Understanding the impact of massive star formation on its surroundings in Messier 8

Abstract

Massive stars inject an immense amount of energy into their surroundings, which affect the physics and chemistry of the interstellar medium (ISM). Massive stars play a significant role in the evolution of galaxies. The best laboratories to study the effects of massive stars on their surrounding medium are massive star-forming regions. The emission of the UV and FUV photons from massive stars give rise to hot ionised HII regions and warm photodissociation regions (PDRs), respectively. PDRs comprise the neutral atomic gas and most of the molecular gas in the galaxies, where FUV photons dominate the heating and regulate the chemistry. With the advent of high resolution observing facilities in the Far-Infrared (FIR) and (sub)millimeter (submm) wavelengths, we are now able to study PDRs in great detail. Cooling in PDRs occurs mainly through the fine structure lines of [CII] , [OI] and through rotational transitions of CO, which are observable at FIR and submm wavelengths. <br /> Interaction of FUV photons with different chemical species in the vicinity of massive stars results into a rich hydrocarbon chemistry and the formation processes of the observed small hydrocarbons (species like C₂H and c-C₃H₂, observable at submm wavelengths) in PDRs can be understood by comparing the observational data with the PDR modeling results. <br /> Messier 8 (M8) is one of the brightest massive star-forming regions known in our galaxy and it hosts high-UV flux PDRs and HII regions. We performed a detailed survey toward M8, using the world’s leading FIR and submm wavelength observing facilities, the Institut de Radioastronomie Millimétrique (IRAM) 30 m,the Atacama Pathfinder EXperiment (APEX) 12 m and the Stratospheric Observatory for Infrared Astronomy (SOFIA). We were able to quantify the physical conditions of the PDR of M8 and of the gas in the star-forming region of M8 east. From the kinetic information obtained from our data sets and from the ancillary data, we explored the morphology of the region around the bright ionising stellar system of M8. We found that gas phase chemistry is responsible for the observed hydrocarbon abundances in M8. Furthermore, a more embedded star formation is taking place in M8 E compared to M8.