2021MNRAS.503.4748R

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), W_eq(Na I D) - and dust - E(B - V) from both stars and gas. Our sample shows strong, significant correlations of total W_eq with E(B - V)_* 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 Å. The sample occupies regions in the space of N(Na I) and W_eq^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 ≳100 km s^–1 or have |v_ abs_ - v_ em_|≳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 W_eq(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.