104 research outputs found
Primordial Non-Gaussianity from LAMOST Surveys
The primordial non-Gaussianity (PNG) in matter density perturbation is a very
powerful probe of the physics of the very early Universe. The local PNG can
induce a distinct scale-dependent bias on the large scale structure
distribution of galaxies and quasars, which could be used for constraining it.
We study the detection limits on PNG from the surveys of the LAMOST telescope.
The cases of the main galaxy survey, the luminous red galaxy (LRG) survey, and
the quasar survey of different magnitude limits are considered. We find that
the MAIN1 sample (i.e. the main galaxy survey with one magnitude deeper than
the SDSS main galaxy survey, or r<18.8) could only provide very weak constraint
on PNG. For the MAIN2 sample (r<19.8) and the LRG survey, the 2\sigma (95.5%)
limit on the PNG parameter f_{NL} are |f_{NL}|<145 and |f_{NL}|<114
respectively, comparable to the current limit from cosmic microwave background
(CMB) data. The quasar survey could provide much more stringent constraint, and
we find that the 2\sigma limit for |f_{NL}| is between 50 and 103, depending on
the magnitude limit of the survey. With Planck-like priors on cosmological
parameters, the quasar survey with g<21.65 would improve the constraints to
|f_{NL}|<43 (2\sigma). We also discuss the possibility of further tightening
the constraint by using the relative bias method proposed by Seljak(2008).Comment: 8 pages, 2 figures, RAA accepte
Forecasts on the Dark Energy and Primordial Non-Gaussianity Observations with the Tianlai Cylinder Array
The Tianlai experiment is dedicated to the observation of large scale
structures (LSS) by the 21 cm intensity mapping technique. In this paper we
make forecasts on its capability at observing or constraining the dark energy
parameters and the primordial non-Gaussianity. From the LSS data one can use
the baryon acoustic oscillation (BAO) and the growth rate derived from the
redshift space distortion (RSD) to measure the dark energy density and equation
of state. The primordial non-Gaussianity can be constrained either by looking
for scale-dependent bias in the power spectrum, or by using the bispectrum.
Here we consider three cases: the Tianlai cylinder array pathfinder which is
currently being built, an upgrade of the pathfinder array with more receiver
units, and the full-scale Tianlai cylinder array. Using the full-scale Tianlai
experiment, we expect and
from the BAO and RSD measurements,
from the power spectrum measurements with scale-dependent bias, and
and from the bispectrum measurements.Comment: Accepted for publication in Ap
BSG alignment of SDSS galaxy groups
We study the alignment signal between the distribution of brightest satellite
galaxies (BSGs) and the major axis of their host groups using SDSS group
catalog constructed by Yang et al. (2007). After correcting for the effect of
group ellipticity, a statistically significant (~ 5\sigma) major-axis alignment
is detected and the alignment angle is found to be 43.0 \pm 0.4 degrees. More
massive and richer groups show stronger BSG alignment. The BSG alignment around
blue BCGs is slightly stronger than that around red BCGs. And red BSGs have
much stronger major-axis alignment than blue BSGs. Unlike BSGs, other
satellites do not show very significant alignment with group major axis. We
further explore the BSG alignment in semi-analytic model (SAM) constructed by
Guo et al. (2011). We found general good agreement with observations: BSGs in
SAM show strong major-axis alignment which depends on group mass and richness
in the same way as observations; and none of other satellites exhibit prominent
alignment. However, discrepancy also exists in that the SAM shows opposite BSG
color dependence, which is most probably induced by the missing of large scale
environment ingredient in SAM. The combination of two popular scenarios can
explain the detected BSG alignment. The first one: satellites merged into the
group preferentially along the surrounding filaments, which is strongly aligned
with the major axis of the group. The second one: BSGs enter their host group
more recently than other satellites, then will preserve more information about
the assembling history and so the major-axis alignment. In SAM, we found
positive evidence for the second scenario by the fact that BSGs merged into
groups statistically more recently than other satellites. On the other hand,
although is opposite in SAM, the BSG color dependence in observation might
indicate the first scenario as well.Comment: 8 pages, 11 figures, ApJ accepte
Topology of large scale structure as test of modified gravity
The genus of the iso-density contours is a robust measure of the topology of
large scale structure, and it is relatively insensitive to nonlinear
gravitational evolution, galaxy bias and redshift-space distortion. We show
that the growth of density fluctuations is scale-dependent even in the linear
regime in some modified gravity theories, which opens a new possibility of
testing the theories observationally. We propose to use the genus of the
iso-density contours, an intrinsic measure of the topology of large scale
