315 research outputs found
Generating Log-normal Mock Catalog of Galaxies in Redshift Space
We present a public code to generate a mock galaxy catalog in redshift space
assuming a log-normal probability density function (PDF) of galaxy and matter
density fields. We draw galaxies by Poisson-sampling the log-normal field, and
calculate the velocity field from the linearised continuity equation of matter
fields, assuming zero vorticity. This procedure yields a PDF of the pairwise
velocity fields that is qualitatively similar to that of N-body simulations. We
check fidelity of the catalog, showing that the measured two-point correlation
function and power spectrum in real space agree with the input precisely. We
find that a linear bias relation in the power spectrum does not guarantee a
linear bias relation in the density contrasts, leading to a cross-correlation
coefficient of matter and galaxies deviating from unity on small scales. We
also find that linearising the Jacobian of the real-to-redshift space mapping
provides a poor model for the two-point statistics in redshift space. That is,
non-linear redshift-space distortion is dominated by non-linearity in the
Jacobian. The power spectrum in redshift space shows a damping on small scales
that is qualitatively similar to that of the well-known Fingers-of-God (FoG)
effect due to random velocities, except that the log-normal mock does not
include random velocities. This damping is a consequence of non-linearity in
the Jacobian, and thus attributing the damping of the power spectrum solely to
FoG, as commonly done in the literature, is misleading.Comment: 38 pages, 16 figures, code publicly available as "lognormal_galaxies"
at http://wwwmpa.mpa-garching.mpg.de/~komatsu/codes.html Matches published
version : added figures and explanatory comment
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
Joint analysis of the thermal Sunyaev-Zeldovich effect and 2MASS galaxies: Probing gas physics in the local Universe and beyond
We present a first joint analysis of the power spectra of the thermal
Sunyaev-Zeldovich (tSZ) effect measured by the Planck and the number density
fluctuations of galaxies in the 2MASS redshift survey (2MRS) catalog, including
their cross-correlation. Combining these measurements with the cosmic microwave
background (CMB) data and CMB lensing of Planck assuming a flat CDM
model, we constrain the mass bias parameter as
[, where ], i.e., the Planck
cluster mass should be lower than the true mass. The mass bias
determined by the 2MRS-tSZ cross-power spectrum alone is consistent with that
determined by the tSZ auto-power spectrum alone, suggesting that this large
mass bias is not due to obvious systematics in the tSZ data. We find that the
2MRS-tSZ cross-power spectrum is more sensitive to less massive halos than the
tSZ auto-power spectrum and it significantly improves a constraint on the mass
dependence of the mass bias. The redshift dependence is not strongly
constrained since the multipole range in which high redshift clusters mainly
contribute to the tSZ auto is dominated by the contaminating sources. We
conclude that no strong mass or redshift evolution of the mass bias is needed
to explain the data.Comment: 14 pages, 11 figures, MNRAS accepted, references correcte
The thermal and gravitational energy densities in the large-scale structure of the Universe
As cosmic structures form, matter density fluctuations collapse
gravitationally and baryonic matter is shock-heated and thermalized. We
therefore expect a connection between the mean gravitational potential energy
density of collapsed halos, , and the mean thermal
energy density of baryons, . These quantities can be obtained
using two fundamentally different estimates: we compute
using the theoretical framework of the halo model which is driven by dark
matter statistics, and measure using the Sunyaev-Zeldovich
(SZ) effect which probes the mean thermal pressure of baryons. First, we derive
that, at the present time, about 90% of originates from
massive halos with . Then, using our measurements of the SZ
background, we find that accounts for about 80% of the
kinetic energy of the baryons available for pressure in halos at . This constrains the amount of non-thermal pressure, e.g., due to bulk and
turbulent gas motion sourced by mass accretion, to be about at .Comment: 11 pages + references, 4 figures, 2 tables. (v2) Expanded discussion
on the modelling uncertainty. (v3) Fixed a minor typo in Eq.(22). Accepted
for publication in the Astrophysical Journal. Julia codes to reproduce the
figures and tables are available in
