Benjamin D. Oppenheimer's
Movies of Cosmological Simulations

Presented here are movies/visualizations made from our cosmological hydrodynamic simulations created using our modified version of the Gadget-2 code (Springel 2005). This page is meant for both the general public and researchers within astronomy. I, Benjamin D. Oppenheimer, am part of a group led by Romeel Davé, which uses simulations to research the physics of galaxy formation with a focus on explaining the evolutionary trends seen in the observations of galaxies and the intergalactic medium (IGM), the matter outside of galaxies that makes up most of the mass of the Universe. For information on me, please check out my research interests or download my CV (pdf file) and publication list (pdf file).

The focus of these movies is to conceptualize the formation and evolution of galaxies, plus explore the state of the IGM. For astronomers interested in published results from these simulations, check out this link. If you are not an astronomer, these visualizations will show some of the fundamental processes at work in the formation of galaxies like ours, the Milky Way. For astronomers and the general public alike, if you see something in these movies that raises a question, comment, or recommendations, please feel free to e-mail me, Benjamin D. Oppenheimer, at oppen@as.arizona.edu.

General Background: These movies begin soon after the Big Bang. Soon after in this case is tens of millions years, which is relatively small compared to the age of the Universe today, about 14 billion years. The early Universe initially has no stars, which do not form until the Universe is a few hundred million years old. As the Universe ages it expands; this is a key discovery made by Edwin Hubble that our Universe is in a constantly evolving state with galaxies moving away from us and each other. These movies follow a volume of space that expands at the same rate as the Universe expands, therefore the actual distance between objects grows with time.

Not everything expands in the Universe. Fluctuations in the primordial gas grow under the force of gravity, reversing the expansion of the Universe locally and collapsing into dense objects. Many stars form in these collapsing objects resulting in the birth of galaxies. Galaxies formed early in the Universe look very different than the spiral and elliptical galaxies we see today in our local Universe. The challenge of galaxy formation is to make a unified model that can explain all the observed galaxies. This is an extremely difficult problem in astronomy, which will take astronomers many years to figure out requiring larger telescopes to make the observations, as well as more powerful simulations to understand and connect these observations in a model based on physics and chemistry.

I study the IGM, the matter in between galaxies that makes up 90% of the mass of the Universe yet remains nearly completely unobservable because it is almost completely dark. In fact, an observer must look at a bright object lying behind the IGM to see any signature of the IGM as it absorbs this light. Usually these objects are the brightest objects in the Universe: quasars, or accreting black holes emitting energetic light as they eat surrounding gas and stars in the centers of massive galaxies.

One surprising observation is that the IGM contains metals. Metals in an astronomical context are not the shiny, hard materials we are used to seeing, but instead any element other than hydrogen and helium that must be formed in the centers of stars. This is surprising because the IGM is not dense enough to form stars and getting the metals to travel up to millions of light years from galaxies into the IGM requires a very energetic mechanism.

This energy is a form of feedback. The energy from stars exploding as supernovae, the ultraviolet radiation from massive stars, and the formation of black holes at the center of all large galaxies is large enough to drive out a large fraction of the mass of a galaxy into the IGM. Without feedback, the Universe would look very different, and a galaxy such as ours, the Milky Way, probably would not form in the same way. The exact nature of feedback is an on-going debate in astronomy, but our research group finds that the ultraviolet radiation from massive stars is capable of providing the source of energy for much of the feedback.

Research Description: Our goal is to find a self-consistent feedback mechanism that reproduces the widest variety of observations including the galaxy luminosity functions, the galaxy mass-metallicity relationship, and the evolving metallicity and energetic state of the IGM between z = 0 and 6 and beyond. The wind models depicted here do not necessarily reproduce all observations. The constant wind velocity model (v = 484 km/s) efficiently enriches the IGM especially at high redshift, but injects too much hot gas to reproduce the observations at low redshift. A wind model where velocity scales with galactic velocity dispersion (momentum winds) inspired by observations from Martin (2005) and theory by Murray et al. (2005) shows promise especially at lower redshift but fails to enrich the IGM at high redshift especially in underdense regions indicating a need for a different mechanism at these redshifts. Variations of the momentum wind model where high-redshift galactic winds are boosted from higher UV flux in low-metallicity stars make a large difference in early enrichment and can reproduce a wide range of metallicity observations at all epochs from z>6 to the local Universe.

