Tilted Dark Halos are Common, Long-Lived, and can Warp Galactic Disks

TL;DR

This study demonstrates that dark matter halos in galaxies are often tilted relative to their stellar disks, can persist for billions of years, and influence the formation of warped galactic disks, providing insights into galaxy evolution.

Contribution

It reveals that tilted dark halos are common, long-lived, and can cause stable warps in galactic disks, based on cosmological simulations.

Findings

Tilted dark halos are common in simulated galaxies.

Tilted halos can persist for over 5 billion years.

Tilted halos can induce long-lived warps in galactic disks.

Abstract

In the $\Lambda$-CDM paradigm, the dark halo governs the gravitational potential within which a galaxy can form and evolve. In this Letter we show that the present-day inner ($r<50\text{ kpc}$) dark halo can be significantly misaligned with the stellar disk. To this end, we use the TNG50 run from the cosmological magneto-hydrodynamic IllustrisTNG simulation suite. Such "tilted" dark halos can arise from a variety of processes including major mergers, massive fly-bys, or interactions with satellite companions. Furthermore, we show that tilted dark halos: (1) are well traced by tilted stellar halos, (2) can maintain their tilt for $>$ 5 Gyr in isolated evolution, and (3) can generate warps in the outer disks that are stable over many Gyr. A tilted dark halo holds clues to important events in the formation history of a galaxy, and could help explain the abundance of warped disks in galaxy observations, including the Milky Way.