A Model For Intergalactic Filaments and Galaxy Formation During the First Gigayear

TL;DR

This paper introduces an analytic model for intergalactic filaments during the universe's first gigayear, emphasizing the role of gas hydrodynamics in structure formation and galaxy evolution.

Contribution

It presents a novel isothermal-cylinder model that predicts filament mass based on gas sound speed, highlighting gas's active role in structure formation.

Findings

Model accurately predicts filament mass per unit length from gas sound speed

Explains baryon deficits in galaxies through differential collapse rates

Provides a potential solution to the 'too big to fail' galaxy problem

Abstract

We propose a physically based, analytic model for intergalactic filaments during the first gigayear of the universe. The structure of a filament is based upon a gravitationally bound, isothermal cylinder of gas. The model successfully predicts for a cosmological simulation the total mass per unit length of a filament (dark matter plus gas) based solely upon the sound speed of the gas component, contrary to the expectation for collisionless dark matter aggregation. It argues that the gas, through its hydrodynamic properties, plays a key role in filament structure rather than being a passive passenger in a preformed dark matter potential. The dark matter of a galaxy follows the classic equation of collapse of a spherically symmetric overdensity in an expanding universe. In contrast, the gas usually collapses more slowly. The relative rates of collapse of these two components for individual galaxies can explain the varying baryon deficits of the galaxies under the assumption that matter moves along a single filament passing through the galaxy centre, rather than by spherical accretion. The difference in behaviour of the dark matter and gas can be simply and plausibly related to the model. The range of galaxies studied includes that of the so-called "too big to fail" galaxies, which are thought to be problematic for the standard Lambda-CDM model of the universe. The isothermal-cylinder model suggests a simple explanation for why these galaxies are, unaccountably, missing from the night sky.