[Paper Review] Simulating Cosmic Structure Formation

David H. Weinberg, Neal Katz+1 more|Scholarworks (University of Massachusetts Amherst)|Jan 1, 1997

Galaxies: Formation, Evolution, Phenomena2 references3 citations

TL;DR

This paper presents cosmological simulations combining N-body dynamics and hydrodynamics to model cosmic structure formation, focusing on high-redshift galaxy formation and the Lyman-alpha forest. It demonstrates that cold dark matter models with inflation predict abundant high-redshift galaxies and a realistic Lyman-alpha forest as a 1D tracer of the intergalactic medium, offering a powerful test for cosmological models.

ABSTRACT

We describe cosmological simulation techniques and their application to studies of cosmic structure formation, with particular attention to recent hydrodynamic simulations of structure in the high redshift universe. Collisionless N-body simulations with Gaussian initial conditions produce a pattern of sheets, filaments, tunnels, and voids that resembles the observed large scale galaxy distribution. Simulations that incorporate gas dynamics and dissipation form dense clumps of cold gas with sizes and masses similar to the luminous parts of galaxies. Models based on inflation and cold dark matter predict a healthy population of high redshift galaxies, including systems with star formation rates of 20 M_{\sun}/year at z=6. At z~3, most of the baryons in these models reside in the low density intergalactic medium, which produces fluctuating Lyman-alpha absorption in the spectra of background quasars. The physical description of this ``Lyman-alpha forest'' is particularly simple if the absorption spectrum is viewed as a 1-dimensional map of a continuous medium instead of a collection of lines. The combination of superb observational data and robust numerical predictions makes the Lyman-alpha forest a promising tool for testing cosmological models.

Motivation & Objective

• To model the formation of cosmic structures from primordial density fluctuations using cosmological simulations.
• To investigate the role of gas dynamics and dissipation in forming galaxies at high redshift.
• To understand the physical origin and observational signature of the Lyman-alpha forest in quasar spectra.
• To test whether cold dark matter and inflation-based models reproduce observed large-scale structure and intergalactic medium properties.
• To establish the Lyman-alpha forest as a robust tool for cosmological model testing through simulation and observation synergy.

Proposed method

• Employing collisionless N-body simulations with Gaussian initial conditions to model dark matter collapse into sheets, filaments, and voids.
• Incorporating hydrodynamics and radiative cooling to simulate baryonic gas collapse into dense, cold clumps resembling galaxies.
• Using high-resolution simulations to track the evolution of baryons in the intergalactic medium at redshifts z ≈ 6 and z ≈ 3.
• Modeling the Lyman-alpha forest as a continuous 1D density field rather than discrete absorption lines to simplify physical interpretation.
• Comparing simulated quasar spectra with observed Lyman-alpha absorption to validate model predictions.
• Utilizing the SPH (Smoothed Particle Hydrodynamics) technique to model gas dynamics in cosmological volumes.

Experimental results

Research questions

• RQ1 How do N-body and hydrodynamic simulations reproduce the observed large-scale structure of galaxies?
• RQ2 What are the predicted properties of high-redshift galaxies in cold dark matter models with inflationary initial conditions?
• RQ3 How does the distribution of baryons in the intergalactic medium at z ≈ 3 produce the observed Lyman-alpha forest in quasar spectra?
• RQ4 Can the Lyman-alpha forest be interpreted as a continuous 1D map of the intergalactic medium, simplifying cosmological modeling?
• RQ5 To what extent can the Lyman-alpha forest serve as a diagnostic tool for testing cosmological models?

Key findings

• N-body simulations with Gaussian initial conditions successfully reproduce the observed large-scale structure of sheets, filaments, tunnels, and voids.
• Hydrodynamic simulations produce dense clumps of cold gas with masses and sizes comparable to luminous galaxies, indicating viable galaxy formation pathways.
• Inflation-based cold dark matter models predict a substantial population of high-redshift galaxies with star formation rates up to 20 M☉/year at z = 6.
• At z ≈ 3, most baryons reside in the low-density intergalactic medium, consistent with the observed fluctuating Lyman-alpha forest in quasar spectra.
• The Lyman-alpha forest is best interpreted as a 1D map of the continuous intergalactic medium, simplifying its physical description and enhancing its utility for cosmological testing.
• The synergy between high-quality observational data and robust numerical simulations positions the Lyman-alpha forest as a powerful probe for validating cosmological models.