Constraining cosmological simulations with peculiar velocities: a forward-modeling approach

TL;DR

This paper introduces Hamlet-PM, a forward-modeling method that constrains initial conditions of cosmological simulations using peculiar velocity data, enabling highly accurate local universe reconstructions for comparison with observations.

Contribution

The paper presents Hamlet-PM, a novel Bayesian forward-modeling approach that produces constrained initial conditions for cosmological simulations based on peculiar velocity measurements.

Findings

Produced 100 high-resolution constrained simulations of the local universe.

Successfully matched simulated galaxy clusters with observed counterparts in mass and position.

Outperforms previous methods in the quality of local universe reconstructions.

Abstract

Numerical simulations are a key tool to decipher the dynamics of gravitation. Yet, they fail to spatially reproduce the Universe we observe, limiting comparison between observations and simulations to a statistical level. This is highly problematic for rare, faint or well studied nearby objects that are observed in a single environment. The computational cost of recovering this environment in random simulations is prohibitive. We present Hamlet-PM, a method that enables the constraining of initial conditions for cosmological simulations so as to produce evolved numerical universes that can be directly compared to observations of the Local Universe: constrained simulations. Our method implements the field-level forward modeling of the early-time density field from sparse and noisy measurements of late-time peculiar velocities. The dynamics are integrated with a particle-mesh gravity solver, thus probing the mildly non-linear regime. The code is applied to the Cosmicflows-4 compilation of peculiar velocities up to z < 0.05 (160 Mpc/h). The constrained ICs a re-simulated with a high precision N-body code. A series of one hundred dark-matter only cosmological constrained simulations with a resolution of 512^3 particles in a 500^3 [Mpc/h]3 box is presented. Special attention is given to twelve prominent nearby galaxy clusters, whose simulated counterparts are matched on criteria of mass and separation. We provide a mass estimate constrained by the dynamical environment for each cluster. Field-level forward modeling of the initial conditions produces highly constrained cosmological simulations. Currently, this method already overtakes in quality the pipeline in use in the peculiar-velocity community, although systematic biases still need to be addressed. Furthermore, improving the model is easy thanks to the inherent flexibility of the Bayesian approach.