https://github.com/komatsu5147/OmegaGrav.j
Mitigating the impact of fiber assignment on clustering measurements from deep galaxy redshift surveys
We examine the impact of fiber assignment on clustering measurements from
fiber-fed spectroscopic galaxy surveys. We identify new effects which were
absent in previous, relatively shallow galaxy surveys such as Baryon
Oscillation Spectroscopic Survey . Specifically, we consider deep surveys
covering a wide redshift range from z=0.6 to z=2.4, as in the Subaru Prime
Focus Spectrograph survey. Such surveys will have more target galaxies than we
can place fibers on. This leads to two effects. First, it eliminates
fluctuations with wavelengths longer than the size of the field of view, as the
number of observed galaxies per field is nearly fixed to the number of
available fibers. We find that we can recover the long-wavelength fluctuation
by weighting galaxies in each field by the number of target galaxies. Second,
it makes the preferential selection of galaxies in under-dense regions. We
mitigate this effect by weighting galaxies using the so-called individual
inverse probability. Correcting these two effects, we recover the underlying
correlation function at better than 1 percent accuracy on scales greater than
10 Mpc/h.Comment: 17 pages, 11 figure
Investigating the influence of magnetic fields upon structure formation with AMIGA - a C code for cosmological magnetohydrodynamics
Despite greatly improved observational methods, the presence of magnetic
fields at cosmological scales and their role in the process of large-scale
structure formation still remains unclear. In this paper we want to address the
question how the presence of a hypothetical primordial magnetic field on large
scales influences the cosmic structure formation in numerical simulations. As a
tool for carrying out such simulations, we present our new numerical code
AMIGA. It combines an N-body code with an Eulerian grid-based solver for the
full set of MHD equations in order to conduct simulations of dark matter,
baryons and magnetic fields in a self-consistent way in a fully cosmological
setting. Our numerical scheme includes effective methodes to ensure proper
capturing of shocks and highly supersonic flows and a divergence-free magnetic
field. The high accuracy of the code is demonstrated by a number of numerical
tests. We then present a series of cosmological MHD simulations and confirm
that, in order to have a significant effect on the distribution of matter on
large scales, the primordial magnetic field strength would have to be
significantly higher than the current observational and theoretical
constraints.Comment: accepted by MNRAS, 24 pages, 14 figure
Baryon history and cosmic star formation in non-Gaussian cosmological models: numerical simulations
We present the first numerical, N-body, hydrodynamical, chemical simulations
of cosmic structure formation in the framework of non-Gaussian models. We study
the impact of primordial non-Gaussianities on early chemistry (e, H, H+, H-,
He, He+, He++, H2, H2+, D, D+, HD, HeH+), molecular and atomic gas cooling,
star formation, metal (C, O, Si, Fe, Mg, S) enrichment, population III (popIII)
and population II-I (popII) transition, and on the evolution of "visible"
objects. We find that non-Gaussianities can have some consequences on baryonic
structure formation at very early epochs, but the subsequent evolution at later
times washes out any difference among the various models. When assuming
reasonable values for primordial non-Gaussian perturbations, it turns out that
they are responsible for: (i) altering early molecular fractions in the cold,
dense gas phase of ~10 per cent; (ii) inducing small temperature fluctuations
of <~10 per cent during the cosmic evolution of primordial objects; (iii)
influencing the onset of the first star formation events, at z>~15, and of the
popIII/popII transition of up to some 10^7yr; (iv) determining variations of
<~10 per cent in the gas cloud and stellar mass distributions after the
formation of the first structures; (v) causing only mild variations in the
chemical history of the Universe. We stress, though, that purely non-Gaussian
effects might be difficult to address, since they are strictly twisted with
additional physical phenomena (e.g. primordial gas bulk flows, unknown
primordial popIII stellar mass function, etc.) that have similar or stronger
impact on the behaviour of the baryons.Comment: Accepted for publications on MNRAS, on April 13, 2011. Minor
revision
Primordial magnetic field constraints from the end of reionization
