  Aging in an attraction-driven colloidal glass is studied by computer
simulations. The system is equilibrated without attraction and instantaneously
``quenched'', at constant colloid volume fraction, to one of two states beyond
the glass transition; one is close to the transition, and the other one deep in
the glass. The evolution of structural properties shows that bonds form in the
system, increasing the local density, creating density deficits (holes)
elsewhere. This process slows down with the time elapsed since the quench. As a
consequence of bond formation, there is a slowing down of the dynamics, as
measured by the mean squared displacement and the density, bond, and
environment correlation functions. The density correlations can be
time-rescaled to collapse their long time (structural) decay. The time scale
for structural relaxation shows for both quenches a super-linear dependence on
waiting time; it grows faster than the bond lifetime, showing the collective
origin of the transition. At long waiting times and high attraction strength,
we observe {\rem completely} arrested dynamics for more than three decades in
time, although individual bonds are not permanent on this time scale. The
localization length decreases as the state moves deeper in the glass; the
non-ergodicity parameter oscillates in phase with the structure factor. Our
main results are obtained for systems with a barrier in the pair potential that
inhibits phase separation. However, when this barrier is removed for the case
of a deep quench, we find changes in the static structure but almost none in
the dynamics. Hence our results for the aging behavior remain relevant to
experiments in which the glass transition competes with phase separation.
