Angular momentum of disc galaxies with a lognormal density distribution

Abstract

By postulating that the majority of the mass and angular momentum of a disc galaxy is confined to the disc with a lognormal surface density distribution, and that galactic discs are substantially, if not fully, self-gravitating, it may be shown that the resultant rotation curves (RCs) display a good overall fit to observational data for a wide range of galaxy types. With this hypothesis, the total angular momentum $J$, and total energy |$E$| of 38 disc galaxies was computed and plotted against the derived disc masses, with best fit slopes for $J$ of $1.683\pm 0.018$ and |$E$| of $1.643\pm 0.038$, and a universal disc spin parameter $\lambda =0.423\pm 0.014$. Using the disc parameters $V_{max}$ and $R_{max}$ as surrogates for the virial velocity and radius, a virial mass estimator $M_{disc}\propto R_{max}{V}_{max}^2$ was generated, with a log-log slope of $1.024\pm 0.014$ for the 38 galaxies, and a proportionality constant ${\lambda }^{\ast }=1.47\pm 0.20\times 10^5{M}_{\odot }kp{c}^{-1}k{m}^{-2}{s}^2$. This relationship has less scatter than $M_{\odot }\propto V^{\alpha }$, and may provide an alternative to the Tully-Fisher relation in determining virial disc masses.

Submitted to MNRAS June 2015 Accepted for publication 27 July 2015 after minor changes and additional references

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• Stability and Damping in the Disks of Massive Galaxies
• A lognormal luminosity function for SWIRE in flat cosmology
• Mining the SPARC Galaxy Database: Finding "Hidden Variables" in the Baryonic Tully-Fisher Relation
• On a Generalized Mass-Velocity Relation for Disk Galaxies and Galaxy Clusters