MUSE 3D Spectroscopy and Kinematics of the gigahertz peaked spectrum Radio Galaxy PKS 1934-63: Interaction, Recently Triggered AGN and Star Formation

We observe the radio galaxy PKS 1934-63 (at \(z=0.1825\)) using MUSE (Multi Unit Spectroscopic Explorer) on the Very Large Telescope (VLT). The radio source is GigaHertz Peaked Spectrum and compact (0.13 kpc), implying an early stage of evolution (\(\leq 10^4\) yr). Our data show an interacting pair of galaxies, projected separation 9.1 kpc, velocity difference \(\Delta(v)=216\) km \(\rm s^{-1}\). The larger galaxy is a \(\rm M_{*}\simeq 10^{11}M_{\odot}\) spheroidal with the emission-line spectrum of a high-excitation young radio AGN, e.g. strong [OI]6300 and [OIII]5007. Emission-line ratios indicate a large contribution to the line luminosity from high-velocity shocks (\(\simeq 550\) km \(\rm s^{-1}\)) . The companion is a non-AGN disk galaxy, with extended \(\rm H\alpha\) emission from which its star-formation rate is estimated as \(\rm 0.61~M_{\odot}yr^{-1}\). Both galaxies show rotational velocity gradients in \(\rm H\alpha\) and other lines, with the interaction being prograde-prograde. The SE-NW velocity gradient of the AGN host is misaligned from the E-W radio axis, but aligned with a previously discovered central ultraviolet source, and a factor 2 greater in amplitude in \(\rm H\alpha\) than in other (forbidden) lines (e.g. [OIII]5007). This could be produced by a fast rotating (100-150 km \(\rm s^{-1}\)) disk with circumnuclear star-formation. We also identify a broad component of [OIII]5007 emission, blueshifted with a velocity gradient aligned with the radio jets, and associated with outflow. However, the broad component of [OI]6300 is redshifted. In spectral fits, both galaxies have old stellar populations plus \(\sim 0.1\%\) of very young stars, consistent with the galaxies undergoing first perigalacticon, triggering infall and star-formation from \(\sim 40\) Myr ago followed by the radio outburst.