Disk formation and the origin of clumpy galaxies at high redshift
  Observations of high redshift galaxies have revealed a multitude of large
clumpy rapidly star-forming galaxies. Their formation scenario and their link
to present day spirals is still unknown. In this Letter we perform adaptive
mesh refinement simulations of disk formation in a cosmological context that
are unrivalled in terms of mass and spatial resolution. We find that the so
called "chain-galaxies" and "clump-clusters" are a natural outcome of early
epochs of enhanced gas accretion from cold dense streams as well as tidally and
ram-pressured stripped material from minor mergers and satellites. Through
interaction with the hot halo gas, this freshly accreted cold gas settles into
a large disk-like system, not necessarily aligned to an older stellar
component, that undergoes fragmentation and subsequent star formation, forming
large clumps in the mass range 10^7-10^9 M_sun. Galaxy formation is a complex
process at this important epoch when most of the central baryons are being
acquired through a range of different mechanisms - we highlight that a rapid
mass loading epoch is required to fuel the fragmentation taking place in the
massive arms in the outskirts of extended disks, an accretion mode that occurs
naturally in the hierarchical assembly process at early epochs.
