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2021-12-16 | Split link detection for sl(P) link homology in characteristic P | If $P$ is a prime number, we show that reduced $\mathfrak{sl}(P)$ link
homology with coefficients in $\mathbf{Z}/P$ detects split links. The argument
uses Dowlin's spectral sequence and sutured Floer homology with twisted
coefficients. When $P = 2$, we recover Lipshitz-Sarkar's split link detection
result for Khovanov homology with $\mathbf{Z}/2$ coefficients. | 2112.09110v2 |
2022-01-17 | On Hochschild homology of uniform Roe algebras with coefficients in uniform Roe bimodules | It was shown recently by M. Lorentz and R. Willett that all bounded
derivations of the uniform Roe algebras of metric spaces of bounded geometry
are inner. Here we calculate the space of outer derivations of the uniform Roe
algebras with coefficients in uniform Roe bimodules related to various metrics
on the two copies of the given space. We also give some results on the higher
Hochschild cohomology with coefficients in uniform Roe bimodules. | 2201.06488v1 |
2022-02-21 | Maximum principle for time-fractional parabolic equations with a reaction coefficient of arbitrary sign | We consider time-fractional parabolic equations with a Caputo time derivative
of order $\alpha\in(0,1)$. For such equations, we give an elementary proof of
the weak maximum principle under no assumptions on the sign of the reaction
coefficient. This proof is also extended for weak solutions, as well as for
various types of boundary conditions and variable-coefficient variable-order
multiterm time-fractional parabolic equations. | 2202.10220v2 |
2022-05-13 | Discrete m-functions with Doubly Palindromic Continued Fraction Coefficients | We demonstrate that discrete m-functions with eventually periodic continued
fraction coefficients have an algebraic relationship to their second solution
if and only if the periodic part of the sequence of continued fraction
coefficients is doubly palindromic. In this setting, doubly palindromic means
that each sequence is a repeated concatenation of two palindromes and a
compatibility condition between the lengths of these palindromes is satisfied. | 2205.06653v1 |
2022-06-21 | Lipschitz Continuity for Elliptic Free Boundary Problems with Dini Mean Oscillation Coefficients | We establish local interior Lipschitz continuity of the solutions of a class
of free boundary elliptic problems assuming the coefficients of the equation of
Dini mean oscillation in at least one direction. The novelty in this regularity
result lies in the fact that it allows discontinuous coefficients in all but
one variable. | 2206.10239v1 |
2022-06-30 | Yet another proof that the roots of a polynomial depend continuously on the coefficients | The roots of a complex polynomial depend continuously on the coefficients;
that is, an infinitesimal perturbation of the coefficients results in an
infinitesimal perturbation of the roots. A short, straightforward proof of this
is possible using infinitesimals. | 2207.00123v2 |
2022-07-20 | Recovery of coefficients in semilinear transport equations | We consider the inverse problem for time-dependent semilinear transport
equations. We show that time-independent coefficients of both the linear
(absorption or scattering coefficients) and nonlinear terms can be uniquely
determined, in a stable way, from the boundary measurements by applying a
linearization scheme and Carleman estimates for the linear transport equations.
We establish results in both Euclidean and general geometry settings. | 2207.10194v1 |
2022-09-21 | Finite polynomial cohomology with coefficients | We introduce a theory of finite polynomial cohomology with coefficients in
this paper. We prove several basic properties and introduce an Abel-Jacobi map
with coefficients. As applications, we use such a cohomology theory to study
arithmetics of compact Shimura curves over $\mathbb{Q}$, and simplify proofs of
the works of Darmon-Rotger and Bertolini-Darmon-Prasanna. | 2209.10289v2 |
2022-09-30 | Independence of Linear Statistics with Random Coefficients and Characterizations of Geometric and Poisson Distributions | There is given a characterization of the geometric distribution by the
independence of linear forms with random coefficients. The result is a discrete
analog of the corresponding theorem on exponential distribution. The property
of linear statistics independence is also a characterization of Poisson law.