structure, as a statistic to be used in such tests. In Einstein's general
theory of relativity, density fluctuations are growing at the same rate on all
scales in the linear regime, and the genus per comoving volume is almost
conserved as structures are growing homologously, so we expect that the
genus-smoothing scale relation is basically time-independent. However, in some
modified gravity models where structures grow with different rates on different
scales, the genus-smoothing scale relation should change over time. This can be
used to test the gravity models with large scale structure observations. We
studied the case of the f(R) theory, DGP braneworld theory as well as the
parameterized post-Friedmann (PPF) models. We also forecast how the modified
gravity models can be constrained with optical/IR or redshifted 21cm radio
surveys in the near future.Comment: Introduction and discussion expanded and refined, conclusion
unchanged, 10 pages, 8 figures. ApJ accepte
On Measuring the 21 cm Global Spectrum of the Cosmic Dawn with an Interferometer Array
We theoretically investigate the recovery of global spectrum (monopole) from
visibilities (cross-correlation only) measured by the interferometer array and
the feasibility of extracting 21 cm signal of cosmic dawn. In our approach, the
global spectrum is obtained by solving the monopole and higher-order components
simultaneously from the visibilities measured with up to thousands of
baselines. Using this algorithm, the monopole of both foreground and the 21 cm
signal can be correctly recovered in a broad range of conditions. We find that
a 3D baseline distribution can have much better performance than a 2D (planar)
baseline distribution, particularly when there is a lack of shorter baselines.
We simulate for ground-based 2D and 3D array configurations, and a cross-shaped
space array located at the Sun-Earth L2 point that can form 3D baselines
through orbital precession. In all simulations we obtain good recovered global
spectrum, and successfully extract the 21 cm signal from it, with reasonable
number of antennas and observation time.Comment: 18 pages, 23 figures, accepted for publication in Ap
Observational constraints on cosmic neutrinos and dark energy revisited
Using several cosmological observations, i.e. the cosmic microwave background
anisotropies (WMAP), the weak gravitational lensing (CFHTLS), the measurements
of baryon acoustic oscillations (SDSS+WiggleZ), the most recent observational
Hubble parameter data, the Union2.1 compilation of type Ia supernovae, and the
HST prior, we impose constraints on the sum of neutrino masses (\mnu), the
effective number of neutrino species (\neff) and dark energy equation of
state (), individually and collectively. We find that a tight upper limit on
\mnu can be extracted from the full data combination, if \neff and are
fixed. However this upper bound is severely weakened if \neff and are
allowed to vary. This result naturally raises questions on the robustness of
previous strict upper bounds on \mnu, ever reported in the literature. The
best-fit values from our most generalized constraint read
\mnu=0.556^{+0.231}_{-0.288}\rm eV, \neff=3.839\pm0.452, and
at 68% confidence level, which shows a firm lower limit on
total neutrino mass, favors an extra light degree of freedom, and supports the
cosmological constant model. The current weak lensing data are already helpful
in constraining cosmological model parameters for fixed . The dataset of
Hubble parameter gains numerous advantages over supernovae when ,
particularly its illuminating power in constraining \neff. As long as is
included as a free parameter, it is still the standardizable candles of type Ia
supernovae that play the most dominant role in the parameter constraints.Comment: 39 pages, 15 figures, 7 tables, accepted to JCA
The 21-cm forest as a simultaneous probe of dark matter and cosmic heating history
The absorption features in spectra of high-redshift background radio sources,
caused by hyperfine structure lines of hydrogen atoms in the intervening
structures, are known collectively as the 21-cm forest. They provide a unique
probe of small-scale structures during the epoch of reionization, and can be
used to constrain the properties of the dark matter (DM) thought to govern
small-scale structure formation. However, the signals are easily suppressed by
heating processes that are degenerate with a warm DM model. Here we propose a
probe of both the DM particle mass and the heating history of the Universe,
using the one-dimensional power spectrum of the 21-cm forest. The
one-dimensional power spectrum measurement not only breaks the DM model
degeneracy but also increases the sensitivity, making the probe actually
feasible. Making 21-cm forest observations with the upcoming Square Kilometre
Array has the potential to simultaneously determine both the DM particle mass
and the heating level in the early Universe, shedding light on the nature of DM
and the first galaxies.Comment: 53 pages, 6 figures, 2 extended data figures, 9 supplementary
figures. Published in Nature Astronom
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