Movie Format Note: Please do not open mpeg4 movies (mp4's) with your browser. Instead download them using the right click button or hold the control button on a Mac, and select download. For newer movies I have put up two versions: a high-quality .avi file, which requires the DivX codec (which you can download usually for free if it isn't installed already), and a lower quality .mpeg file that should be universally playable.

New movies as of 8/25/08!!!

d32n256vzw Simulation
32 Mpc/h box
17,000,000 gas particles
Momentum-driven wind model

3-D fly-through showing C II, C IV, and O VI tracing IGM metals from z=30-0

Metallicity-Ion Movie (Mp4, 119 MB)

Lower quality (Mpeg, 23 MB)

Ions tracing metals in a forming group

Metallicity-Ion Movie (Mp4, 76 MB)

Lower quality (Mpeg, 16 MB)

Density-Temperature Movies

Fly-through (Mp4, 10 MB)

Still frame (Mp4, 7 MB)

New Movies Showing Galaxy Formation

New Movies Showing the Behavior of Galactic Superwinds

d16n128vzw15 Simulation
16 Mpc/h box
2,000,000 gas particles
Momentum winds (v ∝ σ)

T=0.1-14.2 Gyr

Density-Temperature (avi, 12 MB)

Lower Quality (mpeg 8 MB)

Four Parameters (avi, 40 MB)

Lower Quality (mpeg 8 MB)

Central Cluster, zoomed (avi, 30 MB)

Lower Quality (mpeg 8 MB)

e16n128vzw15 Simulation
16 Mpc/h box
2,000,000 gas particles
Omega(M)=1 Universe (example of extreme structure)
Momentum winds (v ∝ σ)

T=0.1-9.3 Gyr

Density-Temperature (avi, 22 MB)

Lower Quality (mpeg 6 MB)

Four Parameters (avi, 32 MB)

Lower Quality (mpeg 6 MB)

Central Cluster, zoomed (avi, 23 MB)

Lower Quality (mpeg 6 MB)

w16n256mzw Simulation
16 Mpc/h box
16,000,000 gas particles
Metallicity-boosted momentum winds (v ∝ σ)

15 Mpc/h box, 100 km/s slice shown
between z = 8.0 - 1.5

Combination Movie (Mpeg-4, 186 MB)

Density-Temperature Movie (Mpeg-4, 31 MB)

Metallicity-CIV Movie (Mpeg-4, 19 MB)

HI Transmission Movie (Mpeg-4, 23 MB)

Everything! Movie (Mpeg-4, 23 MB)

Stellar Movie (Mpeg-4, 35 MB)

w64n256mzw Simulation
64 Mpc/h box
16,000,000 gas particles
Metallicity-boosted momentum winds (v ∝ σ)

60 Mpc/h box, 100 km/s slice shown
between z = 8.0 - 0.0

Density-Temperature Movie (Mpeg-4, 20 MB)

Density-HI Transmission Movie (Mpeg-4, 18 MB)

Metallicity-CIV Movie (Mpeg-4, 19 MB)

Density-Velocity Movie (Mpeg-4, 22 MB)

w32n192cw Simulation
32 Mpc/h box
7,000,000 gas particles
Constant Wind Velocity (484 km/s)

16 Mpc/h box, 2 Mpc/h thickness shown
between z = 30.0 - 0.0
focused on a large cluster

Temperature Movie (log scale)

Metallicity Movie (log scale)

Combination Movie (log scale)

29 Mpc/h box, thin slice shown
between z = 8.0 - 0.0

Combination & Absorption Movie

w32n192 Simulation
32 Mpc/h box
7,000,000 gas particles
Momentum Winds (v ∝ σ)

16 Mpc/h box, 2 Mpc/h thickness shown
between z = 30.0 - 0.0
focused on a large cluster

Temperature Movie (log scale)

Metallicity Movie (log scale)

Combination Movie (log scale)

w32n192cw vs.
w32n192 Simulation
29 Mpc/h box, thin slice shown
between z = 8.0-0.0

Combination Movie (log scale)

Absorption Movie (log scale)

w8n192cw Simulation
8 Mpc/h box
7,000,000 gas particles
Constant Wind Velocity (484 km/s)

4 Mpc/h box, 1 Mpc/h thickness shown
between z = 30.0 - 3.0