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Abstract We report the discovery of two companion sources to a strongly lensed galaxy SPT0418-47 (“ring”) at redshift 4.225, targeted by the JWST Early Release Science program. We confirm that these sources are at a similar redshift to the ring based on Hαdetected in the NIRSpec spectrum and [Cii]λ158μm line from the Atacama Large Millimeter/submillimeter Array (ALMA). Using multiple spectral lines detected in JWST/NIRSpec, the rest-frame optical to infrared images from NIRCam and MIRI and far-infrared dust continuum detected by ALMA, we argue that the newly discovered sources are actually lensed images of the same companion galaxy SPT0418-SE, hereafter referred to “SE,” located within 5 kpc in the source plane of the ring. The star formation rate derived using [Cii] and the dust continuum puts a lower limit of 17M_☉yr⁻¹, while the SFR_Hαis estimated to be >2 times lower, thereby confirming that SE is a dust-obscured star-forming galaxy. Analysis using optical strong line diagnostics suggests that SE has near-solar elemental abundance, while the ring appears to have supersolar metallicity O/H and N/O. We attempt to reconcile the high metallicity in this system by invoking early onset of star formation with continuous high star-forming efficiency or by suggesting that optical strong line diagnostics need revision at high redshift. We suggest that SPT0418-47 resides in a massive dark-matter halo with yet-to-be-discovered neighbors. This work highlights the importance of joint analysis of JWST and ALMA data for a deep and complete picture of the early universe. 

We report molecular gas observations of IRAS 20100-4156 and IRAS 03158+4227, two local ultraluminous infrared galaxies (ULIRGs) hosting some of the fastest and most massive molecular outflows known. Using ALMA and PdBI observations, we spatially resolve the CO(1-0) emission from the outflowing molecular gas in both and find maximum outflow velocities of $$ v_{\rm max} \sim 1600$$ and $$\sim 1700$$ km/s for IRAS 20100-4156 and IRAS 03158+4227, respectively. We find total gas mass outflow rates of $$\dot M_{\rm OF} \sim 670$$ and $$\sim 350$$ Msun/yr, respectively, corresponding to molecular gas depletion timescales $$\tau^{\rm dep}_{\rm OF} \sim 11$$ and $$\sim 16$$ Myr. This is nearly 3 times shorter than the depletion timescales implied by star formation, $$\tau^{\rm dep}_{\rm SFR} \sim 33$$ and $$\sim 46$$ Myr, respectively. To determine the outflow driving mechanism, we compare the starburst ($$L_{*}$$) and AGN ($$L_{\rm AGN}$$) luminosities to the outflowing energy and momentum fluxes, using mid-infrared spectral decomposition to discern $$L_{\rm AGN}$$. Comparison to other molecular outflows in ULIRGs reveals that outflow properties correlate similarly with $$L_{*}$$ and $$L_{\rm IR}$$ as with $$L_{\rm AGN}$$, indicating that AGN luminosity alone may not be a good tracer of feedback strength and that a combination of AGN and starburst activity may be driving the most powerful molecular outflows. We also detect the OH 1.667 GHz maser line from both sources and demonstrate its utility in detecting molecular outflows.