The ALMA-ATOMS survey: Vibrationally excited HC₃N lines in hot cores

¹ School of Physics and Astronomy, Yunnan University, Kunming 650091, PR China
² Shanghai Astronomical Observatory, Chinese Academy of Sciences, 80 Nandan Road, Shanghai 200030, PR China
³ Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena CA 91109, USA
⁴ Department of Physics, Faculty of Science, Kunming University of Science and Technology, Kunming 650500, PR China
⁵ Xinjiang Astronomical Observatory, Chinese Academy of Sciences, 150 Science 1-Stree, Urumqi, Xinjiang 830011, PR China
⁶ Xinjiang Key Laboratory of Radio Astrophysics, 150 Science 1-Street, Urumqi, Xinjiang 830011, PR China
⁷ Departamento de Astronomía, Universidad de Chile, Las Condes, 7591245 Santiago, Chile
⁸ Chinese Academy of Sciences South America Center for Astronomy, National Astronomical Observatories, CAS, Beijing 100101, PR China
⁹ University of Chinese Academy of Sciences, Beijing 100049, PR China
¹⁰ Institute of Astrophysics, School of Physics and Electronical Science, Chuxiong Normal University, Chuxiong 675000, PR China
¹¹ Department of Earth and Planetary Sciences, Institute of Science Tokyo, Meguro, Tokyo 152-8551, Japan
¹² National Astronomical Observatory of Japan, National Institutes of Natural Sciences, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
¹³ Department of Astronomical Science, SOKENDAI (The Graduate University for Advanced Studies), 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
¹⁴ Rosseland Centre for Solar Physics, University of Oslo, PO Box 1029 Blindern, 0315 Oslo, Norway
¹⁵ Institute of Theoretical Astrophysics, University of Oslo, PO Box 1029 Blindern, 0315 Oslo, Norway
¹⁶ Physical Research Laboratory, Navrangpura, Ahmedabad 380 009, India
¹⁷ Instituto de Astronomïa, Universidad Católica del Norte, Antofagasta, Chile
¹⁸ Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
¹⁹ Korea Astronomy and Space Science Institute, 776 Daedeokdaero, Yuseong-gu, Daejeon 34055, Republic of Korea
²⁰ University of Science and Technology, Korea (UST), 217 Gajeong-ro, Yuseong-gu, Daejeon 34113, Republic of Korea
²¹ Department of Astronomy, Eötvös Loránd University, Pázmány Péter sétány 1/A, 1117, Budapest, Hungary
²² University of Debrecen, Faculty of Science and Technology, Egyetemtér 1, 4032 Debrecen, Hungary
²³ Department of Mathematical Sciences, University of South Africa, Cnr Christian de Wet Rd and Pioneer Avenue, Florida Park, 1709 Roodepoort, South Africa
²⁴ Centre for Space Research, North-West University, Potchefstroom Campus, Private Bag X6001, Potchefstroom 2520, South Africa
²⁵ Department of Physics and Astronomy, Faculty of Physical Sciences, University of Nigeria, Carver Building, 1 University Road, Nsukka 410001, Nigeria
²⁶ I. Physikalisches Institut, Universität zu Köln, Zülpicher Straße 77, 50937 Köln, Germany
²⁷ Kavli Institute for Astronomy and Astrophysics, Peking University, 5 Yiheyuan Road, Haidian District, Beijing 100871, China
²⁸ School of Physics and Astronomy, Sun Yat-sen University, 2 Daxue Road, Zhuhai, Guangdong 519082, PR China

^★ Corresponding authors; li.chen@mail.ynu.edu.cn; qin@ynu.edu.cn; liutie@shao.ac.cn

Received: 14 October 2024
Accepted: 16 December 2024

Abstract

Context. Interstellar molecules are excellent tools for studying the physical and chemical environments of massive star-forming regions. In particular, the vibrationally excited HC₃N (HC₃N*) lines are the key tracers for probing hot cores environments.

Aims. We present the Atacama Large Millimeter/submillimeter Array (ALMA) 3 mm observations of HC₃N* lines in 60 hot cores and investigate how the physical conditions affect the excitation of HC₃N* transitions.

Methods. We used the XCLASS for line identification. Under the assumption of local thermodynamic equilibrium, we derived the rotation temperature and column density of HC₃N* transitions in hot cores. Additionally, we calculated the H₂ column density and number density, along with the abundance of HC₃N* relative to H₂, to enable a comparison of the physical properties of hot cores with different numbers of HC₃N* states.

Results. We have detected HC₃N* lines in 52 hot cores, 29 of which show more than one vibrationally excited state. Hot cores with higher gas temperatures have more detections of these vibrationally excited lines. The excitation of HC₃N* requires dense environments, and its spatial distribution is affected by the presence of UC HII regions. The observed column density of HC₃N* contributes to the number of HC₃N* states in hot-core environments.

Conclusions. After analyzing the various factors influencing HC₃N* excitation in hot cores, we conclude that the excitation of HC₃N* is mainly driven by mid-IR pumping, while collisional excitation is ineffective.