A new galactic chemical evolution model with dust: results for dwarf
  irregular galaxies and DLA systems
  We present a galactic chemical evolution model which adopts updated
prescriptions for all the main processes governing the dust cycle. We follow in
detail the evolution of the abundances of several chemical species (C, O, S,
Si, Fe and Zn) in the gas and dust of a typical dwarf irregular galaxy. The
dwarf irregular galaxy is assumed to evolve with a low but continuous level of
star formation and experience galactic winds triggered by supernova explosions.
We predict the evolution of the gas to dust ratio in such a galaxy and discuss
critically the main processes involving dust, such as dust production by AGB
stars and Type II SNe, destruction and accretion (gas condensation in clouds).
We then apply our model to Damped Lyman-Alpha systems which are believed to be
dwarf irregulars, as witnessed by their abundance patterns. Our main
conclusions are: i) we can reproduce the observed gas to dust ratio in dwarf
galaxies. ii) We find that the process of dust accretion plays a fundamental
role in the evolution of dust and in certain cases it becomes the dominant
process in the dust cycle. On the other hand, dust destruction seems to be a
negligible process in irregulars. iii) Concerning Damped Lyman-Alpha systems,
we show that the observed gas-phase abundances of silicon, normalized to
volatile elements (zinc and sulfur), are in agreement with our model. iv) The
abundances of iron and silicon in DLA systems suggest that the two elements
undergo a different history of dust formation and evolution. Our work casts
light on the nature of iron-rich dust: the observed depletion pattern of iron
is well reproduced only when an additional source of iron dust is considered.
Here we explore the possibility of a contribution from Type Ia SNe as well as
an efficient accretion of iron nano-particles.
