First constraints on fuzzy dark matter from Lyman-$α$ forest data and hydrodynamical simulations (1703.04683v2)

Abstract: We present constraints on the masses of extremely light bosons dubbed fuzzy dark matter from Lyman-$\alpha$ forest data. Extremely light bosons with a De Broglie wavelength of $\sim 1$ kpc have been suggested as dark matter candidates that may resolve some of the current small scale problems of the cold dark matter model. For the first time we use hydrodynamical simulations to model the Lyman-$\alpha$ flux power spectrum in these models and compare with the observed flux power spectrum from two different data sets: the XQ-100 and HIRES/MIKE quasar spectra samples. After marginalization over nuisance and physical parameters and with conservative assumptions for the thermal history of the IGM that allow for jumps in the temperature of up to $5000\rm\,K$, XQ-100 provides a lower limit of 7.1$\times 10^{-22}$ eV, HIRES/MIKE returns a stronger limit of 14.3$\times 10^{-22}$ eV, while the combination of both data sets results in a limit of 20 $\times 10^{-22}$ eV (2$\sigma$ C.L.). The limits for the analysis of the combined data sets increases to 37.5$\times 10^{-22}$ eV (2$\sigma$ C.L.) when a smoother thermal history is assumed where the temperature of the IGM evolves as a power-law in redshift. Light boson masses in the range $1-10 \times10^{-22}$ eV are ruled out at high significance by our analysis, casting strong doubts that FDM helps solve the "small scale crisis" of the cold dark matter models.

• The paper establishes first constraints on fuzzy dark matter by comparing simulated Lyman-α forest spectra with observed quasar data.
• It employs hydrodynamical simulations and Monte Carlo Markov Chain methods to explore cosmological and thermal history parameters.
• The study rules out FDM boson masses of 1–10×10⁻²² eV and sets a lower limit of 20–37.5×10⁻²² eV, challenging the FDM model's viability.

Constraints on Fuzzy Dark Matter from Lyman-$\alpha$ Forest Observations

The paper, titled "First constraints on fuzzy dark matter from Lyman-$\alpha$ forest data and hydrodynamical simulations," investigates the constraints on fuzzy dark matter (FDM) models, a proposed alternative to the traditional cold dark matter (CDM) paradigm. The researchers employ Lyman-$\alpha$ forest data, using hydrodynamical simulations to provide the first direct constraints on FDM models.

Fuzzy dark matter models consider dark matter as composed of ultra-light bosons with masses as low as $10^{-22}$ eV. Such models propose that dark matter has wave-like properties on kiloparsec scales (due to their long de Broglie wavelengths) and may address the small scale challenges of CDM, such as the "core-cusp" problem and the missing satellite problem.

Methodology

The authors utilize hydrodynamical simulations to model the Lyman-$\alpha$ forest flux power spectrum and compare this against observed spectral data from two quasar samples: XQ-100 and HIRES/MIKE. These spectra provide insights into the intergalactic medium (IGM) and its thermal history, which are sensitive to the properties of dark matter. The paper focuses on using these proxies to infer the presence and characteristics of FDM by detecting any departures from predictions made by CDM.

Key cosmological and nuisance parameters are varied to understand the sensitivity of the results. The analysis employs Monte Carlo Markov Chain methods to explore the parameter space, with assumptions on thermal history included to account for possible variations such as jumps in IGM temperature up to 5000 K.

Results and Implications

Numerically, under their joint analysis of the two data sets, the researchers establish a conservative lower limit on the FDM boson mass of $20 \times 10^{-22}$ eV at a 2$\sigma$ confidence level (C.L.). Upon assuming a smoother thermal history for the IGM, this constraint improves to $37.5 \times 10^{-22}$ eV. These results rule out the mass range of $1-10 \times 10^{-22}$ eV, a mass range previously suggested to alleviate small scale structure issues in CDM models.

The paper builds confidence in the robustness of these limits by demonstrating that similar constraints are obtained even when substantially smoothing thermal history assumptions. Furthermore, the conversion of FDM constraints to equivalent thermal dark matter relic masses suggests that past approximations used to map WDM constraints onto FDM were overly simplistic, particularly when translating between observational data from different cosmological epochs.

Broader Impacts and Future Directions

The comprehensive modelling of non-linear hydrodynamical effects contributes significantly to this work's credibility, indicating that full simulations of FDM scenarios are crucial for accurate constraints. The results challenge the viability of FDM models in explaining discrepancies observed in small scale structures within the universe, reinforcing the necessity to consider other possible resolutions to the CDM's small-scale issues.

These constraints on FDM models may guide future theoretical developments and suggest directions for observational campaigns, potentially encouraging further improvements in high-redshift Lyman-$\alpha$ data gathering. Moreover, future studies might extend these methodologies to other dark matter models with additional complexities such as self-interactions or alternative particle physics motivations.

In conclusion, the paper establishes important constraints on fuzzy dark matter through detailed simulations and analysis of comprehensive quasar data, reflecting a significant advancement towards understanding the nature of dark matter within the universe.