From galaxies to the cosmic web and back: the interplay of different scales in galaxy formation and cosmic reionization

The evolution of the Universe is primarily governed by gravity, that triggers the development of a complex web-like distribution of galaxies. The latter are embedded in larger structures, called haloes, mainly composed by an exotic form of matter that does not interact with light, and is therefore called dark. Within this cosmic web, astrophysical phenomena occur on a large variety of spatial scales. Although ubiquitous, the interaction between them is often neglected because of the difficulties in their simultaneous modeling. In this Thesis we employ advanced numerical simulations of structure formation in the universe to investigate three cases where this interplay is of primary importance, namely: the assembly bias, the radial acceleration relation and the epoch of cosmic reionization. Assembly bias denotes the fact that dark matter haloes of the same mass have clustering properties that depend on their formation time. This effect is due to the cosmic environment of such haloes, that halts the accretion of new material in regions where the tidal field exerted by nearby structures is strong. Therefore, the assembly of objects strongly clustered is more efficiently suppressed. In this Thesis, we study the properties of satellite galaxies that reside within haloes with different assembly histories, and therefore cosmic environments. We show that their content is insensitive to the large-scale geometry of the matter distribution. However, the latter has a strong impact on the satellite dynamics, producing a preferentially-radial motion in objects embedded in a knot of the cosmic web, and isotropically-distributed velocities in region within filaments. We apply this knowledge to the satellites of the Milky Way and infer that our Galaxy must reside in a prominent filamentary structure. Recent observations of a large sample of galaxies unveiled a tight correlation between the total radial acceleration experienced by bodies orbiting around the galactic center and the same quantity inferred only from the galactic baryonic content. Theoretical models of structure formation have been tested against this radial acceleration relation (RAR) only for large structures. Here, we predict for the first time the RAR of small satellite galaxies, opening up the possibility to test our knowledge of galaxy formation mechanisms in an uncharted territory. Additionally, we study the redshift evolution of this relation and its secondary dependence on physical properties of the satellites. We then make use of these results to devise an observational test that can distinguish between the standard cosmological model and one popular alternative theory, the Modified Newtonian Dynamics. Finally, we study the role of quasars in the reionization of the Universe on the largest scales. We do so by simulating a reionization scenario where the ionizing photons production is dominated by quasars and compare it with one where galaxies are the main source of such photons. We show that, despite the peculiar emission properties of quasars, the former leads to global properties of the inter-galactic medium that are in agreement with observations. Additionally, we produce synthetic absorption spectra and use them to show that, in a quasar-dominated scenario, the properties of helium absorption features are incompatible with available observations. However, we also find indications that a modest contribution from quasars can explain the observed distribution of patches of inter-galactic neutral hydrogen. To unravel these apparently-controversial findings, we identify and investigate two promising methods that, using future observations, will enable a determination of the quasar contribution to cosmic reionization

CoReCon: an open, community-powered collection of Reionization constraints

The number of available constraints on the Universe during and before cosmic reionization is rapidly growing. These are often scattered across inhomogeneous formats, unit systems and sampling strategies. In this paper, I introduce CoReCon, a Python package designed to provide a growing set of constraints on key physical quantities related to the Epoch of Reionization and a platform for the high-redshift research community to collect and store, in an open way, current and forthcoming observational constraints.Comment: Published in the Journal of Open Source Softwar

Dynamic Zoom Simulations: a fast, adaptive algorithm for simulating lightcones

The advent of a new generation of large-scale galaxy surveys is pushing cosmological numerical simulations in an uncharted territory. The simultaneous requirements of high resolution and very large volume pose serious technical challenges, due to their computational and data storage demand. In this paper, we present a novel approach dubbed Dynamic Zoom Simulations -- or DZS -- developed to tackle these issues. Our method is tailored to the production of lightcone outputs from N-body numerical simulations, which allow for a more efficient storage and post-processing compared to standard comoving snapshots, and more directly mimic the format of survey data. In DZS, the resolution of the simulation is dynamically decreased outside the lightcone surface, reducing the computational work load, while simultaneously preserving the accuracy inside the lightcone and the large-scale gravitational field. We show that our approach can achieve virtually identical results to traditional simulations at half of the computational cost for our largest box. We also forecast this speedup to increase up to a factor of 5 for larger and/or higher-resolution simulations. We assess the accuracy of the numerical integration by comparing pairs of identical simulations run with and without DZS. Deviations in the lightcone halo mass function, in the sky-projected lightcone, and in the 3D matter lightcone always remain below 0.1%. In summary, our results indicate that the DZS technique may provide a highly-valuable tool to address the technical challenges that will characterise the next generation of large-scale cosmological simulations.Comment: 17 pages, 13 figures, version accepted for publication in MNRA

