Breathless BEARS: [O${}_{\mathrm{III}}$] 88$\mu$m Emission of Dusty Star-Forming Galaxies at $z=3-4$

Abstract

We present [O${}_{\mathrm{III}}$] 88$\mu$m observations towards four $Herschel$-selected dusty star-forming galaxies (DSFGs; log${}_{10}$ $\mu$L${}_{\mathrm{IR}}$/L${}_{\odot }$ = 13.5 - 14 at $z=2.9-4$) using the Atacama Compact Array (ACA) in Bands 9 and 10. We detect [O${}_{\mathrm{III}}$] emission in all four targets at >3$\sigma$, finding line luminosity ratios ($L_{[{\mathrm{O}}_{\mathrm{III}}]}$ / L${}_{\mathrm{IR}}$ = 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${}_{\mathrm{III}}$] emission at low redshift from space missions and at high redshift from ground-based studies. The difference in [O${}_{\mathrm{III}}$] emission between these DSFGs and other high-redshift galaxies reflects their more evolved stellar populations (> 10 Myr), larger dust reservoirs (M${}_{\mathrm{dust}}$ $\sim$ 10${}^{9-11}$ M${}_{\odot }$), metal-rich interstellar medium ($Z\sim 0.5-2$ Z${}_{\odot }$), and likely weaker ionization radiation fields. Ancillary [C${}_{\mathrm{II}}$] emission on two targets provide $L_{[{\mathrm{O}}_{\mathrm{III}}]}/L_{[{\mathrm{C}}_{\mathrm{II}}]}$ 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${}_{\mathrm{III}}$] emission will be key to place this heterogeneous, poorly-understood galactic phase in its astrophysical context.

Accepted in MNRAS Letters, 8 pages, 5 figures. Comments warmly welcomed