Radio Views of a Spiral Galaxy
Joachim Köppen Kiel Sep 2017

Some brief explanations

This Monte Carlo simulation computes how the rotating gas disk in a spiral galaxy is observed by a (radio) telescope which makes images of the object, but also takes spectra, from which the radial velocity of each pixel is measured. The simulation shows how an object which is arbitrarily oriented in the sky appears to the observer and what information one can extract from images and spectral data.

How it works: the simulation picks at random a gas element in the disk, according to the prescribed geometry, and follows what happens to a photon emitted by the element. Since depending on the radial scale the inner parts are brighter, these elements are picked more often, thus they produce more photons. According to the rotation speed, each emitted photon receives its velocity components. Then, the position and velocities are recomputed according to the specified rotation angles, and the photon appears in the observer's X-Y-plane - but with randomly deviations which correspond to the finite spatial resolution of the telescope - and with a radial velocity which comes from the Z-component of the velocity. This process is carried out as many times as the displayed plot or image has become sufficiently stable, so that the user can stop the simulation.

Galaxy properties: Simulation display:
Galaxy properties
inner radius [kpc]
outer radius [kpc]
radial scale [kpc]
disk thickness [kpc]
rotation speed [km/s]
velocity dispersion [km/s]

inclinationY [°]
inclinationZ [°]

antenna HPBW [kpc]
Simulation display
photons now
no. of bins

X-axis =
Set range: ...
Y-axis =
Set range: ...

Mouse position:

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