Keywords: geometric distribution; exponential distribution; Poisson
distribution; linear forms; random coefficients | 2210.01121v1 |
2022-08-26 | Integral operator on certain subclass of analytic function with negative coefficients | In this paper, we study subclass of analytic function with negative
coefficient defined by integral operator in the unit disc $U = \left\{ {z \in
C:\left| z \right| < 1} \right\}$. The results are included coefficient
estimates, closure theorem and distortion theorems of functions belonging to
this subclass. Also, we presented detailed study of uniformly convex and
uniformly starlike functions. | 2211.06422v1 |
2022-11-23 | The first negative Fourier coefficient of an Eisenstein series newform | There have been a number of papers on statistical questions concerning the
sign changes of Fourier coefficients of newforms. In one such paper, Linowitz
and Thompson gave a conjecture describing when, on average, the first negative
sign of the Fourier coefficients of an Eisenstein series newform occurs. In
this paper, we correct their conjecture and prove the corrected version. | 2211.12985v2 |
2023-01-16 | Factorization of certain Macdonald Littlewood-Richardson coefficients | We find and prove a factorization formula for certain Macdonald
Littlewood-Richardson coefficients $c_{\lambda\mu}^{\nu}(q,t)$. Namely, we
consider the case that the Kostka number $K_{\mu, \nu -\lambda}$ is $1$. This
settles a particular case of a more general conjecture of Richard Stanely. This
conjecture proposes that a factorization formula exists whenever the
corresponding regular Littlewood-Richardson coefficient $c^{\nu}_{\lambda \mu}$
is $1$. | 2301.06500v1 |
2023-02-14 | Eigenvalue location of certain matrix polynomials | It is known that a matrix polynomial with unitary matrix coefficients has its
eigenvalues in the annular region $\frac{1}{2} < |\lambda| < 2$. We prove in
this short note that under certain assumptions, matrix polynomials with either
doubly stochastic matrix coefficients or Schur stable matrix coefficients also
have eigenvalues in similar annular regions. | 2302.06788v1 |
2023-02-16 | Continuous group cohomology with coefficients in locally analytic vectors of admissible $ \mathbb{Q}_p $-Banach space representations | We show that the continuous cohomology groups of a $ p $-adic reductive group
with coefficients in the locally analytic vectors of an admissible $
\mathbb{Q}_p $-Banach space representation are homeomorphic to those with
coefficients in the Banach space representation itself. Moreover, we deduce
that the canonical topologies on those continuous cohomology groups are
Hausdorff and are the uniquely determined finest locally convex topologies. | 2302.08369v1 |
2023-02-23 | On the spectrum of the differential operators of even order with periodic matrix coefficients | In this paper, we consider the band functions, Bloch functions and spectrum
of the self-adjoint differential operator L with periodic matrix coefficients.
Conditions are found for the coefficients under which the number of gaps in the
spectrum of the operator L is finite | 2302.11807v1 |
2023-07-05 | A remark on the quantum complexity of the Kronecker coefficients | We prove that the computation of the Kronecker coefficients of the symmetric
group is contained in the complexity class #BQP. This improves a recent result
of Bravyi, Chowdhury, Gosset, Havlicek, and Zhu. We use only the quantum
computing tools that are used in their paper and additional classical
representation theoretic insights. We also prove the analogous result for the
plethysm coefficients. | 2307.02389v1 |
2023-08-31 | An extension of Lucas Theorem | We give elementary proofs of some congruence criteria to compute binomial
coefficients in modulo a prime. These criteria are analogues to the symmetry
property of binomial coefficients. We give extended version of Lucas Theorem by
using those criteria. We give applications of these criteria by describing a
method to derive identities and congruences involving sums of binomial
coefficients. | 2309.00109v1 |
2023-09-11 | On the Cauchy problem for $p$-evolution equations with variable coefficients: a necessary condition for Gevrey well-posedness | In this paper we consider a class of $p$-evolution equations of arbitrary
order with variable coefficients depending on time and space variables $(t,x)$.
