Neutral versus ionized gas kinematics at z similar or equal to 2.6 : the AGN-host starburst galaxy PKS 0529-549

We present a multiwavelength study of the AGN-host starburst galaxy PKS 0529-549 at z similar or equal to 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 [OIII] 5007 angstrom line, tracing ionized gas, and (3) ATCA radio continuum images, tracing synchrotron emission. Both [CI] and [O III] show regular velocity gradients, but their systemic velocities and position angles differ by similar to 300 km s(-1) and similar to 30 degrees, respectively. The [CI] is consistent with a rotating disc, aligned with the dust and stellar continuum, while the [OIII] likely traces an outflow, aligned with two AGN-driven radio lobes. We model the [CI] cube using 3D disc models, which give best-fitting rotation velocities V-rot similar or equal to 310 km s(-1) and velocity dispersions sigma(V) less than or similar to 30 km s(-1). Hence, the [CI] disc has V-rot/sigma(V) greater than or similar to 10 and is not particularly turbulent, similar to local galaxy discs. The dynamical mass (similar to 10(11) M-circle dot) is comparable to the baryonic mass within the errors. This suggests that baryons dominate the inner galaxy dynamics, similar to massive galaxies at z similar or equal to 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 similar or equal to 2.6. This work highlights the potential of the [CI] line to trace galaxy dynamics at high z, as well as the importance of multiwavelength data to interpret gas kinematics.