Marco Baldi

Cosmic voids in coupled dark energy cosmologies: the impact of halo bias

In this work, we analyse the properties of cosmic voids in standard and coupled dark energy cosmologies. Using large numerical simulations, we investigate the effects produced by the dark energy coupling on three statistics: the filling factor, the size distribution and the stacked profiles of cosmic voids. We find that the bias of the tracers of the density field used to identify the voids strongly influences the properties of the void catalogues, and, consequently, the possibility of using the identified voids as a probe to distinguish coupled dark energy models from the standard Lambda cold dark matter cosmology. In fact, on one hand coupled dark energy models are characterized by an excess of large voids in the cold dark matter distribution as compared to the reference standard cosmology, due to their higher normalization of linear perturbations at low redshifts. Specifically, these models present an excess of large voids with R-eff > 20, 15, 12h(-1) Mpc, at z = 0, 0.55, 1, respectively. On the other hand, we do not find any significant difference in the properties of the voids detected in the distribution of collapsed dark matter haloes. These results imply that the tracer bias has a significant impact on the possibility of using cosmic void catalogues to probe cosmology.

Imprint of f(R) gravity on nonlinear structure formation

We test the imprint of f(R) modified gravity on the halo mass function, using N-body simulations and a theoretical model developed in [M. Kopp et al., Phys. Rev. D 88, 084015 (2013)]. We find a good agreement between theory and simulations similar to 5%. We extend the theoretical model to the conditional mass function and apply it to the prediction of the linear halo bias in f(R) gravity. Using the halo model we obtain a prediction for the nonlinear matter power spectrum accurate to similar to 10% at z = 0 and up to k = 2h/Mpc. We also study halo profiles for the f(R) models and find a deviation from the standard general relativity (GR) result up to 40%, depending on the halo masses and redshift. This has not been pointed out in previous analysis. Finally we study the number density and profiles of voids identified in these f(R) N-body simulations. We underline the effect of the bias and the sampling to identify voids. We find significant deviation from GR when measuring the f(R) void profiles with f(R0) < -10(-6).

On the linearity of tracer bias around voids

The large-scale structure of the Universe can be observed only via luminous tracers of the dark matter. However, the clustering statistics of tracers are biased and depend on various properties, such as their host-halo mass and assembly history. On very large scales, this tracer bias results in a constant offset in the clustering amplitude, known as linear bias. Towards smaller non-linear scales, this is no longer the case and tracer bias becomes a complicated function of scale and time. We focus on tracer bias centred on cosmic voids, i.e. depressions of the density field that spatially dominate the Universe. We consider three types of tracers: galaxies, galaxy clusters and active galactic nuclei, extracted from the hydrodynamical simulation Magneticum Pathfinder. In contrast to common clustering statistics that focus on auto-correlations of tracers, we find that void-tracer cross-correlations are successfully described by a linear bias relation. The tracer-density profile of voids can thus be related to their matter-density profile by a single number. We show that it coincides with the linear tracer bias extracted from the large-scale auto-correlation function and expectations from theory, if sufficiently large voids are considered. For smaller voids we observe a shift towards higher values. This has important consequences on cosmological parameter inference, as the problem of unknown tracer bias is alleviated up to a constant number. The smallest scales in existing data sets become accessible to simpler models, providing numerous modes of the density field that have been disregarded so far, but may help to further reduce statistical errors in constraining cosmology.

The mass accretion rate of galaxy clusters: a measurable quantity

We explore the possibility of measuring the mass accretion rate (MAR) of galaxy clusters from their mass profiles beyond the virial radius

Fast Weak Lensing Simulations with Halo Model

R_{200}

Effects of coupled dark energy on the Milky Way and its satellites

. We derive the accretion rate from the mass of a spherical shell whose inner radius is

Fitting and forecasting coupled dark energy in the non-linear regime

2R_{200}

Nonlinear growing neutrino cosmology

, whose thickness changes with redshift, and whose infall velocity is assumed to be equal to the mean infall velocity of the spherical shells of dark matter halos extracted from

AX-GADGET: a new code for cosmological simulations of Fuzzy Dark Matter and Axion models

N

The kinematic Sunyaev-Zel'dovich effect of the large-scale structure (II): the effect of modified gravity

-body simulations. This approximation is rather crude in hierarchical clustering scenarios where both smooth accretion and aggregation of smaller dark matter halos contribute to the mass accretion of clusters.Nevertheless, in the redshift range