ALMA Imaging of the CO(7-6) Line Emission in the Submillimeter Galaxy LESS 073 at redshift 4.755${}^{\star }$

Abstract

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^{\prime \prime }.2\times 0^{\prime \prime }.9$ ($8\times 6$~kpc${}^2$), the CO(7-6) emission is largely unresolved (with a deconvolved size of $1^{\prime \prime }.1(\pm 0^{\prime \prime }.5)\times 0^{\prime \prime }.9(\pm 0^{\prime \prime }.8)$), 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, and a line width of $343\pm 40$ km/s. 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 $T_{\mathrm{dust}}=57.6\pm 3.5$ K, 60-to-100 $\hat{I}¼$m flux density ratio $f_{60}/f_{100}=0.86\pm 0.08$, and total infrared luminosity $L_{\mathrm{IR}}=(5.8\pm 0.9)\times 10^{12}{L}_{\odot }$. 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.

8 pages, 6 figures, accepted for publication in ApJ