We prove necessary conditions on the decay rates of the coefficients for the
well-posedness of the related Cauchy problem in Gevrey spaces. | 2309.05571v1 |
2023-09-22 | On the $ψ$-mixing coefficients of Rényi-type maps | Via dependence with complete connections we investigate the $\psi$-mixing
coefficients of the sequence $(a_n)_{n \in \mathbb{N}}$ of incomplete quotients
and also of the doubly infinite sequence $(\overline{a}_l)_{l \in \mathbb{Z}}$
of extended incomplete quotients of the R\'enyi-type continued fraction
expansions. A L\'evy-type approach allows us to obtain good upper bounds for
these coefficients. | 2309.12649v1 |
2023-10-13 | Convexification for a Coefficient Inverse Problem of Mean Field Games | The globally convergent convexification numerical method is constructed for a
Coefficient Inverse Problem for the Mean Field Games System. A coefficient
characterizing the global interaction term is recovered from the single
measurement data. In particular, a new Carleman estimate for the Volterra
integral operator is proven, and it stronger than the previously known one.
Numerical results demonstrate accurate reconstructions from noisy data. | 2310.08878v1 |
2023-10-19 | Stable recovery of coefficients in an inverse fault friction problem | We consider the inverse fault friction problem of determining the friction
coefficient in the Tresca friction model, which can be formulated as an inverse
problem for differential inequalities. We show that the measurements of elastic
waves during a rupture uniquely determine the friction coefficient at the
rupture surface with explicit stability estimates. | 2310.12698v1 |
2023-11-06 | Hilbert coefficients of quadratic algebras | If $R=k[x_1,\ldots,x_n]/I$ is a graded artinian algebra, then the length of
$k[x_1,\ldots,x_n]/I^s$ becomes a polynomial in $s$ of degree $n$ for large
$s$. If we write this polynomial as $\sum_{i=0}^n(-1)^ie_i{s+n-i-1\choose
n-i}$, then the $e_i$'s are called Hilbert coefficients of $I$. We will study
length and Hilbert coefficients of some classes of quadratic algebras. | 2311.02860v1 |
2023-12-05 | On pair correlation of Hermite coefficients of functions from the Hardy class | Assuming that a function and its Fourier transform are dominated by a
Gaussian, Vemuri found a sharp estimate for the decay rate of the Hermite
coefficients in terms of the variance of the dominating Gaussian. Here we show
that under the same assumptions, certain combinations of Hermite coefficients
have a better rate of decay. | 2312.02606v1 |
2024-01-01 | Walsh coefficients and circuits for several alleles | Walsh coefficients have been applied extensively to biallelic systems for
quantifying pairwise and higher order epistasis, in particular for
demonstrating the empirical importance of higher order interactions. Circuits,
or minimal dependence relations, and related approaches that use triangulations
of polytopes have also been applied to biallelic systems. Here we provide
biological interpretations of Walsh coefficients for several alleles, and
discuss circuits in the same general setting. | 2401.00743v2 |
2024-01-02 | Comment on `Index-free Heat Kernel Coefficients' | The article by Anton E. M. van de Ven, Class. Quantum Grav. \textbf{15}
(1998), is one of the fundamental references for higher-order heat kernel
coefficients in curved backgrounds and with non-abelian gauge connections. In
this manuscript, we point out two errors and ambiguities in the $\mathsf{a}_5$
coefficient, which may also affect the higher-order ones. | 2401.01296v1 |
2024-01-19 | Some coefficient estimates on complex valued kernel $α$-harmonic mappings | We call a kind of mappings induced by a kind of weighted Laplace operator as
complex valued kernel $\alpha$-harmonic mappings. In this article, for this
class of mappings, the Heinz type lemma is established, and the best Heinz type
inequality is obtained. Next, the extremal function of Schwartz's Lemma is
discussed. Finally, the coefficients are estimated for the subclass of complex
valued kernel alpha harmonic mappings whose coefficients are real numbers. | 2401.10434v1 |
2024-01-24 | Optimal regularity for the variable coefficients parabolic Signorini problem | In this paper we discuss the optimal regularity of the variable coefficient
parabolic Signorini problem with $W^{1,1}_p$ coefficients and $L^p$
inhomogeneity, where $p>n+2$ with $n$ being the space dimension. Relying on an
parabolic Carleman estimate and an epiperimetric inequality, we show the
optimal regularity of the solutions as well as the regularity of the regular
free boundary. | 2401.13305v1 |
2024-03-24 | Determination of Hilbert modular forms using squarefree coefficients | Let $F$ (over $\mathbb{Q}$) be a totally real number field of narrow class
number $1$. We generalize a result of Kohnen on the determination of half
integral weight modular forms by their Fourier coefficients supported on
squarefree (algebraic) integers. We also give a soft proof that infinitely many
Fourier coefficients supported on squarefree integers are non-vanishing. | 2403.16012v1 |
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 |
1997-09-12 | 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 |
1999-11-03 | Tensor Microwave Anisotropies from a Stochastic Magnetic Field | We derive an expression for the angular power spectrum of cosmic microwave
background anisotropies due to gravity waves generated by a stochastic magnetic
field and compare the result with current observations; we take into account
the non-linear nature of the stress energy tensor of the magnetic field.
