The Earliest Phases of Star Formation (EPoS): A Herschel Key Program - The precursors to high-mass stars and clusters

TL;DR

This study characterizes cold cores in high-mass star-forming regions using Herschel data, revealing their properties, evolutionary stages, and potential starless candidates, advancing understanding of early star formation phases.

Contribution

It provides a comprehensive analysis of 496 cores in IRDCs, including their temperature, mass, luminosity, and evolutionary indicators, with new insights into the cold, early stages of high-mass star formation.

Findings

Cores have median temperature of 20K and span wide mass and luminosity ranges.

Cores with 24 micron counterparts are warmer and more evolved.

Approximately 10% of cloud mass is in core populations, with many cold starless candidates.

Abstract

(Abridged) We present an overview of the sample of high-mass star and cluster forming regions observed as part of the Earliest Phases of Star Formation (EPoS) Herschel Guaranteed Time Key Program. A sample of 45 infrared-dark clouds (IRDCs) were mapped at PACS 70, 100, and 160 micron and SPIRE 250, 350, and 500 micron. In this paper, we characterize a population of cores which appear in the PACS bands and place them into context with their host cloud and investigate their evolutionary stage. We construct spectral energy distributions (SEDs) of 496 cores which appear in all PACS bands, 34% of which lack counterparts at 24 micron. From single-temperature modified blackbody fits of the SEDs, we derive the temperature, luminosity, and mass of each core. These properties predominantly reflect the conditions in the cold, outer regions. Taking into account optical depth effects and performing simple radiative transfer models, we explore the origin of emission at PACS wavelengths. The core population has a median temperature of 20K and has masses and luminosities that span four to five orders of magnitude. Cores with a counterpart at 24 micron are warmer and bluer on average than cores without a 24 micron counterpart. We conclude that cores bright at 24 micron are on average more advanced in their evolution, where a central protostar(s) have heated the outer bulk of the core, than 24 micron-dark cores. The 24 micron emission itself can arise in instances where our line of sight aligns with an exposed part of the warm inner core. About 10% of the total cloud mass is found in a given cloud's core population. We uncover over 300 further candidate cores which are dark until 100 micron. These are candidate starless objects, and further observations will help us determine the nature of these very cold cores.