We use the photon flux and absorption tracer algorithm presented in Katz et al .
2018 , to characterise the contribution of haloes of different mass and stars of different age and metallicity to the reionization of the Universe .
We employ a suite of cosmological multifrequency radiation hydrodynamics AMR simulations that are carefully calibrated to reproduce a realistic reionization history and galaxy properties at z \geq 6 .
In our simulations , haloes with mass 10 ^ { 9 } { M _ { \odot } } h ^ { -1 } < M < 10 ^ { 10 } { M _ { \odot } } h ^ { -1 } , stars with metallicity 10 ^ { -3 } Z _ { \odot } < Z < 10 ^ { -1.5 } Z _ { \odot } , and stars with age 3 { Myr } < t < 10 { Myr } dominate reionization by both mass and volume .
We show that the sources that reionize most of the volume of the Universe by z = 6 are not necessarily the same sources that dominate the meta-galactic UV background at the same redshift .
We further show that in our simulations , the contribution of each type of source to reionization is not uniform across different gas phases .
The IGM , CGM , filaments , ISM , and rarefied supernova heated gas have all been photoionized by different classes of sources .
Collisional ionisation contributes at both the lowest and highest densities .
In the early stages of the formation of individual HII bubbles , reionization proceeds with the formation of concentric shells of gas ionised by different classes of sources , leading to large temperature variations as a function of galacto-centric radius .
The temperature structure of individual HII bubbles may thus give insight into the star formation history of the galaxies acting as the first ionising sources .
Our explorative simulations highlight how the complex nature of reionization can be better understood by using our photon tracer algorithm .