About me

I am Andrej Dvornik, a postdoc at Ruhr-Universität Bochum.

Welcome on my personal website and blog. Here you can also find my research interests, publications, and CV. Please do get in touch!

Research interests and highlights


+ Weak gravitational lensing + Large scale structure + Cosmology + Dark matter + Dark energy + Galaxy-dark matter connection + Halo model +


cosmology constraints from galaxy abundance, galaxy clustering and galaxy-galaxy lensing

We present constraints on the flat ΛCDM cosmological model through a joint analysis of galaxy abundance, galaxy clustering and galaxy-galaxy lensing observables with the Kilo-Degree Survey. Our theoretical model combines a flexible conditional stellar mass function, to describe the galaxy-halo connection, with a cosmological N-body simulation-calibrated halo model to describe the non-linear matter field. Our magnitude-limited bright galaxy sample combines 9-band optical-to-near-infrared photometry with an extensive and complete spectroscopic training sample to provide accurate redshift and stellar mass estimates. Our faint galaxy sample provides a background of accurately calibrated lensing measurements. We constrain the structure growth parameter, and the matter density parameter. This analysis therefore brings attention to the significant constraining power in the often-excluded non-linear scales for galaxy clustering and galaxy-galaxy lensing observables. By adopting a theoretical model that accounts for non-linear halo bias, halo exclusion, scale-dependent galaxy bias and the impact of baryon feedback, this work demonstrates the potential and a way forward to include non-linear scales in cosmological analyses. 

Galaxy bias

We measure the projected galaxy clustering and galaxy-galaxy lensing signals using the Galaxy And Mass Assembly (GAMA) survey and Kilo-Degree Survey (KiDS) to study galaxy bias. We use the concept of non-linear and stochastic galaxy biasing in the framework of halo occupation statistics to constrain the parameters of the halo occupation statistics and to unveil the origin of galaxy biasing. The bias function Γ is evaluated using the analytical halo model from which the scale dependence of Γ, and the origin of the non-linearity and stochasticity in halo occupation models can be inferred.

Assembly bias

I have investigated possible signatures of halo assembly bias for spectroscopically selected galaxy groups from GAMA survey using weak lensing measurements from the KiDS survey. The GAMA galaxies are split into two samples, with similar mean halo masses but different spatial distributions of satellite galaxies. We find no evidence of halo assembly bias on galaxy group scales.