Testing tidal-torque theory – II. Alignment of inertia and shear and the characteristics of protohaloes

By C. Porciani, A. Dekel, Y. Hoffman. 2001

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We investigate the cross-talk between the two key components of tidal-torque theory, the inertia (I) and shear (T) tensors, using a cosmological N-body simulation with thousands of well-resolved haloes. We find that the principal axes of I and T are strongly aligned, even though I characterizes the protohalo locally while T is determined by the large-scale structure. Thus, the resultant galactic spin, which plays a key role in galaxy formation, is only a residual due to ∼10 per cent deviations from the perfect alignment of T and I. The T–I correlation induces a weak tendency for the protohalo spin to be perpendicular to the major axes of T and I, but this correlation is erased by non-linear effects at late times, making the observed spins poor indicators of the initial shear field. However, the T–I correlation implies that the shear tensor can be used for identifying the positions and boundaries of protohaloes in cosmological initial conditions – a missing piece in galaxy formation theory. The typical configuration is of a prolate protohalo lying perpendicular to a large-scale high-density ridge, with the surrounding voids inducing compression along the major and intermediate inertia axes of the protohalo. This leads to a transient sub-halo filament along the large-scale ridge, whose subclumps then flow along the filament and merge into the final halo. The centres of protohaloes tend to lie in ∼1σ overdensity regions, but their association with linear density maxima smoothed on galactic scales is vague: only ∼40 per cent of the protohaloes contain peaks. Several other characteristics distinguish protohaloes from density peaks, e.g. they tend to compress along two principal axes while many peaks compress along three axes.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/59d86a815518d7fac4d2ba3d74a5f04e90a70368

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Citations in the corpus

Internal and External Alignment of the Shapes and Angular Momenta of ΛCDM Halos (2004, methodology): “Linear tidal torque theory (Doroshkevich 1970; White 1984) can be used to predict the directions of the angular momentum vectors and their correlations with the surrounding structure (Pen et al. 2000; Lee & Pen 2000, 2001; Crittenden et al. 2001; Porciani et al. 2002a,b).”
The Intrinsic Alignment of Galaxies and its Impact on Weak Gravitational Lensing in an Era of Precision Cosmology (2014, methodology): “elative to the power spectrum. Other investigations of intrinsic alignment in dark matter only simulations have also been carried out, for example, by Dekel et al. (2001); Faltenbacher et al. (2002); Porciani et al. (2002a,b); Aubert et al. (2004); Hopkins et al. (2005); Lee et al. (2005); Altay et ”
The alignment between the distribution of satellites and the orientation of their central galaxy (2006, background): “…are oriented with respect to their surrounding large scale structure, the alignment on these two different scales may well be very different (see e.g., Barnes & Efstathiou 1987; Porciani et al. 2002a,b; Navarro, Abadi & Steinmetz 2004; Bailin & Steinmetz 2005; Trujillo, Carretero & Patiri 2005).”