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 ( ALMA ) .
At the achieved resolution of \sim 1 \arcsec . 2 \times 0 \arcsec . 9 ( 8 \times 6 kpc ^ { 2 } ) , the CO ( 7 - 6 ) emission is largely unresolved ( with a deconvolved size of 1 \arcsec . 1 ( \pm 0 \arcsec . 5 ) \times 0 \arcsec . 9 ( \pm 0 \arcsec . 8 ) .
) , and the continuum emission is totally unresolved .
The CO ( 7 - 6 ) line emission has an integrated flux of 0.86 \pm 0.08 Jy km s ^ { -1 } , and a line width of 343 \pm 40 km s ^ { -1 } .
The continuum emission has a flux density of 0.51 mJy .
By fitting the observed far-infrared ( FIR ) spectral energy distribution of LESS 073 with a single-temperature modified blackbody function , we obtained a dust temperature T _ { dust } = 57.6 \pm 3.5 K , 60-to-100 \mu m flux density ratio f _ { 60 } / f _ { 100 } = 0.86 \pm 0.08 , and total infrared luminosity L _ { IR } = ( 5.8 \pm 0.9 ) \times 10 ^ { 12 } ~ { } L _ { \odot } .
The SED-fit-based f _ { 60 } / f _ { 100 } is consistent with those estimated from various line ratios as advocated by our earlier work , indicating that those proposed line-ratio-based method can be used to practically derive f _ { 60 } / f _ { 100 } for high- z sources .
The total molecular gas mass of LESS 073 is ( 3.3 \pm 1.7 ) \times 10 ^ { 10 } ~ { } M _ { \odot } , and the inferred gas depletion time is about 43 Myr .