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Unlike a channel map that shows the distribution of a gas moving at a single velocity, a velocity-space diagram shows how gas travelling at various velocities is distributed along a line through the object. In the diagram on the left, this line is shown in red.
The velocity-space diagram below shows the velocities (plotted along the vertical axis) and abundances (indicated by the brightness of color) of carbon monoxide (CO) gas distributed along the red line (represented here by the horizontal axis).
Velocity Space diagram of M82
By examining this diagram, you can see that at
each point along the line some of the CO gas moves at 300 km/sec, while another part
moves at 200 km/sec, and so on.
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Velocity-space diagrams can be constructed for several points throughout the object. In separating the different velocities of the gases, velocity-space diagrams provide a more detailed understanding of their relative motions in space.
Notice that gaseous material located at 42 degrees right ascension is moving at two different velocities. At the center of M82 lies a ring of material which could be expanding outwards. While visible in the the above diagram, the expansion of the gas can only be discrerned with great difficulty when using channel maps alone.
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