Which technique allows astronomers to map molecular clouds and measure their speed to plot galactic structure?

Answer

Radio Waves using Doppler shift

Molecules like Carbon Monoxide emit radio waves in star-forming regions, and by measuring the Doppler shift of these waves, astronomers calculate distance and plot locations.

Which technique allows astronomers to map molecular clouds and measure their speed to plot galactic structure?
galaxyastronomystructurearmsMilky Way