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2021-12-08
|
IGM damping wing constraints on reionisation from covariance reconstruction of two $z\gtrsim7$ QSOs
|
Bright, high redshift ($z>6$) QSOs are powerful probes of the ionisation
state of the intervening intergalactic medium (IGM). The detection of
Ly$\alpha$ damping wing absorption imprinted in the spectrum of high-z QSOs can
provide strong constraints on the epoch of reionisation (EoR). In this work, we
perform an independent Ly$\alpha$ damping wing analysis of two known $z>7$
QSOs; DESJ0252-0503 at $z=7.00$ (Wang et al.) and J1007+2115 at $z=7.51$ (Yang
et al.). For this, we utilise our existing Bayesian framework which
simultaneously accounts for uncertainties in: (i) the intrinsic Ly$\alpha$
emission profile (reconstructed from a covariance matrix of measured emission
lines; extended in this work to include NV) and (ii) the distribution of
ionised (H\,{\scriptsize II}) regions within the IGM using a $1.6^3$ Gpc$^3$
reionisation simulation. This approach is complementary to that used in the
aforementioned works as it focuses solely redward of Ly$\alpha$ ($1218 <
\lambda < 1230$\AA) making it more robust to modelling uncertainties while also
using a different methodology for (i) and (ii). We find, for a fiducial EoR
morphology, $\bar{x}_{\rm HI} = 0.64\substack{+0.19 \\ -0.23}$ (68 per cent) at
$z=7$ and $\bar{x}_{\rm HI} = 0.27\substack{+0.21 \\ -0.17}$ at $z=7.51$
consistent within $1\sigma$ to the previous works above, though both are
slightly lower in amplitude. Following the inclusion of NV into our
reconstruction pipeline, we perform a reanalysis of ULASJ1120+0641 at $z=7.09$
(Mortlock et al.) and ULASJ1342+0928 at $z=7.54$ (Ba\~nados et al.) finding
$\bar{x}_{\rm HI} = 0.44\substack{+0.23 \\ -0.24}$ at $z=7.09$ and
$\bar{x}_{\rm HI} = 0.31\substack{+0.18 \\ -0.19}$ at $z=7.54$. Finally, we
combine the QSO damping wing constraints for all four $z\gtrsim7$ QSOs to
obtain a single, unified constraint of $\bar{x}_{\rm HI} = 0.49\substack{+0.11
\\ -0.11}$ at $z=7.29$.
|
2112.04091v1
|
2022-01-24
|
A blow-up result for a Nakao-type weakly coupled system with nonlinearities of derivative-type
|
In this paper, we consider a weakly coupled system of a wave and damped
Klein-Gordon equation with nonlinearities of derivative type. We prove a
blow-up result for the Cauchy problem associated with this system for
nonnegative and compactly supported data by means of an iteration argument.
|
2201.09462v1
|
2022-03-11
|
On the small noise limit in the Smoluchowski-Kramers approximation of nonlinear wave equations with variable friction
|
We study the validity of a large deviation principle for a class of
stochastic nonlinear damped wave equations, of Klein-Gordon type, in the joint
small mass and small noise limit. The friction term is assumed to be state
dependent.
|
2203.05923v2
|
2022-03-28
|
The higher order nonlinear Schrödinger equation with quadratic nonlinearity on the real axis
|
The initial value problem is considered for a higher order nonlinear
Schr\"odinger equation with quadratic nonlinearity. Results on existence and
uniqueness of weak solutions are obtained. In the case of an effective at
infinity additional damping large-time decay of solutions without any smallness
assumptions is also established. The main difficulty of the study is the
non-smooth character of the nonlinearity.
|
2203.14830v1
|
2022-04-03
|
Strong Solution of Modified Anistropic 3D-Navier-Stokes Equations
|
In this paper we study the anisotropic incompressible Navier-Stokes equations
with a logarithm damping $\alpha \log(e+|u|^2)|u|^2u$ in $H^{0.1}$, where we
used new methods, new tools and Fourier analysis.
|
2204.01717v2
|
2022-04-28
|
Coupling between turbulence and solar-like oscillations: A combined Lagrangian PDF/SPH approach. II - Mode driving, damping and modal surface effect
|
The first paper of this series established a linear stochastic wave equation
for solar-like p-modes, correctly taking the effect of turbulence thereon into
account. In this second paper, we aim at deriving simultaneous expressions for
the excitation rate, damping rate, and modal surface effect associated with any
given p-mode, as an explicit function of the statistical properties of the
turbulent velocity field. We reduce the stochastic wave equation to complex
amplitude equations for the normal oscillating modes of the system. We then
derive the equivalent Fokker-Planck equation for the real amplitudes and phases
of all the oscillating modes of the system simultaneously. The effect of the
finite-memory time of the turbulent fluctuations (comparable to the period of
the modes) on the modes themselves is consistently and rigorously accounted
for, by means of the simplified amplitude equation formalism. This formalism
accounts for mutual linear mode coupling in full, and we then turn to the
special single-mode case. This allows us to derive evolution equations for the
mean energy and mean phase of each mode, from which the excitation rate, the
damping rate, and the modal surface effect naturally arise.
We show that the expression for the excitation rate of the modes is identical
to previous results obtained through a different modelling approach, thus
supporting the validity of the formalism presented here. We also recover the
fact that the damping rate and modal surface effect correspond to the real and
imaginary part of the same single complex quantity. We explicitly separate the
different physical contributions to these observables, in particular the
turbulent pressure contribution and the joint effect of the
pressure-rate-of-strain correlation and the turbulent dissipation. We show that
the former dominates for high-frequency modes and the latter for low-frequency
modes.
|
2204.13367v1
|
2022-05-05
|
Blow-up solutions of damped Klein-Gordon equation on the Heisenberg group
|
Inthisnote,weprovetheblow-upofsolutionsofthesemilineardamped Klein-Gordon
equation in a finite time for arbitrary positive initial energy on the
Heisenberg group. This work complements the paper [21] by the first author and
Tokmagambetov, where the global in time well-posedness was proved for the small
energy solutions.
|
2205.02705v1
|
2022-05-23
|
Extended random-phase-approximation study of fragmentation of giant quadrupole resonance in $^{16}$O
|
The damping of isoscalar giant quadrupole resonance in $^{16}$O is studied
using extended random-phase-approximation approaches derived from the
time-dependent density-matrix theory. It is pointed out that the effects of
ground-state correlations bring strong fragmentation of quadrupole strength
even if the number of two particle--two hole configurations is strongly
limited.
|
2205.11654v2
|
2022-06-21
|
Nonlinear Compton scattering and nonlinear Breit-Wheeler pair production including the damping of particle states
|
In the presence of an electromagnetic background plane-wave field, electron,
positron, and photon states are not stable, because electrons and positrons
emit photons and photons decay into electron-positron pairs. This decay of the
particle states leads to an exponential damping term in the probabilities of
single nonlinear Compton scattering and nonlinear Breit-Wheeler pair
production. In this paper we investigate analytically and numerically the
probabilities of nonlinear Compton scattering and nonlinear Breit-Wheeler pair
production including the particle states' decay. For this we first compute
spin- and polarization-resolved expressions of the probabilities, provide some
of their asymptotic behaviors and show that the results of the total
probabilities are independent of the spin and polarization bases. Then, we
present several plots of the total and differential probabilities for different
pulse lengths and for different spin and polarization quantum numbers. We
observe that it is crucial to take into account the damping of the states in
order for the probabilities to stay always below unity and we show that the
damping factors also scale with the intensity and pulse duration of the
background field. In the case of nonlinear Compton scattering we show
numerically that the total probability behaves like a Poissonian distribution
in the regime where the photon recoil is negligible. In all considered cases,
the kinematic conditions are such that the final particles momenta transverse
to the propagation direction of the plane wave are always much smaller than the
particles longitudinal momenta and the main spread of the momentum distribution
on the transverse plane is along the direction of the plane-wave electric
field.
|
2206.10345v2
|
2022-06-23
|
Nonlinear Landau damping for the 2d Vlasov-Poisson system with massless electrons around Penrose-stable equilibria
|
In this paper, we prove the nonlinear asymptotic stability of the
Penrose-stable equilibria among solutions of the $2d$ Vlasov-Poisson system
with massless electrons.
|
2206.11744v2
|
2022-07-25
|
Inviscid limit for the compressible Navier-Stokes equations with density dependent viscosity
|
We consider the compressible Navier-Stokes system describing the motion of a
barotropic fluid with density dependent viscosity confined in a
three-dimensional bounded domain $\Omega$. We show the convergence of the weak
solution to the compressible Navier-Stokes system to the strong solution to the
compressible Euler system when the viscosity and the damping coefficients tend
to zero.
|
2207.12222v1
|
2022-08-25
|
Polynomial energy decay rate of a 2D Piezoelectric beam with magnetic effect on a rectangular domain without geometric conditions
|
In this paper, we investigate the stability of coupled equations modelling a
2D piezoelectric beam with magnetic effect with only one local viscous damping
on a rectangular domain without geometric conditions. We prove that the energy
of the system decays polynomially with the rate 1/t .
|
2208.12012v1
|
2022-10-12
|
Backward problem for the 1D ionic Vlasov-Poisson equation
|
In this paper, we study the backward problem for the one-dimensional
Vlasov-Poisson system with massless electrons, and we show the Landau damping
by fixing the asymptotic behaviour of our solution.
|
2210.06123v2
|
2022-10-28
|
Oblique Quasi-Kink Modes in Solar Coronal Slabs Embedded in an Asymmetric Magnetic Environment: Resonant Damping, Phase and Group Diagrams
|
There has been considerable interest in magnetoacoustic waves in static,
straight, field-aligned, one-dimensional equilibria where the exteriors of a
magnetic slab are different between the two sides. We focus on trapped,
transverse fundamental, oblique quasi-kink modes in pressureless setups where
the density varies continuously from a uniform interior (with density
$\rho_{\rm i}$) to a uniform exterior on either side (with density $\rho_{\rm
L}$ or $\rho_{\rm R}$), assuming $\rho_{\rm L}\le\rho_{\rm R}\le\rho_{\rm i}$.
