1. Initiative in Innovative Computing at Harvard, Cambridge, Massachusetts 02138, USA
2. Harvard-Smithsonian Center for Astrophysics, Cambridge, Massachusetts 02138, USA
3. Department of Physics, University of British Columbia, Okanagan, Kelowna, British Columbia V1V 1V7, Canada
4. Surgical Planning Laboratory and Department of Radiology, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts 02115, USA
5. Present address: School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, USA.

Correspondence to: Alyssa A. Goodman^1,2 Correspondence and requests for materials should be addressed to A.A.G. (Email: agoodman@cfa.harvard.edu).

Abstract

Self-gravity plays a decisive role in the final stages of star formation, where dense cores (size 0.1 parsecs) inside molecular clouds collapse to form star-plus-disk systems¹. But self-gravity's role at earlier times (and on larger length scales, such as 1 parsec) is unclear; some molecular cloud simulations that do not include self-gravity suggest that 'turbulent fragmentation' alone is sufficient to create a mass distribution of dense cores that resembles, and sets, the stellar initial mass function². Here we report a 'dendrogram' (hierarchical tree-diagram) analysis that reveals that self-gravity plays a significant role over the full range of possible scales traced by ¹³CO observations in the L1448 molecular cloud, but not everywhere in the observed region. In particular, more than 90 per cent of the compact 'pre-stellar cores' traced by peaks of dust emission³ are projected on the sky within one of the dendrogram's self-gravitating 'leaves'. As these peaks mark the locations of already-forming stars, or of those probably about to form, a self-gravitating cocoon seems a critical condition for their existence. Turbulent fragmentation simulations without self-gravity—even of unmagnetized isothermal material—can yield mass and velocity power spectra very similar to what is observed in clouds like L1448. But a dendrogram of such a simulation⁴ shows that nearly all the gas in it (much more than in the observations) appears to be self-gravitating. A potentially significant role for gravity in 'non-self-gravitating' simulations suggests inconsistency in simulation assumptions and output, and that it is necessary to include self-gravity in any realistic simulation of the star-formation process on subparsec scales.

1. Initiative in Innovative Computing at Harvard, Cambridge, Massachusetts 02138, USA
2. Harvard-Smithsonian Center for Astrophysics, Cambridge, Massachusetts 02138, USA
3. Department of Physics, University of British Columbia, Okanagan, Kelowna, British Columbia V1V 1V7, Canada
4. Surgical Planning Laboratory and Department of Radiology, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts 02115, USA
5. Present address: School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, USA.

Correspondence to: Alyssa A. Goodman^1,2 Correspondence and requests for materials should be addressed to A.A.G. (Email: agoodman@cfa.harvard.edu).

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