Orbits and adiabatic contraction in scalar-field dark matter halos: revisiting the cusp-core problem in dwarf galaxies

Abstract

ABSTRACT Bose–Einstein-condensed dark matter, also called scalar field dark matter (SFDM), has become a popular alternative to cold dark matter (CDM), because it predicts galactic cores, in contrast to the cusps of CDM halos (‘cusp-core problem’). We continue the study of SFDM with a strong, repulsive self-interaction; the Thomas–Fermi (TF) regime of SFDM (SFDM-TF). In this model, structure formation is suppressed below a scale related to the TF radius RTF, which is close to the radius of central cores in these halos. We investigate for the first time the impact of baryons onto realistic galactic SFDM-TF halo profiles by studying the process of adiabatic contraction (AC) in such halos. In doing so, we first analyse the underlying quantum Hamilton–Jacobi framework appropriate for SFDM and calculate dark matter orbits, in order to verify the validity of the assumptions usually required for AC. Then, we calculate the impact of AC onto SFDM-TF halos of mass $\sim 10^{11}\, {\rm M}_{\odot }$, with various baryon fractions and core radii, RTF ∼ (0.1–4) kpc, and compare our results with observational velocity data of dwarf galaxies. We find that AC-modified SFDM-TF halos with kpc-size core radii reproduce the data well, suggesting stellar feedback may not be required. On the other hand, halos with sub-kpc core radii face the same issue than CDM, in that they are not in accordance with galaxy data in the central halo parts.