Neutral versus ionized gas kinematics at z~2.6: The AGN-host starburst galaxy PKS 0529-549
Résumé
We present a multiwavelength study of the AGN-host starburst galaxy PKS 0529-549 at |$z$| ≃ 2.6. We use (1) new ALMA observations of the dust continuum and of the [Ci] 370 |$\mu$|m line, tracing molecular gas, (2) SINFONI spectroscopy of the [O iii] 5007 Å line, tracing ionized gas, and (3) ATCA radio continuum images, tracing synchrotron emission. Both [C i] and [O iii] show regular velocity gradients, but their systemic velocities and position angles differ by ∼300|$\, \mathrm{km}\, \mathrm{s}^{-1}$| and ∼30°, respectively. The [C i] is consistent with a rotating disc, aligned with the dust and stellar continuum, while the [O iii] likely traces an outflow, aligned with two AGN-driven radio lobes. We model the [C i] cube using 3D disc models, which give best-fitting rotation velocities V_rot ≃ 310|$\, \mathrm{km}\, \mathrm{s}^{-1}$|and velocity dispersions σ_V ≲ 30|$\, \mathrm{km}\, \mathrm{s}^{-1}$|. Hence, the [C i] disc has V_rot/σ_V ≳10 and is not particularly turbulent, similar to local galaxy discs. The dynamical mass (∼10^11 M_⊙) is comparable to the baryonic mass within the errors. This suggests that baryons dominate the inner galaxy dynamics, similar to massive galaxies at |$z$| ≃ 0. Remarkably, PKS 0529-549 lies on the local baryonic Tully–Fisher relation, indicating that at least some massive galaxies are already in place and kinematically relaxed at |$z$| ≃ 2.6. This work highlights the potential of the [C i] line to trace galaxy dynamics at high |$z$|, as well as the importance of multiwavelength data to interpret gas kinematics.