Angular momentum transfer to a Milky Way disk at high redshift

TL;DR

This study uses high-resolution cosmological simulations to demonstrate that cold gas filaments are the primary drivers of angular momentum growth in Milky Way-like disks at high redshift, overshadowing satellite mergers.

Contribution

It introduces algorithms to identify filaments and their impact on disk evolution, providing quantitative evidence for cold gas inflows as key to disk formation at z≥3.

Findings

Filaments at z>5.5 drive angular momentum and mass build-up.

Satellite mergers contribute negligibly to disk growth.

Cold gas inflows support thin disk formation in halos below 10^{12} M_{sun}.

Abstract

An Adaptive Mesh Refinement cosmological resimulation is analyzed in order to test whether filamentary flows of cold gas are responsible for the build-up of angular momentum within a Milky Way like disk at z>=3. A set of algorithms is presented that takes advantage of the high spatial resolution of the simulation (12 pc) to identify: (i) the central gas disk and its plane of orientation; (ii) the complex individual filament trajectories that connect to the disk, and; (iii) the infalling satellites. The results show that two filaments at z>5.5, which later merge to form a single filament at z<4, drive the angular momentum and mass budget of the disk throughout its evolution, whereas luminous satellite mergers make negligible fractional contributions. Combined with the ubiquitous presence of such filaments in all large-scale cosmological simulations that include hydrodynamics, these findings provide strong quantitative evidence that the growth of thin disks in haloes with masses below 10^{12} M_{sun}, which host the vast majority of galaxies, is supported via inflowing streams of cold gas at intermediate and high redshifts.