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We present a multiwavelength study of the infrared dark cloud MSXDC G034.43+00.24. Dust emission, traced by millimeter/submillimeter images obtained with the IRAM, JCMT, and CSO telescopes, reveals three compact cores within this infrared dark cloud with masses of 170--800 Msun and sizes < 0.5 pc. Spitzer 3.6-8.0 um images show slightly extended emission toward these cores, with a spectral enhancement at 4.5 um that probably arises from shocked H2. In addition, the broad line widths (Delta V ~ 10 km/s) of HCN (4-3), and CS (3-2), and the detection of SiO (2-1), observed with the JCMT and IRAM telescopes, also indicate active star formation. Spitzer 24 um 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 Lsun. Because such large luminosities cannot arise from low-mass protostars, MSXDC G034.43+00.24 is actively forming massive (~ 10 Msun) stars.Comment: 6 pages, 3 figures (1 colour), accepted ApJ

Identified as extinction features against the bright Galactic mid-infrared background, infrared dark clouds (IRDCs) are thought to harbor the very earliest stages of star and cluster formation. In order to better characterize the properties of their embedded cores, we have obtained new 24 µm, 60-100 µm, and submillimeter continuum data toward a sample of 38 IRDCs. The 24 µm Spitzer images reveal that while the IRDCs remain dark, many of the cores are associated with bright 24 µm emission sources, which suggests that they contain one or more embedded protostars. Combining the 24 µm, 60-100 µm, and submillimeter continuum data, we have constructed broadband spectral energy distributions (SEDs) for 157 of the cores within these IRDCs and, using simple gray-body fits to the SEDs, have estimated their dust temperatures, emissivities, opacities, bolometric luminosities, masses and densities. Based on their Spitzer/IRAC 3-8 µm colors and the presence of 24 µm point source emission, we have separated cores that harbor active, high-mass star formation from cores that are quiescent. The active 'protostellar' cores typically have warmer dust -2temperatures and higher bolometric luminosities than the more quiescent, perhaps 'pre-protostellar', cores. Because the mass distributions of the populations are similar, however, we speculate that the active and quiescent cores may represent different evolutionary stages of the same underlying population of cores. Although we cannot rule out low-mass star-formation in the quiescent cores, the most massive of them are excellent candidates for the 'high-mass starless core' phase, the very earliest in the formation of a high-mass star.Subject headings: dust, extinction -stars: formation -infrared: stars -submillimeter which achieved a 1σ sensitivity of ∼ 30, 70, and 150 mJy at 60, 75, and 90 µm respectively. For the remaining 7 bright cores (those with 1.2 mm fluxes between 1-2 Jy), 4 repeats of a 3 sec exposure were combined. All spectra were obtained in the pointed observation mode. At these wavelengths, Spitzer has an angular resolution of ∼13-24 (9.8 pixels).Because of the contamination by the second order diffracted light and an inoperative detector module, the wavelength coverage of the spectra was restricted to 65-97 µm. The spectra were acquired in two epochs: 2006 October and 2007 May. Data from 2006 were processed using the S14.4.0 pipeline version, while 2007 data were reduced using version S16.1.0. The pointed SED-mode observation provides a set of six pairs of data frames between the target position ('on') and nearby sky position ('off'). For all analysis, we use the pipeline produced post-basic calibrated data (post-BCDs), which deliver mosaic images for the 'on' and 'off' spectra.We set the scan mirror to chop between the 'on' and 'off' positions with a chop throw of 1 to 3 . The 'off' position was selected for each individual core to be nearby and free from 1.2 mm continuum emission. However, because the chop distance and visibility of the cores were limited, many of the...

We present high angular resolution submillimeter continuum images and molecular line spectra obtained with the Submillimeter Array toward two massive cores that lie within infrared dark clouds (IRDCs), one actively star-forming (G034.43+00.24 MM1) and the other more quiescent (G028.53À00.25 MM1). The high angular resolution submillimeter continuum image of G034.43+00.24 MM1 reveals a compact ($0.03 pc) and massive ($29 M ) structure, while the molecular line spectrum shows emission from numerous complex molecules. Such a rich molecular line spectrum from a compact region indicates that G034.43+00.24 MM1 contains a hot molecular core, an early stage in the formation of a high-mass protostar. Moreover, the velocity structure of its 13 CO (3-2) emission indicates that this B0 protostar may be surrounded by a rotating circumstellar envelope. In contrast, the submillimeter continuum image of G028.53À00.25 MM1 reveals three compact (P0.06 pc), massive (9-21 M ) condensations, but there are no lines detected in its spectrum. We suggest that the core G028.53À00.25 MM1 is in a very early stage in the high-mass star formation process; its size and mass are sufficient to form at least one high-mass star, yet it shows no signs of localized heating. Because the combination of high-velocity line wings with a large IR-to-millimeter bolometric luminosity ($10 2 L ) indicates that this core has already begun to form accreting protostars, we speculate that the condensations may be in the early phase of accretion and may eventually become high-mass protostars. Therefore, we have found the possible existence of two high-mass star-forming cores: one in a very early phase of star formation and one in the later hot-core phase. Together, the properties of these two cores support the idea that the earliest stages of high-mass star formation occur within IRDCs.

Abstract.Results are presented from a multi-wavelength study of the giant pillars within the Carina Nebula. Using near-IR data from 2MASS, mid-IR data from MSX, 843 MHz radio continuum maps from the MOST and molecular line and continuum observations from the SEST, we investigate the nature of the pillars and search for evidence of ongoing star formation within them. Photodissociation regions (PDRs) exist across the whole nebula and trace the giant pillars, as well as many ridges, filaments and condensations (A v > 7 mag). Morphological similarities between emission features at 21 µm and 843 MHz adjacent to the PDRs, suggests that the molecular material has been carved by the intense stellar winds and UV radiation from the nearby massive stars. In addition, star forming cores are found at the tips of several of the pillars. Using a stellar density distribution, several candidate embedded clusters are also found. One is clearly seen in the 2MASS images and is located within a dense core (G287.84-0.82). A search for massive young stellar objects and compact H II regions using mid-IR colour criteria, reveal twelve candidates across the complex. Grey-body fits to SEDs for four of these objects are suggestive of OB-stars. We find that massive star formation in the Carina Nebula is occurring across the whole complex and confirm it has been continuous over the past 3 Myrs.