Felix: A Topology based Framework for Visual Exploration of Cosmic
  Filaments
  The large-scale structure of the universe is comprised of virialized
blob-like clusters, linear filaments, sheet-like walls and huge near empty
three-dimensional voids. Characterizing the large scale universe is essential
to our understanding of the formation and evolution of galaxies. The density
range of clusters, walls and voids are relatively well separated, when compared
to filaments, which span a relatively larger range. The large scale filamentary
network thus forms an intricate part of the cosmic web.
  In this paper, we describe Felix, a topology based framework for visual
exploration of filaments in the cosmic web. The filamentary structure is
represented by the ascending manifold geometry of the 2-saddles in the
Morse-Smale complex of the density field. We generate a hierarchy of
Morse-Smale complexes and query for filaments based on the density ranges at
the end points of the filaments. The query is processed efficiently over the
entire hierarchical Morse-Smale complex, allowing for interactive
visualization.
  We apply Felix to computer simulations based on the heuristic Voronoi
kinematic model and the standard $\Lambda$CDM cosmology, and demonstrate its
usefulness through two case studies. First, we extract cosmic filaments within
and across cluster like regions in Voronoi kinematic simulation datasets. We
demonstrate that we produce similar results to existing structure finders.
Filaments that form the spine of the cosmic web, which exist in high density
regions in the current epoch, are isolated using Felix. Also, filaments present
in void-like regions are isolated and visualized. These filamentary structures
are often over shadowed by higher density range filaments and are not easily
characterizable and extractable using other filament extraction methodologies.
