22 research outputs found
The three-point correlation function of galaxies: comparing halo occupation models with observations
We present models for the three-point correlation function (3PCF) of both dark matter and galaxies. We show that models based on the halo model can reasonably match the dark-matter 3PCF obtained from high-resolution N-body simulations. On small scales (r≲ 0.5 h−1 Mpc) the 3PCF is sensitive to details regarding the density distributions of dark-matter haloes. On larger scales (r≳ 2.0 h−1 Mpc) the results are very sensitive to the abundance of the few most prominent haloes. Using the conditional luminosity function, we also construct models for the 3PCF of galaxies, which we test against large mock galaxy samples. The bias of the galaxy distribution with respect to the dark matter, and the finite number of galaxies that can be hosted by individual haloes, significantly reduce the normalized three-point correlation function with respect to that of dark matter. Contrary to the 3PCF of the dark matter, the galaxy 3PCF is much less sensitive to details regarding the spatial number density distribution of galaxies in individual haloes or to the abundance of the few most massive systems. Finally, we show that our model based on the conditional luminosity function is in good agreement with results obtained from the 2-degree Field Galaxy Redshift Survey. In particular, the model nicely reproduces the observational finding that the 3PCF for early-type galaxies is slightly higher than that of late-type galaxies, and that there is no significant dependence of the 3PCF on galaxy luminosit
The Three-point Correlation Function of Galaxies: Comparing Halo Occupation Models with Observations
We present models for the three-point correlation function (3PCF) of both
dark matter and galaxies. We show that models based on the halo model can
reasonably match the dark matter 3PCF obtained from high-resolution -body
simulations. On small scales (r\la 0.5\mpch) the 3PCF is sensitive to details
regarding the density distributions of dark matter haloes. On larger scales (r
\ga 2.0\mpch) the results are very sensitive to the abundance of the few most
prominant haloes. Using the conditional luminosity function, we also construct
models for the 3PCF of galaxies, which we test against large mock galaxy
samples. The bias of the galaxy distrubution with respect to the dark matter,
and the finite number of galaxies that can be hosted by individual haloes,
significantly reduce the normalized three-point correlation function with
respect to that of dark matter. Contrary to the 3PCF of the dark matter, the
galaxy 3PCF is much less sensitive to details regarding the spatial number
density distribution of galaxies in individual haloes or to the abundance of
the few most massive systems. Finally, we show that our model based on the
conditional luminosity function is in good agreement with results obtained from
the 2-degree Field Galaxy Redshift Survey. In particular, the model nicely
reproduces the observational finding that the 3PCF for early-type galaxies is
slightly higher than that of late-type galaxies, and that there is no
significant dependence of the 3PCF on galaxy luminosity.Comment: 15 pages, 13 figures. 1 figure added, accepted for publication in
MNRA
Measuring the galaxy power spectrum with multiresolution decomposition -- II. diagonal and off-diagonal power spectra of the LCRS galaxies
The power spectrum estimator based on the discrete wavelet transform (DWT)
for 3-dimensional samples has been studied. The DWT estimator for
multi-dimensional samples provides two types of spectra with respect to
diagonal and off-diagonal modes, which are very flexible to deal with
configuration-related problems in the power spectrum detection. With simulation
samples and mock catalogues of the Las Campanas redshift survey (LCRS), we show
(1) the slice-like geometry of the LCRS doesn't affect the off-diagonal power
spectrum with ``slice-like'' mode; (2) the Poisson sampling with the LCRS
selection function doesn't cause more than 1- error in the DWT power
spectrum; and (3) the powers of peculiar velocity fluctuations, which cause the
redshift distortion, are approximately scale-independent. These results insure
that the uncertainties of the power spectrum measurement are under control. The
scatter of the DWT power spectra of the six strips of the LCRS survey is found
to be rather small. It is less than 1- of the cosmic variance of mock
samples in the wavenumber range h Mpc. To fit the detected
LCRS diagonal DWT power spectrum with CDM models, we find that the best-fitting
redshift distortion parameter is about the same as that obtained from
the Fourier power spectrum. The velocity dispersions for SCDM and
CDM models are also consistent with other detections with
the LCRS. A systematic difference between the best-fitting parameters of
diagonal and off-diagonal power spectra has been significantly measured. This
indicates that the off-diagonal power spectra are capable of providing
information about the power spectrum of galaxy velocity field.Comment: AAS LaTeX file, 41 pages, 10 figures included, accepted for
publication in Ap
ELM of ELM-WD: An extremely low mass hot donor star discovered in LAMOST survey
The Extremely Low Mass White Dwarfs (ELM WDs) and pre-ELM WDs are helium core
white dwarfs with mass . They are formed in close binaries
and have lost over half of their initial masses via Common Envelope (CE)
ejection or stable Roche Lobe Over Flow (RLOF). Both evolution simulations and
observations show that a lower mass limit for ELM WDs exists at
. Here we report the discovery of an extremely low mass
ELM WD, ID70904216 in LAMOST survey, that may be lower than the ELM WD mass
limit. Based on LAMOST and P200 spectroscopic observations, ID70904216 shows
orbital period 0.219658 days and radial velocity semi-amplitude
, which gives the mass function of 0.73, indicating
the companion is a compact star. The low resolution spectra shows a F type star
with without emission features. The temperature is
consistent with that derived from SED fitting() and multi-color light
curve solution(). The optical light curves, in ZTF g, r and i bands and
