Abstract
We describe a new method for simulating ionizing radiation and supernova
feedback in galaxy simulations. In this method, which we call star-forming
molecular cloud (SFMC) particles, we use a ray-tracing technique to solve the
radiative transfer equation for ultraviolet photons emitted by thousands of
distinct particles on the fly. Joined with high numerical resolution of 3.8 pc,
the realistic description of stellar feedback helps to self-regulate star
formation. This new feedback scheme also enables us to study the escape of
ionizing photons from star-forming clumps and from a galaxy, and to examine the
evolving environment of star-forming gas clumps. By simulating a galactic halo
of 2.3e11 Msun, we find that the galactic escape fraction, f_esc, fluctuates
between 0.08% to 5.9% during a ~20 Myr period with a mean value of 1.1%. The
flux of escaped photons is not strongly beamed, but manifests a large opening
angle of more than 60 degree from the galactic pole. Further, we investigate
the escape fraction per SFMC particle, f_esc(i), and how it evolves as the
particle ages. We discover that the galactic escape fraction is dominated by a
small number of SFMC particles with high f_esc(i). On average, the escape
fraction from a SFMC particle rises from 0.27% at its birth to 2.1% at the end
of a particle lifetime, 6 Myrs. This is because SFMC particles drift away from
the dense gas clumps in which they were born, and because the gas around the
star-forming clumps is dispersed by ionizing radiation and supernova feedback.
The framework established in this study brings deeper insight into the physics
of photon escape fraction from an individual star-forming clump, and from a
galaxy.
Users
Please
log in to take part in the discussion (add own reviews or comments).