MUSE three-dimensional spectroscopy and kinematics of the gigahertz peaked spectrum radio galaxy PKS 1934-63: interaction, recently triggered active galactic nucleus and star formation

N. Roche, A. Humphrey, P. Lagos, P. Papaderos, M. F. Silva, L. S. M. Cardoso, J. M. Gomes

Abstract
We observe the radio galaxy PKS 1934-63 (at z = 0.1825) using the Multi-Unit Spectroscopic Explorer (MUSE) on the Very Large Telescope (VLT). The radio source is a gigahertz peaked spectrum source and is compact (0.13 kpc), implying an early stage of evolution (≤10⁴ yr). Our data show an interacting pair of galaxies, with projected separation 9.1 kpc and velocity difference Δ(v) = 216 km s^-1. The larger galaxy is a M_* ≃ 10¹¹ M_☉ spheroidal with the emission-line spectrum of a high-excitation young radio active galactic nucleus (AGN; e.g. strong [O I]6300 and [O III]5007). Emission-line ratios indicate a large contribution to the line luminosity from high-velocity shocks (≃ 550 km s^-1). The companion is a non-AGN disc galaxy, with extended Hα emission from which its star formation rate is estimated as 0.61 M_☉ yr^-1. Both galaxies show rotational velocity gradients in Hα 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 of 2 greater in amplitude in Hα than in other (forbidden) lines (e.g. [O III]5007). This could be produced by a fast rotating (100-150 km s^-1) disc with circumnuclear star formation. We also identify a broad component of [O III]5007 emission, blueshifted with a velocity gradient aligned with the radio jets, and associated with outflow. However, the broad component of [O I]6300 is redshifted. In spectral fits, both galaxies have old stellar populations plus ̃0.1 per cent of very young stars, consistent with the galaxies undergoing first perigalacticon, triggering infall and star formation from ̃40 Myr ago followed by the radio outburst.

Keywords
galaxies: active, galaxies: evolution, galaxies: individual: PKS 1934-63, galaxies: interactions, galaxies: kinematics and dynamics, quasars: emission lines

Monthly Notices of the Royal Astronomical Society
Volume 459, Page 4259
April 2016

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