Abstract
abridged The ever increasing size and complexity of data coming from
simulations of cosmic structure formation demands equally sophisticated tools
for their analysis. During the past decade, the art of object finding in these
simulations has hence developed into an important discipline itself. A
multitude of codes based upon a huge variety of methods and techniques have
been spawned yet the question remained as to whether or not they will provide
the same (physical) information about the structures of interest. This concern
gave rise to a series of workshops and comparison papers of which we here
present a brief summary. But we also go one step further and investigate in
more detail the (possible) origin of any deviations across finders. To this
extent we decipher and discuss differences in halo finding methods, clearly
separating them from the disparity in definitions of halo properties. We
observe that different codes not only find different numbers of objects leading
to a scatter of up to 20 per cent in the halo mass and Vmax function, but also
that the particulars of those objects that are identified by all finders
differ. ... We close with a discussion of the relevance and implications of
the scatter across different codes for other fields such as semi-analytical
galaxy formation models, gravitational lensing, and observables in general. In
summary we conclude that while the majority of codes give results with a
scatter below 1 per cent (at least for the most basic halo properties) once a
particular definition has been specified, the residual differences for more
complex quantities such as spin parameter are more sensitive to the particular
implementation of the initial particle collection. We therefore caution any
user of halo finders and their catalogues to not use the data blindly but to
consider the mode of operation and definitions used during its generation.
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