The onset of star formation in IRDCs: From embedded Herschel point sources to early molecular outflows traced in SiO Hendrik Linz Max-Planck-Institut fuer Astronomie, Heidelberg, Germany
The Herschel far-infrared satellite has provided the star-formation community with a powerful new tool to investigate the very early and deeply embedded phases of star formation. Our group has conceived a Herschel key programme (whimsically termed EPoS), where one main purpose is to map a selection pre-selected IRDCs and other cold higher-mass star-forming clumps in the FIR and sub-mm continuum from 70 - 500 micron. First results on the recovered population of spatially unresolved cold cores has been reported in a number of publications already (Henning et al. 2010, Beuther et al. 2010, Linz et al. 2010). In my contribution here, I want to concentrate on particularly interesting findings in these studies, like (a) point sources detected by Herschel but not seen by Spitzer/MIPS at 24 micron, and (b) cores that remain undetected in emission even at 70 and 100 micron, but have sub-mm peaked emission. I discuss whether such objects can be placed within an evolutionary scheme, and to what extent also orientation and line-of-sight effects have to be taken into account. Furthermore, I present complementary molecular line data taken with the IRAM 30-m telescope and the Mopra 22-m telescope for part of our Herschel targets, and discuss the connection between the findings in dense gas tracers like HCO+, CS, SiO, and N2H+ and the continuum point sources. In particular, our SiO data reveal a few examples where SiO emission is detected and probably indicates recent outflow activity, but no Herschel 70 micron point sources have been detected. This demonstrates that Herschel detections might not be the exclusive means of deciding about the onset of star formation activity. By means of one case study, we demonstrate how the Herschel data and interferometric follow-up studies in SiO (here done with ATCA) are important to get a refined picture on the nature of such deeply embedded young sources.
Collaborators: S. Ragan, MPIA Heidelberg, Germany T. Vasyunina, University of Virginia Charlottesville, USA A. Schmiedeke, University of Cologne, Germany H. Beuther, MPIA Heidelberg, Germany O. Krause, MPIA Heidelberg, Germany Th. Henning, MPIA Heidelberg, Germany