Rapid galactic disk settling

I showed that galactic disk settling accompanies the end of bursty star formation in the FIRE simulations. ADS link

A prediction of the the FIRE simulations is that the progenitors of star forming Milky Way-mass disk galaxies are irregular galaxies with time-variable (“bursty”) star formation rates (SFRs). In the simulations, the SFR can change by a factor of 30 in as little as 100 Myr at high redshift, in contrast to the relatively time-steady SFR at low-redshift that remains constant to ~10-20%. Visualizations of the simulations also clearly show an evolution from a highly dynamic or “exploding” state at early times to a dynamically cold thin disk at late times. The physics that drive these transitions is still not certain.

However, in this paper I showed that the two transitions coincide and, for the first time, quantified the settling of the galactic disk in the FIRE simulations. In-so-doing, I revealed that galactic disk settling proceeds rapidly (~1 Gyr) and at the same time as bursty star formation ends, suggesting that a galaxy’s ability to regulate its own star formation rate is tied to whether or not is able to sustain a thin galactic disk. Furthermore, I identified a period of evolution early in the galaxy’s history where the total energy outweighs the gravitational binding energy by a factor of 3-10, i.e. the galaxy is dynamic and not in equilibrium.

For more details, see the paper.