SFDM: A new formation mechanism of tidal debris

TL;DR

This paper proposes a novel formation mechanism for tidal debris, such as shells and rings, driven by the wave-like properties of ultra-light scalar field dark matter, independent of merger events.

Contribution

It introduces the SFDM model's ability to naturally produce tidal features through halo density ripples, offering an alternative to merger-based explanations.

Findings

Tidal structures can form due to scalar field dark matter wave interference.

Stable multistate halos exhibit ripples that lead to tidal features.

The model explains observed tidal debris without requiring recent mergers.

Abstract

Recent observations of tidal debris around galaxies have revealed that the structural properties of the spheroidal components of tidally disturbed galaxies are similar to those found in non-interacting early-type galaxies(ETGs), likely due to minor merging events that do not strongly affect the bulge region or to major mergers that happened a long time ago. We show that independently of merger events, tidal features like shells or rings can also arise if the the dark matter is an ultra light scalar field of mass ~10$^{-22}$eV/c$^2$. In the scalar field dark matter (SFDM) model the small mass precludes halo formation below ~10$^8$ M$_{\odot}$ reducing the number of small galaxies today, it produces shallow density profiles due to the uncertainty principle in contrast to the steep profiles found in the standard cold dark matter (CDM) paradigm, in addition to the usual soliton solution there exists dark matter haloes in multistates, characterized by ripples in their density profiles, which are stable provided that most of the halo mass resides in the ground state. We use the hydrodynamics code ZEUS to track the gas evolution in a background potential given by a superposition of the ground and first excited state of the scalar field, we study this configuration when it is initially unstable (excited state more massive than ground state) but by a population inversion in the states it eventually becomes stable, this could happen when haloes decoupled from the expansion of the universe and collapse to reach a state of equilibrium. We found that tidal structures like rings are formed at a particular radii as a direct consequence of the wavelike structure of the dark matter halo(abridged)