Question

This multi part question needs only brief 1-2 sentence descriptions as answers, so I tried not to split them up for the sake of continuity. Thank you in advance for asnwers this question!

a) When one looks at the Milky Way at near-infrared wavelengths (∼2μm), what is a typical
temperature of the objects at which one is looking? Thus, what are the (very general) kind
of objects that you see when you look in these wavelengths? Besides the temperature of the
emitting objects, how does this view differ from that seen in the optical (and why)?
b) When one looks in far-infrared wavelengths (∼ 100 μ m), what dominates this view, and why? Where is this material in the Galaxy?

c) When one looks at a wavelength of 21 cm, what are you looking at? Where is this stuff in the Galaxy? e) When one looks in the γ -ray regime, what stuff produces the majority of the emission? How does it produce this emission?

Answer 1

a] Use Wein's Displacement law

so, for a wavelength of 2 x 10^-6 m, the temperature will be:

hot invisible gases/red stars/red giants can be viewed at this wavelength. It is different from visible spectrum in the sense that the molecular vibrations of the gases can be studied [which does not lie in the visible region].

b]

For wavelength of 100 micro-meters:

for such temperatures, very cold molecular clouds and emissions from the cold dust can be studied where some of the stars are just beginning to form.

c] for 21 cm wavelength

which lies in the microwave region. This region is particularly useful for study of the origins of the universe (cosmic microwave background).