What the Spatial Distribution of Stars tells us about Star Formation, Clusters, and the IMF Eli Bressert ESO / Univ. of Exeter, Garching bei Muenchen, Germany
We present a dissertation study on two recent results regarding the clustering properties of young stars. First, we discuss a global study of young stellar object (YSO) surface densities in star forming regions based on a comprehensive collection of Spitzer Space Telescope surveys, which encompasses nearly all star formation in the solar neighbourhood. It is shown that the distribution of YSO surface densities is a smooth distribution, being adequately described by a lognormal function from a few to 103 YSOs pc-2, with a peak at ~22 YSOs pc-2 and a dispersion of ~0.85. We find no evidence for multiple discrete modes of star-formation (e.g. clustered and distributed) and that not all stars form in clusters. A Herschel Space Observatory study confirms the YSO surface density results by observing and analysing the prestellar core population in several star forming regions. Secondly, we address the issue of whether massive stars exclusively form in large stellar clusters or if they can form (albeit rarely) in relative isolation. Many studies have addressed this question from a variety of angles, however they have all been limited due to the unknown frequency of runaway high-mass stars (i.e. high-mass stars that formed in clusters but have been ejected due to dynamical interactions within the dense cluster cores). We use the VLT-FLAMES Tarantula Survey (PI Evans) to by-pass this limitation. We select O-stars outside the dense cluster R 136 but within 30 Doradus that have the same radial velocity as their surrounding gas, are spatially associated with large gaseous filaments. We find many examples of such stars, which rules out the possibility that they were ejected from R 136 (although some clear runaways are also found). Including deep optical and near-IR imaging rules out large clusters around these stars, showing that high-mass stars can and do form in relative isolation. We briefly discuss the implications of these results concerning star-formation theories, clusters, and the IMF
Collaborators: Nate Bastian, Excellence Cluster Universe, Germany Leonardo Testi, ESO, Germany Chris Evans, Royal Observatory Edinburgh, UK Robert Gutermuth, UMASS, USA Steve Longmore, ESO, Germany Lori Allen, NOAO, USA Tom Megeath, University of Toledo, USA Neal J. Evans II, University of Texas at Austin, USA Doug Johnstone, NRCC / HIoAstrophysics, Canada Hugues Sana, Univ. of Amsterdam, the Netherlands Vincent Henault-Brunet, Univ. of Edinburgh, UK Simon Goodwin, Univ. of Sheffield, UK Richard Parker, ETH Zurich, Switzerland Mark Gieles, IoA, UK Jenny Hatchell, Univ. of Exeter, UK Tyler Bourke, CfA, USA Joachim Bestenlehner, Armagh Obs., UK Jorick Vink, Armagh Obs., UK William Taylor, Univ. of Edinburgh, UK Paul Crowther, Univ. of Sheffield, UK Goetz Grafener, Armagh Obs., UK Jesus Maız Apellaniz, Instit. de Astro. de Andalucía, Spain Alex de Koter, Univ. of Amsterdam, the Netherlands Matteo Cantiello, UC Santa Barbara, USA Diederik Kruijssen, MPA, Germany	Key publication