The journey of ionising photons through the porous ISM of galaxies
Final Report Abstract
The overall main aim of it project was to provide a measure of the ionising power of the stellar component in galaxies and its effect on the interstellar and intergalactic medium (ISM and IGM). Hot stars, which emit most of the ionising photons are generally found in stellar clusters and associations, which may contain a certain amount of gas which could absorb photons before they get into the interstellar medium of galaxies. Therefore before calculating the escape fraction of photons from galaxies one needs to quantify the escape fraction of photons from HII regions surrounding stellar clusters. We performed this first step successfully by analysing sets of Smooth Particle Hydrodynamic simulations including ionisation and wind feedback constructed by ourselves and extracting the ionising photon escape fraction as a function of time from the clusters. At the same time we produced analytical models of galaxies whose ISM is sculpted by star formation via feedback from high mass stars. For this part we sought a simple analytical description of the density distribution in order to be able to describe the dependance of the ionising escape fraction on basic quantities, like star formation rate and density. This part of the project turned out to be very computationally expensive, and to make it feasible we wrote a new efficient Monte Carlo transfer code to be able to handle the problem at the required resolution. The large computational development involved in this part has been now completed and we have run a first suite of calculations which are currently being analysed in order to find possible physical correlations with the galactic environment. The code developed for the large grid of semi-analytical simulations does not allow to perform photoionisation calculations to investigate the physical properties of the gas in our toy galaxies, furthermore this code is not suitable for the analysis of complex hydrodynamical simulations of galaxies, which is our final aim. For that reason we have also developed a new transfer module for our three-dimensional photoionisation code MOCASSIN which is based on Delauney tassellation and therefore perfectly suitable to complex density and radiation field distribution. We are currently in the best position to push forward with the project, with the bulk of the development behind us and are equipped now with state of the art codes to tackle this ambitious but fundamental astrophysical problem.
Publications
- 2013, MNRAS, 430, 234: Ionizing feedback from massive stars in massive clusters - III. Disruption of partially unbound clouds
Dale, Ercolano & Bonnell
(See online at https://doi.org/10.1093/mnras/sts592) - 2013, MNRAS, 436, 343: Massive stars in massive clusters - IV. Disruption of clouds by momentum-driven winds
Dale, Ngoumou, Ercolano, Bonnell
(See online at https://doi.org/10.1093/mnras/stt1822)
