Fitting Parameters

Being the Northern shallow H i survey with a wide field radio telescope, wnshs will work closely together with it complementary Southern survey wallaby. Many of the science drivers are identical, and wnshs and wallaby will make a maximum use of the obvious synergies to make both surveys an outstanding success and to finally provide one all-sky H i survey accessible to the public.

To provide this accessibility involves an effort on various levels. Together with the Apertif team, wnshs will be actively engaged in the production of high-quality low-level data products (i.e. data cubes) and higher level data products (catalogues, moment maps, ...). wnshs aims at defining and exploring the science the survey will make possible and at delivering the necessary scientific data analysis software.

To provide a physical proximity to Apertif, the survey is coordinated from ASTRON. wnshs is in the course of defining working groups focusing on the various technical- and scientific aspects of the survey, largely orientating on the structure of wallaby. While we expect a large overlap of the wnshs and wallaby working groups, wnshs will concentrate the group coordination towards the Northern hemisphere. A close collaboration of wnshs and wallaby working groups will enable us to maximise the output of both efforts in the Northern and Southern hemisphere.

wnshs is currently in the phase of being structured, and defining its prime science targets.

wallaby will cover the sky at declinations -90° ≥; δ ≥ 30°. To provide a good alignment of both surveys, an overlap of 1 Apertif field-of-view is required. wnshs will hence observe the complete sky with declinations of 27° ≥ δ ≥ 90°.

To mosaic this area (11262 square degrees), ~1410 pointings are required. With the smallest provided frequency resolution and the full bandwidth (frequency range 1130-1430 MHz, divided into 16384 channels, corresponding to ~4 km s^-1 velocity resolution), a full match of wnshs and wallaby is achieved.

An integration time of 4 h per pointing, resulting in a line sensitivity of 0.64 mJy beam^-1 (at 30″ resolution) and 0.53 mJy beam^-1 (at 13″ resolution) per 100 kHz (5.5 channels) would provide a match of wnshs and wallaby in sensitivity, and requires a total on-source survey time of 5,630 h. The currently favoured strategy, however, is to integrate for a full WSRT synthesis (i.e., 12 h per pointing). The enhancement of the survey sensitivity (0.37 and 0.31  mJy beam^-1 100 kHz at 30″ and 13″ resolution, respectively) by a factor of 1.7 opens new research windows and leads to a significant increase in the science- and legacy output of the survey. The required on-source survey time in this mode is 16,900 h.

The standard WSRT maxi-short configuration has been proven in many H i observations to be the best telescope configuration for our aims.

The following table summarises the technical characteristics of wnshs: