A Tight Scaling Relationship

This tight and robust scaling relation for galaxies, which arises without considering a dark matter component of a galaxy, is just the kind of relationship you'd expect if dark matter phenomena in galaxies were due to modified gravity. 

This relationship also provides a reliable means to estimate the gas component of a galaxy, which is harder to directly observe, from its stellar component and its angular momentum. This could provide a means to resolve gas component driven outliers in other observed scaling relations.

The relations between specific angular momenta (j) and masses (M) of galaxies are often used as a benchmark in analytic models and hydrodynamical simulations, as they are considered among the most fundamental scaling relations. Using accurate measurements of the stellar (j∗), gas (jgas) and baryonic (jbar) specific angular momenta for a large sample of disc galaxies, we report the discovery of tight correlations between j, M, and the cold gas fraction of the interstellar medium (fgas). At fixed fgas, galaxies follow parallel power-laws in the 2D (j,M) spaces, with gas-rich galaxies having a larger j∗ and jbar (but lower jgas) than gas-poor ones. The slopes of the relations have a value around 0.7. These new relations are amongst the tightest known scaling laws for galaxies. In particular, the baryonic relation (jbar−Mbar−fgas), arguably the most fundamental of the three, is followed not only by typical discs but also by galaxies with extreme properties such as size and gas content, and by galaxies previously claimed to be outliers of the standard 2D j−M relations. The stellar relation (j∗−M∗−fgas) may be connected to the known j∗−M∗−bulge fraction relation, while we argue that the jbar−Mbar−fgas relation can originate from the radial variation of the star formation efficiency in galaxies, although it is not explained by current disc instability models.

Pavel E. Mancera Piña, et al., "A tight angular-momentum plane for disc galaxies" arXiv 2107:02809 (July 6, 2021) (accepted for publication in A&A Letters).