We present detections of the CO ( 4-3 ) and [ C i ] 609 \micron 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 , \sim 3.6 \times 10 ^ { 11 } M _ { \odot } , and is undergoing an episode of vigorous star formation , at a rate of \sim 350 M _ { \odot } yr ^ { -1 } , and active galactic nucleus ( AGN ) activity , with radio-emitting lobes extended over \sim 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 \alpha _ { 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 ( FIR ) 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 ( R _ { 23 } method ) .
Both methods agree on a sub-solar gas-phase metallicity of \sim 0.3 Z _ { \odot } .
Intriguingly , comparing the molecular-gas mass estimated using this sub-solar metallicity , M _ { gas } \sim 6.4 \times 10 ^ { 10 } M _ { \odot } , to dust-mass estimates from multi-component spectral energy distribution ( SED ) modeling , M _ { dust } \sim 1.4 \times 10 ^ { 8 } M _ { \odot } , yields a gas-to-dust ratio within \sim 15 % of the accepted value for a metallicity of 0.3 Z _ { \odot } .
The derived gas mass puts 3C 368 on par with other galaxies at z \sim 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 .