The Quasar Feedback Survey: Ionised Outflows in type 2 QSOs with MUSE data

Abstract

We study ionised gas properties in a sample of 18 luminous (log L$_{\rm bol}\geq45$ erg/s) obscured QSOs at 0.085<z<0.2 observed with VLT/MUSE as part of the multi-wavelength Quasar Feedback Survey (QFeedS) and with VLA at low- and high-resolution data. We compare the outflow-related quantities with values reported in the literature and investigate possible correlations between the outflows and other properties of the ionised gas such as the electron density. We adopt a non-parametric approach to characterise the ionised gas kinematics, traced by the [O III]5007 emission line, and use $W_{80}$ measured from the unresolved nuclear spectra as a threshold to identify outflow-dominated spaxels. A qualitative comparison between the radio and the $W_{80}$ maps shows that, in general, the peak of the radio coincides with the peak of the $W_{80}$. The [O III]5007 is used as a proxy for the ionised gas mass, and the outflow-related properties are obtained in two different ways: the global, which uses flux-weighted velocities and radii; and the peak, relying on radial profiles. We correct the [O III]5007 flux for extinction using the Balmer decrement. We take advantage of the MUSE sensitivity and use the [Ar IV]4711,4740 doublet, only observable in the integrated r=1.5'' spectra, to measure the electron density in each galaxy. We obtain $500<n_{e}{\rm[ cm^{-3}]}<27700$, leading to 0.03$<\dot{M}_{\rm out}/{\rm (M_{\odot} yr^{-1})}<$4.17 and $39<\dot{E}_{\rm kin}/{\rm [erg/s]}<42$. Our results emphasise the importance of accurate n$_e$ determination, leading to a difference of ~1 dex in the outflow rates and kinetic powers. We observe a positive correlation between $n_e$ and $V_{\rm out}$, interpreted as compression of the gas at higher velocities. This correlation should be further investigated at other luminosity and redshift ranges, but it can inform future outflow simulation studies.