Galactic cold cores

Abstract

Context. The Galactic Cold Cores (GCC) project has made Herschel photometric observations of interstellar clouds where Planck detected compact sources of cold dust emission. The fields are in different environments and stages of star formation. Aims. Our aim is to characterise the structure of the clumps and their parent clouds, and to study the connections between the environment and the formation of gravitationally bound objects. We also examine the accuracy to which the structure of dense clumps can be determined from sub-millimetre data. Methods. We use standard statistical methods to characterise the GCC fields. Individual clumps are extracted using column density thresholding. Based on sub-millimetre measurements, we construct a three-dimensional radiative transfer (RT) model for each field. These are used to estimate the relative radiation field intensities, to probe the clump stability, and to examine the uncertainty of column density estimates. We examine the structural parameters of the clumps, including their radial column density profiles. Results. In the GCC fields, the structure noise follows the relations previously established at larger scales and in lower-density clouds. The fractal dimension has no significant dependence on column density and the values DP = 1.25 ± 0.07 are only slightly lower than in typical molecular clouds. The column density probability density functions (PDFs) exhibit large variations, for example, in the case of externally compressed clouds. At scales r > 0.1 pc, the radial column density distributions of the clouds follow an average relation of N ~ r−1. In spite of a great variety of clump morphologies (and a typical aspect ratio of 1.5), clumps tend to follow a similar N ~ r−1 relation below r ~ 0.1 pc. RT calculations indicate only factor 2.5 variation in the local radiation field intensity. The fraction of gravitationally bound clumps increases significantly in regions with AV > 5 mag but most bound objects appear to be pressure-confined. Conclusions. The host clouds of the cold clumps in the GCC sample have statistical properties similar to general molecular clouds. The gravitational stability, peak column density, and clump orientation are connected to the cloud background while most other statistical clump properties (e.g. DP and radial profiles) are insensitive to the environment. The study of clump morphology should be continued with a comparison with numerical simulations.

H II regions and high-mass starless clump candidates

“…17 (a) and (b), respectively. The median value of p N H 2 is −0.17, which is much larger than the value of −0.85 in Juvela et al (2018). There are several reasons for this difference.…”

“…The corresponding radial N H 2 profiles are N H 2 ∝ r and N H 2 ∝ r −1 , respectively. Owing to the limited resolution, a flat central region and truncated radius are usually set when fitting the N H 2 profile to the observational data (Juvela et al 2018;Tang et al 2018). The Galactic cold cores N H 2 structures investigated with Herschel data indicate that radial N H 2 distribution follows a power law of N H 2 ∝ r −1 in spite of the broad variety of clump morphology, which suggests the universality of the r −1 profile for cold cores with gravitational contraction (Juvela et al 2018;Li 2018).…”

Molecular Cloud Cores with a High Deuterium Fraction: Nobeyama Single-pointing Survey

“…Most recently, the Planck all-sky survey has been made and provides a catalog of Planck Galactic Cold Clumps (PGCC, hereafter) (Planck Collaboration et al 2011, which includes 13,188 sources of ∼5-10 arcmin-sized structures "clumps" with temperatures of 10-20 K in various environments. An unbiased selection of PGCCs was mapped with Herschel in far-IR band (e.g., Juvela et al 2010Juvela et al , 2012Juvela et al , 2018. A series of follow-up observations have been conducted with ground-based radio telescopes such as PMO, CSO, SMT, APEX, NANTEN2, IRAM, Mopra, Effelsberg, SMA, JCMT, and TRAO, and are summarized by Liu et al (2015Liu et al ( , 2018.…”

SOC program for dust continuum radiative transfer

“…SOC is a Monte Carlo radiative transfer program for the calculation of dust emission and scattering. It has been used in some publications (Gordon et al 2017;Juvela et al 2018b,a) but we describe here in more detail some of the implementation details.…”