  [Abridged] Debris disks are extrasolar analogs to the solar system
planetesimal belts. The star Fomalhaut harbors a cold debris belt at 140 AU as
well as evidence of a warm dust component, which is suspected of being a bright
analog to the solar system's zodiacal dust.
  Interferometric observations obtained with the VLTI and the KIN have
identified near- and mid-infrared excesses attributed to hot and warm
exozodiacal dust in the inner few AU of the star.
  We performed parametric modeling of the exozodiacal disk using the GRaTeR
radiative transfer code to reproduce the interferometric data, complemented by
mid- to far-infrared measurements. A detailed treatment of sublimation
temperatures was introduced to explore the hot population at the sublimation
rim. We then used an analytical approach to successively testing several source
mechanisms.
  A good fit to the data is found by two distinct dust populations: (1) very
small, hence unbound, hot dust grains confined in a narrow region at the
sublimation rim of carbonaceous material; (2) bound grains at 2 AU that are
protected from sublimation and have a higher mass despite their fainter flux
level. We propose that the hot dust is produced by the release of small carbon
grains following the disruption of aggregates that originate from the warm
component. A mechanism, such as gas braking, is required to further confine the
small grains for a long enough time. In situ dust production could hardly be
ensured for the age of the star, so the observed amount of dust must be
triggered by intense dynamical activity.
  Fomalhaut may be representative of exozodis that are currently being surveyed
worldwide. We propose a framework for reconciling the hot exozodi phenomenon
with theoretical constraints: the hot component of Fomalhaut is likely the tip
of the iceberg since it could originate from a warm counterpart residing near
the ice line.
