The Last Journey. I. An Extreme-Scale Simulation on the Mira Supercomputer

TL;DR

This paper presents the execution of an unprecedented large-scale cosmological N-body simulation on the Mira supercomputer, producing extensive data and analysis tools for studying cosmic structure formation.

Contribution

It introduces a new in situ analysis pipeline with a novel subhalo tracking method and generates synthetic sky maps from a trillion-particle simulation.

Findings

Simulation evolved over 1.24 trillion particles

In situ analysis enabled diverse science projects

Generated data supports synthetic galaxy catalog creation

Abstract

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.