Angular Momentum Accretion onto Disc Galaxies
  Throughout the Hubble time, gas makes its way from the intergalactic medium
into galaxies fuelling their star formation and promoting their growth. One of
the key properties of the accreting gas is its angular momentum, which has
profound implications for the evolution of, in particular, disc galaxies. Here,
we discuss how to infer the angular momentum of the accreting gas using
observations of present-day galaxy discs. We first summarize evidence for
ongoing inside-out growth of star forming discs. We then focus on the chemistry
of the discs and show how the observed metallicity gradients can be explained
if gas accretes onto a disc rotating with a velocity 20-30% lower than the
local circular speed. We also show that these gradients are incompatible with
accretion occurring at the edge of the discs and flowing radially inward.
Finally, we investigate gas accretion from a hot corona with a cosmological
angular momentum distribution and describe how simple models of rotating
coronae guarantee the inside-out growth of disc galaxies.
