Interactions between large-scale radio structures and gas in a sample of optically selected type 2 quasars

Abstract

Context. The role of radio mode feedback in non radio-loud quasars needs to be explored in depth to determine its true importance. Its effects can be identified based on the evidence of interactions between the radio structures and the ambient ionised gas. Aims. We investigate this in a sample of 13 optically selected type-2 quasars (QSO2) at z <0.2 with Very Large Array (VLA) FIRST Survey radio detections. None are radio loud. The ranges of [OIII]λ5007 and monochromatic radio luminosities are log(L[OIII]/erg s−1)∼42.08-42.79 and log(P1.4 GHz/erg s−1 Hz−1) ∼30.08-31.76. All show complex optical morphologies, with signs of distortion across tens of kpc due to mergers/interactions. Methods. We have searched for evidence of interactions between the radio structures and the ionised gas by characterising and comparing their morphologies. The first is traced by narrow band Hα images obtained with the GTC 10.4m Spanish telescope and the Osiris instrument. The second is traced by VLA radio maps obtained with A and B configurations to achieve both high resolution and brightness sensitivity. Results. The radio luminosity has an active galatic nucleus (AGN) component in 11/13 QSO2, which is spatially extended in our radio data in 9 of them (jets/lobes/other). The relative contribution of the extended radio emission to the total P1.4 GHz is in most cases in the range 30% to 90%. The maximum sizes are in the range dmax ∼few-500 kpc. QSO2 undergoing interaction/merger events appear to be invariably associated with ionised gas spread over large spatial scales with maximum distances from the AGN in the range rmax ∼12-90 kpc. The morphology of the ionised gas at <30 kpc is strongly influenced by AGN related processes. Evidence for radio-gas interactions exist in 10/13 QSO2; that is, all but one with confirmed AGN radio components. The interactions are identified across different spatial scales, from the nuclear narrow line region up to tens of kpc. Conclusions. Although this sample cannot be considered representative of the general population of QSO2, it supports the idea that large scale low/modest power radio sources can exist in radio-quiet QSO2, which can provide a source of feedback on scales of the spheroidal component of galaxies and well into the circumgalactic medium, in systems where radiative mode feedback is expected to dominate.