Abstract
In recent years, Bose-Einstein-condensed dark matter (BEC-DM) has become a popular alternative to standard, collisionless cold dark matter (CDM). This BEC-DM -also called scalar field dark matter (SFDM)- can suppress structure formation and thereby resolve the small-scale crisis of CDM for a range of boson masses. However, these same boson masses also entail implications for BEC-DM substructure within galaxies, especially within our own Milky Way. Observational signature effects of BEC-DM substructure depend upon its unique quantum-mechanical features and have the potential to reveal its presence. Ongoing efforts to determine the dark matter substructure in our Milky Way will continue and expand considerably over the next years. In this contribution, we will discuss some of the existing constraints and potentially new ones with respect to the impact of BEC-DM onto baryonic tracers. Studying dark matter substructure in our Milky Way will soon resolve the question, whether dark matter behaves classical or quantum on scales of≲1 kpc.
Highlights
According to the theme of this Research Topic article collection, we might imagine a fictitious conversation in the Parnassos of deceased scholars, involving Rubin, Einstein and Planck: while Rubin would elaborate on her observational findings of dark matter (DM) from the dynamics of galaxies, the question will arise whether we understand gravity sufficiently well to explain this phenomenology
Ultralight bosonic DM with particle masses of m ∼ (10−23 − 10−18) eV/c2 belongs to this category, and the literature has seen a recent explosion in the interest for this candidate, under the header of “scalar field dark matter (SFDM)”, “fuzzy dark matter (FDM)”, “wave dark matter”, “ultralight axion DM”, “Bose-Einstein-condensed dark matter (BEC-DM)”, etc
The authors investigate dynamical friction acting on a satellite which moves through an FDM background. They identify basically three distinct regimes in FDM dynamical friction: i) λdeB is large and the wake created in the process is set by the quantum pressure, dynamical friction is well described by linear perturbation theory; ii) the background has a velocity dispersion, λdeB is small, the wake behaves to a classical Chandrasekhar wake; and iii) the length scales of the wake and λdeB of the velocity dispersion are comparable, the wake has a stochastic character, arising from interference crests of the background, with overdensities and underdensities strongly influencing the motion of the satellite, and the dynamical friction force becomes uncertain
Summary
According to the theme of this Research Topic article collection, we might imagine a fictitious conversation in the Parnassos of deceased scholars, involving Rubin, Einstein and Planck: while Rubin would elaborate on her observational findings of dark matter (DM) from the dynamics of galaxies, the question will arise whether we understand gravity sufficiently well to explain this phenomenology. We will call the model often fuzzy dark matter (FDM), in observance of the early paper by (Hu et al, 2000), wherein that term was coined, fiducial FDM models usually require ultralight bosons, m ∼ (10−23 − 10−22) eV/c2, in order for quantum phenomena to be visible on galactic scales (i.e., the mere absence of self-interaction does not constitute FDM as it was originally conceived). Since we discuss boson masses intermediate between ultralight and QCD axion-like, we will call self-gravitating objects, which follow the relation Eq 7, “solitonic drops”, or “drops” for short These ground-state solitons describe individual BEC-DM drops, they respresent the central parts of BEC-DM halos, which formed from mergers either in a static or expanding background, the so-called “solitonic cores”, whose size is of order Eq 7. The astrophysics literature uses both formalisms, and the choice for one over the other is influenced by taste and numerical method at hand
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