Publication : t99/038

Vorticity generation in large-scale structure caustics

Pichon C. (Canadian Institute for Theoretical Astrophysics (CITA), University of Toronto, 60 St. George Street, Toronto, M5S 3H8 Ontario, CANADA)
Bernardeau F. (CEA, DSM, SPhT (Service de Physique Théorique), F-91191 Gif-sur-Yvette, FRANCE)
A fundamental hypothesis for the interpretation of the measured large-scale line-of-sight peculiar velocities of galaxies is that the large-scale cosmic flows are irrotational. In order to assess the validity of this assumption, we estimate, within the frame of the gravitational instability scenario, the amount of vorticity generated after the first shell crossings in large-scale caustics. In the Zel'dovich approximation the first emerging singularities form sheet like structures. Here we compute the expectation profile of an initial overdensity under the constraint that it hoes through its first shell crossing at the present time. We find that this profile corresponds to rather oblate structures in Lagrangian space. Assuming the Zel'dovich approximation is still adequate not only at the first stages of the evolution but also slightly after the first shell crossing, we calculate the size and shape of those caustics and their vorticity content as a function of time and for different cosmologies. The average vorticity created in these caustics is small: of the order of one (in units of the Hubble constant). To illustrate this point we compute the contribution of such caustics to the probability distribution function of the filtered vorticity at large scales. We find that this contribution that this yields a negligible contribution at the 10 to 15 $h^{-1}$Mpc scales. It becomes significant only at the scales of 3 to 4 $h^{-1}$Mpc, that is, slightly above the galaxy cluster scales.
Année de publication : 1999
Revue : Astron. Astrophys. 343 663-681 (1999)
Preprint : arXiv:astro-ph/9902142
Keywords : Cosmology: large-scale structures, dark matter, theory; galaxie formation
Langue : Anglais

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