3,967 research outputs found
Explosions and Outflows during Galaxy Formation
We consider an explosion at the center of a halo which forms at the
intersection of filaments inside a cosmological pancake, a convenient test-bed
model for galaxy formation. ASPH/P3M simulations reveal that such explosions
are anisotropic. The energy and metals are channeled into the low density
regions, away from the pancake. The pancake remains essentially undisturbed,
even if the explosion is strong enough to blow away all the gas located inside
the halo and reheat the IGM surrounding the pancake. Infall quickly replenishes
this ejected gas and gradually restores the gas fraction as the halo continues
to grow. Estimates of the collapse epoch and SN energy-release for galaxies of
different mass in the CDM model can relate these results to scale-dependent
questions of blow-out and blow-away and their implication for early IGM heating
and metal enrichment and the creation of gas-poor dwarf galaxies.Comment: To appear in "The 20th Texas Symposium on Relativistic Astrophysics",
eds. H. Martel and J.C. Wheeler, AIP, in press (2001) (3 pages, 2 figures
The Evolution of Dark-Matter Dominated Cosmological Halos
Adaptive SPH and N-body simulations were carried out to study the evolution
of the equilibrium structure of dark matter halos that result from the
gravitational instability and fragmentation of cosmological pancakes. Such
halos resemble those formed by hierarchical clustering from realistic initial
conditions in a CDM universe and, therefore, serve as a test-bed model for
studying halo dynamics. The dark matter density profile is close to the
universal halo profile identified previously from N-body simulations of
structure formation in CDM, with a total mass and concentration parameter which
grow linearly with scale factor a. When gas is included, this concentration
parameter is slightly larger than the pure N-body result. We also find that the
dark matter velocity distribution is less isotropic and more radial than found
by N-body simulations of CDM.Comment: To appear in "The 20th Texas Symposium on Relativistic Astrophysics",
eds. H. Martel and J.C. Wheeler, AIP, in press (2001) (3 pages, 2 figures
Anisotropic Galactic Outflows and Enrichment of the Intergalactic Medium. I: Monte Carlo Simulations
We have developed an analytical model to describe the evolution of
anisotropic galactic outflows. With it, we investigate the impact of varying
opening angle on galaxy formation and the evolution of the IGM. We have
implemented this model in a Monte Carlo algorithm to simulate galaxy formation
and outflows in a cosmological context. Using this algorithm, we have simulated
the evolution of a comoving volume of size [12h^(-1)Mpc]^3 in the LCDM
universe. Starting from a Gaussian density field at redshift z=24, we follow
the formation of ~20,000 galaxies, and simulate the galactic outflows produced
by these galaxies. When these outflows collide with density peaks, ram pressure
stripping of the gas inside the peak may result. This occurs in around half the
cases and prevents the formation of galaxies. Anisotropic outflows follow the
path of least resistance, and thus travel preferentially into low-density
regions, away from cosmological structures (filaments and pancakes) where
galaxies form. As a result, the number of collisions is reduced, leading to the
formation of a larger number of galaxies. Anisotropic outflows can
significantly enrich low-density systems with metals. Conversely, the
cross-pollution in metals of objects located in a common cosmological
structure, like a filament, is significantly reduced. Highly anisotropic
outflows can travel across cosmological voids and deposit metals in other,
unrelated cosmological structures.Comment: 32 pages, 9 figures (2 color). Revised version accepted in Ap
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