Revealing the Dark Threads of the Cosmic Web (2003.04393v1)

Abstract: Modern cosmology predicts that matter in our Universe has assembled today into a vast network of filamentary structures colloquially termed the Cosmic Web. Because this matter is either electromagnetically invisible (i.e., dark) or too diffuse to image in emission, tests of this cosmic web paradigm are limited. Wide-field surveys do reveal web-like structures in the galaxy distribution, but these luminous galaxies represent less than 10% of baryonic matter. Statistics of absorption by the intergalactic medium (IGM) via spectroscopy of distant quasars support the model yet have not conclusively tied the diffuse IGM to the web. Here, we report on a new method inspired by the Physarum polycephalum slime mold that is able to infer the density field of the Cosmic Web from galaxy surveys. Applying our technique to galaxy and absorption-line surveys of the local Universe, we demonstrate that the bulk of the IGM indeed resides in the Cosmic Web. From the outskirts of Cosmic Web filaments, at approximately the cosmic mean matter density (rho_m) and approx. 5 virial radii from nearby galaxies, we detect an increasing H I absorption signature towards higher densities and the circumgalactic medium, to approx. 200 rho_m. However, the absorption is suppressed within the densest environments, suggesting shock-heating and ionization deep within filaments and/or feedback processes within galaxies.

• The paper introduces the Monte-Carlo Physarum Machine to map the Cosmic Web’s density field from galaxy surveys and intergalactic medium data.
• It identifies density-dependent hydrogen absorption up to five virial radii, highlighting the presence of the circumgalactic medium.
• The study strengthens the Cosmic Web paradigm and offers a computationally efficient tool for validating ΛCDM large-scale structure models.

An Analytical Overview of "Revealing the Dark Threads of the Cosmic Web"

The paper by Burchett et al., titled "Revealing the Dark Threads of the Cosmic Web," presents a novel computational approach to infer the Cosmic Web's density field, employing a method inspired by the behavioral patterns of the Physarum polycephalum slime mold. This approach aims to enhance our understanding of matter distribution in the universe, which forms a complex network known as the Cosmic Web. The Cosmic Web is a large-scale structure formed by the gravitational pull on dark matter, with galaxies and baryonic matter constituting a minor fraction of the total mass.

Methodology and Computational Technique

Central to the paper is the Monte-Carlo Physarum Machine (MCPM), a novel algorithmic framework that seeks to map the Cosmic Web's filamentary structure based on galaxy surveys. This methodology emulates the slime mold's ability to develop efficient networks. Such networks are formed through feedback loops between particles, akin to the slime mold, and a substrate consisting of "chemo-attractants."

The researchers refined the original model by incorporating a probabilistic approach to agent movement, allowing for a more statistically representative exploration of possible paths to model the density field. This technique was applied to data from the Sloan Digital Sky Survey (SDSS) and intergalactic medium absorption data obtained from Hubble Space Telescope/Cosmic Origins Spectrograph observations.

Key Findings

The primary finding is that the bulk of the intergalactic medium (IGM) resides within the Cosmic Web. The paper identifies a density-dependent hydrogen absorption signature that appears to increase as one moves from the Cosmic Web's mean matter density toward higher decays. Particularly, this absorption signal is significant up to approximately five virial radii from the nearest galaxy, highlighting the presence of the circumgalactic medium (CGM). However, within the densest regions of the Cosmic Web, absorption is suppressed, suggesting that shock-heating and feedback processes in galaxies ionize the hydrogen.

Theoretical and Practical Implications

From a theoretical perspective, the findings reinforce the Cosmic Web paradigm and provide a critical test for the ΛCDM cosmological model. The use of the MCPM approach represents a significant step toward computationally efficient mapping of the Cosmic Web, thus offering a practical tool for corroborating large-scale structure models with observational data.

The implications of this paper extend to refine our broader understanding of galaxy evolution and interplay with intergalactic media. By calibrating the Cosmic Web's density field to known observational data, the paper reveals the structural and dynamic interactions between different cosmic components. This work underscores the potential for computational simulation frameworks inspired by natural biological processes to reveal intricate cosmological structures.

Future Directions

Future research can leverage this methodology to explore varying redshifts, extending the analysis into different epochs of cosmic evolution. Additionally, improvements in accuracy and resolution can provide insights into finer structures within the Cosmic Web, bridging the gap between simulations and real observational constraints. The extension of MCPM in this context might allow for a more detailed investigation into the nature of dark matter and its role in hierarchical galaxy formation and clustering.

Overall, the work by Burchett et al. lays important groundwork for more sophisticated models of the Cosmic Web, enhancing our understanding of the universe's composition, structure, and evolution.