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Arxiv: RUBIES: JWST/NIRSpec resolves evolutionary phases of dusty star-forming galaxies at z\sim2 Published: 10/11/2024 12:46:54 AM Updated: 10/11/2024 12:46:54 AM

Paper abstract: The dearth of high quality spectroscopy of dusty star-forming galaxies(DSFGs) -- the main drivers of the assembly of dust and stellar mass at thepeak of activity in the Universe -- greatly hinders our ability to interprettheir physical processes and evolutionary pathways. We present JWST/NIRSpecobservations from RUBIES of four submillimeter-selected, ALMA-detected DSFGs atcosmic noon, z~2.3-2.7. While photometry uniformly suggests vigorousongoing star formation for the entire sample in line with canonical DSFGs, thespectra differ: one source has spectroscopic evidence of an evolved stellarpopulation, indicating a recent transition to a post-starburst phase, while theremainder show strong spectroscopic signatures of ongoing starbursts. All fourgalaxies are infrared-luminous (log_{10}L_{\rm{IR}}/L_{\rm \odot}>12.4), massive (log_{10}\,M_*/M_{\rm \odot} >11), and verydust-obscured (A_V~3-4 ABmag). Leveraging detections of multiple Balmerand Paschen lines, we derive an optical attenuation curve consistent withCalzetti overall, yet an optical extinction ratio R_V~2.5, potentiallyindicating smaller dust grains or differences in star-dust geometry. This casestudy provides some of the first detailed spectroscopic evidence that the DSFGsencompass a heterogeneous sample spanning a range of star formation propertiesand evolutionary stages, and illustrates the advantages of synergistic JWST andALMA analysis of DSFGs.