2. The sample of southern ultraluminous galaxies

The redshift survey compiled by Strauss et al. (1992), from which we have extracted our sample of ultraluminous infrared galaxies, includes objects from the IRAS Point Source Catalog with a 60 m\ flux greater than 1.936 Jy. A flux color constraint was also applied by these authors to exclude stars and galactic sources (f₆₀² > f₁₂f₂₅). From the 2658 galaxies of the original sample, we have selected the most luminous objects in the far infrared according to the following criteria:

1. Declination, .
2. Absolute Galactic Latitude, .
3. 60 m  Flux, f₆₀ > 3 Jy.
4. Far Infrared Luminosity, .

The choice of the southern hemisphere was motivated by the desire to cover a region of the sky not present in the ULIRG sample of Sanders et al. (1988a). The second constraint excludes galaxies contaminated by the galactic plane.
was calculated using the formula:

which is an approximation of the luminosity (Lonsdale et al. 1985), and assuming . A value of is comparable to the canonical limit , originally used in ULIRG studies, where is an approximation of the luminosity, given by Perault (1989), as:

was preferentially chosen instead of because the 1.9 Jy survey includes fluxes from the Point Source Catalog (PSC), which has a low sensitivity in the mid-infrared bands, 12 m and 25 m, used in the determination of .

With all the criteria above-mentioned, we found the 24 galaxies listed in Table 1 (click here). The optical positions in Cols. 2-3 are given by Strauss et al. (1992); the redshifts in Col. 4 have been calculated from our spectrophotometric data, when available. For systems made of close merging disks, the mean redshift is indicated, whereas in loose interacting systems, the quoted redshift is that of the nearest galaxy from the IRAS position. The mid and far infrared fluxes from the IRAS Faint Source Catalog (FSC) version 2, more sensitive than the PSC initially used by Strauss et al. (1992), are given in Cols. 5-8. The infrared, , and far-infrared luminosities, , have been recalculated with our new redshifts and with the FSC fluxes (Cols. 9-10). Figure 1 (click here) and Fig. 2 present the redshift and luminosity distributions. Redshifts, z, range between 0.04 and 0.13; with our selection criteria, the SULIRG sample is complete up to z=0.1. The most luminous object is IRAS 20100-4156, with .

 

IRAS name RA DEC z FSC flux densities (Jy)

B1950 B1950

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)

00199-7426 00 19 56.4 -74 26 10 0.0963 0.11 0.33 4.16 6.42 12.02 12.08

05189-2524 05 18 58.6 -25 24 39 0.0427 0.73 3.44 13.67 11.36 11.82 12.02

06035-7102 06 03 34.6 -71 02 58 0.0794 0.12 0.57 5.13 5.65 11.91 12.00

06206-6315 06 20 40.3 -63 15 51 0.0920 0.07 0.29 3.96 4.58 11.92 11.98

09061-1248 09 06 11.7 -12 48 48 0.0738 0.12 0.19 3.63 5.32 11.75 11.81

09111-1007 09 11 11.1 -10 07 01 0.0537 0.17 0.47 7.08 11.06 11.80 11.86

11095-0238 11 09 30.2 -02 38 01 0.1065 0.13 0.42 3.25 2.53 11.89 12.02

14348-1447 14 34 52.3 -14 47 24 0.0823 0.14 0.49 6.87 7.07 12.06 12.13

14378-3651 14 37 53.4 -36 51 43 0.0682 0.12 0.52 6.19 6.34 11.87 11.94

15462-0450 15 46 17.6 -04 50 26 0.0998 0.13 0.45 2.92 3.00 11.83 11.97

16090-0139 16 09 04.3 -01 39 27 0.1334 0.09 0.26 3.61 4.87 12.17 12.23

17208-0014 17 20 48.2 -00 14 17 0.0429 0.20 1.66 31.14 34.90 12.22 12.25

19254-7245 19 25 27.8 -72 45 39 0.0617 0.22 1.24 5.48 5.79 11.74 11.91

20046-0623 20 04 39.2 -06 23 10 0.0845 0.09 0.22 3.23 3.91 11.77 11.85

20087-0308 20 08 46.4 -03 08 52 0.1055 0.13 0.24 4.70 6.54 12.12 12.18

20100-4156 20 10 05.8 -41 56 39 0.1298 0.13 0.34 5.23 5.16 12.27 12.34

20414-1651 20 41 28.3 -16 51 12 0.0870 0.65 0.35 4.36 5.25 11.92 12.14

20551-4250 20 55 09.3 -42 50 37 0.0426 0.28 1.91 12.78 9.95 11.78 11.90

21130-4446 21 13 00.5 -44 46 14 0.0929 0.07 0.16 3.11 3.78 11.83 11.88

21504-0628 21 50 28.4 -06 28 55 0.0775 0.09 0.39 3.48 2.89 11.69 11.80

22491-1808 22 49 09.5 -18 08 18 0.0777 0.12 0.55 5.44 4.45 11.89 11.98

23128-5919 23 12 50.6 -59 19 37 0.0445 0.24 1.59 10.80 10.99 11.77 11.88

23230-6926 23 23 02.5 -69 26 47 0.1063 0.06 0.29 3.74 3.42 11.97 12.04

23389-6139 23 38 59.4 -61 39 28 0.0932 0.06 0.24 3.63 4.26 11.89 11.95

 

  
Figure 1: Redshift distribution of SURILGs

  
Figure 2: Infrared (dotted) and far infrared (plain) luminosity distributions of SURILGs

The SULIRG sample includes the list of ULIRGs compiled by Melnick & Mirabel (1990). The more northern objects are also present in the catalog of Murphy et al. (1996) (however these authors present only imaging data); three galaxies belong to the IRAS Bright Galaxy Sample (Soifer et al. 1987) and are therefore in common with the ULIRG sample of Sanders et al. (1988a). Some of the nearest objects have already been studied in details: IRAS 14348-1447 (Sanders et al. 1988c), IRAS 19254-7245 ("The Super-Antennae'', Mirabel et al. 1991; Colina et al. 1991), IRAS 20551-4251 (Johansson 1991) and IRAS 23128-5919 (Bergvall & Johansson1985). Moreover Mirabel et al. (1988) have published CO measurements for 15 galaxies. One object, IRAS 17208-0014, is known as an OH megamaser (Martin et al. 1989).

We have obtained optical CCD images for all the galaxies in our sample, but IRAS 05189-2524, one of the BGS members, and optical spectra for 18 of them; 17 galaxies have also been imaged in the near infrared.