measurements in the consecutive phases of the experiment were analysed. Results. Decreases of activity of regions known for contributing to pain reception were found, probably as an effect of analgesic suggestion. This effect was seen especially in the area of L-thalamus. Suggestion (more precisely - the reception of its content) was related mainly to the R-ACG area activity growth. Hypnotic induction was correlated with increasing activity of the L-orbitofrontal gyrus. Concentration of attention was linked with activity increase within inferior parietal lobule, occipital middle/superior gyri; in the left hemisphere in the orbital frontal gyri and insula/frontal operculum. Conclusion. Both hypnosis and reception of analgesic suggestion are linked with increasing activity in particular brain areas, whereas the effect of analgesic suggestion demonstrates itself in the fMRI mainly by diminishing the reaction on painful stimuli
3D MHD simulations of magnetic field evolution and radio polarization of barred galaxies
Aims. We study numerically the large-scale gas and magnetic field
evolution of barred galaxies in the gravitational potential of a disk, bulge, halo, and
bar. We solve non-linear MHD equations including the back-reaction of the magnetic field
to the gas. We do not take into account any dynamo process.
Methods. We apply the numerical MHD code to calculate the model of the
galaxy in three dimensions. We construct realistic maps of high-frequency (Faraday
rotation free) polarized radio emission on the basis of the simulated magnetic fields. The
polarization model includes the effects of projection and limited resolution.
Results. The main result is that our modeled polarization maps resemble
the radio polarization structures observed in barred galaxies. The modeled polarization
B-vectors distribution along the bar and between spiral
arms resembles the observed topology of the magnetic field in barred galaxies. Our
calculations for several different rotational velocities and sound speeds give the same
result we got in our previous earlier published model. The reason of this behaviour is the
dynamical evolution of the bar that causes gas to form spiral waves going radially
outward. A gaseous spiral arms in turn generates magnetic ones, which live much longer in
the inter-arm disk space than the gaseous pattern
Large-scale magnetized outflows from the Virgo Cluster spiral NGC 4569 : a galactic wind in a ram pressure wind
Using the Effelsberg radio telescope at 4.85 GHz and 8.35 GHz we
discovered large symmetric lobes of polarized radio emission around the
strongly H
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