Spatially associated clump populations in Rosette from CO and dust maps

Abstract

Spatial association of clumps from different tracers turns out to be a valuable tool to determine the physical properties of molecular clouds. It provides a reliable estimate for the X-factors, serves to trace the density of clumps seen in column densities only and allows to measure the velocity dispersion of clumps identified in dust emission. We study the spatial association between clump populations, extracted by use of the Gaussclumps technique from 12 CO (1 − 0), 13 CO (1 − 0) line maps and Herschel dust-emission maps of the star-forming region Rosette, and analyse their physical properties. All CO clumps that overlap with another CO or dust counterpart are found to be gravitationally bound and located in the massive star-forming filaments of the molecular cloud. They obey a single mass-size relation M cl ∝ R γ cl with γ ≃ 3 (implying constant mean density) and display virtually no velocity-size relation. We interpret their population as low-density structures formed through compression by converging flows and still not evolved under the influence of self-gravity. The high-mass parts of their clump mass functions are fitted by a power law dN cl /d log M cl ∝ M Γ cl and display a nearly Salpeter slope Γ ∼ −1.3. On the other hand, clumps extracted from the dust-emission map exhibit a shallower mass-size relation with γ = 2.5 and mass functions with very steep slopes Γ ∼ −2.3 even if associated with CO clumps. They trace density peaks of the associated CO clumps at scales of a few tenths of pc where no single density scaling law should be expected.

Fragmentation and kinematics in high-mass star formation

“…It is interesting to note that also in the recent comparison between the extreme environments of the nuclear starburst of the extragalactic system NGC253 and the central molecular zone of our Milky Way mass-size relations consistent with M ∝ r 3 were found (Krieger et al 2020). Ballesteros-Paredes et al (2012 discuss in detail the notion that mass-size relations with power-law indices from below 2 up to 3 have been reported in the literature (e.g., Mookerjea et al 2004;Lada et al 2008;Román-Zúñiga et al 2010;Kainulainen et al 2011;Könyves et al 2015;Zhang & Li 2017;Veltchev et al 2018). They reiterate that mass-size relations derived from constant column density thresholds (which is approximately the case for the 5σ intensity thresholds used here in the core finding algorithm), if the filling factor of the densest portions of the cores is small, should necessarily exhibit constant mean column densities, and thus, a M ∝ r 2.0 relationship.…”

What is the physics behind the Larson mass–size relation?

“…(ii) When multi-threshold methods are used, but still the reported mass-size relation is that of the cores without inner substructure, there is not necessarily a single slope, as it may be the case of the algorithms getsources, gaussclumps, or the leaves in dendrograms (e.g., Könyves et al 2015;Kirk et al 2017;Veltchev et al 2018;Sanhueza et al 2019).…”

Fragmentation and kinematics in high-mass star formation: CORE-extension targeting two very young high-mass star-forming regions

“…Ballesteros-Paredes et al (2012,2019,2020) discuss in detail the notion that mass-size relations with power-law indices from below 2 up to 3 have been reported in the literature (e.g., Mookerjea et al 2004;Lada et al 2008;Román-Zúñiga et al 2010;Kainulainen et al 2011;Könyves et al 2015;Zhang & Li 2017;Veltchev et al 2018). They reiterate that mass-size relations derived from constant column density thresholds (which is approximately the case for the 5σ intensity thresholds used here in the core finding algorithm), if the filling factor of the densest portions of the cores is small, should necessarily exhibit constant mean column densities, and thus, a M ∝ r 2.0 relationship.…”