The Tully-Fisher relation provides a method of determining distances to galaxies by estimating the galaxy luminosity from a measurement of which parameter relating to the 21-cm atomic hydrogen radio emission line?
A) width
B) position and hence Doppler shift from the rest wavelength
C) intensity
D) split between its two components

Question

Quizplus · Accepted Answer

The Tully-Fisher relation estimates the luminosity of a galaxy based on its rotational velocity, which is inferred from the width of the 21-cm atomic hydrogen emission line. A broader line indicates a faster rotating galaxy, which in turn suggests a more luminous galaxy.

The Tully-Fisher Relation Provides a Method of Determining Distances to Galaxies