Formation and Settling of a Disc Galaxy During the Last 8 Billion Years in a Cosmological Simulation

Daniel Ceverino, Joel Primack, Avishai Dekel, Susan A. Kassin

Published 2016-08-06Version 1

We present results of a high-resolution zoom cosmological simulation of the evolution of a low-mass galaxy with a maximum velocity of V=100 km/s at z=0, using the initial conditions from the AGORA project (Kim et al 2014). The final disc-dominated galaxy matches local disc scaling relations. The galaxy evolves from a compact, dispersion-dominated galaxy into a rotation-dominated but dynamically hot disc in about 0.5 Gyr (from z=1.4 to z=1.2). The disc dynamically cools down for the following 7 Gyr, as the gas velocity dispersion decreases over time, in agreement with observations. The primary cause of this slow evolution of velocity dispersion in this low-mass galaxy is stellar feedback. It is related to the decline in gas fraction, and to the associated gravitational disk instability, as the disc slowly settles from a global Toomre Q>1 turbulent disc to a marginally unstable disc (Q=1).