The Evolution of the Baryon Distribution in the Universe from Cosmological Simulations

The evolution of the baryon distribution in different phases, derived from cosmological simulations, are here reported. These computations indicate that presently most of baryons are in a warm-hot intergalactic (WHIM) medium (about 43%) while at z = 2.5 most of baryons constitute the diffuse medium (about 74%). Stars and the cold gas in galaxies represent only 14% of the baryons at z = 0. For z < 4 about a half of the metals are locked into stars while the fraction present in the WHIM and in the diffuse medium increases with a decreasing redshift. In the redshift range 0 < z < 2.5, the amount of metals in the WHIM increases from 4% to 22% while in the diffuse medium it increases from 0.6% to 4%. This enrichment process is due essentially to a turbulent diffusion mechanism associated to mass motions driven by supernova explosions. At z = 0, simulated blue (late type) galaxies show a correlation of the oxygen abundance present in the cold gas with the luminosity of the considered galaxy that agrees quite well with data derived from HII regions.Comment: 12 pages, 6 figures, to be published in IJMP

Evolution of the Phase-Space Density of Dark Matter Halos and Mixing Effects in Merger Events

Cosmological N-body simulations were performed to study the evolution of the phase-space density Q = rho/sigma^3 of dark matter halos. No significant differences in the scale relations Q ~ sigma^(-2.1) or Q ~ M^(-0.82) are seen for "cold" or "warm" dark matter models. The follow up of individual halos from z = 10 up to the present time indicate the existence of two main evolutionary phases: an early and fast one (10 > z > 6.5), in which Q decreases on the average by a factor of 40 as a consequence of the randomization of bulk motions and a late and long one (6.5 > z > 0), in which Q decreases by a factor of 20 because of mixing induced by merger events. The study of these halos has also evidenced that rapid and positive variations of the velocity dispersion, induced by merger episods, are related to a fast decrease of the phase density Q.Comment: 6 pages, accepted by MNRA

Accretion onto black holes formed by direct collapse

One possible scenario for the formation of massive black holes (BHs) in the early Universe is from the direct collapse of primordial gas in atomic-cooling dark matter haloes in which the gas is unable to cool efficiently via molecular transitions. We study the formation of such BHs, as well as the accretion of gas onto these objects and the high energy radiation emitted in the accretion process, by carrying out cosmological radiation hydrodynamics simulations. In the absence of radiative feedback, we find an upper limit to the accretion rate onto the central object which forms from the initial collapse of hot (~ 10^4 K) gas of the order of 0.1 MSun per year. This is high enough for the formation of a supermassive star, the immediate precursor of a BH, with a mass of the order of 10^5 MSun. Assuming that a fraction of this mass goes into a BH, we track the subsequent accretion of gas onto the BH self-consistently with the high energy radiation emitted from the accretion disk. Using a ray-tracing algorithm to follow the propagation of ionizing radiation, we model in detail the evolution of the photoionized region which forms around the accreting BH. We find that BHs with masses of the order of 10^4 MSun initially accrete at close to the Eddington limit, but that the accretion rate drops to of order 1 percent of the Eddington limit after ~ 10^6 yr, due to the expansion of the gas near the BH in response to strong photoheating and radiation pressure. One signature of the accretion of gas onto BHs formed by direct collapse, as opposed to massive Pop III star formation, is an extremely high ratio of the luminosity emitted in He II 1640 to that emitted in H_alpha (or Ly_alpha); this could be detected by the James Webb Space Telescope. Finally, we briefly discuss implications for the coevolution of BHs and their host galaxies.Comment: 16 pages; 17 figures, slightly reduced quality; MNRAS in pres

CARMA Project

Non UBCUnreviewedAuthor affiliation: University of ArizonaPostdoctora

Formation et évolution des galaxies (propriétés photométriques, dynamiques et chimiques)

