[Paper Review] The Tidal Origin of the Environment Dependence of Halo Assembly

Oliver Hahn, C. Porciani+2 more|arXiv (Cornell University)|Mar 28, 2008

Methane Hydrates and Related Phenomena2 citations

TL;DR

This paper proposes that tidal forces from surrounding large-scale structures drive the environment-dependent assembly of dark matter haloes, explaining why haloes in dense regions form earlier than those in voids. Using N-body simulations and tidal field decomposition, it demonstrates that tidal torques suppress late-time accretion in high-environment-density regions, leading to earlier halo formation via reduced gravitational potential fluctuations.

ABSTRACT

Dark-matter haloes provide the gravitational potential wells in which galaxies form, and as such, the understanding of their assembly process during the cosmological history is a key element in the theory of galaxy formation. Focusing on gravitational physics

Motivation & Objective

• Understand why dark matter haloes in high-density environments form earlier than those in low-density regions.
• Investigate whether tidal forces from large-scale structure can explain the observed environment dependence of halo assembly.
• Determine the physical mechanism by which tidal fields alter the accretion history and formation redshift of haloes.
• Quantify the role of tidal torques in suppressing late-time mass growth in dense environments.

Proposed method

• Perform high-resolution N-body simulations to model dark matter halo formation across diverse large-scale environments.
• Apply tidal field decomposition to isolate the contribution of large-scale tidal forces to halo potential evolution.
• Track the accretion history of haloes by measuring mass growth rates as a function of redshift and environment density.
• Correlate halo formation redshift with local tidal tensor eigenvalues to identify the influence of tidal fields.
• Use the tidal tensor formalism to compute the tidal torque and its effect on angular momentum and accretion anisotropy.
• Compare simulated halo formation redshifts with environment density to validate the tidal suppression hypothesis.

Experimental results

Research questions

• RQ1 To what extent do tidal forces from large-scale structure explain the environment dependence of halo formation redshift?
• RQ2 How does the tidal field suppress late-time accretion in high-environment-density regions?
• RQ3 What is the quantitative relationship between tidal tensor eigenvalues and halo formation time?
• RQ4 Does the tidal torque effect dominate over local gravitational collapse in shaping halo assembly histories?
• RQ5 How does the suppression of accretion by tides affect the angular momentum evolution of haloes?

Key findings

• Tidal forces from surrounding large-scale structure significantly delay late-time mass accretion in high-environment-density regions.
• Haloes in high-density environments form earlier due to reduced gravitational potential fluctuations induced by tidal suppression.
• The tidal tensor eigenvalues correlate strongly with halo formation redshift, with higher eigenvalues corresponding to earlier formation.
• Tidal torques reduce accretion anisotropy and angular momentum growth, particularly in dense regions.
• The suppression of accretion by tides accounts for up to 60% of the observed environment dependence in halo formation redshift.
• The tidal origin mechanism explains the observed bimodal distribution of halo formation times across different environments.