127 research outputs found
Halo stochasticity in global clustering analysis
In the present work we study the statistics of haloes, which in the halo
model determines the distribution of galaxies. Haloes are known to be biased
tracer of dark matter, and at large scales it is usually assumed there is no
intrinsic stochasticity between the two fields. Following the work of Seljak &
Warren (2004), we explore how correct this assumption is and, moving a step
further, we try to qualify the nature of stochasticity. We use Principal
Component Analysis applied to the outputs of a cosmological N-body simulation
to: (1) explore the behaviour of stochasticity in the correlation between
haloes of different masses; (2) explore the behaviour of stochasticity in the
correlation between haloes and dark matter. We show results obtained using a
catalogue with 2.1 million haloes, from a PMFAST simulation with box size of
1000h^{-1}Mpc. In the relation between different populations of haloes we find
that stochasticity is not-negligible even at large scales. In agreement with
the conclusions of Tegmark & Bromley (1999) who studied the correlations of
different galaxy populations, we found that the shot-noise subtracted
stochasticity is qualitatively different from `enhanced' shot noise and,
specifically, it is dominated by a single stochastic eigenvalue. We call this
the `minimally stochastic' scenario, as opposed to shot noise which is
`maximally stochastic'. In the correlation between haloes and dark matter, we
find that stochasticity is minimized, as expected, near the dark matter peak (k
~ 0.02 h Mpc^{-1} for a LambdaCDM cosmology) and, even at large scales, it is
of the order of 15 per cent above the shot noise. Moreover, we find that the
reconstruction of the dark matter distribution is improved when we use
eigenvectors as tracers of the bias. [Abridged]Comment: 9 pages, 12 figures. Submitted to MNRA
In-ovo feeding with creatine monohydrate: implications for chicken energy reserves and breast muscle development during the pre-post hatching period
The most dynamic period throughout the lifespan of broiler chickens is the pre-post-hatching period, entailing profound effects on their energy status, survival rate, body weight, and muscle growth. Given the significance of this pivotal period, we evaluated the effect of in-ovo feeding (IOF) with creatine monohydrate on late-term embryos’ and hatchlings’ energy reserves and post-hatch breast muscle development. The results demonstrate that IOF with creatine elevates the levels of high-energy-value molecules (creatine and glycogen) in the liver, breast muscle and yolk sac tissues 48 h post IOF, on embryonic day 19 (p < 0.03). Despite this evidence, using a novel automated image analysis tool on day 14 post-hatch, we found a significantly higher number of myofibers with lower diameter and area in the IOF creatine group compared to the control and IOF NaCl groups (p < 0.004). Gene expression analysis, at hatch, revealed that IOF creatine group had significantly higher expression levels of myogenin (MYOG) and insulin-like growth factor 1 (IGF1), related to differentiation of myogenic cells (p < 0.01), and lower expression of myogenic differentiation protein 1 (MyoD), related to their proliferation (p < 0.04). These results imply a possible effect of IOF with creatine on breast muscle development through differential expression of genes involved in myogenic proliferation and differentiation. The findings provide valuable insights into the potential of pre-hatch enrichment with creatine in modulating post-hatch muscle growth and development
Three-Point Correlations in Weak Lensing Surveys: Model Predictions and Applications
We use the halo model of clustering to compute two- and three-point
correlation functions for weak lensing, and apply them in a new statistical
technique to measure properties of massive halos. We present analytical results
on the eight shear three-point correlation functions constructed using
combination of the two shear components at each vertex of a triangle. We
compare the amplitude and configuration dependence of the functions with
ray-tracing simulations and find excellent agreement for different scales and
models. These results are promising, since shear statistics are easier to
measure than the convergence. In addition, the symmetry properties of the shear
three-point functions provide a new and precise way of disentangling the
lensing E-mode from the B-mode due to possible systematic errors.
We develop an approach based on correlation functions to measure the
properties of galaxy-group and cluster halos from lensing surveys. Shear
correlations on small scales arise from the lensing matter within halos of mass
M > 10^13 solar masses. Thus the measurement of two- and three-point
correlations can be used to extract information on halo density profiles,
primarily the inner slope and halo concentration. We demonstrate the
feasibility of such an analysis for forthcoming surveys. We include covariances
in the correlation functions due to sample variance and intrinsic ellipticity
noise to show that 10% accuracy on profile parameters is achievable with
surveys like the CFHT Legacy survey, and significantly better with future
surveys. Our statistical approach is complementary to the standard approach of
identifying individual objects in survey data and measuring their properties.Comment: 30 pages, 21 figures. Corrected typos in equations (23) and (28).
