Not So Windy After All: MUSE Disentangles AGN-driven Winds from Merger-induced Flows in Galaxies along the Starburst Sequence

Abstract

Poststarburst galaxies are believed to be in a rapid transition between major merger starbursts and quiescent ellipticals, where active galactic nucleus (AGN) feedback is suggested as one of the processes responsible for the quenching. To study the role of AGN feedback, we constructed a sample of poststarburst candidates with AGN and indications of ionized outflows in optical. We use MUSE/VLT observations to spatially resolve the properties of the stars and multiphase gas in five of them. All galaxies show signatures of interaction/merger in their stellar or gas properties, with some at an early stage of interaction with companions ∼50 kpc, suggesting that optical poststarburst signatures may be present well before the final starburst and coalescence. We detect narrow and broad kinematic components in multiple transitions in all the galaxies. Our detailed analysis of their kinematics and morphology suggests that, contrary to our expectation, the properties of the broad kinematic components are inconsistent with AGN-driven winds in three out of five galaxies. The two exceptions are also the only galaxies in which spatially resolved NaID P-Cygni profiles are detected. In some cases, the observations are more consistent with interaction-induced galactic-scale flows, an often overlooked process. These observations raise the question of how to interpret broad kinematic components in interacting and perhaps also in active galaxies, in particular when spatially resolved observations are not available or cannot rule out merger-induced galactic-scale motions. We suggest that NaID P-Cygni profiles are more effective outflow tracers, and use them to estimate the energy that is carried by the outflow.