Kaho Morii – Defining Initial Conditions of High-Mass Star Formation from the ASHES Project

Titre: Defining Initial Conditions of High-Mass Star Formation from the ASHES Project

Par : Kaho Morii (University of Tokyo/NAOJ)

Abstract: Physical properties in infrared dark clouds (IRDCs) provide insights into the initial conditions for the formation of high-mass stars and clusters. We have performed the ALMA Survey of 70 µm Dark High-mass Clumps in Early Stages (ASHES) on thirty-nine high-mass clumps, the dense parts of IRDCs. These targets are dark at 24 µm and 70 µm and have low temperatures, high masses, and high densities, making them the best candidates to study the earliest stages of high-mass star formation. Our ALMA observations reveal their internal structure and have identified an unprecedented number of 839 cores from dust continuum emission.  We find that less than 1% (7/839) of the cores have masses of more than 27 Msun. All of these cores are gravitationally bound and associated with molecular outflows. No high-mass prestellar cores were observed. Furthermore, 90% (35 out of 39) of our sample host only low- to intermediate-mass cores, implying that additional mass input is required for high-mass star formation. The observed core properties generally follow the thermal Jeans fragmentation of the clumps. In this talk, I will present the first results of the statistical study of the 839 cores, as well as a summary of the pilot survey, and discuss the properties of the early stages of high-mass star formation.