Fan Beam Observations of Bright Galaxies at 408 MHz

The fan-beam of the east–west arm of the cross-type radio telescope at the Molonglo Radio Observatory has been used to observe 143 galaxies at a frequency of 408 MHz in declination range $+{18}^{\circ}\,\text{to}\,-{90}^{\circ}$. These represent a sufficiently complete sample of galaxies to a limiting optical magnitude of $\sim\,11.0$ when corrected for Galactic absorption and internal absorption due to the tilt of the emitting galaxy. Of these, 54 were detected down to a limiting flux of 0.4 f.u. at which level the probability of a misidentification is 12 per cent. The galaxies have been examined for correlations between radio and optical properties such as dependence on galaxy type in the Hubble, Morgan (Yerkes) and Van den Bergh (DDO) classification schemes. In the Hubble classification the highest proportion of detected galaxies are of type She and Sc while only a low proportion of SO/a, Sa and Sab galaxies were detected. There is a large dispersion in the radio index for a given Hubble type. A correlation has been established between the radio index of a galaxy and the degree of central concentration of light in the galaxy, which is the basis of the Morgan classification. Absolute radio magnitudes have been determined for the detected galaxies and it is shown that this absolute radio magnitude correlates with the Van den Bergh galaxy type.