Tully–Fisher relation

Correlation between luminosity and emission line width of spiral galaxies

In astronomy, the Tully–Fisher relation (TFR) is an empirical relationship between the mass or intrinsic luminosity of a spiral galaxy and its asymptotic rotation velocity or emission line width. The line width of the 21cm hydrogen line is used to calculate the velocity dispersion of the galaxy's spiral arms. In general, the more luminous a spiral galaxy is, the faster the rotation of its disk.

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