15 research outputs found
Precedents, parliaments, and foreign policy:Historical analogy in the House of Commons vote on Syria
The properties of the ISM in disc galaxies with stellar feedback
We perform calculations of isolated disc galaxies to investigate how the
properties of the ISM, the nature of molecular clouds, and the global star
formation rate depend on the level of stellar feedback. We adopt a simple
physical model, which includes a galactic potential, a standard cooling and
heating prescription of the ISM, and self gravity of the gas. Stellar feedback
is implemented by injecting energy into dense, gravitationally collapsing gas,
but is independent of the Schmidt-Kennicutt relation. We obtain fractions of
gas, and filling factors for different phases of the ISM in reasonable ageement
with observations. Supernovae are found to be vital to reproduce the scale
heights of the different components of the ISM, and velocity dispersions. The
GMCs formed in the simulations display mass spectra similar to the
observations, their normalisation dependent on the level of feedback. We find
~40 per cent of the clouds exhibit retrograde rotation, induced by cloud-cloud
collisions. The star formation rates we obtain are in good agreement with the
observed Schmidt-Kennicutt relation, and are not strongly dependent on the star
formation efficiency we assume, being largely self regulated by the feedback.
We also investigate the effect of spiral structure by comparing calculations
with and without the spiral component of the potential. The main difference
with a spiral potential is that more massive GMCs are able to accumulate in the
spiral arms. Thus we are able to reproduce massive GMCs, and the spurs seen in
many grand design galaxies, even with stellar feedback. The presence of the
spiral potential does not have an explicit effect on the star formation rate,
but can increase the star formation rate indirectly by enabling the formation
of long-lived, strongly bound clouds.Comment: 19 pages, 23 figures, accepted by MNRA