96 research outputs found
The Formation History of Subhalos and the Evolution of Satellite Galaxies
Satellites constitute an important fraction of the overall galaxy population
and are believed to form in dark matter subhalos. Here we use the cosmological
hydrodynamic simulation TNG100 to investigate how the formation histories of
subhalos affect the properties and evolution of their host galaxies. We use a
scaled formation time () to characterize the mass assembly
histories of the subhalos before they are accreted by massive host halos. We
find that satellite galaxies in young subhalos (low ) are less
massive and more gas rich, and have stronger star formation and a higher
fraction of ex situ stellar mass than satellites in old subhalos (high ). Furthermore, these low satellites require longer timescales
to be quenched as a population than the high counterparts. We find
very different merger histories between satellites in fast accretion (FA,
) subhalos. For FA
satellites, the galaxy merger frequency dramatically increases just after
accretion, which enhances the star formation at accretion. While, for SA
satellites, the mergers occur smoothly and continuously across the accretion
time. Moreover, mergers with FA satellites happen mainly after accretion, while
a contrary trend is found for SA satellites. Our results provide insight into
the evolution and star formation quenching of the satellite population.Comment: 21 pages, 10 figures, accepted for publication in Ap
Revealing the cosmic web dependent halo bias
Halo bias is the one of the key ingredients of the halo models. It was shown
at a given redshift to be only dependent, to the first order, on the halo mass.
In this study, four types of cosmic web environments: clusters, filaments,
sheets and voids are defined within a state of the art high resolution -body
simulation. Within those environments, we use both halo-dark matter
cross-correlation and halo-halo auto correlation functions to probe the
clustering properties of halos. The nature of the halo bias differs strongly
among the four different cosmic web environments we describe. With respect to
the overall population, halos in clusters have significantly lower biases in
the {} mass range. In other
environments however, halos show extremely enhanced biases up to a factor 10 in
voids for halos of mass {}. Such a strong
cosmic web environment dependence in the halo bias may play an important role
in future cosmological and galaxy formation studies. Within this cosmic web
framework, the age dependency of halo bias is found to be only significant in
clusters and filaments for relatively small halos \la 10^{12.5}\msunh.Comment: 14 pages, 14 figures, ApJ accepte
ELUCID - Exploring the Local Universe with reConstructed Initial Density field III: Constrained Simulation in the SDSS Volume
A method we developed recently for the reconstruction of the initial density
field in the nearby Universe is applied to the Sloan Digital Sky Survey Data
Release 7. A high-resolution N-body constrained simulation (CS) of the
reconstructed initial condition, with particles evolved in a 500 Mpc/h
box, is carried out and analyzed in terms of the statistical properties of the
final density field and its relation with the distribution of SDSS galaxies. We
find that the statistical properties of the cosmic web and the halo populations
are accurately reproduced in the CS. The galaxy density field is strongly
correlated with the CS density field, with a bias that depend on both galaxy
luminosity and color. Our further investigations show that the CS provides
robust quantities describing the environments within which the observed
galaxies and galaxy systems reside. Cosmic variance is greatly reduced in the
CS so that the statistical uncertainties can be controlled effectively even for
samples of small volumes.Comment: submitted to ApJ, 19 pages, 22 figures. Please download the
high-resolution version at http://staff.ustc.edu.cn/~whywang/paper
Multifactor dimensionality reduction analysis of syndrome characteristics of chronic persistent asthma
AbstractObjectiveTo analyze the syndrome characteristics in patients with chronic persistent asthma.Methods365 patients (121 males, 244 females, 60.8Β Β±Β 29.1 years old) with chronic persistent asthma were enrolled in this cross-sectional study. The information of syndrome, symptoms, signs, tongue coating and pulse were collected from all patients. The syndrome characteristics of chronic persistent asthma were examined through the multifactor dimensionality reduction (MDR) analysis and the results were verified by the Chi-square test.ResultsThe results of the MDR analysis and the Chi-square test showed the following positive correlation of the interaction among: the deficiency syndrome of the lung and spleen and deep pulse, disinclination to talk due to lack of qi, fatigue, lassitude and thick tongue coating; the deficiency syndrome of the lung and kidney and dizziness and disinclination to talk due to lack of qi, fatigue, lassitude and pallid complexion; the syndrome of phlegm-heat obstructing the lung and rapid pulse, abdominal distension, disinclination to talk due to lack of qi, frequent urination and lassitude; the syndrome of phlegm-dampness obstructing the lung and disinclination to talk due to lack of qi, greasy coating, fatigue and lassitude. (PΒ <Β .05 for all).ConclusionThe syndrome of chronic persistent asthma is characterized by fatigue and lassitude due to dysfunction of the lung, spleen and kidney
Mapping the real space distributions of galaxies in SDSS DR7: I. Two Point Correlation Functions
Using a method to correct redshift space distortion (RSD) for individual
galaxies, we mapped the real space distributions of galaxies in the Sloan
Digital Sky Survey (SDSS) Data Release 7 (DR7). We use an ensemble of mock
catalogs to demonstrate the reliability of our method. Here as the first paper
in a series, we mainly focus on the two point correlation function (2PCF) of
galaxies. Overall the 2PCF measured in the reconstructed real space for
galaxies brighter than agrees with the direct
measurement to an accuracy better than the measurement error due to cosmic
variance, if the reconstruction uses the correct cosmology. Applying the method
to the SDSS DR7, we construct a real space version of the main galaxy catalog,
which contains 396,068 galaxies in the North Galactic Cap with redshifts in the
range . The Sloan Great Wall, the largest known
structure in the nearby Universe, is not as dominant an over-dense structure as
appears to be in redshift space. We measure the 2PCFs in reconstructed real
space for galaxies of different luminosities and colors. All of them show clear
deviations from single power-law forms, and reveal clear transitions from
1-halo to 2-halo terms. A comparison with the corresponding 2PCFs in redshift
space nicely demonstrates how RSDs boost the clustering power on large scales
(by about at scales ) and suppress it on
small scales (by about at a scale of ).Comment: 19 pages, 13 figure
Mapping the Real Space Distributions of Galaxies in SDSS DR7: II. Measuring the growth rate, clustering amplitude of matter and biases of galaxies at redshift
We extend the real-space mapping method developed in Shi et at. (2016) so
that it can be applied to flux-limited galaxy samples. We use an ensemble of
mock catalogs to demonstrate the reliability of this extension, showing that it
allows for an accurate recovery of the real-space correlation functions and
galaxy biases. We also demonstrate that, using an iterative method applied to
intermediate-scale clustering data, we can obtain an unbiased estimate of the
growth rate of structure , which is related to the clustering
amplitude of matter, to an accuracy of . Applying this method to the
Sloan Digital Sky Survey (SDSS) Data Release 7 (DR7), we construct a real-space
galaxy catalog spanning the redshift range , which
contains 584,473 galaxies in the north Galactic cap (NGC). Using this data, we
infer \fss at a median redshift , which is consistent with the WMAP9
cosmology at the level. By combining this measurement with the
real-space clustering of galaxies and with galaxy-galaxy weak lensing
measurements for the same sets of galaxies, we are able to break the degeneracy
between , , and . From the SDSS DR7 data alone, we obtain the
following cosmological constraints at redshift :
, , and
, ,
, and for galaxies within
different absolute magnitude bins and , respectively
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