Systematic Variations of CO J = 2−1/1–0 Ratio and Their Implications in The Nearby Barred Spiral Galaxy M83

Jin Koda , Tsuyoshi Sawada , Kazushi Sakamoto , Akihiko Hirota , Fumi Egusa , Samuel Boissier (1) , Daniela Calzetti , J. Donovan Meyer , Bruce Elmegreen , Armando Gil de Paz , Nanase Harada , L. C. Ho , M. I. N. Kobayashi , Nario Kuno , Sergio Martín , Kazuyuki Muraoka , Kouichiro Nakanishi , Nick Scoville , Mark Seibert , Catherine Vlahakis , Yoshimasa Watanabe , Jennifer Donovan Meyer , Armando Gil de Paz , Masato Kobayashi

1 LAM - Laboratoire d'Astrophysique de Marseille

We present spatial variations of the CO J=2-1/1-0 line ratio in M83 using Total Power array data from ALMA. While the intensities of these two lines correlate tightly, the ratio varies over the disk, with a disk average ratio of 0.69, and shows the galactic center and a two-arm spiral pattern. It is high (>0.7) in regions of high molecular gas surface density, but ranges from low to high ratios in regions of low surface density. The ratio correlates well with the spatial distributions and intensities of FUV and IR emissions, with FUV being the best correlated. It also correlates better with the ratio of IR intensities (70/350mic), a proxy for dust temperature, than with the IR intensities. Taken together, these results suggest either a direct or indirect link between the dust heating by the interstellar radiation field and the condition of GMCs, even though no efficient mechanism is known for a thermal coupling of dust and bulk gas in GMCs.

Domaines: Planète et Univers [physics]

Jin Koda, Tsuyoshi Sawada, Kazushi Sakamoto, Akihiko Hirota, Fumi Egusa, et al.. Systematic Variations of CO J = 2−1/1–0 Ratio and Their Implications in The Nearby Barred Spiral Galaxy M83. The Astrophysical journal letters, 2020, 890 (1), pp.L10. ⟨10.3847/2041-8213/ab70b7⟩. ⟨hal-02995933⟩