Posters

Galaxy clusters are a powerful cosmological probe: they track the latest evolution of large scale structure and are therefore fundamental for testing the cosmological model in the recent Universe. To compare the observations of galaxy clusters with the theoretical prediction and thus constrain the cosmological parameters of the underlying model, a precise knowledge of clusters’ masses and redshift is required. Scaling relations relating the mass with a given cluster observable (like the richness in optical wavelength, Ysz in the mm-band or Yx in X-rays) are usually used to compute the mass of clusters. My work aims at estimating a new scaling relation using a sample of clusters from the Planck ESZ catalogue that was observed in X-rays by Chandra [1], and ultimately combining all available SZ and X-ray data in a single likelihood to compute cosmological parameters.

XMM-Newton data being available for a large part of the Chandra-Planck sample, I also compare profiles and integrated values for cluster observed by both telescopes.

In 1990s the COBE/FIRAS mission showed that the CMB spectral energy distribution is close to a perfect blackbody. However, the CMB spectrum contains tiny departures from a perfect blackbody to \( \Delta I/I \simeq 10^{-5} \), referred to as spectral distortions, that encode information about the full thermal history of the Universe [1]. High-precision spectroscopy of the CMB is one of the three themes that have been selected by the ESA Voyage 2050 programme. I will present an effort undertaken to define future missions and instruments dedicated to the measurement of the CMB spectral distortions based on FOSSIL, an ESA M7 proposal and BISOU, a CNES Phase 0 study for a balloon-borne mission [2].

Most strong gravitational lensing systems can be modeled by a strong lens plus perturbers along the line-of-sight. In [1], the authors model the line-of-sight effects within the dominant lens approximation in the tidal regime, where the line-of-sight shear and convergence across the image are homogeneous. However, as shown in [2], beyond tidal effects appear when simulating realistic lines of sight. I will present an extension of the formalism developped in [1], which focuses on the aforementioned beyond tidal effects, with the flexion regime. I will derive a minimal model which encodes parameter degeneracies, alongside time delay corrections, cosmic line-of-sight flexion expressions and two point correlation functions.

We measure the linear bias of dark matter halos in a suite of cosmological simulations. We compare our results to the existing fitting functions in the literature, in particular to the one given in Tinker et al., 2010. We show the possibility of improving the numerically calibrated prescription for the linear bias function, exploiting high-resolution cosmological simulations. Moreover, our results suggest the possibility of a time evolution of the parameters controlling the linear bias function. Such evolution is shown to be better captured in terms of clustering amplitude at a given cosmology-independent scale.

In any cosmological analysis based on the galaxy cluster number count, a very important ingredient is the selection function of the detection method used to produce the galaxy cluster catalog. Indeed, an incorrect determination of this function can lead to biases in the cosmological parameters estimated from the data. In this work we study the impact of complex cluster morphology on the selection function of the matched multi-filter (MMF) algorithm [1], used to detect galaxy clusters through the Sunyaev-Zel’dovich (SZ) effect. For the determination of the selection function, we apply the same method as in [2], using mock cluster images from hydrodynamical simulations injected in the Planck high frequency maps. We compare our results with a commonly used analytical approximation for the completeness, used for example in [3].

An accurate mass calibration of galaxy clusters is a crucial step towards precise constraints on the cosmological parameters \( \sigma_8 \) and \( \Omega_m \) from clusters. In the millimeter, via the Sunyaev-Zel'dovich (SZ) effect, and X-rays domains, cluster masses can be estimated assuming hydrostatic equilibrium, but several physical and observational effects can alter this calculation. Constrained cosmological simulations of the local Universe [1] permit us to study those various effects on the nearby cluster population, it will help us to quantify the biases due to our peculiar position of observation. On this poster I will present a case study of the projection effects on the hydrostatic mass estimation of the Virgo cluster extracted from the CLONE constrained cosmological simulation [2].

The 21cm hydrogen line is present during all the eras following the cosmological recombination, containing information about both the cosmology and the astrophysical processes at work in the universe[1]. I will discuss the 21cm line from the dark ages, using the recombination code \texttt{CHEMFAST} we develop, whose particularity is to describe the whole chemical network evolution, including molecules [2]. I will also present another aspect of 21cm line computation from the collapsing halos,and will particularly focus on the effects of thermal molecular functions.

This poster is based on a recent theoretical tool [1] developed to predict, for a given set of cosmological parameters, the multi-scale density probability function of convergence maps like the one that will be observed with Euclid. This can be used to build an accurate map emulator similar to what was done for 2-point statistics [2], but which accurately respects the predictions of higher order statistics. This hybrid approach, consisting of a likelihood less cosmological parameter inference that is based on high-order static theoretical prediction rather than n-body simulations, would therefore make this approach highly competitive for constraining the cosmological model using high-order statistics in future surveys.

A powerful alternative to N-body simulations comes in the form of analytical/numerical framework describing the evolution of DM, without the need to follow complex, non-linear dynamics in detail. Unlike simulations the excursion set formalism coupled with DM collapse models, can resolve down to the smallest scales [1]. To date this method proves to make accurate statistical predictions (i.e. halo mass functions, progenitor distributions and the merger rate histories). However, the collapse models make other detailed predictions for the DM fluid particles (i.e. collapse times, densities, morphology class), which have not yet been investigated against simulations. We aim test these models thoroughly.