The continuous structuring and oblique propagation make our study new relative
to pertinent studies, and lead to wave damping via the Alfv$\acute{\rm e}$n
resonance. We compute resonantly damped quasi-kink modes as resistive
eigenmodes, and isolate the effects of system asymmetry by varying $\rho_{\rm
i}/\rho_{\rm R}$ from the ``Fully Symmetric'' ($\rho_{\rm i}/\rho_{\rm
R}=\rho_{\rm i}/\rho_{\rm L}$) to the ``Fully Asymmetric'' limit ($\rho_{\rm
i}/\rho_{\rm R}=1$). We find that the damping rates possess a nonmonotonic
$\rho_{\rm i}/\rho_{\rm R}$-dependence as a result of the difference between
the two Alfv$\acute{\rm e}$n continua, and resonant absorption occurs only in
one continuum when $\rho_{\rm i}/\rho_{\rm R}$ is below some threshold. We also
find that the system asymmetry results in two qualitatively different regimes
for the phase and group diagrams. The phase and group trajectories lie
essentially on the same side (different sides) relative to the equilibrium
magnetic field when the configuration is not far from a ``Fully Asymmetric''
(``Fully Symmetric'') one. Our numerical results are understood by making
analytical progress in the thin-boundary limit, and discussed for imaging
observations of axial standing modes and impulsively excited wavetrains.
|
2210.16091v1
|
2022-11-02
|
Data-driven modeling of Landau damping by physics-informed neural networks
|
Kinetic approaches are generally accurate in dealing with microscale plasma
physics problems but are computationally expensive for large-scale or
multiscale systems. One of the long-standing problems in plasma physics is the
integration of kinetic physics into fluid models, which is often achieved
through sophisticated analytical closure terms. In this paper, we successfully
construct a multi-moment fluid model with an implicit fluid closure included in
the neural network using machine learning. The multi-moment fluid model is
trained with a small fraction of sparsely sampled data from kinetic simulations
of Landau damping, using the physics-informed neural network (PINN) and the
gradient-enhanced physics-informed neural network (gPINN). The multi-moment
fluid model constructed using either PINN or gPINN reproduces the time
evolution of the electric field energy, including its damping rate, and the
plasma dynamics from the kinetic simulations. In addition, we introduce a
variant of the gPINN architecture, namely, gPINN$p$ to capture the Landau
damping process. Instead of including the gradients of all the equation
residuals, gPINN$p$ only adds the gradient of the pressure equation residual as
one additional constraint. Among the three approaches, the gPINN$p$-constructed
multi-moment fluid model offers the most accurate results. This work sheds
light on the accurate and efficient modeling of large-scale systems, which can
be extended to complex multiscale laboratory, space, and astrophysical plasma
physics problems.
|
2211.01021v3
|
2022-11-04
|
New Clues About Light Sterile Neutrinos: Preference for Models with Damping Effects in Global Fits
|
This article reports global fits of short-baseline neutrino data to
oscillation models involving light sterile neutrinos. In the commonly-used 3+1
plane wave model, there is a well-known 4.9$\sigma$ tension between data sets
sensitive to appearance versus disappearance of neutrinos. We find that models
that damp the oscillation prediction for the reactor data sets, especially at
low energy, substantially improve the fits and reduce the tension. We consider
two such scenarios. The first scenario introduces the quantum mechanical
wavepacket effect that accounts for the source size in reactor experiments into
the 3+1 model. We find that inclusion of the wavepacket effect greatly improves
the overall fit compared to a 3$\nu$ model by $\Delta \chi^2/$DOF$=61.1/4$
($7.1\sigma$ improvement) with best-fit $\Delta m^2=1.4$ eV$^2$ and wavepacket
length of 67fm. The internal tension is reduced to 3.4$\sigma$. If reactor-data
only is fit, then the wavepacket preferred length is 91 fm ($>20$ fm at 99\%
CL). The second model introduces oscillations involving sterile flavor and
allows the decay of the heaviest, mostly sterile mass state, $\nu_4$. This
model introduces a damping term similar to the wavepacket effect, but across
all experiments. Compared to a three-neutrino fit, this has a $\Delta
\chi^2/$DOF$=60.6/4$ ($7\sigma$ improvement) with preferred $\Delta m^2=1.4$
eV$^2$ and decay $\Gamma = 0.35$ eV$^2$. The internal tension is reduced to
3.7$\sigma$.
For many years, the reactor event rates have been observed to have structure
that deviates from prediction. Community discussion has focused on an excess
compared to prediction observed at 5 MeV; however, other deviations are
apparent. This structure has $L$ dependence that is well-fit by the damped
models. Before assuming this points to new physics, we urge closer examination
of systematic effects that could lead to this $L$ dependence.
|
2211.02610v5
|
2022-12-07
|
A recipe for orbital eccentricity damping in the type-I regime for low viscosity 2D-discs
|
It is known that gap opening depends on the disc's viscosity; however,
eccentricity damping formulas have only been derived at high viscosities,
ignoring partial gap opening. We aim at obtaining a simple formula to model
$e$-damping of the type-I regime in low viscosity discs, where even small
planets may start opening partial. We perform high resolution 2D locally
isothermal hydrodynamical simulations of planets with varying masses on fixed
orbits in discs with varying aspect ratios and viscosities. We determine the
torque and power felt by the planet to derive migration and eccentricity
damping timescales. We first find a lower limit to the gap depths below which
vortices appear; this happens roughly at the transition between type-I and
type-II regimes. For the simulations that remain stable, we obtain a fit to the
observed gap depth in the limit of vanishing eccentricities that is similar to
the one currently used in the literature but is accurate down to
$\alpha=3.16\times 10^{-5}$. We record the $e$-damping efficiency as a function
of the observed gap depth and $e$: when the planet has opened a deep enough
gap, a linear trend is observed independently of $e$; at shallower gaps this
linear trend is preserved at low $e$, while it deviates to more efficient
damping when $e$ is comparable to the disc's scale height. Both trends can be
understood on theoretical grounds and are reproduced by a simple fitting
formula. Our combined fits yield a simple recipe to implement type-I
$e$-damping in $N$-body for partial gap opening planets that is consistent with
high-resolution 2D hydro-simulations. The typical error of the fit is of the
order of a few percent, and lower than the error of type-I torque formulas
widely used in the literature. This will allow a more self-consistent treatment
of planet-disc interactions of the type-I regime for population synthesis
models at low viscosities.
|
2212.03608v1
|
2022-12-10
|
Linear stabilization for a degenerate wave equation in non divergence form with drift
|
We consider a degenerate wave equation in one dimension, with drift and in
presence of a leading operator which is not in divergence form. We impose a
homogeneous Dirichlet boundary condition where the degeneracy occurs and a
boundary damping at the other endpoint. We provide some conditions for the
uniform exponential decay of solutions for the associated Cauchy problem.
|
2212.05264v1
|
2022-12-31
|
On the stability of shear flows in bounded channels, II: non-monotonic shear flows
|
We give a proof of linear inviscid damping and vorticity depletion for
non-monotonic shear flows with one critical point in a bounded periodic
channel. In particular, we obtain quantitative depletion rates for the
vorticity function without any symmetry assumptions.
|
2301.00288v2
|
2023-03-18
|
Spin waves in a superconductor
|
Spin waves that can propagate in normal and superconducting metals are
investigated. Unlike normal metals, the velocity of spin waves becomes
temperature-dependent in a superconductor. The low frequency spin waves survive
within the narrow region below the superconducting transition temperature. At
low temperatures the high frequency waves alone can propagate with an
additional damping due to pair-breaking.
|
2303.10468v1
|
2023-04-07
|
Echo disappears: momentum term structure and cyclic information in turnover
|
We extract cyclic information in turnover and find it can explain the
momentum echo. The reversal in recent month momentum is the key factor that
cancels out the recent month momentum and excluding it makes the echo regress
to a damped shape. Both rational and behavioral theories can explain the
reversal. This study is the first explanation of the momentum echo in U.S.
stock markets.
|
2304.03437v1
|
2023-04-26
|
Plasma echoes in graphene
|
Plasma echo is a dramatic manifestation of plasma damping process
reversibility. In this paper we calculate temporal and spatial plasma echoes in
graphene in the acoustic plasmon regime when echoes dominate over plasmon
emission. We show an extremely strong spatial echo response and discuss how
electron collisions reduce the echo. We also discuss differences between
various electron dispersions, and differences between semiclassical and quantum
model of echoes.
|
2304.13440v1
|
2023-06-01
|
JWST Measurements of Neutral Hydrogen Fractions and Ionized Bubble Sizes at $z=7-12$ Obtained with Ly$α$ Damping Wing Absorptions in 26 Bright Continuum Galaxies
|
We present volume-averaged neutral hydrogen fractions $x_{\rm \HI}$ and
ionized bubble radii $R_{\rm b}$ measured with Ly$\alpha$ damping wing
absorption of galaxies at the epoch of reionization. We combine JWST/NIRSpec
spectra taken by CEERS, GO-1433, DDT-2750, and JADES programs, and obtain a
sample containing 26 bright UV-continuum ($M_{\rm UV}<-18.5~{\rm mag}$)
galaxies at $7<z<12$. We construct 4 composite spectra binned by redshift, and
find the clear evolution of softening break towards high redshift at the
rest-frame $1216$ {\AA}, suggesting the increase of Ly$\alpha$ damping wing
absorption. We estimate Ly$\alpha$ damping wing absorption in the galaxy
spectra with realistic templates including Ly$\alpha$ emission and
circum-galactic medium absorptions. Assuming the standard inside-out
reionization picture having an ionized bubble with radius $R_b$ around a galaxy
embedded in the intergalactic medium with $x_{\rm \HI}$, we obtain $x_{\rm
\HI}$ ($R_{\rm b}$) values generally increasing (decreasing) from $x_{\rm
\HI}={0.54}^{+0.13}_{-0.54}$ to ${0.94}^{+0.06}_{-0.41}$ ($\log R_{\rm
b}={1.89}^{+0.49}_{-1.54}$ to ${-0.72}^{+1.57}_{-0.28}$ comoving Mpc) at
redshift $7.12^{+0.06}_{-0.08}$ to $10.28^{+1.12}_{-1.40}$. The redshift
evolution of $x_{\rm \HI}$ indicates a moderately late reionization history
consistent with the one previously suggested from the electron scattering of
cosmic microwave background and the evolution of UV luminosity function with an
escape fraction $f_{\rm esc}\sim 0.2$. Our ${R_{\rm b}}$ measurements suggest
that bubble sizes could be up to a few dex larger than the cosmic average
values estimated by analytic calculations for a given $x_{\rm \HI}$, while our
$R_{\rm b}$ measurements are roughly comparable with the values for merged
ionized bubbles around bright galaxies predicted by recent numerical
simulations.
