Studying the effects and cause of the massive star formation in Messier 8 East

Abstract

Messier 8 (M8), one of the brightest HII regions in our Galaxy, is associated with two prominent massive star-forming regions: M8-Main, the particularly bright part of the large scale HII region (mainly) ionised by the stellar system Herschel 36 (Her 36) and M8 East (M8 E), which is mainly powered by a deeply embedded young stellar object (YSO), a bright infrared (IR) source, M8E-IR. We aim to study the interaction of the massive star-forming region M8 E with its surroundings and to compare the star-forming environments of M8-Main and M8 E. We used the IRAM 30 m telescope to perform an imaging spectroscopy survey of the molecular environment of M8E-IR. We imaged and analysed data for the $J$ = 1 $\to$ 0 rotational transitions of ${}^{12}$CO, ${}^{13}$CO, N${}_2$H${}^{+}$, HCN, H${}^{13}$CN, HCO${}^{+}$, H${}^{13}$CO${}^{+}$, HNC and HN${}^{13}$C observed for the first time toward M8~E. We used LTE and non-LTE techniques to determine column densities of the observed species and to constrain the physical conditions of the gas responsible for their emission. Examining the YSO population in M8~E allows us to explore the observed ionization front (IF) as seen in GLIMPSE 8~$\mu$m emission image. We find that ${}^{12}$CO probes the warm diffuse gas also traced by the GLIMPSE 8~$\mu$m emission, while N${}_2$H${}^{+}$ and HN${}^{13}$C trace the cool and dense gas. We find that the star-formation in M8~E appears to be triggered by the earlier formed stellar cluster NGC~6530, which powers an HII region giving rise to an IF that is moving at a speed $\ge$ 0.26~km~s${}^{-1}$ across M8~E. We derive temperatures of 80 K and 30 K for the warm and cool gas components, respectively, and constrain H${}_2$ volume densities to be in the range of 10${}^4$--10${}^6$~cm${}^{-3}$. Comparison of the observed abundances of various species reflects the fact that M8~E is at an earlier stage of massive star formation than M8-Main.

References in corpus (16)

• MAMBO Mapping of Spitzer c2d Small Clouds and Cores
• The Critical Density and the Effective Excitation Density of Commonly Observed Molecular Dense Gas Tracers
• Early Science with SOFIA, the Stratospheric Observatory for Infrared Astronomy
• The anatomy of the Orion B Giant Molecular Cloud: A local template for studies of nearby galaxies
• Molecular Line Emission as a Tool for Galaxy Observations (LEGO). I. HCN as a tracer of moderate gas densities in molecular clouds and galaxies
• Electron Excitation of High Dipole Moment Molecules Reexamined
• LEGO II: A 3 mm molecular line study covering 100 pc of one of the most actively star-forming portions within the Milky Way Disc
• Molecular-Cloud-Scale Chemical Composition I: Mapping Spectral Line Survey toward W51 in the 3 mm Band
• The Gaia-ESO Survey: age spread in the star forming region NGC6530 from the HR diagram and gravity indicators
• A tale of two cores: Triggered massive star formation in the bright-rimmed cloud SFO 75
• Pre-main sequence stars in the Lagoon Nebula (M8)
• Small-scale physical and chemical structure of diffuse and translucent molecular clouds along the line of sight to Sgr B2
• A wide-area photometric and astrometric (Gaia DR2) study of the young cluster NGC 6530
• Observational study of hydrocarbons in the bright photodissociation region of Messier 8
• An imaging line survey of OMC-1 to OMC-3
• A study of the massive star forming region M8 using Spitzer IRAC images

Cited by in corpus (5)

• The evolution of the internal structure of massive star forming regions in the Milky Way as revealed by ALMA
• Turbulence in compact to giant H II regions
• The effects of stellar feedback on molecular clumps in the Lagoon Nebula (M8)
• SDSS-V LVM: A spatially resolved study of the physical conditions and the chemical abundance discrepancy in the Lagoon Nebula (M 8)
• Investigating star formation scenarios in the Milky Way using YSO distributions -- A pilot study