HI Surveys with APERTIF

Abstract

Apertif, the innovative new Focal Plane Array for the Westerbork Synthesis Radio Telescope (WSRT), will significantly increase the instantaneous field-of-view and bandwidth of the WSRT between 1.0 and 1.75 GHz. Installing Apertif will tranform the WSRT into an effective survey telescope, enabling efficient northern-sky HI surveys as well as searches for pulsars and transients. In this contribution, we will describe a few strawman HI surveys to illustrate the possibilities. A shallow survey of the northern sky at δ > 30◦ will yield some 105 8σ detections. A similar number of detections can be expected from a medium-deep survey of part of the SLOAN area, reaching lower HI masses and lower column densities to study the extended HI disks and filaments. A deep survey of the Lockman Hole could yield 104 detections out to a reshift of z=0.4, probing the cosmic evolution of the gas content of galaxies in various environments.