Astronomy and Astrophysics – Astrophysics
Scientific paper
Dec 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992phdt.........8l&link_type=abstract
Ph.D. Thesis Virginia Univ., Charlottesville.
Astronomy and Astrophysics
Astrophysics
Cooling Flows (Astrophysics), Galactic Clusters, Galaxies, Gravitational Fields, Hydrodynamics, Steady State, Adiabatic Conditions, Finite Difference Theory, Rosat Mission, Symmetry, Time Dependence
Scientific paper
Time-dependent effects for cluster cooling flows are examined in the cases of 1-D spherical symmetry and 2-D axisymmetry. Physical effects included in the simulations are radiative cooling, mass deposition and time-dependent gravitational potentials. The gravitational potential is assumed generally to be due to three sources: a smooth cluster distribution, a massive central galaxy, and in the 2-D case, a perturbing galaxy on a radial orbit. A 2-D axisymmetric finite difference code is developed and tested for these applications. At modest resolution, the code is accurate to one tenth of one percent in the fundamental fluid variables, making it a good tool for observing wave phenomena and departures from spherical symmetry. In the 1-D case, flows with mass deposition reach a steady state after an initial central cooling time. The mass accretion rate generally remains nearly constant thereafter. The spatial structure of the flow agrees in detail with previous steady-state models. Even if the cluster potential is allowed to deepen with time, it is found that adiabatic compression delays neither the cooling of the gas nor the onset of steady-state flow. On the other hand, flows for which the self-gravity of the gas is dynamically important are shown to be unstable to collapse on a hydrodynamic timescale. Despite the relative success of the spherical model, there is considerable observational evidence that the cooling accretion takes place preferentially in clumps rather than uniformly. Recent ROSAT images also indicate that the gas in clusters is nonuniformly distributed. We therefore investigate the formation and evolution of finite-amplitude and finite-wavelength disturbances through axisymmetric numerical simulations of cluster cooling flows perturbed by a single galaxy orbiting along the symmetry axis.
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