49 research outputs found
Dynamical System of Scalar Field from 2-Dimension to 3-D and its Cosmological Implication
We give the three-dimensional dynamical autonomous systems for most of the
popular scalar field dark energy models including (phantom) quintessence,
(phantom) tachyon, k-essence and general non-canonical scalar field models,
change the dynamical variables from variables to observable
related variables , and show the intimate
relationships between those scalar fields that the three-dimensional system of
k-essence can reduce to (phantom) tachyon, general non-canonical scalar field
can reduce to (phantom) quintessence and k-essence can also reduce to (phantom)
quintessence for some special cases. For the applications of the
three-dimensional dynamical systems, we investigate several special cases and
give the exactly dynamical solutions in detail. In the end of this paper, we
argue that, it is more convenient and also has more physical meaning to express
the differential equations of dynamical systems in instead of variables and to investigate the
dynamical system in 3-Dimension instead of 2-Dimension. We also raise a
question about the possibility of the chaotic behavior in the spatially flat
single scalar field FRW cosmological models in the presence of ordinary matter.Comment: 20 pages, 8 figures,some references added. Minor changes according to
the suggestions from referee
The Host Haloes of Lyman Break Galaxies and Sub-millimeter Sources
We use the observed sizes and star formation rates of Lyman-break galaxies
(LBGs) to understand their properties expected in the hierarchical scenario of
galaxy formation. The observed size distribution constrains the masses of the
host haloes of LBGs from below, while the observed star-formation distribution
constrains the masses from above. Assuming a flat CDM model with a cosmological
constant (), we find that consistency with observations
requires the circular velocities of LBG host haloes to be in the range
100--. The predicted comoving correlation length of these
objects is , and the predicted velocity dispersion of
their stellar contents is typically . The same prescription
applied to larger haloes in the CDM cosmogony predicts the existence of
galaxies with star formation rates at
redshift . We explore the possibility of identifying these galaxies to
be the bright sub-millimeter (sub-mm) sources detected by SCUBA. The model
predicts that the host haloes of these sub-mm sources are massive. These
galaxies are predicted to be strongly correlated, with a comoving correlation
length of . The descendants of the bright sub-mm
sources should reside in clusters of galaxies at the present time, and it is
likely that these objects are the progenitors of giant ellipticals. The model
predicts the existence of a relatively bright and red population of galaxies at
, which may be observed in the K-band.Comment: 27 pages, 14 figures, submitted to MNRA
The Fundamental Plane of Spiral Galaxies: Theoretical Expectations
Current theory of disk galaxy formation is used to study fundamental-plane
(FP) type of relations for disk galaxies. We examine how the changes in model
parameters affect these relations and explore the possibility of using such
relations to constrain theoretical models. The distribution of galaxy disks in
the space of their fundamental properties are predicted to be concentrated in a
plane, with the Tully-Fisher (TF) relation (a relation between luminosity
and maximum rotation velocity ) being an almost edge-on view. Using
rotation velocities at larger radii generally leads to larger TF scatter. In
searching for a third parameter, we find that both the disk scale-length
(or surface brightness) and the rotation-curve shape are correlated with the TF
scatter. The FP relation in the (\Log L, \Log V_m, \Log R_d)-space obtained
from the theory is , with and , consistent with the preliminary result we obtain
from observational data. Among the model parameters we probe, variation in any
of them can generate significant scatter in the TF relation, but the effects of
the spin parameter and halo concentration can be reduced significantly by
introducing while the scatter caused by varying (the ratio between
disk mass and halo mass) is most effectively reduced by introducing the
parameters which describes the rotation-curve shape. The TF and FP relations
combined should therefore provide useful constraints on models of galaxy
formation.Comment: 25 pages, 11 figures, 4 tables; submitted to MNRA
Mass Reconstruction of Galaxy-scale Strong Gravitational Lenses Using a Broken Power-law Model
With mock strong gravitational lensing images, we investigate the performance
of the broken power-law (BPL) model proposed by \citet{2020ApJ...892...62D} on
the mass reconstruction of galaxy-scale lenses. An end-to-end test is carried
out, including the creation of mock strong lensing images, the subtraction of
lens light, and the reconstruction of lensed images, where the lenses are
selected from the galaxies in the Illustris-1 simulation. We notice that,
regardless of the adopted mass models (the BPL model or its special cases), the
Einstein radius can be robustly determined from imaging data alone, and the
median bias is typically less than . Away from the Einstein radius, the
lens mass distribution tends to be harder to measure, especially at radii where
there are no lensed images detected. We find that, with rigid priors, the BPL
model can clearly outperform the single power-law models by achieving
median bias on the radial convergence profile within the Einstein radius. As
for the source light reconstructions, they are found to be sensitive to both
lens light contamination and lens mass models, where the BPL model with rigid
priors still performs best when there is no lens light contamination. We show
that, by correcting for the projection effect, the BPL model can estimate the
aperture and luminosity weighted line-of-sight velocity dispersions to an
accuracy of scatter. These results highlight the great potential of
the BPL model in strong lensing related studies.Comment: Accepted for publication in ApJ, 24 pages, 13 figures, 2 table
Galaxy-galaxy weak-lensing measurement from SDSS: II. host halo properties of galaxy groups
As the second paper of a series on studying galaxy-galaxy lensing signals
using the Sloan Digital Sky Survey Data Release 7 (SDSS DR7), we present our
measurement and modelling of the lensing signals around groups of galaxies. We
divide the groups into four halo mass bins, and measure the signals around four
different halo-center tracers: brightest central galaxy (BCG),
luminosity-weighted center, number-weighted center and X-ray peak position. For
X-ray and SDSS DR7 cross identified groups, we further split the groups into
low and high X-ray emission subsamples, both of which are assigned with two
halo-center tracers, BCGs and X-ray peak positions. The galaxy-galaxy lensing
signals show that BCGs, among the four candidates, are the best halo-center
tracers. We model the lensing signals using a combination of four
contributions: off-centered NFW host halo profile, sub-halo contribution,
stellar contribution, and projected 2-halo term. We sample the posterior of 5
parameters i.e., halo mass, concentration, off-centering distance, sub halo
mass, and fraction of subhalos via a MCMC package using the galaxy-galaxy
lensing signals. After taking into account the sampling effects (e.g. Eddington
bias), we found the best fit halo masses obtained from lensing signals are
quite consistent with those obtained in the group catalog based on an abundance
matching method, except in the lowest mass bin. Subject headings: (cosmology:)
gravitational lensing, galaxies: clusters: generalComment: 12 pages, 7 figures, submitted to Ap