Blog #37: Illustris Simulation

The Halo Mass Function

When I zoomed in on a random region of high density, this is what I found:

Because I am technologically inept, here is a hand-drawn histogram of the masses of the subhaloes that I zoomed in. It appears that low-mass haloes are more common than high-mass haloes.

Because I'm only mostly technologically inept, I was able to use Excel to calculate that approximately 91% on average of the mass of the subhaloes (or at least the subhaloes that Illustris provided me with) was stellar mass.


Exploring Structure and Reionization in the Illustris Simulation 

Large scale:

Dark matter density

Gas density 

Small scale:

Dark matter density

Gas density 

The dark matter appears to be more confined to the filamentary structure than the gas is. This could be because it is denser than the gas and therefore it is more favorable for it to aggregate along the filaments, whereas gas is less affected by gravity and therefore more free to diffuse throughout space. On the smaller scale, however, the gas appears to aggregate more tightly than the dark matter does.

In medium to large galaxies, the gas appears to be densest near the center of the disk. This makes sense given what we have learned about the structure of the Milky Way, that a higher density of matter, including gas, towards its center.

Gas density (blue is denser) relative to galaxies (circles)

The most massive galaxies tend to cluster, which makes sense given their gravitational attraction to each other. 

The clustering of galaxies (circles) 

After watching the video, it seems clear that the dark matter is leading the structure formation. The formation of filaments is apparent much earlier in the dark energy box. 

This is only a bit after the beginning of the "Epoch of Reionization," when hydrogen atoms become ionized (indicated by the color that is starting to appear in the gas box). According to the video, it appeared to start around a redshift of 7.7, or 0.7 billion years. 

One of the fastest rates of star formation appears to be at redshift of between 3.50-2.90 or so, although it seems that star formation goes through cycles of speeding up and slowing down. It also appears that new objects are formed when large objects break up, as there are explosions occurring in the gas box, which will eject matter away to form smaller objects later. 

Structures probably form along these filaments because that is where the dark matter is. The dark matter gravitationally attracts normal matter, which makes it more favorable for structures to form there instead of in random regions of space.