The distribution of galactic baryons in the GIMIC simulation.

  • Richard Taylor

Student thesis: Master of Science by Research


Galaxies today are missing a significant proportion of their baryons. In orderto investigate this issue, we analysed regions which varied by sigma = -2, sigma = -1,sigma = 0 and sigma = 1 about the cosmic mean, taken from the GIMIC simulations. Intotal we found 70 galaxies which matched the mass of the Milky Way and theconstraint that they have no neighbours within 780h-1 kpc. We found the particlesassociated with these galaxies in the dark matter only simulation then matchedthese to those in the simulation with baryons. The difference in the orbits of thedark matter between the two simulations was shown to be sufficiently small thatthey may be used to find the same objects in both. We found that the fraction of baryons associated with the galaxy that formedstars was roughly independent of the overall density of the region, remainingat ∼ 20%, whilst also having a highly centralised concentration. Of all baryons,30% were found to remain within the central 20h-1 kpc region associated with thecentral galaxy. Around 40% remained within the 200h-1 kpc region defined bythe virial halo and ∼ 90% were found to still be within 1.2Mpc of the galaxy theywould otherwise be part of. Stars were found to have the most highly centrallyconcentrated distribution with around 95% still within the galaxy. The baryonfraction in cold gas (< 105 K) was found to have a central spike and decrease outto the edge of the halo. The fraction of hot gas (> 105 K) on the other handwas found to increase out to the edge of the halo where it peaked before fallingoff. The dark matter distribution on galactic scales was found to be roughlyindependent of the density of the environment.
Date of Award1 Aug 2011
Original languageEnglish
Awarding Institution
  • The University of Manchester
SupervisorScott Kay (Supervisor)


  • Cosmological simulations
  • Milky-Way

Cite this