Poster Presentation
Debris Disc Formation via External Photoevaporation
Presenter: Heather Fenwick Johnston (University of Exeter)
Debris discs are commonly observed around stars of various masses and ages, with their dust continuously replenished by ongoing planetesimal collisions - analogous to our own Kuiper belt. A key open question in debris disc research is: where and how do these planetesimals form? The streaming instability is a leading mechanism, requiring a locally enhanced dust-to-gas ratio to trigger gravitational collapse into planetesimals. However, it remains unclear what physical process preferentially drives this enrichment at the disc outer edge, setting the eventual architecture of the debris disc. We propose that external photoevaporation (EPE) - prevalent in the high-irradiation environments of massive star-forming regions where the majority of planetary systems are thought to originate - is a natural and efficient trigger. Using the dust and gas evolution code DustPy coupled with an FUV external photoevaporation prescription, we model the evolution of protoplanetary discs over 15 Myr. We find that strong EPE naturally drives planetesimal formation via the streaming instability at the truncated disc outer edge, with the resulting planetesimal belt width directly sensitive to the FUV field strength. Notably, high FUV levels (>500 G0) provide a viable pathway to form wide planetesimal belts at large orbital radii, with important implications for the diversity of observed debris disc architectures.
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