Flows around galaxies I -- The dependency of galaxy connectivity on cosmic environments and effects on the star-formation rate

With the aim of bringing substantial insight to the fundamental question of how galaxies acquire their material for star-formation, we present the first comprehensive characterisation of the galaxy connectivity (i.e. the number of small-scale filamentary streams connected to a galaxy) in relation with the cosmic environment, and a statistical exploration of the impact of connectivity on the star-formation rate at z=2. We detect kpc-scale filaments directly connected to galaxies by applying the DisPerSE filament finder to the DM density around 2942 central galaxies ($M_* > 10^{8}$ $\mathrm{M}_\odot / h$) of the TNG50-1 simulation. Our results demonstrate that galaxy connectivity spans a broad range (from 0 to 9), with more than half of the galaxies connected to two or three streams. We examine a variety of factors that could influence the connectivity finding out that it increases with mass, decreases with local density for low mass galaxies, and does not depend on local environment, estimated by the Delaunay tessellation, for high mass galaxies. We further classify galaxies according to their location in different cosmic web environments, and we highlight the influence of the large-scale structure on the number of connected streams. Our results reflect the different strengths of the cosmic tides, which can prevent the formation of coherent streams feeding the galaxies, or even disconnect the galaxy from its local web. Finally, we show that, at fixed local density, the star-formation rate (SFR) of low mass galaxies is up to $5.9\sigma$ enhanced due to connectivity. This SFR boost is even more significant ($6.3\sigma$) for galaxies embedded in cosmic filaments, where the available matter reservoirs are large. A milder impact is found for high mass galaxies, hinting at different relative efficiencies of matter inflow via small-scale streams in galaxies of different masses.Comment: re-submitted version after positive referee report, comments welcom

Cosmic variance suppression in radiation-hydrodynamic modeling of the reionization-era 21-cm signal

The 21-cm line emitted by neutral hydrogen is the most promising probe of the Epoch of Reionization (EoR). Multiple radio interferometric instruments are on the cusp of detecting its power spectrum. It is therefore essential to deliver robust theoretical predictions, enabling sound inference of the coeval Universe properties. The nature of this signal traditionally required the modelling of $\mathcal{O}(10^{7-8} \, {\rm Mpc}^3)$ volumes to suppress the impact of cosmic variance. However, the recently-proposed Fixed & Paired (F&P) approach uses carefully-crafted simulation pairs to achieve equal results in smaller volumes. In this work, we thoroughly test the applicability of and improvement granted by this technique to different observables of the 21-cm signal from the EoR. We employ radiation-magneto-hydrodynamics simulations to ensure the most realistic physical description of this epoch, greatly improving over previous studies using a semi-numerical approach without accurate galaxy formation physics and radiative transfer. We estimate the statistical improvement granted by the F&P technique on predictions of the skewness, power spectrum, bispectrum and ionized regions size distribution of the 21-cm signal at redshift $7 \leq z \leq 10$ (corresponding to $\geq80\%$ of the gas being neutral). We find that the effective volume of F&P simulations is at least 3.5 times larger than traditional simulations. This directly translates into an equal improvement in the computational cost (in terms of time and memory). Finally, we confirm that a combination of different observables like skewness, power spectrum and bispectrum across different redshifts can be utilised to maximise the improvement.Comment: 13 pages, 11 figures, 2 tables. Accepted for publication in the Monthly Notices of the Royal Astronomical Society (MNRAS

