"From simulations to observations: synthetic HI observations of spiral galaxies and synthetic galactic plane surveys" By David Acreman (University of Exeter)

The formation of molecular clouds from cold, dense atomic gas is a key process in the evolution of the interstellar medium. Molecular cloud formation is studied using both observations and numerical models but the two approaches yield different information. Models calculate fields such as density and temperature, which are not directly observable, however radiative transfer modelling allows a simulation to be converted into a synthetic observation. A spiral galaxy, simulated using Smoothed Particle Hydrodynamics, is mapped onto an adaptive grid and spectral cubes of 21cm hydrogen emission are calculated using ray tracing. The observer may be placed outside the grid, to simulate an observation of an external galaxy, or the observer can be placed inside the grid to produce a synthetic galactic plane survey. Features seen in the synthetic observations can be related back to physical processes in the simulation thus allowing the properties of molecular clouds seen in self-absorption to be determined.

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