The identification of IRAS point sources- I. A 304 deg2 field centred on the South Galactic Pole.

Identifications are given of IRAS point sources in a 304 deg² area centred on the South Galactic Pole. The positions and magnitudes of identification candidates were obtained using 10 UK Schmidt Telescope IIIa-J plates, which were measured by the automatic high-speed measuring machine, COSMOS, at the Royal Observatory, Edinburgh. We have determined the reliability of the proposed identifications using the criterion of the likelihood ratio. There are 312 IRAS point sources in this area of which 148 are identified with stars, 154 with galaxies and 10 are unidentified down to 21st magnitude. The statistical properties of the sample are discussed, with emphasis on the properties of the IRAS galaxies. The main results are: (a) our infrared selected sample, when compared to an optically selected (RSA) sample of galaxies detected by IRAS, contains more galaxies in the combined E/S0 class and relatively more early-type rather than late-type spirals; (b) the luminosity ratio L_IR/L_B correlates well with temperature, or flux density ratio (F₁₀₀/F60), over a range of 0.2 to 200 in L_IR/L_B, with the warmest galaxies having the highest luminosity ratios; (c) the average early-type spiral galaxy has a luminosity ratio 3.3 times larger than that of the average late-type spiral; (d) of the 10 empty field sources with no identification (B_J < 21) within the 2σ error ellipse, five have possible or probable identifications (B_J < 21) outside the error ellipse with small likelihood ratios (L_R lt; 10), one is a confused source, one is probably due to cirrus and the remaining three are due either to faint cirrus or are 'true' empty field sources (B_J > 21).