14,364 research outputs found
Scale dependence of galaxy biasing investigated by weak gravitational lensing: An assessment using semi-analytic galaxies and simulated lensing data
Galaxies are biased tracers of the matter density on cosmological scales. For
future tests of galaxy models, we refine and assess a method to measure galaxy
biasing as function of physical scale with weak gravitational lensing. This
method enables us to reconstruct the galaxy bias factor as well as the
galaxy-matter correlation on spatial scales between for redshift-binned lens galaxies below redshift .
In the refinement, we account for an intrinsic alignment of source
ellipticities, and we correct for the magnification bias of the lens galaxies,
relevant for the galaxy-galaxy lensing signal, to improve the accuracy of the
reconstructed . For simulated data, the reconstructions achieve an
accuracy of (68\% confidence level) over the above -range for a
survey area and a typical depth of contemporary ground-based surveys.
Realistically the accuracy is, however, probably reduced to about ,
mainly by systematic uncertainties in the assumed intrinsic source alignment,
the fiducial cosmology, and the redshift distributions of lens and source
galaxies (in that order). Furthermore, our reconstruction technique employs
physical templates for and that elucidate the impact of central
galaxies and the halo-occupation statistics of satellite galaxies on the
scale-dependence of galaxy bias, which we discuss in the paper. In a first
demonstration, we apply this method to previous measurements in the
Garching-Bonn-Deep Survey and give a physical interpretation of the lens
population.Comment: 31 pages, 16 figures; corrected typos in Eqs. (31), (34), and (36
Weak-lensing shear estimates with general adaptive moments, and studies of bias by pixellation, PSF distortions, and noise
In weak gravitational lensing, weighted quadrupole moments of the brightness
profile in galaxy images are a common way to estimate gravitational shear. We
employ general adaptive moments (GLAM) to study causes of shear bias on a
fundamental level and for a practical definition of an image ellipticity. The
GLAM ellipticity has useful properties for any chosen weight profile: the
weighted ellipticity is identical to that of isophotes of elliptical images,
and in absence of noise and pixellation it is always an unbiased estimator of
reduced shear. We show that moment-based techniques, adaptive or unweighted,
are similar to a model-based approach in the sense that they can be seen as
imperfect fit of an elliptical profile to the image. Due to residuals in the
fit, moment-based estimates of ellipticities are prone to underfitting bias
when inferred from observed images. The estimation is fundamentally limited
mainly by pixellation which destroys information on the original, pre-seeing
image. We give an optimized estimator for the pre-seeing GLAM ellipticity and
quantify its bias for noise-free images. To deal with pixel noise, we consider
a Bayesian approach where the posterior of the GLAM ellipticity can be
inconsistent with the true ellipticity if we do not properly account for our
ignorance about fit residuals. This underfitting bias is S/N-independent but
changes with the pre-seeing brightness profile and the correlation or
heterogeneity of pixel noise over the post-seeing image. Furthermore, when
inferring a constant ellipticity or, more relevantly, constant shear from a
source sample with a distribution of intrinsic properties (sizes, centroid
positions, intrinsic shapes), an additional, now noise-dependent bias arises
towards low S/N if incorrect priors for the intrinsic properties are used. We
discuss the origin of this prior bias.Comment: 18 pages; 5 figures; accepted by A&A after major revision, especially
of Sect. 3.3 that corrects the previous discussion on the bias by
marginalizatio
Baryon production from cluster hadronization
We present an extension to the colour reconnection model in the Monte-Carlo
event generator Herwig to account for the production of baryons and compare it
to a series of observables for soft physics. The new model is able to improve
the description of charged-particle mutliplicities and hadron flavour
observables in pp collisionsComment: 13 pages; v3: updated to match journal versio
improved quark mass renormalization for a non-perturbative matching of HQET to three-flavor QCD
The use of Heavy Quark Effective Theory (HQET) on the lattice as an approach
to B-physics phenomenology is based on a non-perturbative matching of HQET to
QCD in finite volume. As a first step to apply the underlying strategy in the
three-flavor () theory, we determine the renormalization constant
and improvement coefficients relating the renormalized current and subtracted
quark mass of (quenched) valence quarks in improved
lattice QCD. We present our strategy and first results for the relevant
parameter region towards weak couplings along a line of constant physics, which
corresponds to lattice resolutions fm and fixes the physical
extent of the matching volume to fm.Comment: 7 pages including 7 figures, latex2e; Proceedings of the 36th
International Symposium on Lattice Field Theory (Lattice 2018), 22-28 July
2018, Michigan State University, East Lansing, Michigan, US
A New Generation of Cool White Dwarf Atmosphere Models Using Ab Initio Calculations
Due to their high photospheric density, cool helium-rich white dwarfs
(particularly DZ, DQpec and ultracool) are often poorly described by current
atmosphere models. As part of our ongoing efforts to design atmosphere models
suitable for all cool white dwarfs, we investigate how the ionization ratio of
heavy elements and the H-He collision-induced absorption (CIA) spectrum are
altered under fluid-like densities. For the conditions encountered at the
photosphere of cool helium-rich white dwarfs, our ab initio calculations show
that the ionization of most metals is inhibited and that the H-He CIA
spectrum is significantly distorted for densities higher than 0.1 g/cm.Comment: 4 pages, 2 figures, submitted for publication in the proceedings of
the 20th European Workshop on White Dwarf
- …