35 research outputs found
An analytical model for the non-linear redshift-space power spectrum
We use N-body simulations to test the predictions of the redshift distortion
in the power spectrum given by the halo model in which the clustering of dark
matter particles is considered as a result both of the clustering of dark halos
in space and of the distribution of dark matter particles in individual dark
halo. The predicted redshift distortion depends sensitively on several model
parameters in a way different from the real-space power spectrum. An accurate
model of the redshift distortion can be constructed if the following properties
of the halo population are modelled accurately: the mass function of dark
halos, the velocity dispersion among dark halos, and the non-linear nature of
halo bias on small scales. The model can be readily applied to interpreting the
clustering properties and velocity dispersion of different populations of
galaxies once a cluster-weighted bias (or equivalently an halo occupation
number model) is specified for the galaxies. Some non-trivial bias features
observed from redshift surveys of optical galaxies and of IRAS galaxies
relative to the standard low-density cold dark matter model can be easily
explained in the cluster weighted bias model. The halo model further indicates
that a linear bias can be a good approximation only on for k <= 0.1 hMpc^{-1}.Comment: 10 pages, 10 figures, accepted for publication in MNRA
Cosmological Reionization Around the First Stars: Monte Carlo Radiative Transfer
We study the evolution of ionization fronts around the first proto-galaxies
by using high resolution numerical cosmological (Lambda+CDM model) simulations
and Monte Carlo radiative transfer methods. We present the numerical scheme in
detail and show the results of test runs from which we conclude that the scheme
is both fast and accurate. As an example of interesting cosmological
application, we study the reionization produced by a stellar source of total
mass M=2 10^8 M_\odot turning on at z=12, located at a node of the cosmic web.
The study includes a Spectral Energy Distribution of a zero-metallicity stellar
population, and two Initial Mass Functions (Salpeter/Larson). The expansion of
the I-front is followed as it breaks out from the galaxy and it is channeled by
the filaments into the voids, assuming, in a 2D representation, a
characteristic butterfly shape. The ionization evolution is very well tracked
by our scheme, as realized by the correct treatment of the channeling and
shadowing effects due to overdensities. We confirm previous claims that both
the shape of the IMF and the ionizing power metallicity dependence are
important to correctly determine the reionization of the universe.Comment: 8 pages, 8 figures. Revised version, accepted for publication by
MNRA
On the Distribution of Haloes, Galaxies and Mass
The stochasticity in the distribution of dark haloes in the cosmic density
field is reflected in the distribution function which gives
the probability of finding haloes in a volume with mass density
contrast . We study the properties of this function using
high-resolution -body simulations, and find that is
significantly non-Poisson. The ratio between the variance and the mean goes
from (Poisson) at to (sub-Poisson) at
to (super-Poisson) at . The mean bias
relation is found to be well described by halo bias models based on the
Press-Schechter formalism. The sub-Poisson variance can be explained as a
result of halo-exclusion while the super-Poisson variance at high
may be explained as a result of halo clustering. A simple phenomenological
model is proposed to describe the behavior of the variance as a function of
. Galaxy distribution in the cosmic density field predicted by
semi-analytic models of galaxy formation shows similar stochastic behavior. We
discuss the implications of the stochasticity in halo bias to the modelling of
higher-order moments of dark haloes and of galaxies.Comment: 10 pages, 6 figures, Latex using MN2e style. Minor changes. Accepted
for publication in MNRA
Sunyaev-Zel'dovich profiles and scaling relations: modelling effects and observational biases
We use high-resolution hydrodynamic re-simulations to investigate the
properties of the thermal Sunyaev-Zel'dovich (SZ) effect from galaxy clusters.
