Determining the relative evolutionary stages of very young massive star formation regions

TL;DR

This study uses ammonia emission data to estimate temperatures and assess the evolutionary stages of massive star formation cores, proposing temperature as an indicator of core age.

Contribution

It introduces the use of NH3-derived temperature measurements combined with kinematic data to determine the relative evolutionary stages of massive star formation cores.

Findings

Cores exhibit temperatures from ~10 K to >200 K.

Temperature and kinematics can indicate core evolutionary stages.

Most cores fit single-temperature models.

Abstract

We have recently completed an observing program with the Australia Telescope Compact Array towards massive star formation regions traced by 6.7 GHz methanol maser emission. We found the molecular cores could be separated into groups based on their association with/without methanol maser and 24 GHz continuum emission. Analysis of the molecular and ionised gas properties suggested the cores within the groups may be at different evolutionary stages. In this contribution we derive the column densities and temperatures of the cores from the NH3 emission and investigate if this can be used as an indicator of the relative evolutionary stages of cores in the sample. The majority of cores are well fit using single-temperature large velocity gradient models, and exhibit a range of temperatures from ~10 K to >200 K. Under the simple but reasonable assumption that molecular gas in the cores will heat up and become less quiescent with age due to feedback from the powering source(s), the molecular gas kinetic temperature combined with information of the core kinematics seems a promising probe of relative core age in the earliest evolutionary stages of massive star formation.