|
2306.00487v2
|
2023-06-20
|
New results on controllability and stability for degenerate Euler-Bernoulli type equations
|
In this paper we study the controllability and the stability for a degenerate
beam equation in divergence form via the energy method. The equation is clamped
at the left end and controlled by applying a shearing force or a damping at the
right end.
|
2306.11851v3
|
2023-08-01
|
Aerodynamics of the square-back Ahmed body under rainfall conditions
|
We report an experimental investigation about the aerodynamics of a
simplified road vehicle, the so-called square-back Ahmed body, under rainfall
conditions. A particular emphasis is put on the evolution of the body base
pressure distribution with respect to the operating conditions. It is found
that rainfall significantly damps both mean base pressure drag and wake
dynamics in comparison to dry conditions.
|
2308.00276v1
|
2023-09-11
|
Study of damped oscillating structures from charged and neutral K-meson electromagnetic form factors data
|
The damped oscillating structures (OS) were recently revealed in the proton
"effective" form factor (FF) data. For the time being they can be neither
confirmed nor disproved by investigations of timelike data on the individual
proton electric and proton magnetic FFs because their precision and reliability
(especially of the proton electric FF data) has not achieved required level for
this aim. On the other hand, conjectures that the OS are direct manifestations
of the quark-gluon structure of the proton indicate that they must not be
specific only for the proton and neutron, but that they should be present also
for other hadrons. This opens a plausibility to find damped oscillatory
structures also from the EM FFs data of such hadrons, for which adequate EM FFs
data exist, by using the same procedure as for the proton. Consequently in this
paper damped oscillatory structures are investigated in the EM FFs data of the
charged and neutral $K$-mesons to be extracted from the corresponding
production cross sections, $\sigma^{bare}_{tot}(e^+e^-\to K^+ K^-)$ measured
from the threshold up to 64 GeV$^2$ and $\sigma^{bare}_{tot}(e^+e^-\to K_s
K_L)$ measured from the threshold up to 9.5 GeV$^2$ of the total c.m. energy
squared. The following results have been obtained. If the charged and neutral
K-meson EM FFs timelike data are described by the three parametric formula by
means of which OS have been revealed from the "effective" proton FF data then
OS appear. If physically well founded Unitary and Analytic model of the K-meson
EM structure is used for a description of the charged K-meson EM FFs data, no
OS are visible. However, in the case of the neutral K-meson EM FF data one
cannot make a definite decision. The overall results indicate that OS obtained
from the "effective" proton FF data are likely an artefact of the three
parametric formula which does not describe these data well.
|
2309.05354v1
|
2023-10-31
|
Variational principle for a damped, quadratically interacting particle chain with nonconservative forcing
|
A method for designing variational principles for the dynamics of a possibly
dissipative and non-conservatively forced chain of particles is demonstrated.
Some qualitative features of the formulation are discussed.
|
2311.00106v2
|
2024-01-30
|
Linear stability analysis of the Couette flow for the 2D Euler-Poisson system
|
This paper is concerned with the linear stability analysis for the Couette
flow of the Euler-Poisson system for both ionic fluid and electronic fluid in
the domain $\bb{T}\times\bb{R}$. We establish the upper and lower bounds of the
linearized solutions of the Euler-Poisson system near Couette flow. In
particular, the inviscid damping for the solenoidal component of the velocity
is obtained.
|
2401.17102v1
|
2024-03-21
|
Non-resonant invariant foliations of quasi-periodically forced systems
|
We show the existence and uniqueness of invariant foliations about invariant
tori in analytic discrete-time dynamical systems. The parametrisation method is
used prove the result. Our theory is a foundational block of data-driven model
order reduction, that can only be carried out using invariant foliations. The
theory is illustrated by two mechanical examples, where instantaneous
frequencies and damping ratios are calculated about the invariant tori.
|
2403.14771v1
|
1999-08-09
|
On the possibility of variation of the fundamental constants of physics in the static universe
|
A variation of fundamental constants of physics is proposed in a frame of
static universe. It is shown when the velocity of light increases (decreases)
the Planck's constant increases (decreases) and mass of bodies decreases
(increases). This variation of constants leads to the variation of dimensions
of bodies and the energy levels of atoms, but a fine structure constant remains
unaltered.
|
9908082v1
|
2002-06-17
|
Cosmological constant and curved 5D geometry
|
We study the value of cosmological constant in de Sitter brane embedded in
five dimensions with positive, vanishing and negative bulk cosmological
constant. In the case of negative bulk cosmological constant, we show that not
zero but tiny four-dimensional cosmological constant can be realized by tiny
deviation from bulk curvature of the Randall-Sundrum model.
|
0206153v1
|
2003-06-30
|
Convex Bodies of Constant Width and Constant Brightness
|
In 1926 S. Nakajima (= A. Matsumura) showed that any convex body in $\R^3$
with constant width, constant brightness, and boundary of class $C^2$ is a
ball. We show that the regularity assumption on the boundary is unnecessary, so
that balls are the only convex bodies of constant width and brightness.
|
0306437v1
|
2010-07-27
|
The GL-l.u.st.\ constant and asymmetry of the Kalton-Peck twisted sum in finite dimensions
|
We prove that the Kalton-Peck twisted sum $Z_2^n$ of $n$-dimensional Hilbert
spaces has GL-l.u.st.\ constant of order $\log n$ and bounded GL constant. This
is the first concrete example which shows different explicit orders of growth
in the GL and GL-l.u.st.\ constants. We discuss also the asymmetry constants of
$Z_2^n$.
|
1007.4692v1
|
2019-04-02
|
On geometric constants for (small) Morrey spaces
|
In this article, we compute Von Neumann-Jordan constant, James constant, and
Dunkl-Williams constant for small Morrey spaces. Our approach can also be seen
as an alternative way in computing the three constants for the (classical)
Morrey spaces. In addition, we prove constructively that Morrey spaces are not
uniformly non-octahedral.
|
1904.01712v3
|
2021-08-11
|
Gravity can be caused by the difference of Coulomb's constants
|
Coulomb's constant is defined as a value for attraction and repulsion.
However, it is strange that only one value can be applied for both attraction
and repulsion. A very little difference between coulomb's constant for
attraction and coulomb's constant for repulsion can be the source of gravity.
The author verified if that theory is correct by calculating with slightly
bigger coulomb's constant for attraction.
|
2108.05114v1
|
2007-10-22
|
The Hubble constant and dark energy from cosmological distance measures
|
We study how the determination of the Hubble constant from cosmological
distance measures is affected by models of dark energy and vice versa. For this
purpose, constraints on the Hubble constant and dark energy are investigated
using the cosmological observations of cosmic microwave background, baryon
acoustic oscillations and type Ia suprenovae. When one investigates dark
energy, the Hubble constant is often a nuisance parameter, thus it is usually
marginalized over. On the other hand, when one focuses on the Hubble constant,
simple dark energy models such as a cosmological constant and a constant
equation of state are usually assumed. Since we do not know the nature of dark
energy yet, it is interesting to investigate the Hubble constant assuming some
types of dark energy and see to what extent the constraint on the Hubble
constant is affected by the assumption concerning dark energy. We show that the
constraint on the Hubble constant is not affected much by the assumption for
dark energy. We furthermore show that this holds true even if we remove the
assumption that the universe is flat. We also discuss how the prior on the
Hubble constant affects the constraints on dark energy and/or the curvature of
the universe.
|
0710.3995v2
|
2016-08-19
|
Kinetic stability and energetics of simulated glasses created by constant pressure cooling
|
We use computer simulations to study the cooling rate dependence of the
stability and energetics of model glasses created at constant pressure
conditions and compare the results with glasses formed at constant volume
conditions. To examine the stability, we determine the time it takes for a
glass cooled and reheated at constant pressure to transform back into a liquid,
$t_{\mathrm{trans}}$, and calculate the stability ratio $S =
t_{\mathrm{trans}}/\tau_\alpha$, where $\tau_\alpha$ is the equilibrium
relaxation time of the liquid. We find that, for slow enough cooling rates,
cooling and reheating at constant pressure results in a larger stability ratio
$S$ than for cooling and reheating at constant volume. We also compare the
energetics of glasses obtained by cooling while maintaining constant pressure
with those of glasses created by cooling from the same state point while
maintaining constant volume. We find that cooling at constant pressure results
in glasses with lower average potential energy and average inherent structure
energy. We note that in model simulations of the vapor deposition process
glasses are created under constant pressure conditions, and thus they should be
compared to glasses obtained by constant pressure cooling.
|
1608.05703v1
|
2007-04-24
|
On C$^2$-smooth Surfaces of Constant Width
|
A number of results for C$^2$-smooth surfaces of constant width in Euclidean
3-space ${\mathbb{E}}^3$ are obtained. In particular, an integral inequality
for constant width surfaces is established. This is used to prove that the
ratio of volume to cubed width of a constant width surface is reduced by
shrinking it along its normal lines. We also give a characterization of
surfaces of constant width that have rational support function.
