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Register a new userThe TOP-SCOPE survey of Planck Galactic Cold Clumps: Survey overview and results of an exemplar source, PGCC G26.53+0.17
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The low dust temperatures (<14 K) of Planck Galactic Cold Clumps (PGCCs) make them ideal targets to probe the initial conditions and very early phase of star formation. TOP-SCOPE is a joint survey program targeting ~2000 PGCCs in J=1-0 transitions of CO isotopologues and ~1000 PGCCs in 850 micron continuum emisison. The objective of the TOP-SCOPE survey and the joint surveys (SMT 10-m, KVN 21-m and NRO 45-m) is to statistically study the initial conditions occurring during star formation and the evolution of molecular clouds, across a wide range of environments. The observations, data analysis and example science cases for these surveys are introduced with an exemplar source, PGCC G26.53+0.17 (G26), which is a filamentary infrared dark cloud (IRDC). The total mass, the length and the mean line-mass (M/L) of the G26 filament are ~6200 Msun, ~12 pc and ~500 Msun/pc, respectively. Ten massive clumps including eight starless ones are found along the filament. The most massive Clump as a whole may be still in global collapse while its denser part seems to be undergoing expansion due to outflow feedback. The fragmentation in G26 filament from cloud scale to clump scale is in agreement with gravitational fragmentation of an isothermal, non-magnetized, and turbulent supported cylinder. A bimodal behavior in dust emissivity spectral index ($beta$) distribution is found in G26, suggesting grain growth along the filament. The G26 filament may be formed due to large-scale compression flows evidenced by the temperature and velocity gradients across its natal cloud.
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Planck Galactic Cold Clumps (PGCCs) are contemplated to be the ideal targets to probe the early phases of star formation. We have conducted a survey of 72 young dense cores inside PGCCs in the Orion complex with the Atacama Large Millimeter/submillimeter Array (ALMA) at 1.3,mm (band 6) using three different configurations (resolutions $sim$ 0$farcs$35, 1$farcs$0, and 7$farcs$0) to statistically investigate their evolutionary stages and sub-structures. We have obtained images of the 1.3,mm continuum and molecular line emission ($^{12}$CO, and SiO) at an angular resolution of $sim$ 0$farcs$35 ($sim$ 140,au) with the combined arrays. We find 70 substructures within 48 detected dense cores with median dust-mass $sim$ 0.093,M$_{sun}$ and deconvolved size $sim$ 0$farcs$27. Dense substructures are clearly detected within the central 1000,au of four candidate prestellar cores. The sizes and masses of the substructures in continuum emission are found to be significantly reduced with protostellar evolution from Class,0 to Class,I. We also study the evolutionary change in the outflow characteristics through the course of protostellar mass accretion. A total of 37 sources exhibit CO outflows, and 20 ($>$50%) show high-velocity jets in SiO. The CO velocity-extents ($Delta$Vs) span from 4 to 110 km/s with outflow cavity opening angle width at 400,au ranging from $[Theta_{obs}]_{400}$ $sim$ 0$farcs$6 to 3$farcs$9, which corresponds to 33$fdg$4$-$125$fdg$7. For the majority of the outflow sources, the $Delta$Vs show a positive correlation with $[Theta_{obs}]_{400}$, suggesting that as protostars undergo gravitational collapse, the cavity opening of a protostellar outflow widens and the protostars possibly generate more energetic outflows.
We present a pilot HI survey of 17 Planck Galactic Cold Clumps (PGCCs) with the Five-hundred-meter Aperture Spherical radio Telescope (FAST). HI Narrow Self-Absorption (HINSA) is an effective method to detect cold HI being mixed with molecular hydrogen H$_2$ and improves our understanding of the atomic to molecular transition in the interstellar medium. HINSA was found in 58% PGCCs that we observed. The column density of HINSA was found to have an intermediate correlation with that of $^{13}$CO, following $rm log( N(HINSA)) = (0.52pm 0.26) log(N_{^{13}CO}) + (10 pm 4.1) $. HI abundance relative to total hydrogen [HI]/[H] has an average value of $4.4times 10^{-3}$, which is about 2.8 times of the average value of previous HINSA surveys toward molecular clouds. For clouds with total column density N$rm_H >5 times 10^{20}$ cm$^{-2}$, an inverse correlation between HINSA abundance and total hydrogen column density is found, confirming the depletion of cold HI gas during molecular gas formation in more massive clouds. Nonthermal line width of $^{13}$CO is about 0-0.5 km s$^{-1}$ larger than that of HINSA. One possible explanation of narrower nonthermal width of HINSA is that HINSA region is smaller than that of $^{13}$CO. Based on an analytic model of H$_2$ formation and H$_2$ dissociation by cosmic ray, we found the cloud ages to be within 10$^{6.7}$-10$^{7.0}$ yr for five sources.
We present the Planck Catalogue of Galactic Cold Clumps (PGCC), an all-sky catalogue of Galactic cold clump candidates detected by Planck. This catalogue is the full version of the Early Cold Core (ECC) catalogue, which was made available in 2011 with the Early Release Compact Source Catalogue (ERCSC) and contained 915 high S/N sources. It is based on the Planck 48 months mission data that are currently being released to the astronomical community. The PGCC catalogue is an observational catalogue consisting exclusively of Galactic cold sources. The three highest Planck bands (857, 545, 353 GHz) have been combined with IRAS data at 3 THz to perform a multi-frequency detection of sources colder than their local environment. After rejection of possible extragalactic contaminants, the PGCC catalogue contains 13188 Galactic sources spread across the whole sky, i.e., from the Galactic plane to high latitudes, following the spatial distribution of the main molecular cloud complexes. The median temperature of PGCC sources lies between 13 and 14.5 K, depending on the quality of the flux density measurements, with a temperature ranging from 5.8 to 20 K after removing sources with the 1% largest temperature estimates. Using seven independent methods, reliable distance estimates have been obtained for 5574 sources, which allows us to derive their physical properties such as their mass, physical size, mean density and luminosity. The PGCC sources are located mainly in the solar neighbourhood, up to a distance of 10.5 kpc towards the Galactic centre, and range from low-mass cores to large molecular clouds. Because of this diversity and because the PGCC catalogue contains sources in very different environments, the catalogue is useful to investigate the evolution from molecular clouds to cores. Finally, the catalogue also includes 54 additional sources located in the SMC and LMC.
In order to understand the initial conditions and early evolution of star formation in a wide range of Galactic environments, we carried out an investigation of 64 textit{Planck} Galactic Cold Clumps (PGCCs) in the second quadrant of the Milky Way. Using the $^{13}$CO and C$^{18}$O $J = 1 - 0$ lines, and 850,$mu$m continuum observations, we investigated cloud fragmentation and evolution associated with star formation. We extracted 468 clumps and 117 cores from the $^{13}$CO line and 850,$mu$m continuum maps, respectively. We make use of the Bayesian Distance Calculator and derived the distances of all 64 PGCCs. We found that in general, the mass-size plane follows a relation of $msim r^{1.67}$. At a given scale, the masses of our objects are around 1/10 of that of typical Galactic massive star-forming regions. Analysis of the clump and core masses, virial parameters, densities, and mass-size relation suggests that the PGCCs in our sample have a low core formation efficiency ($sim$3.0%), and most PGCCs are likely low-mass star-forming candidates. Statistical study indicates that the 850,$mu$m cores are more turbulent, more optically thick, and denser than the $^{13}$CO clumps for star formation candidates, suggesting that the 850,$mu$m cores are likely more appropriate future star-formation candidates than the $^{13}$CO clumps.
(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.
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