For almost scale invariant spectra, the amplitude of the magnetic field at
galactic scales is constrained to be of order 10^{-9} Gauss. If we assume that
the magnetic field is damped below the Alfven damping scale, we find that its
amplitude at
0.1 h^{-1}Mpc, B_\lambda, is constrained to be B_\lambda<7.9 x10^{-6} e^{3n}
Gauss, for n<-3/2, and B_\lambda<9.5x10^{-8} e^{0.37n} Gauss, for n>-3/2, where
n is the spectral index of the magnetic field and H_0=100h km s^{-1}Mpc^{-1} is
the Hubble constant today. | 9911040v1 |
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 |
2001-04-24 | 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 |
2001-10-16 | A simple analytical model for the abundance of damped Ly-α absorbers | A simple analytical model for estimating the fraction (\Omega_{gas}) of
matter in gaseous form within the collapsed dark matter (DM) haloes is
presented. The model is developed using (i) the Press-Schechter formalism to
estimate the fraction of baryons in DM haloes, and (ii) the observational
estimates of the star formation rate at different redshifts. The prediction for
\Omega_{gas} from the model is in broad agreement with the observed abundance
of the damped Ly-\alpha systems. Furthermore, it can be used for estimating the
circular velocities of the collapsed haloes at different redshifts, which could
be compared with future observations. | 0110359v2 |
2001-10-16 | Unusual Metal Abundances in a Pair of Damped Lyman Alpha Systems at z~2 | We present high resolution spectroscopic observations of two neighbouring
damped Lya systems (DLAs) along the same line of sight towards B2314-409. Due
to their separation (v ~ 2000 km/s) and the high spectral resolution of the
data, it is possible to fit not only the weak metal transitions, but also the
separate HI absorption profiles. This has permitted, for the first time, a
detailed study of metal abundances in two neighbouring galaxy-scale absorbers.
The two DLAs have z_abs = 1.8573 and 1.8745 and have column densities log N(HI)
= 20.9+/-0.1 and 20.1+/-0.2 respectively. We have determined abundances for a
range of chemical elements, and find that BOTH absorbers towards B2314-409 have
low alpha/Fe-peak abundances compared with other known DLAs. This indicates
that not only has the recent star formation history of these absorbers been
relatively passive, but that the group environment, or some other external
factor, may have influenced this. | 0110391v2 |
2001-12-18 | NICMOS Snapshot Survey of Damped Lyman Alpha Quasars | We image 19 quasars with 22 damped Lyman alpha (DLA) systems using the F160W
filter and the Near-Infrared Camera and Multiobject Spectrograph aboard the
Hubble Space Telescope, in both direct and coronagraphic modes. We reach 5
sigma detection limits of ~H=22 in the majority of our images. We compare our
observations to the observed Lyman-break population of high-redshift galaxies,
as well as Bruzual & Charlot evolutionary models of present-day galaxies
redshifted to the distances of the absorption systems. We predict H magnitudes
for our DLAs, assuming they are producing stars like an L* Lyman-break galaxy
(LBG) at their redshift. Comparing these predictions to our sensitivity, we
find that we should be able to detect a galaxy around 0.5-1.0 L* (LBG) for most
of our observations. We find only one new possible candidate, that near
LBQS0010-0012. This scarcity of candidates leads us to the conclusion that most
DLA systems are not drawn from a normal LBG luminosity function nor a local
galaxy luminosity function placed at these high redshifts. | 0112416v1 |
2002-02-19 | Saturation of the R-mode Instability | Rossby waves (r-modes) in rapidly rotating neutron stars are unstable because
of the emission of gravitational radiation. We study saturation of this
instability by nonlinear transfer of energy to stellar "inertial" oscillation
modes. We present detailed calculations of stellar inertial modes in the WKB
limit, their linear damping by bulk and shear viscosity, and the nonlinear
coupling forces among these modes. The saturation amplitude is derived in the
extreme limits of strong or weak driving by radiation reaction, as compared to
the damping rate of low order inertial modes. We find the saturation energy is
{\it extremely small}, at least four orders of magnitude smaller than that
found by previous investigators. We discuss the consequences of this result for
