Winds and radiation in unison: a new semi-analytic feedback model for cloud dissolution

Star clusters interact with the interstellar medium (ISM) in various ways, most importantly in the destruction of molecular star-forming clouds, resulting in inefficient star formation on galactic scales. On cloud scales, ionizing radiation creates \hii regions, while stellar winds and supernovae drive the ISM into thin shells. These shells are accelerated by the combined effect of winds, radiation pressure and supernova explosions, and slowed down by gravity. Since radiative and mechanical feedback is highly interconnected, they must be taken into account in a self-consistent and combined manner, including the coupling of radiation and matter. We present a new semi-analytic one-dimensional feedback model for isolated massive clouds ($\geq 10^5\,M_{\odot}$) to calculate shell dynamics and shell structure simultaneously. It allows us to scan a large range of physical parameters (gas density, star formation efficiency, metallicity) and to estimate escape fractions of ionizing radiation $f_{\rm{esc,i}}$, the minimum star formation efficiency $\epsilon_{\rm{min}}$ required to drive an outflow, and recollapse time scales for clouds that are not destroyed by feedback. Our results show that there is no simple answer to the question of what dominates cloud dynamics, and that each feedback process significantly influences the efficiency of the others. We find that variations in natal cloud density can very easily explain differences between dense-bound and diffuse-open star clusters. We also predict, as a consequence of feedback, a $4-6$ Myr age difference for massive clusters with multiple generations.Comment: 17 pages, 11 figures (additional 4 pages and 33 figures in appendix), Accepted MNRAS June 15, 201

Reframing the Fields

The conception of metaphoric process elaborated by Mary Gerhart and Allan Russell illuminates a key mechanism often involved in the most significant advances in science and religion. Attention to this conceptual device provides a productive way to reframe the relationships and dialogues between the fields. The theory has compelling implications for reframing the understanding of theology and its task