Breathless BEARS: [O  iii ] 88 μm Emission of Dusty Star-Forming Galaxies at z = 3 − 4

We present [O iii] 88 μm observations towards four Herschel-selected dusty star-forming galaxies (DSFGs; log10μLIR/L⊙ = 13.5 − 14 at z = 2.9 − 4) using the Atacama Compact Array (ACA) in Bands 9 and 10. We detect [O iii] emission in all four targets at >3σ, finding line luminosity ratios (L_ [OIII] / LIR = 10-4.2 to 10−3) similar to local spiral galaxies, and an order of magnitude lower when compared with local dwarf galaxies as well as high-redshift Lyman-break galaxies. Using the short-wavelength capabilities of the ACA, these observations bridge the populations of galaxies with [O iii] emission at low redshift from space missions and at high redshift from ground-based studies. The difference in [O iii] emission between these DSFGs and other high-redshift galaxies reflects their more evolved stellar populations (>10 Myr), larger dust reservoirs (Mdust ∼ 109 − 11 M⊙), metal-rich interstellar medium (Z ∼ 0.5 − 2 Z⊙), and likely weaker ionization radiation fields. Ancillary [C ii] emission on two targets provide L_[O\, III]/L_[C\, II] ratios at 0.3 − 0.9, suggesting that ionized gas represents a smaller fraction of the total gas reservoir in DSFGs, consistent with theoretical models of DSFGs as transitional systems between gas-rich, turbulent disks and more evolved, gas-poor galaxies. Expanding samples of DSFGs with [O iii] emission will be key to place this heterogeneous, poorly-understood galactic phase in its astrophysical context.