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 $k$ with weak gravitational lensing. This method enables us to reconstruct the galaxy bias factor $b(k)$ as well as the galaxy-matter correlation $r(k)$ on spatial scales between $0.01\,h\,{\rm Mpc^{-1}}\lesssim k\lesssim10\,h\,{\rm Mpc^{-1}}$ for redshift-binned lens galaxies below redshift $z\lesssim0.6$. 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 $r(k)$. For simulated data, the reconstructions achieve an accuracy of $3-7\%$ (68\% confidence level) over the above $k$-range for a survey area and a typical depth of contemporary ground-based surveys. Realistically the accuracy is, however, probably reduced to about $10-15\%$, 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 $b(k)$ and $r(k)$ 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

O(a)\mathcal{O}(a) 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 ($N_f = 2+1$) theory, we determine the renormalization constant and improvement coefficients relating the renormalized current and subtracted quark mass of (quenched) valence quarks in $\mathcal{O}(a)$ improved $N_f=3$ 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 $a\leq 0.02\,$fm and fixes the physical extent of the matching volume to $L\approx 0.5\,$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$_2$-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$_2$-He CIA spectrum is significantly distorted for densities higher than 0.1 g/cm$^3$.Comment: 4 pages, 2 figures, submitted for publication in the proceedings of the 20th European Workshop on White Dwarf