Global instability of stellar discs in presence of dark matter halos

Cantarella, Sebastiano (2023) Global instability of stellar discs in presence of dark matter halos. [Laurea magistrale], Università di Bologna, Corso di Studio in Astrofisica e cosmologia [LM-DM270]
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Abstract

Since the 1970s, numerical studies have shown that highly flattened rotationally supported galactic discs are globally unstable: in particular, they are subject to large-scale bar-like instabilities. Ostriker and Peebles (1973) proposed a global stability criterion through the ratio t_OP=T/|W| between the total kinetic energy of rotation of the system T and its total gravitational energy W. Even though t_OP is widely used as a global stability parameter, its applicability has been questioned from both theoretical and numerical perspectives. Efstathiou, Lake and Negroponte (1982) presented an alternative criterion based on the parameter t^*=T_d/[(1+f_ext)^2|W_D|], where T_d represents the stellar kinetic energy of rotation, W_D is the gravitational energy related to the stars in the total disc-halo potential and f_ext=W_dh/W_d is the ratio of the gravitational energy of the stars due to the halo potential and the self-energy of the stellar disc. In this master thesis we have studied the behaviour of t_OP and t^* and their relationship with global instability through N-body simulations with the FVFPS code (Londrillo et al. 2003). Together with t_OP and t^*, we also present and study a new global stability parameter t_W=T_d/|W_D|. At the beginning of the simulations, the disc particles move around circular orbits in the disc-halo potential, where the dark matter halo is rigid, non-rotating and modelled by a Hernquist (1990) profile. In the subsequent part of the thesis, we perform N-body simulations using the FVFPS code for the initial disc-halo systems. In a diagnostic phase, the results of the numerical simulations are analysed. The main results of this work are the following: i) we have found unstable systems even though T_d=0 (i.e. t_OP=t^*=0), which are thus counterexamples of Ostriker and Peebles's and Efstathiou, Lake and Negroponte's criteria; ii) the t_W parameter has some problems too: in all the simulations it is not sensitive to the presence of the halo.

Abstract
Tipologia del documento
Tesi di laurea (Laurea magistrale)
Autore della tesi
Cantarella, Sebastiano
Relatore della tesi
Correlatore della tesi
Scuola
Corso di studio
Ordinamento Cds
DM270
Parole chiave
instabilities galaxies fundamental parameters galaxies structure galaxies kinematics and dynamics galaxies evolution galaxies halos
Data di discussione della Tesi
27 Ottobre 2023
URI

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