A multiwavelength study of a massive, active galaxy at z ∼ 2: coupling the kinematics of the ionized and molecular gas

We report a multiwavelength study of the massive (M_{\star } ≳ 10^{11} {M}_{\odot }), z ∼ 2 star-forming galaxy GMASS 0953, which hosts an obscured AGN. We combined near-infrared observations of the GNIRS, SINFONI and KMOS spectrographs to study the kinematics of the [O III] λ5007 and H α emission lines. Our analysis shows that GMASS 0953 may host an ionized disc extending up to 13 kpc, which rotates at a velocity of V_{ion} = 203^{+17}_{-20} km s^-1 at the outermost radius. Evidence of rotation on a smaller scale (R ∼ 1 kpc) arises from the CO(J = 6-5) line. The central velocity V_{CO} = 320^{+ 92}_{-53} km s^-1 traced by the molecular gas is higher than V_ion, suggesting that the galaxy harbours a multiphase disc with a rotation curve that peaks in the very central regions. The galaxy appears well located on the z = 0 baryonic Tully-Fisher relation. We also discuss the possibility that the [O III] λ5007 and H α velocity gradients are due to a galactic-scale wind. Besides, we found evidence of an AGN-driven outflow traced by a broad blueshifted wing affecting the [O III] λ5007 line, which presents a velocity offset Δv = -535 ± 152 km s^-1 from the systemic velocity. Because of the short depletion time-scale (τ_dep ∼ 10⁸ yr) due to gas ejection and gas consumption by star formation activity, GMASS 0953 may likely evolve into a passive galaxy. However, the role of the AGN in depleting the gas reservoir of the galaxy is quite unclear because of the uncertainties affecting the outflow rate.