We present a systematic study of the extraplanar gas ( EPG ) in a sample of 15 nearby late-type galaxies at intermediate inclinations using publicly available , deep interferometric H I data from the HALOGAS survey .
For each system we mask the H I emission coming from the regularly rotating disc and use synthetic datacubes to model the leftover ‘ anomalous ’ H I flux .
Our model consists of a smooth , axisymmetric thick component described by 3 structural and 4 kinematical parameters , which are fit to the data via a Bayesian MCMC approach .
We find that extraplanar H I is nearly ubiquitous in disc galaxies , as we fail to detect it in only two of the systems with the poorest spatial resolution .
The EPG component encloses \sim 5 - 25 \% of the total H I mass , with a mean value of 14 \% , and has a typical thickness of a few kpc , incompatible with expectations based on hydrostatic equilibrium models .
The EPG kinematics is remarkably similar throughout the sample , and consists of a lagging rotation with typical vertical gradients of \sim - 10 { km s } ^ { -1 } { { kpc } } ^ { -1 } , a velocity dispersion of 15 - 30 { km s } ^ { -1 } and , for most galaxies , a global inflow in both the vertical and radial directions with speeds of 20 - 30 { km s } ^ { -1 } .
The EPG H I masses are in excellent agreement with predictions from simple models of the galactic fountain powered by stellar feedback .
The combined effect of photo-ionisation and interaction of the fountain material with the circumgalactic medium can qualitatively explain the kinematics of the EPG , but dynamical models of the galactic fountain are required to fully test this framework .