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Galaxies in the local Universe are thought to require ongoing replenishmentof their gas reservoir in order to maintain the observed star formation rates.Cosmological simulations predict that such accretion can occur in both adynamically hot and cold mode. However, until now observational evidence of theaccretion required to match the observed star formation histories is lacking.This paper attempts to determine whether galaxies in the local Universe possessa significant reservoir of HI and what would be the accretion rates derivedfrom such reservoirs. We search the vicinity of 22 nearby galaxies for isolatedHI clouds or distinct streams in a systematic and automated manner. The HALOGASobservations represent one of the most sensitive and detailed HI surveys todate. These observations typically reach column density sensitivities of 10^19cm^-2 over a 20 km/s width. We find 14 secure HI cloud candidates without anobserved optical counterpart. These cloud candidates appear to be analogues tothe most massive clouds detected around the Milky Way and M31. However, onaverage their numbers seem significantly reduced. We constrain upper limits forHI accretion in the local Universe. The average HI mass currently observedamounts to a rate of 0.05 Msun/yr with a stringent upper limit of 0.22 Msun/yr,confirming previous estimates. This is much lower than the average starformation rate in this sample. Our best estimate, based on GBT detection limitsof several galaxies, suggests that another 0.04 Msun/yr could be accreted fromundetected clouds and streams. These results show that in nearby galaxies HI isnot being accreted at the same rate as stars are currently being formed. Ourstudy can not exclude that other forms of gas accretion are at work. However,these observations also do not reveal extended neutral gas reservoirs aroundmost nearby spiral galaxies.

HALOGAS: Strong Constraints on the Neutral Gas Reservoir and Accretion Rate in Nearby Spiral Galaxies