Abstract

Using a waveguide-type sideband-separating receiver (2SB receiver) on the Tokyo-NRO 60-cm telescope (renamed the AMANOGAWA telescope), we carried out simultaneous observations in the 12CO (J= 2–1) and 13CO (J= 2–1) lines over the galactic plane l= 10–245 along b= 0 with a 3.75 grid. Using the 12CO (J= 1–0) data of Dame et al. (2001, ApJ, 547, 792), who used a beam size almost the same as ours, we show 12CO (J= 2–1)/12CO (J= 1–0) and 13CO (J= 2–1)/12CO (J= 2–1) intensity ratios on the lv map and the intensity correlations among the 12CO (J= 2–1), 13CO (J= 2–1), and 12CO (J= 1–0) lines. As a result, a linear correlation between 12CO (J= 2–1) and 12CO (J= 1–0) and a curved correlation between 12CO (J= 2–1) and 13CO (J= 2–1), as produced by most of the data, have been found. We investigated these correlations with simple radiative transfer equations to ascertain a number of restrictions on the physical quantities of molecular gas on a galactic scale.

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