spin evolution of young neutron stars, and neutron stars being spun up by
accretion in Low Mass X-ray Binaries.We also discuss the detection of these
gravitational waves by LIGO. | 0202345v2 |
2002-04-05 | HI 21cm imaging of a nearby Damped Lyman-alpha system | We present Giant Metrewave Radio Telescope (GMRT) HI 21cm emission images of
the z=0.009 damped Lyman-alpha (DLA) absorber towards the QSO HS 1543+5921. The
DLA has been earlier identified as a low surface brightness galaxy SBS 1543+593
at an impact parameter of ~ 400 pc to the QSO line of sight. The extremely low
redshift of the absorber allows us to make spatially resolved images of the
21cm emission; besides the HI mass, this also enables us to determine the
velocity field of the galaxy and, hence, to estimate its dynamical mass.
We obtain a total HI mass of ~ 1.4x10^9 Msun, considerably smaller than the
value of M*(HI) determined from blind 21cm emission surveys. This continues the
trend of low HI mass in all low redshift DLAs for which HI emission
observations have been attempted. We also find that the QSO lies behind a
region of low local HI column density in the foreground galaxy. This is
interesting in view of suggestions that DLA samples are biased against high HI
column density systems. The dynamical mass of the galaxy is found to be Mdyn ~
5x10^9 Msun. | 0204094v1 |
2002-07-15 | On the Structure of the Iron K-Edge | It is shown that the commonly held view of a sharp Fe K edge must be modified
if the decay pathways of the series of resonances converging to the K
thresholds are adequately taken into account. These resonances display damped
Lorentzian profiles of nearly constant widths that are smeared to impose
continuity across the threshold. By modeling the effects of K damping on
opacities, it is found that the broadening of the K edge grows with the
ionization level of the plasma and that the appearance at high ionization of a
localized absorption feature at 7.2 keV is identified as the K-beta unresolved
transition array. | 0207324v2 |
2002-08-26 | Damped Lyman alpha systems and disk galaxies: number density, column density distribution and gas density | We present a comparison between the observed properties of damped Lyman alpha
systems (DLAs) and the predictions of simple models for the evolution of
present day disk galaxies, including both low and high surface brightness
galaxies. We focus in particular on the number density, column density
distribution and gas density of DLAs, which have now been measured in
relatively large samples of absorbers. From the comparison we estimate the
contribution of present day disk galaxies to the population of DLAs, and how it
varies with redshift. Based on the differences between the models and the
observations, we also speculate on the nature of the fraction of DLAs which
apparently do not arise in disk galaxies. | 0208457v1 |
2002-09-10 | A search for molecules in damped Lyman-alpha absorbers occulting millimetre-loud quasars | We have used the SEST 15-metre and Onsala 20-metre telescopes to perform deep
(r.m.s. >~ 30 mJy) integrations of various molecular rotational transitions
towards damped Lyman-alpha absorption systems (DLAs) known to occult
millimetre-loud quasars. We have observed 6 new systems and improved the
existing limits for 11 transitions. These limits may be approaching the
sensitivities required to detect new systems and we present a small number of
candidate systems which we believe warrant further observation. | 0209175v1 |
2002-11-13 | Strong Absorption-line Systems at Low Redshift: MgII and Damped Lyman Alpha | We detail a powerful indirect method for the study of damped Lyman alpha
systems (DLAs) at low redshift. We increase the probability of finding a
low-redshift DLA to nearly 50% by targeting QSOs that are known to have strong
low-redshift MgII and FeII absorption lines in their spectra. We are using
Sloan Digital Sky Survey QSO spectra complemented by a survey we are conducting
at the MMT to study the metal-line systems. The Hubble Space Telescope is being
used to confirm low-redshift DLAs. In addition, we are imaging low-redshift DLA
galaxies with several ground-based telescopes to directly study their
environments. | 0211295v1 |
2002-11-22 | On the Origin of Nitrogen in Damped Ly-alpha Systems | Recent measurements of nitrogen and alpha elements in over 20 damped Ly-alpha
