# ATLASGAL-selected high-mass clumps in the inner Galaxy. VII. Characterisation of mid-J CO emission

## TL;DR

This study characterizes mid-J CO emission in 99 high-mass clumps from the ATLASGAL survey, revealing correlations with clump properties and differences in emission regions related to the clumps' evolutionary stages.

## Contribution

It provides the first detailed analysis of mid-J CO emission in a large, representative sample of high-mass star-forming clumps, linking CO emission properties to physical characteristics.

## Key findings

- CO emission correlates with clump size, luminosity, and mass.
- Higher-J CO lines originate from different regions than lower-J lines.
- High-mass clumps show systematically higher CO luminosities than lower-mass counterparts.

## Abstract

High-mass stars are formed within massive molecular clumps, where a large number of stars form close together. The evolution of the clumps with different masses and luminosities is mainly regulated by its high-mass stellar content and the formation of such objects is still not well understood. In this work, we characterise the mid-J CO emission in a statistical sample of 99 clumps (Top100) selected from the ATLASGAL survey that are representative of the Galactic proto-cluster population. High-spatial resolution APEX-CHAMP+ maps of the CO(6-5) and CO(7-6) transitions were obtained and combined with additional single-pointing APEX-FLASH+ spectra of the CO(4-3) line. We study the correlations of the CO line luminosities and profiles for the three CO transitions with the clump properties and investigate if and how they change as a function of the evolution. All sources were detected above 3-$\sigma$ in all three CO transitions and most of the sources exhibit broad CO emission likely associated with molecular outflows. We found that the extension of the mid-J CO emission is correlated with the size of the dust emission traced by the Herschel-PACS 70 $\mu$m maps. The CO line luminosity is correlated with the luminosity and mass of the clumps. However, it does not correlate with the L/M ratio. The dependency of the CO luminosity with the properties of the clumps is steeper for higher-J transitions. Our data seem to exclude that this trend is biased by self-absorption features in the CO emission, but rather suggest that different J transitions arise from different regions of the inner envelope. Moreover, high-mass clumps show similar trends in CO luminosity as lower mass clumps, but are systematically offset towards larger values, suggesting that higher column density and/or temperature (of unresolved) CO emitters are found inside high-mass clumps.