# High-mass Starless Clumps in the inner Galactic Plane: the Sample and Dust Properties

## TL;DR

This study identifies and characterizes 463 high-mass starless clump candidates in the inner Galactic Plane, revealing their properties and potential to evolve into high-mass star-forming regions, thus advancing understanding of early high-mass star formation stages.

## Contribution

It presents a large, carefully selected sample of high-mass starless clumps with detailed dust property analysis, highlighting their early evolutionary stage and potential as high-mass star progenitors.

## Key findings

- Most HMSCs are infrared dark and associated with large-scale filaments.
- Over 90% of HMSCs exceed density thresholds for high-mass star formation.
- Some HMSCs are potential high-mass starless cores with specific size and density criteria.

## Abstract

We report a sample of 463 high-mass starless clump (HMSC) candidates within $-60\deg<l<60\deg$ and $-1\deg<b<1\deg$. This sample has been singled out from 10861 ATLASGAL clumps. All of these sources are not associated with any known star-forming activities collected in SIMBAD and young stellar objects identified using color-based criteria. We also make sure that the HMSC candidates have neither point sources at 24 and 70 \micron~nor strong extended emission at 24 $\mu$m. Most of the identified HMSCs are infrared ($\le24$ $\mu$m) dark and some are even dark at 70 $\mu$m. Their distribution shows crowding in Galactic spiral arms and toward the Galactic center and some well-known star-forming complexes. Many HMSCs are associated with large-scale filaments. Some basic parameters were attained from column density and dust temperature maps constructed via fitting far-infrared and submillimeter continuum data to modified blackbodies. The HMSC candidates have sizes, masses, and densities similar to clumps associated with Class II methanol masers and HII regions, suggesting they will evolve into star-forming clumps. More than 90% of the HMSC candidates have densities above some proposed thresholds for forming high-mass stars. With dust temperatures and luminosity-to-mass ratios significantly lower than that for star-forming sources, the HMSC candidates are externally heated and genuinely at very early stages of high-mass star formation. Twenty sources with equivalent radius $r_\mathrm{eq}<0.15$ pc and mass surface density $\Sigma>0.08$ g cm$^{-2}$ could be possible high-mass starless cores. Further investigations toward these HMSCs would undoubtedly shed light on comprehensively understanding the birth of high-mass stars.