Probing the initial conditions of high-mass star formation -- IV. Gas dynamics and NH${}_2$D chemistry in high-mass precluster and protocluster clumps

Abstract

The initial stage of star formation is a complex area study because of its high density and low temperature. Under such conditions, many molecules become depleted from the gas phase by freezing out onto dust grains. However, the deuterated species could remain gaseous and are thus ideal tracers. We investigate the gas dynamics and NH${}_2$D chemistry in eight massive pre/protocluster clumps. We present NH${}_2$D 1${}_{11}$-1${}_{01}$ (at 85.926 GHz), NH${}_3$ (1, 1) and (2, 2) observations in the eight clumps using the PdBI and the VLA, respectively. We find that the distribution between deuterium fractionation and kinetic temperature shows a number density peak at around $T_{\mathrm{kin}}=16.1$ K, and the NH${}_2$D cores are mainly located at a temperature range of 13.0 to 22.0 K. We detect seven instances of extremely high deuterium fractionation of $1.0⩽D_{\mathrm{frac}}⩽1.41$. We find that the NH${}_2$D emission does not appear to coincide exactly with either dust continuum or NH${}_3$ peak positions, but often surrounds the star-formation active regions. This suggests that the NH${}_2$D has been destroyed by the central young stellar object (YSO) due to its heating. The detected NH${}_2$D lines are very narrow with a median width of $0.98\pm 0.02km/s$. The extracted NH${}_2$D cores are gravitationally bound (${\alpha }_{\mathrm{vir}}<1$), are likely prestellar or starless, and can potentially form intermediate-mass or high-mass stars. Using NH${}_3$ (1, 1) as a dynamical tracer, we find very complicated dynamical movement, which can be explained by a combined process with outflow, rotation, convergent flow, collision, large velocity gradient, and rotating toroids. High deuterium fractionation strongly depends on the temperature condition. NH${}_2$D is a poor evolutionary indicator of high-mass star formation in evolved stages, but a useful tracer in the starless and prestellar cores.

27 pages, 25 figures, 6 tables, accepted for publication in A&A

References in corpus (20)

• Trigonometric Parallaxes of Massive Star Forming Regions: VI. Galactic Structure, Fundamental Parameters and Non-Circular Motions
• Cold Dark Clouds: The Initial Conditions for Star Formation
• A Catalog of Extended Green Objects (EGOs) in the GLIMPSE Survey: A new sample of massive young stellar object outflow candidates
• The earliest phases of high-mass star formation: a 3 square degree millimeter continuum mapping of Cygnus X
• Resolution of the Distance Ambiguity for Galactic HII Regions
• The importance of the ortho:para H2 ratio for the deuteration of molecules during pre-protostellar collapse
• On the frequency of N2H+ and N2D+
• Trigonometric Parallaxes of Massive Star Forming Regions: V. G23.01-0.41 and G23.44-0.18
• Benchmarking spin-state chemistry in starless core models
• Low Temperature Surface Formation of NH3 and HNCO: hydrogenation of nitrogen atoms in CO-rich interstellar ice analogues
• Searching for massive pre--stellar cores through observations of N2H+ and N2D+
• High-mass Star Formation through Filamentary Collapse and Clump-fed Accretion in G22
• Probing the initial conditions of High Mass Star formation -- I. Deuteration and depletion in high mass pre/protocluster clumps
• Revealing H2D+ depletion and compact structure in starless and protostellar cores with ALMA
• Methanol Maser Associated Outflows: Detection statistics and properties
• L1188: a promising candidate of cloud-cloud collision triggering the formation of the low- and intermediate-mass stars
• Multi-wavelength study of the supernova remnant Kes 79 (G33.6+0.1): On its supernova properties and expansion into a molecular environment
• Deuterium enrichment of ammonia produced by surface N+H/D addition reactions at low temperature
• Molecular clumps and star formation associated with the infrared dust bubble N131
• Probing the initial conditions of high-mass star formation. III. Fragmentation and triggered star formation

Cited by in corpus (4)

• Identification of prestellar cores in high-mass star forming clumps via ${\mathrm{H}}_2{\mathrm{D}}^{+}$ observations with ALMA
• The role of magnetic fields in the formation of multiple massive stars
• Unraveling the inner substructure of new candidate hub-filament system in the HII region G25.4NW
• Spatial distribution of NH2D in massive star-forming regions