Wednesday, 30 April 2014

Baby Galaxies in the Early Universe

Over the last few weeks I've been working quite hard to get together a suite of galaxies formed in high resolution cosmological simulations, so that I can study the nitty-gritty of how gas gets into galaxies from the cosmic web, and how energetic feedback from supernovae (violent explosions as massive stars die) and growing super-massive black holes affects this picture. I really should have been focussing on finishing a few papers and preparing lecture notes for an advanced undergraduate course I've got to deliver in a couple of weeks -- but this was just too much fun. Here are some cool images…

This is an image centred on the galaxy at about half the age of the Universe, on a spatial scale of 100,000 light years. The galaxy will eventually end up with properties similar to our own Milky Way. Individual particles represent gas (coloured hues of red) and stars (coloured white) -- these are the particles that are evolved by a sophisticated bit of software called GADGET, run on a powerful supercomputer.

In this image I've ignored all of the stars and shown only the gas in the galaxy - note how it's concentrated in a thin rotationally supported disc, with fairly pronounced spiral features. There's also a hole in the centre of the galaxy - that's because the gas temperature and density in this region usually satisfies the conditions for it to become star forming...

 … while in this image I'm ignoring the gas and showing only the stars. The stars are distributed in a vertically extended disc with a central spheroid. If you squint carefully, you can see that some of the small clumps of stars surrounding the main galaxy -- satellites -- are being tidally disrupted, showing the characteristic "S-shape" as stars are stripped off in the gravitational field of the galaxy.

Finally, this is what the underlying dark matter halo looks like. Pretty featureless! Currently favoured theories of galaxy formation assume that galaxies form within scaffolding provided by some form of dark matter, whose precise properties remain elusive. 

One of the fun things you can do with simulations is look in detail at what happens over the history of the galaxy and make little movies. Here is what happens to the proto-Milky Way galaxy in the very early Universe -- during the first billion years after the Big Bang… It's a bit jerky -- I don't have the patience to make it pretty -- but it's fascinating to see what happens to the newly formed disc as it experiences close interactions with some lower-mass galaxies.


Now.. back to finishing those papers...