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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 [math]CO ([math] 2–1) and [math]CO ([math] 2–1) lines over the galactic plane [math] 10[math]–245[math] along [math] 0[math] with a 3[math]75 grid. Using the [math]CO ([math] 1–0) data of Dame et al. (2001, ApJ, 547, 792), who used a beam size almost the same as ours, we show [math]CO ([math] 2–1)[math]CO ([math] 1–0) and [math]CO ([math] 2–1)[math]CO ([math] 2–1) intensity ratios on the [math]–[math] map and the intensity correlations among the [math]CO ([math] 2–1), [math]CO ([math] 2–1), and [math]CO ([math] 1–0) lines. As a result, a linear correlation between [math]CO ([math] 2–1) and [math]CO ([math] 1–0) and a curved correlation between [math]CO ([math] 2–1) and [math]CO ([math] 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.

*Keywords: *
Galaxy: disk;
Galaxy: structure;
ISM: molecules;
surveys

*Journal Article.*
*6922 words.*
*Illustrated.*

*Subjects: *
Galaxies
;
Astronomy and Astrophysics
;
Interstellar Medium

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