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

TL;DR

This paper identifies a break in the scaling relations of super spiral galaxies at high masses, revealing limits in stellar mass growth and implications for dark matter halo properties and galaxy formation theories.

Contribution

It presents the first measurement of rotation curves for super spirals, demonstrating a break in the baryonic Tully-Fisher relation at high galaxy masses.

Findings

Super spirals with stellar mass > 10^11.5 Msun deviate from the BTFR.

The BTFR slope changes from 3.75 to 0.25 above 340 km/s rotation speed.

Super spirals are under-massive for their dark matter halos, with a critical halo mass of 10^12.7 Msun.

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).