Rotation curves and scaling relations of extremely massive spiral galaxies

TL;DR

This study analyzes the kinematics and scaling relations of 43 extremely massive spiral galaxies, finding they follow established relations without significant deviations at high masses, suggesting self-similarity across galaxy sizes.

Contribution

It provides detailed rotation curves for massive spirals using a hybrid 3D-1D modeling approach and extends the scaling relations to the high-mass regime, confirming their continuity.

Findings

Massive spirals reach flat rotation curves within optical radii.

High-mass galaxies follow the same Tully-Fisher and Fall relations as less massive ones.

Derived slopes: Tully-Fisher (4.25±0.19), Fall (0.64±0.11).

Abstract

We study the kinematics and scaling relations of a sample of 43 giant spiral galaxies that have stellar masses exceeding $10^{11}$ $M_\odot$ and optical discs up to 80 kpc in radius. We use a hybrid 3D-1D approach to fit 3D kinematic models to long-slit observations of the H$\alpha$-[NII] emission lines and we obtain robust rotation curves of these massive systems. We find that all galaxies in our sample seem to reach a flat part of the rotation curve within the outermost optical radius. We use the derived kinematics to study the high-mass end of the two most important scaling relations for spiral galaxies: the stellar/baryonic mass Tully-Fisher relation and the Fall (mass-angular momentum) relation. All galaxies in our sample, with the possible exception of the two fastest rotators, lie comfortably on both these scaling relations determined at lower masses, without any evident break or bend at the high-mass regime. When we combine our high-mass sample with lower-mass data from the Spitzer Photometry & Accurate Rotation Curves catalog, we find a slope of $\alpha=4.25\pm0.19$ for the stellar Tully-Fisher relation and a slope of $\gamma=0.64\pm0.11$ for the Fall relation. Our results indicate that most, if not all, of these rare, giant spiral galaxies are scaled up versions of less massive discs and that spiral galaxies are a self-similar population of objects up to the very high-mass end.