Publication Date


Journal or Book Title

The Astrophysical Journal


We present moderate- (1'') and high-resolution (02) observations of the CO (2–1) emission at 43 GHz and radio continuum emission at 1.47 GHz from the z = 4.7 QSO BRI 1202-0725 and the z = 4.4 QSO BRI 1335-0417 using the Very Large Array. The moderate-resolution observations show that in both cases the CO emission is spatially resolved into two components separated by 1'' for BRI 1335-0417 and 4'' for BRI 1202-0725. The high-resolution observations show that each component has substructure on scales ~02–05, with intrinsic brightness temperatures ≥20 K. The CO ladder from (2–1) up to (7–6) suggests a high kinetic temperature for the gas (Tkin 70 K) and a high column density [N(H2) 1024 cm-2]. In both sources the continuum-to-line ratio is LFIR/L 335. All these characteristics (brightness temperature, excitation temperature, column density, and continuum-to-line ratio) are comparable to conditions found in low-redshift, ultraluminous nuclear starburst galaxies. We find that the CO-emitting regions in BRI 1202-0725 and BRI 1335-0417 must be close to face-on in order to avoid having the gas mass exceed the gravitational mass, implying perhaps unreasonably large rotational velocities. While this problem is mitigated by lowering the CO luminosity–to–H2 mass conversion factor (X), the required X values become comparable to, or lower than, the minimum values dictated by optically thin CO emission. We considered the possibility of magnification by gravitational lensing in order to reduce the molecular gas masses.


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