76 research outputs found
Alignments of galaxies within cosmic filaments from SDSS DR7
Using a sample of galaxy groups selected from the Sloan Digital Sky Survey
Data Release 7 (SDSS DR7), we examine the alignment between the orientation of
galaxies and their surrounding large scale structure in the context of the
cosmic web. The latter is quantified using the large-scale tidal field,
reconstructed from the data using galaxy groups above a certain mass threshold.
We find that the major axes of galaxies in filaments tend to be preferentially
aligned with the directions of the filaments, while galaxies in sheets have
their major axes preferentially aligned parallel to the plane of the sheets.
The strength of this alignment signal is strongest for red, central galaxies,
and in good agreement with that of dark matter halos in N-body simulations.
This suggests that red, central galaxies are well aligned with their host
halos, in quantitative agreement with previous studies based on the spatial
distribution of satellite galaxies. There is a luminosity and mass dependence
that brighter and more massive galaxies in filaments and sheets have stronger
alignment signals. We also find that the orientation of galaxies is aligned
with the eigenvector associated with the smallest eigenvalue of the tidal
tensor. These observational results indicate that galaxy formation is affected
by large-scale environments, and strongly suggests that galaxies are aligned
with each other over scales comparable to those of sheets and filaments in the
cosmic web.Comment: 11 pages, 10 figures, accepted for publication in Ap
Spin alignments of spiral galaxies within the large-scale structure from SDSS DR7
Using a sample of spiral galaxies selected from the Sloan Digital Sky Survey
Data Release 7 (SDSS DR7) and Galaxy Zoo 2 (GZ2), we investigate the alignment
of spin axes of spiral galaxies with their surrounding large scale structure,
which is characterized by the large-scale tidal field reconstructed from the
data using galaxy groups above a certain mass threshold. We find that the spin
axes of only have weak tendency to be aligned with (or perpendicular to) the
intermediate (or minor) axis of the local tidal tensor. The signal is the
strongest in a \cluster environment where all the three eigenvalues of the
local tidal tensor are positive. Compared to the alignments between halo spins
and local tidal field obtained in N-body simulations, the above observational
results are in best agreement with those for the spins of inner regions of
halos, suggesting that the disk material traces the angular momentum of dark
matter halos in the inner regions.Comment: 8 pages, 7 figures, accepted for publication in Ap
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
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
Evolution of the Galaxy - Dark Matter Connection and the Assembly of Galaxies in Dark Matter Halos
We present a new model to describe the galaxy-dark matter connection across
cosmic time, which unlike the popular subhalo abundance matching technique is
self-consistent in that it takes account of the facts that (i) subhalos are
accreted at different times, and (ii) the properties of satellite galaxies may
evolve after accretion. Using observations of galaxy stellar mass functions out
to , the conditional stellar mass function at obtained
from SDSS galaxy group catalogues, and the two-point correlation function
(2PCF) of galaxies at as function of stellar mass, we constrain
the relation between galaxies and dark matter halos over the entire cosmic
history from to the present. This relation is then used to predict
the median assembly histories of different stellar mass components within dark
matter halos (central galaxies, satellite galaxies, and halo stars). We also
make predictions for the 2PCFs of high- galaxies as function of stellar
mass. Our main findings are the following: (i) Our model reasonably fits all
data within the observational uncertainties, indicating that the CDM
concordance cosmology is consistent with a wide variety of data regarding the
galaxy population across cosmic time. (ii) ... [abridged]Comment: 37pages, 20 figures, major revision, data updated to SDSS DR7, main
conclusions remain unchange
ELUCID IV: Galaxy Quenching and its Relation to Halo Mass, Environment, and Assembly Bias
We examine the quenched fraction of central and satellite galaxies as a
function of galaxy stellar mass, halo mass, and the matter density of their
large scale environment. Matter densities are inferred from our ELUCID
simulation, a constrained simulation of local Universe sampled by SDSS, while
halo masses and central/satellite classification are taken from the galaxy
group catalog of Yang et al. The quenched fraction for the total population
increases systematically with the three quantities. We find that the
`environmental quenching efficiency', which quantifies the quenched fraction as
function of halo mass, is independent of stellar mass. And this independence is
the origin of the stellar mass-independence of density-based quenching
efficiency, found in previous studies. Considering centrals and satellites
separately, we find that the two populations follow similar correlations of
quenching efficiency with halo mass and stellar mass, suggesting that they have
experienced similar quenching processes in their host halo. We demonstrate that
satellite quenching alone cannot account for the environmental quenching
efficiency of the total galaxy population and the difference between the two
populations found previously mainly arises from the fact that centrals and
satellites of the same stellar mass reside, on average, in halos of different
mass. After removing these halo-mass and stellar-mass effects, there remains a
weak, but significant, residual dependence on environmental density, which is
eliminated when halo assembly bias is taken into account. Our results therefore
indicate that halo mass is the prime environmental parameter that regulates the
quenching of both centrals and satellites.Comment: 21 pages, 16 figures, submitted to Ap
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