systems (DLA) are compared with similar measurements for numerous emission line
objects and stars. It is found that the DLA distribution in the N/alpha-alpha/H
plane is bimodal, where most sample DLAs fall along the N/alpha plateau defined
at low Z by dwarf irregulars, while a small group possesses N/alpha values
roughly 0.7 dex less than those on the plateau at similar alpha/H values. We
demonstrate with chemical evolution models that a top-heavy or truncated IMF
can account for the low N in this second group. | 0211512v1 |
2002-12-16 | Fragmentation and Collapse of Turbulent Molecular Clouds | We performed simulations of self-gravitating hydrodynamic turbulence to model
the formation of filaments, clumps and cores in molecular clouds. We find that
when the mass on the initial computational grid is comparable to the Jeans
mass, turbulent pressure is able to prevent gravitational collapse. When the
turbulence has damped away sufficiently, gravitational collapse can occur, and
the resulting structure closely resembles the pre-singularity collapse of an
isothermal sphere of Penston (1969). If several Jeans masses are initially
placed on the grid, turbulence may not be sufficient to prevent collapse before
turbulence can be significantly damped. In this case, the cores have density
structures which are considerably shallower than expected for an isothermal
gas, and resemble the solutions for a logatropic equation of state. | 0212359v1 |
2003-02-20 | One-Armed Spiral Instability in Differentially Rotating Stars | We investigate the dynamical instability of the one-armed spiral m=1 mode in
differentially rotating stars by means of 3+1 hydrodynamical simulations in
Newtonian gravitation. We find that both a soft equation of state and a high
degree of differential rotation in the equilibrium star are necessary to excite
a dynamical m=1 mode as the dominant instability at small values of the ratio
of rotational kinetic to potential energy, T/|W|. We find that this spiral mode
propagates outward from its point of origin near the maximum density at the
center to the surface over several central orbital periods. An unstable m=1
mode triggers a secondary m=2 bar mode of smaller amplitude, and the bar mode
can excite gravitational waves. As the spiral mode propagates to the surface it
weakens, simultaneously damping the emitted gravitational wave signal. This
behavior is in contrast to waves triggered by a dynamical m=2 bar instability,
which persist for many rotation periods and decay only after a
radiation-reaction damping timescale. | 0302436v2 |
2003-03-21 | Molecular Hydrogen in Damped Ly-alpha Systems: Spatial Distribution | To interpret H_2 quasar absorption line observations in Damped Ly-alpha
clouds (DLAs), we model the H_2 spatial distribution within a DLA. Based on
numerical simulations of disk structures with parameters similar to those
derived for such absorbers, we calculate the H_2 distribution as a function of
ultraviolet background (UVB) intensity and dust-to-gas ratio. For typical
values of these two quantities we find that the area in which the H_2 fraction
exceeds 10^{-6} (typical observational detection limit) only covers $\la 10$%
of the disk surface, i.e. H_2 has a very inhomogeneous, clumpy distribution
even at these low abundance levels. This explains the relative paucity of H_2
detections in DLAs. We also show the dependence of the covering fraction of H_2
on dust-to-gas ratio and UVB intensity and we comment on the physics governing
the H_2 chemical network at high redshift. | 0303495v1 |
2003-05-02 | The Critical Rotation of Strange Stars and Rapidly Rotating Pulsars | We utilize the bulk viscosity of interacting strange quark matter to
reevaluate the damping time scale. The presence of medium effect of bulk
viscosity leads to a stronger damping of r-modes, which can be over an order of
magnitude for realistic parameters. We find that the r-mode instability window
is narrowed due to the medium effect, and hence when a pulsar reaches the
instability window it will only slow down by gravitational wave emission to a
period of 1.78msec instead of 2.5msec given by early estimate. As a theoretical
upper rotation limit of pulsars, the period of 1.78msec is very close to the
two most rapidly spinning pulsars known, with periods of about 1.6msec. | 0305034v1 |
2003-06-02 | Chemical Evolution of Damped Lyman Alpha Systems | By means of detailed chemical evolution models for galaxies of different