Our techniques, which are complex differential geometric in nature, allow us
to construct explicit smooth surfaces of constant width in ${\mathbb{E}}^3$,
and their focal sets. They also allow for easy construction of tetrahedrally
symmetric surfaces of constant width.
|
0704.3248v1
|
2009-05-09
|
Time-like Salkowski and anti-Salkowski curves in Minkowski space $\e_1^3$
|
Salkowski \cite{salkow}, one century ago, introduced a family of curves with
constant curvature but non-constant torsion (Salkowski curves) and a family of
curves with constant torsion but non-constant curvature (anti-Salkowski curves)
in Euclidean 3-space $\e^3$. In this paper, we adapt definition of such curves
to time-like curves in Minkowski 3-space $\e_1^3$. Thereafter, we introduce an
explicit parametrization of a time-like Salkowski curves and a time-like
Anti-Salkowski curves in Minkowski space $\e_1^3$. Also, we characterize them
as space curve with constant curvature or constant torsion and whose normal
vector makes a constant angle with a fixed line.
|
0905.1404v1
|
2009-08-17
|
The Interacting and Non-constant Cosmological Constant
|
We propose a time-varying cosmological constant with a fixed equation of
state, which evolves mainly through its interaction with the background during
most of the long history of the universe. However, such interaction does not
exist in the very early and the late-time universe and produces the
acceleration during these eras when it becomes very nearly a constant. It is
found that after the initial inflationary phase, the cosmological constant,
that we call as lambda parameter, rolls down from a large constant value to
another but very small constant value and further dominates the present epoch
showing up in form of the dark energy driving the acceleration.
|
0908.2303v1
|
2012-06-04
|
The Yamabe constant on noncompact manifolds
|
We prove several facts about the Yamabe constant of Riemannian metrics on
general noncompact manifolds and about S. Kim's closely related "Yamabe
constant at infinity". In particular we show that the Yamabe constant depends
continuously on the Riemannian metric with respect to the fine C^2-topology,
and that the Yamabe constant at infinity is even locally constant with respect
to this topology. We also discuss to which extent the Yamabe constant is
continuous with respect to coarser topologies on the space of Riemannian
metrics.
|
1206.0610v2
|
2018-10-01
|
Three geometric constants for Morrey spaces
|
In this paper we calculate three geometric constants, namely the von
Neumann-Jordan constant, the James constant, and the Dunkl-Williams constant,
for Morrey spaces and discrete Morrey spaces. These constants measure uniformly
nonsquareness of the associated spaces. We obtain that the three constants are
the same as those for $L^1$ and $L^\infty$ spaces.
|
1810.00963v3
|
2019-09-03
|
Maximal Chow constant and cohomologically constant fibrations
|
Motivated by the study of rationally connected fibrations (and the MRC
quotient) we study different notions of birationally simple fibrations. We say
a fibration of smooth projective varieties is Chow constant if pushforward
induces an isomorphism on the Chow group of 0-cycles. Likewise we say a
fibration is cohomologically constant if pullback induces an isomorphism on
holomorphic p-forms for all p. Our main result is the construction of maximal
Chow constant and cohomologically constant fibrations. The paper is largely
self contained and we prove a number of basic properties of these fibrations.
One application is to the classification of "rationalizations of singularities
of cones." We also consider consequences for the Chow groups of the generic
fiber of a Chow constant fibration.
|
1909.01483v1
|
2020-04-08
|
On Seshadri constants and point-curve configurations
|
In the note we study the multipoint Seshadri constants of
$\mathcal{O}_{\mathbb{P}^{2}_{\mathbb{C}}}(1)$ centered at singular loci of
certain curve arrangements in the complex projective plane. Our first aim is to
show that the values of Seshadri constants can be approximated with use of a
combinatorial invariant which we call the configurational Seshadri constant. We
study specific examples of point-curve configurations for which we provide
actual values of the associated Seshadri constants. In particular, we provide
an example based on Hesse point-conic configuration for which the associated
Seshadri constant is computed by a line. This shows that multipoint Seshadri
constants are not purely combinatorial.
|
2004.04043v1
|
2021-10-07
|
Biconservative hypersurfaces with constant scalar curvature in space forms
|
Biconservative hypersurfaces are hypersurfaces which have conservative
stress-energy tensor with respect to the bienergy, containing all minimal and
constant mean curvature hypersurfaces. The purpose of this paper is to study
biconservative hypersurfaces $M^n$ with constant scalar curvature in a space
form $N^{n+1}(c)$. We prove that every biconservative hypersurface with
constant scalar curvature in $N^4(c)$ has constant mean curvature. Moreover, we
prove that any biconservative hypersurface with constant scalar curvature in
$N^5(c)$ is ether an open part of a certain rotational hypersurface or a
constant mean curvature hypersurface. These solve an open problem proposed
recently by D. Fetcu and C. Oniciuc for $n\leq4$.
|
2110.03438v1
|
2008-03-15
|
Constant-Rank Codes and Their Connection to Constant-Dimension Codes
|
Constant-dimension codes have recently received attention due to their
significance to error control in noncoherent random linear network coding. What
the maximal cardinality of any constant-dimension code with finite dimension
and minimum distance is and how to construct the optimal constant-dimension
code (or codes) that achieves the maximal cardinality both remain open research
problems. In this paper, we introduce a new approach to solving these two
problems. We first establish a connection between constant-rank codes and
constant-dimension codes. Via this connection, we show that optimal
constant-dimension codes correspond to optimal constant-rank codes over
matrices with sufficiently many rows. As such, the two aforementioned problems
are equivalent to determining the maximum cardinality of constant-rank codes
and to constructing optimal constant-rank codes, respectively. To this end, we
then derive bounds on the maximum cardinality of a constant-rank code with a
given minimum rank distance, propose explicit constructions of optimal or
asymptotically optimal constant-rank codes, and establish asymptotic bounds on
the maximum rate of a constant-rank code.
|
0803.2262v7
|
1994-02-17
|
Power Spectrum Constraints from Spectral Distortions in the Cosmic Microwave Background
|
%The content of this replacement paper is identical to the original. %We have
attempted to fix the postscript so that it will print out on %a larger number
of printers. Using recent experimental limits on $\mu$ distortions from COBE
FIRAS, and the large lever-arm spanning the damping of sub-Jeans scale
fluctuations to the scale of the COBE DMR fluctuations, we set a constraint on
the slope of the primordial power spectrum $n$. It is possible to analytically
calculate the contribution over the full range of scales and redshifts,
correctly taking into account fluctuation growth and damping as well as
thermalization processes. We find that the 95\% upper limit is weakly dependent
on cosmological parameters, e.g. $n<1.54 (h=0.5)$ and $n<1.56 (h=1.0)$ for
$\Omega_0=1$ with marginally weaker constraints for $\Omega_0<1$ in a flat
$\Omega_0 +\Omega_\Lambda=1$ universe.
|
9402045v2
|
1995-06-01
|
The epoch of structure formation in blue mixed dark matter models
|
Recent data on the high--redshift abundance of damped Ly$\alpha$ systems are
compared with theoretical predictions for `blue' (i.e. $n>1$) Mixed Dark Matter
models. The results show that decreasing the hot component fraction
$\Omega_\nu$ and/or increasing the primordial spectral index $n$ implies an
earlier epoch of cosmic structure formation. However, we also show that varying
$\Omega_\nu$ and $n$ in these directions makes the models barely consistent
with the observed abundance of galaxy clusters. Therefore, requiring at the
same time observational constraints on damped Ly$\alpha$ systems and cluster
abundance to be satisfied represents a challenge for the Mixed Dark Matter
class of models.
|
9506003v2
|
1996-04-16
|
Cosmic Emissivity and Background Intensity from Damped Lyman-Alpha Galaxies
|
We present a new method to compute the cosmic emissivity $\E_\nu$ and
background intensity $J_\nu$. Our method is based entirely on data from quasar
absorption-line studies, namely, the comoving density of HI and the mean
metallicity and dust-to-gas ratio in damped Ly$\alpha$ galaxies. These
observations, when combined with models of cosmic chemical evolution, are
sufficient to determine the comoving rate of star formation as a function of
redshift. From this, we compute $\E_\nu $ and $J_\nu$ using stellar population
synthesis models. Our method includes a self-consistent treatment of the
absorption and reradiation of starlight by dust. In all of our calculations,
the near-UV emissivity declines rapidly between $z\approx1$ and $z=0$, in
agreement with estimates from the Canada-France Redshift Survey. The background
intensity is consistent with a wide variety of observational limits and with a
tentative detection at far-IR wavelengths.
|
9604091v1
|
1996-05-24
|
Identification of a Galaxy Responsible for a High-Redshift Damped Ly-alpha Absorption System
|
Galaxies believed to be responsible for damped Ly-alpha absorption (DLA)
systems in the spectra of high-redshift quasars represent a viable population
of progenitors of normal disk galaxies. They appear to contain a substantial
fraction of the baryons known to exist in normal galaxies today. Here we report
on the detection of an object, designated DLA 2233+131, responsible for a
previously known DLA system at z(abs)=3.150 in the spectrum of a quasar
2233+131 [z(QSO)=3.295]. This is the first unambiguous detection of a DLA
galaxy, in both emission line and stellar continuum. Its properties correspond
closely to what may be expected from a young disk galaxy in the early stages of
formation, with no sign of an active nucleus. This gives a strong support to
the idea that DLA systems represent a population of young galaxies at high
redshifts.
|
9605154v1
|
1996-10-18
|
The absorbers towards Q0836+113
|
We have performed RIJHK_S imaging of the field around the z=2.67 quasar
Q0836+113, which presents several metal line and a damped Ly\alpha absorption
systems in its spectrum. The images reveal the existence of a red K_S=18.9
object \approx 11 arcsec from the quasar. On the basis of the empirical
relationships between absorption radius and luminosity we conclude that this
object may be the CIV absorber at z=1.82. This could be the first detection of
a high redshift galaxy causing high-ionisation absorption. After carefully
subtracting the QSO, we do not detect, up to a 3\sigma limiting magnitude for
extended objects of K_S=20.8, the damped Ly\alpha absorber apparently detected
as a Ly\alpha emitter at z=2.47. It is also suggested, that object ``SW'' from
Wolfe et al. (1992) could be the galaxy responsible for the claimed MgII
absorption at z=0.37.
|
9610141v1
|
1996-12-13
|
The 67 Hz Feature in the Black Hole Candidate GRS 1915+105 as a Possible ``Diskoseismic'' Mode
|
The Rossi X-ray Timing Explorer (RXTE) has made feasible for the first time
the search for high-frequency (~ 100 Hz) periodic features in black hole
candidate (BHC) systems. Such a feature, with a 67 Hz frequency, recently has
been discovered in the BHC GRS 1915+105 (Morgan, Remillard, & Greiner). This
feature is weak (rms variability ~0.3%-1.6%), stable in frequency (to within ~2
Hz) despite appreciable luminosity fluctuations, and narrow (quality factor Q ~
20). Several of these properties are what one expects for a ``diskoseismic''
g-mode in an accretion disk about a 10.6 M_sun (nonrotating) - 36.3 M_sun
(maximally rotating) black hole (if we are observing the fundamental mode
frequency). We explore this possibility by considering the expected luminosity
modulation, as well as possible excitation and growth mechanisms---including
turbulent excitation, damping, and ``negative'' radiation damping. We conclude
that a diskoseismic interpretation of the observations is viable.
|
9612142v2
|
1997-01-15
|
Gravitational Lensing of Quasars by Spiral Galaxies
|
Gravitational lensing by a spiral galaxy occurs when the line-of-sight to a
background quasar passes within a few kpc from the center of the galactic disk.
