The seeds of star formation in the filamentary infrared-dark cloud
  G011.11-0.12
  Infrared-dark clouds (IRDCs) are the precursors to massive stars and stellar
clusters. G011.11-0.12 is a well-studied filamentary IRDC, though, to date, the
absence of far-infrared data with sufficient spatial resolution has limited the
understanding of the structure and star-formation activity. We use Herschel to
study the embedded population of young pre- and protostellar cores in this
IRDC. We examine the cloud structure, which appears in absorption at short
wavelength and in emission at longer wavelength. We derive the properties of
the massive cores from the spectral energy distributions of bright far-infrared
point sources detected with the PACS instrument aboard Herschel. We report on
the detection and characterization of pre- and protostellar cores in a massive
filamentary infrared-dark cloud G011.11-0.12 using PACS. We characterize 18
cores directly associated with the filament, two of which have masses over 50
Msun, making them the best candidates to become massive stars in G011.11-0.12.
These cores are likely at various stages of protostar formation, showing
elevated temperature (<T> ~ 22 K) with respect to the ambient gas reservoir.
The core masses (<M> ~ 24 Msun) are small compared to that in the cold
filament. The mean core separation is 0.9 pc, well in excess of the Jeans
length in the filament. We confirm that star formation in IRDCs is underway and
diverse, and IRDCs have the capability of forming massive stars and clusters.
