Dust temperature tracing the ISRF intensity in the Galaxy 01/2010; DOI: 10.1051/0004-6361/201014540

ABSTRACT New observations with ensuremath Herschelensuremath<?iensuremath> allow accurate measurement of the equilibrium temperature of large dust grains heated by the interstellar radiation field (ISRF), which is critical in deriving dust column density and masses. We present temperature maps derived from the ensuremath Herschelensuremath<?iensuremath> SPIRE and PACS data in two fields along the Galactic plane, obtained as part of the Hi-GAL survey during the ensuremath Herschelensuremath<?iensuremath> science demonstration phase (SDP). We analyze the distribution of the dust temperature spatially, as well as along the two lines-of-sight (LOS) through the Galaxy. The zero-level offsets in the ensuremath Herschelensuremath<?iensuremath> maps were established by comparison with the IRAS and ensuremath Planckensuremath<?iensuremath> data at comparable wavelengths. We derive maps of the dust temperature and optical depth by adjusting a detailed model for dust emission at each pixel. The dust temperature maps show variations in the ISRF intensity and reveal the intricate mixture of the warm dust heated by massive stars and the cold filamentary structures of embedded molecular clouds. The dust optical depth at 250 ensuremath Î?ensuremath<?iensuremath>m is well correlated with the gas column density, but with a significantly higher dust emissivity than in the solar neighborhood. We correlate the optical depth with 3-D cubes of the dust extinction to investigate variations in the ISRF strength and dust abundance along the line of sight through the spiral structure of the Galaxy. We show that the warmest dust along the LOS is located in the spiral arms of the Galaxy, and we quantify their respective IR contribution.

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    ABSTRACT: As a preliminary result of the Herschel Gould Belt survey (André et al. 2010) in the Orion B cloud complex we find a clear connection between the locations of the detected prestellar cores and the column density values. We find that the vast majority of the gravitationally bound prestellar cores are detected above a high column density of about 6-7 × 1021 cm-2 (A V ̃ 6-7). This is in very good agreement with dense core formation thresholds found in other regions. For Orion B, a similar limit appears both in the distribution of background column density values of the prestellar cores, and in the column density PDF of the region. Within our core formation scenario, the found threshold can be translated as the column density above which the filaments become gravitationally unstable and fragment into cores.
    11/2013; DOI:10.1007/978-3-319-03041-8_50
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    ABSTRACT: We use PACS and SPIRE continuum data at 160 um, 250 um, 350 um, and 500 um from the Herschel Gould Belt Survey to sample seven clumps in Perseus: B1, B1-E, B5, IC348, L1448, L1455, and NGC1333. Additionally, we identify and characterize the embedded Class 0 protostars using detections of compact Herschel sources at 70 um as well as archival Spitzer catalogues and SCUBA 850 um photometric data. We identify 28 candidate Class 0 protostars, four of which are newly discovered sources not identified with Spitzer. We find that the star formation efficiency of clumps, as traced by Class 0 protostars, correlates strongly with the flatness of their respective column density distributions at high values. This correlation suggests that the fraction of high column density material in a clump reflects only its youngest protostellar population rather than its entire source population. We propose that feedback from either the formation or evolution of protostars changes the local density structure of clumps.
    The Astrophysical Journal Letters 04/2014; 787(2). DOI:10.1088/2041-8205/787/2/L18 · 5.60 Impact Factor
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    ABSTRACT: Context. Dust grains absorb the interstellar far ultra-violet and visible photons and re-emit them in far-infrared (FIR) wavebands. The dust FIR continuum can be predicted by a grid of models using various values of the interstellar radiation field. Aims. We analyze the dust continuum emission in two Hi-GAL science-demonstration phase (SDP) fields using both the radiative transfer code. Cloudy, and the DustEM dust model, to explore the effect of radiative transfer on dust temperature. The 500 mu m submillimeter excess emission and the very small grain (VSG) contribution to the 70 mu m intensity are investigated by spectral energy distribution (SED) fitting using the Cloudy model. Methods. By comparing the observation with the model prediction, we derive dust temperature maps of the two SDP fields by fitting the dust SED with 4-band data (SPIRE bands plus PACS 160 mu m) using both Cloudy and DustEM models. Considering radiative transfer and grain physics simultaneously, we investigate the existence of a 500 mu m excess and estimate the VSG contribution to the 70 mu m intensity by fitting the dust SED with 3-band data (160, 250, and 350 mu m) and 5-band data (SPIRE and PACS bands), respectively. Results. We confirm that the field with star formation activities have a higher temperature (18.7 +/- 0.9 K) than the quiescent region (15.2 +/- 0.6 K). We find that the radiative transfer affects the FIR SED of the SDP fields and results in a higher temperature distribution than the dust-only model fit. There is no significant detection of a 500 mu m excess in the two SDP fields. The relative contribution from the VSGs to the 70 mu m intensity can be up to 50%.
    Astronomy and Astrophysics 03/2014; 564. DOI:10.1051/0004-6361/201322723 · 4.48 Impact Factor

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