Properties of galaxies found in a deep multibeam survey for extragalactic neutral hydrogen: HIDEEP

We have carried out a deep 21-cm blind survey of a 4 by 8 degree region in Centaurus using the Parkes multibeam system. The noise continues to fall as the square-root of the integration time throughout, making this the deepest such survey to date, reaching a potential neutral hydrogen (HI) column-density limit of 0.03 solar masses per square parsec integrated over a velocity width of 200 km/s. We find 173 sources out to the bandpass limit of 12,700 km/s. The HI observations were accompanied by a deep optical survey on the UK Schmidt Telescope, stacking eight 1-hour R-band plates to reach an isophotal limit of 26.5 R mag per square arcsec. All the sources appear to have optical counterparts. The surface-brightness distribution is significantly different from that derived from the ESO-LV, containing significantly more galaxies at lower surface-brightnesses despite the peak of the distribution being in the same place. When a volumetric correction is made, the surface-brightness distribution is flat down to the end of the data at an effective R-band surface-brightness of 25 R mag per square arcsec. The bivariate brightness distribution in the surface-brightness - luminosity plane appears fairly uniform except that we find no giant low surface-brightness galaxies (such as Malin 1). There is indirect evidence, based on the optical radii, that there are no low column-density galaxies in the sample, despite our being sensitive to such systems. We estimate the contribution of gas-rich low surface-brightness galaxies to the global averages as a percentage of the contribution of all gas-rich galaxies. This gives us the result that low surface-brightness galaxies contribute 8.3 +/- 4.7% of the light, 15 +/- 9% of the baryon density, 25 +/- 15% of the dynamical mass-density and 30 +/- 17% of the neutral hydrogen density.