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.

The Properties of Planck Galactic Cold Clumps in the L1495 Dark Cloud

“…Specifically, the data were all run with the same reduction tailored for compact sources, filtering out scales larger than 200″ on a 4″ pixel scale. A Flux Conversion Factor (FCF) of 554 Jy/pW/beam was used to convert data from pW to Jy/beam (Liu et al 2018). The FCF in this paper is higher than the canonical value derived by Dempsey et al (2013).…”

“…To understand better the properties of PGCCs, we have been conducting a series of follow-up surveys toward the PGCCs with several ground-based telescopes such as the PMO (Purple Mountain Observatory) 13.7 m, the TRAO (Taeduk Radio Astronomy Observatory) 14 m, the JCMT (James Clerk Maxwell Telescope) 15 m, and the NRO (Nobeyama Radio Observatory) 45 m telescopes (Liu et al , 2014Wu et al 2012;Meng et al 2013;Yuan et al 2016;Zhang et al 2016;Kim et al 2017;Juvela et al 2017;Tatematsu et al 2017). Using the SCUBA-2 submillimeter camera on the JCMT 15 m telescope, we have been carrying out a legacy survey toward 1000 PGCCs in the 850 μm continuum, namely "SCOPE: SCUBA-2 Continuum Observations of Pre-protostellar Evolution" (Liu et al 2018). Thousands of dense cores have been identified by the "SCOPE" survey, and most of them are either starless cores or protostellar cores with very young (Class 0/I) objects.…”

Multiscale dynamics in star-forming regions: the interplay between gravity and turbulence

“…Peretto et al 2013), with evidence that large-scale motions driven by selfgravity occur simultaneously and are coupled to the local motions, with a net increase of supersonic motions along the embedded clumps due to the longitudinal collapse of the whole cloud, like in SDC13 (Peretto et al 2014), or along the junctions of filaments, where dense clumps are forming, like in Monoceros OB1 (Montillaud et al 2019). The gravitational fragmentation along a filament may also be regulated by the turbulence that acts at all spatial scales, as suggested from the dynamics observed in G26 (Liu et al 2018). In contrast, a cloud such as G035 shows that the dynamics of the filaments and the embedded clumps are different and they may be considered as independent structures, with nonthermal motions that are only mildly supersonic (Henshaw et al 2014).…”

SCOPE: SCUBA-2 Continuum Observations of Pre-protostellar Evolution – survey description and compact source catalogue

“…The SCOPE selection of PGCCs was chosen randomly from the full PGCC sample to sample varying Galactic environments (Liu et al 2018a). Sources from the catalogue of PGCCs were excluded if they had already been observed at the JCMT with SCUBA-2 at an rms sensitivity of at least 6 mJy beam −1 .…”