Since galactic disks are rich in neutral hydrogen, the quasar spectrum will
likely be marked by a damped Lyman-alpha absorption trough at the lens
redshift. Therefore, the efficiency of searches for gravitational lensing with
sub-arcsecond splitting can be enhanced by 1-2 orders of magnitude by focusing
on a subset of all bright quasars which show low-redshift (z<1) strong
Lyman-alpha absorption (N>10^{21} cm^{-2}}). The double-image signature of
lensing could, in principle, be identified spectroscopically and without the
need for high-resolution imaging. The absorption spectrum of a spiral lens
would show a generic double-step profile due to the superposition of the two
absorption troughs of the different images. Finally, we note that searches for
microlensing signatures of quasars with damped Lyman-alpha absorption could
calibrate the fraction of MACHOs in galactic halos at high redshift.
|
9701100v1
|
1997-02-27
|
Interacting Hot Dark Matter
|
We discuss the viability of a light particle ($\sim 30$ eV neutrino) with
strong self-interactions as a dark matter candidate. The interaction prevents
the neutrinos from free-streaming during the radiation dominated regime so
galaxy sized density perturbations can survive. Smaller scale perturbations are
damped due to neutrino diffusion. We calculate the power spectrum in the
imperfect fluid approximation, and show that it is damped at the length scale
one would estimate due to neutrino diffusion. The strength of the
neutrino--neutrino coupling is only weakly constrained by observations, and
could be chosen by fitting the power spectrum to the observed amplitude of
matter density perturbations. The main shortcoming of our model is that
interacting neutrinos can not provide the dark matter in dwarf galaxies.
|
9702236v1
|
1997-05-20
|
Detection of the First Star Clusters With NGST
|
We calculate the observable signatures of the first generation of stars at
high redshift (5<z<100). To determine the cosmic star-formation history, we use
an extension of the Press-Schechter formalism for Cold Dark Matter (CDM)
cosmologies that incorporates gas pressure. We calibrate the fraction of gas
converted into stars to be 6% so as to reproduce the 1% solar C/H ratio
observed in the intergalactic medium (IGM) at z=3. With this star-formation
efficiency, we find that NGST would be able to image more than 10^4 star
clusters from high redshifts (z>10) within its 4'x4' field of view. If stars
occupy a region comparable to the virial radius of the cluster, then 1% of
these clusters could be resolved. We calculate the expected number-flux
relation and angular size distribution for these early star clusters. We also
describe the reionization of the IGM due to the first generation of stars, and
the consequent damping of the CMB anisotropies on small angular scales. This
damping could be detected below 10 degree angular scales by MAP and PLANCK.
|
9705144v1
|
1997-09-04
|
Cosmic-Ray Momentum Diffusion In Magnetosonic Versus Alfvenic Turbulent Field
|
Energetic particle transport in a finite amplitude magnetosonic and Alfvenic
turbulence is considered using Monte Carlo particle simulations, which involve
an integration of particle equation of motion. We show that in a low-Betha
plasma cosmic ray can be the most important damping process for magnetosonic
waves. Assuming such conditions we derive the momentum diffusion coefficient
for relativistic particles in the presence of anisotropic finite-amplitude
turbulent wave field, for flat and Kolmogorov-type turbulence spectra. We
confirm the possibility of larger values of a momentum diffusion coefficient
occuring due to transit-time damping resonance interaction in the presence of
isotropic fast-mode waves in comparison to the Alfven waves of the same
amplitude.
|
9709039v2
|
1997-09-12
|
Baryonic Features in the Matter Transfer Function
|
We provide scaling relations and fitting formulae for adiabatic cold dark
matter cosmologies that account for all baryon effects in the matter transfer
function to better than 10% in the large-scale structure regime. They are based
upon a physically well-motivated separation of the effects of acoustic
oscillations, Compton drag, velocity overshoot, baryon infall, adiabatic
damping, Silk damping, and cold-dark-matter growth suppression. We also find a
simpler, more accurate, and better motivated form for the zero baryon transfer
function than previous works. These descriptions are employed to quantify the
amplitude and location of baryonic features in linear theory. While baryonic
oscillations are prominent if the baryon fraction exceeds $\Omega_0 h^2 + 0.2$,
the main effect in more conventional cosmologies is a sharp suppression in the
transfer function below the sound horizon. We provide a simple but accurate
description of this effect and stress that it is not well approximated by a
change in the shape parameter $\Gamma$.
|
9709112v1
|
1997-09-23
|
Nonlinear spherical Alfven waves
|
We present an one-dimensional numerical study of Alfven waves propagating
along a radial magnetic field. Neglecting losses, any spherical Alfven wave, no
matter how small its initial amplitude is, becomes nonlinear at sufficiently
large radii. From previous simulations of Alfven waves in plane parallel
atmospheres we did expect the waves to steepen and produce current sheets in
the nonlinear regime, which was confirmed by our new calculations. On the other
hand we did find that even the least nonlinear waves were damped out almost
completely before 10 solar radii. A damping of that kind is required by models
of Alfven wave-driven winds from old low-mass stars as these winds are mainly
accelerated within a few stellar radii.
|
9709222v1
|
1997-12-10
|
Effects of Disks on Gravitational Lensing by Spiral Galaxies
|
Gravitational lensing of a quasar by a spiral galaxy should often be
accompanied by damped Lyman-alpha absorption and dust extinction due to the
intervening gaseous disk. In nearly edge-on configurations, the surface mass
density of the gas and stars in the disk could by itself split the quasar image
and contribute significantly to the overall lensing cross section. We calculate
the lensing probability of a disk+halo mass model for spiral galaxies,
including cosmic evolution of the lens parameters. A considerable fraction of
the lens systems contains two images with sub-arcsecond separation, straddling
a nearly edge-on disk. Because of that, extinction by dust together with
observational selection effects (involving a minimum separation and a maximum
flux ratio for the lensed images), suppress the detection efficiency of spiral
lenses in optical wavebands by at least an order of magnitude. The missing
lenses could be recovered in radio surveys. In modifying the statistics of
damped Lyman-alpha absorbers, the effect of extinction dominates over the
magnification bias due to lensing.
|
9712138v1
|
1998-03-20
|
HI 21cm absoprtion in two low redshift damped Ly-alpha systems
|
We report the discovery of two low redshift HI 21cm absorbers, one at z =
0.2212 towards the z_{em} = 0.630 quasar OI 363 (B0738+313), and the other at z
= 0.3127 towards PKS B1127-145 (z_{em} = 1.187). Both were found during a
survey of MgII selected systems at redshifts 0.2 < z < 1 using the new UHF-high
system at the Westerbork Synthesis Radio Telescope (WSRT). New HST/FOS
observations also identify both systems as damped Ly-alpha (DLa) absorbers. By
comparing the column density from the DLa line with that from the HI 21cm line,
we calculate the spin temperature, and find that T_s is approximately 1000 K
for both of these low redshift absorbers. We briefly discuss some implications
of this result.
|
9803243v1
|
1998-05-08
|
Infrared emission-line galaxies associated with damped Lyman-alpha and strong metal absorber redshifts
|
Eighteen candidates for emission line galaxies were discovered in a
narrow-band infrared survey that targeted the redshifts of damped Lyman-alpha
or metal lines in the spectra of quasars. The presence of emission lines is
inferred from the photometric magnitudes in narrow and broad band interference
filters, corresponding to H-alpha at redshifts of 0.89 (6 objects) and 2.4 (10
objects), and [OII] at a redshift of 2.3 (2 objects). Most of the candidates
are small resolved objects, compatible with galaxies at the redshifts of the
absorbers. Because a similar survey targeted at the redshifts of quasars
themselves uncovered only one emission-line galaxy in a larger volume, the
results imply substantial clustering of young galaxies or formation within
filaments or sheets whose locations are indicated by the redshifts of strong
absorption along the lines of sight to more distant quasars.
|
9805103v1
|
1998-05-12
|
Resonant Thickening of Disks by Small Satellite Galaxies
|
We study the vertical heating and thickening of galaxy disks due to accretion
of small satellites. Our simulations are restricted to axial symmetry, which
largely eliminates numerical evolution of the target galaxy but requires the
trajectory of the satellite to be along the symmetry axis of the target. We
find that direct heating of disk stars by the satellite is not important
because the satellite's gravitational perturbation has little power at
frequencies resonant with the vertical stellar orbits. The satellite does
little damage to the disk until its decaying orbit resonantly excites
large-scale disk bending waves. Bending waves can damp through dynamical
friction from the halo or internal wave-particle resonances; we find that
wave-particle resonances dominate the damping. The principal vertical heating
mechanism is therefore dissipation of bending waves at resonances with stellar
orbits in the disk. Energy can thus be deposited some distance from the point
of impact of the satellite. The net heating from a tightly bound satellite can
be substantial, but satellites that are tidally disrupted before they are able
to excite bending waves do not thicken the disk.
|
9805145v1
|
1998-09-14
|
Collisionless Relaxation of Stellar Systems
|
The objective of the work summarised here has been to exploit and extend
ideas from plasma physics and accelerator dynamics to formulate a unified
description of collisionless relaxation that views violent relaxation, Landau
damping, and phase mixing as (manifestations of) a single phenomenon. This
approach embraces the fact that the collisionless Boltzmann equation (CBE), the
basic object of the theory, is an infinite-dimensional Hamiltonian system, with
the distribution function f playing the role of the fundamental dynamical
variable, and that, interpreted appropriately, an evolution described by the
{\it CBE} is no different fundamentally from an evolution described by any
other Hamiltonian system. Equilibrium solutions correspond to extremal points
of the Hamiltonian subject to the constraints associated with Liouville's
Theorem. Stable equilibria correspond to energy minima. The evolution of a
system out of equilibrium involves (in general nonlinear) phase space
oscillations which may -- or may not -- interfere destructively so as to damp
away.
|
9809178v1
|
1998-09-30
|
Discovery of a z=0.808 damped Lyman-alpha system candidate in a UV selected quasar spectrum
|
We present the observation of a new intermediate redshift damped Lyman-alpha
absorption system candidate, discovered in the course of a spectroscopic
follow-up for identifying the sources detected in a 150 A wide bandpass
UV-imaging survey at 2000 A. The system displays very strong MgII and FeII
lines and a high FeII/MgII ratio, which, following photoionization models,
indicates a very high neutral hydrogen column density. Such kind of systems
being very rare at redshifts <1.7, but of prime importance for understanding
the evolution of star formation in galaxies, the newly discovered candidate
deserves further investigations in a near future
|
9809402v1
|
1998-10-02
|
Gravity-modes in ZZ Ceti Stars. II. Effects of Turbulent Dissipation
|
We investigate dynamical interactions between turbulent convection and g-mode
pulsations in ZZ Ceti variables (DAVs). Since our understanding of turbulence
is rudimentary, we are compelled to settle for order of magnitude results. A
key feature of these interactions is that convective response times are much
shorter than pulsation periods. Thus the dynamical interactions enforce near
uniform horizontal velocity inside the convection zone. They also give rise to
a narrow shear layer in the region of convective overshoot at the top of the
radiative interior. Turbulent damping inside the convection zone is negligible
for all modes, but that in the region of convective overshoot may be
significant for a few long period modes near the red edge of the instability
strip. These conclusions are in accord with those reached earlier by Brickhill.
