Westerbork Northern Sky H i Survey

Westerbork Northern Sky H i Survey

This is the official web page of wnshs. Currently, it is designed to inform professional astronomers about wnshs, a proposed Neutral Hydrogen survey with the Dutch Westerbork Radio Synthesis Telescope (WSRT). For non-astronomers we therefore apologise for the very specific jargon, but we welcome every visitor of these pages.

A complete Northern-sky H i survey with Apertif

The Westerbork Northern Sky H i Survey (wnshs) is a Neutral Hydrogen (H i) survey of the Northern sky above a declination of δ ≥ 27°, covering the velocity range between -2000 km s-1 and 77.000 km s-1 (cz, corresponding to a redshift between 0 and 0.26 and hence to distances between 0 and 1 Gpc), proposed to be conducted with the Westerbork Radio Synthesis Telescope (WSRT) in The Netherlands.

It will make use of the Apertif phased-array feed (PAF) receiver system, which will be commissioned at the WSRT in 2013. With this instrument, it will become possible to map the Neutral Hydrogen line in the Northern sky with the spatial resolution (13″) and the sensitivity of a radio interferometer, but at the same time with an instantaneous field-of-view that allows to observe a large area (of 8 square degrees) on the sky in one single observation. The WSRT is hence being transformed into a radio telescope ideal for surveys of large areas on the sky.

To prepare for the new era in operating the WSRT, the Radio Observatory at ASTRON issued a Call for Expressions of Interest for Apertif surveys, requesting the international astronomical community to formulate their ideas of how the new capabilities of the WSRT can be used to generate a maximum scientific output of the instrument. WSNHS was submitted as one of 18 Expressions of Interest (EOIs).

With WSNHS we put forward the opinion that a complete Northern sky survey of the most abundant element in the interstellar- and intergalactic medium, covering distances from our immediate surroundings out to distances, at which we are overcoming the cosmic variance, should be part of the WSRT observing program in the Apertif era. With this legacy survey, new windows will be opened for the community to address science of highest relevance in the fields of galaxy evolution and cosmology. It will provide a census of the gaseous structure of the nearby universe, from the smallest gas concentrations within the Local Group around the Milky Way and the Andromeda Nebula with masses of 103 M, up to the most massive gaseous disks with masses of 5 · 1010 M at distances of up to 1 Gpc.

Together with its sister survey wallaby with the Australian Square Kilometre Array Pathfinder (ASKAP), wnshs will provide a public H i survey covering the complete sky and thus provide an invaluable legacy for the scientific community.

This web page is intended to briefly inform the reader about the science addressed by wnshs and the suggested technical layout.

wnshs is in the build-up phase. We are currently structuring the survey team and tying down main survey goals that directly influence the survey strategy and technical focuses. While we have formulated scientific cornerstones to be addressed by the survey, the number of those and the final scientific layout is not carved in stone (yet). Suggestions and critics are welcome. It is still possible for interested astronomers to join the wnshs team.