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We present a systematic study of the extraplanar gas (EPG) in a sample of 15nearby late-type galaxies at intermediate inclinations using publiclyavailable, deep interferometric HI data from the HALOGAS survey. For eachsystem we mask the HI emission coming from the regularly rotating disc and usesynthetic datacubes to model the leftover "anomalous" HI flux. Our modelconsists of a smooth, axisymmetric thick component described by 3 structuraland 4 kinematical parameters, which are fit to the data via a Bayesian MCMCapproach. We find that extraplanar HI is nearly ubiquitous in disc galaxies, aswe fail to detect it in only two of the systems with the poorest spatialresolution. The EPG component encloses ~5-25% of the total HI mass, with a meanvalue of 14%, and has a typical thickness of a few kpc, incompatible withexpectations based on hydrostatic equilibrium models. The EPG kinematics isremarkably similar throughout the sample, and consists of a lagging rotationwith typical vertical gradients of about -10 km/s/kpc, a velocity dispersion of15-30 km/s and, for most galaxies, a global inflow in both the vertical andradial directions with speeds of 20-30 km/s. The EPG HI masses are in excellentagreement with predictions from simple models of the galactic fountain poweredby stellar feedback. The combined effect of photo-ionisation and interaction ofthe fountain material with the circumgalactic medium can qualitatively explainthe kinematics of the EPG, but dynamical models of the galactic fountain arerequired to fully test this framework.

HALOGAS: the properties of extraplanar HI in disc galaxies