The ALMA Survey of 70 μm Dark High-mass Clumps in Early Stages (ASHES). V. Deuterated Molecules in the 70 μm Dark IRDC G14.492-00.139

Abstract

We have observed the 70 μm dark infrared dark cloud (IRDC) G14.492-00.139 in the N2D+ J = 3–2, DCO+ J = 3–2, DCN J = 3–2, and C18O J = 2–1 lines, using the Atacama Large Millimeter/submillimeter Array (ALMA) as part of the ALMA Survey of 70 μm Dark High-mass Clumps in Early Stages. We find that the spatial distribution is different among the observed emission from the deuterated molecular lines. The N2D+ emission traces relatively quiescent regions, while both the DCO+ and DCN emission emanate mainly from regions with signs of active star formation. In addition, the DCO+/N2D+ ratio is found to be lower in several dense cores than in starless cores embedded in low-mass star-forming regions. By comparing the observational results with chemical-model calculations, we discuss the origin of the low DCO+/N2D+ ratio in this IRDC clump. The low DCO+/N2D+ ratio can be explained if the temperature of the dense cores is in the range between the sublimation temperatures of N2 (∼20 K) and CO (∼25 K). The results suggest that the dense cores in G14.492-00.139 are warmer and denser than the dense cores in low-mass star-forming regions.

ALMA Survey of Orion Planck Galactic Cold Clumps (ALMASOP): Evidence for a Molecular Jet Launched at an Unprecedented Early Phase of Protostellar Evolution

“…As starless cores evolve toward collapse, the molecular deuterium fraction in the gas phase (e.g., N 2 D + /N 2 H + ) increases and reaches a maximum at the onset of star formation (Crapsi et al 2005;Emprechtinger et al 2009;Tatematsu et al 2021). Once the protostar is formed inside the core, the deuterium fraction declines (Gerner et al 2015;Sakai et al 2022) as the star heats up the surrounding medium and dissociates deuterated species. As a consequence, the center of the observed N 2 D + peak could be shifted away from the protostar, whereas the dust continuum peak remains unaltered and represents the envelope emission around the central protostar.…”

The Core Population and Kinematics of a Massive Clump at Early Stages: An Atacama Large Millimeter/submillimeter Array View

“…Several bright peaks identified in dust thermal emission lack a counterpart in o-H 2 D + emission above the 3σ level. D + (1 1,0 − 1 1,1 ) 0 The Band 6 data of the continuum emission and of the N 2 D + (3-2) line at ν rest = 231321.8283 MHz 1 have been published by Sanhueza et al (2019) and Sakai et al (2022), respectively, and we refer to those papers for a complete description of the observations and of the data reduction. Briefly, the data were observed in Cycle 3 (Project ID: 2015.1.01539.S; PI: Sanhueza), with the 12, array, the 7m ar-1 According to the Cologne Database for Molecular Spectroscopy, CDMS, available at https://cdms.astro.uni-koeln.de/.…”

“…The Band 6 data of the continuum emission and of the N 2 D + (3-2) line at ν rest = 231321.8283 MHz 9 have been published by Sanhueza et al (2019) and Sakai et al (2022), respectively, and we refer to those papers for a complete description of the observations and of the data reduction. Briefly, the data were observed in Cycle 3 (Project ID: 2015.1.01539.S; PI: Sanhueza), with the 12, array, the 7 m array (baselines ranging from 8 to 330 m), and the Total Power (the latter for spectral lines only).…”

“…Throughout this work, we will refer to these cores as protostellar (or protostars). More recently, Sakai et al (2022) studied the emission of several deuterated molecules (N 2 D + , DCO + , and DCN) found in ALMA Band 6.…”

“…In this work, we present an extensive ALMA data set on AG14, from 90 up to 370 GHz in Section 2, consisting of Band 3 data covering the N 2 H + (1-0) line, Band 7 data of the o-H 2 D + (1 1,0 -1 1,1 ) line, and Band 6 data of the N 2 D + (3-2) transition (already published in Sakai et al 2022). These different lines are used to trace distinct parts of the clump.…”