Formation of disc galaxies from cosmological simulations: galactic outflows and chemical evolution

In this Thesis, I study the formation of late-type galaxies and the role that feedback from stars and supermassive black holes (SMBHs) plays in galaxy evolution across cosmic time. By carrying out cosmological hydrodynamical simulations, I investigate how different processes, such as the cosmological gas accretion from the large scale environment, star formation and chemical enrichment, stellar and AGN (Active Galactic Nucleus) feedback, affect the early stages of forming galaxies and contribute to determine their present-day properties. Driven by the challenging task of simulating late-type galaxies with a limited bulge and a dominant disc in a cosmological context, I study the impact of galactic outflow modelling on the formation and evolution of a disc galaxy. I find that galactic outflows regulate the timing of gas accretion and determine the star formation history of the forming galaxy. Also, I quantify the strong interplay between the adopted hydrodynamical scheme and the sub-resolution model describing star formation and stellar feedback. Throughout this Thesis, I devote particular emphasis to connect chemical evolution and gas dynamics, in order to interpret observations of metal abundance in the interstellar medium (ISM) and circumgalactic medium (CGM). I investigate the metal content of gas and stars, and explore how the variation of the essential elements contributing to define the model of chemical evolution determine final metal abundance trends. The investigation that I present is guided by observations and focusses on the results at redshift z = 0, with particular emphasis on the role played by the high-mass end of the IMF. Moreover, I introduce a novel methodology to generate synthetic stars from star particles. The technique that I developed takes properties of star particles from simulations as input and allows to obtain a catalogue of mock stars, provided with photometric properties, whose characteristics are drawn from the input features. The ultimate goal of this method is to translate the populations of star particles of a simulation into stellar populations, thereby enabling a direct and accurate comparison with observations. This technique will be of paramount importance with ongoing survey data releases (e.g. GAIA and surveys of resolved stellar populations). Also, I investigate the role of AGN feedback in regulating the formation and evolution of late-type galaxies. I introduce a new model aimed at investigating the interaction between the central SMBH and the various gas phases which coexist in the ISM of the host galaxy

Supermassive black hole spin evolution in cosmological simulations with OpenGadget3

Mass and spin of massive black holes (BHs) at the centre of galaxies evolve due to gas accretion and mergers with other BHs. Besides affecting e.g. the evolution of relativistic jets, the BH spin determines the efficiency with which the BH radiates energy. Using cosmological, hydrodynamical simulations, we investigate the evolution of the BH spin across cosmic time and its role in controlling the joint growth of supermassive BHs and their host galaxies. We implement a sub-resolution prescription that models the BH spin, accounting for both BH coalescence and misaligned accretion through a geometrically thin, optically thick disc. We investigate how BH spin evolves in two idealised setups, in zoomed-in simulations, and in a cosmological volume. The latter simulation allows us to retrieve statistically robust results as for the evolution and distribution of BH spins as a function of BH properties. We find that BHs with $M_{\rm BH}\lesssim 2 \times 10^{7}\;{\rm M}_{\odot}$ grow through gas accretion, occurring mostly in a coherent fashion that favours spin-up. Above $M_{\rm BH}\gtrsim 2 \times 10^{7}~{\rm M}_{\odot}$ the gas angular momentum directions of subsequent accretion episodes are often uncorrelated with each other. The probability of counter-rotating accretion and hence spin-down increases with BH mass. In the latter mass regime, BH coalescence plays an important role. The spin magnitude displays a wide variety of histories, depending on the dynamical state of the gas feeding the BH and the relative contribution of mergers and gas accretion. As a result of their combined effect, we observe a broad range of values of the spin magnitude at the high-mass end. Our predictions for the distributions of BH spin and spin-dependent radiative efficiency as a function of BH mass are in very good agreement with observations.Comment: 20 pages, 17 figures, submitted to A&A. Comments welcome

Supermassive black hole spin evolution in cosmological simulations with OpenGadget3

Mass and spin of massive black holes (BHs) at the centre of galaxies evolve due to gas accretion and mergers with other BHs. Besides affecting e.g. the evolution of relativistic jets, the BH spin determines the efficiency with which the BH radiates energy. Using cosmological, hydrodynamical simulations, we investigate the evolution of the BH spin across cosmic time and its role in controlling the joint growth of supermassive BHs and their host galaxies. We implement a sub-resolution prescription that models the BH spin, accounting for both BH coalescence and misaligned accretion through a geometrically thin, optically thick disc. We investigate how BH spin evolves in two idealised setups, in zoomed-in simulations, and in a cosmological volume. The latter simulation allows us to retrieve statistically robust results as for the evolution and distribution of BH spins as a function of BH properties. We find that BHs with MBH≲2×107M⊙ grow through gas accretion, occurring mostly in a coherent fashion that favours spin-up. Above MBH≳2×107 M⊙ the gas angular momentum directions of subsequent accretion episodes are often uncorrelated with each other. The probability of counter-rotating accretion and hence spin-down increases with BH mass. In the latter mass regime, BH coalescence plays an important role. The spin magnitude displays a wide variety of histories, depending on the dynamical state of the gas feeding the BH and the relative contribution of mergers and gas accretion. As a result of their combined effect, we observe a broad range of values of the spin magnitude at the high-mass end. Our predictions for the distributions of BH spin and spin-dependent radiative efficiency as a function of BH mass are in very good agreement with observations

