"Merger Trees"
These "merger trees" are images of the evolution of star formation in the
MUGS galaxies. They are created from where stars formed in the simulation.
Conveniently, the galaxies move at a constant velocity through the simulation
volume to leave a path. The trees are colored by star formation time. The
redder colors indicate new stars, while bluer is older (but you already knew
that since the blue colors are at the trunk of the tree, where the galaxy
is in its final state).
Holes
There are holes in a some of the trees. These are errors where we lost data
due to file system crashes during the long duration of these simulations.
Closer examination
It's hard to see the details of the galaxies forming in these images on the
webpage. It's informative to open these files in the simulation viewer
tipsy where you can zoom in and rotate them around. One of things
you quickly notice are the high density star formation at the center of all the
galaxy lines. This highlights yet again the overcooling problem that plagues
these simulations. Merger tree tipsy files are available on request from
the author.