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Solving small-scale clustering problems in approximate light-cone mocks

Smith, Alex; Cole, Shaun; Grove, Cameron; Norberg, Peder; Zarrouk, Pauline

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Pauline Zarrouk


Realistic light-cone mocks are important in the clustering analyses of large galaxy surveys. For simulations where only the snapshots are available, it is common to create approximate light-cones by joining together the snapshots in spherical shells. We assess the two-point clustering measurements of central galaxies in approximate light-cones built from the Millennium-XXL simulation, which are constructed using different numbers of snapshots. The monopole and quadrupole of the real-space correlation function is strongly boosted on small scales below 1 h−1 Mpc, due to some galaxies being duplicated at the boundaries between snapshots in the light-cone. When more snapshots are used, the total number of duplicated galaxies is approximately constant, but they are pushed to smaller separations. The effect of this in redshift space is small, as long as the snapshots are cut into shells in real space. Randomly removing duplicated galaxies is able to reduce the excess clustering signal. Including satellite galaxies will reduce the impact of the duplicates, since many small-scale pairs come from satellites in the same halo. Galaxies that are missing from the light-cone at the boundaries can be added to the light-cone by having a small overlap between each shell. This effect will impact analyses that use very small-scale clustering measurements, and when using mocks to test the impact of fibre collisions.


Smith, A., Cole, S., Grove, C., Norberg, P., & Zarrouk, P. (2022). Solving small-scale clustering problems in approximate light-cone mocks. Monthly Notices of the Royal Astronomical Society, 516(1), 1062 - 1071.

Journal Article Type Article
Acceptance Date Aug 2, 2022
Online Publication Date Aug 6, 2022
Publication Date 2022
Deposit Date Nov 17, 2022
Publicly Available Date Nov 18, 2022
Journal Monthly Notices of the Royal Astronomical Society
Print ISSN 0035-8711
Electronic ISSN 1365-2966
Publisher Royal Astronomical Society
Peer Reviewed Peer Reviewed
Volume 516
Issue 1
Pages 1062 - 1071


Published Journal Article (Advance online version) (981 Kb)

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Copyright Statement
Advance online version This is an Open Access article distributed under the terms of the Creative Commons Attribution License (, which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.

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