This is the astro-ph blog of the Theoretical Modelling of Cosmic Structures group (TMoX) at the Max-Planck-Institute for Extraterrestrial Physics. We are an independent Max-Planck Research Group focusing on the various aspects in the formation and evolution of galaxies. Part of our focus is on the formation and evolution of early-type galaxies, super-massive black holes, the formation of the first structures in the universe and the enrichment history of the Universe. We are theoreticians using analytic modelling as well as numerical simulations in our work.

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20 January 2012

The cosmic web and the orientation of angular momenta

This paper (link) uses a dark matter only simulation to see if a collapsed, virialized halo remembers the cosmic web out of which it formed. The new work in this paper uses the eigenvalues of the velocity shear tensor to determine if a halo is in a knot, filament, sheet, or void. Then, they measure the angle between the halo angular momentum and the eigenvectors, and the subhalo orbital angular momentum and the eigenvectors. Interestingly, the internal angular momentum correlates with the eigenvectors in sheets and filaments, implying that even virialized halos retain memory of the initial conditions. The orbital angular momentum in substructures is aligned in knots, filaments, and sheets, implying that halo accretion is not isotropic. This work has impact in understanding the spatial distribution of satellites around host galaxies, as is seen in the Milky Way and the SDSS sample.


  1. I liked this paper, but have one comment/question regarding the resolution. It's been shown (e.g. Davis & Natarajan 2010) that resolving the direction of the angular momentum vector requires a lot of particles ( > ~3000), whereas here they used halos with > 300 particles. How might this affect the conclusions?

  2. There is a general question as to how well the angular momentum of the dark matter halo correlates with that of gas in haloes. In a recent paper Kimm et al (arXiv1106.0538K) show it does not in general. Thus can we draw conclusion form observations of individual galaxies on the assembly of haloes? As for the satellites this might be possible since they are collisionless.