λ = 2 mm spectroscopy observations toward the circumnuclear disk of NGC 1068^⋆

¹ School of Physics and Astronomy, Sun Yat-sen University, Guangzhou 510275, PR China
e-mail: qiujianjie2007@126.com
² Center For Astrophysics, Guangzhou University, Guangzhou 510006, PR China
e-mail: jszhang@gzhu.edu.cn
³ Laboratory for Space Research, University of Hong Kong, Hong Kong, PR China
e-mail: zhangyong5@mail.sysu.edu.cn
⁴ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
⁵ Xinjiang Astronomical Observatory, Chinese Academy of Sciences, 830011 Urumqi, PR China
⁶ Key Laboratory of Radio Astronomy, Chinese Academy of Sciences, PR China

Received: 29 April 2019
Accepted: 29 November 2019

Abstract

Aims. We investigate the physical and chemical conditions of molecular gas in the circumnuclear disk (CND) region of NGC 1068.

Methods. We carried out a spectral line survey with the IRAM 30 m telescope toward the center of NGC 1068 and mainly focused on the 2 mm band with a frequency coverage of 160.7–168.6 GHz and 176.5–184.3 GHz.

Results. Fifteen lines are detected in NGC 1068, eight of which are new detections for this galaxy. We derive the rotation temperatures and column densities of fourteen molecular species.

Conclusions. Based on the [HCO⁺ (2 − 1)]/[HOC⁺ (2 − 1)] ratio, we obtain a high ionization degree in the CND of NGC 1068. It is found that HC₃N is concentrated in the east knot, while ¹³CCH, CH₃CN, SO, HOC⁺, CS, CH₃CCH, and H₂CO are concentrated in the west knot. Compared to the star-forming galaxies M 82 and NGC 253, the chemistry of NGC 1068 might be less strongly affected by the UV radiation field, and its kinetic temperature might be lower.