Comparisons between Resolved Star Formation Rate and Gas Tracers in the Strongly Lensed Galaxy SDSS J0901+1814 at Cosmic Noon

Abstract

We report new radio observations of SDSS J090122.37+181432.3, a strongly lensed star-forming galaxy at z = 2.26. We image 1.4 GHz ( L -band) and 3 GHz ( S -band) continuum using the Very Large Array (VLA) and 1.2 mm (band 6) continuum with Atacama Large Millimeter/submillimeter Array, in addition to the CO(7–6) and C i ( ^3 P _2 → ^3 P _1 ) lines, all at ≲1.″7 resolution. Based on the VLA integrated flux densities, we decompose the radio spectrum into its free–free (FF) and nonthermal components. The infrared–radio correlation parameter ${q}_{\mathrm{TIR}}={2.65}_{-0.31}^{+0.24}$ is consistent with expectations for star-forming galaxies. We obtain radio continuum-derived star formation rates (SFRs) that are free of dust extinction, finding ${620}_{-220}^{+280}\,{M}_{\odot }\,{\mathrm{yr}}^{-1}$ , ${230}_{-160}^{+570}\,{M}_{\odot }\,{\mathrm{yr}}^{-1}$ , and ${280}_{-120}^{+460}\,{M}_{\odot }\,{\mathrm{yr}}^{-1}$ from the FF emission, nonthermal emission, and when accounting for both emission processes, respectively, in agreement with previous results. We estimate the gas mass from the C i ( ^3 P _2 → ^3 P _1 ) line as M _gas = (1.2 ± 0.2) × 10 ^11 M _☉ , which is consistent with prior CO(1–0)-derived gas masses. Using our new IR and radio continuum data to map the SFR, we assess the dependence of the Schmidt–Kennicutt relation on choices of SFR and gas tracer for ∼kpc scales. The different SFR tracers yield different slopes, with the IR being the steepest, potentially due to highly obscured star formation in J0901. The radio continuum maps have the lowest slopes and overall fidelity for mapping the SFR, despite producing consistent total SFRs. We also find that the Schmidt–Kennicutt relation slope is flattest when using CO(7–6) or C i ( ^3 P _2 → ^3 P _1 ) to trace gas mass, suggesting that those transitions are not suitable for tracing the bulk molecular gas in galaxies like J0901.

Keywords

• Star formation
• High-redshift galaxies
• Molecular gas
• Radio continuum emission