Submillimeter Observations of [ITAL]Midcourse Space Experiment[/ITAL] Galactic Infrared-Dark Clouds

TLDR

Infrared‑dark clouds are large (1–10 pc) molecular cores with densities ~10⁶ cm⁻³ and temperatures ~15 K. We obtained 850 µm and 450 µm continuum images of IRDCs with the SCUBA camera on the James Clerk Maxwell Telescope. All eight clouds show bright 850 µm sources (≈1 Jy beam⁻¹) whose emission coincides with mid‑IR extinction envelopes; the compact cores have dust temperatures 10–25 K, masses tens to ~1000 M⊙, column densities up to 10²³ cm⁻², some emit at 8 µm, and two exhibit HCO⁺ infall signatures, suggesting they are in early star‑forming stages.

Abstract

We present 850 and 450 μm continuum images of infrared-dark clouds (IRDCs) taken with the Submillimeter Common-User Bolometer Array (SCUBA) submillimeter camera at the James Clerk Maxwell Telescope. The IRDCs are large (1-10 pc diameter) molecular cores with gas densities ~106 cm-3 and temperatures ≈15 K. We detected strong submillimeter sources with peak flux densities of ≈1 Jy beam-1 at 850 μm in all eight clouds that were observed. The submillimeter emission generally lies within the envelope of the mid-infrared extinction where dense gas has been detected using H2CO as a tracer. The dust temperatures in the bright, compact sources are calculated to lie in the range 10-25 K. The masses of these sources are estimated to be in the range of several tens up to about a thousand solar masses. The corresponding gas column densities range over an order of magnitude, up to about 1023 cm-2. Several of the sources are detected in emission at both 850 and 8 μm. Two of the sources have HCO+ line profiles characteristic of molecular infall. It is likely that the bright, compact sources seen in the SCUBA images are in various early stages of star formation, from preprotostellar cores to class I objects.