morphological types (i.e. spirals, irregular/starburst galaxies and
ellipticals) we study the nature of Damped Lyman-Alpha systems. Our concern is
to infer which systems represent likely candidates for the DLA population and
which do not. By focusing on individual systems, we can derive some constraints
on both the nature of the associated galaxy and its age. Our results indicate
that, owing to their high metallicities and [alpha/Fe] ratios, big spheroids
represent unlikely DLA candidates whereas spirals (observed at different
galactocentric distances) and irregulars are ideal sites where DLA absorptions
can occur. | 0306037v1 |
2003-07-01 | Clustering of galaxies at z=3 around the probable Damped Ly-alpha absorber towards QSO APM 08279+5255 | [Abridged] We present results on the clustering og Lyman break galaxies
(LBGs) around a probable damped Ly-alpha absorption (DLA) line cloud at
z_DLA=2.974 from deep UBVI images of the field containing the quasar APM
08279+5255 (z=3.91). The large area covered by our images, 0.31 deg^2 or 40x40
Mpc co-moving at z=3, and their depth (27.6 mag arcsec^{-2}), allow us to
identify 450 LBG candidates brighter than I(AB)=24.80 at 2.75<z<3.25. LBG
candidates were selected using photometric redshift techniques that include
priors within a redshift slice of width Wz=0.15 centered at z_DLA.
Within that redshift slice, we find an enhancement of galaxies near the DLA
using both the surface density and an estimator of the 3-D spatial
over-density. The surface overdensity (3\times) is significant at the >95%
significance level on scales 2.5<r<5 Mpc co-moving and imply that some DLA
could reside in high density regions. | 0307033v1 |
2003-08-11 | Imaging and spectroscopy of galaxies associated with two z~0.7 damped Lyman-alpha absorption systems | We have identified galaxies near two quasars which are at the redshift of
damped Lyman-alpha (DLA) systems in the UV spectra of the quasars. Both
galaxies are actively forming stars. One galaxy has a luminosity close to the
break in the local galaxy luminosity function, L*, the other is significantly
fainter than L* and appears to be interacting with a nearby companion. Despite
the strong selection effects favoring spectroscopic identification of the most
luminous DLA galaxies, many of the spectroscopically-identified DLA galaxies in
the literature are sub-L*, suggesting that the majority of the DLA population
is probably sub-L*, in contrast to MgII absorbers at similar redshifts whose
mean luminosity is close to L*. | 0308193v1 |
2003-09-03 | The Thermal Stability of Mass-Loaded Flows | We present a linear stability analysis of a flow undergoing
conductively-driven mass-loading from embedded clouds. We find that
mass-loading damps isobaric and isentropic perturbations, and in this regard is
similar to the effect of thermal conduction, but is much more pronounced where
many embedded clumps exist. The stabilizing influence of mass-loading is
wavelength independent against isobaric (condensing) perturbations, but
wavelength dependent against isentropic (wave-like) perturbations. We derive
equations for the degree of mass-loading needed to stabilize such
perturbations. We have also made 1D numerical simulations of a mass-loaded
radiative shock and demonstrated the damping of the overstability when
mass-loading is rapid enough. | 0309086v1 |
2003-09-22 | Hierarchical Structure Formation and Chemical Evolution of Damped Ly alpha Systems | We present a model for chemical evolution of damped Ly alpha systems
considering production of metals by SNe II and infall associated with
hierarchical structure formation. The growth of metallicity in these systems is
a reflection of the competition between astration and infall. The apparent late
turn-on of these systems is due to the late cut-off of infall. The wide range
in [Fe/H] at a given redshift is explained by the range of the times for onset
of star formation and the range of the times for infall cessation in different
systems. The observed lower bound of [Fe/H] = -3 follows from the very rapid
initial rise of [Fe/H] subsequent to onset of star formation. To reach [Fe/H] =
-3 from a metal-free initial state requires only about 30 Myr so that the
probability of observing lower [Fe/H] values is very small. | 0309600v1 |
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