Dark matter and stellar populations in the central region of early-type galaxies

This thesis work is aimed at the investigation of the dark matter (DM) amount and distribution in early-type galaxies (ETGs), in relation with the stellar properties, constrained by observations of the kinematic fields of galaxies. In particular, we focus on observations of the projected stellar velocity dispersion in the central region of ETGs. A robust determination of the DM amount and distribution is an open issue, which we explore from two complementary points of view. A top-down approach, with priority given to cosmology, based on the predictions of numerical cosmological simulations, and a bottom-up approach, with priority given to the galactic astrophysics. This is accomplished by using the original numerical code JASMINE (Jeans AxiSymmetric Models of galaxies IN Equilibrium), first developed by Posacki et al. 2013, to build dynamical models of ETGs, based on the solution of the Jeans equations. Our Jeans modelling produces axisymmetric (oblate) spheroids with anisotropic stellar orbits. In this thesis work, we focus on spherical isotropic galaxy models, composed of stars, DM and a central supermassive black hole (BH). The stellar component is modelled by a deprojected de Vaucouleurs or Jaffe density profile and satisfies the Faber-Jackson and size-luminosity Scaling Laws. The BH mass, M_BH, is related to the total stellar mass, M_star, by the Magorrian relation. The DM component is modelled by the NFW density profile. We explore the effect on the dynamics of stars, due to the stellar and DM properties, such as the assumption of a fixed stellar mass-to-light ratio, Upsilon_star,dyn, and fixed halo parameters beta and c (halo-to-stellar scale radius ratio and halo concentration, respectively). We intend to investigate how much the DM amount and distribution can vary, while reproducing a given value for the projected central velocity dispersion of stars, sigma_e8 (luminosity-weighted within R_e/8). Our study suggests that sigma_e8 is not a good [...

Dynamical models of spheroidal multi-component stellar systems

We present a significantly improved version of our numerical code JASMINE, that can now solve the Jeans equations for axisymmetric models of stellar systems, composed of an arbitrary number of stellar populations, a Dark Matter halo, and a central Black Hole. The stellar components can have different structural (density profile, flattening, mass, scale length), dynamical (rotational support, velocity dispersion anisotropy), and population (age, metallicity, Initial Mass Function, mass-to-light ratio) properties. These models, when combined with observations, will allow to investigate important issues, such as quantifying the systematic effects of IMF variations, of mass-to-light ratio gradients, and of different stellar kinematic components (e.g. counter rotating disks, kinematically decoupled cores) on luminosity-weighted properties. The developed analytical and numerical framework aims at modeling Early-Type Galaxies, but it can also be applied to dwarf Spheroidal galaxies and Globular Clusters.Comment: 4 pages 2 figures. To appear in the Proceedings of the 351 IAU Symposium "Star Clusters: From the Milky Way to the Early Universe

An efficient Jeans modelling of axisymmetric galaxies with multiple stellar components

Dynamical models of stellar systems represent a powerful tool to study their internal structure and dynamics, to interpret the observed morphological and kinematical fields, and also to support numerical simulations of their evolution. We present a method especially designed to build axisymmetric Jeans models of galaxies, assumed as stationary and collisionless stellar systems. The aim is the development of a rigorous and flexible modelling procedure of multicomponent galaxies, composed of different stellar and dark matter distributions, and a central supermassive black hole. The stellar components, in particular, are intended to represent different galaxy structures, such as discs, bulges, halos, and can then have different structural (density profile, flattening, mass, scale-length), dynamical (rotation, velocity dispersion anisotropy), and population (age, metallicity, initial mass function, mass-to-light ratio) properties. The theoretical framework supporting the modelling procedure is presented, with the introduction of a suitable nomenclature, and its numerical implementation is discussed, with particular reference to the numerical code JASMINE2, developed for this purpose. We propose an approach for efficiently scaling the contributions in mass, luminosity, and rotational support, of the different matter components, allowing for fast and flexible explorations of the model parameter space. We also offer different methods of the computation of the gravitational potentials associated of the density components, especially convenient for their easier numerical tractability. A few galaxy models are studied, showing internal, and projected, structural and dynamical properties of multicomponent galaxies, with a focus on axisymmetric early-type galaxies with complex kinematical morphologies. The application of galaxy models to the study of initial conditions for hydro-dynamical and $N$-body simulations of galaxy evolution is also addressed, allowing in particular to investigate the large number of interesting combinations of the parameters which determine the structure and dynamics of complex multicomponent stellar systems

A Parameter Space Exploration of High-resolution Numerically Evolved Early Type Galaxies Including AGN Feedback and Accurate Dynamical Treatment of Stellar Orbits

