ALMA Resolves the Molecular Gas in a Young Low-metallicity Starburst Galaxy at z=1.7

摘要

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_(450 μm) = 23.5_(-8.1)~(+26.8)μJy and intrinsic CO luminosities L'_(CO(3-2))=2.90_(-0.23)~(+0.21)×10~8 K km s~(-1) pc~2 and L'_(CO(6-5))=8.0_(-1.3)~(-1.4)×10~7 K km s~(-1) pc~2. We used the resolved properties in the source plane to obtain molecular gas and star formation rate surface densities of ∑_(H2)=16.2_(3.5)~(+5.8) M_⊙ pc~(-2) and ∑_(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.