The cosmological simulation code OpenGadget3 – implementation of meshless finite mass

Subsonic turbulence plays a major role in determining properties of the intracluster medium (ICM). We introduce a new meshless finite mass (MFM) implementation in OPENGADGET3 and apply it to this specific problem. To this end, we present a set of test cases to validate our implementation of the MFM framework in our code. These include but are not limited to: the soundwave and Kepler disc as smooth situations to probe the stability, a Rayleigh-Taylor and Kelvin-Helmholtz instability as popular mixing instabilities, a blob test as more complex example including both mixing and shocks, shock tubes with various Mach numbers, a Sedov blast wave, different tests including self-gravity such as gravitational freefall, a hydrostatic sphere, the Zeldovich-pancake, and a 1015 M⊙ galaxy cluster as cosmological application. Advantages over smoothed particle hydrodynamics (SPH) include increased mixing and a better convergence behaviour. We demonstrate that the MFM-solver is robust, also in a cosmological context. We show evidence that the solver preforms extraordinarily well when applied to decaying subsonic turbulence, a problem very difficult to handle for many methods. MFM captures the expected velocity power spectrum with high accuracy and shows a good convergence behaviour. Using MFM or SPH within OPENGADGET3 leads to a comparable decay in turbulent energy due to numerical dissipation. When studying the energy decay for different initial turbulent energy fractions, we find that MFM performs well down to Mach numbers M≈0.01 . Finally, we show how important the slope limiter and the energy-entropy switch are to control the behaviour and the evolution of the fluids

Chemical evolution of disc galaxies from cosmological simulations

We perform a suite of cosmological hydrodynamical simulations of disc galaxies, with zoomedin initial conditions leading to the formation of a halo of mass M-halo, DM similar or equal to 2 x 10(12) M-circle dot at redshift z = 0. These simulations aim at investigating the chemical evolution and the distribution of metals in a disc galaxy, and at quantifying the effect of (i) the assumed IMF, (ii) the adopted stellar yields, and (iii) the impact of binary systems originating SNe Ia on the process of chemical enrichment. We consider either a Kroupa, Tout & Gilmore (1993) or a more top-heavy Kroupa (2001) IMF, two sets of stellar yields and different values for the fraction of binary systems suitable to give rise to SNe Ia. We investigate stellar ages, SN rates, stellar and gas metallicity gradients, and stellar alpha-enhancement in simulations, and compare predictions with observations. We find that a Kroupa et al. (1993) IMF has to be preferred when modelling late-type galaxies in the local Universe. On the other hand, the comparison of stellar metallicity profiles and alpha-enhancement trends with observations of Milky Way stars shows a better agreement when a Kroupa (2001) IMF is assumed. Comparing the predicted SN rates and stellar alpha-enhancement with observations supports a value for the fraction of binary systems producing SNe Ia of 0.03, at least for late-type galaxies and for the considered IMFs. Adopted stellar yields are crucial in regulating cooling and star formation, and in determining patterns of chemical enrichment for stars, especially for those located in the galaxy bulge

Insights on the origin of ORCs from cosmological simulations

We investigate shock structures driven by merger events in high-resolution simulations that result in a galaxy with a virial mass M ~ 1e12 Msol. We find that the sizes and morphologies of the internal shocks resemble remarkably well those of the newly-detected class of odd radio circles (ORCs). This would highlight a so-far overlooked mechanism to form radio rings, shells and even more complex structures around elliptical galaxies. Mach numbers of M = 2-3 for such internal shocks are in agreement with the spectral indices of the observed ORCs. We estimate that ~5 percent of galaxies could undergo merger events which occasionally lead to such prominent structures within the galactic halo during their lifetime, explaining the low number of observed ORCs. At the time when the shock structures are matching the physical sizes of the observed ORCs, the central galaxies are typically classified as early-type galaxies, with no ongoing star formation, in agreement with observational findings. Although the energy released by such mergers could potentially power the observed radio luminosity already in Milky-Way-like halos, our predicted luminosity from a simple, direct shock acceleration model is much smaller than the observed one. Considering the estimated number of candidates from our cosmological simulations and the higher observed energies, we suggest that the proposed scenario is more likely for halo masses around 1e13 Msol in agreement with the observed stellar masses of the galaxies at the center of ORCs. Such shocks might be detectable with next generation X-ray instruments like the Line Emission Mapper (LEM).Comment: modified figure 4 to match published versio

