Initial conditions for massive star formation.pdf

a r X i v : 0 7 1 2 .2 9 0 9 v 1 [ a s t r o - p h ] 1 8 D e c 2 0 0 7 **FULL TITLE** ASP Conference Series, Vol. **VOLUME**, **YEAR OF PUBLICATION** **NAMES OF EDITORS** Initial conditions for massive star formation Friedrich Wyrowski Max-Planck-Institut fu?r Radioastronomie, Bonn, Germany Abstract. In this contribution, our knowledge of the initial conditions under which massive star formation takes place is reviewed. Massive stars are born in massive clumps of giant molecular clouds (GMCs), hence first the properties of GMCs are summarized. As a potentially early stage of molecular clouds, infrared dark clouds have been discovered a decade ago as dark patches in mid- infrared (MIR) images of the Galactic plane and many studies of the physical conditions within them have been conducted recently. Without the guidance of MIR absorption, large scale, unbiased cold dust surveys can be used as well to identify massive cold clumps. In the absence of indicators of ongoing massive star formation, like compact HII regions and bright IR sources, these clumps are the most promising objects for the study of the initial conditions of massive star formation. Current observational approaches to find IR quiet clumps and their physical and chemical properties are summarized. 1. Introduction In the last decade, much progress has been made towards understanding of the earliest phases of massive star formation. While in the nineties most studies of early stages targeted hot objects, namely compact HII regions and hot molecular cores (e.g. Kurtz et al. 2000; Churchwell 2002), we learned only in indirect ways, for example through chemical properties, about their initial conditions. Time was ripe then for advances in the field of also colder stages with the advent of new IR mission, mm/submm bolometer arrays and clever molecular line observ- ing strategies. Previously, the initial conditions of massive star formation were covered in depths in the reviews by Evans et al. (2002),