ASTRONOMY 402T – Spring 2018
Problems for Tutorial Week #1

I. Multiwavelength Milky Way

Explore the Multiwavelength Milky Way website. – http://mwmw.gsfc.nasa.gov/mmw_sci.html

(It will help you to become familiar with galactic coordinates. – http://www.thinkastronomy.com/M13/Manual/common/galactic_coords.html )

Use what you learn with what you already know (or can look up) to understand the kinds of objects detectable at different wavelengths. Be sure to read all the available information for each wavelength band! Note that you can click on any region and zoom/pan. Be aware of the distinction between diffuse emission, which extends over a relatively large area vs. compact emission, which is highly localized.

Answer the following questions, employing physical arguments to bolster your conclusions.

1. Give two reasons why the plane of the Milky Way is all but invisible at optical wavelengths, while it is bright in the near infrared.
2. Why is the diffuse γ-ray emission an excellent tracer of interstellar gas? (possibly of interest: this article.)
3. The Crab Nebula is located at l ≈ 185°. It’s bright in the radio, X-ray and γ-ray regimes of the spectrum. Explain, in terms of physical processes, why it is seen in these three regimes.

 II. Properties of the Milky Way: Stars and Gas

1.  Compare the distributions of stars and gas in the Milky Way; consider cold molecular gas, warm atomic gas, and hot ionized gas separately.
2. Discuss the relative amounts that each of the above contributes to the total mass of the Milky Way. What are we not considering?