Here we introduce GAMESH, a novel pipeline which implements self-consistent radiative and chemical feedback in a computational model of galaxy formation. By combining the cosmological chemical-evolution model GAMETE with the radiative transfer code C
RASH, GAMESH can post process realistic outputs of a N-body simulation describing the redshift evolution of the forming galaxy. After introducing the GAMESH implementation and its features, we apply the code to a low-resolution N-body simulation of the Milky Way formation and we investigate the combined effects of self-consistent radiative and chemical feedback. Many physical properties, which can be directly compared with observations in the Galaxy and its surrounding satellites, are predicted by the code along the merger-tree assembly. The resulting redshift evolution of the Local Group star formation rates, reionisation and metal enrichment along with the predicted Metallicity Distribution Function of halo stars are critically compared with observations. We discuss the merits and limitations of the first release of GAMESH, also opening new directions to a full implementation of feedback processes in galaxy formation models by combining semi-analytic and numerical methods.
We present a tree-tensor-network-state (TTNS) method study of the ionic-neutral curve crossing of LiF. For this ansatz, the long-range correlation deviates from the mean-field value polynomially with distance, thus for quantum chemical applications t
he computational cost could be significantly smaller than that of previous attempts using the density matrix renormalization group (DMRG) method. Optimization of the tensor network topology and localization of the avoided crossing are discussed in terms of entanglement.
We calculate the dust formed around AGB and SAGB stars of metallicity Z=0.008 by following the evolution of models with masses in the range 1M<M<8M throughthe thermal pulses phase, and assuming that dust forms via condensation of molecules within a w
ind expanding isotropically from the stellar surface. We find that, because of the strong Hot Bottom Burning (HBB) experienced, high mass models produce silicates, whereas lower mass objects are predicted to be surrounded by carbonaceous grains; the transition between the two regimes occurs at a threshold mass of 3.5M. These fndings are consistent with the results presented in a previous investigation, for Z=0.001. However, in the present higher metallicity case, the production of silicates in the more massive stars continues for the whole AGB phase, because the HBB experienced is softer at Z=0.008 than at Z=0.001, thus the oxygen in the envelope, essential for the formation of water molecules, is never consumed completely. The total amount of dust formed for a given mass experiencing HBB increases with metallicity, because of the higher abundance of silicon, and the softer HBB, both factors favouring a higher rate of silicates production. This behaviour is not found in low mass stars,because the carbon enrichment of the stellar surface layers, due to repeated Third Drege Up episodes, is almost independent of the metallicity. Regarding cosmic dust enrichment by intermediate mass stars, we find that the cosmic yield at Z=0.008 is a factor 5 larger than at Z=0.001. In the lower metallicity case carbon dust dominates after about 300 Myr, but at Z=0.008 the dust mass is dominated by silicates at all times,with a prompt enrichment occurring after about 40 Myr, associated with the evolution of stars with masses M =7.5 -8M.
The Particle-in-Cell (PIC) method was used to study two different ion thruster concepts - Stationary Plasma Thrusters (SPT) and High Efficiency Multistage Plasma Thrusters (HEMP-T), in particular the plasma properties in the discharge chamber due to
the different magnetic field configurations. Special attention was paid to the simulation of plasma particle fluxes on the thrusters channel surfaces. In both cases, PIC proved itself as a powerful tool, delivering important insight into the basic physics of the different thruster concepts. The simulations demonstrated that the new HEMP thruster concept allows for a high thermal efficiency due to both minimal energy dissipation and high acceleration efficiency. In the HEMP thruster the plasma contact to the wall is limited only to very small areas of the magnetic field cusps, which results in much smaller ion energy flux to the thruster channel surface as compared to SPT. The erosion yields for dielectric discharge channel walls of SPT and HEMP thrusters were calculated with the binary collision code SDTrimSP. For SPT, an erosion rate on the level of 1 mm of sputtered material per hour was observed. For HEMP, thruster simulations have shown that there is no erosion inside the dielectric discharge channel.
We explore the effect of cosmic radiative feedback from the sources of reionization on the thermal evolution of the intergalactic medium. We find that different prescriptions for this feedback predict quite different thermal and reionization historie
s. In spite of this, current data can not discriminate among different reionization scenarios. We find that future observations both from 21-cm and CMB experiments can be used to break the degeneracy among model parameters provided that we will be able to remove the foreground signal at the percent (or better) level.
We use a semi-analytical model to study the impact of reionization, and the associated radiative feedback, on galaxy formation. Two feedback models have been considered: (i) a standard prescription, according to which star formation is totally suppre
ssed in galaxies with circular velocity below a critical threshold (model CF06) and (ii) a characterization based on the filtering scale (model G00), allowing for a gradual reduction of the gas available for star formation in low-mass galaxies. In model CF06 reionization starts at z ~ 15-20, is 85% complete by z ~ 10; at the same z, the ionized fraction is 16% in model G00. The models match SDSS constraints on the evolution of the neutral hydrogen fraction at z < 7, but predict different Thomson optical depths, tau_e = 0.1017 (CF06), and 0.0631 (G00); such values are within 1 sigma of the WMAP 3-yr determination. Both models are in remarkable good agreement with additional existing data (evolution of Lyman-limit systems, cosmic star formation history, high-z galaxy counts, IGM thermal history), which therefore cannot be used to discriminate among different feedback models. Deviations among radiative feedback prescriptions emerge when considering the expected HI 21 cm background signal, where a ~ 15 mK absorption feature in the range 75-100 MHz is present in model G00 and a global shift of the emission feature preceding reionization towards larger frequencies occurs in the same model. Single dish observations with existing or forthcoming low-frequency radio telescopes can achieve mK sensitivity, allowing the identification of these features provided that foregrounds can be accurately subtracted.
A PopIII/Pop II transition from massive to normal stars is predicted to occur when the metallicity of the star forming gas crosses the critical range Z_cr = 10^(-5 +/- 1) Z_sun. To investigate the cosmic implications of such process we use numerical
simulations which follow the evolution, metal enrichment and energy deposition of both Pop III and Pop II stars. We find that: (i) due to inefficient heavy element transport by outflows and slow genetic transmission during hierarchical growth, large fluctuations around the average metallicity arise; as a result Pop III star formation continues down to z=2.5, but at a low peak rate of 10^-5 M_sun yr^-1 Mpc^-3 occurring at z~6 (about 10^-4 of the PopII one); (ii) Pop III star formation proceeds in a inside-out mode in which formation sites are progressively confined at the periphery of collapsed structures, where the low gas density and correspondingly long free-fall timescales result in a very inefficient astration. These conclusions strongly encourage deep searches for pristine star formation sites at moderate (2<z<5) redshifts where metal free stars are likely to be hidden.
