The onion universe: all sky lightcone simulations in spherical shells
P. Fosalba, E. Gaztanaga, F. Castander, M. Manera

TL;DR
This paper introduces a new large-scale N-body simulation and a novel onion-like lightcone map representation of the universe, enabling efficient analysis of large-scale structure and dark energy constraints.
Contribution
The authors develop a high-resolution simulation and create compressed lightcone maps that facilitate large-scale structure analysis and dark energy studies, addressing radial resolution limitations.
Findings
The onion maps are over 1000 times smaller than raw data at arcminute resolution.
Sampling variance on degree scales can cause a 25% bias in variance measurements.
Projection effects can induce significant bias in weak lensing mass reconstruction.
Abstract
Galaxy surveys provide a large-scale view of the universe that typically has a limited line-of-sight or redshift resolution. The lack of radial accuracy in these surveys can be modelled by picturing the universe as a set of concentric radial shells of finite width around the observer, i.e, an onion-like structure. We present a new N-body simulation with 2048^3 particles developed at the Marenostrum supercomputer with the GADGET-2 code. Using the lightcone output we build a set of angular maps that mimic this onion-like representation of the universe. The onion maps are a highly compressed version of the raw data (i.e. a factor >1000 smaller size for arcminute resolution maps) and they provide a new and powerful tool to exploit large scale structure observations. We introduce two basic applications of these maps that are especially useful for constraning dark energy properties: the…
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