AAS 201st Meeting, January, 2003
Session 128. Galaxy Evolution and Surveys" ``Nearby"
Oral, Thursday, January 9, 2003, 10:00-11:30am, 602-604

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

R. F. Minchin, M. J. Disney (Cardiff University), P. J. Boyce (University of Bristol), G. D. Banks, W. J. G. de Blok (Cardiff University), Q. A. Parker (Macquarie University), HIDEEP Team

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.

The author(s) of this abstract have provided an email address for comments about the abstract: Robert.Minchin@astro.cf.ac.uk

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