53 research outputs found
Seeking large-scale magnetic fields in a pure-disk dwarf galaxy NGC 2976
It is still unknown how magnetic field-generation mechanisms could operate in
low-mass dwarf galaxies. Here, we present a detailed study of a nearby
pure-disk dwarf galaxy NGC 2976. Unlike previously observed dwarf objects, this
galaxy possesses a clearly defined disk. For the purpose of our studies, we
performed deep multi-frequency polarimetric observations of NGC 2976 with the
VLA and Effelsberg radio telescopes. Additionally, we supplement them with
re-imaged data from the WSRT-SINGS survey. The magnetic field morphology
discovered in NGC 2976 consists of a southern polarized ridge. This structure
does not seem to be due to just a pure large-scale dynamo process (possibly
cosmic-ray driven) at work in this object, as indicated by the RM data and
dynamo number calculations. Instead, the field of NGC 2976 is modified by past
gravitational interactions and possibly also by ram pressure inside the M 81
galaxy group environment. The estimates of total (7 muG) and ordered (3 muG)
magnetic field strengths, as well as degree of field order (0.46), which is
similar to those observed in spirals, suggest that tidally generated magnetized
gas flows can further enhance dynamo action in the object. NGC 2976 is
apparently a good candidate for the efficient magnetization of its
neighbourhood. It is able to provide an ordered (perhaps also regular) magnetic
field into the intergalactic space up to a distance of about 5 kpc. Tidal
interactions (and possibly also ram pressure) can lead to the formation of
unusual magnetic field morphologies (like polarized ridges) in galaxies out of
the star-forming disks, which do not follow any observed component of the
interstellar medium (ISM), as observed in NGC 2976. These galaxies are able to
provide ordered magnetic fields far out of their main disks.Comment: 16 page
The magnetic fields of large Virgo cluster spirals: Paper II
The Virgo cluster of galaxies provides excellent conditions for studying
interactions of galaxies with the cluster environment. Both the high-velocity
tidal interactions and effects of ram pressure stripping by the intracluster
gas can be investigated in detail. We extend our systematic search for possible
anomalies in the magnetic field structures of Virgo cluster spirals in order to
characterize a variety of effects and attribute them to different disturbing
agents. Six angularly large Virgo cluster spiral galaxies (NGC4192, NGC4302,
NGC4303, NGC4321, NGC4388, and NGC4535) were targets of a sensitive total power
and polarization study using the 100-m radio telescope in Effelsberg at 4.85GHz
and 8.35GHz (except for NGC4388 observed only at 4.85GHz, and NGC4535 observed
only at 8.35GHz). Magnetic field structures distorted to various extent are
found in all galaxies. Three galaxies (NGC4302, NGC4303, and NGC4321) show some
signs of possible tidal interactions, while NGC4388 and NGC4535 have very
likely experienced strong ram-pressure and shearing effects, respectively,
visible as distortions and asymmetries of polarized intensity distributions. As
in our previous study, even strongly perturbed galaxies closely follow the
radio-far-infrared correlation. In NGC4303 and NGC4321, we observe symmetric
spiral patterns of the magnetic field and in NGC4535 an asymmetric pattern.
Magnetic fields allow us to trace even weak interactions that are difficult to
detect with other observations. Our results show that the degree of distortions
of a galaxy is not a simple function of the distance to the cluster center but
reflects also the history of its interactions. The angle between the velocity
vector and the rotation vector of a galaxy may be a general parameter that
describes the level of distortions of galactic magnetic fields.Comment: 12 pages, 18 figures, 2 tables. Accepted for publication in Astronomy
and Astrophysic
The Principle of Valence Bond Amplitude Maximization in Cuprates: How it breeds Superconductivity, Spin and Charge Orders
A simple microscopic principle of `Valence bond (nearest neighbor singlet)
amplitude maximization '(VBAM) is shown to be present in undoped and optimally
doped cuprates and unify the very different orderings such as
antiferromagnetism in the Mott insulator and the robust superconductivity
accompanied by an enhanced charge and stripe correlations in the optimally
doped cuprates. VBAM is nearly synonymous with the energy minimization
principle. It is implicit in the RVB theory and thereby makes the predictions
of RVB mean field theory of superconductivity qualitatively correct.Comment: 4 pages, RevTe
The diffuse radio emission around NGC 5580 and NGC 5588
The galaxy pair NGC 5580 and NGC 5588 is part of a loose group of galaxies. They are surrounded by steep-spectrum, extended radio emission which was previously suggested to be a down-scaled example of Mpc-size radio haloes present in galaxies clusters. We present a multifrequency study of the radio emission aimed to clarify its nature. The source has been observed with the Giant Metrewave Radio Telescope at 235, 325 and 610 MHz and the images obtained were combined with archival data to cover the frequency range 150-1400 MHz. The new observations revealed the presence of a second, fainter lobe on the south-east of NGC 5580. The spectral index study of the source shows a flattening of the spectrum (which implies a younger particle population) close to the two galaxies. We argue that the extended radio emission is the remnant of a past activity cycle of the active galactic nucleus present in NGC 5580 and therefore a notable example of a dying radio galaxy located outside dense environments. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society
Magnetic field evolution in interacting galaxies
Violent gravitational interactions can change the morphologies of galaxies
and, by means of merging, transform them into elliptical galaxies. We aim to
investigate how they affect the evolution of galactic magnetic fields. We
selected 16 systems of interacting galaxies and compared their radio emission
and estimated magnetic field strengths with their star-forming activity,
far-infrared emission, and the stage of tidal interaction. We find a general
evolution of magnetic fields: for weak interactions the strength of magnetic
field is almost constant (10-15muG) as interaction advances, then it increases
up to 2x, peaks at the nuclear coalescence (25muG), and decreases again, down
to 5-6muG, for the post-merger remnants. The magnetic field strength for whole
galaxies is weakly affected by the star formation rate (SFR), while the
dependence is higher for galactic centres. We show that the morphological
distortions visible in the radio total and polarized emission do not depend
statistically on the global or local SFRs, while they do increase with the
advance of interaction. The constructed radio-far-infrared relations for
interacting and non-interacting galaxies display a similar balance between the
generation of cosmic rays, magnetic fields, and the production of the thermal
energy and dust radiation. The process of strong gravitational interactions can
efficiently magnetize the merger's surroundings, having a similar magnetizing
effect on intergalactic medium as supernova explosions or galactic winds. If
interacting galaxies generate some ultra-high energy cosmic rays (UHECRs), the
disk or magnetized outflows can deflect them (up to 23 degrees), and make an
association of the observed UHECRs with the sites of their origin very
uncertain.Comment: 17 pages, 16 figures, 5 tables. Published in Astronomy and
Astrophysics, minor changes to v
FIELD-INDUCED MAGNETIZATION IN Ho0.53Er0.47Co3.04Ni1.95
The magnetization process of Ho0.53Er0.47Co3.04Ni1.95 single crystals was investigated in a field up to 10 T from 4.2 to 300 K as a function of the angle between the c-axis and the magnetic field. The magnetic spin structure is interpreted in a crystal-field-with-exchange-field model
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