ALMA Imaging of the CO (7–6) Line Emission in the Submillimeter Galaxy LESS 073 at z = 4.755*

In this paper we present our imaging observations on the CO.(7-6) line and its underlying continuum emission of the young submillimeter galaxy LESS.073 at redshift 4.755, using the Atacama Large Millimeter/submillimeter Array. At the achieved resolution of 1.. 2 ' 0.. 9 (8 x 6 kpc2), the CO.(7-6) emission is largely unresolved (with a deconvolved size of 1.. 1(.0.. 5) ' 0.. 9(. 0.. 8)), and the continuum emission is totally unresolved. The CO.(7 -6) line emission has an integrated flux of 0.86.+/-. 0.08.Jy.km s-1, and a line width of 343.+/-.40.km s-1. The continuum emission has a flux density of 0.51.mJy. By fitting the observed far-infrared spectral energy distribution (SED) of LESS.073 with a single-temperature modified blackbody function, we obtained a dust temperature Tdust = 57.6. 3.5 K, 60-100. mu m flux density ratio f60 f100 = 0.86. 0.08, and total infrared luminosity LIR = (5.8. 0.9) ' 10 L.12. The SED-fit-based f f 60 100 is consistent with those estimated from various line ratios as advocated by our earlier work, indicating that the proposed line-ratio-based method can be used to practically derive f60 f100 for high-z sources. The total molecular gas mass of LESS.073 is (3.3. 1.7) ' 1010 M., and the inferred gas depletion time is about 43.Myr.