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.

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A blind survey for H I bright galaxies in the southern Zone of Avoidance, (212 • ≤ ℓ ≤ 36 • , |b| ≤ 5 • ), has been made with the 21 cm multibeam receiver on the Parkes 64 m radiotelescope. The survey, sensitive to normal spiral galaxies to a distance of ∼ 40 Mpc and more nearby dwarfs, detected 110 galaxies. Of these, 67 have no counterparts cataloged in the NASA/IPAC Extragalactic Database. In general, the uncataloged galaxies lie behind thicker obscuration than do the cataloged objects. All of the newly-discovered galaxies have H I flux integrals more than an order of magnitude lower than the Circinus galaxy. The survey recovers the Puppis cluster and foreground group (Kraan-Korteweg & Huchtmeier 1992), and the Local Void remains empty. The H I mass function derived for the sample is satisfactorily fit by a Schechter function with parameters α = 1.51 ± 0.12, Φ * = 0.006 ± 0.003, and log M * = 9.7 ± 0.10.

At low radio frequencies ( P 100 MHz), classical H ii regions may become optically thick (optical depth ! 1) and can be observed as discrete absorption regions against the Galactic nonthermal background emission created by Galactic cosmic-ray electrons spiraling around magnetic fields. However, the historically poor angular resolution (>30 0 ) of previous low-frequency surveys has limited such observations to the largest and nearest H ii regions. The significantly enhanced resolution and surface brightness sensitivity of the 74 MHz system on the Very Large Array now allow for the detection of absorption regions on scale sizes of just a few arcminutes that can be readily identified with many more H ii regions previously cataloged in emission at higher frequencies. These absorption measurements directly constrain the brightness temperature of the cosmic-ray synchrotron emission emanating from behind the H ii regions based on reasonable physical assumptions. Many such observations could be used to map out the threedimensional cosmic-ray emissivity in the Galaxy without resorting to a priori assumptions about Galactic structure. This measurement is unique to low-frequency radio astronomy. In this work we present 74 MHz observations in the region 26 > l > À15 , À5 < b < 5 ; report the detection of 92 absorption features associated with known H ii regions; and derive the brightness temperature of the Galactic cosmic-ray electron synchrotron emission emanating from the column behind these regions. For the 42 H ii regions with known distances, the average emissivity of the column behind the H ii region is derived. The 74 MHz emissivity values range between 0.3 and 1.0 K pc À1 for a model assuming uniform distribution of emissivity. Methods for using this type of data to model the three-dimensional distribution of cosmic-ray emissivity and the possibility of using this method to break the H ii region kinematic distance degeneracy are discussed.

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