10,387 research outputs found
Interaction between the Intergalactic Medium and Galactic Outflows from Dwarf Galaxies
We have carried out 2D hydrodynamical simulations in order to study the
interaction between supernova-powered gas outflows from low-mass galaxies and
the local intergalactic medium (IGM). We are specifically interested in
investigating whether a high pressure IGM, such as that in clusters of
galaxies, can prevent the gas from escaping from the galaxy. The interface
between the outflow and ambient IGM is demarcated by a dense expanding shell
formed by the gas swept-up by the outflow. A sufficiently high IGM pressure can
bring the shell to a halt well before it escapes the galaxy. Galaxies in such
high pressure environments are, however, to be ploughing through the IGM at
relatively high velocities. Hence, they will also be subject to ram pressure,
which acts to strip the gas from the galaxy. We have carried out simulations
that take into account the combined impact of ram pressure and thermal
pressure. We find that ram pressure deforms the shell into a tail-like
structure, fragments it into dense clouds and eventually drags the clouds away
from the galaxy. The clouds are potential sites of star formation and if viewed
during this transient phase, the galaxy will appear to have a low-surface
brightness tail much like the galaxies with diffuse comet-like tail seen in
z=1.15 cluster 3C324. In contrast, the relatively unhindered outflows in low
density, low temperature environments can drive the shells of swept-up gas out
to large distances from the galaxy. Such shells, if they intersect a quasar
line-of-sight, would give rise to Ly absorption lines of the kind seen
in quasar spectra.Comment: 32 pages, 6 encapsulated Postscript figures, 7 gif figures. Accepted
for publication in MNRA
Yang-Mills theory constructed from Cho--Faddeev--Niemi decomposition
We give a new way of looking at the Cho--Faddeev--Niemi (CFN) decomposition
of the Yang-Mills theory to answer how the enlarged local gauge symmetry
respected by the CFN variables is restricted to obtain another Yang-Mills
theory with the same local and global gauge symmetries as the original
Yang-Mills theory. This may shed new light on the fundamental issue of the
discrepancy between two theories for independent degrees of freedom and the
role of the Maximal Abelian gauge in Yang-Mills theory. As a byproduct, this
consideration gives new insight into the meaning of the gauge invariance and
the observables, e.g., a gauge-invariant mass term and vacuum condensates of
mass dimension two. We point out the implications for the Skyrme--Faddeev
model.Comment: 17pages, 1 figure; English improved; a version appeared in Prog.
Theor. Phy
The Reionization History and Early Metal Enrichment inferred from the Gamma-Ray Burst Rate
Based on the gamma-ray burst (GRB) event rate at redshifts of , which is assessed by the spectral peak energy-to-luminosity relation
recently found by Yonetoku et al., we observationally derive the star formation
rate (SFR) for Pop III stars in a high redshift universe. As a result, we find
that Pop III stars could form continuously at . Using the
derived Pop III SFR, we attempt to estimate the ultraviolet (UV) photon
emission rate at in which redshift range no observational
information has been hitherto obtained on ionizing radiation intensity. We find
that the UV emissivity at can make a noticeable contribution
to the early reionization. The maximal emissivity is higher than the level
required to keep ionizing the intergalactic matter at .
However, if the escape fraction of ionizing photons from Pop III objects is
smaller than 10%, then the IGM can be neutralized at some redshift, which may
lead to the double reionization. As for the enrichment, the ejection of all
metals synthesized in Pop III objects is marginally consistent with the IGM
metallicity, although the confinement of metals in Pop III objects can reduce
the enrichment significantly.Comment: 12 pages, 2 figures, ApJL accepte
Spin Hall effects in diffusive normal metals
We consider spin and charge flow in normal metals. We employ the Keldysh
formalism to find transport equations in the presence of spin-orbit
interaction, interaction with magnetic impurities, and non-magnetic impurity
scattering. Using the quasiclassical approximation, we derive diffusion
equations which include contributions from skew scattering, side-jump
scattering and the anomalous spin-orbit induced velocity. We compute the
magnitude of various spin Hall effects in experimental relevant geometries and
discuss when the different scattering mechanisms are important.Comment: 10 pages, 4 figure
Spin-torque efficiency enhanced by Rashba spin splitting in three dimensions
We examine a spin torque induced by the Rashba spin-orbit coupling in three
dimensions within the Boltzmann transport theory. We analytically calculate the
spin torque and show how its behavior is related with the spin topology in the
Fermi surfaces by studying the Fermi-energy dependence of the spin torque.
Moreover we discuss the spin-torque efficiency which is the spin torque divided
by the applied electric current in association with the current-induced
magnetization reversal. It is found that high spin-torque efficiency is
achieved when the Fermi energy lies on only the lower band and there exists an
optimal value for the Rashba parameter, where the spin-torque efficiency
becomes maximum.Comment: 7 pages, 5 figure
Resonant spin polarization and spin current in a two-dimensional electron gas
We study the spin polarization and its associated spin-Hall current due to
EDSR in disordered two-dimensional electron systems. We show that the disorder
induced damping of the resonant spin polarization can be strongly reduced by an
optimal field configuration that exploits the interference between Rashba and
Dresselhaus spin-orbit interaction. This leads to a striking enhancement of the
spin susceptibility while the spin-Hall current vanishes at the same time. We
give an interpretation of the spin current in geometrical terms which are
associated with the trajectories the polarization describes in spin space.Comment: (5 pages), updated references, corrected typo
UV and X-ray Spectral Lines of FeXXIII Ion for Plasma Diagnostics
We have calculated X-ray and UV spectra of Be-like Fe (FeXXIII) ion in
collisional-radiative model including all fine-structure transitions among the
2s^2, 2s2p, 2p^2, 2snl, and 2pnl levels where n=3 and 4, adopting data for the
collision strengths by Zhang & Sampson (1992) and by Sampson, Goett, & Clark
(1984). Some line intensity ratios can be used for the temperature diagnostics.
We show 5 ratios in UV region and 9 ratios in X-ray region as a function of
electron temperature and density at 0.3keV < T_e < 10keV and . The effect of cascade in these line ratios and in the level
population densities are discussed.Comment: LaTeX, 18 pages, 10 Postscript figures. To appear in Physica Script
Recommended Data on Electron-ion Collision Strengths and Effective Collision Strengths for Fe X. Fe XI and Fe XIII Ions
Data obtained for electron-induced excitation transitions between levels with principal quantum numbers n=3 in Cl-like Fe X, S-like Fe XI, and Si-like Fe XIII ions by different theoretical methods were compared, and recommended data for electron collision strengths and effective collision strengths have been chosen. Simple analytical formulas with 7 free parameters were used to describe electron temperature dependence of effective collision strengths in a wide temperature range. The values of free parameters have been determined by fitting the recommended numerical data. The obtained results can be used for plasma kinetics calculations and for spectroscopic methods of plasma diagnostics
Carbon stars in the IRTS survey
We have identified 139 cool carbon stars in the near-infrared
spectro-photometric survey of the InfraRed Telescope in Space (IRTS) from the
conspicuous presence of molecular absorption bands at 1.8, 3.1 and 3.8 microns.
Among them 14 are new, bright (K ~ 4.0-7.0), carbon stars. We find a trend
relating the 3.1 microns band strength to the K-L' color index, which is known
to correlate with mass-loss rate. This could be an effect of a relation between
the depth of the 3.1 microns feature and the degree of development of the
extended stellar atmosphere where dust starts to form.Comment: accepted by the PASP; December 7, 200
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