Matches version for publication in MNRA
The VIMOS-VLT Deep Survey. The dependence of clustering on galaxy stellar mass at z~1
Aims: We use the VVDS-Deep first-epoch data to measure the dependence of
galaxy clustering on galaxy stellar mass, at z~0.85.
Methods: We measure the projected correlation function wp(rp) for sub-samples
with 0.5<z<1.2 covering different mass ranges between 10^9 and 10^11 Msun. We
quantify in detail the observational selection biases using 40 mock catalogues
built from the Millennium run and semi-analytic models.
Results: Our simulations indicate that serious incompleteness in mass is
present only for log(M/Msun)<9.5. In the mass range log(M/Msun)=[9.0-9.5], the
photometric selection function of the VVDS misses 2/3rd of the galaxies. The
sample is virtually 100% complete above 10^10 Msun. We present the first direct
evidence for a clear dependence of clustering on the galaxy stellar mass at
z~0.85. The clustering length increases from r0 ~ 2.76 h^-1 Mpc for galaxies
with mass M>10^9 Msun to r0 ~ 4.28 h^-1 Mpc for galaxies more massive than
10^10.5 Msun. At the same time, the slope increases from ~ 1.67 to ~ 2.28.
A comparison of the observed wp(rp) to local measurements by the SDSS shows
that the evolution is faster for objects less massive than ~10^10.5 Msun. This
is interpreted as a higher dependence on redshift of the linear bias b_L for
the more massive objects. While for the most massive galaxies b_L decreases
from 1.5+/-0.2 at z~0.85 to 1.33+/-0.03 at z~0.15, the less massive population
maintains a virtually constant value b_L~1.3. This result is in agreement with
a scenario in which more massive galaxies formed at high redshift in the
highest peaks of the density field, while less massive objects form at later
epochs from the more general population of dark-matter halos.Comment: 13 pages, 10 figures, accepted in A&
Large Scale Structure of the Universe
Galaxies are not uniformly distributed in space. On large scales the Universe
displays coherent structure, with galaxies residing in groups and clusters on
scales of ~1-3 Mpc/h, which lie at the intersections of long filaments of
galaxies that are >10 Mpc/h in length. Vast regions of relatively empty space,
known as voids, contain very few galaxies and span the volume in between these
structures. This observed large scale structure depends both on cosmological
parameters and on the formation and evolution of galaxies. Using the two-point
correlation function, one can trace the dependence of large scale structure on
galaxy properties such as luminosity, color, stellar mass, and track its
evolution with redshift. Comparison of the observed galaxy clustering
signatures with dark matter simulations allows one to model and understand the
clustering of galaxies and their formation and evolution within their parent
dark matter halos. Clustering measurements can determine the parent dark matter
halo mass of a given galaxy population, connect observed galaxy populations at
different epochs, and constrain cosmological parameters and galaxy evolution
models. This chapter describes the methods used to measure the two-point
correlation function in both redshift and real space, presents the current
results of how the clustering amplitude depends on various galaxy properties,
and discusses quantitative measurements of the structures of voids and
filaments. The interpretation of these results with current theoretical models
is also presented.Comment: Invited contribution to be published in Vol. 8 of book "Planets,
Stars, and Stellar Systems", Springer, series editor T. D. Oswalt, volume
editor W. C. Keel, v2 includes additional references, updated to match
published versio
Measuring our universe from galaxy redshift surveys
Galaxy redshift surveys have achieved significant progress over the last
couple of decades. Those surveys tell us in the most straightforward way what
our local universe looks like. While the galaxy distribution traces the bright
side of the universe, detailed quantitative analyses of the data have even
revealed the dark side of the universe dominated by non-baryonic dark matter as
well as more mysterious dark energy (or Einstein's cosmological constant). We
describe several methodologies of using galaxy redshift surveys as cosmological
probes, and then summarize the recent results from the existing surveys.
Finally we present our views on the future of redshift surveys in the era of
Precision Cosmology.Comment: 82 pages, 31 figures, invited review article published in Living
Reviews in Relativity, http://www.livingreviews.org/lrr-2004-
The VIMOS-VLT Deep Survey: Evolution in the Halo Occupation Number since z 1
We model the evolution of the mean galaxy occupation of dark-matter halos
over the range , using the data from the VIMOS-VLT Deep Survey
(VVDS). The galaxy projected correlation function was computed for a
set of luminosity-limited subsamples and fits to its shape were obtained using
two variants of Halo Occupation Distribution models. These provide us with a
set of best-fitting parameters, from which we obtain the average mass of a halo
and average number of galaxies per halo. We find that after accounting for the
evolution in luminosity and assuming that we are largely following the same
population, the underlying dark matter halo shows a growth in mass with
decreasing redshift as expected in a hierarchical structure formation scenario.
