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Telescope Parameters and Search Strategy

Galaxies Detected by the Dwingeloo Obscured Galaxies Survey

A. J. Rivers , P. A. Henning , R.C. Kraan-Korteweg ,, PASA, 16 (1), in press.
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Telescope Parameters and Search Strategy

The 25-m Dwingeloo telescope operating at 21-cm has a half-power-beamwidth (HPBW) of 0$^{\circ}\!\!$.6 which may be thought of as the survey resolution. A DAS-1000 channel autocorrelator spectrometer is utilized in the telescope backend; the rms noise per channel is typically $\sigma_{ch}$=40 mJy for a 1 hr integration.

Figure 2: Distribution of survey grid points. Galactic longitude spacing is

$\Delta \ell =0^{\circ}\!\!.4$ while the successive rows of constant Galactic latitude are separated by

$\Delta b=0^{\circ}\!\!.35$. Each grid point is marked with a + surrounded by a circle indicating the HPBW of

$0^{\circ}\!\!.6$.
\begin{figure} \centerline{\psfig{file=grid.eps,height=3.cm,width=10cm}}\end{figure}

Each DOGS observation consists of a sequence of 5 contiguous pointings at constant Galactic latitude (figure 2). Five On-Off pairs created from the sequence ensure that a real galaxy will appear twice, once as a positive signal, and again as a negative one, referenced against two independent scans. Overlapping the constant latitude grids to form a honeycombed coverage of the sky allows for detection of galaxies in adjacent pointings and facilitates a more accurate determination of their positions. A similar observing strategy was employed during the Westerbork portion of the survey; beam size and velocity coverage were identical and a similar survey sensitivity achieved. A 15 pointing grid was used for efficiency reasons, but the core On-Off pair strategy remained the same. The complete survey incorporates approximately 15,000 partially overlapping pointings.

Next Section: Results
Title/Abstract Page: Galaxies Detected by the
Previous Section: Introduction
Contents Page: Volume 16, Number 1

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