The ALMA Survey of 70 $\mu$m Dark High-mass Clumps in Early Stages (ASHES). IX. Physical Properties and Spatial Distribution of Cores in IRDCs

TL;DR

This study uses ALMA observations to analyze the physical properties and spatial distribution of cores in IRDCs, revealing that high-mass cores are rare, lack preferred locations, and are correlated with clump density, providing insights into early high-mass star formation.

Contribution

First high-resolution survey of IRDC cores showing detailed core mass distribution and spatial arrangement, highlighting the scarcity of high-mass prestellar cores and their relation to clump density.

Findings

Most cores are low-mass, with few high-mass cores.

High-mass cores lack sufficient mass to form high-mass stars alone.

Core mass correlates with clump surface density.

Abstract

The initial conditions found in infrared dark clouds (IRDCs) provide insights on how high-mass stars and stellar clusters form. We have conducted high-angular resolution and high-sensitivity observations toward thirty-nine massive IRDC clumps, which have been mosaicked using the 12m and 7m arrays from the Atacama Large Millimeter/submillimeter Array (ALMA). The targets are 70 $\mu$m dark massive (220-4900 $M_\odot$), dense ($>$10$^4$ cm$^{-3}$), and cold ($\sim$10-20K) clumps located at distances between 2 and 6 kpc. We identify an unprecedented number of 839 cores, with masses between 0.05 and 81 $M_\odot$ using 1.3 mm dust continuum emission. About 55% of the cores are low-mass ($<$1 $M_\odot$), whereas $\lesssim$1% (7/839) are high-mass ($\gtrsim$27 $M_\odot$). We detect no high-mass prestellar cores. The most massive cores (MMC) identified within individual clumps lack sufficient mass to form high-mass stars without additional mass feeding. We find that the mass of the MMCs is correlated with the clump surface density, implying denser clumps produce more massive cores and a larger number of cores. There is no significant mass segregation except for a few tentative detections. In contrast, most clumps show segregation once the clump density is considered instead of mass. Although the dust continuum emission resolves clumps in a network of filaments, some of which consist of hub-filament systems, the majority of the MMCs are not found in the hubs. Our analysis shows that high-mass cores and MMCs have no preferred location with respect to low-mass cores at the earliest stages of high-mass star formation.