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2003A&A...406..829B - Astronomy and Astrophysics, volume 406, 829-846 (2003/8-2)

The WSRT wide-field HI survey. I. The background galaxy sample.

BRAUN R., THILKER D. and WALTERBOS R.A.M.

Abstract (from CDS):

We have used the Westerbork array to carry out an unbiased wide-field survey for HI emission features, achieving an rms sensitivity of about 18mJy/Beam at a velocity resolution of 17km/s over 1800deg2 and between -1000<VHel<+6500km/s. The primary data consists of auto-correlation spectra with an effective angular resolution of 49' FWHM, although cross-correlation data were also acquired. The survey region is centered approximately on the position of Messier 31 and is Nyquist-sampled over 60x30° in RAxDec. More than 100 distinct features are detected at high significance in each of the two velocity regimes (negative and positive LGSR velocities). In this paper we present the results for our HI detections of external galaxies at positive LGSR velocity. We detect 155 external galaxies in excess of 8σ in integrated HI flux density. Plausible optical associations are found within a 30' search radius for all but one of our HI detections in DSS images, although several are not previously cataloged or do not have published red-shift determinations. Our detection without a DSS association is at low galactic latitude. Twenty-three of our objects are detected in HI for the first time. We classify almost half of our detections as confused'', since one or more companions is cataloged within a radius of 30' and a velocity interval of 400km/s. We identify a handful of instances of significant positional offsets exceeding 10kpc of unconfused optical galaxies with the associated HI centroid, possibly indicative of severe tidal distortions or uncataloged gas-rich companions. A possible trend is found for an excess of detected HI flux in unconfused galaxies within our large survey beam relative to that detected previously in smaller telescope beams, both as function of increasing distance and increasing gas mass. This may be an indication for a diffuse gaseous component on 100kpc scales in the environment of massive galaxies or a population of uncataloged low mass companions. We use our galaxy sample to estimate the HI mass function from our survey volume. Good agreement is found with the HIPASS BGC results, but only after explicit correction for galaxy density variations with distance.

Journal keyword(s): galaxies: distances and redshifts - galaxies: evolution - galaxies: formation - galaxies: fundamental parameters - galaxies: luminosity function, mass function

VizieR on-line data: <Available at CDS (J/A+A/406/829): wsrtgals.dat>

Nomenclature: Table 1: [BTW2003] JHHMM+DDMM N=146.