One of the biggest challenges in understanding the fuelling of supermassive
black holes in active galactic nuclei (AGN) is not on accounting
for the source of fuel, as a galaxy can comfortably supply
the required mass budget, but on its actual delivery. While a clear
picture has been developed for the large scale (~ kpc) down to the
intermediate one (~ 100 pc), and for the smallest scales (~ 0.1 pc)
where an accretion disc likely forms, a bridge that has proven difficult
to build is that between ~ 100 pc and ~ 0.1 pc. It is feared that
gas at these scales might still retain enough angular momentum and
settle into a larger scale disc with very low or no inflow to form or
replenish the inner accretion disc (on ~ 0.01 pc scales). In this Thesis,
we present numerical simulations in which a rotating gaseous shell
flows towards a SMBH because of its lack of rotational support. As inflow
proceeds, gas from the shell impacts an already present nuclear
(~ 10pc) disc. The cancellation of angular momentum and redistribution
of gas, due to the misalignment between the angular momentum
of the shell and that of the disc, is studied in this scenario. The underlying
hypothesis is that even if transport of angular momentum
at these scales may be inefficient, the interaction of an inflow with a
nuclear disc would still provide a mechanism to bring mass inwards
because of the cancellation of angular momentum. We quantify the
amount of gas such a cancellation would bring to the central parsec
under different circumstances: Co- and counter-rotation between the
disc and the shell and the presence or absence of an initial turbulent
kick; we also discuss the impact of self gravity in our simulations.
The scenario we study is highly idealized and designed to capture
the specific outcomes produced by the mechanism proposed. We find
that angular momentum cancellation and redistribution via hydrodynamical
shocks leads to sub-pc inflows enhanced by more than 2-3
orders of magnitude. In all of our simulations, the gas inflow rate
across the inner parsec is higher than in the absence of the interaction.
Gas mixing changes the orientation of the nuclear disc as the
interaction proceeds until warped discs or nested misaligned rings
form as relic structures. The amount of inflow depends mainly on
the spin orientation of the shell relative to the disc, while the relic
warped disc structure depends mostly on the turbulent kick given to
the gaseous shell in the initial conditions.
The main conclusion of this Thesis is that actual cancellation of angular
momentum within galactic nuclei can have a significant impact
on feeding super massive black holes. Such cancellation by inflowdisc
interactions would leave warped 10 - 20 pc discs as remnants.