Our major new result concerns nonlinear damping arising from the
Kelvin-Helmholtz instability of the aforementioned shear layer. Amplitudes of
overstable modes saturate where dissipation due to this instability balances
excitation by convective driving. This mechanism of amplitude saturation is
most effective for long period modes, and it may play an important role in
defining the red edge of the instability strip.
|
9810038v1
|
1999-02-11
|
Element Abundances at High Redshifts
|
I review measurements of element abundances in different components of the
high redshift universe, including the Lyman alpha forest, damped Lyman alpha
systems, and Lyman break galaxies. Although progress is being made in all three
areas, recent work has also produced some surprises and shown that established
ideas about the nature of the damped Lyman alpha systems in particular may be
too simplistic. Overall, our knowledge of metal abundances at high z is still
very sketchy. Most significantly, there seems to be an order of magnitude
shortfall in the comoving density of metals which have been measured up to now
compared with those produced by the star formation activity seen in Lyman break
galaxies. At least some of the missing metals are likely to be in hot gas in
galactic halos and proto-clusters.
|
9902173v1
|
1999-03-09
|
Numerical simulation of prominence oscillations
|
We present numerical simulations, obtained with the Versatile Advection Code,
of the oscillations of an inverse polarity prominence. The internal prominence
equilibrium, the surrounding corona and the inert photosphere are well
represented. Gravity and thermodynamics are not taken into account, but it is
argued that these are not crucial. The oscillations can be understood in terms
of a solid body moving through a plasma. The mass of this solid body is
determined by the magnetic field topology, not by the prominence mass proper.
The model also allows us to study the effect of the ambient coronal plasma on
the motion of the prominence body. Horizontal oscillations are damped through
the emission of slow waves while vertical oscillations are damped through the
emission of fast waves.
|
9903128v1
|
1999-03-26
|
Nature and evolution of Damped Lyman alpha systems
|
The main properties of Damped Lyman alpha (DLA) systems are briefly reviewed
with the aim of studying the nature and evolution of the galaxies associated
with this class of QSO absorbers. Candidate DLA galaxies identified at z </= 1
in the fields of background QSOs show a variety of morphological types without
a predominance of spirals. Most properties inferred from spectroscopic studies
at z >/= 1.65 differ from those expected for spiral galaxies. The observational
results instead suggest that a significant fraction of DLA systems originate in
low-mass and/or LSB galaxies. Evolution effects are generally not detected in
DLA systems. This fact suggests that the differences between the properties of
present-day spirals and those of high-z DLA systems may not be ascribed to
evolution. Several selection effects can bias the observed population of DLA
absorbers. Analysis of these effects indicates that the fraction of spiral
galaxies tends to be underestimated relative to the fraction of low-mass or LSB
galaxies.
|
9903406v1
|
1999-11-09
|
Viscous Boundary Layer Damping of R-Modes in Neutron Stars
|
Recent work has raised the exciting possibility that r-modes (Rossby waves)
in rotating neutron star cores might be strong gravitational wave sources. We
estimate the effect of a solid crust on their viscous damping rate and show
that the dissipation rate in the viscous boundary layer between the oscillating
fluid and the nearly static crust is >10^5 times higher than that from the
shear throughout the interior. This increases the minimum frequency for the
onset of the gravitational r-mode instability to at least 500 Hz when the core
temperature is less than 10^10 K. It eliminates the conflict of the r-mode
instability with the accretion-driven spin-up scenario for millisecond radio
pulsars and makes it unlikely that the r-mode instability is active in
accreting neutron stars. For newborn neutron stars, the formation of a solid
crust shortly after birth affects their gravitational wave spin-down and hence
detectability by ground-based interferometric gravitational wave detectors.
|
9911155v1
|
1999-11-30
|
The formation and evolution of supermassive black holes and their host galaxies
|
We discuss constraints on the assembly history of supermassive black holes
from the observed remnant black holes in nearby galaxies and from the emission
caused by accretion onto these black holes. We also summarize the results of a
specific model for the evolution of galaxies and their central black holes
which traces their hierachical build-up in CDM-like cosmogonies. The model
assumes (i) that black holes, ellipticals and starburts form during major
mergers of galaxies (ii) that the gas fraction in galaxies decreases with
decreasing redshift (iii) that the optical bright phase of a QSO lasts for
about 10^7 years. The model succesfully reproduces the evolution of cold gas as
traced by damped damped Lyman alpha systems, the evolution of optically bright
QSOs, the remnant black hole mass distribution and the host galaxy luminosities
of QSOs.
|
9911514v1
|
1999-12-06
|
The Metallicity evolution of Damped Lyman-alpha systems
|
We have collected data for 69 Damped Lyman-alpha (DLA) systems, to
investigate the chemical evolution of galaxies in the redshift interval 0.0 < z
< 4.4. In doing that, we have adopted the most general approach used so far to
correct for dust depletion. The best solution, obtained through chi^2
minimization, gives as output parameters the global DLA metallicity and the
dust-to-metals ratio. Clear evolution of the metallicity vs. redshift is found
(99.99% significance level), with average values going from ~1/30 solar at
z~4.1 to ~3/5 solar at z~0.5. We also find that the majority of DLAs (~60%)
shows dust depletion patterns which most closely resemble that of the warm halo
clouds in the Milky Way, and have dust-to-metals ratios very close to warm halo
clouds.
|
9912112v2
|
1999-12-22
|
Alfvenic Heating of Protostellar Accretion Disks
|
We investigate the effects of heating generated by damping of Alfven waves on
protostellar accretion disks. Two mechanisms of damping are investigated,
nonlinear and turbulent, which were previously studied in stellar winds
(Jatenco-Pereira & Opher 1989a, b). For the nominal values studied, f=delta
v/v_{A}=0.002 and F=varpi/Omega_{i}=0.1, where delta v, v_{A} and varpi are the
amplitude, velocity and average frequency of the Alfven wave, respectively, and
Omega_{i} is the ion cyclotron frequency, we find that viscous heating is more
important than Alfven heating for small radii. When the radius is greater than
0.5 AU, Alfvenic heating is more important than viscous heating. Thus, even for
the relatively small value of f=0.002, Alfvenic heating can be an important
source of energy for ionizing protostellar disks, enabling angular momentum
transport to occur by the Balbus-Hawley instability.
|
9912478v1
|
2000-01-18
|
Metallicity in damped Lyman-alpha systems: evolution or bias?
|
Assuming that damped Lyman-alpha(DLA) systems are galactic discs, we
calculate the corresponding evolution of metal abundances. We use detailed
multi-zone models of galactic chemical evolution (reproducing successfully the
observed properties of disc galaxies) and appropriate statistics (including
geometrical propability factors) to calculate the average metallicity as a
function of redshift. The results are compatible with available observations,
provided that observational biases are taken into account, as suggested by
Boisse et al. (1998). In particular, high column density and high metallicity
systems are not detected because the light of backround quasars is severely
extinguished, while low column density and low metallicity systems are not
detectable through their absorption lines by current surveys. We show that
these observational constraints lead to a ``no-evolution'' picture for the DLA
metallicity, which does not allow to draw strong conclusions about the nature
of those systems or about their role in ``cosmic chemical evolution''.
|
0001313v1
|
2000-02-24
|
Optical Counterparts to Damped Lyman Alpha Systems
|
Previously we have shown (Maller et al, 1998) that the kinematics of Damped
Lyman Alpha Systems (DLAS) as measured by Prochaska and Wolfe (1998) can be
reproduced in a multiple disk model (MDM) if the gaseous disks are of
sufficient radial extent. Here we discuss this model's predictions for the
relationship between DLAS and Lyman break galaxies (LBGs), which we here take
to be objects at z~3 brighter than R=25.5. We expect that future observations
of the correlations between DLAS and LBGs will provide a new data set able to
discriminate between different theoretical models of the DLAS. Djorgovski
(1997) has already detected a few optical counterparts and more studies are
underway.
|
0002452v1
|
2000-02-24
|
Damped Ly-alpha Systems in Semi-Analytic Models: Sensitivity to dynamics, disk properties, and cosmology
|
Previously we have shown that it is possible to account for the kinematic
properties of damped Lyman alpha systems (DLAS) in the context of semi-analytic
models. In these models, hierarchical structure formation is approximated by
constructing a merger tree for each dark matter halo. A natural consequence is
that every virialized halo may contain not only a central galaxy, but also a
number of satellite galaxies as determined by its merging history. Thus the
kinematics of the DLAS arise from the combined effects of the internal rotation
of gas disks and the motions between gas disks within a common halo. Here we
investigate the sensitivity of this model to some of the assumptions made
previously, including the modeling of satellite dynamics, the scale height of
the gas, and the cosmology.
