Ecole Evry Schatzman 2010: Star Formation in the Local Universe. Eds: C. Charbonnel & T. Montmerle, EAS Publications Series, 2011.
astro-ph/1101.3112

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TRIGGERED STAR FORMATION

Bruce G. Elmegreen


IBM T. J. Watson Research Center, 1101 Kitchawan Road, Yorktown Heights, New York 10598 USA


Abstract: Triggered star formation in bright rims and shells is reviewed. Shells are commonly observed in the Milky Way and other galaxies, but most diffuse shells seen in HI or the infrared do not have obvious triggered star formation. Dense molecular shells and pillars around HII regions often do have such triggering, although sometimes it is difficult to see what is triggered and what stars formed in the gas before the pressure disturbances. Pillar regions without clear age gradients could have their stars scattered by the gravity of the heads. Criteria and timescales for triggering are reviewed. The insensitivity of the average star formation rate in a galaxy to anything but the molecular mass suggests that triggering is one of many processes that lead to gravitational collapse and star formation.


Table of Contents

INTRODUCTION: LARGE-SCALE SHELLS

SHELL EXPANSION

TRIGGERING: BRIGHT RIMMED CLOUDS AND PILLARS

AGE SEQUENCES IN BRIGHT RIMS

SHELL EXPANSION: COLLECT AND COLLAPSE

GENERAL ASPECTS OF TRIGGERING

ISM ENERGY SOURCES THAT MAY TRIGGER STAR FORMATION

SUMMARY

REFERENCES

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