2D stellar population and gas kinematics of the inner 1.5 kpc of the post-starburst quasar SDSS J0210−0903

Abstract

Post-starburst quasars (PSQs) are hypothesized to represent a stage in the evolution of massive galaxies in which the star formation has been recently quenched due to the feedback of the nuclear activity. In this paper, our goal is to test this scenario with a resolved stellar population study of the PSQ J0210−0903, as well as of its emitting gas kinematics and excitation. We have used optical integral field spectroscopy obtained with the Gemini Multi-Object Spectrograph instrument at a velocity resolution of ≈120 km s-ˡ and a spatial resolution of ≈0.5 kpc. We find that old stars dominate the luminosity (at 4700 Å) in the inner 0.3 kpc (radius), while beyond this region (at ≈0.8 kpc) the stellar population is dominated by both intermediate-age and young ionizing stars. The gas emission-line ratios are typical of Seyfert nuclei in the inner 0.3 kpc, where an outflow is observed. Beyond this region, the line ratios are typical of low-ionization nuclear emission-line regions and may result from the combination of diluted radiation from the nucleus and ionization from young stars. The gas kinematics show a combination of rotation in the plane of the galaxy and outflows, observed with a maximum blueshift of−670 km s-ˡ. We have estimated a mass outflowrate in ionized gas in the range 0.3–1.1Mʘ yr-ˡ and a kinetic power for the outflow of ˙Eout ≈ 1.4–5.0 × 1040 erg s-ˡ ≈ 0.03–0.1 per cent × Lbol. This outflow rate is two orders of magnitude higher than the nuclear accretion rate of ≈8.7 × 10−3Mʘ yr−1, thus being the result of mass loading of the nuclear outflow by circumnuclear galactic gas. Our observations support an evolutionary scenario in which the feeding of gas to the nuclear region has triggered a circumnuclear starburst 100 Myr ago, followed by the triggering of the nuclear activity, producing the observed gas outflow which may have quenched further star formation in the inner 0.3 kpc.