Can we trace very cold dust from its emission alone ?

Abstract

Context. Dust is a good tracer of cold dark clouds but its column density is difficult to quantify. Aims. We want to check whether the far-infrared and submillimeter high-resolution data from Herschel SPIRE and PACS cameras combined with ground-based telescope bolometers allow us to retrieve the whole dust content of cold dark clouds. Methods. We compare far-infrared and submillimeter emission across L183 to the 8 $\mu$m absorption map from Spitzer data and fit modified blackbody functions towards three different positions. Results. We find that none of the Herschel SPIRE channels follow the cold dust profile seen in absorption. Even the ground-based submillimeter telescope observations, although more closely following the absorption profile, cannot help to characterize the cold dust without external information such as the dust column density itself. The difference in dust opacity can reach up to a factor of 3 in prestellar cores of high extinction. Conclusions. In dark clouds, the amount of very cold dust cannot be measured from its emission alone. In particular, studies of dark clouds based only on Herschel data can miss a large fraction of the dust content. This has an impact on core and filament density profiles, masse and stability estimates.

arXiv commentLetter to A&A (accepted for publication). must be viewed with ACROBAT READER for full enhancement. Otherwise, check images in Appendix A

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• Herschel Space Observatory - An ESA facility for far-infrared and submillimetre astronomy
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• The Photodetector Array Camera and Spectrometer (PACS) on the Herschel Space Observatory
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• Can we trace very cold dust from its emission alone ?
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• Dust spectrum and polarisation at 850 um in the massive IRDC G035.39-00.33
• Herschel and SCUBA-2 observations of dust emission in a sample of Planck cold clumps
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• Prestellar core modeling in the presence of a filament - The dense heart of L1689B
• Will ALMA Reveal the True Core Mass Function of Protoclusters?
• A CO survey on a sample of Herschel cold clumps
• Dust properties of the cometary globule Barnard 207 (LDN 1489)
• Constraining the Dust Opacity Law in Three Small and Isolated Molecular Clouds
• First map of D${}_2$H${}^{+}$ emission revealing the true centre of a prestellar core: further insights into deuterium chemistry
• Multi-wavelength observations and modelling of a quiescent cloud LDN1512
• Dust evolution in pre-stellar cores
• The Cold Dust Content of the Nearby Galaxies IC 5325, NGC 7496, NGC 7590, and NGC 7599
• Mass estimates for very cold (< 8 K) gas in molecular cloud cores
• Deuterium fractionation of the starless core L 1498
• Comparison of modified black-body fits for the estimation of dust optical depths in interstellar clouds
• Chemical analysis of prestellar cores in Ophiuchus yields short timescales and rapid collapse