A Break in Spiral Galaxy Scaling Relations at the Upper Limit of Galaxy Mass

Abstract

Super spirals are the most massive star-forming disk galaxies in the universe (Ogle et al. 2016, 2019). We measured rotation curves for 23 massive spirals and find a wide range of fast rotation speeds (240-570 km/s), indicating enclosed dynamical masses of 0.6 - 4E12 Msun. Super spirals with mass in stars log Mstars / Msun > 11.5 break from the baryonic Tully-Fisher relation (BTFR) established for lower mass galaxies. The BTFR power-law index breaks from 3.75 +/- 0.11 to 0.25 +/- 0.41 above a rotation speed of 340 km/s. Super spirals also have very high specific angular momenta that break from the Fall (1983) relation. These results indicate that super spirals are under-massive for their dark matter halos, limited to a mass in stars of log Mstars / Msun < 11.8. Most giant elliptical galaxies also obey this fundamental limit, which corresponds to a critical dark halo mass of log Mhalo / Msun = 12.7. Once a halo reaches this mass, its gas can no longer cool and collapse in a dynamical time. Super spirals survive today in halos as massive as log Mhalo / Msun = 13.6, continuing to form stars from the cold baryons they captured before their halos reached critical mass. The observed high-mass break in the BTFR is inconsistent with the Modified Newtonian Dynamics (MOND) theory (Bekenstein and Milgrom 1984).