442 research outputs found
Physical Processes in Star-Gas Systems
First we present a recently developed 3D chemodynamical code for galaxy
evolution from the K**2 collaboration. It follows the evolution of all
components of a galaxy such as dark matter, stars, molecular clouds and diffuse
interstellar matter (ISM). Dark matter and stars are treated as collisionless
N-body systems. The ISM is numerically described by a smoothed particle
hydrodynamics (SPH) approach for the diffuse (hot) gas and a sticky particle
scheme for the (cool) molecular clouds. Physical processs such as star
formation, stellar death or condensation and evaporation processes of clouds
interacting with the ISM are described locally. An example application of the
model to a star forming dwarf galaxy will be shown for comparison with other
codes. Secondly we will discuss new kinds of exotic chemodynamical processes,
as they occur in dense gas-star systems in galactic nuclei, such as
non-standard ``drag''-force interactions, destructive and gas producing stellar
collisions. Their implementation in 1D dynamical models of galactic nuclei is
presented. Future prospects to generalize these to 3D are work in progress and
will be discussed.Comment: 4 pages, 4 figures, "The 5th Workshop on Galactic Chemodynamics" -
Swinburne University (9-11 July 2003). To be published in the Publications of
the Astronomical Society of Australia in 2004 (B.K. Gibson and D. Kawata,
eds.). Accepted version, minor changes relative to origina
Simulation of the Gravitational Collapse and Fragmentation of Rotating Molecular Clouds
In this paper we study the process of the subsequent (runaway) fragmentation
of the rotating isothermal Giant Molecular Cloud (GMC) complex. Our own
developed Smoothed Particle Hydrodynamics (SPH) gas-dynamical model
successfully reproduce the observed Cloud Mass-distribution Function (CMF) in
our Galaxy (even the differences between the inner and outer parts of our
Galaxy). The steady state CMF is established during the collapse within a
free-fall timescale of the GMC. We show that one of the key parameters, which
defines the observed slope of the present day CMF, is the initial ratio of the
rotational (turbulent) and gravitational energy inside the fragmented GMC.Comment: 8 pages, 9 EPS figures, special forma.cls class file is use
On the bar formation mechanism in galaxies with cuspy bulges
We show by numerical simulations that a purely stellar dynamical model
composed of an exponential disc, a cuspy bulge, and an NFW halo with parameters
relevant to the Milky Way Galaxy is subject to bar formation. Taking into
account the finite disc thickness, the bar formation can be explained by the
usual bar instability, in spite of the presence of an inner Lindblad resonance,
that is believed to damp any global modes. The effect of replacing the live
halo and bulge by a fixed external axisymmetric potential (rigid models) is
studied. It is shown that while the e-folding time of bar instability increases
significantly (from 250 to 500 Myr), the bar pattern speed remains almost the
same. For the latter, our average value of 55 km/s/kpc agrees with the
assumption that the Hercules stream in the solar neighbourhood is an imprint of
the bar--disc interaction at the outer Lindblad resonance of the bar. Vertical
averaging of the radial force in the central disc region comparable to the
characteristic scale length allows us to reproduce the bar pattern speed and
the growth rate of the rigid models, using normal mode analysis of linear
perturbation theory in a razor thin disc. The strong increase of the e-folding
time with decreasing disc mass predicted by the mode analysis suggests that
bars in galaxies similar to the Milky Way have formed only recently.Comment: 13 pages, 15 figures, submitted to MNRAS Dec 2015, accepted Jul 29,
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