Spitzer's mid-infrared view on an outer Galaxy Infrared Dark Cloud candidate toward NGC 7538

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 Camera Array 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 back ground such as the outer Galaxy it takes some effort to find them.

Accepted for publication in ApJL -- 11 pages, 2 figures (1 colour)

References in corpus (13)

• Interpreting Spectral Energy Distributions from Young Stellar Objects. II. Fitting observed SEDs using a large grid of pre-computed models
• Infrared Dark Clouds: precursors to star clusters
• The Origin of Massive O-type Field Stars. Part II: Field O stars as runaways
• A Catalog of MSX Infrared Dark Cloud Candidates
• Spitzer observations of HH54 and HH7-11: mapping the H2 ortho-to-para ratio in shocked molecular gas
• Massive Protostars in the Infrared Dark Cloud MSXDC G034.43+00.24
• The Protostar in the massive Infrared Dark Cloud IRDC18223-3
• Highly Collimated Jets and Wide-Angle Outflows in HH46/47: New Evidence from Spitzer IR Images
• Radio-millimetre investigation of galactic infrared dark clouds
• Initial Conditions for Massive Star Birth -- Infrared Dark Clouds
• Interactions between a Bright YSO and the MSX Infrared-Dark Cloud G79.3+0.3: An Early Stage of Triggered Star Formation?
• The Modelling of InfraRed Dark Clouds
• Physical Characteristics of a Dark Cloud in an Early Stage of Star Formation toward NGC 7538: an Outer Galaxy Infrared Dark Cloud?

Cited by in corpus (6)

• The Hi-GAL catalogue of dusty filamentary structures in the Galactic Plane
• The stellar contents and star formation in the NGC 7538 region
• Herschel Reveals Massive Cold Clumps in NGC 7538
• Infrared Dark Cloud Cores in the SCUBA Legacy Catalogue
• Infrared dark clouds on the far side of the Galaxy
• Searching for dark clouds in the outer galactic plane I -- A statistical approach for identifying extended red(dened) regions in 2MASS