SPICE: the connection between cosmic reionisation and stellar feedback in the first galaxies

We present SPICE, a new suite of RHD cosmological simulations targeting the epoch of reionisation. The goal of these simulations is to systematically probe a variety of stellar feedback models, including "bursty" and "smooth" forms of supernova energy injection, as well as poorly-explored scenarios such as hypernova explosions and radiation pressure. Subtle differences in the behaviour of supernova feedback drive profound differences in reionisation histories, with burstier forms of feedback causing earlier reionisation. We also find that some global galaxy properties, such as the dust-attenuated luminosity functions and star formation main sequence, remain degenerate between models. Stellar feedback and its strength determine the morphological mix of galaxies emerging by z = 5 and that the reionisation history is inextricably connected to intrinsic properties such as galaxy kinematics and morphology. While star-forming, massive disks are prevalent if supernova feedback is "smooth", "bursty" feedback preferentially generates dispersion-dominated systems. Different modes of feedback produce different strengths of outflows, altering the ISM/CGM in different ways, and in turn strongly affecting the escape of LyC photons. We establish a correlation between galaxy morphology and LyC escape fraction, revealing that dispersion-dominated systems have escape fractions 10-50 times higher than their rotation-dominated counterparts at all redshifts. Dispersion-dominated systems should thus preferentially generate large HII regions as compared to their rotation-dominated counterparts. Since dispersion-dominated systems are more prevalent if stellar feedback is more explosive, reionisation occurs earlier in our simulation with burstier feedback. Statistical samples of post-reionisation galaxy morphologies probed with JWST, ALMA and MUSE can constrain stellar feedback and models of cosmic reionisation

Bridging the Gap between Cosmic Dawn and Reionization favors Faint Galaxies-dominated Models

It has been claimed that traditional models struggle to explain the tentative detection of the 21\,cm absorption trough centered at $z\sim17$ measured by the EDGES collaboration. On the other hand, it has been shown that the EDGES results are consistent with an extrapolation of a declining UV luminosity density, following a simple power-law of deep Hubble Space Telescope observations of $4 < z < 9$ galaxies. We here explore the conditions by which the EDGES detection is consistent with current reionization and post-reionization observations, including the neutral hydrogen fraction at $z\sim6$--$8$, Thomson scattering optical depth, and ionizing emissivity at $z\sim5$. By coupling a physically motivated source model derived from radiative transfer hydrodynamic simulations of reionization to a Markov Chain Monte Carlo sampler, we find that it is entirely possible to reconcile the high-redshift (cosmic dawn) and low-redshift (reionization) existing constraints. In particular, we find that high contribution from low-mass halos along with high photon escape fractions are required to simultaneously reproduce cosmic dawn and reionization constraints. Our analysis further confirms that low-mass galaxies produce a flatter emissivity evolution, which leads to an earlier onset of reionization with gradual and longer duration, resulting in a higher optical depth. While our faint-galaxies dominated models successfully reproduce the measured globally averaged quantities over the first one billion years, they underestimate the late redshift-instantaneous measurements in efficiently star-forming and massive systems. We show that our (simple) physically-motivated semi-analytical prescription produces consistent results with the (sophisticated) state-of-the-art \thesan radiation-magneto-hydrodynamic simulation of reionization.Comment: 14 pages, 6 figures. Accepted for publication in ApJ. Comments are welcom

