Dark matter halos and scaling relations of extremely massive spiral galaxies from extended HI rotation curves

TL;DR

This study analyzes the dark matter halos and scaling relations of the most massive spiral galaxies using extended HI rotation curves, confirming their adherence to known relations and exploring baryon-halo connections.

Contribution

It provides new extended HI rotation curves for massive spirals and investigates their dark matter and angular momentum properties, highlighting their self-similarity and smooth growth.

Findings

Massive spirals follow the Tully-Fisher and Fall relations without deviations.

Baryon-to-halo mass ratio increases with galaxy mass.

Specific angular momentum ratios remain near unity across mass range.

Abstract

We present new and archival atomic hydrogen (\hi) observations of \galnum\ of the most massive spiral galaxies in the local Universe ($M_\star>10^{11} \, \mathrm{M}_\odot$). From 3D kinematic modeling of the datacubes, we derive extended \hi\ rotation curves, and from these, we estimate masses of the dark matter halos and specific angular momenta of the discs. We confirm that massive spiral galaxies lie at the upper ends of the Tully-Fisher relation (mass vs velocity, $M \propto V^{4}$) and Fall relation (specific angular momentum vs mass, $j \propto M^{0.6}$), in both stellar and baryonic forms, with no significant deviations from single power laws. We study the connections between baryons and dark matter through the stellar (and baryon)-to-halo ratios of mass $f_\mathrm{M} \equiv M_\star/M_\mathrm{h}$ and specific angular momentum $f_\mathrm{j} \equiv j_\star/j_\mathrm{h}$ and $f_\mathrm{j,bar} \equiv j_\mathrm{bar}/j_\mathrm{h}$. Combining our sample with others from the literature for less massive disc-dominated galaxies, we find that $f_\mathrm{M}$ rises monotonically with $M_\star$ and $M_\mathrm{h}$ (instead of the inverted-U shaped $f_\mathrm{M}$ for spheroid-dominated galaxies), while $f_\mathrm{j}$ and $f_\mathrm{j,bar}$ are essentially constant near unity over four decades in mass. Our results indicate that disc galaxies constitute a self-similar population of objects closely linked to the self-similarity of their dark halos. This picture is reminiscent of early analytical models of galaxy formation wherein discs grow by relatively smooth and gradual inflow, isolated from disruptive events such as major mergers and strong AGN feedback, in contrast to the more chaotic growth of spheroids.