1,828 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

### A Convenient Set of Comoving Cosmological Variables and Their Application

We present a set of cosmological variables, called "supercomoving variables,"
which are particularly useful for describing the gas dynamics of cosmic
structure formation. For ideal gas with gamma=5/3, the supercomoving position,
velocity, density, temperature, and pressure are constant in time in a uniform,
isotropic, adiabatically expanding universe. Expressed in terms of these
supercomoving variables, the cosmological fluid conservation equations and the
Poisson equation closely resemble their noncosmological counterparts. This
makes it possible to generalize noncosmological results and techniques to
cosmological problems, for a wide range of cosmological models. These variables
were initially introduced by Shandarin for matter-dominated models only. We
generalize supercomoving variables to models with a uniform component
corresponding to a nonzero cosmological constant, domain walls, cosmic strings,
a nonclumping form of nonrelativistic matter (e.g. massive nettrinos), or
radiation. Each model is characterized by the value of the density parameter
Omega0 of the nonrelativistic matter component in which density fluctuation is
possible, and the density parameter OmegaX of the additional, nonclumping
component. For each type of nonclumping background, we identify FAMILIES within
which different values of Omega0 and OmegaX lead to fluid equations and
solutions in supercomoving variables which are independent of Omega0 and
OmegaX. We also include the effects of heating, radiative cooling, thermal
conduction, viscosity, and magnetic fields. As an illustration, we describe 3
familiar cosmological problems in supercomoving variables: the growth of linear
density fluctuations, the nonlinear collapse of a 1D plane-wave density
fluctuation leading to pancake formation, and the Zel'dovich approximation.Comment: 38 pages (AAS latex) + 2 figures (postscript) combined in one gzip-ed
tar file. Identical to original posted version, except for addition of 2
references. Monthly Notices of the R.A.S., in pres

### Formation and Evolution of Self-Interacting Dark Matter Halos

We study the formation and evolution of self-interacting dark matter (SIDM)
halos. We find analytical, fully cosmological similarity solutions taking
account of the collisional interaction of SIDM particles. This interaction
results in a thermal conductivity that heats the halo core and flattens its
density profile. These similarity solutions are relevant to galactic and
cluster halo formation in the CDM model. We assume an initial mass profile dM/M
M^{-eps}, as in the familiar secondary infall model. If eps=1/6, SIDM halos
will evolve self-similarly, with a cold, supersonic infall terminated by a
strong accretion shock. Different solutions arise for different values of the
collisionality parameter, Q= sigma rho_b r_s, where sigma is the scattering
cross section, rho_b is the cosmic mean density, and r_s is the shock radius.
For all these solutions, a flat-density, isothermal core is present which grows
in size as a fixed fraction of r_s. We find two different regimes for these
solutions: 1) for Q \leq Q_{th}, the core density decreases and core size
increases as Q increases; 2) for Q \geq Q_{th}, the core density increases and
core size decreases as Q increases. Our similarity solutions are in agreement
with previous N-body simulations of SIDM halos, which correspond to the low-Q
regime, if Q=[8.4e-4 - 4.9e-2]Q_{th} (low-Q), or sigma=[0.56-5.6]cm^2/g. As
Q=\infty, our similarity solution aquires a central density cusp, in agreement
with some simulation results which used an ordinary collisional fluid to
approximate the effects of SIDM collisionality. When Q=[18.6-231]Q_{th} or
sigma=[1.2e4 - 2.71e4]cm^2/g, for which we find flat-density cores comparable
to those of the observationally acceptable low-Q solutions, has not previously
been identified. Further study of this regime is warranted.Comment: 7 pages, 5 figures, talk presented at the Second Korean Astrophysics
Workshop (APCTP Workshop) on Formation and Interaction of Galaxies, published
in a special issue of Journal of Korean Astronomical Society, ed. H. M Le

- â€¦