Resolved Molecular Gas and Star Formation Properties of the Strongly Lensed z = 2.26 Galaxy SDSS J0901+1814

We present ∼1″ resolution (∼2 kpc in the source plane) observations of the CO (1-0), CO (3-2), Hα, and [N II] lines in the strongly lensed z = 2.26 star-forming galaxy SDSS J0901+1814. We use these observations to constrain the lensing potential of a foreground group of galaxies, and our source-plane reconstructions indicate that SDSS J0901+1814 is a nearly face-on (i ≈ 30°) massive disk with r _1/2 ≳ 4 kpc for its molecular gas. Using our new magnification factors (μ _tot ≈ 30), we find that SDSS J0901+1814 has a star formation rate (SFR) of {268}_-61⁺⁶³ {M}_⊙ {yr}}^-1, {M}_gas}=({1.6}_-0.2^+0.3)× {10}¹¹({α }_CO}/4.6) {M}_⊙ , and {M}_\star =({9.5}_-2.8^+3.8)× {10}¹⁰ {M}_⊙ , which places it on the star-forming galaxy “main sequence.” We use our matched high angular resolution gas and SFR tracers (CO and Hα, respectively) to perform a spatially resolved (pixel-by-pixel) analysis of SDSS J0901+1814 in terms of the Schmidt-Kennicutt relation. After correcting for the large fraction of obscured star formation ({SFR}}_{{H}α }/{SFR}}_TIR}={0.054}_-0.014^+0.015), we find that SDSS J0901+1814 is offset from “normal” star-forming galaxies to higher star formation efficiencies independent of assumptions for the CO-to-H₂ conversion factor. Our mean best-fit index for the Schmidt-Kennicutt relation for SDSS J0901+1814, evaluated with different CO lines and smoothing levels, is \bar{n}=1.54+/- 0.13; however, the index may be affected by gravitational lensing, and we find \bar{n}=1.24+/- 0.02 when analyzing the source-plane reconstructions. While the Schmidt-Kennicutt index largely appears unaffected by which of the two CO transitions we use to trace the molecular gas, the source-plane reconstructions and dynamical modeling suggest that the CO (1-0) emission is more spatially extended than the CO (3-2) emission.

Based on observations carried out with the IRAM Plateau de Bure Interferometer. IRAM is supported by INSU/CNRS (France), MPG (Germany), and IGN (Spain).