The Deuterium Fraction in Massive Starless Cores and Dynamical Implications

Kong, Shuo; Tan, Jonathan C.; Caselli, P.; Fontani, F.; Pillai, T.; Butler, Michael J.; Shimajiri, Yoshito; Nakamura, Fúmitaka; Sakai, Takeshi

doi:10.3847/0004-637x/821/2/94

Cited by 57 publications

(65 citation statements)

References 42 publications

(62 reference statements)

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“…irdc Bergin & Tafalla 2007). As suggested in the literature, these chemical features (e.g., depletion, deuteration) may indicate evolutionary stages in IRDCs (Kong et al 2015(Kong et al , 2016.…”

Section: Introductionsupporting

confidence: 52%

A multiwavelength observation and investigation of six infrared dark clouds

Zhang

Yuan

et al. 2017

A&A

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Context. Infrared dark clouds (IRDCs) are ubiquitous in the Milky Way, yet they play a crucial role in breeding newly-formed stars. Aims. With the aim of further understanding the dynamics, chemistry, and evolution of IRDCs, we carried out multi-wavelength observations on a small sample. Methods. We performed new observations with the IRAM 30 m and CSO 10.4 m telescopes, with tracers HCO + , HCN, N 2 H + , C 18 O, DCO + , SiO, and DCN toward six IRDCs G031.97+00.07, G033.69-00.01, G034.43+00.24, G035.39-00.33, G038.95-00.47, and G053.11+00.05. Results. We investigated 44 cores including 37 cores reported in previous work and seven newly-identified cores. Toward the dense cores, we detected 6 DCO + , and 5 DCN lines. Using pixel-by-pixel spectral energy distribution (SED) fits of the Herschel 70 to 500 µm, we obtained dust temperature and column density distributions of the IRDCs. We found that N 2 H + emission has a strong correlation with the dust temperature and column density distributions, while C 18 O showed the weakest correlation. It is suggested that N 2 H + is indeed a good tracer in very dense conditions, but C 18 O is an unreliable one, as it has a relatively low critical density and is vulnerable to freezing-out onto the surface of cold dust grains. The dynamics within IRDCs are active, with infall, outflow, and collapse; the spectra are abundant especially in deuterium species. Conclusions. We observe many blueshifted and redshifted profiles, respectively, with HCO + and C 18 O toward the same core. This case can be well explained by model "envelope expansion with core collapse (EECC)".

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Section: Introductionsupporting

confidence: 52%

A multiwavelength observation and investigation of six infrared dark clouds

Zhang

Yuan

et al. 2017

A&A

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“…b Originally 15 ′′ but convolved to 20 ′′ . Kong et al (2016) detected N 2 H + J = 4 → 3 emission toward the C1 clump and found that the N 2 H + peak emission occurs to the west of the C1-S and C1-N cores. They interpret this emission as coming from a volume of hotter gas along the periphery of the clump and consider both gas accretion and turbulent dissipation as possible heating sources.…”

Section: Low-j Comentioning

confidence: 99%

Mid-J Co Shock Tracing Observations of Infrared Dark Clouds. Iii. Sled Fitting

Pon

Kaufman

Johnstone

et al. 2016

ApJ

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Giant molecular clouds contain supersonic turbulence that can locally heat small fractions of gas to over 100 K. We run shock models for low-velocity, C-type shocks propagating into gas with densities between 10 3 and 10 5 cm −3 and find that CO lines are the most important cooling lines. Comparison to photodissociation region (PDR) models indicates that mid-J CO lines (J = 8 → 7 and higher) should be dominated by emission from shocked gas. In Papers I and II we presented CO J = 3 → 2, 8 → 7, and 9 → 8 observations toward four primarily quiescent clumps within infrared dark clouds. Here we fit PDR models to the combined spectral line energy distributions and show that the PDR models that best fit the low-J CO emission underpredict the mid-J CO emission by orders of magnitude, strongly hinting at a hot gas component within these clumps. The low-J CO data clearly show that the integrated intensities of both the CO J = 8 → 7 and 9 → 8 lines are anomalously high, such that the line ratio can be used to characterize the hot gas component. Shock models are reasonably consistent with the observed mid-J CO emission, with models with densities near 10 4.5 cm −3 providing the best agreement. Where this mid-J CO is detected, the mean volume filling factor of the hot gas is 0.1%. Much of the observed mid-J CO emission, however, is also associated with known protostars and may be due to protostellar feedback.

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“…The latter are characterized by large amounts of molecular freeze-out (e.g., Chen et al 2011;Hernandez et al 2011;Giannetti et al 2014), which favor a high level of deuteration Fontani et al 2011). Several studies reported a [D/H] ratio well above the expected cosmic value of ∼10 −5 , with values ranging from 0.001 to 0.1 (Chen et al 2011;Fontani et al 2011;Barnes et al 2016;Kong et al 2016).…”

Section: Introductionmentioning

confidence: 99%

H₂ Ortho-to-para Conversion on Grains: A Route to Fast Deuterium Fractionation in Dense Cloud Cores?

Bovino

Schleicher

Caselli

2017

ApJL

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Deuterium fractionation, i.e., the enhancement of deuterated species with respect to non-deuterated ones, is considered to be a reliable chemical clock of star-forming regions. This process is strongly affected by the ortho-topara H 2 ratio. In this Letter we explore the effect of the ortho-para (o-p) H 2 conversion on grains on the deuteration timescale in fully-depleted dense cores, including the most relevant uncertainties that affect this complex process. We show that (i) the o-p H 2 conversion on grains is not strongly influenced by the uncertainties on the conversion time and the sticking coefficient, and (ii) that the process is controlled by the temperature and the residence time of ortho-H 2 on the surface, i.e., by the binding energy. We find that for binding energies between 330 and 550 K, depending on the temperature, the o-p H 2 conversion on grains can shorten the deuterium fractionation timescale by orders of magnitude, opening a new route for explaining the large observed deuteration fraction D frac in dense molecular cloud cores. Our results suggest that the star formation timescale, when estimated through the timescale to reach the observed deuteration fractions, might be shorter than previously proposed. However, more accurate measurements of the binding energy are needed in order to better assess the overall role of this process.

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The Deuterium Fraction in Massive Starless Cores and Dynamical Implications

Cited by 57 publications

References 42 publications

A multiwavelength observation and investigation of six infrared dark clouds

A multiwavelength observation and investigation of six infrared dark clouds

Mid-J Co Shock Tracing Observations of Infrared Dark Clouds. Iii. Sled Fitting

H₂ Ortho-to-para Conversion on Grains: A Route to Fast Deuterium Fractionation in Dense Cloud Cores?

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The Deuterium Fraction in Massive Starless Cores and Dynamical Implications

Cited by 57 publications

References 42 publications

A multiwavelength observation and investigation of six infrared dark clouds

A multiwavelength observation and investigation of six infrared dark clouds

Mid-J Co Shock Tracing Observations of Infrared Dark Clouds. Iii. Sled Fitting

H2 Ortho-to-para Conversion on Grains: A Route to Fast Deuterium Fractionation in Dense Cloud Cores?

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H₂ Ortho-to-para Conversion on Grains: A Route to Fast Deuterium Fractionation in Dense Cloud Cores?