A STUDY OF SOUTHERN EXTREME IRAS GALAXIES .1. OPTICAL OBSERVATIONS

In order to study the processes that (strongly) enhance the star formation rate in some galaxies we have selected 62 galaxies from the IRAS point source catalogue with far-infrared to blue luminosity ratios (L(FIR)/L(B)0) of three or larger. These galaxies form a subset of a far-infrared complete sample of 254 sources in two fields covering in total 1500 square degrees of the southern sky (10h less-than-or-equal-to alpha less-than-or-equal-to 14h and -40-degrees less-than-or-equal-to delta less-than-or-equal-to -20-degrees; 20h less-than-or-equal-to alpha less-than-or-equal-to 22h and -40-degrees less-than-or-equal-to delta less-than-or-equal-to -20-degrees). The sources in the far-infrared complete sample all have flux densities larger than 1 and 2.5 Jy at 60 and 100-mu-m, respectively, to ensure completeness. Furthermore, in order to select mainly galaxies, for all sources the flux densities at 60 and 100-mu-m are larger than at 12 and 25-mu-m. We initially used B-band magnitudes estimated from ESO/SRC and POSS sky survey plates to estimate L(FIR)/L(B) ratios for all galaxies in the far-infrared complete sample, and we selected only those galaxies for the optical observations that have L(FIR)/L(B)0 greater-than-or-equal-to 4.3, thus obtaining a sample of 62 galaxies. Comparison of the estimated with the observed, corrected CCD B-band magnitudes later revealed that the actual L(FIR)/L(B)0 selection criterium is less sharp and corresponds to L(FIR)/L(B)0 greater-than-or-similar-to 3. For these 62 sources we also obtained far-infrared co-added flux-densities, so that 100%, 95%, and 70% of the sources are detected at 60 and 100, 25 and 12-mu-m, respectively. Due to the L(FIR)/L(B) selection criterion and the correlation between L(FIR)/L(B) and the S100/S60 flux density ratio the subsample of 62 galaxies consists only of warm sources with log (S100/S60) less-than-or-equal-to 0.4. The optical observations comprise long-slit CCD spectra in the 4800-7300 angstrom wavelength range, broad-band B, V and R, and narrow-band H-alpha CCD images. In this paper we present the optical observations and show spectra, and broad-band, colour and continuum-subtracted H-alpha CCD images for more than 50 galaxies. The spectra are mostly HII-types although some 25% are AGN-types. The broad-band images show, among other things, that our sample predominantly consists of barred spirals and distorded interacting system, while the H-alpha images show in most cases small compact sources. From the spectra we derived redshifts, line-ratios, equivalent widths, and extinction determinations from the H-beta/H-alpha line ratios. We also derived integrated magnitudes, colours, H-alpha fluxes, diameters and luminosities of the galaxies from the CCD images. We determined average luminosity profiles of all early-type galaxies and all possible merger candidates in our sample, and we found that all these galaxies have exponential disks except two objects that follow a de Vaucouleurs r1/4 law: a merger candidate, and an elliptical galaxy in a close interacting pair (the latter is not an IRAS galaxy, however).