81 research outputs found
Chasing Unbiased Spectra of the Universe
The cosmological power spectrum of the coherent matter flow is measured
exploiting an improved prescription for the apparent anisotropic clustering
pattern in redshift space. New statistical analysis is presented to provide an
optimal observational platform to link the improved redshift distortion
theoretical model to future real datasets. The statistical power as well as
robustness of our method are tested against 60 realizations of 8 Gpc/h^3 dark
matter simulation maps mocking the precision level of upcoming wide--deep
surveys. We showed that we can accurately extract the velocity power spectrum
up to quasi linear scales of k~0.1 h/Mpc at z = 0.35 and up to k~0.15 h/Mpc at
higher redshifts within a couple of percentage precision level. Our
understanding of redshift space distortion is proved to be appropriate for
precision cosmology, and our statistical method will guide us to righteous path
to meet the real world.Comment: 9 pages, 7 figure
Non-Gaussian Tails of Cosmological Density Distribution Function from Dark Halo Approach
We present a simple model based on the dark halo approach which provides a
useful way to understand key points determining the shape of the non-Gaussian
tails of the dark matter one-point probability distribution function(PDF). In
particular, using the scale-free models with power-law profile of dark halos,
we derive a simple analytic expression for the one-point PDF. It is found that
the shape of the PDF changes at the characteristic value of which is
defined by the smoothed density of a halo with the characteristic mass at
the epoch. In cold dark matter models with top-hat smoothing filters, the
characteristic smoothed density at present time typically takes the value
for a small smoothing scale \rth\sim 1Mpc and conversely
for a large smoothing scale \rth > 10Mpc. On the range
, the shape of the PDF is almost solely determined by the
outer slope of halos and scales as a power-law. The resultant non-Gaussian
tails of PDF then resemble the log-normal PDFs in that range and show a good
agreement with N-body simulations, which can be ascribed to the universality of
the outer slope of the halo profile. In contrast, tails of one-point PDF in the
range basically follow the steep exponential tails of the
halo mass function, which exhibit a strong sensitivity to both the outer slope
of the halo profile and the initial power spectrum. Based on these results, the
discussion on the PDF of galaxy distribution and the application to the weak
lensing statistics are also presented.Comment: 13 pages, 7 figures, accepted for publication in MNRA
Ray-tracing log-normal simulation for weak gravitational lensing: application to the cross-correlation with galaxies
We present an algorithm to self-consistently generate mock weak gravitational
lensing convergence fields and galaxy distributions in redshift space. We
generate three-dimensional cosmic density fields that follow a log-normal
distribution, and ray-trace them to produce convergence maps. As we generate
the galaxy distribution from the same density fields in a manner consistent
with ray-tracing, the galaxy-convergence cross-power spectrum measured from the
mock agrees with the theoretical expectation with high precision. We use this
simulation to forecast the quality of galaxy-shear cross-correlation
measurements from the Subaru Hyper Suprime-Cam (HSC) and Prime Focus
Spectrograph (PFS) surveys. We find that the nominal HSC and PFS surveys would
detect the cross power spectra with signal-to-noise ratios of 20 and 5 at the
lowest () and highest () redshift bins, respectively.Comment: 22 pages, 10 figures, accepted to JCAP. The simulation code is
available at https://wwwmpa.mpa-garching.mpg.de/~komatsu/codes.htm
Modeling peculiar velocities of dark matter halos
We present a simple model that accurately describes various statistical
properties of peculiar velocities of dark matter halos. We pay particular
attention to the following two effects; first, the evolution of the halo
peculiar velocity depends on the local matter density, instead of the global
density. Second, dark matter halos are biased tracers of the underlying mass
distribution, thus halos tend to be located preferentially at high density
regions. For the former, we develop an empirical model calibrated with N-body
simulations, while for the latter, we use a conventional halo bias models based
on the extended Press-Schechter model combined with an empirical log-normal
probability distribution function of the mass density distribution. We find
that compared with linear theory, the present model significantly improves the
accuracy of predictions of statistical properties of the halo peculiar velocity
field including the velocity dispersion, the probability distribution function,
and the pairwise velocity dispersion at large separations. Thus our model
predictions may be useful in analyzing future observations of the peculiar
velocities of galaxy clusters.Comment: This paper was published in MNRAS, 343, 1312 (2003). Owing to an
error in numerical computations, some incorrect results were presented there.
Erratum is to be published in MNRAS. Conclusions of the original version are
unaffected by the correction. This version supersedes the original versio
Properties of host haloes of Lyman-break galaxies and Lyman-alpha Emitters from their number densities and angular clustering
We explore empirical relations between three different populations of
high-redshift galaxies and their hosting dark halos employing the halo model
approach. Specifically we consider Lyman-break galaxies at z\sim4 and at
z\sim5, and Lyman-Alpha emitters at z\simeq 4.86. We adopt a halo occupation
function prescription to parameterize the properties of their hosting halos and
the efficiency of halo-dependent star formation. We find that the two LBG
samples are well described by the halo model with an appropriate HOF. We obtain
constraints on properties of their hosting halos. A typical mass of hosting
halos for LBGs is 5\times10^{11}h^{-1}M_\odot and the expected number of LBGs
per halo is \sim0.5, therefore there is an approximate one-to-one
correspondence between halos and LBGs. We also find a sign of the minimum mass
of LBG hosting halos decreasing with time. We discuss implications of these
findings on the star formation history of LBGs. On the other hand, for LAEs,
our simple HOF prescription fails to reproduce simultaneously the observed
angular correlation function and the number density. This might imply either
that the distribution of LAEs within hosting halos differs from that of dark
matter, or that the strong large-scale correlation is due to the existence of
an unusual, large overdense region, and so the survey region is not a
representative of the z\sim5 universe, the definite answer should wait for a
much wider survey of LAEs at high redshifts.Comment: 12 pages, 14 figures, revised version accepted for Publication in
MNRA
Modeling the anomaly of surface number densities of galaxies on the Galactic extinction map due to their FIR emission contamination
The most widely used Galactic extinction map (Schlegel, Finkbeiner, & Davis
1998, SFD) is constructed assuming that the observed FIR fluxes entirely come
from the Galactic dust. According to the earlier suggestion by Yahata et al.
(2007), we consider how far-infrared (FIR) emission of galaxies affects the SFD
map. We first compute the surface number density of SDSS DR7 galaxies as a
function of the -band extinction, . We confirm that the
surface densities of those galaxies positively correlate with
for , as first discovered by Yahata et al. (2007) for SDSS
DR4 galaxies. Next we construct an analytic model to compute the surface
density of galaxies taking account of the contamination of their FIR emission.
We adopt a log-normal probability distribution for the ratio of and -band luminosities of each galaxy, . Then we search for the mean and r.m.s values of that fit
the observed anomaly using the analytic model. The required values to reproduce
the anomaly are roughly consistent with those measured from the stacking
analysis of SDSS galaxies (Kashiwagi, Yahata, & Suto 2013). Due to the
limitation of our statistical modeling, we are not yet able to remove the FIR
contamination of galaxies from the extinction map. Nevertheless the agreement
with the model prediction suggests that the FIR emission of galaxies is mainly
responsible for the observed anomaly. While the corresponding systematic error
in the Galactic extinction map is 0.1 to 1mmag, it is directly correlated with
galaxy clustering, and thus needs to be carefully examined in precision
cosmology.Comment: 20 pages, 12 figures, accepted for publication in Ap
- âŚ