2013MNRAS.435.3376H

An analysis of 44GHz Very Large Array observations of the z = 1.574 radio-loud quasar 3C 318 has revealed emission from the redshifted J = 1 ⟶ 0 transition of the CO molecule and spatially resolved the 6.3kpc radio jet associated with the quasar at 115GHz rest frame. The continuum-subtracted line emitter is spatially offset from the quasar nucleus by 0.33arcsec (2.82kpc in projection). This spatial offset has a significance of >8σ and, together with a previously published -400km/s velocity offset measured in the J = 2 ⟶ 1 CO line relative to the systemic redshift of the quasar, rules out a circumnuclear starburst or molecular gas ring and suggests that the quasar host galaxy is either undergoing a major merger with a gas-rich galaxy or is otherwise a highly disrupted system. If the merger scenario is correct, then the event may be in its early stages, acting as the trigger for both the young radio jets in the quasar and a starburst in the merging galaxy. The total molecular gas mass in the spatially offset line emitter as measured from the ground-state CO line MH2 = 3.7 (±0.4)x10¹⁰ (αCO/0.8)M_☉. Assuming that the line emitter can be modelled as a rotating disc, an inclination-dependent upper limit is derived for its dynamical mass Mdyn sin2(i) < 3.2x10⁹M_☉, suggesting that for MH2 to remain less than Mdyn the inclination angle must be i < 16°. The far-infrared and CO luminosities of 246 extragalactic systems are collated from the literature for comparison. The high molecular gas content of 3C 318 is consistent with that of the general population of high-redshift quasars and submillimetre galaxies.