88 research outputs found
Evaluation of microalbuminuria in obese adolescents
Background: Obesity is a risk factor for metabolic syndrome with insulin resistance. Its effect on renal and cardiovascular diseases is reported in developed countries, but rarely established among adolescents in developing countries.Subjects and methods: A crosssectional study of 846 adolescents selected from 12 secondary schools in Port Harcourt, Nigeria. Obese subjects with Body Mass Index (BMI) equal to or greater than the 95th percentile for age and sex on the United States CDC growth chart were selected and studied. Urine samples of subjects without overt proteinuria were tested for microalbuminuria using the micral test strips.Results: Seventy-three of the subjects were obese giving the prevalence of obesity to be 8.6%. Microalbuminuria was present in 23 (35.4%) of the 65 obese subjects without overt proteinuria. The proportional prevalence was higher in females (42.9%), in age group 10-14years (42.2%), in subjects with hypertension (57.1%), and family history of hypertension (50.0%) and diabetes mellitus (37.5%) [p > 0.05].Conclusion: There is high prevalence of adolescent obesity, and a high prevalence of microalbuminuria among obese adolescents in Port Harcourt. We recommend efforts at reducing obesity as a means of preventing renal disease in adolescents
The clustering of galaxies as a function of their photometrically-estimated atomic gas content
We introduce a new photometric estimator of the HI mass fraction (M_HI/M_*)
in local galaxies, which is a linear combination of four parameters: stellar
mass, stellar surface mass density, NUV-r colour, and g-i colour gradient. It
is calibrated using samples of nearby galaxies (0.025<z<0.05) with HI line
detections from the GASS and ALFALFA surveys, and it is demonstrated to provide
unbiased M_HI/M_* estimates even for HI-rich galaxies. We apply this estimator
to a sample of ~24,000 galaxies from the SDSS/DR7 in the same redshift range.
We then bin these galaxies by stellar mass and HI mass fraction and compute
projected two point cross-correlation functions with respect to a reference
galaxy sample. Results are compared with predictions from current semi-analytic
models of galaxy formation. The agreement is good for galaxies with stellar
masses larger than 10^10 M_sun, but not for lower mass systems. We then extend
the analysis by studying the bias in the clustering of HI-poor or HI-rich
galaxies with respect to galaxies with normal HI content on scales between 100
kpc and ~5 Mpc. For the HI-deficient population, the strongest bias effects
arise when the HI-deficiency is defined in comparison to galaxies of the same
stellar mass and size. This is not reproduced by the semi-analytic models,
where the quenching of star formation in satellites occurs by "starvation" and
does not depend on their internal structure. HI-rich galaxies with masses
greater than 10^10 M_sun are found to be anti-biased compared to galaxies with
"normal" HI content. Interestingly, no such effect is found for lower mass
galaxies.Comment: 14 pages, 10 figures, accepted for publication in MNRAS, slightly
revised in the tex
New constraints on dark energy from the observed growth of the most X-ray luminous galaxy clusters
We present constraints on the mean matter density, Omega_m, the normalization
of the density fluctuation power spectrum, sigma_8, and the dark-energy
equation-of-state parameter, w, obtained from measurements of the X-ray
luminosity function of the largest known galaxy clusters at redshifts z<0.7, as
compiled in the Massive Cluster Survey (MACS) and the local BCS and REFLEX
galaxy cluster samples. Our analysis employs an observed mass-luminosity
relation, calibrated by hydrodynamical simulations, including corrections for
non-thermal pressure support and accounting for the presence of intrinsic
scatter. Conservative allowances for all known systematic uncertainties are
included, as are standard priors on the Hubble constant and mean baryon
density. We find Omega_m=0.28 +0.11 -0.07 and sigma_8=0.78 +0.11 -0.13 for a
spatially flat, cosmological-constant model, and Omega_m=0.24 +0.15 -0.07,
sigma_8=0.85 +0.13 -0.20 and w=-1.4 +0.4 -0.7 for a flat, constant-w model.
