Spitzer's Mid-Infrared View on an Outer-Galaxy Infrared Dark Cloud Candidate toward NGC 7538

September 2008 • 2008ApJ...685L..51F

Authors • Frieswijk, W. F. • Spaans, M. • Shipman, R. F. • Teyssier, D. • Carey, S. J. • Tielens, A. G. G. M.

Abstract • Infrared dark clouds (IRDCs) represent the earliest observed stages of clustered star formation, characterized by large column densities of cold and dense molecular material observed in silhouette against a bright background of mid-IR emission. Up to now, IRDCs were predominantly known toward the inner Galaxy where background infrared emission levels are high. We present Spitzer observations with the Infrared Array Camera toward object G111.80+0.58 (G111) in the outer Galactic plane, located at a distance of ~3 kpc from us and ~10 kpc from the Galactic center. Earlier results show that G111 is a massive, cold molecular clump very similar to IRDCs. The mid-IR Spitzer observations unambiguously detect object G111 in absorption. We have identified for the first time an IRDC in the outer Galaxy, which confirms the suggestion that cluster-forming clumps are present throughout the Galactic plane. However, against a low mid-IR background such as the outer Galaxy it takes some effort to find them.


IPAC Authors

Sean Carey

Senior Scientist