Properties of dust in the high-latitude translucent cloud L1780

Ristorcelli

Marshall

et al. 2015

A&A

Self Cite

Context. The project Galactic Cold Cores has carried out Herschel photometric observations of interstellar clouds where the Planck satellite survey has located cold and compact clumps. The sources represent different stages of cloud evolution from starless clumps to protostellar cores and are located in different Galactic environments. Aims. We examine this sample of 116 Herschel fields to estimate the submillimetre dust opacity and to search for variations that might be attributed to the evolutionary stage of the sources or to environmental factors, including the location within the Galaxy. Methods. The submillimetre dust opacity was derived from Herschel data, and near-infrared observations of the reddening of background stars are converted into near-infrared optical depth. We investigated the systematic errors affecting these parameters and used modelling to correct for the expected biases. The ratio of 250 μm and J band opacities is correlated with the Galactic location and the star formation activity. We searched for local variations in the ratio τ(250 μm)/τ(J) using the correlation plots and opacity ratio maps. Results. We find a median ratio of τ(250 μm)/τ(J) = (1.6 ± 0.2) × 10 −3 , which is more than three times the mean value reported for the diffuse medium. Assuming an opacity spectral index β = 1.8 instead of β = 2.0, the value would be lower by ∼30%. No significant systematic variation is detected with Galactocentric distance or with Galactic height. Examination of the τ(250 μm)/τ(J) maps reveals six fields with clear indications of a local increase of submillimetre opacity of up to τ(250 μm)/τ(J) ∼ 4 × 10 −3 towards the densest clumps. These are all nearby fields with spatially resolved clumps of high column density. Conclusions. We interpret the increase in the far-infrared opacity as a sign of grain growth in the densest and coldest regions of interstellar clouds.

Section: Comparison With Other Studiesmentioning

confidence: 69%

Galactic cold cores

Ristorcelli

Marshall

et al. 2015

A&A

Self Cite

“…The shorter wavelengths are more sensitive to temperature differences in the thin surface layers of the clouds and can trace variations in the heating radiation field or in the relative abundance of small and large grains (Laureijs et al 1989;Bernard et al 1992;Ridderstad & Juvela 2010). Therefore, these data can give further clues to the nature and the formation process of the clumps.…”

Section: Comparison With Other Infrared Datamentioning

confidence: 99%

Galactic cold cores

Ristorcelli

Pagani

et al. 2012

A&A

Self Cite

143

221

Context. In the project galactic cold cores we are carrying out Herschel photometric observations of cold regions of the interstellar clouds as previously identified with the Planck satellite. The aim of the project is to derive the physical properties of the population of cold clumps and to study its connection to ongoing and future star formation. Aims. We examine the cloud structure around the Planck detections in 71 fields observed with the Herschel SPIRE instrument by the summer of 2011. We wish to determine the general physical characteristics of the fields and to examine the morphology of the clouds where the cold high column density clumps are found. Methods. Using the Herschel SPIRE data, we derive colour temperature and column density maps of the fields. Together with ancillary data, we examine the infrared spectral energy distributions of the main clumps. The clouds are categorised according to their large scale morphology. With the help of recently released WISE satellite data, we look for signs of enhanced mid-infrared scattering ("coreshine"), an indication of growth of the dust grains, and have a first look at the star formation activity associated with the cold clumps. Results. The mapped clouds have distances ranging from ∼100 pc to several kiloparsecs and cover a range of sizes and masses from cores of less than 10 M to clouds with masses in excess of 10 000 M . Most fields contain some filamentary structures and in about half of the cases a filament or a few filaments dominate the morphology. In one case out of ten, the clouds show a cometary shape or have sharp boundaries indicative of compression by an external force. The width of the filaments is typically ∼0.2-0.3 pc. However, there is significant variation from 0.1 pc to 1 pc and the estimates are sensitive to the methods used and the very definition of a filament. Enhanced mid-infrared scattering, coreshine, was detected in four clouds with six additional tentative detections. The cloud LDN 183 is included in our sample and remains the best example of this phenomenon. About half of the fields are associated with active star formation as indicated by the presence of mid-infrared point sources. The mid-infrared sources often coincide with structures whose sub-millimetre spectra are still dominated by the cold dust.

“…Increased far-infrared and submillimetre opacity has been reported by many authors (Kramer et al 2003;Lehtinen et al 2004;del Burgo & Laureijs 2005;Ridderstad & Juvela 2010;Bernard et al 2010;Suutarinen et al 2013, etc.). One famous example is the Taurus filament L1506, for which the models of Stepnik et al (2003) suggested an increase by more than a factor of three.…”

Section: Comparison With Other Studiesmentioning

confidence: 75%

Galactic cold cores

2012

Proc. IAU

Self Cite

on behalf of the Planck and Herschel projects on cold coresDepartment of physics, University of Helsinki, FI-00014 Helsinki, Finland email: mika.juvela@helsinki.fiAbstract. The project Galactic Cold Cores is studying the early stages of Galactic star formation using far-infrared and sub-millimetre observations of dust emission. The Planck satellite has located many sources of cold dust emission that are likely to be pre-stellar clumps in interstellar clouds. We have mapped a sample of Planck-detected clumps with the Herschel satellite at wavelengths 100-500 μm. Herschel has confirmed the Planck detections of cold dust and have revealed a significant amount of sub-structure in the clumps. The cloud cores have colour temperatures in the range of 10-15 K. However, star formation is often already in progress with cold clumps coinciding with mid-infrared point sources. In less than half of the cases, the cloud morphology is clearly dominated by filamentary structures. The sources include both nearby isolated globules and more distant, massive clouds that may be off-the-plane counterparts of infrared dark clouds. The Herschel observations have been completed and the processed maps will be released to the community in 2013.