2,483 research outputs found
Numerical Simulations of the Lyman-alpha forest - A comparison of Gadget-2 and Enzo
We compare simulations of the Lyman-alpha forest performed with two different
hydrodynamical codes, Gadget-2 and Enzo. A comparison of the dark matter power
spectrum for simulations run with identical initial conditions show differences
of 1-3% at the scales relevant for quantitative studies of the Lyman-alpha
forest. This allows a meaningful comparison of the effect of the different
implementations of the hydrodynamic part of the two codes. Using the same
cooling and heating algorithm in both codes the differences in the temperature
and the density probability distribution function are of the order of 10%.
These differences can be mainly attributed to a slight mismatch in the
resolution. The differences are smaller than or equal to the effects of boxsize
and resolution on these statistics. Once resolution effects are taken into
account the differences in the flux power spectrum - the statistics most widely
used for estimating the matter power spectrum and cosmological parameters from
Lyman-alpha forest data - are about 5%. This is again smaller than or equal to
the effects of boxsize and resolution. Numerical uncertainties due to a
particular implementation of solving the hydrodynamic or gravitational
equations appear therefore to contribute only moderately to the error budget in
estimates of the flux power spectrum from numerical simulations. We further
find that the differences in the flux power spectrum for Enzo simulations run
with and without adaptive mesh refinement are also of order 5% or smaller. The
latter require 10 times less CPU time making the CPU time requirement similar
to that of a version of Gadget-2 that is optimised for Lyman-alpha forest
simulations.Comment: 10 pages, 8 figures. Submitted to MNRA
The effect of neutrinos on the matter distribution as probed by the Intergalactic Medium
We present a suite of full hydrodynamical cosmological simulations that
quantitatively address the impact of neutrinos on the (mildly non-linear)
spatial distribution of matter and in particular on the neutral hydrogen
distribution in the Intergalactic Medium (IGM), which is responsible for the
intervening Lyman-alpha absorption in quasar spectra. The free-streaming of
neutrinos results in a (non-linear) scale-dependent suppression of power
spectrum of the total matter distribution at scales probed by Lyman-alpha
forest data which is larger than the linear theory prediction by about 25% and
strongly redshift dependent. By extracting a set of realistic mock quasar
spectra, we quantify the effect of neutrinos on the flux probability
distribution function and flux power spectrum. The differences in the matter
power spectra translate into a ~2.5% (5%) difference in the flux power spectrum
for neutrino masses with Sigma m_{\nu} = 0.3 eV (0.6 eV). This rather small
effect is difficult to detect from present Lyman-alpha forest data and nearly
perfectly degenerate with the overall amplitude of the matter power spectrum as
characterised by sigma_8. If the results of the numerical simulations are
normalized to have the same sigma_8 in the initial conditions, then neutrinos
produce a smaller suppression in the flux power of about 3% (5%) for Sigma
m_{\nu} = 0.6 eV (2
sigma C.L.), comparable to constraints obtained from the cosmic microwave
background data or other large scale structure probes.Comment: 38 pages, 21 figures. One section and references added. JCAP in pres
Expansion and Collapse in the Cosmic Web
We study the kinematics of the gaseous cosmic web at high redshift with Lyman
alpha forest absorption in multiple QSO sightlines. Using a simple analytic
model and a cosmological hydrodynamic simulation we constrain the underlying
three-dimensional distribution of velocities from the observed line-of-sight
distribution of velocity shear across the plane of the sky. The distribution is
found to be in good agreement with the intergalactic medium (IGM) undergoing
large scale motions dominated by the Hubble flow. Modeling the Lyman alpha
clouds analytically and with a hydrodynamics simulation, the average expansion
velocity of the gaseous structures causing the Lyman alpha forest in the lower
redshift (z = 2) sample appears about 20 percent lower than the local Hubble
expansion velocity. We interpret this as tentative evidence for some clouds
undergoing gravitational collapse. However, the distribution of velocities is
highly skewed, and the majority of clouds at redshifts from 2 to 3.8 expand
typically about 5 - 20 percent faster than the Hubble flow. This behavior is
explained if most absorbers in the column density range typically detectable
are expanding filaments that stretch and drain into more massive nodes. We find
no evidence for the observed distribution of velocity shear being significantly
influenced by processes other than Hubble expansion and gravitational
instability, like galactic winds. To avoid overly disturbing the IGM, winds may
be old and/or limp by the time we observe them in the Lyman alpha forest, or
they may occupy only an insignificant volume fraction of the IGM. (abridged)Comment: 63 pages, 26 figures, AAS Latex; ApJ, in pres
Galactic winds and extended Lyα emission from the host galaxies of high column density quasi-stellar object absorption systems
We present three-dimensional (3D) resonant radiative transfer simulations of the spatial and spectral diffusion of the Lyα radiation from a central source in the host galaxies of high column density absorption systems at z∼ 3. The radiative transfer simulations are based on a suite of cosmological galaxy formation simulations which reproduce a wide range of observed properties of damped Lyα absorption systems. The Lyα emission is predicted to be spatially extended up to several arcsec, and the spectral width of the Lyα emission is broadened to several hundred (in some case more than thousand) km s−1. The distribution and the dynamical state of the gas in the simulated galaxies are complex, the latter with significant contributions from rotation and both in- and out-flows. The emerging Lyα radiation extends to gas with column densities of NH I∼ 1018 cm−2 and its spectral shape varies strongly with viewing angle. The strong dependence on the central H i column density and the H i velocity field suggests that the Lyα emission will also vary strongly with time on time-scales of a few dynamical times of the central region. Such variations with time should be especially pronounced at times where the host galaxy undergoes a major merger and/or starburst. Depending on the pre-dominance of in- or out-flow along a given sightline and the central column density, the spectra show prominent blue peaks, red peaks or double-peaked profiles. Both spatial distribution and spectral shape are very sensitive to details of the galactic wind implementation. Stronger galactic winds result in more spatially extended Lyα emission and - somewhat counterintuitively - a narrower spectral distributio
Braneworld inflation from an effective field theory after WMAP three-year data
In light of the results from the WMAP three-year sky survey, we study an
inflationary model based on a single-field polynomial potential, with up to
quartic terms in the inflaton field. Our analysis is performed in the context
of the Randall-Sundrum II braneworld theory, and we consider both the
high-energy and low-energy (i.e. the standard cosmology case) limits of the
theory. We examine the parameter space of the model, which leads to both
large-field and small-field inflationary type solutions. We conclude that small
field inflation, for a potential with a negative mass square term, is in
general favored by current bounds on the tensor-to-scalar perturbation ratio
rs.Comment: 11 pages, 5 figures; references updated and a few comments added;
final version to appear in Phys. Rev.