Dans cette thèse, nous présentons les résultats de simulations hydrodynamiques qui décrivent à la fois les mécanismes de feedback et l enrichissement chimique du milieu interstellaire dans un contexte cosmologique. L action combinée du feedback des supernovae (à la fois les types II et les types Ia) et des trous noirs super-massifs contrôle alors la conversion du gaz en étoiles. Un choix judicieux de l efficacité de ces mécanismes nous a permis de reproduire la bimodalité observée dans la distribution de couleur des galaxies. Dans un tel contexte, nous montrons que les galaxies rouges satisfont la relation de Faber-Jackson pendant que les objets bleus reproduisent correctement la relation de Tully-Fisher. De plus, en accord avec les observations, les galaxies massives possèdent des populations stellaire plus vieilles et plus métalliques que celles des petits objets. Un tel comportement anti-hiérarchique peut en réalité s expliquer par les interactions complexes introduites par les sources de feedback. Pour finir, malgré l utilisation d une loi de formation stellaire cosmique pour contraindre le taux de formation stellaire de façon volumique, les galaxies simulées possèdent des histoires d assemblage de masse qui suivent les indications observationnelles : les objets rouges montrent une activité de formation stellaire précoce et importante tandis que les objets bleus présentent une succession de périodes d activité intense étalées sur de plus longues périodes de temps.In this thesis, we report the results of cosmological hydrodynamical simulations that describe accurately both feedback mecanisms and the chemical enrichment of the interstellar medium. The joint action of the feedback from supernovae (both type II and type Ia) and central black holes controls the conversion of gas into stars and the accretion process responsible for the growth of central black holes. An adequate choice of the efficiency of these feedback mecanisms allows us to reproduce the bimodality observed in the colour distribution of galaxies. In this context, we show that red galaxies satisfy the Faber-Jackson relation whilst blue galaxies reproduce the Tully-Fisher relation quite well. Furthermore, in agreement with observations, massive galaxies have older and more metal-rich stellar populations than the ones of less massive objects. Such an anti-hierarchical behaviour is simply a consequence of the complex effects introduced by the feedback sources. Finally, despite the use of a cosmic star formation law to constrain the star formation rate, simulated galaxies present histories of mass assembly that follow observational expectations : red objects show an early and strong star formation activity whilst blue ones display periods of intense activity over larger time scales.NICE-BU Sciences (060882101) / SudocSudocFranceF

Practical Transient System-level ESD Modeling - Environment Contribution

International audienceA methodology for building a transient model of an analog system is detailed. It does not require proprietary knowledge for integrated circuits (IC). At IC level, it combines a protection structure characterization and behavioral modeling with a core description. A specific test board is developed with a smart voltage regulator to validate the methodology. A system model is assembled to perform powered-on transient ESD simulations. A soft-failure criterion is chosen and the prediction of trends in soft-failure generation is carried out. The strong influence of the electrical environment is demonstrated through this case study

Vaccine effectiveness against COVID-19 hospitalization in adults in France: A test negative case control study

International audienceBACKGROUND: Measuring vaccine effectiveness (VE) using real-life data is critical to confirm the effectiveness of licensed vaccine, which could strengthen vaccination adherence. METHODS: We measured VE against adult COVID-19 hospitalization in five hospitals in France using a test negative design. We compared the odds of vaccinated patients hospitalized with COVID-19 with the odds of vaccinated patients hospitalized for the same symptoms with a negative test. RESULTS: A total of 853 patients (463 cases and 390 controls) were included, with a total of 170 patients vaccinated (104 with one dose, 65 with two doses, and one with three doses). There were four cases of breakthrough infections, all in immunocompromised patients. The VE was 84.0% (CI(0.95)=[72.6; 90.6]) for one dose and 96.2% (CI(0.95)=[86.8; 98.9]) for two doses. CONCLUSION: Our results confirm the high VE of COVID-19 vaccine in France to prevent hospitalizations due to the alpha variant