Tully-Fisher: Spiral rotational speed and brightness. The fundamental finding of the Tully-Fisher connection is that a spiral galaxy's brightness and material rotational speed are correlated: High brightness galaxies experience high speeds.
The Tully-Fisher relation (TFR) in astronomy is an empirical link between a spiral galaxy's mass or intrinsic brightness and its asymptotic rotation speed or emission line width. Astronomers R. Brent Tully and J. Richard Fisher initially published it in 1977. Long-slit spectroscopy is used to estimate the spectral-line width, and luminosity is computed by multiplying the galaxy's apparent brightness by, where d is its distance from Earth.
Depending on whether exact measurements of mass, brightness, or rotation velocity one considers it to refer to, the TFR exists in a number of distinct forms. Tully and Fisher measured brightness using optical means, but later research revealed that the relationship was closer when measured using microwave to infrared (K band) radiation.
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