The spatially resolved gas and dust connection in neutral inflows and outflows in nearby AGN

Dusty, neutral outflows and inflows are a common feature of nearby star-forming galaxies. We characterize these flows in eight galaxies - mostly active galactic nuclei (AGN) - selected for their widespread Na i D signatures from the Siding Spring Southern Seyfert Spectroscopic Snapshot Survey (S7). This survey employs deep, wide field-of-view (FOV) integral field spectroscopy at moderate spectral resolution (R = 7000 at Na i D). We significantly expand the sample of sightlines in external galaxies in which the spatially resolved relationship has been studied between cool, neutral gas properties - N(Na i), Weq(Na i D) - and dust - E(B - V) from both stars and gas. Our sample shows strong, significant correlations of total Weq with E(B - V)pdbl and g - i colour within individual galaxies; correlations with E(B - V)gas are present but weaker. Regressions yield slope variations from galaxy to galaxy and intrinsic scatter ∼1 A. The sample occupies regions in the space of N(Na i) and $W_\mathrm{eq}\mathrm{abs}$ versus E(B - V)gas that are consistent with extrapolations from other studies to higher colour excess [E(B - V)gas ∼1]. For perhaps the first time in external galaxies, we detect inverse P Cygni profiles in the Na i D line, presumably due to inflowing gas. Via Doppler-shifted Na i D absorption and emission lines, we find ubiquitous flows that differ from stellar rotation by $\gtrsim$100 km s-1 or have $|v-{\mathrm{ abs}} - v-{\mathrm{ em}}|\gtrsim 100$ km s-1. Inflows and outflows extend towards the edge of the detected stellar disc/FOV, together subtend 10-40 per cent of the projected disc, and have similar mean N(Na i) and Weq(Na i D). Outflows are consistent with minor axis or jet-driven flows, while inflows tend towards the projected major axis. The inflows may result from non-axisymmetric potentials, tidal motions, or halo infall.