CO Observations of High-z Objects

Extract

We have made a CO (J=2−1) observation using the Nobeyama 45m telescope aimed at examining physical properties of the molecular gas in the object. Upper limit obtained is 1.8 mK (3σ) at a velocity resolution of 100 km s⁻¹, which leads to an upper limit on the molecular gas mass of 5.3 × 10¹¹M_⊙, if we assume a line width of 250 km s⁻¹ obtained in J = 5–4 line and the Galactic CO-to-H₂ conversion factor of 4.5 M_⊙ K km s⁻¹ pc². The line ratio between 2–1 line and 5–4 line as well as those from 7–6 and 4–3 lines (Omont et al. 1996) imply that the mean gas density is as high as 10^3–5 cm⁻³, which is comparable to that in nearby star burst galaxies (e.g., Solomon et al. 1992).