We compare results obtained using different physical models for the
intracluster medium (ICM), and show how they modify the SZ emission in terms of
cluster profiles and scaling relations. We also produce realistic mock
observations to verify whether the results from hydrodynamic simulations can be
confirmed. We find that SZ profiles depend marginally on the modelled physical
processes, while they exhibit a strong dependence on cluster mass. The central
and total SZ emission strongly correlate with the cluster X-ray luminosity and
temperature. The logarithmic slopes of these scaling relations differ from the
self-similar predictions by less than 0.2; the normalization of the relations
is lower for simulations including radiative cooling. The observational test
suggests that SZ cluster profiles are unlikely to be able to probe the ICM
physics. The total SZ decrement appears to be an observable much more robust
than the central intensity, and we suggest using the former to investigate
scaling relations.Comment: 13 pages, 12 figures, accepted by MNRA
The mass density field in simulated non-Gaussian scenarios
In this work we study the properties of the mass density field in the
non-Gaussian world models simulated by Grossi et al. 2007. In particular we
focus on the one-point density probability distribution function of the mass
density field in non-Gausian models with quadratic non-linearities quantified
by the usual parameter f_NL. We find that the imprints of primordial
non-Gaussianity are well preserved in the negative tail of the probability
function during the evolution of the density perturbation. The effect is
already noticeable at redshifts as large as 4 and can be detected out to the
present epoch. At z=0 we find that the fraction of the volume occupied by
regions with underdensity delta < -0.9, typical of voids, is about 1.3 per cent
in the Gaussian case and increases to ~2.2 per cent if f_NL=-1000 while
decreases to ~0.5 per cent if f_NL=+1000. This result suggests that void-based
statistics may provide a powerful method to detect non-Gaussianity even at low
redshifts which is complementary to the measurements of the higher-order
moments of the probability distribution function like the skewness or the
kurtosis for which deviations from the Gaussian case are detected at the 25-50
per cent level.Comment: revised version, 9 Pages, 8 figures, MNRAS in pres
Predicting the clustering properties of galaxy clusters detectable for the Planck satellite
We study the clustering properties of the galaxy clusters detectable for the
Planck satellite due to their thermal Sunyaev-Zel'dovich effect. We take the
past light-cone effect and the redshift evolution of both the underlying dark
matter correlation function and the cluster bias factor into account. A
theoretical mass-temperature relation allows us to convert the sensitivity
limit of a catalogue into a minimum mass for the dark matter haloes hosting the
clusters. We confirm that the correlation length is an increasing function of
the sensitivity limits defining the survey. Using the expected characteristics
of the Planck cluster catalogue, which will be a quite large and unbiased
sample, we predict the two-point correlation function and power spectrum for
different cosmological models. We show that the wide redshift distribution of
the Planck survey, will allow to constrain the cluster clustering properties up
to z=1. The dependence of our results on the main cosmological parameters (the
matter density parameter, the cosmological constant and the normalisation of
the density power-spectrum) is extensively discussed. We find that the future
Planck clustering data place only mild constraints on the cosmological
parameters, because the results depend on the physical characteristics of the
intracluster medium, like the baryon fraction and the mass-temperature
relation. Once the cosmological model and the Hubble constant are determined,
the clustering data will allow a determination of the baryon fraction with an
accuracy of few per cent.Comment: 11 pages, MNRAS in press. Minor changes to match the accepted versio
Effects of Star Formation Stochasticity on the Ly-alpha & Lyman Continuum Emission from Dwarf Galaxies during Reionization
Observations of distant galaxies play a key role in improving our
understanding of the Epoch of Reionization (EoR). The observed Ly-alpha