|
0002454v1
|
2000-07-31
|
UVES observations of QSO 0000-2620: Molecular hydrogen abundance in the damped Ly-alpha system at z_abs = 3.3901
|
We have discovered molecular hydrogen in a fourth quasar damped Ly-alpha
system (hereafter DLA). The UVES spectrograph on the 8.2m ESO Kueyen telescope
has allowed the detection of H2 in gas with low metallicity, Z/Z_solar ~=
10^{-2}, and high neutral hydrogen column density, N(HI) ~= 2.6*10^{21}
cm^{-2}, at redshift z_abs = 3.3901 toward QSO 0000-2620. The measured H2
fractional abundance of f(H2) ~= 4*10^{-8} is lower than a typical value for
Galactic interstellar clouds of high N(HI) column density by a factor of
(2-3)*10^6. Since H2 molecules are formed efficiently on dust grains, it
implies that the dust condensation in this DLA is negligible, and hence the
abundances derived from metal absorption lines are the actual ones. The
obtained f(H2) value leads to an estimate of the dust number density of < n_d
>_DLA ~= 10^{-3}*< n_d >_ISM, which is consistent with the dust-to-gas ratio k
<= 1.6 10^{-3} derived independently from the [Cr/Zn] and [Fe/Zn] ratios.
|
0007472v1
|
2000-08-11
|
The Evolution and Space Density of Damped Lyman-alpha Galaxies
|
The results of a new spectroscopic survey of 66 $z \simgt 4$ quasars for
Damped Lyman-alpha absorption systems are presented. The search led to the
discovery of 30 new DLA candidates which are analysed in order to compute the
comoving mass density of neutral gas in a non-zero lambda Universe. The
possible sources of uncertainty are discussed and the implications of our
results for the theories of galaxy formation and evolution are emphasized. A
subsequent paper will present details of the calculations summarised here and a
more extensive explanation of the consequences of our observations for the
understanding of the nature of DLAs.
|
0008172v1
|
2000-09-06
|
Damped Lyman-Alpha Galaxies
|
Some results from an imaging program to identify low-redshift (0.09<z<1.63)
damped Lyman-alpha (DLA) galaxies are presented. The standard paradigm that was
widely accepted a decade ago, that DLA galaxies are the progenitors of luminous
disk galaxies, is now being seriously challenged. The indisputable conclusion
from imaging studies at low redshift is that the morphological types of DLA
galaxies are mixed and that they span a range in luminosities and surface
brightnesses.
|
0009096v2
|
2000-09-07
|
On ionisation effects and abundance ratios in damped Lyman-alpha systems
|
The similarity between observed velocity structures of Al III and singly
ionised species in damped Lyman-alpha systems (DLAs) suggests the presence of
ionised gas in the regions where most metal absorption lines are formed.
To explore the possible implications of ionisation effects we construct a
simplified two-region model for DLAs consisting of an ionisation bounded region
with an internal radiation field and a neutral region with a lower metal
content. Within this framework we find that ionisation effects are important.
If taken into account, the element abundance ratios in DLAs are quite
consistent with those observed in Milky Way stars and in metal-poor H II
regions in blue compact dwarf galaxies. In particular we cannot exclude the
same primary N origin in both DLAs and metal-poor galaxies. From our models no
dust depletion of heavy elements needs to be invoked; little depletion is
however not excluded.
|
0009107v1
|
2000-10-20
|
An Imaging and Spectroscopic Study of the z=3.38639 Damped Lyman Alpha System in Q0201+1120: Clues to Star Formation Rate at High Redshift
|
We present the results of a series of imaging and spectroscopic observations
aimed at identifying and studying the galaxy responsible for the z = 3.38639
damped lya system in the z = 3.61 QSO Q0201+1120. We find that the DLA is part
of a concentration of matter which includes at least four galaxies (probably
many more) over linear comoving dimensions, greater than 5h^-1Mpc. The absorber
may be a 0.7 L* galaxy at an impact parameter of 15 h^-1 kpc, but follow-up
spectroscopy is still required for positive identification. The gas is
turbulent, with many absorption components distributed over approximately 270
km/s and a large spin temperature, T_s greater than 4000K. The metallicity is
relatively high for this redshift, Z(DLA) approximately 1/20 Z(solar). From
consideration of the relative ratios of elements which have different
nucleosynthetic timescales, it would appear that the last major episode of star
formation in this DLA occurred at z greater than 4.3, more than approximately
500 Myr prior to the time when we observe it.
|
0010427v1
|
2000-10-31
|
Non-Linear Evolution of the r-Modes in Neutron Stars
|
The evolution of a neutron-star r-mode driven unstable by gravitational
radiation (GR) is studied here using numerical solutions of the full non-linear
fluid equations. The amplitude of the mode grows to order unity before strong
shocks develop which quickly damp the mode. In this simulation the star loses
about 40% of its initial angular momentum and 50% of its rotational kinetic
energy before the mode is damped. The non-linear evolution causes the fluid to
develop strong differential rotation which is concentrated near the surface and
especially near the poles of the star.
|
0010653v2
|
2000-11-07
|
Damped Lyman-alpha absorption from a nearby Low Surface Brightness galaxy
|
Ground-based & HST images of the nearby galaxy SBS 1543+593 (z=0.009) show it
to be a Low Surface Brightness (LSB) galaxy with a central surface brightness
of mu_B(0)=23.2 mag/arcsec-2 and scale length 0.9 h-1 kpc, values typical for
the local LSB galaxy population. The galaxy lies directly in front of the QSO
HS 1543+5921 (z=0.807); an HST STIS spectrum of the quasar reveals a damped
Lyman-alpha (DLA) line at the redshift of the interloper with an HI column
density of log N(HI) = 20.35, as well as several low-ionization metal lines
with strengths similar to those found in the Milky Way interstellar medium. Our
data show that LSB galaxies are certainly able to produce the DLA lines seen at
higher redshift, and fuels the speculation that LSB galaxies are a major
contributor to that population of absorbers.
|
0011134v1
|
2000-11-25
|
Molecular hydrogen abundance in the dust-free damped Ly-alpha galaxy at z = 3.4
|
New results from the search for H2 absorption in the damped Ly-alpha galaxy
at redshift z = 3.4 toward QSO 0000-2620 (z_em = 4.1) are reported. The
high-resolution (lambda/Delta lambda = 48,000) spectra of Q0000-2620 were
obtained using the Ultraviolet - Visual Echelle Spectrograph (UVES) on the 8.2m
ESO Kueyen telescope. The ortho-H2 column density is found to be N(J=1) = (5.55
+/- 1.35) 10^{13} cm^{-2} (2sigma C.L.). The combination of N(J=1) with the
limits available for other low rotational levels restricts the excitation
temperature T_ex in the range (290-540) K. This gives the total H2 column
density of N(H2) = (8.75 +/- 1.25) 10^{13} cm^{-2} and the corresponding
fraction of hydrogen atoms bound in molecules of f(H2) = (6.8 +/- 2.0) 10^{-8}.
|
0011470v1
|
2000-11-25
|
The Metallicity Evolution of Damped Lyman-alpha Systems
|
According to Pei, Fall & Hauser (1999), the global metallicity evolution of
the Universe can be represented by the ratio of the total metal content to the
total gas content measured in Damped Lyman-alpha (DLA) systems (the ``column
density weighted metallicity'' `a la Pettini). To minimize dust obscuration
effects, a DLA sample with negligible dust content is considered, namely, 50
DLAs with log N(HI) < 20.8. The global metallicity found shows clear evidence
of redshift evolution that goes from \sim1/30 solar at z\sim4.1 to solar at z
\sim 0.4. More generally, DLAs with measured heavy elements probe the ISM of
high redshift galaxies. The whole sample collected from the literature contains
75 DLAs. The metallicity is calculated adopting for the dust correction the
most general method used so far, based on models of the ISM dust depletions in
the Galaxy. The intrinsic metallicity evolution of DLA galaxies is dlog
Z(DLA)/dz \propto -0.33 +/- 0.06.
|
0011473v1
|
2000-12-04
|
ATCA search for 21 cm emission from a candidate damped Ly-$α$ absorber at z = 0.101
|
We report a deep search for 21 cm emission/absorption from the $z \sim 0.101$
candidate damped Lyman-$\alpha$ system towards PKS 0439-433, using the
Australia Telescope Compact Array (ATCA). The spectrum shows a weak absorption
feature --- at the $3.3 \sigma$ level --- which yields a lower limit of 730 K
on the spin temperature of the system. No HI emission was detected: the
$3\sigma$ upper limit on the HI mass of the absorber is $2.25 \times 10^9
M_{\odot}$, for a velocity spread of $\sim 70$ km s$^{-1}$. The low HI mass and
the high spin temperature seem to rule out the possibility that the absorber is
a large gas-rich spiral galaxy.
|
0012079v1
|
2000-12-05
|
Lost and Found: The Damped Lyman Alpha Absorbers in the QSO OI 363
|
The galaxy giving rise to the damped Ly$\alpha$ absorbing system in the QSO
OI 363 with z=0.221 has been found. A galaxy which is probably associated with
the second DLA in this same QSO at z=0.0912 has also been found. Neither galaxy
is very luminous, and neither galaxy shows signs of extensive current star
formation, a massive disk or lots of gas. The impact parameters for each of the
two galaxies with respect to the QSO are reasonable. If most DLA absorbers
arise in such low luminosity galaxies, it will be difficult to pick out the
correct galaxy giving rise to DLA systems at high redshift within the large
projected areal density on the sky of faint galaxies around distant QSOs.
|
0012109v1
|
2001-01-05
|
Constraints from the damping tail
|
The detection of anisotropy in the cosmic microwave background on arcminute
scales by the Cosmic Background Imager (CBI) provides us with our first
measurement of the damping tail and closes one chapter in the CMB story. We now
have experimental verification for all of the features in the temperature
anisotropy spectrum predicted theoretically two decades ago. The CBI result
allows us to constrain both parameterized models based on the inflationary cold
dark matter (CDM) paradigm and to examine model independent constraints on the
matter content, the distance to last scattering and the thickness of the last
scattering surface. By providing a lower limit on the duration of recombination
it implies a lower limit on the polarization of the sub-degree scale anisotropy
which is close to current experimental upper limits.
|
0101086v2
|
2001-01-10
|
Magnetized gravitational waves
|
We investigate the influence of cosmic magnetic fields on gravitational wave
perturbations, and find exact solutions on large scales. We show that a
large-scale magnetic field can generate large-scale non-decaying gravitational
waves. In the general case where gravitational waves are generated by other
mechanisms, a large-scale magnetic field introduces a new decaying tensor mode
and modifies the non-decaying mode. The direct effect of the magnetic field is
to damp the gravitational waves, while an indirect magneto-curvature effect can
either damp or boost the waves. A magnetic field also leads to a breaking of
statistical isotropy, and the magnetic imprint on the tensor spectrum in
principle provides a means of detecting a primordial field.
|
0101151v3
|
2001-01-15
|
Damping time and stability of density fermion perturbations in the expanding universe
|
The classic problem of the growth of density perturbations in an expanding
Newtonian universe is revisited following the work of Bisnovatyi-Kogan and
Zel'dovich. We propose a more general analytical approach: a system of free
particles satisfying semi-degenerate Fermi-Dirac statistics on the background
of an exact expanding solution is examined in the linear approximation. This
differs from the corresponding work of Bisnovatyi-Kogan and Zel'dovich where
classical particles fulfilling Maxwell-Boltzmann statistics were considered.
