Over the years, the development of large-scale structure simulations has given us more and more cluster samples from which we can infer cosmological information via cluster counts. As a matter of...Show moreOver the years, the development of large-scale structure simulations has given us more and more cluster samples from which we can infer cosmological information via cluster counts. As a matter of fact, we can use this probes to constraint some cosmological parameters like the matter density Ωm or the amplitude of density fluctuations at 8 Mpc h−1, σ8. However, this kind of data analysis is heavily affected by systematic errors of astrophysical kind. A recent proxy has been proposed to overcome this difficulties: the cluster sparsity, defined as the ratio of different halo mass definitions. In this thesis we will test this observable on the halo catalogue of the new simulation FLAMINGO, studying its property in a fullhydrodynamics simulation for the first time. We will test its dependence on different cosmologies, showing that the effects of baryonic matter are almost an order of magnitude higher than the differences between two valid cosmologies (in this case Planck-18 and DES). Finally, we will use the hot gas particles included in FLAMINGO to perform a mock X-ray measurement of the sparsity in order to predict the systematics that could affect a real-life observation. We find that indeed a significant bias affects the halo mass, while the sparsity is way less biased and is actually compatible with accurate values extracted from the simulation. We conclude that the sparsity does seem as a reliable and effective proxy for cosmological constraints.Show less
Different models of dark matter can be distinguished through the amount of free streaming they exhibit. A consequence of free streaming is the suppression of small-scale cosmic structure, which in...Show moreDifferent models of dark matter can be distinguished through the amount of free streaming they exhibit. A consequence of free streaming is the suppression of small-scale cosmic structure, which in turn could be detected through the Ly-α forest, a series of absorption features in quasar spectra. This thesis considers how peculiar velocities in the intergalactic medium, the gas that produces the absorption of the Ly-α forest, influence the flux power spectrum (FPS) of the Ly-α forest. We do this by calculating the FPS from high-resolution hydrodynamical simulations, performed using the SWIFT code, while taking into account peculiar velocities or ignoring them; it is shown that at large scales, peculiar velocities may introduce a Gaussian cutoff to the FPS. A model that relates the spatial scale corresponding to this cutoff to the density, thermal state and peculiar velocity dispersion of the intergalactic medium is proposed and tested at redshifts 4.0 ≤ z ≤ 6.0. It is found to be acceptable at 4.0 ≤ z ≤ 5.5, although only the average dependence on the peculiar velocity dispersion is correctly described; at z = 6.0, the proposed model can be rejected. The main venue for extending the research done here is thought to be the development of a model that describes the influence of peculiar velocities on smaller scales as well.Show less
The ever-increasing accuracy of telescopes like Planck has allowed for the measurements of anisotropies in the CMB. For this project, the influence of heavy neutral leptons (HNLs) on the upper...Show moreThe ever-increasing accuracy of telescopes like Planck has allowed for the measurements of anisotropies in the CMB. For this project, the influence of heavy neutral leptons (HNLs) on the upper bound of the neutrino mass sum, as determined from the CMB anisotropies and additional datasets, has been studied. Specifically, an HNL with mass mN ∼ 500 MeV and lifetime τN ∼ 0.05 s is considered, which would cause a change of the number of relativistic species to Neff = 2.45 and of the primordial helium fraction to YP = 0.26. With these conditions, the mass bound is found to be ∑ mν < 0.12 at 95% CL, while the bound in standard ΛCDM + ∑ mν resulted in ∑ mν < 0.13 eV at 95% CL. The bound thus decreases slightly. This can be explained if Neff and ∑ mν have distinct effects, and other pa- rameters’ effects are able to counter changes due to the change in Neff, so that the mass sum does not need to change much. HNLs thus have a tiny effect on the mass bound, but there may also be no effect, as the results could be slightly off if we have not run the fitting program long enough.Show less