On the effect of galactic outflows in cosmological simulations of disc galaxies

We investigate the impact of galactic outflow modelling on the formation and evolution of a disc galaxy, by performing a suite of cosmological simulations with zoomed-in initial conditions of a Milky Way-sized halo. We verify how sensitive the general properties of the simulated galaxy are to the way in which stellar feedback triggered outflows are implemented, keeping initial conditions, simulation code and star formation (SF) model all fixed. We present simulations that are based on a version of the GADGET3 code where our sub-resolution model is coupled with an advanced implementation of Smoothed Particle Hydrodynamics that ensures a more accurate fluid sampling and an improved description of gas mixing and hydrodynamical instabilities. We quantify the strong interplay between the adopted hydrodynamic scheme and the sub-resolution model describing SF and feedback. We consider four different galactic outflow models, including the one introduced by Dalla Vecchia and Schaye (2012) and a scheme that is inspired by the Springel and Hernquist (2003) model. We find that the sub-resolution prescriptions adopted to generate galactic outflows are the main shaping factor of the stellar disc component at low redshift. The key requirement that a feedback model must have to be successful in producing a disc-dominated galaxy is the ability to regulate the high-redshift SF (responsible for the formation of the bulge component), the cosmological infall of gas from the large-scale environment, and gas fall-back within the galactic radius at low redshift, in order to avoid a too high SF rate at z=0

The formation history of the Milky Way disc with high-resolution cosmological simulations

We analyse from an observational perspective the formation history and kinematics of a Milky Way-like galaxy from a high- resolution zoom-in cosmological simulation that we compare to those of our Galaxy as seen by Gaia DR2 to better understand the origin and evolution of the Galactic thin and thick discs. The cosmological simulation was carried out with the GADGET-3 TreePM+SPH code using the MUlti-Phase Particle Integrator (MUPPI) model. We disentangle the complex overlapping of stellar generations that rises from the top-down and inside-out formation of the galactic disc. We investigate cosmological signatures in the phase-space of mono-age populations and highlight features stemming from past and recent dynamical perturbations. In the simulation, we identify a satellite with a stellar mass of 1.2 × 109 M⊙, i.e. stellar mass ratio ∼ 5.5 per cent at the time, accreted at z ∼ 1.6, which resembles the major merger Gaia–Sausage–Enceladus that produced the Galactic thick disc, i.e. ∼ 6 per cent. We found at z ∼ 0.5–0.4 two merging satellites with a stellar mass of 8.8 × 108 M⊙ and 5.1 × 108 M⊙ that are associated to a strong starburst in the star formation history, which appears fairly similar to that recently found in the solar neighbourhood. Our findings highlight that detailed studies of coeval stellar populations kinematics, which are made available by current and future Gaia data releases and in synergy with simulations, are fundamental to unravel the formation and evolution of the Milky Way discs

Is the star formation rate in z∼6z\sim 6 quasars overestimated?

The large total infrared (TIR) luminosities ($L_{\rm TIR} \gtrsim 10^{12}~L_\odot$) observed in $z \sim 6$ quasars are generally converted into high star formation rates ($SFR \gtrsim 10^2~M_\odot$ yr$^{-1}$) of their host galaxies. However, these estimates rely on the assumption that dust heating is dominated by stellar radiation, neglecting the contribution from the central Active Galactic Nuclei (AGN). We test the validity of this assumption by combining cosmological hydrodynamic simulations with radiative transfer calculations. We find that, when AGN radiation is included in the simulations, the mass (luminosity)-weighted dust temperature in the host galaxies increases from $T\approx 50$ K ($T \approx 70$ K) to $T\approx 80$ K ($T\approx 200$ K), suggesting that AGN effectively heat the bulk of dust in the host galaxy. We compute the AGN-host galaxy $SFR$ from the synthetic spectral energy distribution by using standard $SFR - L_{\rm TIR}$ relations, and compare the results with the "true" values in the simulations. We find that the $SFR$ is overestimated by a factor of $\approx 3$ ($\gtrsim 10$) for AGN bolometric luminosities of $L_{\rm bol} \approx 10^{12}~L_\odot$ ($\gtrsim 10^{13}~ L_\odot$), implying that the star formation rates of $z\sim 6$ quasars can be overestimated by over an order of magnitude.Comment: 9 pages, 6 figures. Accepted for publication by MNRA

Audiodescrição: e agora, que tecnologias digitais têm sido adotadas neste processo?

Este artigo investiga quais Tecnologias Digitais têm sido adotadas e descritas como facilitadoras do processo de Audiodescrição (AD) em publicações de periódicos brasileiros no período de 2010 a 2018. Para tanto, realizou-se uma Revisão Sistemática da Literatura (RSL), em que 47 artigos científicos foram analisados e classificados nas categorias Audiodescrição e Audiodescrição para a Educação. Os resultados revelaram aspectos como (a) a baixa produção científica sobre AD para Educação, (b) as regiões brasileiras Nordeste e Sudeste como os principais polos de publicação e (c) um baixo número de publicações que revelam quais Tecnologias Digitais são adotadas na AD. Contudo, destaca-se a adesão por softwares proprietários e gratuitos para diferentes finalidades na AD