Formation of Dark Matter Haloes in a Homogeneous Dark Energy Universe

Several independent cosmological tests have shown evidences that the energy density of the Universe is dominated by a dark energy component, which cause the present accelerated expansion. The large scale structure formation can be used to probe dark energy models, and the mass function of dark matter haloes is one of the best statistical tools to perform this study. We present here a statistical analysis of mass functions of galaxies under a homogeneous dark energy model, proposed in the work of Percival (2005), using an observational flux-limited X-ray cluster survey, and CMB data from WMAP. We compare, in our analysis, the standard Press-Schechter (PS) approach (where a Gaussian distribution is used to describe the primordial density fluctuation field of the mass function), and the PL (Power Law) mass function (where we apply a nonextensive q-statistical distribution to the primordial density field). We conclude that the PS mass function cannot explain at the same time the X-ray and the CMB data (even at 99% confidence level), and the PS best fit dark energy equation of state parameter is $\omega=-0.58$, which is distant from the cosmological constant case. The PL mass function provides better fits to the HIFLUGCS X-ray galaxy data and the CMB data; we also note that the $\omega$ parameter is very sensible to modifications in the PL free parameter, $q$, suggesting that the PL mass function could be a powerful tool to constrain dark energy models.Comment: 4 pages, 2 figures, Latex. Accepted for publication in the International Journal of Modern Physics D (IJMPD)

The metal and dust yields of the first massive stars

We quantify the role of Population (Pop) III core-collapse supernovae (SNe) as the first cosmic dust polluters. Starting from a homogeneous set of stellar progenitors with masses in the range [13 - 80] Msun, we find that the mass and composition of newly formed dust depend on the mixing efficiency of the ejecta and the degree of fallback experienced during the explosion. For standard Pop III SNe, whose explosions are calibrated to reproduce the average elemental abundances of Galactic halo stars with [Fe/H] < -2.5, between 0.18 and 3.1 Msun (0.39 - 1.76 Msun) of dust can form in uniformly mixed (unmixed) ejecta, and the dominant grain species are silicates. We also investigate dust formation in the ejecta of faint Pop III SN, where the ejecta experience a strong fallback. By examining a set of models, tailored to minimize the scatter with the abundances of carbon-enhanced Galactic halo stars with [Fe/H ] < -4, we find that amorphous carbon is the only grain species that forms, with masses in the range 2.7 10^{-3} - 0.27 Msun (7.5 10^{-4} - 0.11 Msun) for uniformly mixed (unmixed) ejecta models. Finally, for all the models we estimate the amount and composition of dust that survives the passage of the reverse shock, and find that, depending on circumstellar medium densities, between 3 and 50% (10 - 80%) of dust produced by standard (faint) Pop III SNe can contribute to early dust enrichment.Comment: Accepted by MNRAS, 22 pages, 12 figures, 12 table

Where does galactic dust come from?

Here we investigate the origin of the dust mass (Mdust) observed in the Milky Way (MW) and of dust scaling relations found in a sample of local galaxies from the DGS and KINGFISH surveys. To this aim, we model dust production from Asymptotic Giant Branch (AGB) stars and supernovae (SNe) in simulated galaxies forming along the assembly of aMW-like halo in a well-resolved cosmic volume of 4 cMpc using the GAMESH pipeline. We explore the impact of different sets of metallicity and mass-dependent AGB and SN dust yields on the predicted Mdust. Our results show that models accounting for grain destruction by the SN reverse shock predict a total dust mass in the MW, that is a factor of ~4 less than observed, and cannot reproduce the observed galaxy-scale relations between dust and stellar masses, and dust-togas ratios and metallicity, with a smaller discrepancy in galaxies with low metallicity (12 + log(O/H) &lt; 7.5) and low stellar masses (Mstar &lt; 107 M⊙). In agreement with previous studies, we suggest that competing processes in the interstellar medium must be at play to explain the observed trends. Our result reinforces this conclusion by showing that it holds independently of the adopted AGB and SN dust yields

New Constraints on the Variable Equation of State Parameter from X-Ray Gas Mass Fractions and SNe Ia

