This page contains movies of FIRE simulations. The movies show simulations of individual galaxies forming, starting at a time when the Universe was just a a few million years old (redshift of 100). They follow the region that will become a single galaxy by the present time, tracing the evolution of dark matter and gas, which eventually turns into stars. Those stars then ‘light up’ the medium around them: they alter it with both their radiation heating up and pushing on the medium, as well as supernova explosions. More galaxy movies can be found at Phil Hopkins’s web site.
A Milky-Way Mass Galaxy in Formation (m12q)
These movies show the formation of a galaxy, similar in mass to the Milky Way, from early times (redshift z=100) to the present. The scale is fixed at 50 physical kiloparsecs on a side (so at early times, the galaxies occupy only a small fraction of this). Massive outflows driven by feedback from stars are plainly evident, and especially at early times have a dramatic impact on the surrounding inter-galactic medium. At later times, things “calm down” and a more relaxed disk starts to form.
Gas and the Formation of Disks from the Cosmic Web
Below, you can see movies of a simulation starting from slightly different initial conditions, with a different color scheme designed to highlight the cosmic web feeding the galaxies.
The Origin of Thin Galactic Disks (m12i)
These videos show the disk of a present-day Milky Way-mass galaxy, in stars and gas, formed in a simulation with an “intermediate” formation history.
Despite the violence of the outflows from the galaxy, we see a remarkably thin disk of young stars. It has been a challenge for decades to produce galaxies with thin disks, and many previous studies suggested that thin disks may be incompatible with strong feedback. The FIRE simulations show that thin galactic disks can form in cosmological simulations, and that they are compatible with strong stellar feedback.
And here is the gas in the same simulation (color coding as above):
A More Violent Alternative (m12v)
These movies are of a galaxy with similar mass, but one which experienced a more violent history. Unlike the previous system, this has many mergers — violent collisions — with other galaxies, over a wide range of times. As a result, the well-ordered disk we saw before never has as much chance to survive and grow before it is destroyed by these encounters.
These show mock three-color image (u/g/r bands) of what this galaxy would look like in visible light wavelengths, like the movie above, from two different projections to help see the mergers clearly.
A Dwarf Galaxy in Formation (m10)
These movies compare, instead, the formation of a much smaller ‘dwarf’ galaxy, with a halo mass of 10^10 solar masses, and present-day mass in stars of a few million solar masses. Outflows are enormously important here — the galaxy is a thousand times smaller in stellar mass than it would be without feedback! But feedback acts quite differently, as can be plainly seen. Outflows are very spherical, because the galaxy and its halo are small compared to the background filament it is forming out of. So accretion onto them is quasi-spherical. The outflows are primarily driven by warm/hot gas, in a series of ‘shells’. There isn’t much cold gas in the galaxy, because even a small mass in young, massive stars can heat up all the gas enough to ionize it and blow quite a large fraction out of the galaxy entirely!
You can also plainly see the effects of reionization at redshift z~8-9, when the Universe ‘lights up’ and the gas in the intergalactic medium becomes ionized.
These movies show the gas in the galaxy. Magenta is cold molecular/atomic gas (T<1000 K), green is warm ionized gas (10^4-10^5 K), and red is ‘hot‘ gas (>10^6 K).
In the absence of these ‘feedback’ effects, nearly 100% of the gas gravitationally bound to the final dark matter ‘halo’ would turn into stars, in stark disagreement with what is observed. But the movies plainly illustrate that feedback leads to massive galactic super-winds that blow out a great deal of the gas.