Gas rotation, shocks and outflow within the inner 3 kpc of the radio galaxy 3C 33

Abstract

We present optical integral field spectroscopy – obtained with the Gemini Multi-Object Spectrograph – of the inner 4.0 × 5.8 kpc2 of the narrow line radio galaxy 3C 33 at a spatial resolution of 0.58 kpc. The gas emission shows three brightest structures: a strong knot of nuclear emission and two other knots at ≈1.4 kpc south-west and north-east of the nucleus along the ionization axis. We detect two kinematic components in the emission lines profiles, with a ‘broader component’ (with velocity dispersion σ ≥ 150 km s−1 ) being dominant within an 1 kpc wide strip (‘the nuclear strip’) running from the south-east to the north-west, perpendicular to the radio jet, and a narrower component (σ ≤ 100 km s−1 ) dominating elsewhere. Centroid velocity maps reveal a rotation pattern with velocity amplitudes reaching ± 350 km s−1 in the region dominated by the narrow component, while residual blueshifts and redshifts relative to rotation are observed in the nuclear strip, where we also observe the highest values of the [NII]/Hα, [SII]/Hα and [O I]/Hα line ratios, and an increase of the gas temperature (18 000 K), velocity dispersion and electron density (500 cm−3 ). We interpret these residuals and increased line ratios as due to a lateral expansion of the ambient gas in the nuclear strip due to shocks produced by the passage of the radio jet. The effect of this expansion in the surrounding medium is very small, as its estimated kinetic power represents only 2.6 × 10−5 − 3.0 × 10−5 of the AGN bolometric luminosity. A possible signature of inflow is revealed by an increase in the [O I]/Hα ratio values and velocity dispersions in the shape of two spiral arms extending to 2.3 kpc north-east and south-west from the nucleus.