Sistemas de Indicadores de Desempenho em Projetos

This study aims to propose a project performance indicators system, based on the analysis of theproject success criteria´s importance. The research took place in a company whose businessincludes engineering and infrastructure integrated solutions in various industrial sectors, based onaction-research method. Multiple sources of evidence were used, such as analysis of the currentsystem of indicators of the company, analysis of projects in the databases and interviews withrepresentatives of the project office and project managers. The results show the lack of causal logicstructure of the performance measure system and a lack customization according to the type ofproject and stakeholders. A new performance measure system was proposed to the studiedorganization, whose pilot project is flexible enough to cater to the contingency theory thatdifferentiates indicators for each type of project and stakeholders.O presente trabalho visa propor um sistema de indicadores de desempenho de projetos, a partir da análise da importância dos critérios de sucesso em projetos. A abordagem metodológica foi a de pesquisa-ação desenvolvida em uma empresa de engenharia, com atuação em diversos setores. Foram utilizadas várias fontes de evidência, tais como análise do atual sistema de indicadores da empresa, análise dos projetos nas bases de dados e entrevistas com representantes do escritório de projetos e com gerentes de projeto. Os resultados da pesquisa apontam para a falta de amarração causa e efeito do sistema de indicadores da organização, bem como da falta de tratamento diferenciado para os diferentes tipos de projeto e de stakeholders da organização. O sistema de indicadores de desempenho proposto busca mitigar essas lacunas encontradas, cujo projeto piloto é flexível o suficiente para captar essas diferentes necessidades.DOI:10.5585/gep.v2i1.3

THESAN-HR: How does reionization impact early galaxy evolution?

Early galaxies were the radiation source for reionization, with the photoheating feedback from the reionization process expected to reduce the efficiency of star formation in low mass haloes. Hence, to fully understand reionization and galaxy formation, we must study their impact on each other. The THESAN project has so far aimed to study the impact of galaxy formation physics on reionization, but here we present the new THESAN simulations with a factor 50 higher resolution ($m_{\rm b} \approx 10^4$~M$_\odot$) that aim to self-consistently study the back-reaction of reionization on galaxies. By resolving haloes with virial temperatures $T_{\rm vir} < 10^4$~K, we are able to demonstrate that simplistic, spatially-uniform, reionization models are not sufficient to study early galaxy evolution. Comparing the self-consistent THESAN model (employing fully coupled radiation hydrodynamics) to a uniform UV background, we are able to show that galaxies in THESAN are predicted to be larger in physical extent (by a factor $\sim 2$), less metal enriched (by $\sim 0.2$~dex), and less abundant (by a factor $\sim 10$ at $M_{\rm 1500}~=~-10$) by $z=5$. We show that differences in star formation and enrichment patterns lead to significantly different predictions for star formation in low mass haloes, low-metallicity star formation, and even the occupation fraction of haloes. We posit that cosmological galaxy formation simulations aiming to study early galaxy formation $z \gtrsim 3$ must employ a spatially inhomogeneous UV background to accurately reproduce galaxy properties.Comment: Accepted for publication in MNRA

The THESAN project: Lyman-alpha emitter luminosity function calibration

The observability of Lyman-alpha emitting galaxies (LAEs) during the Epoch of Reionization can provide a sensitive probe of the evolving neutral hydrogen gas distribution, thus setting valuable constraints to distinguish different reionization models. In this study, we utilize the new THESAN suite of large-volume (95.5 cMpc) cosmological radiation-hydrodynamic simulations to directly model the Ly$\alpha$ emission from individual galaxies and the subsequent transmission through the intergalactic medium. THESAN combines the AREPO-RT radiation-hydrodynamic solver with the IllustrisTNG galaxy formation model and includes high- and medium-resolution simulations designed to investigate the impacts of halo-mass-dependent escape fractions, alternative dark matter models, and numerical convergence. We find important differences in the Ly$\alpha$ transmission based on reionization history, bubble morphology, frequency offset from line centre, and galaxy brightness. For a given global neutral fraction, Ly$\alpha$ transmission reduces when low mass haloes dominate reionization over high mass haloes. Furthermore, the variation across sightlines for a single galaxy is greater than the variation across all galaxies. This collectively affects the visibility of LAEs, directly impacting observed Ly$\alpha$ luminosity functions (LFs). We employ Gaussian Process Regression using SWIFTEmulator to rapidly constrain an empirical model for dust escape fractions and emergent spectral line profiles to match observed LFs. We find that dust strongly impacts the Ly$\alpha$ transmission and covering fractions of $M_{UV} 10^{11} {\rm M}_{\odot}$ haloes, such that the dominant mode of removing Ly$\alpha$ photons in non-LAEs changes from low IGM transmission to high dust absorption around $z \sim 7$.Comment: 20 pages, 18 figures, MNRAS, in press. Please visit www.thesan-project.com for more detail