Fuzzy dark matter at cosmic dawn: new 21-cm constraints

Abstract

Potential small-scale discrepancies in the picture of galaxy formation painted by the ΛCDM paradigm have led to considerations of modified dark matter models. One such dark matter model that has recently attracted much attention is fuzzy dark matter (FDM). In FDM models, the dark matter is envisaged to be an ultra-light scalar field with a particle mass m FDM ∼ 10 −22 eV. This yields astronomically large de Broglie wavelengths which can suppress small-scale structure formation and give rise to the observed kpc-sized density cores in dwarf galaxies. We investigate the evolution of the 21-cm signal during Cosmic Dawn and the Epoch of Reionization (EoR) in ΛFDM cosmologies using analytical models. The delay in source formation and the absence of small halos in ΛFDM significantly postpone the Lyα coupling, heating, as well as the reionization of the neutral hydrogen of the intergalactic medium. As a result, the absorption feature in the evolution of the global 21-cm signal has a significantly smaller full width at half maximum (∆z 3), than ΛCDM (∆z 6). This alone rules out m FDM < 6 × 10 −22 eV as a result of the 2σ lower limit ∆z 4 from EDGES High-Band. As a result, ΛFDM is not a viable solution to the potential small-scale problems facing ΛCDM. Finally, we show that any detection of the 21-cm signal at redshifts z > 14 by interferometers such as the SKA can also exclude ΛFDM models.

The core-cusp problem revisited: ULDM vs. CDM

“…In this case, choosing parameters such that the theoretical profiles overlap with the data at small radii is easy (in this case m 22 = 0.1, M vir 5 × 10 11 M ); however, it is not clear whether this profile would fit data at larger radii were it available. Furthermore, while the choice m 22 = 0.1 provides a reasonable fit to the data in this case, a ULDM particle mass m 22 = 0.1 is in tension with constraints from the Lyman-α forest, as well as high-redshift UV luminosity function comparisons d (Amendola and Barbieri 2006;Bozek et al 2015;Armengaud et al 2017;Ni et al 2019;Nebrin, Ghara, & Mellema 2020). It must be acknowledged, however, that baryonic feedback is expected to have the greatest impact in the innermost regions of realistic halos.…”

“…Interestingly, however, a better fit to the lower velocity SPARC data is obtained from a ULDM profile where m 22 = 0.1 and M vir = 5 × 10 11 M . It must be noted, however, that a ULDM mass this small is in tension with other constraints [36][37][38][39][40]. Tightening these constraints on the plausible ULDM particle mass will inform future investigations of this type [41][42][43].…”

Small-scale structure of fuzzy and axion-like dark matter

“…The 21 cm HI absorption signal reported by the EDGES experiment was used to constrain the FDM mass to m ≥ 5 × 10 −21 eV [120] and m ≥ 8 × 10 −21 eV [121] (see also [122] for a recent analysis). These are the strongest bounds to date that follow from the low-mass cutoff of the halo mass function.…”

Dawn of the dark: unified dark sectors and the EDGES Cosmic Dawn 21-cm signal

“…Subsequently, a number of other works have been devoted to proposing alternative explanations for the anomalous EDGES detection, or utilizing such a signal to place constraints on fundamental physics assuming the signal itself is genuine (see e.g. [157,158,159,160,161,162,163,164,165,166,167,168,169,170,171,172,173,174,175,176,177,178,179,180,181] for a very limited list of works in these directions). We shall also follow this approach here: restricting our attention to the unified dark sector models we discussed in Sec.…”