CO(2–1)/CO(1–0) Line Ratio on a ∼100 Parsec Scale in the Nearby Barred Galaxy NGC 1300

CO(2-1) emission is often used as a tracer of the giant molecular clouds (GMCs) an alternative to CO(1-0) in recent years. Therefore, understanding environmental dependence line ratio CO(2-1)/CO(1-0), $R_{21}$, on GMC scale important accurately estimate mass GMCs. We thus measured $R_{21}$ strongly barred galaxy NGC1300, where star formation activity depends galactic structure, $\sim 100$ pc scale. CO images were obtained from ALMA and Nobeyama 45-m telescope. The resultant typical NGC1300 $0.57 \pm 0.06$. find variations $R_{21}$; it highest bar-end region ($0.72 0.08$), followed by arm ($0.60 0.07$) bar regions ($0.50 0.06$). GMCs with H$\alpha$ show systematically higher ($0.67 than those without ($0.47 0.05$). In region, massive suppressed, not associated most GMCs, resulting lowest $R_{21}$. These results raise possibility that properties derived observations assumption constant are different observations. Furthermore, we kpc tends be lower probably due presence extended diffuse gas NGC1300.