Recent measurements are suggesting that we live in a flat Universe and that its present accelerating stage is driven by a dark energy component whose equation of state may evolve in time. Assuming two different parameterizations for the function $\omega(z)$, we constrain their free parameters from a joint analysis involving measurements from X-Ray luminosity of galaxy clusters and SNe type Ia data.Comment: paper, 6 pages, 1 figure Accepted by Int. Journal of Modern Physics D (IJPMD

Supernova dust yields: the role of metallicity, rotation, and fallback

Supernovae (SNe) are considered to have a major role in dust enrichment of high redshift galaxies and, due to the short lifetimes of interstellar grains, in dust replenishment of local galaxies. Here we explore how SN dust yields depend on the mass, metallicity, and rotation rate of the progenitor stars, and on the properties of the explosion. To this aim, assuming uniform mixing inside the ejecta, we quantify the dust mass produced by a sample of SN models with progenitor masses $13~M_{\odot} \leq M \leq 120~M_{\odot}$, metallicity $\rm -3 \leq [Fe/H] \leq 0$, rotation rate $\rm v_{\rm rot} = 0$ and $300$~km/s, that explode with a fixed energy of $1.2 \times 10^{51}$~erg (FE models) or with explosion properties calibrated to reproduce the $\rm ^{56}Ni$ - $M$ relation inferred from SN observations (CE models). We find that rotation favours more efficient dust production, particularly for more massive, low metallicity stars, but that metallicity and explosion properties have the largest effects on the dust mass and its composition. In FE models, SNe with $M \leq 20 - 25 ~M_{\odot}$ are more efficient at forming dust: between 0.1 and 1 $M_\odot$ is formed in a single explosion, with a composition dominated by silicates, carbon and magnetite grains when $\rm [Fe/H] = 0$, and by carbon and magnetite grains when $\rm [Fe/H] < 0$. In CE models, the ejecta are massive and metal-rich and dust production is more efficient. The dust mass increases with $M$ and it is dominated by silicates, at all [Fe/H].Comment: MNRAS, in pres

Evolution of dwarf galaxies hosting GW150914-like events

Here we present a detailed analysis of the properties and evolution of different dwarf galaxies, candidates to host the coalescence of black hole binary systems generating GW150914-like events. By adopting a novel theoretical framework coupling the binary population synthesis code SEBA with the Galaxy formationmodel GAMESH, we can investigate the detailed evolution of these objects in awell-resolved cosmological volume of 4 cMpc, having aMilkyWay (MW)- like galaxy forming at its centre. We identify three classes of interesting candidate galaxies: MW progenitors, dwarf satellites, and dwarf galaxies evolving in isolation. We find that (i) despite differences in individual histories and specific environments the candidates reduce to only nine representative galaxies; (ii) among them, 3c44 per cent merge into the MW halo progenitors by the redshift of the expected signal, while the remaining dwarfs are found as isolated or as satellites of the MW and their evolution is strongly shaped by both peculiar dynamical history and environmental feedback; (iii) a stringent condition for the environments where GW150914-like binaries can form comes from a combination of the accretion history of their dark matter haloes and the radiative feedback in the high-redshift universe; and (iv) by comparing with the observed catalogues from the DGS and ALLSMOG surveys we find two observed dwarfs respecting the properties predicted by our model. We finally note how the present analysis opens the possibility to build future strategies for host galaxy identification

Stochastic backgrounds of gravitational waves from extragalactic sources

Astrophysical sources emit gravitational waves in a large variety of processes occurred since the beginning of star and galaxy formation. These waves permeate our high redshift Universe, and form a background which is the result of the superposition of different components, each associated to a specific astrophysical process. Each component has different spectral properties and features that it is important to investigate in view of a possible, future detection. In this contribution, we will review recent theoretical predictions for backgrounds produced by extragalactic sources and discuss their detectability with current and future gravitational wave observatories.Comment: 10 pages, 9 figures, proceedings of the GWDAW 10 Conference, submitted to Class. & Quantum Gra

RICERCA DI SISTEMA ELETTRICO. Ricerca di materiali anodici per batterie litio ione operanti in elettroliti organici convenzionali di più elevata energia rispetto a quelle sul mercato

