# Dynamical Properties of Molecular-forming Gas Clumps in Galaxies at the Epoch of Reionization

## TL;DR

This study uses cosmological simulations to analyze the properties and stability of molecular-forming gas clumps in a high-redshift galaxy, revealing their turbulence support, stability, and implications for future observations.

## Contribution

First detailed simulation-based analysis of molecular gas clumps at reionization epoch, comparing their properties to local galaxies and assessing their stability and observability.

## Key findings

- MGCs have masses ~10^6.5 Msun and sizes 45-100 pc, similar to local galaxies.
- MGCs are highly turbulent with velocity dispersions 20-100 km/s.
- Densest star-forming regions have lower virial and Toomre-Q parameters.

## Abstract

We study the properties of molecular-forming gas clumps (MGCs) at the epoch of reionization using cosmological zoom-in simulations. We identify MGCs in a z=6 prototypical galaxy ("Althaea") using an H2 density-based clump finder. We compare their mass, size, velocity dispersion, gas surface density, and virial parameter (alpha_vir) to observations. In Althaea, the typical MGC mass and size are Mgas=10^6.5 Msun and R=45-100 pc, which are comparable to those found in nearby spirals and starburst galaxies. MGCs are highly supersonic and supported by turbulence, with rms velocity dispersions of sigma_gas=20-100 km s^-1 and pressure of P/k_B=10^7.6 K cm^-3 (i.e., >1000x with respect to the Milky Way), similar to those found in nearby and z~2 gas-rich starburst galaxies. In addition, we perform stability analysis to understand the origin and dynamical properties of MGCs. We find that MGCs are globally stable in the main disk of Althaea. Densest regions where star formation is expected to take place in clouds and cores on even smaller scales instead have lower alpha_vir and Toomre-Q values. Detailed studies of the star-forming gas dynamics at the epoch of reionization thus require a spatial resolution of <40 pc (=0.01"), which is within reach with the Atacama Large (sub-)Millimeter Array and the Next Generation Very Large Array.