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Cosmology and Astrophysics - Voids
You might think, why study voids, they are just empty structures in
the Universe... Wrong! Voids are in fact not empty at all! (Well,
depending on your definition of voids, a question which can lead to
heated discussions amongst scientists.) Each void is a miniature
``universe,'' with the same structural elements as the large-scale
galactic distribution, but at lower density. This ensemble of
universes is a unique resource for advancing our understanding of the
Universe as a whole. There are several puzzles which have to be solved
regarding voids. One concerns the number of faint galaxies in voids.
According to the theory of hierarchical structure formation, the first
structures to form are small clumps of dark matter - the halos. Small
halos form everywhere and later stream, merge, and organize to form
yet larger structures, leaving behind voids. Since the flow of matter
within voids is not very strong, small dark matter halos - able to
accrete gas and light up as faint (dwarf) galaxies (~10^9 M_solar) -
should be present. This expectation is confirmed by simulations,
where roughly a thousand such halos per void are found. Observational
yields, however, are lower by over an order of magnitude! Where are
the missing dwarfs? To study this and other questions we were recently
awarded an internal LANL research grant. A first project which we have
completed recently, concerns the shapes and sizes of voids. Are they
spherical or elliptical? How do their sizes depend on the density
threshold picked to identify them? If you want to find out more about
this, you can read our paper (see below). To study the problem of the
missing dwarfs, we have several ideas, new results will be posted when
available.
Publications
- Shapes and Sizes of Voids in the LCDM Universe: Excursion Set Approach,
S. Shandarin, H. Feldman, K. Heitmann, and S. Habib, MNRAS, 367, 1629 (2006),
astro-ph/0509858
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