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We have explored the evolution of gas distributions from cosmological simulations carried out using the RAMSES adaptive mesh refinement (AMR) code, to explore the effects of resolution on cosmological hydrodynamical simulations. It is vital to understand the effect of both the resolution of initial conditions (ICs) and the final resolution of the simulation. Lower initial resolution simulations tend to produce smaller numbers of low-mass structures. This will strongly affect the assembly history of objects, and has the same effect of simulating different cosmologies. The resolution of ICs is an important factor in simulations, even with a fixed maximum spatial resolution. The power spectrum of gas in simulations using AMR diverges strongly from the fixed grid approach - with more power on small scales in the AMR simulations - even at fixed physical resolution and also produces offsets in the star formation at specific epochs. This is because before certain times the upper grid levels are held back to maintain approximately fixed physical resolution, and to mimic the natural evolution of dark matter only simulations. Although the impact of hold-back falls with increasing spatial and IC resolutions, the offsets in the star formation remain down to a spatial resolution of 1 kpc. These offsets are of the order of 10-20 per cent, which is below the uncertainty in the implemented physics but are expected to affect the detailed properties of galaxies. We have implemented a new grid-hold-back approach to minimize the impact of hold-back on the star formation rate. [ABSTRACT FROM AUTHOR]

We study the properties of dark matter haloes in a wide range of modified gravity models, namely, f(R), DGP and interacting dark energy models. We study the effects of modified gravity and dark energy on the internal properties of haloes, such as the spin and the structural parameters. We find that f(R) gravity enhances the median value of the Bullock spin parameter, but could not detect such effects for DGP and coupled dark energy. f(R) also yields a lower median sphericity and oblateness, while coupled dark energy has the opposite effect. However, these effects are very small. We then study the interaction rate of haloes in different gravity and find that only strongly coupled dark energy models enhance the interaction rate. We then quantify the enhancement of the alignment of the spins of interacting halo pairs by modified gravity. Finally, we study the alignment of the major axes of haloes with the large-scale structures. The alignment of the spins of interacting pairs of haloes in DGP and coupled dark energy models show no discrepancy with GR, while f(R) shows a weaker alignment. Strongly coupled dark energy shows a stronger alignment of the halo shape with the large-scale structures. [ABSTRACT FROM AUTHOR]

Interactions such as mergers and flybys play a fundamental role in shaping galaxy morphology. Using the Horizon Run 4 cosmological N-body simulation, we studied the frequency and type of halo interactions, and their redshift evolution as a function of the environment defined by the large-scale density, pair separation, mass ratio, and target halo mass. Most interactions happen at large-scale density contrast δ ≅ 20, regardless of the redshift corresponding to groups and relatively dense part of filaments. However, the fraction of interacting target is maximum at δ ≅ 1000. We provide a new empirical fitting form for the interaction rate as a function of the halo mass, large-scale density, and redshift. We also report the existence of two modes of interactions from the distributions of mass ratio and relative distance, implying two different physical origins of the interaction. Satellite targets lose their mass as they proceed deeper into the host halo. The relative importance of these two trends strongly depends on the large-scale density, target mass, and redshift. [ABSTRACT FROM AUTHOR]

We propose a method using the redshift dependence of the Alcock-Paczynski (AP) test and volume effect to measure the cosmic expansion history. The galaxy two-point correlation function as a function of angle, ξ (μ), is measured at different redshifts. Assuming an incorrect cosmological model to convert galaxy redshifts to distances, the shape of ξ (μ) appears anisotropic due to the AP effect, and the amplitude is shifted by the change in comoving volume. Due to the redshift dependence of the AP and volume effect, both the shape and amplitude of ξ (μ) exhibit redshift dependence. Similar to Li et al. (2014), we find that the redshift-space distortions (RSD) caused by galaxy peculiar velocities, although significantly distorting ξ (μ), exhibit much less redshift evolution compared to the AP and volume effects. By focusing on the redshift dependence of ξ (μ), we can correctly recover the cosmological parameters despite the contamination of RSD. The method is tested by using the Horizon Run 3 N-body simulation, from which we made a series of 1/8-sky mock surveys having eight million physically self-bound haloes and sampled to have roughly a uniform number density in z = 0-1.5.We find the AP effect results in tight, unbiased constraints on the density parameter and dark energy equation of state, with 68.3% CL intervals δΩm ~ 0.03 and δw ~ 0.1, and the volume effect leads to much tighter constraints of δΩm ~ 0.007 and δw ~ 0.035. [ABSTRACT FROM AUTHOR]