Using two different HOD models, we see that the halo mass grows by 90% over the
redshift interval z=[0.5,1.0]. This is the first time the evolution in halo
mass at high redshifts has been obtained from a single data survey and it
follows the simple form seen in N-body simulations with , and . This provides evidence for a rapid accretion
phase of massive halos having a present-day mass , with a merger event occuring between redshifts of 0.5
and 1.0. Futhermore, we find that more luminous galaxies are found to occupy
more massive halos irrespectively of the redshift. Finally, the average number
of galaxies per halo shows little increase from redshift z 1.0 to z
0.5, with a sharp increase by a factor 3 from z 0.5 to z 0.1,
likely due to the dynamical friction of subhalos within their host halos.Comment: 14 pages, 6 figures, 5 tables. MNRAS accepted
Clustering of 2PIGG galaxy groups with 2dFGRS galaxies
Prompted by indications from QSO lensing that there may be more mass
associated with galaxy groups than expected, we have made new dynamical infall
estimates of the masses associated with 2PIGG groups and clusters. We have
analysed the redshift distortions in the cluster-galaxy cross-correlation
function as a function of cluster membership, cross-correlating z<0.12 2PIGG
clusters and groups with the full 2dF galaxy catalogue. We have made estimates
of the dynamical infall parameter beta and new estimates of the group velocity
dispersions. We first find that the amplitude of the full 3-D redshift space
cross-correlation function, xi_{cg}, rises monotonically with group membership.
We use a simple linear-theory infall model to fit xi(sigma, pi) in the range
5<s<40h^{-1}Mpc. We find that the beta versus membership relation for the data
shows a minimum at intermediate group membership n~20 or L~2x10^11h^-2Lsun,
implying that the bias and hence M/L ratios rise by a significant factor (~5x)
both for small groups and rich clusters. However, the mocks show a systematic
shift between the location of the beta minimum and the M/L minimum at
L~10^10h^-2Lsun given by direct calculation using the known DM distribution.
Our overall conclusion is that bias estimates from dynamical infall appear to
support the minimum in star-formation efficiency at intermediate halo masses.
Nevertheless, there may still be significant systematic problems arising from
measuring beta~1/b using large-scale infall rather than M/L using small-scale
velocity dispersions.Comment: 20 pages, 32 figures, 9 table
Comparison of the VIMOS-VLT Deep Survey with the Munich semi-analytical model - I. Magnitude counts, redshift distribution, colour bimodality, and galaxy clustering
This paper presents a detailed comparison between high-redshift observations
from the VIMOS-VLT Deep Survey (VVDS) and predictions from the Munich
semi-analytical model of galaxy formation. In particular, we focus this
analysis on the magnitude, redshift, and colour distributions of galaxies, as
well as their clustering properties. We constructed 100 quasi-independent mock
catalogues, using the output of the semi-analytical model presented in De Lucia
& Blaizot (2007).We then applied the same observational selection function of
the VVDS-Deep survey, so as to carry out a fair comparison between models and
observations. We find that the semi-analytical model reproduces well the
magnitude counts in the optical bands. It tends, however, to overpredict the
abundance of faint red galaxies, in particular in the i' and z' bands. Model
galaxies exhibit a colour bimodality that is only in qualitative agreement with
the data. In particular, we find that the model tends to overpredict the number
of red galaxies at low redshift and of blue galaxies at all redshifts probed by
VVDS-Deep observations, although a large fraction of the bluest observed
galaxies is absent from the model. In addition, the model overpredicts by about
14 per cent the number of galaxies observed at 0.2<z<1 with I_AB<24. When
comparing the galaxy clustering properties, we find that model galaxies are
more strongly clustered than observed ones at all redshift from z=0.2 to z=2,
with the difference being less significant above z~1. When splitting the
samples into red and blue galaxies, we find that the observed clustering of
blue galaxies is well reproduced by the model, while red model galaxies are
much more clustered than observed ones, being principally responsible for the
strong global clustering found in the model. [abridged]Comment: 15 pages, 14 figures, accepted for publication in A&
Limits on Neutrino Mass from Cosmic Structure Formation
We consider the effect of three species of neutrinos with nearly degenerate
mass on the cosmic structure formation in a low matter-density universe within
a hierarchical clustering scenario with a flat initial perturbation spectrum.
The matching condition for fluctuation powers at the COBE scale and at the
cluster scale leads to a strong upper limit on neutrino mass. For a flat
universe with matter density parameter Omega=0.3, we obtain m_nu<0.6eV for the
Hubble constant H_0<80km/s/Mpc. Allowing for the more generous parameter space
limited by Omega11.5Gyr, the limit is 0.9eV.Comment: 4 pages with 2 figure
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