3,406 research outputs found
Massive HI clouds with no optical counterparts as high-density regions of intragroup HI rings and arcs
We present a new scenario in which massive intragroup HI clouds are the
high-density parts of large HI rings/arcs formed by dynamical interaction
between galaxy groups and gas-rich, low surface brightness (LSB) galaxies with
extended gas disks. Our hydrodynamical simulations demonstrate that the group
tidal field is very efficient at stripping the outer HI gas of the disk if the
gaseous disk of the LSB galaxy extends times further than the stellar
disk. We find that a massive, extended `leading stream' orbiting the group's
center can form out of the stripped outer HI envelope, while the severely
shrunk LSB galaxy, whose stellar disk remains unaffected, continues on its
path. The result is a relatively isolated, massive HI cloud with a ring- or
arc-like shape, a very inhomogeneous density distribution ( atoms cm), and, initially, no
stellar content. Only the high density peaks of the simulated intragroup HI
ring/arc can be detected in many current HI observations. These will appear as
relatively isolated `HI islands' near the group center. We also find that star
formation can occur within the ring/arc, if the total gas mass within the
intragroup ring/arc is very large ( 4 ).
We discuss these results in terms of existing observations of intragroup gas
(e.g., the Leo Ring and HIPASS J0731--69) and intergalactic HII regions.Comment: 5 pages with 4 figures, accepted MNRA
Lattice Discretization in Quantum Scattering
The utility of lattice discretization technique is demonstrated for solving
nonrelativistic quantum scattering problems and specially for the treatment of
ultraviolet divergences in these problems with some potentials singular at the
origin in two and three space dimensions. This shows that lattice
discretization technique could be a useful tool for the numerical solution of
scattering problems in general. The approach is illustrated in the case of the
Dirac delta function potential.Comment: 9 page
The z<=0.1 Surface Brightness Distribution
The surface brightness distribution (SBD) function describes the number
density of galaxies as measured against their central surface brightness.
Because detecting galaxies with low central surface brightnesses is both
time-consuming and complicated, determining the shape of this distribution
function can be difficult. In a recent paper Cross, et al. suggested a
bell-shaped SBD disk-galaxy function which peaks near the canonical Freeman
value of 21.7 and then falls off significantly by 23.5 B mag arcsec-2. This is
in contradiction to previous studies which have typically found flat (slope=0)
SBD functions out to 24 - 25 B mag arcsec^-2 (the survey limits). Here we take
advantage of a recent surface-brightness limited survey by Andreon & Cuillandre
which reaches considerably fainter magnitudes than the Cross, et.al sample (M_B
reaches fainter than -12 for Andreon & Cuillandre while the Cross, et.al sample
is limited to M_B < -16) to re-evaluate both the SBD function as found by their
data and the SBD for a wide variety of galaxy surveys, including the Cross, et
al. data. The result is a SBD function with a flat slope out through the survey
limits of 24.5 B mag arcsec^-2, with high confidence limits.Comment: 5 pages including 5 figures. accepted by A&A
Dynamical conformal transformation and classical Euclidean wormholes
We investigate the necessary condition for the existence of classical
Euclidean wormholes in a conformally non-invariant gravitational model
minimally coupled to an scalar field. It is shown that while the original Ricci
tensor with positive eigenvalues does not allow the Euclidean wormholes to
occur, under dynamical conformal transformations the Ricci tensor, with respect
to the original metric, is dynamically coupled with the conformal field and its
eigenvalues may become negative allowing the Euclidean wormholes to occur.
Therefore, it is conjectured that dynamical conformal transformations may
provide us with {\it effective} forms of matter sources leading to Euclidean
wormholes in conformally non-invariant systems.Comment: 6 pages, minor revisio
Renormalization in Nonrelativistic Quantum Mechanics
The importance and usefulness of renormalization are emphasized in
nonrelativistic quantum mechanics. The momentum space treatment of both
two-body bound state and scattering problems involving some potentials singular
at the origin exhibits ultraviolet divergence. The use of renormalization
techniques in these problems leads to finite converged results for both the
exact and perturbative solutions. The renormalization procedure is carried out
for the quantum two-body problem in different partial waves for a minimal
potential possessing only the threshold behavior and no form factors. The
renormalized perturbative and exact solutions for this problem are found to be
consistent with each other. The useful role of the renormalization group
equations for this problem is also pointed out.Comment: 16 page
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