HI disks in nearby galaxies from the HALOGAS survey

The  HALOGAS  (Hydrogen  Accretion  in  LOcal  GAlaxieS)  survey  with the Westerbork  Synthesis  Radio  Telescope  is  the  most  sensitive  systematic survey of the diffuse neutral hydrogen component in nearby spiral galaxies so far.  The  5-sigma  column  density  sensitivity  reached for the sample of 22 galaxies is ~10^19 atoms cm^-2 over the typical line width of the neutral gas in our target galaxies. The 3D observations are sensitive enough to perform detailed  kinematical  and  dynamical  analyses  of  the  extended  (vertical)  disk structure of our targets. Additionally, we are able to provide a census of the complete  cold  neutral  cloud  population  above  the  mass  detection  limit  for individual objects of 10^5 solar masses on average. Our results are relevant in the context of theories describing star formation feedback on the gaseous interface of the galaxy disks with their surroundings, as well as gas accretion from  the  intergalactic  medium.  Most  notably,  we  find  that  the  presence  of anomalous,  slowly  rotating  extraplanar  gas  is  related  to  the  star  formation surface density. I will present the consequences of our observations for the current accretion in local galaxies, and discuss the implied constraints on the accretion process more generally.