The distribution and kinematics of early high-sigma peaks in present-day haloes: implications for rare objects and old stellar populations

Details The distribution and kinematics of early high-sigma peaks in present-day haloes: implications for rare objects and old stellar populations The distribution and kinematics of early high-sigma peaks in present-day haloes: implications for rare objects and old stellar populations

2005-06-25

arxiv.org/abs/astro-ph/0506615v4

Mon.Not.Roy.Astron.Soc.364:367-383,2005

Astronomy and Astrophysics

Astrophysics

19 pages, 12 figures, matches the published version. Increased line-width of plots for better reproduction. A version with hig

Scientific paper

10.1111/j.1365-2966.2005.09604.x

We show that the hierarchical assembly of cold dark matter (CDM) haloes preserves the memory of the initial conditions. Using N-body cosmological simulations, we demonstrate that the present-day spatial distribution and kinematics of objects that formed within early (z > 10) protogalactic systems (old stars, satellite galaxies, globular clusters, massive black holes, etc.) depends mostly on the rarity of the peak of the primordial density field which they originally belonged to. Only for objects forming at lower redshifts the exact formation site within the progenitor halo (e.g. whether near the center or in an extended disk) becomes important. In present-day haloes, material from the rarer early peaks is more centrally concentrated and falls off more steeply with radius compared to the overall mass distribution, it has a lower velocity dispersion, moves on more radial orbits, and has a more elongated shape. Population II stars that formed within protogalactic haloes collapsing from >2.5 sigma fluctuations would follow today a r^{-3.5} density profile with a half-light radius of 17 kpc and a velocity anisotropy that increases from isotropic in the inner regions to nearly radial at the halo edge. This agrees well with the radial velocity dispersion profile of Galaxy halo stars from Battaglia et al. (2005) and with the anisotropic orbits of nearby halo stars.

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