Galaxy Populations in the IllustrisTNG Caustic Skeleton

TL;DR

This study uses the caustic skeleton formalism to analyze how the hierarchical cosmic web influences galaxy properties, revealing a continuum of galaxy characteristics across different web environments in IllustrisTNG simulations.

Contribution

It introduces a multiscale caustic skeleton approach to connect cosmic web structures with galaxy properties, including color and star formation activity.

Findings

Galaxy properties form a continuum across the cosmic web scales.

Galaxy color-density relation is linked to hierarchical structure formation.

Multiscale analysis reveals the impact of formation time on galaxy features.

Abstract

The caustic skeleton is a parameter-free and mathematically rigorous formalism for tracing the hierarchical formation history of the multiscale cosmic web from the singularities in the underlying dark matter flow. In the present study, we explicitly use the multistreaming nature of the cosmic mass distribution to address the influence of the weblike embedding on the galaxy populations and discern their properties in different web environments. To this end, we construct the multiscale caustic skeleton of the dark mass distribution in the state-of-the-art suite of the large-scale IllustrisTNG simulations. In addition to the multistreaming dark matter density field, we assess the characteristic properties of the intergalactic baryonic gas in the vicinity of the caustics. Next, we associate the galaxies with the voids, walls, filaments and cluster nodes, and investigate their colours and star formation activities. A unique feature of the analysis is that it explicitly addresses the multiscale aspects with respect to the galaxy population, assessing issues such as the fraction of (blue) galaxies as a function of the scale of the cosmic web pattern and its caustic features. We find that the galaxy properties form a continuum in the scale-space cosmic web. Intimately coupled to the hierarchical build-up of the cosmic structure, it also allows us to systematically assess the impact of the formation time of the various structural components of the cosmic web on the galaxy properties. This furthers insight into the establishment of the observed colour-density relation of galaxies.