We present a method to link phenomenological parameterizations of dark energy on cosmological scales with theory. We will use the phenomenological parameterization adopted by the Planck...Show moreWe present a method to link phenomenological parameterizations of dark energy on cosmological scales with theory. We will use the phenomenological parameterization adopted by the Planck collaboration [], parameterizing the phenomenological functions $\mu$ and $\eta$ as functions of scale $k$, and time using the scale factor $a$. When linking the phenomenological functions with theory, we restrict ourselves to the Horndeski class of theories [] and neglect time derivatives, i.e. we work with the general and model independent quasi static approximation (QSA), to be able to find analytical expressions for our phenomenological parameterizations. Despite its generality, the QSA forces the phenomenological parameterization adopted by the Planck collaboration into a scale-independent one; which motivated us to propose an alternative phenomenological parameterization using a parameterization of the phenomenological functions $\mu(a,k)$ and $\Sigma(a,k)$. This phenomenological parameterization does allow for scale dependence in $\mu$ under our conditions. The effect of imposing extra conditions on our models, e.g. imposing the speed of gravitational waves to equal the speed of sound, is investigated by searching the parameter space of the phenomenological parameterizations for points that yield physically viable models. The viability here is evaluated by means of ghost and gradient stability conditions.Show less
We will show the weak lensing effects from filaments connecting galaxy pairs for two separate galaxy subsets. The lensing galaxies are selected from the Galaxy And Mass Assembly (GAMA) survey,...Show moreWe will show the weak lensing effects from filaments connecting galaxy pairs for two separate galaxy subsets. The lensing galaxies are selected from the Galaxy And Mass Assembly (GAMA) survey, where we use version 7 of the GAMA galaxy group catalogue in our galaxy selection. We select the background galaxies from the ’KiDS-450’ weak lensing data set. Two galaxies are considered to form a pair when they are within an angular separation of 6h^-1 Mpc and 10h^-1 Mpc and are within a line of sight separation of 10h^-1 Mpc. In addition, we select galaxies with an angular separation between 6h^-1 Mpc and 10h^-1 Mpc, with a line of sight separation between 100h^-1 Mpc and 120h^-1 Mpc, to be ’unphysical pairs’. They appear to be galaxy pairs projected on the sky but are physically to far separated to form a pair. The subtraction of the signal of the unphysical pairs from the physical pairs will then result in the isolation of the filament. We use two subsets of galaxies in our pair selection; galaxies isolated in space, and the central galaxies of galaxy groups with at least 4 group members and consider the lensing effects of both subsets. Using 25 000 and 8 279 galaxy pairs from the isolated galaxy pairs subset and group central galaxy pair subset respectively, we will show the detection of filaments with a significance of 2.3\sigma and 2.9\sigma for these subsets.Show less
A sample of zoomorphic adornos, unearthed at the site of El Flaco (13th - 15th century CE) in the northwest of the Dominican Republic, has been ichnographically analyzed, based on the three-stage...Show moreA sample of zoomorphic adornos, unearthed at the site of El Flaco (13th - 15th century CE) in the northwest of the Dominican Republic, has been ichnographically analyzed, based on the three-stage model as developed by Panofsky (1939), to discover the cultural meaning of the animals identified on the adornos in the known creation narratives and cosmology of the Taíno peoples. This is expected to contribute to the generally unknown cultural relevance of adornos to the pre-colonial communities in the Caribbean archipelago. The iconographical analysis has revealed a close association between the adornos, and the known cosmological views and creation narratives of the Taíno peoples, as recorded by Ramón Pané. A diversity of animals have been identified on the adornos, which include bats, turtles/tortoises, frogs/toads, primates, crocodiles, lizards, rodents and birds. These animals appear to be associated with the spirits of departed ancestors, seduction/deception, fertility, shamanism and the maintenance of a balance between the three realms of the Taíno cosmos.Show less
This thesis studies the organizational principles of the Hàn dynasty text Shuō wén jiě zì 說⽂文解字, written by Xǔ Shèn 許慎. It presents a qualitative case study of three radical sections. In the...Show moreThis thesis studies the organizational principles of the Hàn dynasty text Shuō wén jiě zì 說⽂文解字, written by Xǔ Shèn 許慎. It presents a qualitative case study of three radical sections. In the analysis, special attention is paid to the sociopolitical context in which the text was produced, so as to understand the cultural factors that presumably informed Xǔ Shèn’s organization of the text. On the basis of the analysis, it also discusses Xǔ Shèn’s conception of writing. The analysis shows how the organization of characters was profoundly influenced by the ideologies of its time. It demonstrates how philosophical theories such as yīn–yáng and five phases (yīnyáng wǔxíng 陰陽五行), the doctrine of the unity of heaven and man (tiān rén hé yī 天人合一), and numerology of the Yì jīng 易經 (Book of Changes) all made their way into Xǔ Shèn’s lexicographic system. Furthermore, it shows how many characters are neatly organized in semantic series, which make up large parts of some radical sections. On the basis of the close connection between character organization and cosmological theories, it argues that Xǔ Shèn understood script mainly as a graphic representation of reality, which reflects the order of the cosmos. In linking the original text to the ideologies and customs of its time, this study offers an interpretation of how the organization of characters in three radical sections is best understood.Show less
