Breathless BEARS: [O iii ] 88 µm emission of dusty star-forming galaxies at z = 3−4

ABSTRACT We present [O iii] 88 $\mu {\rm m}$ observations towards four Herschel-selected dusty star-forming galaxies (DSFGs; $\log _{10} \mu L_{\rm IR} / L_{\odot } = 13.5 \!-\! 14$ 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 $\gt\, 3 \sigma$, finding line luminosity ratios ($L_{\rm [O_{III}]} / L_{\rm IR} = 10^{-4.2}$ 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 ($M_{\rm dust} \sim 10^{9 - 11}$ M$_{\rm \odot }$), metal-rich interstellar medium ($Z \sim 0.5\!-\!2$ Z$_{\odot }$), and likely weaker ionization radiation fields. Ancillary [C ii] emission on two targets provide $L_\mathrm{[O\, {\small III}]}/L_\mathrm{[C\, {\small II}]}$ 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.