Molecular Gas and Dust atz = 2.6 in SMM J14011+0252: A Strongly Lensed Ultraluminous Galaxy, Not a Huge Massive Disk

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Abstract
We used the IRAM interferometer to detect CO (3-2), CO (7-6), and 1.3 mm dust continuum emission from the submillimeter galaxy SMM J14011+0252 at z = 2.6. Contrary to a recent claim that the CO was extended over 66 (57 kpc), the new data yield a size of 2''× ≤ 05 for the CO and the dust. Although previous results placed the CO peak in a region with no visible counterpart, the new maps show that the CO and dust are centered on the J1 complex seen on K-band and optical images. We suggest that the CO is gravitationally lensed not only by the foreground cluster A1835 but also by an individual galaxy on the line of sight. Comparison of measured and intrinsic CO brightness temperatures indicates that the CO size is magnified by a factor of 25 ± 5. After correcting for lensing, we derive a true CO diameter of ~008 (700 pc), consistent with a compact circumnuclear disk of warm molecular gas similar to that in Arp 220. The high magnification means that the true size, far-IR luminosity, star formation rate, CO luminosity, and molecular gas mass are all comparable with those in present-epoch ultraluminous IR galaxies, not with a huge, massive, early-universe Galactic disk.
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