The ALMA Survey of 70 \mu m Dark High-mass Clumps in Early Stages (ASHES). XIII. Core Mass Function, Lifetime, and Growth of Prestellar Cores

TL;DR

This study analyzes the core mass function in early high-mass star formation stages, revealing a universal core formation process and the influence of external gas infall on core growth.

Contribution

It provides the first detailed CMF analysis in early high-mass star-forming regions, highlighting the similarity to low-mass regions and the role of external infall in core evolution.

Findings

Prestellar cores tend to have lower masses than protostellar cores.

Prestellar core lifetime exceeds freefall time but approaches it with increasing mass.

Prestellar CMF slope is consistent with the Salpeter IMF slope.

Abstract

The core mass function (CMF) of prestellar cores is essential for understanding the initial conditions of star and cluster formation. However, the universality of the CMF and its relationship to the initial mass function (IMF) remain unclear. We study the CMF in the earliest stage of high-mass star formation using 461 prestellar core candidates and 254 protostellar cores as a part of the ALMA Survey of 70 \mu m Dark High-mass Clumps in Early Stages (ASHES). We find that prestellar core candidates tend to have lower masses than protostellar cores. We also find that the lifetime of prestellar cores is several times longer than the freefall time, although it approaches the freefall time as the core mass increases. The CMF, including both protostellar and prestellar cores, has a power-law slope of $-2.05\pm0.04$, shallower than Salpeter's IMF slope of -2.35. Conversely, the CMF of gravitationally bound, prestellar cores has a steeper slope ($-2.32\pm0.30$), indistinguishable from Salpeter's slope. This finding is consistent with observations in both low-mass star-forming regions and high-mass protoclusters, implying a universal core formation mechanism. The protostellar CMF with a larger maximum core mass can be reproduced by the prestellar CMF when an external gas infall is considered. The inferred mass infall rate is higher than the Bondi-Hoyle-Lyttleton accretion rate and follows a shallower mass dependence (smaller power-law index), more consistent with the tidal-lobe accretion. This may contribute to the evolution of CMFs seen in later stages.