DCO⁺ and DCN 1–0 survey toward a sample of Planck cold clumps

¹ Guangxi Key Laboratory for Relativistic Astrophysics, School of Physical Science and Technology, Guangxi University, Nanning 530004, PR China
² National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100101, PR China
³ Key Laboratory of Radio Astronomy and Technolgoy, Chinese Academy of Sciences, A20 Datun Road, Chaoyang District, Beijing 100101, PR China
⁴ Space Engineering University, Beijing 101416, PR China
⁵ School of Physics and Astronomy, Sun Yat-sen University, Zhuhai 519082, PR China
⁶ Shanghai Astronomical Observatory, Chinese Academy of Sciences, No. 80 Nandan Road, Shanghai 200030, PR China
⁷ School of Astronomy and Space Sciences, University of Chinese Academy of Sciences, No. 19A Yuquan Road, Beijing 100049, PR China
⁸ Department of Electrical and Electronic Engineering, Guilin University of Technology at Nanning, Nanning 530001, PR China

^★ Corresponding author; junzhiwang@gxu.edu.cn

Received: 30 August 2024
Accepted: 4 March 2025

Abstract

Context. Deuterated molecules can be used to study the physical conditions and astro-chemical evolution of molecular clouds.

Aims. Large-sample surveys for deuterated molecules are needed to understand the enhancement of deuterated molecules from diffuse molecular gas to cold cores.

Methods. A single-pointing survey toward the 559 Planck cold clumps of the Early Cold Core Catalogue (ECC) was conducted using the Arizona Radio Observatory 12-meter telescope, focusing on the J = 1–0 transitions of DCO⁺ and DCN. The survey included observations of 309 cores for DCO⁺ and DCN 1–0 simultaneously, followed by 71 of these cores where DCO⁺ 1–0 was detected for H¹³CO⁺ and H¹³CN 1–0 simultaneously, aiming to determine the deuterated fraction (D_frac). Additionally, 250 cores were observed for DCO⁺, DCN, H¹³CO⁺, and H¹³CN 1–0 simultaneously.

Results. DCO⁺ and DCN 1–0 were detected in 79 and 11 of the 309 sources, with detection rates of 25.6% and 3.6%, respectively. In the 250 sources that were observed for all four species, DCO⁺, DCN, H¹³CO⁺, and H¹³CN 1–0 were detected in 58, 9, 57, and 13 sources, with a detection rate of 23.2%, 3.6%, 22.8%, and 5.2%, respectively. The D_frac(HCO⁺) values in 112 sources range from 0.89% to 7.4%, with a median value of 3.1%, while D_frac(HCN) values in 11 sources range from 1.5% to 5.5%, with a median value of 2.3%. The line widths of the DCO⁺ and H¹³CO⁺ 1–0 detections are mostly within 1 km s⁻¹.

Conclusions. The similarity in D_frac values between HCO+ and HCN indicates that the higher detection rate of DCO⁺ 1–0 compared with DCN 1–0 is due to the lower critical density of DCO⁺ 1–0. We suggest that the enhancement of DCO⁺ and DCN likely begins in the early diffuse stage of the molecular cloud and not during the cold-core formation stage.