Comparing mass and size of haloes across halo finders in Aquarius simulation
Ranganath Magadi
University of Nottingham
Accuracy of the halo-finders is increasingly important as many astrophysical applications are dependent on halo-finders for object identification. However the size of a (sub)halo is still not a clearly defined term, as halo-finders use different definitions for defining the edge. In this comparison study, the Aquarius simulation is used to compare the sizes and masses of (sub)halos recovered from different halo finders using two halo-finding analysis. The common-analysis which is very close in construction to AHF(Amiga Halo Finder), is a 'benchmark' analysis employing common methods and common data across all finders. The own-analysis is the analysis procedure run by respective halo finders themselves. The scatter in the mass across these halo finders in own-analysis is currently at 20%. However, the common-analysis has brought the scatter in the halo mass between finders to 10% by using a set of common methods. The mass differences are substantiated by comparing same halo objects across different finders and showing missing substructures, center offsets and artifacts. We then compare the size of halos across halofinders using common-analysis and demonstrate that there is a strong relation between radius(size) and density and hence conclude that different definitions across finders lead to different sizes for same halo objects and thereby making the size of a halo an 'ill-defined' term.