65 research outputs found
GaBoDS: The Garching-Bonn Deep Survey VIII. Lyman-break galaxies in the ESO Deep Public Survey
Aims. The clustering properties of a large sample of U-dropouts are
investigated and compared to very precise results for B-dropouts from other
studies to identify a possible evolution from z=4 to z=3. Methods. A population
of ~8800 candidates for star-forming galaxies at z=3 is selected via the
well-known Lyman-break technique from a large optical multicolour survey (the
ESO Deep Public Survey). The selection efficiency, contamination rate, and
redshift distribution of this population are investigated by means of extensive
simulations. Photometric redshifts are estimated for every Lyman-break galaxy
(LBG) candidate from its UBVRI photometry yielding an empirical redshift
distribution. The measured angular correlation function is deprojected and the
resulting spatial correlation lengths and slopes of the correlation function of
different subsamples are compared to previous studies. Results. By fitting a
simple power law to the correlation function we do not see an evolution in the
correlation length and the slope from other studies at z=4 to our study at z=3.
In particular, the dependence of the slope on UV-luminosity similar to that
recently detected for a sample of B-dropouts is confirmed also for our
U-dropouts. For the first time number statistics for U-dropouts are sufficient
to clearly detect a departure from a pure power law on small scales down to ~2"
reported by other groups for B-dropouts.Comment: 10 pages, 11 figures, accepted by A&A, full resolution version
available at http://www.astro.uni-bonn.de/~hendrik/5880.pd
A fitting formula for the non-Gaussian contribution to the lensing power spectrum covariance
Weak gravitational lensing is one of the most promising tools to investigate
the equation-of-state of dark energy. In order to obtain reliable parameter
estimations for current and future experiments, a good theoretical
understanding of dark matter clustering is essential. Of particular interest is
the statistical precision to which weak lensing observables, such as cosmic
shear correlation functions, can be determined. We construct a fitting formula
for the non-Gaussian part of the covariance of the lensing power spectrum. The
Gaussian contribution to the covariance, which is proportional to the lensing
power spectrum squared, and optionally shape noise can be included easily by
adding their contributions. Starting from a canonical estimator for the
dimensionless lensing power spectrum, we model first the covariance in the halo
model approach including all four halo terms for one fiducial cosmology and
then fit two polynomials to the expression found. On large scales, we use a
first-order polynomial in the wave-numbers and dimensionless power spectra that
goes asymptotically towards for , i.e., the result for
the non-Gaussian part of the covariance using tree-level perturbation theory.
On the other hand, for small scales we employ a second-order polynomial in the
dimensionless power spectra for the fit. We obtain a fitting formula for the
non-Gaussian contribution of the convergence power spectrum covariance that is
accurate to 10% for the off-diagonal elements, and to 5% for the diagonal
elements, in the range and can be used for
single source redshifts in WMAP5-like cosmologies.Comment: 23 pages, 15 figures, submitted to A&
CARS: The CFHTLS-Archive-Research Survey II. Weighing dark matter halos of Lyman-break galaxies at z=3-5
Aims: We measure the clustering properties for a large samples of u- (z~3),
g- (z~4), and r- (z~5) dropouts from the Canada-France-Hawaii Telescope Legacy
Survey (CFHTLS) Deep fields.
Methods: Photometric redshift distributions along with simulations allow us
to de-project the angular correlation measurements and estimate physical
quantities such as the correlation length, halo mass, galaxy bias, and halo
occupation as a function of UV luminosity.
Results: For the first time we detect a significant one-halo term in the
correlation function at z~5. The comoving correlation lengths and halo masses
of LBGs are found to decrease with decreasing rest-frame UV-luminosity. No
significant redshift evolution is found in either quantity. The typical halo
mass hosting an LBG is M>~10^{12}h^{-1}M_\odot and the halos are typically
occupied by less than one galaxy. Clustering segregation with UV luminosity is
clearly observed in the dropout samples, however redshift evolution cannot
clearly be disentangled from systematic uncertainties introduced by the
redshift distributions. We study a range of possible redshift distributions to
illustrate the effect of this choice. Spectroscopy of representative subsamples
is required to make high-accuracy absolute measurements of high-z halo masses.Comment: 12 pages, 9 figures, accepted for publication in A&
The mass-concentration relationship of virialized halos and its impact on cosmological observables
A generic property of the cuspy simulated virialized halos in cold dark
matter cosmogenies is that their concentration is inversely correlated with
their mass. This behavior has also been confirmed in observations, although
differences in the exact form and dispersion of this so-called
mass-concentration relationship have been reported. Some observational studies
of massive halos suggest that they are statistically over-concentrated with
respect to the expectations of Lambda-CDM. Here we investigate the impact that
various published mass-concentration relationships, both from simulations and
derived from observations, would have on other cosmological observables, in
particular considering upcoming surveys. We find that an integral measure of
lensing shear, such as counts of peaks from halos, is very sensitive to the
relationship between mass and concentration at fixed sigma-8, and the disparity
between some reported fits is much larger than the impact of uncertainty in
sigma-8 itself. We also briefly assess the impact of baryonic physics on
cluster scale observables, using state-of-the-art simulations, concluding that
it is unlikely to give rise to the high concentrations reported for some
clusters.Comment: 12 pages, 9 figures, MNRAS accepte
Using computer simulation to aid the research of drilling processes
Drilling wells is one of the primary methods used for mineral exploration. Scientific studies have aimed at improving the technical and economic aspects of drilling because of the current competitive economic conditions. Note that the primary topic of these studies has been developing new effective rock-cutting tools. To design a new rock-cutting tool, a thorough, reliable, and accurate study of the processes that occur during drilling is necessary. During drilling, mechanical, hydraulic, thermal, and chemical phenomena, which are interdependent and affect the performance of a drilling tool, simultaneously occur; therefore, a systematic, integrated approach is required for studying drilling processes. Field-based and laboratory experiments are quite tedious to perform and require high material costs, and it is often not possible to separately evaluate small elements of the drilling model. Therefore, computer simulation is an important research tool that enables accurate and reliable visualization of even small parts of the model. The aim. The aim of this study is to examine the potential for computer simulation of the processes that occur during drilling. Objective. In this study, we evaluated the simulation features of various software products, such as KOMPAS-3D, ANSYS, Delphi, and LabVIEW, for their utility in studying the processes that occur during drilling. The possibility of computer simulation for studying drilling processes, including its advantages and disadvantages, are demonstrated. The results are obtained from a model that simulates a rock cutting tool. The main uses of the rock cutting tool are outlined, and the drilling simulation development is planned. Choice of research method. The study of the capabilities of existing modern software products, for use in drilling process research, is carried out by an analytical review method
Integrated asset modeling and development optimization of a sector of oil-gas condensate field X
Dynamische analyse eines geschichteten K�rpers aus einzelmassen und massebehafteten Kontinua
- …