The Earliest Phases of Star Formation (EPoS): aHerschelkey program

Abstract

Context. Stars are born deeply embedded in molecular clouds. In the earliest embedded phases, protostars emit the bulk of their radiation in the far-infrared wavelength range, where Herschel is perfectly suited to probe at high angular resolution and dynamic range. In the high-mass regime, the birthplaces of protostars are thought to be in the high-density structures known as infrareddark clouds (IRDCs). While massive IRDCs are believed to have the right conditions to give rise to massive stars and clusters, the evolutionary sequence of this process is not well-characterized. Aims. As part of the Earliest Phases of Star formation (EPoS) Herschel guaranteed time key program, we isolate the embedded structures within IRDCs and other cold, massive molecular clouds. We present the full sample of 45 high-mass regions which were mapped at PACS 70, 100, and 160 μm and SPIRE 250, 350, and 500 μm. In the present paper, we characterize a population of cores which appear in the PACS bands and place them into context with their host molecular cloud and investigate their evolutionary stage. Methods. We construct spectral energy distributions (SEDs) of 496 cores which appear in all PACS bands, 34% of which lack counterparts at 24 μm. 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. Results. The core population has a median temperature of 20 K and has masses and luminosities that span four to five orders of magnitude. Cores with a counterpart at 24 μm are warmer and bluer on average than cores without a 24 μm counterpart. We conclude that cores bright at 24 μm are on average more advanced in their evolution, where a central protostar(s) have heated the outer bulk of the core, than 24 μm-dark cores. The 24 μm 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 μm. These are possibly starless objects, and further observations will help us determine the nature of these very cold cores.

Accretion and magnetic field morphology around Class 0 stage protostellar discs

“…The temperature of the low-mass cores is set to 15 K, and that of the high-mass cores to a somewhat higher value of 20 K (see e.g. Ragan et al 2012;Launhardt et al 2013). The cores are embedded in an ambient low-density medium in pressure equilibrium with the edge of the cores.…”

The prevalence of star formation as a function of Galactocentric radius

“…Ragan et al 2012;Traficante et al 2015). Molinari et al (2016) indicate that the 70 µm Hi-GAL catalogue is complete to ∼95% above 0.5 Jy, which we adopt as the threshold for a source to qualify as 70 µm -bright.…”

Mining the VVV: star formation and embedded clusters

“…Cluster candidate 81 is 35 from cluster [MCM2005b] 88 but seems to be an individual compact cluster. Faint nebula 8 is included in a study of embedded structures within IRDCs and other cold, massive molecular clouds (Ragan et al 2012).…”