  The Last Journey is a large-volume, gravity-only, cosmological N-body
simulation evolving more than 1.24 trillion particles in a periodic box with a
side-length of 5.025Gpc. It was implemented using the HACC simulation and
analysis framework on the BG/Q system, Mira. The cosmological parameters are
chosen to be consistent with the results from the Planck satellite. A range of
analysis tools have been run in situ to enable a diverse set of science
projects, and at the same time, to keep the resulting data amount manageable.
Analysis outputs have been generated starting at redshift z~10 to allow for
construction of synthetic galaxy catalogs using a semi-analytic modeling
approach in post-processing. As part of our in situ analysis pipeline we employ
a new method for tracking halo sub-structures, introducing the concept of
subhalo cores. The production of multi-wavelength synthetic sky maps is
facilitated by generating particle lightcones in situ, also beginning at z~10.
We provide an overview of the simulation set-up and the generated data
products; a first set of analysis results is presented. A subset of the data is
publicly available.
