Protostars and Planets VI, Heidelberg, July 15-20, 2013

Poster 1S016

The onset of star formation in EPoS sources: Herschel continuum and ground-based molecular line observations in concert

Linz, Hendrik (MPIA Heidelberg)
Vasyunina, Tatiana (University of Virginia & MPIfR Bonn)
Ragan, Sarah (MPIA Heidelberg)
Beuther, Henrik (MPIA Heidelberg)
Henning, Thomas (MPIA Heidelberg)
Krause, Oliver (MPIA Heidelberg)
Stecklum, Bringfried (TLS Tautenburg)

The Herschel satellite has brought us exciting new insights into the star-formation nurseries of our Galaxy. Our group has conducted a Herschel Key Programme on the Earliest Phases of Star Formation (EPoS) to scrutinise a well-selected sample of low- and high-mass star forming clumps in detail with the Herschel photometers from 70 to 500 microns. The high-mass sample comprises IRDCs and sources from the ISO Serendipity survey. Here, we show the connection between the far-infrared (FIR) appearance of these objects, governed by the dust, and the properties of their dense molecular gas content. For this, we have conducted larger complementary studies, using both single-dish and interferometer observations. We show results especially illuminating the conditions at the onset of higher-mass star formation. We concentrate on two aspects. (1) We trace very early outflow activity, in particular based on SiO detections, and relate it to the embedded population of FIR compact sources. For one key object, IRDC 321.76+0.03, the Mopra observations can now be backed up by ATCA interferometric data at 3 mm with a spatial resolution comparable to the Herschel data. Here, we can confirm that the activity centre is indeed a very red Herschel source that is not readily detected at 24 micron. (2) Furthermore, the Herschel results give us a plethora of filamentary structures. In theory, such filaments can be conducive to the local collapse of cores embedded therein. One of the most striking objects in our list is the filamentary IRDC 316.72+0.07. It attains high column densities (>10^23 cm^-2) in its interior and reaches low dust temperatures below 14 K, based on modified black-body fits to the Herschel maps. Column density and mass make it a candidate for future high-mass star formation. In particular, we speculate that the more chaotic column column density structures at the edges of the IRDC and an intriguing HCO+ enhancement there might be related to ongoing accretion onto the central filament. Final proof, however, will only come from high-resolution ALMA molecular line data.

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