KAgoshima Galactic Object survey with Nobeyama 45 m telescope by Mapping in Ammonia lines (KAGONMA): Discovery of parsec-scale CO depletion in the Canis Major star-forming region

Author:

Hirata Yushi1ORCID,Murase Takeru12,Nishi Junya1,Shimajiri Yoshito1345,Omodaka Toshihiro1,Nakano Makoto6,Sunada Kazuyoshi7,Ito Takumi18,Handa Toshihiro19

Affiliation:

1. Department of Physics and Astronomy, Graduate School of Science and Engineering, Kagoshima University , 1-21-35 Korimoto, Kagoshima, Kagoshima 890-0065 , Japan

2. Faculty of Engineering, Gifu University , 1-1 Yanagido, Gifu, Gifu 501-1193 , Japan

3. National Astronomical Observatory of Japan , 2-21-1 Osawa, Mitaka, Tokyo 181-8588 , Japan

4. Laboratoire d’Astrophysique (AIM) , Université Paris-Saclay, Université Paris Cité, CEA, CNRS, AIM, F-91191 Gif-sur-Yvette , France

5. Kyushu Kyoritsu University , 1-8 Jiyugaoka, Yahatanishi-ku, Kitakyushu, Fukuoka 807-8585 , Japan

6. Faculty of Science and Technology, Oita University , 700 Dannoharu, Oita 870-1192 , Japan

7. Mizusawa VLBI Observatory , NAOJ, 2-12 Hoshigaoka, Mizusawa, Oshu, Iwate 023-0861 , Japan

8. Graduate School of Science and Technology, Kumamoto University , 2-39-1 Kurokami, Chuo, Kumamoto, Kumamoto 860-8555 , Japan

9. Amanogawa Galaxy Astronomy Research Center, Kagoshima University , 1-21-35 Korimoto, Kagoshima, Kagoshima 890-0065 , Japan

Abstract

Abstract In observational studies of infrared dark clouds, the number of detections of CO freeze-out on to dust grains (CO depletion) at the pc scale is extremely limited, and the conditions for its occurrence are, therefore, still unknown. We report a new object where pc-scale CO depletion is expected. As part of the Kagoshima Galactic Object survey with Nobeyama 45 m telescope by Mapping in Ammonia lines (KAGONMA), we have made mapping observations of NH3 inversion transition lines towards the star-forming region associated with Canis Major OB1, including IRAS 07077−1026, IRAS 07081−1028, and PGCC G224.28−0.82. By comparing the spatial distributions of NH3 (1,1) and C18O (J = 1–0), an intensity anti-correlation was found in IRAS 07077−1026 and IRAS 07081−1028 on the ∼1 pc scale. Furthermore, we obtained a lower abundance of C18O at least in IRAS 07077−1026 than in the other parts of the star-forming region. After examining high-density gas dissipation, photodissociation, and CO depletion, we concluded that the intensity anti-correlation in IRAS 07077−1026 is due to CO depletion. On the other hand, in the vicinity of the center of PGCC G224.28−0.82, the emission line intensities of both NH3 (1,1) and C18O (J = 1–0) were strongly detected, although the gas temperature and density were similar to IRAS 07077−1026. This indicates that there are situations where C18O (J = 1–0) cannot trace dense gas on the pc scale and implies that the conditional differences in which C18O (J = 1–0) can and cannot trace dense gas are unclear.

Publisher

Oxford University Press (OUP)

Subject

Space and Planetary Science,Astronomy and Astrophysics

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