emission line strength - quantified by its restframe equivalent width (EW) -
provides a valuable diagnostic of stellar populations and dust in galaxies
during and after the EoR. In this paper we quantify the effects of star
formation stochasticity on the predicted Ly-alpha EW in dwarf galaxies, using
the publicly available code SLUG ('Stochastically Light Up Galaxies'). We
compute the number of hydrogen ionizing photons, as well as flux in the Far UV
for a set of models with star formation rates (SFR) in the range 10-3-1
Msol/yr. From these fluxes we compute the luminosity, L-alpha, and the EW of
the Ly-alpha line. We find that stochasticity alone induces a broad
distribution in L-alpha and EW at a fixed SFR, and that the widths of these
distributions decrease with increasing SFR. We parameterize the EW probability
density function (PDF) as an SFR-dependent double power law. We find that it is
possible to have EW as low as ~EW0/4 and as high as ~3 times the EW0, where EW0
denotes the expected EW in the absence of stochasticity. We argue that
stochasticity may therefore be important when linking drop-out and narrow-band
selected galaxies, when identifying population III galaxies, and that it may
help to explain the large EW (EW > 100 - 200 A) observed for a fraction of
Ly-alpha- selected galaxies. Finally, we show that stochasticity can also
affect the inferred escape fraction of ionizing photons from galaxies. In
particular, we argue that stochasticity may simultaneously explain the observed
anomalous ratios of the Lyman continuum flux density to the (non-ionizing) UV
continuum density in so-called Lyman-Bump galaxies at z = 3.1, as well as the
absence of such objects among a sample of z = 1.3 drop-out galaxies.Comment: 9 pages, 4 figures, accepted for publication in MNRA
Smoothed particle hydrodynamics for galaxy formation simulations: improved treatments of multiphase gas, of star formation and of supernovae feedback
We investigate a new implementation of the Smoothed Particle Hydrodynamics
technique (SPH) designed to improve the realism with which galaxy formation can
be simulated. In situations where cooling leads to the coexistence of phases of
very different density and temperature, our method substantially reduces
artificial overcooling near phase boundaries, prevents the exclusion of hot gas
from the vicinity of cold ``clouds'', and allows relative motion of the two
phases at each point. We demonstrate the numerical stability of our scheme in
the presence of extremely steep density and temperature gradients, as well as
in strong accretion shocks and cooling flows. In addition, we present new
implementations of star formation and feedback which simulate the effect of
energy injection into multiphase gas more successfully than previous schemes.
Our feedback recipes deposit thermal energy separately in cold dense gas and
hot diffuse gas, and can explicitly reinject cold gas into the hot phase. They
make it possible to damp star formation effectively, to reheat cold gas, and to
drive outflows into the galaxy halo and beyond. We show feedback effects to be
strongest in small mass objects where much of the gas can be expelled. After
idealised tests, we carry out a first low resolution study of galaxy formation
in a CDM universe. Feedback results in substantial and mass-dependent
reductions in the total baryonic mass gathered onto the final object as well as
in significant modulation of the star formation history.Comment: 41 pages, 8 figures. Submitted to MNRA
インヨウ サクイン データベース ニ オケル チョシャ ショゾク キカン ノ ゴキサイ ノ ケンキュウ : ニホン ノ ダイガク ト ショザイコク ガ 「ニホン」 ト サレタ ガイコク ノ ダイガク ノ バアイ
引用索引データベースは文献の情報を記録しているが、必ずしもすべて正しくはない。本研究では天文学と材料学の2 分野から、各4 誌の2005 年に掲載された文献、および、その文献を引用した文献を抽出した。これらの文献の国名が日本と記録された16,482 件の所属機関を対象とした。機関情報のうち大学名称の誤記を調査し、58 件を15 の種類に分類した。また、国名の誤記が4 件見つかった。誤記の発生段階を著者・出版者、データベース提供者に区別した。発生段階別の傾向が分かった。Although the citation index database to record information in literatures, it is not necessarily everything correctly. In this study, the literatures were extracted from two fields of astronomy and materials science, literatures was published in from 2005 to current. The number of recorded "Japan" in COUNTRY was 16,482. However, they had been recorded in Japanese universities and foreign universities. Miss records of 58 universities were classified into 15 types. Miss records were identified by an author & a publisher and a database company. Miss records were shown aracteristic