The H I Parkes All-Sky Survey (HIPASS) catalogue forms the largest uniform catalogue of H I sources compiled to date, with 4315 sources identified purely by their H I content. The catalogue data comprise the southern region δ < + 2 • of HIPASS, the first blind H I survey to cover the entire southern sky. The rms noise for this survey is 13 mJy beam −1 and the velocity range is −1280 to 12 700 km s −1 . Data search, verification and parametrization methods are discussed along with a description of measured quantities. Full catalogue data are made available to the astronomical community including positions, velocities, velocity widths, integrated fluxes and peak flux densities. Also available are on-sky moment maps, position-velocity moment maps and spectra of catalogue sources. A number of local large-scale features are observed in the space distribution of sources, including the super-Galactic plane and the Local Void. Notably, large-scale structure is seen at low Galactic latitudes, a region normally obscured at optical wavelengths.

Many of the results in modern astrophysics rest on the notion that the Initial Mass Function (IMF) is universal. Our observations of a sample of H I selected galaxies in the light of Hα and the far-ultraviolet (FUV) challenge this result. The extinction corrected flux ratio F Hα / f FUV from these two tracers of star formation shows strong correlations with the surface-brightness in Hα and the R band: Low Surface Brightness (LSB) galaxies have lower F Hα / f FUV ratios compared to High Surface Brightness (HSB) galaxies as well as compared to expectations from equilibrium models of constant star formation rate (SFR) using commonly favored IMF parameters. Weaker but significant correlations of F Hα / f FUV with luminosity, rotational velocity and dynamical mass are found as well as a systematic trend with morphology. The correlated variations of F Hα / f FUV with other global parameters are thus part of the larger family of galaxy scaling relations. The F Hα / f FUV correlations can not be due to residual extinction correction errors, while systematic variations in the star formation history can not explain the trends with both Hα and R surface brightness nor with other global properties. The possibility that LSB galaxies have a higher escape fraction of ionizing photons seems inconsistent with their high gas fraction, and observations of color-magnitude diagrams of a few systems which indicate a real deficit of O stars. The most plausible explanation for the correlations is the systematic variations of the upper mass limit M u and/or the slope γ which define the upper end of the IMF. We outline a scenario of pressure driving the correlations by setting the efficiency of the formation of the dense star clusters where the highest mass stars preferentially form. Our results imply that the star formation rate measured in a galaxy is highly sensitive to the tracer used in the measurement. A non-universal IMF would also call into question interpretation of metal abundance patterns in dwarf galaxies as well star formation histories derived from color magnitude diagrams.

We present the HIPASS Bright Galaxy Catalog (BGC), which contains the 1000 H i brightest galaxies in the southern sky as obtained from the H i Parkes All-Sky Survey (HIPASS). The selection of the brightest sources is based on their H i peak flux density (S peak k116 mJy) as measured from the spatially integrated HIPASS spectrum. The derived H i masses range from $10 7 to 4 ; 10 10 M . While the BGC (z < 0:03) is complete in S peak , only a subset of $500 sources can be considered complete in integrated H i flux density (F H i k 25 Jy km s À1 ). The HIPASS BGC contains a total of 158 new redshifts. These belong to 91 new sources for which no optical or infrared counterparts have previously been cataloged, an additional 51 galaxies for which no redshifts were previously known, and 16 galaxies for which the cataloged optical velocities disagree. Of the 91 newly cataloged BGC sources, only four are definite H i clouds: while three are likely Magellanic debris with velocities around 400 km s À1 , one is a tidal cloud associated with the NGC 2442 galaxy group. The remaining 87 new BGC sources, the majority of which lie in the zone of avoidance, appear to be galaxies. We identified optical counterparts to all but one of the 30 new galaxies at Galactic latitudes jbj > 10 . Therefore, the BGC yields no evidence for a population of ''free-floating'' intergalactic H i clouds without associated optical counterparts. HIPASS provides a clear view of the local large-scale structure. The dominant features in the sky distribution of the BGC are the Supergalactic Plane and the Local Void. In addition, one can clearly see the Centaurus Wall, which connects via the Hydra and Antlia Clusters to the Puppis Filament. Some previously hardly noticable galaxy groups stand out quite distinctly in the H i sky distribution. Several new structures, including some not behind the Milky Way, are seen for the first time.

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We present a new accurate measurement of the H I mass function of galaxies from the HIPASS Bright Galaxy Catalog, a sample of 1000 galaxies with the highest H I peak flux densities in the southern (δ < 0 • ) hemisphere (Koribalski et al. 2003). This sample spans nearly four orders of magnitude in H I mass (from log(M HI ⁄ M ⊙ ) + 2 log h 75 = 6.8 to 10.6) and is the largest sample of H I selected galaxies to date. We develop a bivariate maximum likelihood technique to measure the space density of galaxies, and show that this is a robust method, insensitive to the effects of large scale structure. The resulting H I mass function can be fitted satisfactorily with a Schechter function with faint-end slope α = −1.30. This slope is found to be dependent on morphological type, with later type galaxies giving steeper slopes. We extensively test various effects that potentially bias the determination of the H I mass function, including peculiar motions of galaxies, large scale structure, selection bias, and inclination effects, and quantify these biases. The large sample of galaxies enables an accurate measurement of the cosmological mass density of neutral gas: Ω HI = (3.8 ± 0.6) × 10 −4 h −1 75 . Low surface brightness galaxies contribute only ∼ 15% to this value, consistent with previous findings.