The Initial Conditions for Protostellar Collapse:Observational Constraints

Abstract

Despite recent progress, the first stages of cloud fragmentation andcore collapse remain poorly known. Significant observational advanceswere achieved in this field over the last decade, thanks to the use oflarge (sub)millimeter radiotelescopes such as the IRAM 30 m and theJCMT. Young protostars ("Class 0" objects), featuring powerful jetsand marked infall motions, were identified at the beginning of themain accretion phase. The density structure of numerous prestellarcondensations was also measured, setting strong constraints on theinitial conditions for individual collapse in molecular clouds. Morerecently, the advent of large-format bolometer arrays has allowedcomplete imaging of several nearby protoclusters in thesubmillimeter. The results suggest that stars are generally built fromfinite reservoirs of mass and imply that the stellar initial massfunction (IMF) is at least partly determined by turbulentfragmentation at the prestellar stage of star formation. This fieldwill greatly benefit from future large submillimeter projects such asFIRST/Herschel and ALMA in which Europe is involved at the highestlevel.