Possible evidence for an inverted temperature-density relation in the intergalactic medium from the flux distribution of the Lyman-alpha forest
We compare the improved measurement of the Lya forest flux probability
distribution at 1.7<z<3.2 presented by Kim et al. (2007) to a large set of
hydrodynamical simulations of the Lya forest with different cosmological
parameters and thermal histories. The simulations are in good agreement with
the observational data if the temperature-density relation for the low density
intergalactic medium (IGM), T=T_0 Delta^{gamma-1}, is either close to
isothermal or inverted (gamma<1). Our results suggest that the voids in the IGM
may be significantly hotter and the thermal state of the low density IGM may be
substantially more complex than is usually assumed at these redshifts. We
discuss radiative transfer effects which alter the spectral shape of ionising
radiation during the epoch of HeII reionisation as a possible physical
mechanism for achieving an inverted temperature-density relation at z~3.Comment: 16 pages, 6 figures, accepted for publication in MNRAS following
minor revision. The accepted version includes an expanded discussion of the
flux power spectru
Constraining Warm Dark Matter candidates including sterile neutrinos and light gravitinos with WMAP and the Lyman-alpha forest
The matter power spectrum at comoving scales of (1-40) h^{-1} Mpc is very
sensitive to the presence of Warm Dark Matter (WDM) particles with large free
streaming lengths. We present constraints on the mass of WDM particles from a
combined analysis of the matter power spectrum inferred from the large samples
of high resolution high signal-to-noise Lyman-alpha forest data of Kim et al.
(2004) and Croft et al. (2002) and the cosmic microwave background data of
WMAP. We obtain a lower limit of m_wdm > 550 eV (2 sigma for early decoupled
thermal relics and m_wdm > 2.0 keV (2 sigma) for sterile neutrinos. We also
investigate the case where in addition to cold dark matter a light thermal
gravitino with fixed effective temperature contributes significantly to the
matter density. In that case the gravitino density is proportional to its mass,
and we find an upper limit m_{3/2} < 16 eV (2 sigma). This translates into a
bound on the scale of supersymmetry breaking, Lambda_{susy} < 260 TeV, for
models of supersymmetric gauge mediation in which the gravitino is the lightest
supersymmetric particle.Comment: 10 pages, 5 figures, 1 table. PRD in pres
The sizes of mini-voids in the local universe: an argument in favor of a warm dark matter model?
Using high-resolution simulations within the Cold and Warm Dark Matter models
we study the evolution of small scale structure in the Local Volume, a sphere
of 8 Mpc radius around the Local Group. We compare the observed spectrum of
mini-voids in the Local Volume with the spectrum of mini-voids determined from
the simulations. We show that the \LWDM model can easily explain both the
observed spectrum of mini-voids and the presence of low-mass galaxies observed
in the Local Volume, provided that all haloes with circular velocities greater
than 20 km/s host galaxies. On the contrary within the LCDM model the
distribution of the simulated mini-voids reflects the observed one if haloes
with maximal circular velocities larger than 35 km/s host galaxies. This
assumption is in contradiction with observations of galaxies with circular
velocities as low as 20 km/s in our Local Universe. A potential problem of the
LWDM model could be the late formation of the haloes in which the gas can be
efficiently photo-evaporated. Thus star formation is suppressed and low-mass
haloes might not host any galaxy at all.Comment: 13 pages, 10 figures, version 2, subsection 3.1 added, accepted to
MNRA
Gamma-ray spectrometry for distinguishing acid and basic rocks of the serra geral formation, in the serra gaúcha wine region, Brazil.
The gamma-ray spectrometric research has allowed for observation of the distribution of radioactive elements such as K, U and Th for recognizing the radioactive signatures of different rock types. The objective of this study was to evaluate the possibility to distinguish between acid and basic rocks of the Serra Geral Formation, in the Serra Gaúcha wine region in the state of Rio Grande do Sul (Brazil) through gamma-ray spectrometry techniques. This study contributed to geologically... Keywords: geophysical method, wine terroir, volcanic rock. A pesquisa por gamaespectrometria tem permitido observar a distribuição de elementos radioativos, tais como K, U e Th reconhecendo as assinaturas radioativas de diferentes tipos de rocha. O objetivo deste estudo foi avaliar a possibilidade de distinguir entre as rochas ácidas e básicas da Formação Serra Geral, na região vitivinícola Serra Gaúcha, no estado do Rio Grande do Sul (Brasil) por meio de técnicas de gamaespectrometria Palavras-chave: m´étodos geofísicos, terroir vitivinícola, rocha vulcânica
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