Catalina V band, show ellipsoidal variability with amplitudes ,
suggesting that the visible companion is heavily tidal distorted. Combining
with the distance from Gaia survey, the WD code modeling estimates that the
mass of the visible star is , and the mass of
the invisible star is . The radius of the
visible donor is . The inclination angle is constrained
between 60 and 90. The observations indicate the system is
a pre-ELM WD + WD/NS binary system with an extremely low mass hot donor below
the theoretical limit.Comment: 16 pages, 10 figure
The clustering of SDSS galaxy groups: mass and color dependence
We use a sample of galaxy groups selected from the SDSS DR 4 with an adaptive
halo-based group finder to probe how the clustering strength of groups depends
on their masses and colors. In particular, we determine the relative biases of
groups of different masses, as well as that of groups with the same mass but
with different colors. In agreement with previous studies, we find that more
massive groups are more strongly clustered, and the inferred mass dependence of
the halo bias is in good agreement with predictions for the CDM
cosmology. Regarding the color dependence, we find that groups with red
centrals are more strongly clustered than groups of the same mass but with blue
centrals. Similar results are obtained when the color of a group is defined to
be the total color of its member galaxies. The color dependence is more
prominent in less massive groups and becomes insignificant in groups with
masses \gta 10^{14}\msunh. We construct a mock galaxy redshift survey
constructed from the large Millenium simulation that is populated with galaxies
according to the semi-analytical model of Croton et al. Applying our group
finder to this mock survey, and analyzing the mock data in exactly the same way
as the true data, we are able to accurately recover the intrinsic mass and
color dependencies of the halo bias in the model. This suggests that our group
finding algorithm and our method of assigning group masses do not induce
spurious mass and/or color dependencies in the group-galaxy correlation
function. The semi-analytical model reveals the same color dependence of the
halo bias as we find in our group catalogue. In halos with M\sim
10^{12}\msunh, though, the strength of the color dependence is much stronger
in the model than in the data.Comment: 16 pages, 14 figures, Accepted for publication in ApJ. In the new
version, we add the bias of the shuffled galaxy sample. The errors are
estimated according to the covariance matrix of the GGCCF, which is then
diagonalize
Orbital parameters for an ELM white dwarf with a white dwarf companion: LAMOST J033847.06+413424.2
Double white dwarf systems are of great astrophysical importance in the field
of gravitational wave and Type Ia supernova. While the binary fraction of CO
core white dwarf is about a few percents, the extremely low mass white dwarfs
are all thought to be within binary systems. In this work, we report the
orbital solution of a double degenerate system: J033847.06+413424.24, an
extremely low mass He core white dwarf orbiting a CO core white dwarf. With
LAMOST and P200, time domain spectroscopic observations have been made and
spectral atmosphere parameters are estimated to be K and
log dex. Combining Gaia parallax, 3D extinction, and evolution
tracks, we estimate a radius of and a mass of
. With the 37 single exposure spectra, the radial velocities are
measured and the orbital parameters are estimated to be days,
km/s and km/s. The radial velocity based system
ephemeris is also provided. The light curves from several photometric surveys
show no orbital modulation. The orbital solution suggests that the invisible
companion has a minimum mass of about 0.60 and is
for an inclination of , indicating most probably a CO
core white dwarf. The system is expected to merge in about 1 Gyr. With present
period and distance ( pc) it can not irradiate strong enough
gravitational wave for LISA. More double degenerate systems are expected to be
discovered and parameterized as the LAMOST survey goes on.Comment: 12 pages, 11 figure
Log-Poisson Non-Gaussianity of Ly Transmitted Flux Fluctuations at High Redshift
We investigate the non-Gaussian features of the IGM at redshift
using Ly transmitted flux of quasar absorption spectra and cosmological
hydrodynamic simulation of the concordance CDM universe. We show that
the neutral hydrogen mass density field and Ly transmitted flux
fluctuations possess all the non-Gaussian features predicted by the log-Poisson
hierarchy, which depends only on two dimensionless parameters and
, describing, respectively, the intermittence and singularity of the
random fields. We find that the non-Gaussianity of the Ly transmitted
flux of quasars from to can be well reconstructed by the
hydrodynamical simulation samples. Although the Gunn-Peterson optical depth and
its variance underwent a significant evolution in the redshift range of , the intermittency measured by is almost redshift-independent in
this range. More interesting, the intermittency of quasar's absorption spectra
on physical scales hMpc in redshift are found to be
about the same as that on physical scales hMpc at redshifts . Considering the Jeans length is less than 0.1 hMpc at , and
hMpc at , these results imply that the nonlinear evolution
in high and low redshifts will lead the cosmic baryon fluid to a state similar
to fully developed turbulence. The log-Poisson high order behavior of current
high redshift data of quasar's spectrum can be explained by uniform UV
background in the redshift range considered. We also studied the log-Poisson
non-Gaussianity by considering inhomogeneous background. With several
simplified models of inhomogeneous background, we found the effect of the
inhomogeneous background on the log-Poisson non-Gaussianity is not larger than
1-sigma.Comment: 12 pages 10 figures, accepted by MNRA
Galaxies and stars: basic building blocks of the universe
This paper is a review report which was presented at the "United Nations/European Space Agency workshop on Basic Space Science", Bangalore, IndiaSIGLEITItal