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${}_{\mathrm{bol}}\ge 45$ 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 $500<n_e[\mathrm{c}{\mathrm{m}}^{-3}]<27700$, leading to 0.03$<{\dot{M}}_{\mathrm{out}}/({\mathrm{M}}_{\odot }\mathrm{y}{\mathrm{r}}^{-1})<$4.17 and $39<{\dot{E}}_{\mathrm{kin}}/[erg/s]<42$. 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 $V_{\mathrm{out}}$, 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.

23 pages, 23 figures (16 on the appendix), submitted to A&A