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Triggering and the IMF MW2011, Rome

Triggering and the IMF MW2011, Rome. Larry Morgan, Toby Moore (LJMU) and Mark Thompson (University of Hertfordshire). Zavagno et al. (2010). 3 colour image of H II region in SDP field (5’ x 5’). 8µm / 24µm / 20cm. 2 nd generation massive stars observed on periphery of ionized region.

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Triggering and the IMF MW2011, Rome

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  1. Triggering and the IMF MW2011, Rome Larry Morgan, Toby Moore (LJMU) and Mark Thompson (University of Hertfordshire)

  2. Zavagno et al. (2010) • 3 colour image of HII region in SDP field (5’ x 5’) 8µm/24µm/20cm • 2nd generation massive stars observed on periphery of ionized region • Seen in 20% of ionized bubbles (Deharveng et al.,2010) Contours - 870 µm

  3. Observational Data • Evidence for Triggering • Distribution of IR sources • Presence of embedded cores • Presence of ionization layers • e.g. Morgan, Thompson, Urquhart, Koenig, Allen, Sugitani, Zavagno, Deharveng and others NH3 (1,1) emission ➛ dense gas 8 μm PAH emission ➛ PDR ➛ interior boundary between molecular and ionized gas Free-free emission ➛ IBL

  4. Ionization-Driven Triggering Ionization acts on molecular shell Collect & Collapse Swept-up shell Deharveng et al (2010) schematic

  5. 1 - Small-scale gravitational instabilities Ionization-Driven Triggering Ionization acts on molecular shell Collect & Collapse Swept-up shell Deharveng et al (2010) schematic

  6. 1 - Small-scale gravitational instabilities Ionization-Driven Triggering Ionization acts on molecular shell Collect & Collapse Swept-up shell 2 - Large-scale gravitational instabilities ➛ High-mass fragments Deharveng et al (2010) schematic

  7. 1 - Small-scale gravitational instabilities Ionization-Driven Triggering Ionization acts on molecular shell Collect & Collapse Swept-up shell 3 - Ionizing radiation acting on a turbulent medium 2 - Large-scale gravitational instabilities ➛ High-mass fragments Deharveng et al (2010) schematic

  8. 4 - Radiative-driven implosion of pre-existing dense clumps 1 - Small-scale gravitational instabilities Ionization-Driven Triggering Ionization acts on molecular shell Collect & Collapse Swept-up shell 3 - Ionizing radiation acting on a turbulent medium 2 - Large-scale gravitational instabilities ➛ High-mass fragments Deharveng et al (2010) schematic

  9. The RMS SurveyUrquhart et al (2010) • Complete survey of high-mass star formation over the GLIMPSE I region • Reliable classifications/luminosities/distances • 72/322 Churchwell bubbles associated with RMS YSOs

  10. Distribution of YSOs in and around bubbles • Significant peak at the normalised bubble radius • Clear association of YSOs with bubble shells • By 2 radii there is a constant background level See Poster #73, M.A.Thompson

  11. Bubble YSO Properties • Bubbles associated with RMS YSOs are in general smaller with thinner rims than those that are not • Mean luminosity of bubble associated YSOs is slightly above that of the entire sample • 116/850 RMS YSOs are associated with bubbles • A lower limit for the contribution of triggering to the high end of the IMF of 15%

  12. UKIDSS • Deep JHK survey over northern sky • Combination with GLIMPSE allows colour/extinction classification - e.g. Gutermuth (2005), Lucas et al (2008)

  13. Older sources • Class I - Less significant peak below the normalised bubble radius with more scatter • Class II - Steadily decreasing numbers from bubble centres • Association of sources with bubble radius weakened with age Class I Offset by 0.2 Class II YSOs do not move with the bubble shell!

  14. HiGAL 70 µm 3’ - 4 pc G308 - S145 S144

  15. 12CO contours

  16. Combination of CO mass and mass in dense clumps traced in submm allows CFE to be mapped

  17. CFE Radial Profile • Normalised fraction of mass in submm to gas mass • Large ‘skew’, interior edge is steep up to the peak with a smoother tail

  18. CFE Radial Profile • Similar features seen in other bubbles

  19. CFE Tracing Dynamical Processes? • Star formation is displaced from peak of column density • CFE higher interior to rim, as traced by gas -YSO Star formation being left behind by pressure wave

  20. Triggering process? • Column density peak coincident with turbulent velocity dispersion • The dynamical effects influencing the bubble are moving outward steadily • Rate of bubble expansion comparable to YSO stage lifetimes • Triggering process conforms to ‘shock-like’ interaction

  21. Summary • Bubble rims trace triggered star formation • Triggering a moderate but significant contributor to YSO formation • Source distributions trace history of triggering across bubbles • Triggering process ‘shock-like’, influencing material in place and enhancing density rather than creating it (c.f. Walch et al Poster #32 and paper on ArXiv) • Combination of triggering processes, fronts moving past formation once it’s occurred c.f. Bisbas et al (2011)

  22. Presentation available at • http://www.astro.ljmu.ac.uk/~lkm/

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