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

Koda, Jin and Sawada, Tsuyoshi and Sakamoto, Kazushi and Hirota, Akihiko and Egusa, Fumi and Boissier, Samuel and Calzetti, Daniela and Meyer, Jennifer Donovan and Elmegreen, Bruce G. and Gil de Paz, Armando and Harada, Nanase and Ho, Luis C. and Kobayashi, Masato I. N. and Kuno, Nario and Martín, Sergio and Muraoka, Kazuyuki and Nakanishi, Kouichiro and Scoville, Nick and Seibert, Mark and Vlahakis, Catherine and Watanabe, Yoshimasa (2020) Systematic Variations of CO J = 2−1/1–0 Ratio and Their Implications in The Nearby Barred Spiral Galaxy M83. Astrophysical Journal Letters, 890 (1). Art. No. L10. ISSN 2041-8213. doi:10.3847/2041-8213/ab70b7.

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We present spatial variations of the CO J = 2−1/1–0 line ratio (R₂₁/₁₀) in the barred spiral galaxy M83 using Total Power Array (single-dish telescopes) data from the Atacama Large Millimeter/submillimeter Array. While the intensities of these two lines correlate tightly, R₂₁/₁₀ 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 (Σ_(mol)), but ranges from low to high ratios in regions of low Σ_(mol). The ratio correlates well with the spatial distributions and intensities of far-ultraviolet (FUV) and infrared (IR) emissions, with FUV being the best correlated. It also correlates better with the ratio of specific intensities at 70 and 350 μm, 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 giant molecular clouds (GMCs), even though no efficient mechanism is known for a thermal coupling of dust and bulk gas in GMCs. We speculate that the large spread of R₂₁/₁₀ in low Σ_(mol) regions, mostly at the downstream sides of spiral arms, may be due to the evolution of massive stars after spiral arm passage. Having in a late phase escaped from the spiral arms and their parental clouds, they may contribute to the dust heating by FUV and gas heating by cosmic rays produced by supernovae.

Item Type:Article
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URLURL TypeDescription Paper
Koda, Jin0000-0002-8762-7863
Sakamoto, Kazushi0000-0001-5187-2288
Boissier, Samuel0000-0002-9091-2366
Calzetti, Daniela0000-0002-5189-8004
Elmegreen, Bruce G.0000-0002-1723-6330
Gil de Paz, Armando0000-0001-6150-2854
Ho, Luis C.0000-0001-6947-5846
Kobayashi, Masato I. N.0000-0003-3990-1204
Martín, Sergio0000-0001-9281-2919
Muraoka, Kazuyuki0000-0002-3373-6538
Nakanishi, Kouichiro0000-0002-6939-0372
Scoville, Nick0000-0002-0438-3323
Seibert, Mark0000-0002-1143-5515
Vlahakis, Catherine0000-0003-3745-4228
Watanabe, Yoshimasa0000-0002-9668-3592
Alternate Title:Systematic Variations of CO J = 2−1/1–0 Ratio in The Barred Spiral Galaxy M83
Additional Information:© 2020 The American Astronomical Society. Received 2019 December 10; revised 2020 January 5; accepted 2020 January 28; published 2020 February 11. This Letter makes use of the following ALMA data: ADS/JAO.ALMA#2013.1.01161.S, ADS/JAO.ALMA#2015.1.00121.S, ADS/JAO.ALMA#2016.1.00386.S, and ADS/JAO.ALMA#2017.1.00079.S. ALMA is a partnership of ESO (representing its member states), NSF (USA) and NINS (Japan), together with NRC (Canada), MOST and ASIAA (Taiwan), and KASI (Republic of Korea), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO, and NAOJ. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. J.K. acknowledges support from NSF through grant AST-1812847. The work of L.C.H. was supported by the National Science Foundation of China (11721303, 11991052) and the National Key R&D Program of China (2016YFA0400702). K.S. was supported by MOST 108-2112-M-001-015. We also thank the anonymous referee. Facilities: ALMA - Atacama Large Millimeter Array, IRSA - , Spitzer - , Herschel. - Software: CASA 5.4.1-31 (McMullin et al. 2007).
Group:Astronomy Department
Funding AgencyGrant Number
National Science Foundation of China11721303
National Science Foundation of China11991052
National Key Research and Development Program of China2016YFA0400702
Ministry of Science and Technology (Taipei)108-2112-M-001-015
Subject Keywords:Molecular gas; Spiral galaxies; Interstellar medium
Issue or Number:1
Classification Code:Unified Astronomy Thesaurus concepts: Molecular gas (1073); Spiral galaxies (1560); Interstellar medium (847)
Record Number:CaltechAUTHORS:20200211-112445066
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Official Citation:Jin Koda et al 2020 ApJL 890 L10
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:101224
Deposited By: Tony Diaz
Deposited On:11 Feb 2020 21:21
Last Modified:16 Nov 2021 18:00

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