Observations of feedback from radio-quiet quasars - I. Extents and morphologies of ionized gas nebulae

Black hole feedback - the strong interaction between the energy output of supermassive black holes and their surrounding environments - is routinely invoked to explain the absence of overly luminous galaxies, the black hole versus bulge correlations and the similarity of black hole accretion and star formation histories. Yet direct probes of this process in action are scarce and limited to small samples of active nuclei. In this paper, we present Gemini Integral Field Unit observations of the distribution of ionized gas around luminous, obscured, radio-quiet quasars at z similar to 0.5. We detect extended ionized gas nebulae via [O III] lambda 5007 angstrom emission in every case, with a mean diameter of 28 kpc. These nebulae are nearly perfectly round, with H beta surface brightness declining proportional to R-3.5 +/- (1.0). The regular morphologies of nebulae around radio-quiet quasars are in striking contrast with lumpy or elongated [O III] nebulae seen around radio galaxies at low and high redshifts. We present the uniformly measured size-luminosity relationship of [O III] nebulae around Seyfert 2 galaxies and type 2 quasars spanning six orders of magnitude in luminosity and confirm the flat slope of the correlation (R-[O III] proportional to L-[O III](0.25+/-0.02)). We propose a model of clumpy nebulae in which clouds that produce line emission transition from being ionization-bounded at small distances from the quasar to being matter-bounded in the outer parts of the nebula. The model - which has a declining pressure profile - qualitatively explains line ratio profiles and surface brightness profiles seen in our sample. It is striking that we see such smooth and round large-scale gas nebulosities in this sample, which are inconsistent with illuminated merger debris and which we suggest may be the signature of accretion energy from the nucleus reaching gas at large scales.