Primordial magnetic fields generated in the early universe are subject of
considerable investigation, and observational limits on their strength are
required to constrain the theory. Due to their impact on the reionization
process, the strength of primordial fields can be limited using the latest data
on reionization and the observed UV-luminosity function of high-redshift
galaxies. Given the steep faint-end slope of the luminosity function, faint
galaxies contribute substantial ionizing photons, and the low-luminosity cutoff
has an impact on the total budget thereof. Magnetic pressure from primordial
fields affects such cutoff by preventing collapse in halos with mass below
10^{10} M_solar (B_0 / 3 nG)^3, with B_0 the co-moving field strength. In this
letter, the implications of these effects are consistently incorporated in a
simplified model for reionization, and the uncertainties due to the
cosmological parameters, the reionization parameters and the observed UV
luminosity function are addressed. We show that the observed ionization degree
at z\sim7 leads to the strongest upper limit of B_0\lsim 2-3nG. Stronger limits
could follow from measurements of high ionization degree at z>7.Comment: 6 pages, 3 figures, resubmitted to MNRAS letter
SHOCK WAVES AND COSMIC RAY ACCELERATION IN THE OUTSKIRTS OF GALAXY CLUSTERS
The outskirts of galaxy clusters are continuously disturbed by mergers and gas infall along filaments, which in turn induce turbulent flow motions and shock waves. We examine the properties of shocks that form within r(200) in sample galaxy clusters from structure formation simulations. While most of these shocks are weak and inefficient accelerators of cosmic rays (CRs), there are a number of strong, energetic shocks which can produce large amounts of CR protons via diffusive shock acceleration. We show that the energetic shocks reside mostly in the outskirts and a substantial fraction of them are induced by infall of the warm-hot intergalactic medium from filaments. As a result, the radial profile of the CR pressure in the intracluster medium is expected to be broad, dropping off more slowly than that of the gas pressure, and might be even temporarily inverted, peaking in the outskirts. The volume-integrated momentum spectrum of CR protons inside r200 has the power-law slope of 4.25-4.5, indicating that the average Mach number of the shocks of main CR production is in the range of (Ms)(CR) approximate to 3-4. We suggest that some radio relics with relatively flat radio spectrum could be explained by primary electrons accelerated by energetic infall shocks with M-s greater than or similar to 3 induced in the cluster outskirts.open2
Dynamical Effect of the Turbulence of IGM on the Baryon Fraction Distribution
We investigate the dynamical effect of the turbulence in baryonic
intergalactic medium (IGM) on the baryon fraction distribution. In the fully
developed nonlinear regime, the IGM will evolve into the state of turbulence,
containing strong and curved shocks, vorticity and complex structures.
Turbulence would lead to the density and velocity fields of the IGM to be
different from those of underlying collisionless dark matter. Consequently, the
baryon fraction f_b will deviate from its cosmic mean . We study these
phenomena with simulation samples produced by the weighted essentially
non-oscillatory (WENO) hybrid cosmological hydrodynamic/N-body code, which is
effective of capturing shocks and complex structures. We find that the
distribution of baryon fraction is highly nonuniform on scales from hundreds
kpc to a few of Mpc, and f_b varies from as low as 1% to a few times of the
cosmic mean. We further show that the turbulence pressure in the IGM is weakly
scale-dependent and comparable to the gravitational energy density of halos
with mass around 10^11 h-1 M\odot . The baryon fraction in halos with mass
equal to or smaller than 10^11 h^-1 M\odot should be substantially lower than
f_b^cosmic. Numerical results show that f_b is decreasing from 0.8 f_b^cosmic
at halo mass scales around 10^12 h^-1 M\odot to 0.3f_b^cosmic at 10^11 h^-1
M\odot and shows further decrease when halo mass is less than 10^11 h^-1
M\odot. The strong mass dependence of f_b is similar to the observed results.
Although the simulated f_b in halos are higher than the observed value by a
factor of 2, the turbulence of the
IGM should be an important dynamical reason leading to the remarkable missing
of baryonic matter in halos with mass \leq 10^12 h^-1 M\odot.Comment: Accepted for publication in MNRAS, 12 pages, 10 figure
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