Deep millimeter spectroscopy observations toward NGC 1068^★

¹ School of Astronomy and Space Science, Nanjing University, Nanjing 210093, PR China
e-mail: qiujianjie2007@126.com
² Shanghai Astronomical Observatory, Chinese Academy of Sciences, 80 Nandan Road, Shanghai 200030, PR China
e-mail: jzwang@shao.ac.cn
³ Key Laboratory of Radio Astronomy, Chinese Academy of Sciences, Nanjing 210008, PR China
⁴ Key Laboratory of Modern Astronomy and Astrophysics, Nanjing University, Ministry of Education, Nanjing 210093, PR China
e-mail: yong@nju.edu.cn
⁵ Center For Astrophysics, GuangZhou University, GuangZhou 510006, PR China
⁶ Department of Astronomy, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721, USA
⁷ University of Chinese Academy of Sciences, 19A Yuquanlu, Beijing 100049, PR China

Received: 25 April 2017
Accepted: 11 December 2017

Abstract

Aims. We aim for a better understanding of gas properties in the circum-nuclear disk (CND) region of the nearby gas-rich Seyfert 2 galaxy NGC 1068. We focus on line identification and the basic physical parameters estimation of molecular gas in the CND region.

Methods. We used the IRAM 30 m telescope to conduct deep millimeter spectroscopy observations toward the center of NGC 1068.

Results. Thirty-two lines were detected in this galaxy, 15 lines of wich were detected for the first time. With a sensitivity better by about a factor of 4 than observations in the literature for this source at 3 mm band, we detected several weak lines for the first time in this source, such as lines from CH₃CCH, CH₃OCH₃, and HC¹⁸O⁺. Column densities of these molecules were estimated based on line emissions. Some marginal detections in the literature, such as HN¹³C (1–0), were confirmed. CH₃OCH₃ was detected for the first time in external galaxies. Lines from several carbon chain molecules and shock-related molecules were also detected in this source.