Molecular Cloud Cores with High Deuterium Fraction: Nobeyama Single-Pointing Survey

Abstract

We present the results of a single-pointing survey of 207 dense cores embedded in Planck Galactic Cold Clumps distributed in five different environments ($\lambda$ Orionis, Orion A, B, Galactic plane, and high latitudes) to identify dense cores on the verge of star formation for the study of the initial conditions of star formation. We observed these cores in eight molecular lines at 76-94 GHz using the Nobeyama 45-m telescope. We find that early-type molecules (e.g., CCS) have low detection rates and that late-type molecules (e.g., N${}_2$H${}^{+}$, c-C${}_3$H${}_2$) and deuterated molecules (e.g., N${}_2$D${}^{+}$, DNC) have high detection rates, suggesting that most of the cores are chemically evolved. The deuterium fraction (D/H) is found to decrease with increasing distance, indicating that it suffers from differential beam dilution between the D/H pair of lines for distant cores ($>$1 kpc). For $\lambda$ Orionis, Orion A, and B located at similar distances, D/H is not significantly different, suggesting that there is no systematic difference in the observed chemical properties among these three regions. We identify at least eight high D/H cores in the Orion region and two at high latitudes, which are most likely to be close to the onset of star formation. There is no clear evidence of the evolutionary change in turbulence during the starless phase, suggesting that the dissipation of turbulence is not a major mechanism for the beginning of star formation as judged from observations with a beam size of 0.04 pc.

55 pages, 12 Figures, 8 Tables, accepted for publication in ApJS

References in corpus (18)

• Theory of Star Formation
• Cold Dark Clouds: The Initial Conditions for Star Formation
• Observing the gas temperature drop in the high-density nucleus of L 1544
• Molecular Evolution and Star Formation: From Prestellar Cores to Protostellar Cores
• The Gould's Belt Distances Survey (GOBELINS) II. Distances and structure towards the Orion Molecular Clouds
• Fragmentation of Molecular Clumps and Formation of Protocluster
• Hipparcos distances of Ophiuchus and Lupus cloud complexes
• Depletion and low gas temperature in the L183 prestellar core : the N2H+ - N2D+ tool
• The N2D+/N2H+ ratio as an evolutionary tracer of Class 0 protostars
• Searching for massive pre--stellar cores through observations of N2H+ and N2D+
• Identification of Young Stellar Object candidates in the $Gaia$ DR2 x AllWISE catalogue with machine learning methods
• Chemical evolution in the early phases of massive star formation II: Deuteration
• Formation and Collapse of Quiescent Cloud Cores Induced by Dynamic Compressions
• SCOPE: SCUBA-2 Continuum Observations of Pre-protostellar Evolution - Survey Description and Compact Source Catalogue
• Molecular Line Observations of a Carbon-Chain-Rich Core L492
• Towards a census of the Galactic anticentre star clusters II: exploring lower overdensities
• ALMA Observations of the IRDC Clump G34.43+00.24 MM3: DNC/HNC Ratio
• ALMA ACA and Nobeyama observations of two Orion cores in deuterated molecular lines

Cited by in corpus (13)

• ALMA Survey of Orion Planck Galactic Cold Clumps (ALMASOP) II. Survey overview: a first look at 1.3 mm continuum maps and molecular outflows
• ALMA Survey of Orion Planck Galactic Cold Clumps (ALMASOP): A Hot Corino Survey toward Protostellar Cores in the Orion Cloud
• ALMA Survey of Orion Planck Galactic Cold Clumps (ALMASOP): Detection of extremely high density compact structure of prestellar cores and multiple substructures within
• Planck Cold Clumps in the lambda Orionis Complex. III. A chemical probe of stellar feedback on cores in the lambda Orionis cloud
• HD molecules at high redshift: cosmic-ray ionization rate in the diffuse interstellar medium
• The JCMT BISTRO Survey: Studying the Complex Magnetic Field of L43
• ALMA Survey of Orion Planck Galactic Cold Clumps (ALMASOP): How do dense core properties affect the multiplicity of protostars?
• Molecular Cloud Cores with High Deuterium Fractions: Nobeyama Mapping Survey
• Characterization of dense Planck clumps observed with Herschel and SCUBA-2
• Nobeyama Survey of Inward Motions toward Cores in Orion Identified by SCUBA-2
• ALMA Survey of Orion Planck Galactic Cold Clumps (ALMASOP): A forming quadruple system with continuum `ribbons' and intricate outflows
• DCO${}^{+}$ and DCN 1-0 survey toward a sample of Planck cold clumps
• HOPS-288: A Laboratory for Complex Organics in Proto-multiple Systems