Apr 24, 2020 09:50 PM
Due to the COVID-19 outbreak, ALMA Science Operations have been suspended and the Cycle 8 Call for Proposals has been delayed until 2021 March. The start of ALMA Cycle 8 will now be 2021 October. ALMA continues to carefully monitor the evolving global situation regarding the COVID-19 pandemic and will post ALMA-related updates as News Items to the Science Portal.
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Science Highlight: Spatially Measured CO(2-1)/CO(1-0) Ratios in the Galaxy M83

Apr 24, 2020 09:50 PM
Due to the COVID-19 outbreak, ALMA Science Operations have been suspended and the Cycle 8 Call for Proposals has been delayed until 2021 March. The start of ALMA Cycle 8 will now be 2021 October. ALMA continues to carefully monitor the evolving global situation regarding the COVID-19 pandemic and will post ALMA-related updates as News Items to the Science Portal.

 

 

Koda2020

Figure 1. (a) A map of R21/10 with CO(1-0) contours. (b) Far-UV map with R21/10 contours. (c) 70μm-to-350μm emission map with R21/10 contours.

 

 

 

 

 

While the rotational transition of CO(1-0) is commonly used to derive the bulk molecular gas properties (e.g., the total star-forming molecular gas mass) of galaxies, observations of higher CO transitions are gaining popularity due to their brightness and thus the lower investment in telescope time relative to CO(1-0). In a recent paper, Dr. Koda and his collaborators make use of the Total Power Array of ALMA to map out the distribution of CO(1-0) and CO(2-1) in the spiral galaxy M83. They measure the CO(2-1)/CO(1-0) ratio, R21/10, of M83, and compare it with beam-matched intensity maps of GALEX far-UV and Herschel infrared emission, as well as the ratio of 70μm-to-350μm emission (a proxy for dust temperature). The authors find that R21/10 > 0.7 in regions with high molecular gas surface density, and that R21/10 in excess of 0.55 correlates well with the far-UV intensity (r = 0.82) and the dust temperature (r = 0.83).  They speculate that the correlations may be due to a thermal coupling between the UV-heated dust and the gas. No clear correlation was found for lower values of R21/10.

 

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