The solutions of the Boltzmann equation are obtained by the method of
characteristics. An expression for the damping time of a decaying solution is
discussed and a zone in which free streaming is hampered is found,
corresponding to wavelengths less than the Jeans one. In the evolution of the
system, due to the decrease of the Jeans length, those perturbations may lead
to gravitational collapse. At variance with current opinions, we deduce that
perturbations with lambda >=lambda_(J Max)/1.48 are able to generate structures
and the lower limit for substructures mass is M = M_(J max)/(1.48)^3 ~ M_(J
max)/3, where M_(J max) is the maximum value of the Jeans mass.
|
0101222v1
|
2001-02-09
|
A new deuterium abundance measurement from a damped Ly-alpha system at z_abs = 3.025
|
We present the first D/H measurement in a damped Ly-alpha system at z_abs =
3.025 towards QSO 0347-3819 obtained from the UVES-VLT spectra. The DLA
absorber has a metallicity of [Zn/H] = -1.25 and a relatively simple velocity
structure, with two dominating components detected in several metal lines. The
hydrogen Lyman series can be followed down to Ly12 thanks to the high UV-Blue
efficiency of UVES. The best fit of the Lyman series lines, and in particular
of Ly5, Ly8, Ly10 and Ly12, relatively free of local contamination, is obtained
when the DI absorption is included in the two main components. The measured
deuterium column density yields D/H = (2.24+/-0.67) 10^{-5} close to other low
D/H values from Lyman limit systems. The corresponding values for the baryon to
photon ratio and the baryon density derived from D/H are eta = 6 10^{-10} and
Omega_b h^2 = 0.023 respectively.
|
0102162v1
|
2001-03-19
|
Fluctuations in the Cosmic Microwave Background I: Form Factors and their Calculation in Synchronous Gauge
|
It is shown that the fluctuation in the temperature of the cosmic microwave
background in any direction may be evaluated as an integral involving scalar
and dipole form factors, which incorporate all relevant information about
acoustic oscillations before the time of last scattering. A companion paper
gives asymptotic expressions for the multipole coefficient $C_\ell$ in terms of
these form factors. Explicit expressions are given here for the form factors in
a simplified hydrodynamic model for the evolution of perturbations.
|
0103279v2
|
2001-04-24
|
21-cm H I emission from the Damped Lyman-alpha absorber SBS 1543+593
|
We detect 21-cm emission from the Low Surface Brightness (LSB) galaxy SBS
1543+593, which gives rise to a Damped Lyman-alpha (DLA) absorption line in the
spectrum of the background QSO HS 1543+5921 (z=0.807). We obtain an accurate
measure of the velocity of the H I gas in the LSB galaxy, v=2868 km/s, and
derive a mass of 1.3e9 solar masses. We compare this value with limits obtained
towards two other z~0.1 DLA systems, and show that SBS 1543+593 would not have
been detected. Hence LSB galaxies similar to SBS 1543+593 can be responsible
for DLA systems at even modest redshifts without being detectable from their
21-cm emission.
|
0104396v1
|
2001-05-23
|
Mapping the Dark Matter through the CMB Damping Tail
|
The lensing of CMB photons by intervening large-scale structure leaves a
characteristic imprint on its arcminute-scale anisotropy that can be used to
map the dark matter distribution in projection on degree scales or ~100 Mpc/h
comoving. We introduce a new algorithm for mass reconstruction which optimally
utilizes information from the weak lensing of CMB anisotropies in the damping
tail. It can ultimately map individual degree scale mass structures with high
signal-to-noise. To achieve this limit an experiment must produce a high
signal-to-noise, foreground-free CMB map of arcminute scale resolution,
specifically with a FWHM beam of < 5' and a noise level of < 15 (10^-6-arcmin)
or 41 (uK-arcmin).
|
0105424v2
|
2001-06-30
|
Chandra Detection of X-ray Absorption Associated with a Damped Lyman Alpha System
|
We have observed three quasars, PKS 1127-145, Q 1331+171 and Q0054+144, with
the ACIS-S aboard the Chandra X-ray Observatory, in order to measure soft X-ray
absorption associated with intervening 21-cm and damped Ly$\alpha$ absorbers.
For PKS 1127-145, we detect absorption which, if associated with an intervening
z_{abs}=0.312 absorber, implies a metallicity of 23% solar. If the absorption
is not at z_{abs}=0.312, then the metallicity is still constrained to be less
than 23% solar. The advantage of the X-ray measurement is that the derived
metallicity is insensitive to ionization, inclusion of an atom in a molecule,
or depletion onto grains. The X-ray absorption is mostly due to oxygen, and is
consistent with the oxygen abundance of 30% solar derived from optical nebular
emission lines in a foreground galaxy at the redshift of the absorber.
For Q1331+171 and Q 0054+144, only upper limits were obtained, although the
exposure times were intentionally short, since for these two objects we were
interested primarily in measuring flux levels to plan for future observations.
The imaging results are presented in a companion paper.
|
0107003v1
|
2001-08-08
|
The Evolution of Neutral Gas in the Universe as Traced by Damped Lyman Alpha Systems
|
We discuss our recent results on the statistical properties of damped Lyman
alpha systems (DLAs) at low redshift (z<1.65) (Rao & Turnshek 2000). Contrary
to expectations, we found that the cosmological neutral gas mass density as
traced by DLAs, $\Omega_{DLA}$, does not evolve from redshifts $z \approx 4$ to
$z \approx 0.5$ and that extrapolation to z=0 results in a value that is a
factor of ~6.5 times higher than what is derived from galaxies at the current
epoch using HI 21 cm emission measurements. We review the current status of HI
measurements at low redshift and at the current epoch, and discuss possible
causes of this discrepancy.
|
0108141v1
|
2001-08-08
|
Properties of Low-Redshift Damped Lyman Alpha Galaxies
|
Images of five QSO fields containing six damped Lyman alpha (DLA) systems at
redshifts 0.09<z<0.53 are presented. Identifications for the DLA galaxies
giving rise to the DLA systems are made. The observed and modeled
characteristics of the DLA galaxies are discussed. The DLA galaxies have impact
parameters ranging from < 4 kpc to \approx 34 kpc and luminosities in the range
\approx 0.03L* to \approx 1.3L*. Their morphologies include amorphous low
surface brightness systems, a probable dwarf spiral, and luminous spirals.
|
0108146v1
|
2001-08-29
|
The impact of dust and ionization effects on abundance measurements of Damped Ly alpha systems
|
Studies of elemental abundances are a fundamental tool for unveiling the
nature of the high-redshift (proto-)galaxies associated to Damped Ly alpha
systems (DLAs). The present contribution analyses the impact of dust and
ionization effects on abundance measurements in DLAs. The behaviour of the
alpha/Fe abundance ratio corrected for such effects is used to derive
information on the chemical history and nature of DLA galaxies. The alpha/Fe
data indicate that DLAs at z~2.5 do not represent a homogeneous class of
objects. On average, DLAs show non-enhanced alpha/Fe ratios at low metallicity,
suggesting an origin in galaxies with low or intermittent star formation rates.
|
0108466v2
|
2001-08-30
|
Reconciling Damped Ly-alpha Statistics and 21cm Studies at z=0
|
Blind 21cm surveys in the local universe have shown that the local HI mass
density, Omega_HI, is dominated by luminous, high surface brightness, spiral
galaxies. On the other hand, surveys for host galaxies of damped Ly-alpha
systems have not always been successful in finding bright spiral galaxies. From
an analysis of 21cm aperture synthesis maps of nearby galaxies we show that
this apparent contradiction can be resolved by realizing that the HI mass
density is dominated by L* galaxies, but the HI cross section near the DLA
threshold is more evenly distributed over galaxies with a large range in
luminosity, gas mass, and surface brightness. The distributions of column
densities and impact parameters of optically identified and non-identified DLA
host galaxies in the literature and the HI maps are qualitatively in agreement.
Due to poor number statistics of low redshift DLA systems, there is no firm
indication that the redshift number count of low redshift DLA systems is
inconsistent with that calculated from the nearby galaxy population.
|
0108498v1
|
2001-09-03
|
GRB 000301C: a possible short/intermediate duration burst connected to a DLA system
|
We discuss two main aspects of the GRB 000301C afterglow (Fynbo et al. 2000,
Jensen et al. 2000); its short duration and its possible connection with a
Damped Ly-alpha Absorber (DLA). GRB 000301C falls in the short class of bursts,
though it is consistent with belonging to the proposed intermediate class or
the extreme short end of the distribution of long-duration GRBs. Based on two
VLT spectra we estimate the HI column density to be Log(N(HI))=21.2+/-0.5. This
is the first direct indication of a connection between GRB host galaxies and
Damped Ly-alpha Absorbers.
|
0109020v1
|
2001-10-16
|
The UCSD HIRES/KeckI Damped Lya Abundance Database: I. The Data
|
We present new chemical abundance measurements of 16 damped Lya systems at
z>1.5 and update our previous abundance analyses. The entire database presented
here was derived from HIRES observations on the Keck I telescope, reduced with
the same software package, and analysed with identical techniques. Altogether,
we present a large, homogeneous database of chemical abundance measurements for
protogalaxies in the early universe, ideal for studying a number of important
aspects of galaxy formation. In addition, we have established an online
directory for this database and will continuously update the results.
|
0110350v1
|
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