Galactic Astronomy

what is observed in the milkyway at different wavelengths? (optical, UV, IR, NIR, X-ray, radio, gamma?)

• NIR - can see stars through dust, so the bulge of the milkyway is quite visible. can see cooler, smaller stars much easier as they are often obscured by dust easier.

• IR - able to see the IR emission from the dust itself

• Gamma - highly energetic objects are visible here, like supernova remnants, pulsars, active galactic nuclei (AGN)

• Radio - more energy detection than visible detection - interstellar medium, snrs, pulsars, and cold gas clouds/stellar nebulae

  • 21cm emission line cold ionized HI gas

• X-ray - hot, active objects, supernovae remnants, young stars + clusters

• UV - young, hot stellar nebulae, interstellar gas, agns

how are the galactic coordinates defined? what are special angles?

galactic latitude (b) - angle above or below the galactic plane

• 0 - galactic plane

• 90 - north galactic pole

galactic longitude (l) - angle formed by line connecting the sun and the GC, and another line connecting the sun and object

• 0 - galactic center

• 90 - direction of sun’s orbital motion around the gc

what is a rotation curve?

a plot of rotational/circular velocity against radius - shows the movement of stars about a galaxy

formulas associated with the moving cluster method? (transverse and radial velocity, proper motion, space velocity)

v_r= vcos𝜃

v_t= vsin𝜃 = 4.74𝜇d

d = v_rtan𝜃 / 4.74𝜇

v = √v_t² + v_r²

what is the stellar distribution function?

a probability density distribution of stars at time t for a position, velocity, and chemical composition.

what is the velocity dispersion?

the dispersion of velocities of stars around a mean velocity - i.e. shows the amount of random motion of stars compared to the average motion.

rotation curve V(r) of a circular orbit relation to enclosed mass M(<r)?

V(r)² = GM(<r) / R

integral for enclosed mass?

M(<R) = ∫₀^R 4𝜋𝜌(r)r² dr

What is the Local Standard of Rest?