First star-forming structures in fuzzy cosmic filaments (1910.01653v2)

Abstract: In hierarchical models of structure formation, the first galaxies form in low-mass dark matter potential wells, probing the behavior of dark matter on kiloparsec (kpc) scales. Even though these objects are below the detection threshold of current telescopes, future missions will open an observational window into this emergent world. In this Letter we investigate how the first galaxies are assembled in a `fuzzy' dark matter (FDM) cosmology where dark matter is an ultralight $\sim 10^{-22}$~eV boson and the primordial stars are expected to form along dense dark matter filaments. Using a first-of-its-kind cosmological hydrodynamical simulation, we explore the interplay between baryonic physics and unique wavelike features inherent to FDM. In our simulation, the dark matter filaments show coherent interference patterns on the boson de Broglie scale and develop cylindrical soliton-like cores which are unstable under gravity and collapse into kpc-scale spherical solitons. Features of the dark matter distribution are largely unaffected by the baryonic feedback. On the contrary, the distributions of gas and stars, which do form along the entire filament, exhibit central cores imprinted by dark matter -- a smoking gun signature of FDM.

• The paper demonstrates that fuzzy dark matter creates solitonic cores which stabilize cosmic filaments via quantum pressure, influencing early star formation.
• It employs a Schrödinger-Poisson framework within the AREPO code to model ultralight bosonic dark matter, capturing de Broglie-scale interference patterns.
• The study finds that star formation in fuzzy filaments aligns along cosmic structures, offering potential observational signatures for future telescopes.

First Star-Forming Structures in Fuzzy Cosmic Filaments

The paper presented in "First star-forming structures in fuzzy cosmic filaments" explores the initial formations of galaxies within a cosmological framework where dark matter is assumed to be a form of ultralight bosons, termed 'fuzzy' dark matter (FDM). Through novel cosmological hydrodynamical simulations, this work investigates the interplay of baryonic physics with the wavelike features inherent to FDM, offering insights into the distribution and behavior of primordial stars within dense dark matter filaments.

Simulation Methodology

The simulation utilizes a unique implementation of the Schrödinger-Poisson (SP) equations in a cosmological context to model FDM. This method allows for the exploration of quantum wave effects and their influence on galaxy formation. The simulations are executed on the AREPO code, known for its effectiveness in simulating galaxy formation under cold dark matter (CDM) scenarios. However, in this research, the CDM framework is substituted with FDM to capture the de Broglie-scale interference patterns and soliton structures expected in an FDM universe.

Core Findings

The simulations reveal several critical insights into the behavior of FDM and its impact on the early stages of cosmic structure formation:

• Filament Structures: In both FDM and warm dark matter (WDM) cosmologies, the absence of small-scale power produces elongated, filamentary structures rather than the hierarchical structure formation typical in CDM. However, FDM filaments are marked by interference patterns indicative of wave superposition effects, absent in WDM.
• Solitons and Baryonic Feedback: The soliton cores, crucial to the FDM scenario, provide stability within gravitational collapse by offering quantum pressure support. These cores are pivotal for understanding FDM's role in galaxy formation, as baryonic feedback seems to leave dark matter distributions largely unaffected. As baryons trace the dark matter profile, core signatures are imprinted on the gas and stellar distributions, potentially serving as observable indicators of the presence of FDM.
• Star Formation and Observability: The star formation rates in FDM and WDM filaments were found to be comparable, though slightly suppressed in FDM. Despite the lower mass of formed stars compared to CDM predictions, the alignment of all stars along filaments under FDM represents a notable differentiation, which may be explored by future space observatories like JWST.

Theoretical and Practical Implications

This research provides substantive quantitative and qualitative predictions regarding the nature of dark matter beyond the limits of traditional CDM models. The primary theorized advantage of FDM is its ability to address unresolved small-scale structure problems in cosmology by offering solitonic protection against collapse in places where CDM would suggest otherwise. From a practical perspective, these simulations establish a data-driven blueprint for upcoming observational campaigns aimed at characterizing the nature of dark matter through the lens of early universe structure formation.

The methodologies employed open a potential avenue for refining dark matter candidates based on bosonic properties, shedding light on their quantum aspects that robustly influence large-scale cosmic structures.

Future Directions

Given the moderate tensions with current observational data, particularly Lyman-α constraints and the Milky Way's subhalo mass function, future work is projected to expand on these simulations by exploring a broader range of boson masses possibly ranging up to $10^{-18}~\text{eV}$. Higher resolution models will be vital in confirming FDM's plausibility in explaining phenomena in both high-redshift galaxies and those in the present universe.

In conclusion, this paper lays a foundational framework for understanding the unique cosmic imprints of FDM and advances the astrophysical community's capability to probe the enigmatic identity of dark matter in a more nuanced paradigm that incorporates quantum mechanics at cosmological scales.