The TOP-SCOPE survey of Planck Galactic Cold Clumps: Survey overview and results of an exemplar source, PGCC G26.53+0.17

Tie Liu, Kee-Tae Kim, Mika Juvela, Ke Wang, Ken'ichi Tatematsu, James Di Francesco, Sheng-Yuan Liu, Yuefang Wu, Mark Thompson, Gary Fuller, David Eden, Di Li, I. Ristorcelli, TOP-SCOPE collaborations

Published 2017-11-13Version 1

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 fragmentation in G26 filament seems to be governed by turbulence-dominated cylindrical fragmentation. 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. Sub-filaments in G26 have different velocities and may interact with each other. The most massive clump 6 may still accrete gas along sub-filaments with a total accretion rate of 1*10E-3 Msun/yr. Clump 6 as a whole may be still in global collapse while its denser part traced by HCO+ J=1-0 and H2CO 2(1,2)-1(1,1) lines seems to be undergoing expansion due to outflow feedback. Clump 6 is more chemically evolved than other quiescent clumps in IRDCs and seems to be in a more chemically evolved phase.