Distances to Galaxies

The Tully-Fisher Relation

if you measure the rotation rate of a spiral (here Wmx) this relation tells you M

The Faber-Jackson Relation

if you measure σ for an elliptical, this relation tells you its M

Tip of the Red Giant Branch Stars

uses the luminosity of the brightest red-giant-branch stars in a galaxy as a standard candle to gauge the distance to that galaxy.

1) Observe stars expected to be on the TRGB in the I-band
2) Make a colormagnitude diagram: color vs apparent magnitude for all observed stars
3) Find the apparent magnitude where you suddenly start counting a bunch of stars -> that's the "tip"
4) The difference between m and the known M in the I-band gives you the distance!

Surface Brightness Flucuations

1) Observe an *elliptical* galaxy
2) Fit a smooth model to the galaxy, then subtract it -> taking away smoothness will leave whatever clumpiness is there
3) Measure the galaxy's color vs how much m is changing (fluctuating) in the clumpiness
4) Compare to the same color-magnitude diagrams made for galaxies of known distance (from Cepheids or TRGB)
5) Exactly like MS Fitting: the difference between m and the known M gives you the distance!

limit of TRGB stars

40 MpC

Limit for SBF

100 Mpc

paralax limit

10 KpC

MS limit

30 KpC

Levitt's Law limit

40 MpC