A Dynamical Classification of the Cosmic Web

By J. Forero-Romero, Y. Hoffman, S. Gottlober, Anatoly Klypin, G. Yepes. 2008

218 citations recorded by the source corpus.

In this paper, we propose a new dynamical classification of the cosmic web. Each point in space is classified in one of four possible web types: voids, sheets, filaments and knots. The classification is based on the evaluation of the deformation tensor (i.e. the Hessian of the gravitational potential) on a grid. The classification is based on counting the number of eigenvalues above a certain threshold, λth, at each grid point, where the case of zero, one, two or three such eigenvalues corresponds to void, sheet, filament or a knot grid point. The collection of neighbouring grid points, friends of friends, of the same web type constitutes voids, sheets, filaments and knots as extended web objects. A simple dynamical consideration of the emergence of the web suggests that the threshold should not be null, as in previous implementations of the algorithm. A detailed dynamical analysis would have found different threshold values for the collapse of sheets, filaments and knots. Short of such an analysis a phenomenological approach has been opted for, looking for a single threshold to be determined by analysing numerical simulations. Our cosmic web classification has been applied and tested against a suite of large (dark matter only) cosmological N-body simulations. In particular, the dependence of the volume and mass filling fractions on λth and on the resolution has been calculated for the four web types. We also study the percolation properties of voids and filaments. Our main findings are as follows. (i) Already at λth= 0.1 the resulting web classification reproduces the visual impression of the cosmic web. (ii) Between 0.2 ≲λth≲ 0.4, a system of percolated voids coexists with a net of interconnected filaments. This suggests a reasonable choice for λth as the parameter that defines the cosmic web. (iii) The dynamical nature of the suggested classification provides a robust framework for incorporating environmental information into galaxy formation models, and in particular to semi-analytical models.

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Citations in the corpus

The persistent cosmic web and its filamentary structure II: Illustrations (2010, unknown): “…& Doré 2006; Hahn et al. 2007; Platen, van de Weygaert & Jones 2007; Stoica, Martı́nez & Saar 2007, 2010; Neyrinck 2008; Sousbie et al. 2008a,b; Forero-Romero et al. 2009; Sousbie, Colombi & Pichon 2009; Aragón-Calvo et al. 2010a,b; Paper I), relying on different strategies on how to deal…”
The persistent cosmic web and its filamentary structure I: Theory and implementation (2010, background): “…identification of all types of astrophysically significant features of the large-scale galaxy distribution in the universe (see e.g. Novikov, Colombi & Doré 2006; Hahn et al. 2007; Sousbie et al. 2008a,b; Forero-Romero et al. 2009; Sousbie, Colombi & Pichon 2009; Aragón-Calvo et al. 2010b).”
Detecting filamentary pattern in the cosmic web: a catalogue of filaments for the SDSS (2013, methodology): “Consequently, filaments contain the largest fraction of mass in the Universe and they represent the most salient component of the cosmic web: they form the bridges between all structural features at the group/cluster scale.”
NEXUS: Tracing the cosmic web connection (2012, methodology): “A more elaborate classification scheme on the basis of the manifolds in the tidal field – involving all morphological features in the cosmic matter distribution – has been forwarded by Hahn et al. (2007a) (also see Hahn et al. 2007b; Forero-Romero et al. 2009).”
THE SPIN AND ORIENTATION OF DARK MATTER HALOS WITHIN COSMIC FILAMENTS (2009, background): “Note, however, in a recent paper Forero-Romero et al. (2008) introduced an additional threshold λth for the classification of environment instead of just using the number of positive (negative) eigenvalues.”
A kinematic classification of the cosmic web (2012, methodology): “A partial remedy to this shortcoming was provided by Forero-Romero et al. (2009) (FR09), who relaxed the assumption of the null threshold which is used to classify the web.”
Connecting the cosmic web to the spin of dark haloes: implications for galaxy formation (2012, background): “One recent criterion to classify structures as clusters, filaments, sheets or voids, uses the number of positive eigenvalues of the Hessian matrix of the density or potential fields (Hahn et al. 2007a; Aragón-Calvo et al. 2007; Forero-Romero et al. 2009).”