Massive protostars in the infrared dark cloud MSXDC G034.43+00.24

We present a multiwavelength study of the infrared dark cloud MSXDC G034.43 + 00.24. Dust emission, traced by millimeter/submmillimeter images obtained with the IRAM, JCMT, and CSO telescopes, reveals three compact cores within this infrared dark cloud with masses of 170 - 800 M-circle dot and sizes < 0.5 pc. Spitzer 3.6 - 8.0 mu m images show slightly extended emission toward these cores, with a spectral enhancement at 4.5 mu m that probably arises from shocked H-2. In addition, the broad line widths (Delta V similar to 10) of HCN (4 - 3) and CS (3 - 2) and the DV similar to 10 detection of SiO (2 - 1), observed with the JCMT and IRAM telescopes, also indicate active star formation. Spitzer 24 mm images reveal that each of these cores contains a bright, unresolved continuum source; these sources are most likely embedded protostars. Their millimeter-to-mid-IR continuum spectral energy distributions reveal very high luminosities, 9000 - 32,000 L-circle dot. Because such large luminosities cannot arise from low-mass protostars, MSXDC G034.43 + 00.24 is actively forming massive (similar to 10 M-circle dot) stars.