Il rapporto descrive il lavoro svolto per la preparazione e caratterizzazione di anodi per batterie litio ione costituiti da metalli (Si, Sn, Sb) capaci di formare leghe del tipo LixM con il litio secondo la reazione elettrochimicamente reversibile x Li+ + x e- + M LixM dove x può assumere valori pari a 4.4 per Sn e Si e 3 per Sb con capacità teoriche pari a 993 mAh/g, 4200 mAh/g e 660 mAh/g rispettivamente. I problemi degli elettrodi costituiti da leghe metalliche sono essenzialmente dovuti alle variazioni di volume durante i processi di formazione delle leghe che possono raggiungere valori dell’ordine del 300% (Sn), 360 % (Si) e 200 % (Sb). Le variazioni di volume inducono stress meccanici sugli elettrodi che polverizzano progressivamente con rapida perdita di capacità. In letteratura si trovano moltissimi lavori in cui gli stress meccanici sono tamponati preparando elettrodi compositi nei quali le particelle metalliche sono supportate su matrici di varia natura capaci di compensare le variazioni di volume [1]. Sulla base di recenti lavori di letteratura [2-6] durante questa ricerca è stato utilizzato grafene come supporto per le particelle metalliche. Dal punto di vista strutturale il grafene (GNS) corrisponde a grafite completamente esfoliata: array bidimensionale di atomi di carbonio ibridizzati sp2 con uno spessore di un atomo. In quanto tale può essere considerato come il mattone fondamentale per tutte le forme allotropiche dei fullereni (buckyball, carbon nanotubes etc.) [7]. Proprietà fondamentali del grafene sono: (i) elevata area superficiale( 2630 m2/g), (ii) elevatissima conducibilità ( 64 mS cm-1 circa 60 volte quella dei nanotubi). Nel caso oggetto di questa ricerca nei compositi M/grafene, il grafene serve sia come materiale ad elevata conducibilità elettronica, sia come materiale che può intercalare litio ed allo stesso tempo può agire da tampone per minimizzare gli stress meccanici durante i processi di formazione/dissoluzione delle leghe metalliche. La sintesi dei nano compositi grafene-metallo è stata effettuata mediante impregnazione di grafene ossido (GO), preparato in laboratorio, con diversi tipi di sali. I gruppi funzionali (-OH, -COOH, -OOH) presenti sul GO possono ancorare per coordinazione gli ioni metallici che per successiva riduzione danno origine a nanoparticelle [6]. La procedura di preparazione è stata compiuta aggiungendo un sale ad una sospensione di GO in glicole etilenico. La sospensione è stata successivamente trattata con microonde. Il trattamento determina la riduzione del GO a RGO (Reduced Graphene Oxide) e la formazione di metalli ed ossidi metallici. A causa della disposizione casuale dei gruppi funzionali nel GO, le particelle risultanti sono uniformemente distribuite nella matrice di RGO che funziona da tampone per le variazioni di volume. Le polveri così ottenute sono state caratterizzate mediante SEM, TEM, XRD ed utilizzate per la preparazione degli elettrodi con tecnica doctor-blade. I test elettrochimici sono stati condotti in celle a T con Li metallico come contro-elettrodo ed elettrodo di riferimento, fibra di vetro imbevuta con una soluzione 1M di LiPF6 in etilene carbonato/dimetile carbonato 1:1 in peso, (Merck LP30) come separatore. Le capacità specifiche ottenute a velocità di carica e scarica dell’ordine dei 100 mAh/g sono risultate pari a 600, 1000 e 400 per compositi di Sn, Si e Sb, rispettivamente

The use of protic ionic liquids with cathodes for sodium-ion batteries

Herein, we report for the first time the use of a protic ionic liquid as a component of a new Na-ion battery electrolyte. The protic ionic liquid has been tested in combination with two different types of sodium-ion cathode materials, polyanionic Na3V2(PO4)3 and layered Na0.67Mn0.89Mg0.11O2, in order to reveal its impact on the electrode material electrochemical performance. The results evidence that this novel electrolyte performs very well in combination with a polyanionic electrode material, while it shows poor performance with a layered oxide material