2017ApJ...846L..22G

We present Atacama Large Millimeter/submillimeter Array observations of CO lines and dust continuum emission of the source RCSGA 032727-132609, a young z = 1.7 low-metallicity starburst galaxy. The CO(3-2) and CO(6-5) lines and continuum at rest-frame 450 µm are detected and show a resolved structure in the image plane. We use the corresponding lensing model to obtain a source plane reconstruction of the detected emissions revealing an intrinsic flux density of S_450µm_=23.5-8.1_^+26.8µJy and intrinsic CO luminosities L_CO(3–2)^′^=2.90-0.23_^+0.21 ×10⁸ K km s^–1 pc² and L_CO(6–5)^′^=8.0-1.3_^+1.4×10⁷ K km s^–1 pc². We used the resolved properties in the source plane to obtain molecular gas and star formation rate surface densities of Σ_H2=16.2_–3.5^+5.8 M_☉ pc^–2 and Σ_SFR=0.54_–0.27^+0.89 M_☉ yr^–1 kpc^–2, respectively. The intrinsic properties of RCSGA 032727-132609 show an enhanced star formation activity compared to local spiral galaxies with similar molecular gas densities, supporting the ongoing merger-starburst phase scenario. RCSGA 032727-132609 also appears to be a low-density starburst galaxy similar to local blue compact dwarf galaxies, which have been suggested as local analogs to high-redshift low-metallicity starburst systems. Finally, the CO excitation level in the galaxy is consistent with having the peak at J∼5, with a higher excitation concentrated in the star-forming clumps.