The TOP-SCOPE Survey of Planck Galactic Cold Clumps: Survey Overview and Results of an Exemplar Source, PGCC G26.53+0.17

Abstract

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 μm continuum emission. 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,
length, and mean line mass (M/L) of the G26 filament are ∼6200 M☉, ∼12 pc, and ∼500 M☉pc−1, respectively. Ten
massive clumps, including eight starless ones, are found along the filament. The most massive clump as a whole may
still be in global collapse, while its denser part seems to be undergoing expansion owing to outflow feedback. The
fragmentation in the G26 filament from cloud scale to clump scale is in agreement with gravitational fragmentation of
an isothermal, nonmagnetized, and turbulent supported cylinder. A bimodal behavior in dust emissivity spectral index
(β) distribution is found in G26, suggesting grain growth along the filament. The G26 filament may be formed owing
to large-scale compression flows evidenced by the temperature and velocity gradients across its natal cloud.
Key words: ISM: abundances – ISM: clouds – ISM: kinematics and dynamics – stars: formation – surveys