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Register a new userChemical properties of two dense cores in a Planck Galactic Cold Clump G168.72-15.48
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To deepen our understanding of the chemical properties of the Planck Galactic Cold Clump (PGCC) G168.72-15.48, we performed observations of nine molecular species, namely, ce{c-C3H}, ce{H2CO}, ce{HC5N}, ce{HC7N}, ce{SO}, ce{CCH}, ce{N2H+}, ce{CH3OH}, and ce{CH3CCH}, toward two dense cores in PGCC G168.72-15.48 using the Tianma Radio Telescope and Purple Mountain Observatory Telescope. We detected ce{c-C3H}, ce{H2CO}, ce{HC5N}, ce{N2H+}, ce{CCH}, and ce{CH3OH} in both G168-H1 and G168-H2 cores, whereas ce{HC7N} and ce{CH3CCH} were detected only in G168-H1 and SO was detected only in G168-H2. Mapping observations reveal that the ce{CCH}, ce{N2H+}, ce{CH3OH}, and ce{CH3CCH} emissions are well coupled with the dust emission in G168-H1. Additionally, ce{N2H+} exhibits an exceptionally weak emission in the denser and more evolved G168-H2 core, which may be attributed to the ce{N2H+} depletion. We suggest that the ce{N2H+} depletion in G168-H2 is dominated by ce{N2} depletion, rather than the destruction by CO. The local thermodynamic equilibrium calculations indicate that the carbon-chain molecules of ce{CCH}, ce{HC5N}, ce{HC7N}, and ce{CH3CCH} are more abundant in the younger G168-H1 core. We found that starless core G168-H1 may have the properties of cold dark clouds based on its abundances of carbon-chain molecules. While, the prestellar core G168-H2 exhibits lower carbon-chain molecular abundances than the general cold dark clouds. With our gas-grain astrochemical model calculations, we attribute the observed chemical differences between G168-H1 and G168-H2 to their different gas densities and different evolutionary stages.
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We present the results from a series of ground-based radio observations toward a Planck Galactic Cold Clump (PGCC), PGCC G108.84-00.81, which is located in one curved filamentary cloud in the vicinity of an extended HII region Sh2-152 and SNR G109.1-1.0. PGCC G108.84-00.81 is mainly composed of two clumps, G108-N and G108-S. In the 850 micron dust continuum emission map, G108-N is shown as one component while G108-S is fragmented into four components. There is no infrared source associated with G108-N while there are two infrared sources (IRS 1 and IRS 2) associated with G108-S. The total mass of G108-N is larger than the jeans mass, suggesting that G108-N is gravitationally unstable and a potential place for a future star formation. The clump properties of G108-N and G108-S such as the gas temperature and the column density, are not distinctly different. However, G108-S is slightly more evolved than G108-N, in the consideration of the CO depletion factor, molecular abundances, and association with infrared sources. G108-S seems to be affected by the compression from Sh2-152, while G108-N is relatively protected from the external effect
Offsets of molecular line emission peaks from continuum peaks are very common but frequently difficult to explain with a single spherical cloud chemical model. We propose that the spatial projection effects of an irregular three dimensional (3D) cloud structure can be a solution. This work shows that the idea can be successfully applied to the Planck cold clump G224.4-0.6 by approximating it with four individual spherically symmetric cloud cores whose chemical patterns overlap with each other to produce observable line maps. With the empirical physical structures inferred from the observation data of this clump and a gas-grain chemical model, the four cores can satisfactorily reproduce its 850 $mu$m continuum map and the diverse peak offsets of CCS, HC$_3$N and N$_2$H$^+$ simultaneously at chemical ages of about $8times 10^5sim 3times 10^6$ yrs. The 3D projection effects on chemistry has the potential to explain such asymmetrical distributions of chemicals in many other molecular clouds.
We examine the cloud structure around the Planck detections in 71 fields observed with the Herschel SPIRE instrument. 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. We derive colour temperature and column density maps of the fields. 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 examine the star formation activity associated with the cold clumps. The mapped clouds have distances ranging from ~100pc to several kiloparsecs and cover a range of sizes and masses from cores of less than 10 solar masses to clouds with masses in excess of 10000 solar mass. 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 ~0.2-0.3pc. However, there is significant variation from 0.1pc to 1pc 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 LDN183 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.
(abridged) We perform a detailed investigation of sources from the Cold Cores Catalogue of Planck Objects (C3PO). Our goal is to probe the reliability of the detections, validate the separation between warm and cold dust emission components, provide the first glimpse at the nature, internal morphology and physical characterictics of the Planck-detected sources. We focus on a sub-sample of ten sources from the C3PO list, selected to sample different environments, from high latitude cirrus to nearby (150pc) and remote (2kpc) molecular complexes. We present Planck surface brightness maps and derive the dust temperature, emissivity spectral index, and column densities of the fields. With the help of higher resolution Herschel and AKARI continuum observations and molecular line data, we investigate the morphology of the sources and the properties of the substructures at scales below the Planck beam size.
Planck Galactic Cold Clumps (PGCCs) possibly represent the early stages of star formation. To understand better the properties of PGCCs, we studied 16 PGCCs in the L1495 cloud with molecular lines and continuum data from Herschel, JCMT/SCUBA-2 and the PMO 13.7 m telescope. Thirty dense cores were identified in 16 PGCCs from 2-D Gaussian fitting. The dense cores have dust temperatures of $T_{rm d}$ = 11-14 K, and H$_{2}$ column densities of $N_{rm H_{2}}$ = 0.36-2.5$times10^{22}$ cm$^{-2}$. We found that not all PGCCs contain prestellar objects. In general, the dense cores in PGCCs are usually at their earliest evolutionary stages. All the dense cores have non-thermal velocity dispersions larger than the thermal velocity dispersions from molecular line data, suggesting that the dense cores may be turbulence-dominated. We have calculated the virial parameter $alpha$ and found that 14 of the dense cores have $alpha$ $<$ 2, while 16 of the dense cores have $alpha$ $>$ 2. This suggests that some of the dense cores are not bound in the absence of external pressure and magnetic fields. The column density profiles of dense cores were fitted. The sizes of the flat regions and core radii decrease with the evolution of dense cores. CO depletion was found to occur in all the dense cores, but is more significant in prestellar core candidates than in protostellar or starless cores. The protostellar cores inside the PGCCs are still at a very early evolutionary stage, sharing similar physical and chemical properties with the prestellar core candidates.
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