Future work improving our understanding of redshift evolution and observational
biases affecting the mass--X-ray luminosity relation have the potential to
significantly tighten these constraints. Our results are consistent with those
from recent analyses of type Ia supernovae, cosmic microwave background
anisotropies, the X-ray gas mass fraction of relaxed galaxy clusters, baryon
acoustic oscillations and cosmic shear. Combining the new X-ray luminosity
function data with current supernova, cosmic microwave background and cluster
gas fraction data yields the improved constraints Omega_m=0.269 +- 0.016,
sigma_8=0.82 +- 0.03 and w=-1.02 +- 0.06. (Abridged)Comment: Submitted to MNRAS. 15 pages, 15 figures. v2: Improved modeling of
the mass-luminosity relation, including additional systematic allowances for
evolution in the scatter and non-thermal pressure support. Constraints are
somewhat weaker, but overall conclusions are unchanged
Formation times, mass growth histories and concentrations of dark matter haloes
We develop a simple model for estimating the mass growth histories of dark
matter halos. The model is based on a fit to the formation time distribution,
where formation is defined as the earliest time that the main branch of the
merger tree contains a fraction f of the final mass M . Our analysis exploits
the fact that the median formation time as a function of f is the same as the
median of the main progenitor mass distribution as a function of time. When
coupled with previous work showing that the concentration c of the final halo
is related to the formation time tf associated with f \sim 0.04, our approach
provides a simple algorithm for estimating how the distribution of halo
concentrations may be expected to depend on mass, redshift and the expansion
history of the background cosmology. We also show that one can predict log10 c
with a precision of about 0.13 and 0.09 dex if only its mass, or both mass and
tf are known. And, conversely, one can predict log10 tf from mass or c with a
precision of 0.12 and 0.09 dex, approximately independent of f. Adding the mass
to the c-based estimate does not result in further improvement. These latter
results may be useful for studies which seek to compare the age of the stars in
the central galaxy in a halo with the time the core was first assembled.Comment: 15 pages, 15 figures, MNRAS accepted (minor changes + 1 figure and
some references
Improvements in the X-ray luminosity function and constraints on the Cosmological parameters from X-ray luminous clusters
We show how to improve constraints on \Omega_m, \sigma_8, and the dark-energy
equation-of-state parameter, w, obtained by Mantz et al. (2008) from
measurements of the X-ray luminosity function of galaxy clusters, namely MACS,
the local BCS and the REFLEX galaxy cluster samples with luminosities L> 3
\times 10^{44} erg/s in the 0.1--2.4 keV band. To this aim, we use Tinker et
al. (2008) mass function instead of Jenkins et al. (2001) and the M-L
relationship obtained from Del Popolo (2002) and Del Popolo et al. (2005).
Using the same methods and priors of Mantz et al. (2008), we find, for a
\Lambda while the result of Mantz et al. (2008) gives
less tight constraints and
\sigma_8=0.78^{+0.11}_{-0.13}. In the case of a wCDM model, we find
\Omega_m=0.27^{+0.07}_{-0.06}, and
, while in Mantz et al. (2008) they are again less tight
\Omega_m=0.24^{+0.15}_{-0.07}, \sigma_8=0.85^{+0.13}_{-0.20} and
w=-1.4^{+0.4}_{-0.7}. Combining the XLF analysis with the f_{gas}+CMB+SNIa data
set results in the constraint \Omega_m=0.269 \pm 0.012, \sigma_8=0.81 \pm 0.021
and w=-1.02 \pm 0.04, to be compared with Mantz et al. (2008), \Omega_m=0.269
\pm 0.016, \sigma_8=0.82 \pm 0.03 and w=-1.02 \pm 0.06. The tightness of the
last constraints obtained by Mantz et al. (2008), are fundamentally due to the
tightness of the +CMB+SNIa constraints and not to their XLF analysis.
Our findings, consistent with w=-1, lend additional support to the
cosmological-constant model.Comment: 9 pages, 4 Figures. A&A accepted. Paper Subitted Previously To Mantz
et al 2009, arXiv:0909.3098 and Mantz et al 2009b, arXiv:0909.309
Equilibrium configuration of a bounded inextensible membrane subject to solar radiation pressure
The equilibrium shape of a thin inextensible membrane subject to solar radiation pressure under given boundary constraints is studied. The membrane is assumed to be insusceptible to elastic deformation and to have negligible bending resistance, and its steady-state shape is therefore described by a developable surface (i.e., a surface of zero Gaussian curvature), resulting from an equilibrium between radiation pressure and membrane tension forces. A quantitative understanding of the mechanics of such membranes is essential in characterizing the dynamics of solar sail spacecraft that use sail wing tip displacement as an attitude control mode. The analysis in this paper develops a theoretical foundation for the billowed wing shape. Under reasonable simplifying assumptions, the key result is that solar radiation pressure and a given wing tip displacement yield a billowed solar sail wing with the shape of a generalized cylinder (i.e., a developable ruled surface, whose rulings are all parallel, rather than a general developable with variable ruling directions). The base curve geometry for the solar sail is also determined as the solution to a boundary value problem. The results presented herein allow the shape of the billowed membrane to be computed to any desired precision, for any given tip displacement
The effects of primordial non-Gaussianity on giant-arc statistics
For over a decade, it has been debated whether the concordance LCDM model is
consistent with the observed abundance of giant arcs in clusters. While
previous theoretical studies have focused on properties of the lens and source
populations, as well as cosmological effects such as dark energy, the impact of
initial conditions on the giant-arc abundance is relatively unexplored. Here,
