The Role of Cold Flows in the Assembly of Galaxy Disks

TL;DR

This paper uses high-resolution simulations to show that cold gas flows along filaments significantly influence galaxy disk formation, challenging the traditional hot accretion model and highlighting their role in early star formation.

Contribution

It demonstrates that cold flow accretion along filaments is crucial for galaxy disk growth, especially in low-mass and early-stage galaxies, revising the standard gas accretion paradigm.

Findings

Cold flows deliver cold gas directly to galaxy centers.

Cold accretion dominates star formation in disks up to L* galaxies.

Early disk growth is driven by cold flows, even in massive galaxies.

Abstract

We use high resolution cosmological hydrodynamical simulations to demonstrate that cold flow gas accretion, particularly along filaments, modifies the standard picture of gas accretion and cooling onto galaxy disks. In the standard picture, all gas is initially heated to the virial temperature of the galaxy as it enters the virial radius. Low mass galaxies are instead dominated by accretion of gas that stays well below the virial temperature, and even when a hot halo is able to develop in more massive galaxies there exist dense filaments that penetrate inside of the virial radius and deliver cold gas to the central galaxy. For galaxies up to ~L*, this cold accretion gas is responsible for the star formation in the disk at all times to the present. Even for galaxies at higher masses, cold flows dominate the growth of the disk at early times. Within this modified picture, galaxies are able to accrete a large mass of cold gas, with lower initial gas temperatures leading to shorter cooling times to reach the disk. Although star formation in the disk is mitigated by supernovae feedback, the short cooling times allow for the growth of stellar disks at higher redshifts than predicted by the standard model.