5,484 research outputs found
The Redshift-Space Cluster-Galaxy Cross-Correlation Function: I. Modeling Galaxy Infall onto Millennium Simulation Clusters and SDSS Groups
The large scale infall of galaxies around massive clusters provides a
potentially powerful diagnostic of structure growth, dark energy, and
cosmological deviations from General Relativity. We develop and test a method
to recover galaxy infall kinematics (GIK) from measurements of the
redshift-space cluster-galaxy cross-correlation function \xi_{cg}(r_p,r_\pi).
Using galaxy and halo samples from the Millennium simulation, we calibrate an
analytic model of the galaxy kinematic profiles comprised of a virialized
component with an isotropic Gaussian velocity distribution and an infall
component described by a skewed 2D t-distribution with a characteristic infall
velocity v_r and separate radial and tangential dispersions. We show that
convolving the real-space cross-correlation function with this velocity
distribution accurately predicts the redshift-space \xi_{cg}, and we show that
measurements of \xi_{cg} can be inverted to recover the four distinct elements
of the GIK profiles. These in turn provide diagnostics of cluster mass
profiles, and we expect the characteristic infall velocity v_r(r) in particular
to be insensitive to galaxy formation physics that can affect velocity
dispersions within halos. As a proof of concept we measure \xi_{cg} for rich
galaxy groups in the Sloan Digital Sky Survey and recover GIK profiles for
groups in two bins of central galaxy stellar mass. The higher mass bin has a
v_r(r) curve very similar to that of 10^{14} Msun halos in the Millennium
simulation, and the recovered kinematics follow the expected trends with mass.
GIK modeling of cluster-galaxy cross-correlations can be a valuable complement
to stacked weak lensing analyses, allowing novel tests of modified gravity
theories that seek to explain cosmic acceleration.Comment: Matched to the published version (adding one figure illustrating the
position and velocity vectors). For a brief video explaining the key result
of this paper, see https://www.youtube.com/watch?v=7RB49odfSGo, or
http://v.youku.com/v_show/id_XNDcxMDY3MTQ0.html in countries where YouTube is
not accessibl
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Testing for Cointegration with Nonstationary Volatility
The paper generalises recent unit root tests for nonstationary volatility to a multivariate context. Persistent changes in the innovation variance matrix lead to size distortions in conventional cointegration tests, and possibilities of increased power by taking the time-varying volatilities and correlations into account. The testing procedures are based on a likelihood analysis of the vector autoregressive model with a conditional covariance matrix that may be estimated nonparametrically. We find that under suitable conditions, adaptation with respect to the volatility matrix process is possible, in the sense that nonparametric volatility estimation does not lead to a loss of asymptotic local power
Shape Memory Alloy Nanostructures With Coupled Dynamic Thermo-Mechanical Effects
Employing the Ginzburg-Landau phase-field theory, a new coupled dynamic
thermo-mechanical 3D model has been proposed for modeling the
cubic-to-tetragonal martensitic transformations in shape memory alloy (SMA)
nanostructures. The stress-induced phase transformations and thermo-mechanical
behavior of nanostructured SMAs have been investigated. The mechanical and
thermal hysteresis phenomena, local non-uniform phase transformations and
corresponding non-uniform temperature and deformations distributions are
captured successfully using the developed model. The predicted microstructure
evolution qualitatively matches with the experimental observations. The
developed coupled dynamic model has provided a better understanding of
underlying martensitic transformation mechanisms in SMAs, as well as their
effect on the thermo-mechanical behavior of nanostructures.Comment: 8 pages, 3 figure
Once again: Instanton method vs. WKB
A recent analytic test of the instanton method performed by comparing the
exact spectrum of the Lam potential (derived from representations
of a finite dimensional matrix expressed in terms of generators) with
the results of the tight--binding and instanton approximations as well as the
standard WKB approximation is commented upon. It is pointed out that in the
case of the Lam potential as well as others the WKB--related method
of matched asymptotic expansions yields the exact instanton result as a result
of boundary conditions imposed on wave functions which are matched in domains
of overlap.Comment: 10 pages, no figures. References list revised according to JHE
Corrections to the thermodynamics of Schwarzschild-Tangherlini black hole and the generalized uncertainty principle