An extensive exploration of the model parameter space of axisymmetric early type galaxies (ETGs) hosting a central supermassive black hole (SMBH) is conducted by means of high-resolution hydrodynamical simulations performed with our code MACER. Global properties such as (1) total SMBH accreted mass, (2) final X-ray luminosity and temperature of the X-ray emitting halos, (3) total amount of new stars formed from the cooling gas, and (4) total ejected mass in the form of supernovae and active galactic nuclei (AGN) feedback induced galactic winds, are obtained as a function of galaxy structure and internal dynamics.An extensive exploration of the model parameter space of axisymmetric early type galaxies (ETGs) hosting a central supermassive black hole (SMBH) is conducted by means of high-resolution hydrodynamical simulations performed with our code MACER. Global properties such as (1) total SMBH accreted mass, (2) final X-ray luminosity and temperature of the X-ray emitting halos, (3) total amount of new stars formed from the cooling gas, and (4) total ejected mass in the form of supernovae and active galactic nuclei (AGN) feedback induced galactic winds, are obtained as a function of galaxy structure and internal dynamics. In addition to the galactic dark matter halo, the model galaxies are also embedded in a group/cluster dark matter halo; finally, cosmological accretion is also included, with the amount and time dependence derived from cosmological simulations. Angular momentum conservation leads to the formation of cold H i disks; these disks further evolve under the action of star formation induced by disk instabilities, of the associated mass discharge onto the central SMBH, and of the consequent AGN feedback. At the end of the simulations, the hot (metal-enriched) gas mass is roughly 10% the mass in the old stars, with twice as much having been ejected into the intergalactic medium. The cold gas disks are approximately kiloparsec in size, and the metal-rich new stars are in 0.1 kpc disks. The masses of cold gas and new stars are roughly 0.1% of the mass of the old stars. Overall, the final systems appear to reproduce quite successfully the main global properties of real ETGs

Teorema del viriale e applicazioni astrofisiche

Il teorema del viriale consiste in una relazione tra energia cinetica e energia potenziale totali di un sistema all'equilibrio. Il concetto di Viriale (dal latino vires, plurale di vis, 'forza') è stato introdotto dal fisico e matematico tedesco Rudolf Julius Emanuel Clausius (1822-1888) per indicare la quantità N Fi •xi i=1 che rappresenta la somma, fatta su tutte le N particelle di un sistema, dei prodotti scalari del vettore forza totale agente su ciascuna particella per il vettore posizione della particella stessa, rispetto ad un riferimento inerziale scelto. Tale quantità altro non è che un'energia potenziale. Dire che un sistema di particelle è virializzato equivale a dire che esso è stazionario, cioè all'equilibrio. In questo elaborato sono di nostro interesse sistemi astrofisici gravitazionali, in cui cioè l'energia potenziale sia dovuta solo a campi gravitazionali. Distingueremo innanzitutto sistemi collisionali e non collisionali, introducendo i tempi scala di attraversamento e di rilassamento. Dopo una trattazione teorica del teorema, nell'approssimazione di continuità - per cui sostuiremo alle sommatorie gli integrali - e di non collisionalità, an- dremo a studiarne l'importanza in alcuni sistemi astrofisici: applicazione agli ammassi stellari, alle galassie e agli ammassi di galassie, stima della quantità di materia oscura nei sistemi, instabilità di Jeans in nubi molecolari, rotazione delle galassie ellittiche. Per ragioni di spazio non saranno affrontati altri casi, di cui ne citiamo alcuni: collasso delle stelle, stima della massa dei buchi neri al centro delle galassie, 'mass-to-light ratio' di sistemi sferici. Parleremo in generale di “particelle” costituenti i sistemi per intendere stelle, galassie, particelle di gas a seconda del sistema in esame. Trascureremo in ogni caso le influenze gravitazionali di distribuzioni di densità esterne al sistema

Paradigmi del fotografico

Ad oltre centottanta anni dalla sua nascita ufficiale e a dispetto dei numerosi annunci di “morte” legati all’avvento del sistema digitale, la fotografia continua a occupare e ridefinire i più diversi ambiti della nostra vita, proponendosi, di fatto, come un oggetto culturale in continuo aggiornamento. In questa prospettiva, il volume intende testimoniare, con una pluralità di voci e di metodologie, la complessità e la ricchezza dei dibattiti attualmente in corso attorno al fotografico, chiamando in causa i rapporti con le arti visive, gli utilizzi nelle pratiche sociali, le riflessioni sulle modalità espositive e le relazioni con l’ambiente, i problemi dell’archivio e quelli della documentazione, il tutto accompagnato dalla costante evoluzione del discorso teorico