2019ApJ...882....1L

We present detections of the CO(4-3) and [C I] 609 µm spectral lines, as well as the dust continuum at 480.5 GHz (rest frame), in 3C 368, a Fanaroff-Riley class II (FR-II) galaxy at redshift (z) 1.131. 3C 368 has a large stellar mass, ∼ 3.6 x 10¹¹ M_☉, and is undergoing an episode of vigorous star formation, at a rate of ∼ 350 M_☉ yr^–1, and active galactic nucleus activity, with radio-emitting lobes extended over ∼ 73 kpc. Our observations allow us to inventory the molecular-gas reservoirs in 3C 368 by applying three independent methods: (1) using the CO(4-3)-line luminosity, excitation state of the gas, and an α_CO conversion factor, (2) scaling from the [C I]-line luminosity, and (3) adopting a gas-to-dust conversion factor. We also present gas-phase metallicity estimates in this source, both using far-infrared fine-structure lines together with radio free-free continuum emission and independently employing the optical [O III] 5007 Å and [O II] 3727 Å lines (R₂₃ method). Both methods agree on a subsolar gas-phase metallicity of ∼ 0.3 Z_☉. Intriguingly, comparing the molecular-gas mass estimated using this subsolar metallicity, M_gas ∼ 6.4 x 10¹⁰ M_☉, to dust-mass estimates from multicomponent spectral energy distribution modeling, M_dust ∼ 1.4 x 10⁸ M_☉, yields a gas-to-dust ratio within ∼ 15% of the accepted value for a metallicity of 0.3 Z_☉. The derived gas mass puts 3C 368 on a par with other galaxies at z ∼ 1 in terms of specific star formation rate and gas fraction. However, it does not explain how a galaxy can amass such a large stellar population while maintaining such a low gas-phase metallicity. Perhaps 3C 368 has recently undergone a merger, accreting pristine molecular gas from an external source.