We investigate the thermodynamics of Schwarzschild-Tangherlini black hole in
the context of the generalized uncertainty principle. The corrections to the
Hawking temperature, entropy and the heat capacity are obtained via the
modified Hamilton-Jacobi equation. These modifications show that the GUP
changes the evolution of Schwarzschild-Tangherlini black hole. Specially, the
GUP effect becomes susceptible when the radius or mass of black hole approach
to the order of Planck scale, it stops radiating and leads to black hole
remnant. Meanwhile, the Planck scale remnant can be confirmed through the
analysis of the heat capacity. Those phenomenons imply that the GUP may give a
way to solve the information paradox. Besides, we also investigate the
possibilities to observe the black hole at LHC, the results demonstrate that
the black hole can not be produced in the recent LHC.Comment: 12 pages, 6 figure
The Conditional Colour-Magnitude Distribution: I. A Comprehensive Model of the Colour-Magnitude-Halo Mass Distribution of Present-Day Galaxies
We formulate a model of the conditional colour-magnitude distribution (CCMD)
to describe the distribution of galaxy luminosity and colour as a function of
halo mass. It consists of two populations of different colour distributions,
dubbed pseudo-blue and pseudo-red, respectively, with each further separated
into central and satellite galaxies. We define a global parameterization of
these four colour-magnitude distributions and their dependence on halo mass,
and we infer parameter values by simultaneously fitting the space densities and
auto-correlation functions of 79 galaxy samples from the Sloan Digital Sky
Survey defined by fine bins in the colour-magnitude diagram (CMD). The model
deprojects the overall galaxy CMD, revealing its tomograph along the halo mass
direction. The bimodality of the colour distribution is driven by central
galaxies at most luminosities, though at low luminosities it is driven by the
difference between blue centrals and red satellites. For central galaxies, the
two pseudo-colour components are distinct and orthogonal to each other in the
CCMD: at fixed halo mass, pseudo-blue galaxies have a narrow luminosity range
and broad colour range, while pseudo-red galaxies have a narrow colour range
and broad luminosity range. For pseudo-blue centrals, luminosity correlates
tightly with halo mass, while for pseudo-red galaxies colour correlates more
tightly (redder galaxies in more massive haloes). The satellite fraction is
higher for redder and for fainter galaxies, with colour a stronger indicator
than luminosity. We discuss the implications of the results and further
applications of the CCMD model.Comment: 32 pages, 26 figures, accepted for publication in MNRA
Constraining the HI-Halo Mass Relation From Galaxy Clustering
We study the dependence of galaxy clustering on atomic gas mass using a
sample of 16,000 galaxies with redshift in the range of
and HI mass of , drawn from the 70% complete sample
of the Arecibo Legacy Fast ALFA survey. We construct subsamples of galaxies
with above different thresholds, and make volume-limited
clustering measurements in terms of three statistics: the projected two-point
correlation function, the projected cross-correlation function with respect to
a reference sample selected from the Sloan Digital Sky Survey, and the
redshift-space monopole moment. In contrast to previous studies, which found
no/weak HI-mass dependence, we find both the clustering amplitude on scales
above a few Mpc and the bias factors to increase significantly with increasing
HI mass for subsamples with HI mass thresholds above . For HI
mass thresholds below , while the measurements have large
uncertainties caused by the limited survey volume and sample size, the inferred
galaxy bias factors are systematically lower than the minimum halo bias factor
from mass-selected halo samples. The simple halo model, in which galaxy content
is only determined by halo mass, has difficulties in interpreting the
clustering measurements of the HI-selected samples. We extend the simple model
by including the halo formation time as an additional parameter. A model that
puts HI-rich galaxies into halos that formed late can reproduce the clustering
measurements reasonably well. We present the implications of our best-fitting
model on the correlation of HI mass with halo mass and formation time, as well
as the halo occupation distributions and HI mass functions for central and
satellite galaxies. These results are compared with the predictions from
semi-analytic galaxy formation models and hydrodynamic galaxy formation
simulations.Comment: Accepted for publication in ApJ. The 2PCF measurements are available
at http://sdss4.shao.ac.cn/guoh
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