we quantify the impact of non-Gaussian initial conditions with the local
bispectrum shape on the predicted frequency of giant arcs. Using a
path-integral formulation of the excursion set formalism, we extend a
semi-analytic model for calculating halo concentrations to the case of
primordial non-Gaussianity, which may be useful for applications outside of
this work. We find that massive halos tend to collapse earlier in models with
positive f_NL, relative to the Gaussian case, leading to enhanced concentration
parameters. The converse is true for f_NL < 0. In addition to these effects,
which change the lensing cross sections, non-Gaussianity also modifies the
abundance of supercritical clusters available for lensing. These combined
effects work together to either enhance (f_NL > 0) or suppress (f_NL < 0) the
probability of giant-arc formation. Using the best value and 95% confidence
levels currently available from the Wilkinson Microwave Anisotropy Probe, we
find that the giant-arc optical depth for sources at z_s~2 is enhanced by ~20%
and ~45% for f_NL = 32 and 74 respectively. In contrast, we calculate a
suppression of ~5% for f_NL = -10. These differences translate to similar
relative changes in the predicted all-sky number of giant arcs.Comment: 16 pages, 8 figures, accepted by MNRA
Cosmological Constraints from a Combination of Galaxy Clustering and Lensing -- III. Application to SDSS Data
We simultaneously constrain cosmology and galaxy bias using measurements of
galaxy abundances, galaxy clustering and galaxy-galaxy lensing taken from the
Sloan Digital Sky Survey. We use the conditional luminosity function (which
describes the halo occupation statistics as function of galaxy luminosity)
combined with the halo model (which describes the non-linear matter field in
terms of its halo building blocks) to describe the galaxy-dark matter
connection. We explicitly account for residual redshift space distortions in
the projected galaxy-galaxy correlation functions, and marginalize over
uncertainties in the scale dependence of the halo bias and the detailed
structure of dark matter haloes. Under the assumption of a spatially flat,
vanilla {\Lambda}CDM cosmology, we focus on constraining the matter density,
{\Omega}m, and the normalization of the matter power spectrum, {\sigma}8, and
we adopt WMAP7 priors for the spectral index, the Hubble parameter, and the
baryon density. We obtain that \Omegam = 0.278_{-0.026}^{+0.023} and {\sigma}8
= 0.763_{-0.049}^{+0.064} (95% CL). These results are robust to uncertainties
in the radial number density distribution of satellite galaxies, while allowing
for non-Poisson satellite occupation distributions results in a slightly lower
value for {\sigma}8 (0.744_{-0.047}^{+0.056}). These constraints are in
excellent agreement (at the 1{\sigma} level) with the cosmic microwave
background constraints from WMAP. This demonstrates that the use of a realistic
and accurate model for galaxy bias, down to the smallest non-linear scales
currently observed in galaxy surveys, leads to results perfectly consistent
with the vanilla {\Lambda}CDM cosmology.Comment: 21 pages, 9 figures, 5 tables, submitted to MNRA
Strong lensing statistics and the power spectrum normalisation
We use semi-analytic modelling of the galaxy-cluster population and its
strong lensing efficiency to explore how the expected abundance of large
gravitational arcs on the sky depends on . Our models take all
effects into account that have been shown to affect strong cluster lensing
substantially, in particular cluster asymmetry, substructure, merging, and
variations in the central density concentrations. We show that the optical
depth for long and thin arcs increases by approximately one order of magnitude
when increases from 0.7 to 0.9, owing to a constructive combination
of several effects. Models with high are also several orders of
magnitude more efficient in producing arcs at intermediate and high redshifts.
Finally, we use realistic source number counts to quantitatively predict the
total number of arcs brighter than several magnitude limits in the R and I
bands. We confirm that, while may come close to the known
abundance of arcs, even falls short by almost an order of
magnitude in reproducing known counts. We conclude that, should
be confirmed, we would fail to understand the strong-lensing
efficiency of the galaxy cluster population, and in particular the abundance of
arcs in high-redshift clusters. We argue that early-dark energy or non-Gaussian
density fluctuations may indicate one way out of this problem.Comment: 12 pages, 12 figures. A&A accepte
CARS: the CFHTLS-Archive-Research Survey; I. Five-band multi-colour data from 37 sq. deg. CFHTLS-Wide observations
We present the CFHTLS-Archive-Research Survey (CARS). It is a virtual
multi-colour survey based on public archive images from the CFHT-Legacy-Survey.
Our main scientific interests in CARS are optical searches for galaxy clusters
from low to high redshift and their subsequent study with photometric and
weak-gravitational lensing techniques. As a first step of the project we
present multi-colour catalogues from 37 sq. degrees of the CFHTLS-Wide
component. Our aims are to create astrometrically and photometrically well
calibrated co-added images. Second goal are five-band (u*, g', r', i', z')
multi-band catalogues with an emphasis on reliable estimates for object
colours. These are subsequently used for photometric redshift estimates. The
article explains in detail data processing, multi-colour catalogue creation and
photometric redshift estimation. Furthermore we apply a novel technique, based
on studies of the angular galaxy cross-correlation function, to quantify the
reliability of photo-z's. The accuracy of our high-confidence photo-z sample
(10-15 galaxies per sq. arcmin) is estimated to up to i'<24 with typically only 1-3% outliers. Interested users can
obtain access to our data by request to the authors.Comment: 31 pages, 18 figures, 6 tables; accepted for publication by A&A main
journa
- …