Relative distance estimators.IV

Distances from galaxy kinematics

Galaxies themselves are not standard candles, since their brightnesses vary strongly from system to system (as for example, evidenced by the population of galaxies in distant clusters).

However, they obey certain scaling laws: the more massive a galaxy is, the largest its intrinsic luminosity. The more massive the galaxy, the larger the average speed of its stars. (This derives from the virial theorem; we will show this explicitly in the second part of the course).

Tully-Fisher relation

The luminosity of a spiral galaxy correlates strongly with its rotational velocity.