Radio Astronomy And The Spiral Structure Of The Milky

Way

Jess Broderick

Supervisor: Dr George Warr

Outline

Overview of the spiral arm structure of the Milky Way.

Using radio astronomy to detect the spiral structure.

The Spiral Arm Structure Of The Milky Way

Optical spiral tracers: O & B type stars, open star clusters, emission nebulae (HII) regions.

Optical observations limited in effectiveness due to clouds of interstellar dust.

Solution: Use radio wavelengths to study the spiral structure, eg. 21 cm line of neutral hydrogen.

Using Radio Astronomy To Detect The Spiral Structure

Mapping The Spiral Arms Of The Milky Way

Starting point: Map the intensity of neutral hydrogen along the Galactic plane for various Galactic longitudes.

As a result of this procedure, it has been shown that the neutral hydrogen appears to be concentrated in the spiral arms of the Milky Way.

B. Burke et. al., An Introduction To Radio Astronomy.

Uncertainties Involved In Detecting The Spiral Structure Using Radio

Astronomy Assuming circular model of rotation of

gas. Range of phenomena near the Galactic

plane. Ambiguity in the overall flux density

profile.

H. Karttunen et. al., Fundamental Astronomy.

Galactic Centre

Sun

Intensity

Radial Velocity

Conclusion

Radio observations can be used to provide a more comprehensive analysis of the Milky Way’s spiral structure than optical observations allow.

Uncertainties involved in interpreting the neutral hydrogen flux density profiles.

It can be concluded that 21 cm hydrogen observations do indeed indicate spiral structure on a large scale in the Galactic plane.