Galaxy Formation with BECDM -- II. Cosmic Filaments and First Galaxies (1911.05746v1)

Abstract: Bose-Einstein Condensate Dark Matter (BECDM; also known as Fuzzy Dark Matter) is motivated by fundamental physics and has recently received significant attention as a serious alternative to the established Cold Dark Matter (CDM) model. We perform cosmological simulations of BECDM gravitationally coupled to baryons and investigate structure formation at high redshifts ($z \gtrsim 5$) for a boson mass $m=2.5\cdot 10^{-22}~{\rm eV}$, exploring the dynamical effects of its wavelike nature on the cosmic web and the formation of first galaxies. Our BECDM simulations are directly compared to CDM as well as to simulations where the dynamical quantum potential is ignored and only the initial suppression of the power spectrum is considered -- a Warm Dark Matter-like ("WDM") model often used as a proxy for BECDM. Our simulations confirm that "WDM" is a good approximation to BECDM on large cosmological scales even in the presence of the baryonic feedback. Similarities also exist on small scales, with primordial star formation happening both in isolated haloes and continuously along cosmic filaments; the latter effect is not present in CDM. Global star formation and metal enrichment in these first galaxies are delayed in BECDM/"WDM" compared to the CDM case: in BECDM/"WDM" first stars form at $z\sim 13$/$13.5$ while in CDM star formation starts at $z\sim 35$. The signature of BECDM interference, not present in "WDM", is seen in the evolved dark matter power spectrum: although the small scale structure is initially suppressed, power on kpc scales is added at lower redshifts. Our simulations lay the groundwork for realistic simulations of galaxy formation in BECDM.

• The paper demonstrates that BECDM produces distinct quantum interference patterns in cosmic filaments compared to CDM and WDM.
• It utilizes high-resolution 1.7 h⁻¹ Mpc simulations at z ≥ 5 to capture early galaxy formation and solitonic halo cores.
• The study implies BECDM can address small-scale issues like the cusp-core problem, offering new insights into dark matter behavior.

Evaluating BECDM Cosmology for Galaxy Formation

The paper, titled "Galaxy Formation with BECDM - II. Cosmic Filaments and First Galaxies," examines the implications of forming galaxies under the Bose-Einstein Condensate Dark Matter (BECDM) cosmology. This work highlights notable differences in cosmic structure formation when compared to the prevailing Cold Dark Matter (CDM) model, and it also compares results with a Warm Dark Matter-like (WDM) model, which approximates BECDM by ignoring its dynamical quantum potential but considering the initial suppression of the power spectrum. The primary objective is to ascertain the viability of BECDM as an alternative cosmological model to explain the small-scale structure formation in the universe.

Key Findings

1. Simulations Configuration and Scale: The simulations analyze BECDM, CDM, and WDM cosmologies coupled with baryonic physics using a comoving box of 1.7 h$^{-1}$ Mpc at high redshifts ( $z \geq 5$ ). This setup is designed to explore the first galaxies formed under these models, using a boson mass of $m=2.5\times 10^{-22}$ eV.
2. Cosmic Structure and Filament Formation: The research identifies that BECDM and WDM exhibit a filamentary cosmic structure, whereas CDM reflects subhalo presence. Particularly in BECDM, filaments showcase quantum interference patterns attributed to the wavelike characteristics of the BECDM particles. This distinction is absent in WDM, where structures lack these quantum effects, demonstrating a unique signature of BECDM at small scales.
3. Halo and Filament Star Formation: In comparing the timeline of star formation, BECDM/WDM demonstrate a delayed onset compared to CDM. For instance, in BECDM, the first stars form at redshifts $z \sim 13$, in contrast to $z \sim 35$ in CDM. BECDM structures show reduced star formation and delayed metal enrichment, emphasizing the impacts of inhibited small-scale structure formation inherent to BECDM and WDM cosmologies.
4. Triaxiality and Halo Density Profiles: BECDM displays enhanced halo triaxiality compared to CDM, suggesting increased ellipticity due to sustained filamentary structures. The dark matter profiles in BECDM reveal central soliton cores formed due to a coherent interference of wavelike matter, differing significantly from the NFW-like cusps observed in CDM halos.
5. Dark Matter Power Spectra Developments: While initially similar across models, the evolved power spectra bring out pronounced differences at smaller scales by $z \sim 7$. BECDM adds small-scale power compared to WDM, highlighting quantum dynamical contributions from interference patterns that leave distinct cosmological imprints.

Implications and Speculations

The findings from these simulations solidify the potential of BECDM in resolving some of the small-scale challenges faced by CDM, such as the "cusp-core" problem and providing an explanation for dark matter characteristics at galactic centers. The solitonic cores and unique interference patterns are significant BECDM signatures that could be detectable through astronomical observations in the future.

Future work could explore how BECDM impacts galaxy formation statistics and the alignment of galaxy angular momentum with cosmic filaments. There is a solid foundation here to also explore how different boson masses and interactions may influence the small-scale universe further.

Conclusion

This exploration into BECDM cosmology offers insightful perspectives into alternative dark matter paradigms and introduces distinctive structural formations diverging from classical CDM models. Through comprehensive simulations, the paper elevates BECDM as a compelling candidate that could address long-standing discrepancies in galactic scale predictions, inviting further investigation and observation to validate its cosmological role.