Protostars and Planets VI, Heidelberg, July 15-20, 2013
The Earliest Phases of Star Formation (EPoS): Herschel and APEX Observations of the Precursors to High-Mass Star Formation
Ragan, Sarah (MPIA)
Henning, Thomas (MPIA)
Beuther, Henrik (MPIA)
The question of how high-mass stars form relies fundamentally on the initial conditions. Due to the large distances to high-mass star-forming complexes and their precursors known as infrared-dark clouds (IRDCs), high-angular resolution is required to resolve individual cores. With the advent of Herschel, we now have access to the wavelength regime in which the cold dust comprising the clouds emits at its peak. As part of the Herschel guaranteed time key program \"Earliest Phases of Star Formation (EPoS)\" we obtained far-infrared maps of 45 IRDCs at all photometric bands from 70 to 500 microns. Within these clouds we have isolated a population of 500 protostellar cores closely following the distribution of dense gas. Fitting spectral energy distributions (SEDs) to each core, we estimate their average properties The cores are very cold (20K) and have a range of four orders of magnitude in mass. A counterpart at 24 microns is common (67% of sample) and represents a more evolved sub-sample of cores. With follow-up, high-resolution (7.8\") APEX/SABOCA observations at 350 microns, we better constrain the Rayleigh-Jeans tail of the blackbody SED and also isolate colder and younger sources with no 70 micron Herschel component, indicating that they are pre-stellar/starless core candidates. These cold cores have masses up to 120 Msun, bolometric luminosities below 50 Lsun, and bolometric temperatures below 30K. These datasets together provide the evolutionary sequence from starless to protostellar on small spatial scales. With a full census of the earliest phases of star formation in IRDCs, we connect the mode of star formation back to the large-scale cloud properties to determine the requirements for the most massive stars and clusters to form.
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